摘要:

physicochemical topics, thereby encouraging scientists of different disciplines to contribute their varied viewpoints to a coiiinion theme. A recent Discussion is :- The Royal Soci- of Chemistry- No.75 lntraamolecwlar Kinetics No. 75 in the series, this publication is the result of a general discussion held at the University of Warwick in April 1983. Contents: The Spiers Meniorlal Lecture; Vibrational Redistribution within Excited Electronic States of Polyatomic Molecules Inrraniolecular R e h u t i o n o f 1. vcited States lsomerization of Intcrnal~ncrgy-selected Ions Kinetics of Ion-Molecule Collision Coinple\es in the Gas Phase, E\periinent and Theory lntrainolccular Decay 01' Soinc Open-shell Pulya t o niic Ca lions On tlic Theory u i Iiitrdniolccul~r I n e r g y Transfer Pulsed Laser Preparation and Ouaniuin Superposition Statc Evolution in ReguLtr and Irregular Systems A Ouantuiii-iiicclianical Internal-collision Model for State-sclcctcd Uniinolccular Decoiiiposilio n The Correspondence Principle and Intramolecular Dynamics lntrainoleculdr Dcphasiiig.t'icusecond Evolution of Wavepacket States in a Molecule with Int erinediate-casc level Struct urc Energy Conversion in van der Waals C'u~~iplc\c\ ol s-Tetrarine and Argon Tim-dependent Processes in Polyatuinic Molecules During and After Intense Intrarcd Irradiation Energy Distributions in tlic (.N(X'L+) bragnient froiii tlie Infrared Multiplepholun Dissociation ol' CI. ICN. A Coinparison between 1:xperiiiiental Results and the Predictions ot Statistical Theories of ChFO + Product Energy Partitioning in the Decoiii- position of State-selectively Excited HOON and IIOOD Low-power Inl-rarcd Laser I'hoiolysis o f Tetramethy ldioxetan Uniinolecular Reactions lnduccd by Vibrational Overtone Excitation Uniiiiolecular Decomposition of t-Butylhydro- peroxide by Direct Excitation of the 6-0 0-11 Stretching Overtone I'icosecond-jet Spectroscopy and Photoclieinistry.Energy Redistribution and its Iiiipact'on Coherence, Isoincrization, Ihssociatiun and Solvalioii knergy Redistribution in Large Molecules. Duect St ud y o f In1 rainolucular Rehxa lion in the Gas Phase with Picosecond Gating Rotation-dependent Intrainolecuhr I'r~)cessc.sofSO:(A'A.) in a Superwnic Jct Role of Rotation-Vibration Interaction in Vibrational Keh\ation. Energy Kcdistribution in k,xcitcd Singlet I~'ornialdc1iyde Sub-lhppler.Spectroscopy of Benrcnc in the "('liaiinel-lliree" Region Intraiiiulccular 1:lectronic Kclau~tion and I'liotois~)iiieruati[)n Processes in tlie lsuhted Azabenrene Molecules Pyridinc, Pyrazinc and I'yriiiiidinc Softcover 434pp 0 85186 658 1 Price f25.00 ($48.00) Rest of the World f26.00 RSC Members f 16.25 Faraday Discussions of the Chemical Society 7< lnrruniolei u h r Kincrit I Faraday Symposia are usually held annually and are confined to more specialiscd topics than Discussions, with particular reference to recent rapidly developing lines of rescuch. A recent Symposium is :- No.l?The Hydrophobic Interadion No. 17 in the series, this publication is the result of a symposium on The Hydrophobic Interaction held at the Uiiiversity of Reading in December 1982.Contents: Hydrophobic Interdctionr a llistaric.11 Per spect ivr llydrupliobic Ilydration Geometric Kelaution in Water. Its Role in Precise Vapour-pressure Measureiiients of the SolubilkdtiorI of Benzene by Aqueous Sodiuiii Octylsulphate Solutions Nuclear Magnetic Resonance R e b u t i o n Investigation of Tetrahydrofuran and Methyl Iodide Clathrdtes Infrared and Nuckar Magnetic Kcwnance Studies Pertaining to the (age Model t o r Solutions oS Acetone in Water Irothernial Transport Properties in Solutions o f S y mmet r ica I Tet ra-alk y hmnioniuiii Bromides Thermodynamics of Cavity I'oriiiaiion in Water. A Molecular Dynamics Study Molecular Librations and Solvent Oricnt- ational Correlations in Hydrophobic Phenomena Monte Carlo Computer Siniulation Study of the Hydrophobic Effect.Potential ot Mean Force for ECfir)gaq at 25 and SOv C Hydroplicibic Moments and Protein Structure Application 01' the Kirkwood-Buff Theory to the t'roblcin 01 Hydrophobic Interactions Ihentangleinent of Ilydrophubic and IFlcctrosi~tic Contributions t o the I.ilni Pressures O i Ionic Surfactants llydrophobir. Intcracliuns in Dilute Su lut io ns u t 1'0 1 y (vin y I a Ico lio I) ('onioriii;tiionaI and 1:unc.i ional I'ropertics of tiaeiiwglobin in Water+Alcohol Mixtures. Dependence o f Bull. Electrostatic and tlydrupliohic I n t c r x t i o n s upon ptl and KCI concentrations Softcover 24Opp 0 85186 668 9 Price f36.50 ($70.00) Rest of the World f38.50 RSC Members f 23.75 ORDERING RSC Members should send their orders to: The Royal Society of Chemistry.The Membership Officer. 30 Russell Square, Non-RSC Members The Royal Society of Chemistry, Distribution Centre, Blackhorse Road, L London WC1 B 5DT. Letchworth, Herts SO6 IHN, England. Faradaj Symposia of the Chemical Society hGi 17 I hc HI drophohr' Inrcrm rron 1 9 X ? (viii)physicochemical topics, thereby encouraging scientists of different disciplines to contribute their varied viewpoints to a coiiinion theme. A recent Discussion is :- The Royal Soci- of Chemistry- No.75 lntraamolecwlar Kinetics No. 75 in the series, this publication is the result of a general discussion held at the University of Warwick in April 1983. Contents: The Spiers Meniorlal Lecture; Vibrational Redistribution within Excited Electronic States of Polyatomic Molecules Inrraniolecular R e h u t i o n o f 1.vcited States lsomerization of Intcrnal~ncrgy-selected Ions Kinetics of Ion-Molecule Collision Coinple\es in the Gas Phase, E\periinent and Theory lntrainolccular Decay 01' Soinc Open-shell Pulya t o niic Ca lions On tlic Theory u i Iiitrdniolccul~r I n e r g y Transfer Pulsed Laser Preparation and Ouaniuin Superposition Statc Evolution in ReguLtr and Irregular Systems A Ouantuiii-iiicclianical Internal-collision Model for State-sclcctcd Uniinolccular Decoiiiposilio n The Correspondence Principle and Intramolecular Dynamics lntrainoleculdr Dcphasiiig. t'icusecond Evolution of Wavepacket States in a Molecule with Int erinediate-casc level Struct urc Energy Conversion in van der Waals C'u~~iplc\c\ ol s-Tetrarine and Argon Tim-dependent Processes in Polyatuinic Molecules During and After Intense Intrarcd Irradiation Energy Distributions in tlic (.N(X'L+) bragnient froiii tlie Infrared Multiplepholun Dissociation ol' CI.ICN. A Coinparison between 1:xperiiiiental Results and the Predictions ot Statistical Theories of ChFO + Product Energy Partitioning in the Decoiii- position of State-selectively Excited HOON and IIOOD Low-power Inl-rarcd Laser I'hoiolysis o f Tetramethy ldioxetan Uniinolecular Reactions lnduccd by Vibrational Overtone Excitation Uniiiiolecular Decomposition of t-Butylhydro- peroxide by Direct Excitation of the 6-0 0-11 Stretching Overtone I'icosecond-jet Spectroscopy and Photoclieinistry. Energy Redistribution and its Iiiipact'on Coherence, Isoincrization, Ihssociatiun and Solvalioii knergy Redistribution in Large Molecules.Duect St ud y o f In1 rainolucular Rehxa lion in the Gas Phase with Picosecond Gating Rotation-dependent Intrainolecuhr I'r~)cessc.sofSO:(A'A.) in a Superwnic Jct Role of Rotation-Vibration Interaction in Vibrational Keh\ation. Energy Kcdistribution in k,xcitcd Singlet I~'ornialdc1iyde Sub-lhppler. Spectroscopy of Benrcnc in the "('liaiinel-lliree" Region Intraiiiulccular 1:lectronic Kclau~tion and I'liotois~)iiieruati[)n Processes in tlie lsuhted Azabenrene Molecules Pyridinc, Pyrazinc and I'yriiiiidinc Softcover 434pp 0 85186 658 1 Price f25.00 ($48.00) Rest of the World f26.00 RSC Members f 16.25 Faraday Discussions of the Chemical Society 7< lnrruniolei u h r Kincrit I Faraday Symposia are usually held annually and are confined to more specialiscd topics than Discussions, with particular reference to recent rapidly developing lines of rescuch.A recent Symposium is :- No.l?The Hydrophobic Interadion No. 17 in the series, this publication is the result of a symposium on The Hydrophobic Interaction held at the Uiiiversity of Reading in December 1982. Contents: Hydrophobic Interdctionr a llistaric.11 Per spect ivr llydrupliobic Ilydration Geometric Kelaution in Water. Its Role in Precise Vapour-pressure Measureiiients of the SolubilkdtiorI of Benzene by Aqueous Sodiuiii Octylsulphate Solutions Nuclear Magnetic Resonance R e b u t i o n Investigation of Tetrahydrofuran and Methyl Iodide Clathrdtes Infrared and Nuckar Magnetic Kcwnance Studies Pertaining to the (age Model t o r Solutions oS Acetone in Water Irothernial Transport Properties in Solutions o f S y mmet r ica I Tet ra-alk y hmnioniuiii Bromides Thermodynamics of Cavity I'oriiiaiion in Water.A Molecular Dynamics Study Molecular Librations and Solvent Oricnt- ational Correlations in Hydrophobic Phenomena Monte Carlo Computer Siniulation Study of the Hydrophobic Effect. Potential ot Mean Force for ECfir)gaq at 25 and SOv C Hydroplicibic Moments and Protein Structure Application 01' the Kirkwood-Buff Theory to the t'roblcin 01 Hydrophobic Interactions Ihentangleinent of Ilydrophubic and IFlcctrosi~tic Contributions t o the I.ilni Pressures O i Ionic Surfactants llydrophobir. Intcracliuns in Dilute Su lut io ns u t 1'0 1 y (vin y I a Ico lio I) ('onioriii;tiionaI and 1:unc.i ional I'ropertics of tiaeiiwglobin in Water+Alcohol Mixtures. Dependence o f Bull. Electrostatic and tlydrupliohic I n t c r x t i o n s upon ptl and KCI concentrations Softcover 24Opp 0 85186 668 9 Price f36.50 ($70.00) Rest of the World f38.50 RSC Members f 23.75 ORDERING RSC Members should send their orders to: The Royal Society of Chemistry. The Membership Officer. 30 Russell Square, Non-RSC Members The Royal Society of Chemistry, Distribution Centre, Blackhorse Road, L London WC1 B 5DT. Letchworth, Herts SO6 IHN, England. Faradaj Symposia of the Chemical Society hGi 17 I hc HI drophohr' Inrcrm rron 1 9 X ? (viii)

ISSN:0300-9599    

DOI:10.1039/F198480FX045

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

AUTHOR INDEX xxxv Sabbatini, L., 1029 Sacco, A., 2669 Sanders, J. V., 571 Sangster, D. F., 291 1 Sarka, K., 521 Sasahira, A., 473 Sasse, W. H. F., 571 Satchell, P. W., 2395 Sato, K., 841 Sato, Y., 341 Savino, V., 759 Sayers, C. M., 1217 Schiller, R. L., 1257 Schmidt, J., 1 Schmidt, P. P., 2017 Schneider, H., 3275, 3285 Schulz, R. A., 489, 1323 Scott, J. M. W., 739, 1651, 2287, Scott, S. K., 3409 Segall, R. L., 2609 Sehested, K., 2929, 2969 Seidl, V., 1367 Sem, P., 297 Serratosa, J. M., 2225 Seyama, H., 237 Seyedmonir, S. R., 87, 2269 Shanahan, M. E. R., 37 Sheppard, A., 2999 Sherwood, P. M. A., 135, 2099, Shindo, Y., 879, 2199 Shiotani, H., 2145 Shizuka, H., 383, 341 Siekhaus, W. J., 61 Sircar, S., 1101, 2489 Smart, R. St C., 2957, 2609 Smith, I. M., 3021 Smith, R., 3233 Snow, R.L., 3463 Solar, S., 2929 Solar, W., 2929 Solymosi, F., 1841 Soma, M., 237 Soupart, J-B., 3209 Sourisseau, C., 3257 Spink, J. A., 3469 Spoto, G., 1875, 1891 Spotswood, T. M., 3147 Staricco, E. H., 2631 Stassinopoulou, K., 3095 Stedman, D. H., 285 Stout, D. R., 3481 Strohbusch, F., 1757 Strumolo, D., 1479 Struve, P., 813, 2167 Styring, M. G., 3051 Subramanian, R., 2405 2881, 3359 2549, 2867 Sundar, H. G. K., 3491 Sutcliffe, L. H., 669, 3021 Sutton, H. C., 2301 Sutton, L. E., 635 Suzuki, H., 803 Suzuki, T., 1925, 3157 Symons, M. C. R., 423, 1005, Szamosi, J., 1645 Szczepaniak, W., 2935 Takagi, Y., 1925 Takahashi, K., 803 Takahashi, N., 629 Takanaka, J., 941 Takao, S., 993 Takasaki, S., 803 Takegami, H., 1221 Tam, S-C., 2255 Tamamushi, R., 2751 Tamaru, K., 29, 1567, 1595 Tamilarasan, R., 2405 Tanabe, S., 803 Tanaka, K., 2563,2981 Tanaka, T., 119 Taniewska-Osinska, S., 1409 Tascon, J.M. D., 1089 Teo, H. H., 981, 1787 Tetenyi, P., 3037 Thomas, J. K., 1163 Thompson, L., 1673 Thomson, M., 1867 Thomson, S. J., 1689 Tiddy, G. J. T., 789, 3339 Tittarelli, P., 2209 Tominaga, T., 941 Tomkinson, J., 225 Tonelli, C., 1605 Toprakcioglu, C., 13,413 Tran, T., 1867 Trasatti, S., 913 Tripathi, A. D., 1517 Tronc, E., 2619 Troncoso, G., 2127 Truscott, T. G., 2293 Tsurusaki, T., 879 Tuck, J. J., 309 Turner, P. S., 2609 Tusk, M., 1757 Tvarbikova, Z., 2639 Tyrrell, H. J. V., 1279 Ueki, Y.. 341 Ueno, A., 803 Unno, H., 1059 Valencia, E., 2127 van de Ven, T. G. M., 2677 van Ommen, J. G., 2479 van Truong, N., 3275, 3285 Vargas, I., 1947 2767, 2803, 21 1, 1999 Vedrine, J.C., 1017 Veith, J., 2313 Velasco, J. R., 3429 Vesala, A., 2439 Vickerman, J. C., 1903 Vincent, B., 2599 Vinek, H., 1239 Vink, H., 507, 1297 Waghorne, W. E., 1267 Wagley, D. P., 47 Walker, R. W., 435, 3187, 3195, Wallington, T. J., 2737 Wang, G-W., 1039 Watkins, P. E., 2323 Watkiss, P. J., 1279 Watt, R. A. C., 489 Webb, G., 1689 Webster, B. C., 255, 267 Weiner, E. R., 1491 Wells, C. F., 2155. 2445 Wells, J. D., 1233 Whang, B. C. Y., 291 1 Whittle, E., 2323 Wichterlova, B., 2639 Wiesner, S., 3021 Wilhelmy, D. M., 563 Williams E. H., 3147 Williams, P. A., 403 Williams, R. J. P., 2255 Wokaun, A., 1305 Wolff, T., 2969 Wood, S. W., 3419 Woolf, L. A., 549, 1287 Wright, C. J., 1217 Wu, D. C., 1795 Wiirflinger, A., 3221 Wyn-Jones, E., 1915 Yamabe, M., 1059 Yamamoto, S., 941 Yamashita, H., 1435 Yamauchi, H., 2033 Yamazaki, A., 3245 Yariv, S., 1705 Yasumori, I., 841 Yeates, S.G., 1787 Yide, X., 969, 3103 Ylikoski, J., 2439 Yokokawa, T., 473 Yoneda, N., 879 Yonezawa, T., 1435 Yoshida, S., 119, 1435 Zambonin, P. G., 1029 Zanderighi, L., 1605 Zecchina. A., 2209, 2723, 1875, Zipelli, C., 1777 Zundel, G., 553 348 1, 2827 1891AUTHOR INDEX xxxv Sabbatini, L., 1029 Sacco, A., 2669 Sanders, J. V., 571 Sangster, D. F., 291 1 Sarka, K., 521 Sasahira, A., 473 Sasse, W. H. F., 571 Satchell, P. W., 2395 Sato, K., 841 Sato, Y., 341 Savino, V., 759 Sayers, C. M., 1217 Schiller, R. L., 1257 Schmidt, J., 1 Schmidt, P. P., 2017 Schneider, H., 3275, 3285 Schulz, R. A., 489, 1323 Scott, J. M. W., 739, 1651, 2287, Scott, S.K., 3409 Segall, R. L., 2609 Sehested, K., 2929, 2969 Seidl, V., 1367 Sem, P., 297 Serratosa, J. M., 2225 Seyama, H., 237 Seyedmonir, S. R., 87, 2269 Shanahan, M. E. R., 37 Sheppard, A., 2999 Sherwood, P. M. A., 135, 2099, Shindo, Y., 879, 2199 Shiotani, H., 2145 Shizuka, H., 383, 341 Siekhaus, W. J., 61 Sircar, S., 1101, 2489 Smart, R. St C., 2957, 2609 Smith, I. M., 3021 Smith, R., 3233 Snow, R. L., 3463 Solar, S., 2929 Solar, W., 2929 Solymosi, F., 1841 Soma, M., 237 Soupart, J-B., 3209 Sourisseau, C., 3257 Spink, J. A., 3469 Spoto, G., 1875, 1891 Spotswood, T. M., 3147 Staricco, E. H., 2631 Stassinopoulou, K., 3095 Stedman, D. H., 285 Stout, D. R., 3481 Strohbusch, F., 1757 Strumolo, D., 1479 Struve, P., 813, 2167 Styring, M. G., 3051 Subramanian, R., 2405 2881, 3359 2549, 2867 Sundar, H.G. K., 3491 Sutcliffe, L. H., 669, 3021 Sutton, H. C., 2301 Sutton, L. E., 635 Suzuki, H., 803 Suzuki, T., 1925, 3157 Symons, M. C. R., 423, 1005, Szamosi, J., 1645 Szczepaniak, W., 2935 Takagi, Y., 1925 Takahashi, K., 803 Takahashi, N., 629 Takanaka, J., 941 Takao, S., 993 Takasaki, S., 803 Takegami, H., 1221 Tam, S-C., 2255 Tamamushi, R., 2751 Tamaru, K., 29, 1567, 1595 Tamilarasan, R., 2405 Tanabe, S., 803 Tanaka, K., 2563,2981 Tanaka, T., 119 Taniewska-Osinska, S., 1409 Tascon, J. M. D., 1089 Teo, H. H., 981, 1787 Tetenyi, P., 3037 Thomas, J. K., 1163 Thompson, L., 1673 Thomson, M., 1867 Thomson, S. J., 1689 Tiddy, G. J. T., 789, 3339 Tittarelli, P., 2209 Tominaga, T., 941 Tomkinson, J., 225 Tonelli, C., 1605 Toprakcioglu, C., 13,413 Tran, T., 1867 Trasatti, S., 913 Tripathi, A.D., 1517 Tronc, E., 2619 Troncoso, G., 2127 Truscott, T. G., 2293 Tsurusaki, T., 879 Tuck, J. J., 309 Turner, P. S., 2609 Tusk, M., 1757 Tvarbikova, Z., 2639 Tyrrell, H. J. V., 1279 Ueki, Y.. 341 Ueno, A., 803 Unno, H., 1059 Valencia, E., 2127 van de Ven, T. G. M., 2677 van Ommen, J. G., 2479 van Truong, N., 3275, 3285 Vargas, I., 1947 2767, 2803, 21 1, 1999 Vedrine, J. C., 1017 Veith, J., 2313 Velasco, J. R., 3429 Vesala, A., 2439 Vickerman, J. C., 1903 Vincent, B., 2599 Vinek, H., 1239 Vink, H., 507, 1297 Waghorne, W. E., 1267 Wagley, D. P., 47 Walker, R. W., 435, 3187, 3195, Wallington, T. J., 2737 Wang, G-W., 1039 Watkins, P. E., 2323 Watkiss, P. J., 1279 Watt, R. A. C., 489 Webb, G., 1689 Webster, B. C., 255, 267 Weiner, E. R., 1491 Wells, C. F., 2155. 2445 Wells, J. D., 1233 Whang, B. C. Y., 291 1 Whittle, E., 2323 Wichterlova, B., 2639 Wiesner, S., 3021 Wilhelmy, D. M., 563 Williams E. H., 3147 Williams, P. A., 403 Williams, R. J. P., 2255 Wokaun, A., 1305 Wolff, T., 2969 Wood, S. W., 3419 Woolf, L. A., 549, 1287 Wright, C. J., 1217 Wu, D. C., 1795 Wiirflinger, A., 3221 Wyn-Jones, E., 1915 Yamabe, M., 1059 Yamamoto, S., 941 Yamashita, H., 1435 Yamauchi, H., 2033 Yamazaki, A., 3245 Yariv, S., 1705 Yasumori, I., 841 Yeates, S. G., 1787 Yide, X., 969, 3103 Ylikoski, J., 2439 Yokokawa, T., 473 Yoneda, N., 879 Yonezawa, T., 1435 Yoshida, S., 119, 1435 Zambonin, P. G., 1029 Zanderighi, L., 1605 Zecchina. A., 2209, 2723, 1875, Zipelli, C., 1777 Zundel, G., 553 348 1, 2827 1891

ISSN:0300-9599    

DOI:10.1039/F198480BX047

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

JOURNAL OF THE CHEMICAL SOCIETY FARADAY TRANSACTIONS, PARTS I AND I 1 The Journal of the Chemical Society is published in six sections, of which five are termed Transactions; these are distinguished by their subject matter, as follows: Dalton Transactions (Inorganic Chemistry). All aspects of the chemistry of inorganic and organometallic compounds; including bioinorganic chemistry and solid-state inorganic chemistry; of their structures, properties, and reactions, including kinetics and mechanisms; new or improved experimental techniques and syntheses. Faraday Transactions I (Physical Chemistry). Radiation chemistry, gas-phase kinetics, electrochemistry (other than preparative), surface and interfacial chemistry, heterogeneous catalysis, physical properties of polymers and their solutions, and kinetics of polymerization, etc.Faraday Transactions 11 (Chemical Physics). Theoretical chemistry, especially valence and quantum theory, statistical mechanics, intermolecular forces, relaxation phenomena, spectroscopic studies (including i.r., e.s.r., n.m.r., and kinetic spec- troscopy, etc.) leading to assignments of quantum states, and fundamental theory. Studies of impurities in solid systems. Perkin Transactions I (Organic Chemistry). All aspects of synthetic and natural product organic, organometallic and bio-organic chemistry, including aliphatic, alicyclic, and aromatic systems (carbocyclic and heterocyclic). Perkin Transactions II (Physical Organic Chemistry). Kinetic and mechanistic studies of organic, organometallic and bio-organic reactions.The description and application of physicochemical, spectroscopic, and theoretical procedures to organic chemistry, including structure-activity relationships. Physical aspects of bio-organic chemistry and of organic compounds, including polymers and biopolymers. Authors are requested to indicate, at the time they submit a typescript, the journal for which it is intended. Should this Seem unsuitable, the Editor will inform the author. The sixth section of the Journal of the Chemical Society is Chemical Communications, which is intended as a forum for preliminary accounts of original and significant work, in any area of chemistry that is likely to prove of wide general appeal or exceptional specialist interest. Such preliminary reports should be followed up eventually by full papers in other journals (e.g.the five Transactions) providing detailed accounts of the work. NOTES I t has always been the policy of the Faraday Transactions that brevity should not be a factor influencing acceptability for publication. In addition however to full papers both sections carry at the end of each issue a section headed ‘Notes’, which are short self-contained accounts of experimental observations, results, or theory that will not require enlargement into ‘full’ papers. The Notes section is not used for preliminary communications. The layout of a Note is the same as that of a paper. Short summaries are required. The procedure for submission, administration, refereeing, editing and publication of Notes is the same as for full papers.However, Notes are published more quickly than papers since their brevity facilitates processi,ng at all stages. The Editors endeavour to meet authors’ wishes as to whether anarticle is a full paper or a Note, but since there is no sharp dividing line between the one and the other, either in terms of length or character of content, the right is retained to transfer overlong Notes to the full papers section. As a guide a Note should not exceed 1500 words or word-equivalents. (9NOMENCLATURE AND SYMBOLISM Units and Symbols. The Symbols Committee of The Royal Society, of which The Royal Society ofchemistry is a participatingmember, has produced a set of recommendations in a pamphlet ‘Quantities, Units, and Symbols’ (1975) (copies of this pamphlet and further details can be obtained from the Manager, Journals, The Royal Society of Chemistry, Burlington House, London W 1 V OBN).These recommendations are applied by The Royal Society of Chemistry in all its publications. Their basis is the ‘Systkme International d’Unites’ (SI). A more detailed treatment of units and symbols with specific application to chemistry is given in the IUPAC Manual of Symbols and Terminology for Physicochemical Quantities and Units (Pergamon, Oxford, 1979). Nomenclature. For many years the Society has actively encouraged the use of standard IUPAC nomenclature and symbolism in its publications as an aid to the accurate and unambiguous communication of chemical information between authors and readers. In order to encourage authors to use IUPAC nomenclature rules when drafting papers, attention is drawn to the following publications in which both the rules themselves and guidance on their use are given: Nomenclature of Organic Chemistry, Sections A , B, C, D, E, F, and H (Pergamon, Oxford, 1979 edn). Nomenclature of Inorganic Chemistry (Butterworths, London, 197 1, now published by Pergamon).Biochemical Nomenclature and Related Documents (The Biochemical Society, London, 1978). A complete listing of all IUPAC nomenclature publications appears in the January issues of J. Chem. Soc., Faraday Transactions. It is recommended that where there are no IUPAC rules for the naming of particular compounds or authors find difficulty in applying the existing rules, they should seek the advice of the Society’s editorial staff.FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY Marlow Medal and Prize Applications are invited for the award of the Marlow Medal for 1985 and prize of f 100. The award will be open to any member of the Faraday Division of the Royal Society of Chemistry who, by the age of 32, had made in the judgement of the Council of the Faraday Division, the most meritorious contribution to physical chemistry or chemical physics. The award will be made on the basis of publications (not necessarily in the Transactions) on any subject normally published in J. Chem. SOC., Faraday Transactions I and I / , that carry a date of receipt for publication not later than the candidate‘s 32nd birthday. Candidates should be members and under 34 on 1 st January 1985, the closing date for applications, which may be made either by the candidate himself or on his behalf by another member of the Society.Copies of the rules of the award and application forms may be obtained from: Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1 V OBN (ii)THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM NO. 1 9 Molecular Electronic Structure Calcu lations-M ethods and Applications University of Cambridge, 12-1 3 December 1984 Molecular electronic structure calculations have now developed into a powerful predictive tool and are necessary in several different fields to aid the understanding and interpretation of experimental observations. The meeting will review the current state of this rapidly developing discipline and will bring together experts on some of the most advanced methods and their applications.The meeting will provide an opportunity for discussion and comparison of the various techniques currently in use. It will therefore not only be a valuable forum for discussion among research workers in the field, but should also show the non-specialist what theoretical calculations can be expected to achieve now and in the near future. The final programme and application form may be obtained from: Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 7 9 (in conjunction with the Polymer Physics Group) Polymer Liquid Crystals University of Cambridge, 1-3 April 1985 The object of the meeting will be to discuss all aspects of the developing subject of polymeric liquid crystals.The hope is to bring together scientists from the fields of conventional polymer science and monomeric liquid crystals who are active in this field. The discussion is aimed at understanding the following facets: (a) The chemical characteristics that give rise to polymer liquid crystalline behaviour. (b) The nature of the high local anisotropy of these systems and their structural organisation at the molecular, micron and macroscopic levels. (c) The physical properties and their industrial exploitation, with particular reference to the influence of external force fields such as flow, electric and magnetic fields. (d) The inter-relations of polymer liquid crystals with small-moleculemesophases, conventional flexible polymers and biopolymers which exhibit liquid-crystalline behaviour. The conference will include a Poster Session for which contributions are invited. Abstracts (300 words) should be sent as soon as possible (and in any event no later than 31 January 1985) to the Chairman of the Organising Committee: Professor B.R. Jennings, Electro-Optics Group, Department of Physics, Brunel University, Uxbridge UB8 3PH The preliminary programme may be obtained from : Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN (iii)THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 80 Physical Interactions and Energy Exchange a t the Gas-Solid Interface McMaster University, Hamilton, Ontario, Canada, 23-25 July 1985 Organising Committee : Professor J.A. Morrison (Chairman) Dr M. L. Klein Professor G. Scoles Professor W. A. Steele Professor F. S. Stone Dr R. #. Thomas The discussion will be concerned with certain aspects of current research on the gas-solid interface: elastic, inelastic and dissipative scattering of atoms and molecules from crystal surfaces, and the structure and dynamics of physisorbed species, including overlayers. Emphasis will be placed on the themes of physical interactions and energy exchange rather than on molecular-beam technology or the phenomenology of phase transitions on overlayers. The interplay between theory and experiment will be stressed as they relate to the nature of atom and molecule surface interaction potentials, including many-body effects.The preliminary programme may be obtained from : Professor J. A. Morrison, Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada L8S 4M1 or: Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington youse, London W1V OBN, U.K. THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM NO. 20 Phase Transitions in Adsorbed Layers University of Oxford, 17-1 8 December 1985 Organising Committee : Professor J. S. Rowlinson (Chairman) Dr E. Dickinson Dr R. Evans Mrs Y. A. Fish Dr N. Parsonage Dr D. A. Young The aim of the meeting is t o discuss phase transitions at gas/liquid, liquid/liquid and solid/fluid interfaces, and in other systems of constrained geometry or dimensionality less than three.Emphasis will be placed on molecularly simple systems, whereby liquid crystal interfaces and chemisorption phenomena are excluded. Further information may be obtained from: Professor J. S. Rowlinson, Physical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ.THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 81 Lipid Vesicles and Membranes Loughborough University of Technology, 15-1 7 April 1986 Organising Committee: Professor D. A. Haydon (Chairman) Professor D. Chapman Mrs Y. A. Fish Dr M. J. Jaycock Dr I. G. Lyle Professor R. H. Ottewill Dr A. L. Smith Dr D. A. Young The aim of the meeting is to discuss the physical chemistry of lipid membranes and their interactions, in particular theoretical and spectroscopic studies, polymerised membranes, thermodynamics of bilayers and Iiposomes, mechanical properties, encapsulation and interaction forces between bilayers leading to fusion but excluding preparation and characterisation methodology.Contributions for consideration by the Organising Committee are invited and abstracts of about 300 words should be sent by 1 May 1985 to: Professor D. A. Haydon, Physiological Laboratory, Downing Street, Cambridge CB2 3EG Full papers for publication in the Discussion Volume will be required by December 1985. ~~~~ ~~ FARADAY DIVISION INFORMAL AND GROUP MEETINGS Division - Full- day Endo wed 1 ecture Symposium Phase Equilibrium and Interfacial Structure To be held at Imperial College, London on 10 December 1984 Further information from Mrs Y.A. Fish, The Royal Society of Chemistry, Burlington House, London W1 V OBN High Resolution Spectroscopy Group CARS, Diode Laser and Microwave Spectroscopy To be held at the University of Reading on 16-1 8 December 1984 Further information from Dr J. M. Hollas, Department of Chemistry, University of Reading, Whiteknights, Reading RG6 2AD Colloid and Interface Science Group with the Colloid and Surface Chemistry Group of the SCI Colloidal Aspects of Cohesive Sediments To be held at the SCI Headquarters, London on 18 December 1984 Further information from Dr J. W. Goodwin, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS Neutron Scattering Group Neutrons in Magnetism To be held at the University of Southampton on 20 December 1984 Further information from Dr R.6. Rainford, Department of Chemistry, University of Southampton, Southampton SO9 5NHPolymer Physics Group New Year Soiree To be held in Cambridge on 2 January 1985 Further information from Dr A. Windle, Department of Metallurgy and Materials Science, Pembroke Street, Cambridge CB2 302 Gas Kinetics Group Multiphoton Processes in Chemical Kinetics To be held at the University of Leicester on 4 January 1985 Further information from: Dr I. W. M. Smith, Department of Physical Chemistry, University Chemical Laboratory, Lensfield Road, Cambridge CB2 1 EP Division - Full-day Endowed Lecture Symposium The 4th State of Matter: A Chemical Challenge for the Future To be held at the Scientific Societies Lecture Theatre, London on 10 January 1985 Further information from Mrs Y.A. Fish, The Royal Society of Chemistry, Burlington House, London W1 V OBN Division - Half-day Endowed Lecture Symposium (jointly with Perkin Division) The Physical Organic Chemistry of Hydrogens To be held at University College London on 26 February 1985 Further information from: Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1 V OBN Theoretical Chemistry Group Group Meeting To be held at King’s College, London on 6 March 1985 Further information from Dr G. Doggett, Department of Chemistry, University of York, York YO1 5DD Division Annual Congress: Solid State Chemistry To be held at the University of St Andrews on 25-28 March 1985 Further information from Professor P.A. H. Wyatt, Department of Chemistry, University of St Andrews, The Purdie Building, St Andrews KY16 9ST Polymer Physics Group 6th Churchill Conference To be held at Churchill College, Cambridge on 1-4 April 1985 Further information from Professor I. M. Ward, Department of Physics, University of Lseds, Leeds LS2 9JT Statistical Mechanics and Thermodynamics Group Liquids-Dynamic and Static Properties To be held at the University of Bristol on 10-1 1 April 1985 Further information from Dr E. Dickinson, Procter Department of Food Science, university of Leeds, Leeds LS2 9JT Neutron Scattering Group Small-angle Neutron Scattering from Organised Systems To be held at Imperial College, London on 17-1 8 April 1985 Further information from Dr R. W. Richards, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1 XL Gas Kinetics Group with SERC Summer School in Gas Kinetics To be held at the University of Cambridge on 24 June to 3 July 1985 Further information from Dr I.W. M. Smith, Department of Chemistry, University Chemical Laboratory, Lensfield Road, Cambridge CB2 1 EP Industrial Physical Chemistry Group with the Food Chemistry Group Water Activity: A Credible Measure of Technological Performance and Physiological Via bi I ity To be held at Girton College, Cambridge on 1-3 July 1985 Further information from Professor F. Franks, Department of Botany, Downing Street, Cambridge CB2 3EAPolymer Physics Group Biennial Conference To be held at the University of Reading on 11-1 3 September 1985 Further information from Professor Bassett, J.J. Thompson Physical Chemistry Laboratory, University of Reading, Whiteknights, Reading RG6 2AF Industrial Physical Chemistry Group A Molecular Approach to Lubrication and Wear To be held at Girton College, Cambridge on 23-25 September 1985 Further information from Mr M. P. Dare-Edwards, Shell Research Ltd, Thornton Research Centre, Chester CH1 3SH Neutron Scattering Group jointly with the Materials Testing Group of the Institute of Physics Industrial Uses of Particle Beams To be held at the Institute of Physics, London on 26 September 1985 further information from Dr J. G. Booth, Department of Chemistry, University of Salford, Salford M5 4WT Division Annual Congress: Structure and Reactivity of Gas-Phase Ions To be held at the University of Warwick on 8-1 1 April 1986 Further information from Professor K.R. Jennings, Department of Molecular Sciences, University of Warwick, Coventry CV4 7AL 30TH INTERNATIONAL CONGRESS OF PURE AND APPLIED CHEMISTRY Advances in Physical and Theoretical Chemistry Manchester, 9-1 3 September 1985 The Faraday Division is mounting the following symposia as part of the 30th IUPAC Congress: Reaction Dynamics in the Gas Phase and in Solution This symposium will examine the ways in which modern techniques allow detailed study of the dynamical motion of molecules which are undergoing chemical reaction or energy exchange. Micellar Systems The symposium will discuss various aspects of micellization, including size and shape factors, micellization in biological systems, chemical reactions in micellar systems, micelle structure and solubilization.Emphasis will also be given to modern techniques of examining micellar systems, including small-angle neutron scattering, neutron spin echo, photocorrelation spectroscopy, NM R and use of fluorescent probes. Surface Science of Solids The symposium will centre on recent advances in the study of kinetics and dynamics at surfaces and of phase transitions in adsorbate layers on single crystal surfaces. Both experimental and theoretical aspects will be reviewed with an emphasis on metal single crystal surfaces. New Electrochemical Sensors (in collaboration with the Electroanalytical Group of the Analytical Division) The symposium will cover such topics as the fundamentals of the subject, new gas sensors based on membrane electrodes and on ceramic oxides, the development of new ion- selective electrodes and the synthesis of new guest-host carriers, the development of CHEMFETS and other integrated devices together with the theory of the operation of such devices, and finally the development of biosensors including for instance enzyme electrodes, direct electron transfer to biological molecules and new potentiometric techniques for protein analysis.The second circular, giving details of all the symposia of the Congress and listing invited speakers may be obtained from: Dr J. F. Gibson, 30th IUPAC Congress, Royal Society of Chemistry, Burlington House, London W1V OBN (vii)physicochemical topics, thereby encouraging scientists of different disciplines to contribute their varied viewpoints to a coiiinion theme. A recent Discussion is :- The Royal Soci- of Chemistry- No.75 lntraamolecwlar Kinetics No.75 in the series, this publication is the result of a general discussion held at the University of Warwick in April 1983. Contents: The Spiers Meniorlal Lecture; Vibrational Redistribution within Excited Electronic States of Polyatomic Molecules Inrraniolecular R e h u t i o n o f 1. vcited States lsomerization of Intcrnal~ncrgy-selected Ions Kinetics of Ion-Molecule Collision Coinple\es in the Gas Phase, E\periinent and Theory lntrainolccular Decay 01' Soinc Open-shell Pulya t o niic Ca lions On tlic Theory u i Iiitrdniolccul~r I n e r g y Transfer Pulsed Laser Preparation and Ouaniuin Superposition Statc Evolution in ReguLtr and Irregular Systems A Ouantuiii-iiicclianical Internal-collision Model for State-sclcctcd Uniinolccular Decoiiiposilio n The Correspondence Principle and Intramolecular Dynamics lntrainoleculdr Dcphasiiig. t'icusecond Evolution of Wavepacket States in a Molecule with Int erinediate-casc level Struct urc Energy Conversion in van der Waals C'u~~iplc\c\ ol s-Tetrarine and Argon Tim-dependent Processes in Polyatuinic Molecules During and After Intense Intrarcd Irradiation Energy Distributions in tlic (.N(X'L+) bragnient froiii tlie Infrared Multiplepholun Dissociation ol' CI.ICN. A Coinparison between 1:xperiiiiental Results and the Predictions ot Statistical Theories of ChFO + Product Energy Partitioning in the Decoiii- position of State-selectively Excited HOON and IIOOD Low-power Inl-rarcd Laser I'hoiolysis o f Tetramethy ldioxetan Uniinolecular Reactions lnduccd by Vibrational Overtone Excitation Uniiiiolecular Decomposition of t-Butylhydro- peroxide by Direct Excitation of the 6-0 0-11 Stretching Overtone I'icosecond-jet Spectroscopy and Photoclieinistry. Energy Redistribution and its Iiiipact'on Coherence, Isoincrization, Ihssociatiun and Solvalioii knergy Redistribution in Large Molecules.Duect St ud y o f In1 rainolucular Rehxa lion in the Gas Phase with Picosecond Gating Rotation-dependent Intrainolecuhr I'r~)cessc.sofSO:(A'A.) in a Superwnic Jct Role of Rotation-Vibration Interaction in Vibrational Keh\ation. Energy Kcdistribution in k,xcitcd Singlet I~'ornialdc1iyde Sub-lhppler.Spectroscopy of Benrcnc in the "('liaiinel-lliree" Region Intraiiiulccular 1:lectronic Kclau~tion and I'liotois~)iiieruati[)n Processes in tlie lsuhted Azabenrene Molecules Pyridinc, Pyrazinc and I'yriiiiidinc Softcover 434pp 0 85186 658 1 Price f25.00 ($48.00) Rest of the World f26.00 RSC Members f 16.25 Faraday Discussions of the Chemical Society 7< lnrruniolei u h r Kincrit I Faraday Symposia are usually held annually and are confined to more specialiscd topics than Discussions, with particular reference to recent rapidly developing lines of rescuch. A recent Symposium is :- No.l?The Hydrophobic Interadion No. 17 in the series, this publication is the result of a symposium on The Hydrophobic Interaction held at the Uiiiversity of Reading in December 1982.Contents: Hydrophobic Interdctionr a llistaric.11 Per spect ivr llydrupliobic Ilydration Geometric Kelaution in Water. Its Role in Precise Vapour-pressure Measureiiients of the SolubilkdtiorI of Benzene by Aqueous Sodiuiii Octylsulphate Solutions Nuclear Magnetic Resonance R e b u t i o n Investigation of Tetrahydrofuran and Methyl Iodide Clathrdtes Infrared and Nuckar Magnetic Kcwnance Studies Pertaining to the (age Model t o r Solutions oS Acetone in Water Irothernial Transport Properties in Solutions o f S y mmet r ica I Tet ra-alk y hmnioniuiii Bromides Thermodynamics of Cavity I'oriiiaiion in Water. A Molecular Dynamics Study Molecular Librations and Solvent Oricnt- ational Correlations in Hydrophobic Phenomena Monte Carlo Computer Siniulation Study of the Hydrophobic Effect. Potential ot Mean Force for ECfir)gaq at 25 and SOv C Hydroplicibic Moments and Protein Structure Application 01' the Kirkwood-Buff Theory to the t'roblcin 01 Hydrophobic Interactions Ihentangleinent of Ilydrophubic and IFlcctrosi~tic Contributions t o the I.ilni Pressures O i Ionic Surfactants llydrophobir. Intcracliuns in Dilute Su lut io ns u t 1'0 1 y (vin y I a Ico lio I) ('onioriii;tiionaI and 1:unc.i ional I'ropertics of tiaeiiwglobin in Water+Alcohol Mixtures. Dependence o f Bull. Electrostatic and tlydrupliohic I n t c r x t i o n s upon ptl and KCI concentrations Softcover 24Opp 0 85186 668 9 Price f36.50 ($70.00) Rest of the World f38.50 RSC Members f 23.75 ORDERING RSC Members should send their orders to: The Royal Society of Chemistry. The Membership Officer. 30 Russell Square, Non-RSC Members The Royal Society of Chemistry, Distribution Centre, Blackhorse Road, L London WC1 B 5DT. Letchworth, Herts SO6 IHN, England. Faradaj Symposia of the Chemical Society hGi 17 I hc HI drophohr' Inrcrm rron 1 9 X ? (viii)

ISSN:0300-9599    

DOI:10.1039/F198480FP093

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

J . Chem. SOC., Faraday Trans. 1, 1984, 80, 3233-3238 Kinetics of the Reaction of Lead@) Oxide with Hydrogen Bromide in the Temperature Range 398-548 K BY PHILIP G. HARRISON* AND RICHARD SMITH Department of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD Received 1st June. 1983 The kinetics of the reaction of both the tetragonal and orthorhombic modifications of lead(1r) oxide with hydrogen bromide at a pressure of 1.33 kN m-2 have been studied in the temperature range 398-548 K. Additionally, the reaction with the orthorhombic modification has been examined at HBr pressures of 0.67, 3.33 and 6.65 kN m-2. The kinetic behaviour of the two modifications is substantially different, an observation which is largely attributed to the difference in particle size.Reaction profiles for the orthorhombic modification (mean particle diameter ca. 15 pm) comprise a rapid initial reaction followed by a slow diffusion-controlled reaction giving conversions to lead@) bromide of ca. 5 % at 398 K rising to ca. 62 % at 548 K after 300 min. In contrast, reaction with the tetragonal modification (mean particle diameter ca. 2 pm) is rapid at all temperatures giving much higher conversions of ca. 47 % at 398 K rising to ca. 92 % at 548 K after only 40 min. Analysis of the rapid reaction in terms of a phase-boundary model yields rate constants (kpB) varying from 1.54 x lop4 s-' at 448 K to 2.55 x lop4 s-' at 548 K. The slow, limiting reaction observed for the orthorhombic modification is best described by the diffusion-controlled model of Zhuravlev, Lesokhin and Tempel'man, with derived rate constants (kZLT) varying from 1.65 x lo-* s-l at 398 K to 7.86 x loM6 s-' at 548 K, essentially independent of applied HBr pressure.Activation energies determined from Arrhenius analysis of the rate-constant data showed that for the phase-boundary-controlled reaction with the tetragonal modification is much lower [ 10.6(5) kJ mol-'1 than that for the diffusion-controlled reaction with the orthorhombic phase [71.8(17) kJ mol-'1. The only previous report of the reaction between lead@) oxide and hydrogen bromide is a study of the chemisorption of the gas onto vapour-deposited lead(I1) oxide in the temperature range 113-293 K.l In this study, the reaction was proposed to proceed by the initial chemisorption of a monolayer of HBr and the formation of dilead oxide dibromide on the surface followed by, at room temperature, a rapid reaction with lower layers of oxide.In this investigation we report a detailed account of the reaction of the orthorhombic (massicot) and tetragonal (litharge) modifications of lead(1r) oxide with hydrogen bromide in the temperature range 398-548 K. EXPERIMENTAL The vacuum line, microbalance and general procedure have been described previously.2 Hydrogen bromide (purity 99.8%, B.D.H.) was purified on a gas-purification vacuum line by collection in a 77 K trap after being passed through a stainless-steel coil immersed in a 197 K bath. It was further purified by means of a series of slush baths at 190 and 183 K and was finally collected and stored in storage bulbs.Lead@) oxide of the orthorhombic modification (East Anglia Chemicals) had the specification PbO > 98 % ,chloride < 0.02 % ,insoluble matter < 1 % , Cu < 0.002%, Fe < 0.0005%, Ag < 0.005%, Bi < 0.02%, Sb < 0.005% and As < 0.0005%. The sample of tetragonal lead oxide (Koch Light Chemicals) had a purity specification of 99.999%. 32333234 REACTION OF PbO WITH HBr For each kinetic run ca. 0.15 g of the oxide was accurately weighed into a silica reaction bucket, which was suspended from the quartz spring microbalance. The reaction system was evacuated overnight at a pressure of ca. lo-’ kN mP2 Torr) and brought to thermal equilibrium at the desired temperature. Hydrogen bromide was introduced into the reaction system at the required pressure and the extension of the spring monitored by means of a cathetometer. All experiments were performed in duplicate with a reproducibility of During the course of the reaction the samples of both oxide modifications underwent a colour change from yellow to pale grey because of the formation of lead@) bromide, and also changed from a loose powder into a self-supporting compact because of the greater molar volume of the bromide.Reaction products were examined by X.r.d. and by elemental analysis. X.r.d. showed that lead@) bromide was produced at the expense of lead(@ oxide. However, in reaction products obtained at higher temperatures (> 473 K), traces of dilead oxide dibromide were observed, formed by a subsequent solid-state reaction between lead(@ oxide and newly formed lead(I1) br~rnide.~ Good agreement was found for the amount of bromine in the product by both microanalysis and by calculation from the gravimetric data.5 % . RESULTS AND DISCUSSION Reaction profiles for the reaction of the orthorhombic and tetragonal modifications of lead@) oxide with hydrogen bromine at a pressure of 1.33 kN rn-, in the temperature range 398-548 K are illustrated in fig. 1-3 in terms of percentage conversion of the oxide according to: PbO + 2HBr --+ PbBr, + H20. Quite clearly, the character of the kinetic behaviour of the two modifications is different. The profiles for the orthorhombic modification (fig. 1 and 2) are composed of two distinct components, a rapid initial reaction followed by a much slower, limiting reaction giving a conversion of ca.5% at 398 K rising to ca. 62% at 548 K after a period of 300 min. In contrast, reaction with the tetragonal modification is rapid at all temperatures giving conversions of ca. 47% at 398 K rising to ca. 92% at 548 K after only 40 min. Although the reaction profiles for temperatures > 448 K are smooth curves over this period, those observed at 423 and 398 K exhibit distinct discontinuities after ca. 20 min, indicative of a change of mechanism (fig. 3). For both modifications the rate of reaction increases with increasing temperature, with reaction profiles which are deceleratory throughout the course of the reaction. The observed difference in the behaviour of the two modifications may be attributed to three possible causes: (i) a fundamental difference in the solid-state structure, (ii) the presence or otherwise of impurities in the oxide and.(iii) a difference in the particle size of the two samples.Although the densities of the two modifications are different (the tetragonal phase has a higher density of 9.53 compared with 8.0 for the orthorhombic phase), the solid-state structures are quite similar.*? Structural consi- derations would therefore predict a lower reactivity for the more tightly packed tetragonal phase, contrary to observation. The orthorhombic phase (thermodynami- cally stable at 488 K) is stabilized at ambient temperatures by the presence of impurities, which would be expected to facilitate reaction via nuclei-growth mechan- isms, again contrary to observation.The major difference between the two oxide samples is particle size, the mean particle diameters being ca. 15 and ca. 2 pm for the orthorhombic and tetraganal modifications, respectively, corresponding to surface areas of ca. 2.5 x and ca. 0.2 m2 g-l. Thus, the oxide surface area of the tetragonal modification available for reaction is ca. 8 times that of the orthorhombic phase, which for a heterogeneous solid-gas reaction is a significant difference and would be expected to lead to a more rapid reaction.P. G. HARRISON AND R. SMITH 3235 tlmin Fig. 1. Reaction profiles for the reaction of orthorhombic lead oxide with hydrogen bromide at a pressure of 1.33 kN m-2 and a temperature of 0, 398; A, 423 and 0, 448 K (only every third data point plotted).n s tlmin Fig. 2. Reaction profiles for the reaction of orthorhombic lead oxide with hydrogen bromide at a pressure of 1.33 kN m-2 and a temperature of a, 473; A, 498; A, 523 and 0,548 K (only every third data point plotted). The three principal types of model which have been applied to the interpretation of solid-gas kinetic data are : (i) nuclei-growth models, (ii) phase-boundary models and (iii) diffusion-controlled models. Some of the more commonly used solid-state reaction-rate equations have recently been briefly summarised by O'Brien.g In the present case, the initial rapid reaction component of the reaction profile for the orthorhombic phase corresponds to a surface reaction, during which a coherent layer of lead@) bromide is formed, through which the diffusion of HBr is rate determining for the slower, limiting reaction. The most widely used diffusion model is the one formulated by Jander,',* and described by kJ t = [l -(1 -x);l2 where k, is the rate constant and x is the fraction of the reaction completed in time t .However, plots of the function [ 1 - (1 - x)4I2 against time for the present data deviate from linearity. Of the other models available, that of Zhuravlev, Lesokhin and Tempel'man (ZLT),* in which the Jander analysis is modified by assuming that the activity of the reacting material is proportional to the fraction unreacted, best3236 REACTION OF PbO WITH HBr 1 oc 90 80 70 n 60 5 c *; 50 z O0 40 30 20 10 0 b A . A A 0 * ' Q 0 0 ' 4 b I I I I 1 10 20 30 40 50 t/min Fig. 3. Reaction profiles for the reaction of tetragonal lead oxide with hydrogen bromide at a pressure of 1.33 kN m-2 and a temperature of 0, 398; V, 423; 0, 448; Y7, 473; A, 498; 0, 523 and A, 548 K (only every third data point plotted).describes the experimental data for the diffusion-controlled reaction. In this model, the rate equation is given by 1 --x After a short initial period (ca. 15 min) plots of the ZLT function against time, shown in fig. 4, afforded good linear fits to the experimental data for each temperature over the time period considered (300 min). Rate constants (kzLT) calculated using this analysis are collected in table 1 and range from 1.65 x low8 s-l at 398 K to 7.86 x loL6 s-l at 548 K. Analysis using either nuclei-growth or phase-boundary models gave unsatisfactory results.To investigate the effect of applied pressure of HBr on the reaction, kinetic data for the same temperature were collected for applied pressures of 0.67, 3.33 and 6.65 kN m-2. The reaction profiles obtained were very similar to those for an HBr pressure of 1.33 kN m-2, comprising a fast initial surface reaction and a subsequent much slower diffusion-controlled reaction. Rate constants derived using the ZLT analysis for the four HBr pressures are summarized in table 1, from which it can be seen that the rate constants are essentially independent of applied HBr pressure. Activation energies for the diffusion-controlled reaction calculated from least-squares analysis of linear Arrhenius plots are also summarized in table 1, yielding a mean value of 71.8(1.7) kJ mol-l.P.G. HARRISON AND R. SMITH 0 0 0 0 0 0 0 3237 Fig. 4. Plot of {[l/(l -x)]i- l}z against t for the reaction of orthorhombic PbO with HBr (pressure 1.33 kN m-2) at a temperature of 0 , 4 7 3 ; A, 498; A, 523 and 0, 548 K. Table 1. Rate-constant and activation-energy data for the reaction of orthorhombic lead oxide with hydrogen bromide. -1n kZLT HBr pressure/kN m-2 TIK 0.67 1.33 3.33 6.65 398 423 448 473 498 523 548 activation energy/kJ mol-l 18.13 17.26 16.25 15.46 14.21 13.30 12.01 73.0 17.92 16.76 16.42 15.17 14.03 13.35 11.75 71.1 17.77 17.81 17.08 16.97 16.38 16.30 15.16 15.03 14.03 13.82 13.35 13.08 12.12 11.72 69.7 73.3 The initial rapid component of the reaction profile for the orthorhombic phase is probably to be identified with the whole of the reaction profile for the reaction observed with the tetragonal phase.Not surprisingly, analysis of the kinetic data in this latter case by the KLT method showed that the reaction was not diffusion controlled. The application of nuclei-growth models also proved unsatisfactory. Phase-boundary analyses, however, provide a good representation of the experimental data in the temperature range 448-548 K, indicating that the lead@) bromide product layer is porous to HBr and that bond-making and/or bond-breaking is the rate- determining step. Some deviation from this analysis is observed for the later parts of the reaction profiles, the percentage conversion at which this deviation occurs increasing with increasing temperature, and can be attributed to a change in mechanism from phase-boundary control to diffusion control as the porosity of the product layer decreases.The deviation is most marked in the reaction profiles obtained at 398 and 423 K, where the reaction can be resolved into two distinct parts: an initial3238 REACTION OF PbO WITH HBr Table 2. Rate-constant data for the reaction of tetragonal lead oxide with hydrogen bromide at a pressure of 1.33 kN m-2 -In k,, 448 8.78 473 8.70 498 8.58 523 8.40 548 8.27 fast reaction and a second slower reaction, where diffusion through the product layer is now rate determining. Rate constants (kPB) derived using the expression kt = l-(l-x){ are listed in table 2, from which an activation energy of 10.6(5) kJ mol-l was derived by least-squares analysis of the Arrhenius plot.Thus, in conclusion, it would appear that particle size, rather than some fundamental difference in solid-state constitution, is primarily responsible for the observed difference in kinetic behaviour between the two samples of lead@) oxide studied. The initial reaction with HBr, when the lead@) bromide product layer still allows facile access to the oxide, is phase-boundary controlled. When the product layer becomes coherent, the reaction becomes diffusion controlled. Consequently, for smaller particles with large surface area, the rapid phase-boundary-controlled reaction proceeds to a greater extent. We thank the S.E.R.C. and the Associated Octel Company Ltd for support in the form of a CASE Award to R.S. A. H. Boonstra and R. M. A. Sidler, J. Electrochem. SOC., 1972, 119, 1193. * P. G. Harrison and R. Smith, J. Chem. Soc., Furuduy Trans. I , 1980, 76,442. F. W. Lamb and L. M. Niebylski, J . Am. Chem. Soc., 1953,75, 511. W. J. Moore and L. Pauling, J. Am. Chem. Soc., 1941, 63, 1393. J. Lecleiewicz, Actu Crystallogr., 1961, 14, 66. P. OBrien, J. Chem. SOC., Dalton Trans., 1982, 1173. ’ W. Jander, 2. Anorg. Chem., 1927, 163, 1. * S. F. Hulbert, J. Br. Cerum. SOC., 1969, 6, 1 1. * V. F. Zhuravlev, I. G. Lesokhin and R. G. Tempel’man J. Appl. Chem. USSR, 1948,21, 887. lo N. B. Hannay, Treatise on the Solid State (Plenum Press, New York, 1976), vol. 4. (PAPER 3/867)

ISSN:0300-9599    

DOI:10.1039/F19848003233

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I , 1984,80, 3239-3244 Acidity of Hydrogen Forms of Zeolite T of the Erionite-Offretite Type BY ANDRZEJ CICHOCKI Institute of Chemistry, Jagiellonian University, M. Karasia 3, 30-060 Krakhw, Poland Received 15th August, 1983 The acidity of H forms of zeolite T obtained by various processes have been determined by treatment with 0.1 mol dm-3 NaOH and back-titration of the excess and by treatment of the extract obtained by successive batch treatments with 2 mol dm-3 NaCl. The results of the treatment with NaOH are always higher than those obtained with NaCl. The results of the treatments and chemical analyses have been used to determine the formulae of the unit cells of the H forms and the kind of reaction. The presence of extraskeletal aluminium (A10+), exchangeable with NaC1, and loosely bound silica, soluble in NaOH, has been found.It is postulated that the H forms contain two kinds of acid centre: strong, determinable using NaCl and NaOH, and weak, determinable only using NaOH. The portion of weak centres depends strongly on the method and degree of modification. Identically localized centres have been found to change their strength according to modification conditions. In a series of previous st~diesl-~ the effects of the conditions of modification of zeolite T on the physicochemical and catalytic properties of its H forms were investigated. It has been found that zeolite T induces a shape-selective effect in the transformation of but-1-ene and similarities and differences in comparison with H forms of zeolite Y have been described.6 In a previous study5 the conclusion was reached that in the H forms there is only one kind of acidity, Brarnsted acid centres of equal strength, and that the concentration of these centres is equal to the proton concentration calculated from chemical analysis (from cation deficiency). The aim of the present paper was to investigate and compare the value, strength and sources of acidity in H forms of zeolite T, obtained using different, previously de~cribedl-~ methods.Dealuminated H forms, which often have interesting catalytic properties, were also investigated. This enabled verification of earlier assumptions and conclusions to be drawn about the dependence of acidity on the mode of preparation of the H forms. The methods used in this paper are based on those of Barrer and Klin~wski,~ KuhP and Breck and Skeel~.~ They consist of parallel measurements of acidity based on the treatment of the H forms with NaOH and NaCl and chemical analysis of the solids before and after the treatments.The treatment with NaOH solution is a standard method of assay of ion-exchange capacity of strongly and weakly acidic cationites, while the treatment with NaCl solution is used only for strongly acidic centres (for the weakly acidic groups the value of the equilibrium constant for the exchange reaction is too low). Parallel application of both treatments permits the assay of both strongly and weakly acidic groups in the same H form. The validity of this procedure has been confirmed by the observation of Kiihl,8 who reported the complete agreement of the results of acidity assays by treatments with NaCl and NaOH of so-called ‘true hydrogen forms of mordenite’, where the only source of acidity was protons.32393240 ACIDITY OF H FORMS OF ZEOLITE T Carrying out chemical analysis of solids both before and after treatment with solvents and a theoretical analysis of the course of the reactions enabled the sources of acidity and their contribution in the total acidity to be established. The main advantages of the method are its simplicity, its purely chemical character and the need for no additional thermal or vacuum treatments, which are often necessary in instrumental methods (these treatments may change the preparation and its acididy). The principal disadvantage of the method is that it is time consuming.EXPERIMENTAL The starting material was preparation ET-54, a synthetic zeolite K,Na-T, which was obtained and investigated in a series of previous e~periments.l-~ Hydrogen forms were obtained from the starting material by three methods: samples of B-1 and B-2 by treatment with 0.1 mol dmP3 HCl at 22 "C for 24 h at m (the ratio of the number of acid equivalents to the number of equivalents of cationic positions in the sample) equal to 2 and 10, respectively, sample B-3 by three treatments with 0.01 mol dm-3 HCl at 100 "C for 0.5 h, with stirring, at m = 1, and sample B-4 by treating the highly exchanged NH, form with 3 mol dm-3 NH,C1 solution at 100 "C for 0.5 h, with stirring, at m = 15, and its subsequent decomposition at 500 "C, in a thin (ca. 2 mm) layer, in air, for 4 h.For each modification 11.6 g of the starting material was taken. After the treatment the product was rinsed with water until no further C1- was present, dried at 110 "C for 4 h and conditioned (left for 24 h in contact with the atmosphere). The acidity was determined by two methods. (a) Treatment with 2 mol dm-3 NaC1. Ca. 1 g of the H form was treated with 150 cm3 of 2 mol dm-3 NaCl solution and the mixture was stirred for 15 min. The slurry was filtered through a fritted disc funnel (type G-5) and the residue was washed with water. The filtrate was then titrated with 0.1 mol dm-3 NaOH solution. A mixture (1: 1) of ethanolic solutions of methyl red (0.2%) and methylene blue (0.1 %) was used as indicator.The solid was reslurried with 150 cm3 of 2 mol dm-3 NaCl solution and the treatment was repeated until the amount of titrant required was < 0.1 cm3 for the last batch (usually nine times). The total volume of 0.1 mol dm-3 NaOH used, after recalculation for the unit cell of the H form, equalled the amount of neutralized hydrogen ions after the given number of treatments, Hf,,,,/u.c. The accumulated volumes of 0.1 mol dm-3 NaOH (in cm3) plotted against the number of treatments yielded, after extrapolation, the number of hydrogen ions that would be neutralized after an infinite number of treatments, HZ N a C 1 / ~ . ~ . The treatment was carried out twice and the results were calculated as weighted means. After treatment the solids were centrifuged and washed with water, with the level of sodium in the filtrate being controlled photometrically.After drying and conditioning the samples were weighed and thoroughly mixed. Thus sample B- 1 - 1 was obtained from sample B-1 etc. (b) Treatment with 0.1 rnol dm-3 NaOH. Ca. 1 g of the H form was treated with 100 cm3 of 0.1 mol dm-3 NaOH solution and stirred for 1 h. The treatment was carried out in polypropylene or Teflon vessels protected against atmospheric CO,. The solid was separated and washed with water by several centrifugations in a closed plastic cuvette. From the third washing the sodium level in the filtrate was tested photometrically. The excess of NaOH in pooled filtrate was back-titrated with 0.1 mol dm-3 HCl to measure the amount of NaOH used. The mixed indicator methyl red+methylene blue was used.For each H form two assays were carried out and the results were calculated as weighted means and recalculated for the unit cell, H+,,,,/u.c. Washed solids were weighed and mixed. Thus sample B-1-2 was obtained from sample B-1 etc. All preparations were investigated by powder X-ray analysis, classical wet chemical analysis and microscopically, as described previo~sly.~-~ Additionally, for some of the extracts and washings from the NaOH and NaCl treatments the amount of A1 and Si present was determined.A. CICHOCKI 324 1 CALCULATIONS The general compositions of the unit cells of the preparations, the amount of aluminium removed, rem. Al/u.c., and the amount of silicon removed after NaOH treatment, rem. Si/u.c., were calculated from the chemical composition and the structure of the unit cell.The effective aluminium (eff. Al/u.c.), i.e. the percentage of aluminium potentially associated with H+ ions in the unit cell, was calculated as in the study of Kiihl.8 From the total percentage of aluminium in the unit cell the percentage of aluminium associated with Na+ and K+ was subtracted. The percentage of extraskeletal aluminium, AlO+/u.c., was calculated, e.g. for B- 1, from the difference: rem. Al/u.c. for B-1-1 minus rem. Al/u.c. for B-1. Analogous calculations were carried out for the remaining H forms. The concentration of strong acid centres was calculated using the equation Hitrong/u.c. = (H+NaCI/u.c.) - (AlO+/u.c.) and the concentration of weak acid centres using the equation H:eak/~.~.= (H+NaOH/u.c.) - (H+NaCI/~.c.). RESULTS AND DISCUSSION As shown in table 1, the H forms display almost full retention of crystallinity, as do the solids after the NaCl treatment. However, the samples treated with NaOH display lower crystallinity. All the H forms obtained by the action of HCl solutions showed dealumination, which became more marked after treatment with NaCl (an increase in rem. Al/u.c.). On the other hand, treatment with NaOH resulted in a lowering of the SiO,/Al,O, ratio to values similar to those in the initial samples (an increase in rem. Si/u.c., table 1). This indicates that during the treatment with NaCl the H forms release some aluminium to the solution and during treatment with NaOH the loosely bound silica is removed (the sample changes in the direction of the initial state).This was confirmed by the assays of A1 and Si in the extracts and washings. In the case of sample B-4 the changes in the SiO,/Al,O, ratio were small. In the direction from B-1 to B-4, eff. Al/u.c. increased and this was a measure of the increase in the degree of modification (decatonization) of the H forms. The treatment with NaCl resulted in all cases (except B-1-1) in retention of a considerable percentage of aluminium (cationic positions) not neutralized with Na+ cations. The NaOH treatment in these case was much more effective. Note that the increase in rem. Al/u.c. from an H form (e.g. B- 1) and the preparation resulting from its treatment with NaCl (e.g. B-1-1) was equal or almost equal to the value of eff.Al/u.c. for a preparation after NaOH treatment (e.g. B-1-2). The results of treatments with NaCl and NaOH are presented in table 2. Depending on the method and degree of modification there are large differences in the acidity of the H forms determined by the methods using NaCl and NaOH. Generally, H&,,,/u.c. was always higher than H+, N a C 1 / ~ . ~ . and H&,,,/u.c. The difference increased with increasing eff. Al/u.c. The results from the method using NaCl were similar for the various H forms. To elucidate the differences in acidity one must consider the reactions occurring during the treatments. During the treatment of the H form with NaCl the following reactions take place: exchange of H+ in the zeolite for Na+ from the solution:Table 1. Results of X-ray analysis, chemical analysis and characteristics of changes in the composition of the unit cells X-ray mol oxide/mol Al,O, analysis (Na+K) eff.A1 rem. A1 rem. Si preparation type of treatment (wt%) Na,O K,O SiO, /A1 /u.c. /u.c. /u.c. ET-54 B- 1 B-1-1 B-1-2 B-2 B-2- 1 B-2-2 B-3 B-3-1 B-3-2 B-4 B-4- 1 B-4-2 initial sample 0.1 mol dm-3 HCl, m = 2 2 mol dm-3 NaCl 0.1 mol dmP3 NaOH 0.1 mol dmP3 HC1, m = 10 2 mol dm-3 NaCl 0.1 mol dm-3 NaOH 0.01 mol dmP3 HC1, 100 "C 2 mol dm-, NaCl 0.1 mol dm-3 NaOH 3 mol dm-3 NH,Cl, 500 "C 2 mol dm--3 NaCl 0.1 mol dmP3 NaOH 100 98 100 95 95 98 87 95 98 91 100 98 96 0.13 0.04 0.69 0.49 0.004 0.435 0.68 0.02 0.36 0.64 0.0 1 0.37 0.70 0.87 0.50 0.24 0.41 0.3 1 0.22 0.3 1 0.29 0.28 0.29 0.27 0.19 0.27 7.43 8.35 9.26 7.60 10.22 10.33 7.85 8.69 9.18 7.25 7.32 7.44 7.3 1 1 .oo 0.54 0.93 0.90 0.3 1 0.66 0.99 0.3 1 0.64 0.93 0.28 0.56 0.97 0 3.12 0.43 0.67 3.81 1.89 0.06 4.50 2.2 1 0.44 5.51 3.33 0.23 0 0.87 1.54 0.87 2.1 1 2.17 2.11 1.14 1.49 1.14 0 0.12 0 0 0 0 2.54 0 0 6.56 0 0 4.70 0.30 0.30 0.34 Table 2.Results of treatments with 2 mol dm-, NaCl and 0.1 mol dmP3 NaOH and the characteristics of acidity of the H forms of zeolite T ~~ ~~ treatment 0.1 mol dm-3 2 mol dmW3 NaCl NaOH H&aCl H&NaCl Hf,NaCl eff- A1 A10+ Hsftrong H$eak Hs+trong H$eak H form /u.c. /u.c. /eff. A1 /u.c. /u.c. /u.c. /u.c. /u.c. /eff.Al /eff. A1 B- 1 2.1 1 2.34 0.75 2.47 3.12 0.67 1.44 0.36 0.46 0.1 1 B-2 1.91 2.2 1 0.58 3.76 3.81 0.06 1.85 1.85 0.49 0.49 B-3 1.96 2.19 0.49 4.15 4.50 0.35 1.61 2.19 0.36 0.49 B-4 2.09 2.27 0.4 1 5.41 5.51 0.12 1.97 3.32 0.36 0.60A.CICHOCKI 3243 exchange of AlO+ in the zeolite for Na+ from the solution: AlO; + Na,+ $ A10; + Na: (2) K; +Na,+ K,+ +Na$ (3) (4) ( 5 ) During treatment of the H forms with NaOH, reaction (3) does not occur in three cases and K+ is not removed. On the other hand, the rapidity of reaction (5) accelerates reactions (2) and (4). As a result, the extraskeletal aluminium (A10+) is not released from the H form but precipitates inside as deposit of A100H.' In addition the loosely bound silica depolymerizes : but it does not consume NaOH because of the hydrolysis of the silicates. The course of reaction (6) depends on the method and degree of modification. The reaction runs effectively only for H forms obtained by the action of HCl, particularly when dealumination is considerable (B-2).There is, however, no relationship between rem. Si/u.c. and utilization of NaOH (H&,,&.C.). The different results for treatment with NaOH and NaCl may be explained by the postulation that the H forms of zeolite T contain two types of acid centres: strong and weak. Strong centres (H,+,,,,,/u.c.) and extraskeletal aluminium (in the form of A10+) are determinable by treatment with NaCl. The treatment with NaOH shifts the equilibrium of reaction (1) to the right and permits the assay of both strong and weak centres (Hzeak/u.c.) and the acidity connected with the extraskeletal aluminium, reaction (4). This concept is supported by the agreement between the results of the chemical analyses of the solids after treatment and the results of the treatments [agreement between the sodium content in the preparations and the consumption of sodium during the treatments and agreement between the difference (eff.Al/u.c.) - (AlO+/u.c.) and H&,,,/u.c.]. The results of both treatments and the Na+ content in the preparations showed the best consistency for the assumption that extraskeletal aluminium appears in all the H forms as A10+. If one assumes that there exists a less hydrolysed form of extraskeletal aluminium, according to Kiihl's scheme of hydrolysis :8 A13+ + H20+A10H2+ + H+-ql(OH): + H+ H'o+Al(OH), + HS exchange of K+ in the zeolite for Na+ from the solution: and reactions in the solution during titration of the filtrate with NaOH : A10; + H,O + AlOOH + H,+ Hz + OH; + H20.(SiO,), = xSi0, (6) -HzO A10+ (7) then H+,,,,/u.c. and H&,,,/u.c. would be larger and, simultaneously, the (Na+ + K+) content in the H forms and preparations after treatment would be lowered (a decrease in the number of cationic positions). The assumption of the presence of more complicated oxyaluminium cations, discussed for HY by Breck and Skeel~,~ is even less probable. The data in table 2 indicate that the amount of strong and weak centres depends on the method of modification of the zeolite and the degree of modification. Generally, Hzeak/u.c. and H;,,,/eff. A1 increase with increasing eff. Al/u.c., while H&rong/~.~. depends on the conditions of modification, but its participation in eff. Al/u.c.3244 ACIDITY OF H FORMS OF ZEOLITE T Table 3.Formulae of the unit cells preparation unit cell ET-54 B- 1 B-1-1 B- 1-2 B-2 B-2- 1 B-2-2 B-3 B-3- 1 B-3-2 B-4 B-4- 1 B-4-2 decreases. The assumptions of the existence of two kinds of acidity, the form of the extraskeletal aluminium and consideration of reactions (1)-(6) allows the unit cells of all the preparations to be established (table 3). We have found previously5 in i.r. spectra, that with the decationization of zeolite T the intensity of the OH band at 3615 cm-l increases. This band appears even in the preparations with the lowest amount of modification and is the most prominent. In this study we have found the highest content of less acidic OH groups (determinable only with NaOH) in preparation B-4. This may be explained by the assumption that identically located OH groups in the crystalline network may change their strength depending on the conditions of modification (differences in the environment of the OH group change its acidic strength). Direct information on framework A1 could be obtained by 29Si m.a.s.n.m.r., which has been used successfully for the confirmation of the applicability of Lowenstein's rule in zeolites,1° but this is beyond the scope of this paper. The results of this study indicate the decisive influence of the mode of preparation (the method of modification) of the H forms of zeolites not only on the acidity but also on the presence and proportion of various sources of acidity, of different acidic strength (strong and weak Bronsted centres and extraskeletal aluminium forms), and its influence on the distribution of acidic centres of various strengths in the structure. Changes of the methodological parameters determine the catalytic properties of the H forms. A. Cichocki, Krist. Tech., 1978, 13/8, 991. A. Cichocki, Chem. Stosow., 1980, XXIV/2, 171. A. Cichocki, Krist. Tech., 1980, 15/7, 869. A. Cichocki, Krist. Tech., 1980, 15/9, 1077. A. Cichocki, J. Chem. SOC., Faraday Trans. I , 1980, 76, 1380. S. Cqckiewicz, A. Baranski and J. Galuszka, J. Chem. SOC., Faraday Trans. I , 1978,74, 2027. R. M. Barrer and J. Klinowski, J. Chem. Soc., Faraaizy Trans. I , 1975, 71, 690. D. W. Breck and G. W. Skeels, Am. Chem. SOC. Symp. Ser., 1977,40, 23. * G. H. Kiihl, Am. Chem. SOC. Symp. Ser., 1977,40,96. lo J. Klinowski, J. M. Thomas, C. A. Fyfe and J. S. Hartman, J. Phys. Chem., 1981, 85, 2590. (PAPER 3/ 1442)

ISSN:0300-9599    

DOI:10.1039/F19848003239

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

J. Chem. SOC. Faraday Trans. 1, 1984,80, 3245-3255 Silica-supported Binuclear Copper Oxide Catalysts Derived from Cupric Acetate Monohydrate Their Spectroscopic Characterization and Catalytic Nature in Carbon Monoxide Isotope Equilibriation or Carbon Monoxide Oxidation with Nitrous Oxide BY NORIYOSHI KAKUTA, AKIO KAZUSAKA,* AKIKO YAMAZAKI AND KOSHIRO MIYAHARA Research Institute for Catalysis, Hokkaido University, Sapporo 060, Japan Received 3rd January, 1984 Novel silica-supported copper oxide catalysts have been prepared by impregnating silica with an aqueous solution of cupric acetate monohydrate, a typical binuclear copper complex. Binuclear copper(I1) ions, mononuclear copper(I1) ions and highly dispersed cupric oxide on the calcined samples have been characterized using e.s.r.and/or i.r. spectroscopy using acetic acid as a probe. Significant amounts of binuclear copper(r1) ions were estimated on silica from the spin concentration of the e.s.r. signal. The rate of CO isotope equilibriation or CO oxidation with N,O is a function of the number of binuclear copper ions, indicating that this binuclear structure is responsible for both reactions. The importance of the hydroxyl group in anchoring the cupric acetate complex on silica is stressed, and a reaction mechanism for the oxidation of CO with N,O has been suggested on the basis of the binuclear structure of the copper ions. The states of copper on silica-supported copper catalysts prepared from a cupric ammine complex or cupric nitrate have been studied by various physical and chemical techniques.l-s Highly dispersed CuO and cupric silicate species have been detected on those catalysts.Moreover, the technique of temperature-programmed reduction has revealed that these two kinds of copper species differ from each other in their reactivity for hydrogen; dispersed CuO is reduced by hydrogen at ca. 280 "C, whereas the copper silicate species are reduced at higher temperatures depending on the calcination temperat~re.~q We have attempted to prepare a novel silica-supported copper catalyst from cupric acetate m~nohydrate.~ The latter is known to be a typical binuclear copper complex with a copper-copper bond of 2.61 A,a so that we can expect to prepare a silica-supported binuclear copper catalyst different from those reported previously.In this contribution we report details of the characterization of binuclear copper ions on catalysts derived from the cupric acetate complex and their catalytic behaviour in CO isotope equilibriation and CO oxidation with N,O. EXPERIMENTAL The cupric acetate monohydrate and cupric nitrate employed in this work were of certified grade and purchased from Wako Pure Chemicals. Silica gel was Kiesel Gel 60 from Merck, having a mean pore diameter of 60 A. The gases CO, 0,, N,O and CO, were of high-purity grade and were used without further purification. Carbon monoxide labelled with oxygen- 18 (96.8%) and carbon-13 (90.7%) was purchased from Prochem B.O.C. Ltd. Acetic acid was purified carefully by freezepumpthaw techniques. The silica-supported catalysts derived from the cupric acetate complex were prepared by impregnating silica gel with an aqueous solution of cupric acetate monohydrate and then dried 32453246 SILICA-SUPPORTED COPPER OXIDE CATALYSTS at 100 "C overnight.The concentration of copper was determined by atomic absorption analysis to be 0.5, 1.6,2.8,3.0,3.2,3.7,4.7 or 6.2 wt% . For comparison, a conventional silica-supported copper catalyst was prepared from the cupric ammine complex by ion exchange4v6 and contained 3.4 wt% of copper. Catalysts prepared in this way were activated in a vacuum for 1 h stages at room temperature, 100, 200 and 300 "C and subsequently calcined with 100 Torrt of oxygen at 300 "C. CO,, acetic acid and methyl acetate were observed by mass spectrometry through the activation processes.E.s.r. spectra were obtained with a Varian E4 spectrometer at a frequency of 9 GHz. The g-values were calculated relative to DPPH as standard (g = 2.0036). The spin concentrations of the cupric ions were estimated by comparing the integrated sample spectra with those of CuSO, - 5H,O or Cu,(CH,COO), - 2H,Q. The spin concentration due to the cupric ions in cupric acetate monohydrate was confirmed to be proportional to the sample weight in the range 0-30 mg. The error was estimated to be within 40%. A Jasco IR-G spectrometer was used to obtain the i.r. spectra. Samples were prepared by grinding the catalysts into a powder and pressing into wafers of typically 10-20 mg ern-,. They were pretreated individually in a Pyrex cell fitted with KBr windows. A conventional closed recirculating reactor (ca. 700 cm3) was employed for the kinetic studies of CO isotope equilibriation or CO oxidation with N,O.1 g of sample was placed in a cylindrical reactor and activated in the manner described previously. The isotope composition in carbon monoxide was determined using a Hitachi RMU-6 mass spectrometer and the partial pressures of CO, CO,, N,O and N, were followed using a gas chromatograph connected directly to the reactor. RESULTS AND DISCUSSION E.S.R. SPECTROSCOPIC STUDIES Fig. 1 shows the e.s.r. spectra of a sample of the catalyst derived from the acetate complex containing 3.0 wt% copper under the processes of activation from room temperature to 300 "C and subsequent calcination with oxygen at 300 "C. As shown in fig. 1 (a), the freshly prepared sample exhibits two kinds of e.s.r.signal: a signal characteristic of powdered cupric acetate monohydrate having absorptions at low and high magnetic fields (referred to as signal A), and a familiar axially symmetric signal having the respective e.s.r. parameters of gll = 2.34, gl = 2.06 and All = 138 G (referred to as signal B). The e.s.r. spectrum of powdered cupric acetate monohydrate has been identified by three absorptions at low and high magnetic fields and interpreted by the triplet state arising from the coupling of pairs of CuII i~ns.~-ll The three absorptions in this spectrum are given in fig. 1 (a) and the e.s.r. parameters are estimated to be gll = 2.36, gl = 2.11 and D = 0.32 cm-l, where D is the tetrahedral zero-field splitting parameter.Values of g,, = 2.35, gl = 2.08 and D = 0.34 cm-l have been reported for powdered cupric acetate monohydrate by Lewis et aZ.l0 Signal B, on the other hand, can be attributed to isolated cupric ions coordinated with acetate ligands in distorted octahedral symmetry, suggesting that the binuclear cupric acetate complex is decomposed into a mononuclear structure during its impregnation onto silica. When the catalyst was activated under vacuum stepwise from room temperature to 300 "C, signal A disappeared completely at 100 "C [fig. 1 (c)]. Calcination of the sample with oxygen at 300 "C changed signal B into a new anisotropic signal, giving the parameters g, = 2.50, g, = 2.09 and g, = 2.04. The same signal has been reported for a silica-supported copper catalyst prepared by conventional methods and assigned to isolated cupric ions in distorted tetrahedral ~ymrnetry.~ t 1 Torr = 101325/760 Pa.N.KAKUTA, A. KAZUSAKA, A. YAMAZAKI AND K. MIYAHARA 3247 signal A < J signal B x4 0 1.0 2.5 3.0 3.5 4.0 5.0 6.0 H/kG Fig. 1. E.s.r. spectra of catalyst derived from the cupric acetate complex (3.0 wt% Cu) under processes of activation, calcination and adsorption of acetic acid. Arrows in signal A show position of axial resonance field. The frequency was 9.48 GHz. Temperature shows activation temperature under vacuum and calcination was carried out with 100 Torr of oxygen at 300 "C. (a) Fresh sample, (b) 25 "C, (c) 100 "C, ( d ) oxidation and (e) adsorption of CH,COOH. When the calcined catalyst was exposed to acetic acid vapour at room temperature, signal A reappeared and the anisotropic signal was changed into signal B, as seen in fig.1 (e). The catalyst derived from the ammine complex, on the other hand, gave an anisotropic signal having the parameters g , = 2.47, g , = 2.10 and g , = 2.04, after activation and subsequent calcination. Exposure of the sample to acetic acid vapour showed only the faint signal A with the anisotropic signal becoming axially symmetric. Thus, the catalyst derived from the acetate complex preserves a significant number of binuclear cupric ions on the silica in comparison with the conventional catalyst. In addition, acetic acid is a good probe molecule for detecting binuclear cupric ions supported on silica. The concentrations of isolated or binuclear cupric ions were estimated by doubly integrating signal A or B and comparing the result with that of cupric sulphate or cupric acetate monohydrate. The high-field component of signal A was used to estimate the spin concentration of the binuclear cupric ions, because the low field component is obscure near 0 G.Fig. 2 shows the concentration of binuclear cupric ions for the calcined samples plotted against total copper loading. The numbers of isolated cupric ions are almost constant on all the catalysts in the3248 8 2.0 s a a '"1 O O h 3 z 3.0 Q) 0 .d I .o ' 0 1.0 2.0 3.0 4.0 5.0 6.0 copper loading (wt%) Fig. 2. Concentrations of copper species on catalysts derived from the cupric acetate complex: 0, binuclear Cu" ions; a, highly dispersed CuO; x , isolated CuII ions.range 0.5-6.2 wt% copper, while those of the binuclear cupric ions increased with copper loading. On the other hand, the conventional catalyst containing 3.4 wt% copper gave only one-tenth the amount of binuclear cupric ions as the catalyst derived from the acetate complex at nearly the same copper content (not shown in fig. 2). The sums of the amounts of these two copper species are less than the total copper loading, indicating that the CuII ions, which cannot be detected using e.s.r. spectroscopy with the acetic acid probe molecule, exist on silica. Two kinds of e.s.r.-inactive CuII ions have been reported in the literature:12 one is present in CuO and is diamagnetic and the other is CuII in sites of trigonal symmetry which have relaxation times too short to give e.s.r.signals. The e.s.r.-inactive Curl ions on these samples must be present as highly dispersed CuO on silica, because the latter should become an e.s.r.-active species by adsorbing acetic acid on exposure to acetic acid vapour. CuO with no silica support was confirmed to give no signal on exposure to acetic acid vapour in a separate experiment. Fig. 2 shows the amounts of highly dispersed CuO present, which were obtained by subtracting those of the isolated or binuclear CuII ions from the total loading. I.R. SPECTROSCOPIC STUDIES Fig. 3 shows the i.r. spectra of the catalyst derived from the acetate complex containing 3.2 wt% copper under the processes of activation and subsequent calcination. In the 1300-2500 cm-l range two bands due to overtones of the Si-0 stretching mode were observed at 1650 and I880 cm-l, as for most silica-supported metal catalysts.The fresh sample gave two strong bands at 1565 and 1440 cm-l with a shoulder at 1630 cm-l. On evacuation at room temperature the shoulder at 1630 cm-l dis- appeared along with a decrease in the intensities of the other bands. In a separate experiment a fresh sample of silica support was observed to give a band at 1630 cm-l which was removed on evacuation at room temperature. The 1630 cm-l shoulder can consequently be assigned to water adsorbed on silica. On the other hand, pressed cupric acetate monohydrate without silica was found to give two strong bands at 1595 and 1440 cm-l, which have been assigned, respectively, to the antisymmetric andN.KAKUTA, A. KAZUSAKA, A. YAMAZAKI AND K. MIYAHARA 3249 wavenumberlcm-' Fig. 3. 1.r. spectra of catalyst derived from the cupric acetate complex (3.2 wt% Cu) under processes of activation and calcination. The conditions for each process were the same as those in fig. 1. (a) Fresh sample, (b) 25 "C, (c) 100 "C; (d) 200 "C, (e) 300 "C and (f) oxidation. symmetric stretching modes of -COO- in cupric acetate m0n0hydrate.l~ We therefore assign the 1565 and 1440 cm-l bands to v,(COO) and vs(COO), respectively, of the silica-supported cupric acetate complex. In addition, anchoring of the complex onto silica may shift the v,(COO) band from 1595 to 1565 cm-l. Activation at 100 "C gave rise to a further reduction in the intensities of these bands. However, the triplet e.s.r.signal A (due to the cupric acetate complex supported on silica) was removed completely by activation at this temperature [fig. l(c)], as described previously. These two spectroscopic results suggest that the paramagnetic properties of the cupric acetate complex supported on silica may change to being antiferromagnetic by the loss of some acetate ligands. Raising the activation temperature to 200 and 300 "C almost removed the 1565 and 1440 cm-l bands. Concomitantly new bands developed at 1735 and 1380 cm-l. They were obtained on exposing the silica support to acetic acid vapour and can be assigned to acetic acid physisorbed on silica, in agreement with the results of Kiselev et al.14 These bands were removed completely by calcination with 100 Torr of oxygen at 300 "C for 1 h.When the calcined sample was exposed to acetic acid vapour the 1565 and 1435 cm-l bands again developed, together with bands at 1750 (sh), 1715, 1615, 1415 (sh) and 1385 (sh) cm-l, as shown in fig. 4(a) (sh denotes a shoulder of the spectrum). Fig. 4(6), on the other hand, illustrates the spectrum obtained for the catalyst derived on the conventional ammine complex, no band being observed at 1565 cm-l. Thus it was confirmed from i.r. spectroscopic studies that only the catalyst derived from the acetate complex preserves binuclear cupric ions on silica. The band at 1615 cm-l is seen in the spectra of both fig. 4(a) and (b). It was not observed on the catalyst derived from the fresh acetate complex, as shown in fig. 3, or on both catalysts reduced with 100 Torr of CO at 300 "C for I h.15 E.s.r.studies3250 SILICA-SUPPORTED COPPER OXIDE CATALYSTS 2000 1800 1600 1400 wavenum ber/cm I 1 I I 1 1 I I 2000 1800 1600 1400 wavenum ber/cm -2 Fig. 4.1.r. spectra of adsorbed CH,COOH on (a) the catalyst derived from the acetate complex (3.2 wt % Cu) and (6) that derived from the ammine complex (3.4 wt % Cu) : (A) after calcination at 300 "C; (B) and (C) after exposure to 10-3-10-2 Torr of CH,COOH. have revealed that the isolated cupric ions on each sample are not reduced under these conditions.' Therefore, it is reasonable to attribute the 161 5 cm-l band to acetate ions adsorbed on dispersed Cu0.T The assignments of these bands are given in table 1. The coordination structures of acetate ligands to metals have been discussed from the viewpoint of their antisymmetric and symmetric stretching frequencies and the t The adsorption of acetic acid on another type of copper oxide catalyst, which was prepared by mixing commercial CuO and SO, (3.0 wt% Cu), was studied using i.r.techniques. No absorption band was observed in the range 1650-1 300 cm-l, indicating that the highly dispersed CuO on silica is different from crystalline CuO in the adsorption of acetic acid.N. KAKUTA, A. KAZUSAKA, A. YAMAZAKI AND K. MIYAHARA 325 1 Table 1. Infrared spectrum frequencies and assignments of acetate ions in the cupric acetate complex and adsorbed on catalystsa compound v(C=O) v(C-0) assignment Cu,(CH,COO), 2H,O(s) Cu,(CH,COO), anchored on SiO, CH,COOH adsorbed on catalyst derived from the acetate complex CH,COOH adsorbed on catalyst derived from the ammine complex 1 595b 144Ob 1 565b 1440b o-cuxl / \ / \ CH,-C 0-CU" 1 560b 1435b 0-CU" CH,-C o-cu'l 1615 1430 0 II 1715 1385 CH,COOH on SO, 1615 1430 0 II CH,--C-O-CuO CH,-C-O-CUO 1715 1385 CH,COOH on SO, a All frequencies in wavenumbers (cm-l).These correspond to v,(COO-) and v,(COO-) of the symmetrical COO- group. separation of these.ll Nakamoto,ls for instance, has classified them into three groups : unidentate (I), bidentate (11) or of the bridging (111) type: M-0, M-0, 04C-CH, M/O>C--CH, M-0 ,S-CH, ' 0 (1) (11) (111) and has indicated that these structures are related to the separations between the two stretching-vibration modes of -COO-. In the unidentate complex (I), v(C=O) is higher than v,(COO) of the free acetate ion (1 560 cm-l) and v(C-0) is much lower than v,(COO) (1416 cm-l).As a result the separation between the two v(C-0) bands is much larger in the case of the unidentate complex than for the free ion. The opposite trend is observed in the bidentate complex (11): the separation between the v(C0) is smaller than that of the free ion. In the bridging complex (111), however, the two v(C0) are close to those of the free ion. In agreement with this classification, the acetate ions adsorbed on the binuclear cupric ions gave absorption bands close to those of the free ion at 1565 and 1435 cm-l. On the other hand, those adsorbed on the dispersed CuO would be of unidentate structure, because the separation of the respective absorption bands of v,(COO) and v,(COO) at 1615 and 1440 cm-l is 175 cm-l, and larger than that of the free ions.Besides the sample containing 3.2 wt% copper the sample containing 6.2 wt% copper was used for i.r. spectroscopic studies; similar results were obtained for each process. On the basis of the results obtained in the present work and in the literature, we3252 SILICA-SUPPORTED COPPER OXIDE CATALYSTS suggest a plausible reaction sequence for each process. The water in cupric acetate monohydrate is known to be substituted easily by a weak base like amrnine.l7 The cupric acetate complex may consequently be anchored by substituting the water in the complex by the OH group of silica as follows: (H20)C~(CH,COO),C~(H,0) + 2-OH +(-OH)CU(CH,COO),CU(OH-) + 2H,O. The OH groups of the silica play an important role in this process.Since the i.r. absorption bands due to the acetate ligands were removed on evacuation at 200 "C, and acetic acid, methylacetate and carbon dioxide were detected by mass spectrometry through the activation process, the reaction (-OH)CU(CH~COO),CU(OH-)+-O - CUCU - 0- + 2CH3COOH + CH,COOCH, + CO, can be proposed for the activation process. Here the binuclear CuII ions are reduced to binuclear CuI ions. On calcining the catalyst with oxygen at 300 "C the CuI ions are oxidized to binuclear Cu*I ions bridged by oxygen as 0 / \ -o~CuCu-0-++0, + - 0 . c u Cu-0-. On exposure to acetic acid vapour they are changed into the original acetate complex as 0 / \ -0 * CU CU * 0- + 4CH,COOH + (-OH)CU(CH,COO),CU(OH-) + H20. CATALYTIC STUDIES The acetate-complex-derived catalysts containing 0.5-6.2 wt % copper or the ammine-complex-derived catalysts containing 3.4 wt % copper were employed in catalytic studies of CO isotope equilibriation or CO oxidation with N,O.The CO isotope equilibriation 13C180 + 12C160 ,13C160 + 12C180 was carried out with ca. 10 Torr of an equimolar mixture of 13C180 and l2Cl60 at room temperature. The rate was estimated by the equation 2.30pV (1 +X)(XO-X"O) y=- RTt log(l+XO)(X-Xm) where V is the system's volume p the pressure of CO, t the reaction time and X, Xm and X' the ratio of l2Cl80 and 13Cle0 at t = t , t = GO and t = 0, respectively.18 Fig. 5 illustrates the relationship between log [(XO - Xm) (1 + X)/(X- Xm) (1 + XO)] and the reaction time, indicating that the experimental results fit the above equation well.In fig. 6 are shown the estimated rates and the concentration of binuclear cupric ions plotted against copper loading. The catalytic activity is related well to the concentration of the binuclear cupric ions. Furthermore the catalyst derived from the ammine complex was inactive in this reaction as shown in fig. 5 . Therefore it is concluded that the binuclear cupric ions are active sites for CO isotope equilibriation at room temperature. WinteP and Vorontsov et aZ.19 have studied this reaction on copper oxide, finding that it proceeds at temperatures as low as - 78 "C. Accordingly, the highly dispersed CuO on silica must be different from pure CuO in its catalytic nature for this reaction.N. KAKUTA, A.KAZUSAKA, A. YAMAZAKI AND K. MIYAHARA 3253 30.0 20.0 02 add (22 Torr) 10.0 5.00 I .oo time/min Fig. 5. CO isotope equilibriation at room temperature on catalysts derived from the acetate and ammine complexes. The numbers show the copper loading on the catalysts derived from the acetate complex while 'ion exchange' indicates that derived from the ammine complex (3.4 wt% CU). 1.0 2.0 3.0 4.0 5.0 6.0 Cu loading (wt%) Fig. 6. Variations in catalytic activities for CO isotope equilibriation or CO oxidation with N,O with concentrations of binuclear Cu'I ions as function of copper loading: 0, concentratiov of binuclear Cu" ions; 0, CO isotope equilibriation; x , CO oxidation with N,O. Voronsto~etal.~~ havediscussed thereactionmechanism of COisotopeequilibriation on the basis of kinetic results; at low temperatures it proceeds through the surface intermediate containing two or more CO molecules while at high temperatures the oxygen atom in copper oxide takes part in the reaction intermediate, and the mechanism of dissociation of CO into carbon and oxygen is excluded because of its high dissociation energy (255 kcal mol-l).The l80 concentration in CO was found to be constant throughout the reaction; on the catalyst containing 3.2 wt % of copper, for example, it changed from 47 to 45% . Also, only a small amount of CO, (< 0.1 % of the total pressure) was detected by mass3254 SILICA-SUPPORTED COPPER OXIDE CATALYSTS 2 0.c 5 b 4 1 2" 10.0 0 time/h Fig. 7. N, formation in CO oxidation with N,O at 150 "C. Initial pressure of CO or N,O was 30 Torr.Numbering of the curves is the same as in fig. 5. spectrometry. Therefore, we prefer the mechanism involving the associative CO intermediate. We have studied the state of adsorption of CO using i.r. spectroscopy in connection with the mechanism of this reaction. Upon exposing both types of catalyst (3.2 or 3.4 wt% Cu) to 30 Torr of CO, only a broad absorption band at 2135 cm-l was obtained. This has been reported on conventional silica-supported copper oxide catalysts in the literature. DeJong et al., for example, have ascribed it to adsorbed CO on dispersed CUO.~O Also, against our expectations, there were no absorption bands below 2000 cm-l attributable to associative CO, CO adsorbed on binuclear cupric ions of the bridged type or a carbonate species.The 2135 cm-l band was not affected by the addition of 30 Torr of oxygen. However, the isotope-equilibriation reaction was stopped completely by adding 22 Torr of oxygen, as shown in fig. 5, indicating that CO adsorbed on dispersed CuO is not responsible in this reaction. In a previous paper7 we have suggested that the binuclear CuI ions formed from binuclear CuII ions are active sites for CO oxcidation with N,O: CO+N,O -+ CO,+N, on the acetate-complex-derived catalyst. In order to confirm this suggestion we have studied the effect of binuclear cupric ion concentration on the catalytic activity of this reaction. The reaction was carried out with a mixture of 30 Torr of CO and 30 Torr of N,O at 150 "C on a series of catalysts derived from the acetate complex and from the ammine complex. Fig.7 illustrates the reaction curves describing the change of N, pressure with time. An induction period was observed in each run. The reduction of binuclear CuII ions to Cul ions should occur during the induction period. Logarithmic plots of N,O pressure revealed that the reaction proceeds by first-order kinetics withN. KAKUTA, A. KAZUSAKA, A. YAMAZAKI AND K. MIYAHARA 3255 respect to N,O after the induction period. In fig. 6 the rates of formation of N, under steady state, estimated from the slopes of the reaction curves at 20 Torr of N,O, are plotted together with the concentration of binuclear Cul* ions on the catalysts derived from the acetate complex. A good agreement can be seen between them, and accordingly the binuclear CuI ions are confirmed to be active sites for this reaction.Dell et aL21 have studied this reaction on cuprous oxide at ca. 250 "C and have proposed that it proceeds through a redox reaction involving the cuprous ions: cuprous oxide initially reacts with CO to form CO,, and then the reduced copper is reoxidized by N,O with the formation of N2. We found in our previous work that copper ions on the catalyst employed here could not be reduced to free copper with 100 Torr of CO even at 300 "C for 1 h. Furthermore, Scholten et al. have reported that free copper could not be oxidized to cupric oxide with N,0.22 Therefore, the redox mechanism cannot be valid in this case. One of the authors has studied this reaction kinetically on a partially reduced molybdenum oxide catalyst, proposing that it proceeds through a molecular complex of N,O and CO coordinated to molybdenum cation pairs.23 We may speculate a similar mechanism in the present case : (Co)b+ (N2O) N20+C0 I N, -0cucu0- - -0cu CUO- -b ( c o y + 0 8 - I I co2 -0cu CUO- + -0cucu0--. A detailed study of the reaction mechanisms is now in progress in our laboratory. We thank Prof.K. Tanaka of Tokyo University for valuable discussions and Prof. A. Aramata for help in estimating the spin concentrations of the e.s.r. signal. B. J. Hathaway and C. E. Lewis, J. Chem. SOC. A, 1969, 2295. V. A. Bogdanov, V. A. Shvets and V. B. Kazanskii, Kinet. Katal., 1974, 15, 176. S. A. Surin, B. N. Shelimov, I. D. Mikheikin and V. B. Kazanskii, Kinet. Katal., 1976, 17, 1569. H. Tominaga, Y. Ono and T. Keii, J. Catal., 1975, 40, 197. S. J. Gentry and P. T. Walsh, J. Chem. SOC., Faraday Trans. I , 1982, 78, 1515. M. Shimokawabe, N. Takezawa and H. Kobayashi, Appl. Catal., 1982,2, 379. ' N. Kakuta, A. Kazusaka and K. Miyahara, Chem. Lett., 1982, 913. G. M. Brown and R. Chidambaram, Acta Crystallogr., Sect. B., 1973, 29, 2393. J. R. Wasson, C. Shyr and C. Trapp, Znorg. Chem., 1968, 7 , 469. lo J. Lewis, F. E. Mabbs, L. K. Royston and W. R. Smail, J. Chem. SOC. A , 1969,291. l1 J. Catterick and P. Thornton, Adu. Inorg. Chem. Radiochem., 1977, 20, 291. l2 I. D. Mikheikin, V. A. Shvets and V. B. Kazanskii, Kinet. Katal., 1970,11,747; V. B. Kazanskii and I. D. Mikheikin, Izu. Otd. Khim. Nauk, 1973, 6, 361. l 3 K. Nakamoto, Y. Morimoto and A. E. Martell, J. Am. Chem. SOC., 1961,83,4528. l4 A. V. Kiselev and A. V. Uvarov, Surf: Sci., 1967, 6, 399. l5 A. Kazusaka, A. Yamazaki and K. Miyahara, to be published. l6 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounh (Wiley- Interscience, New York, 3rd edn, 1978). E. Kotot and R. L. Martin, Inorg. Chem., 1964, 3, 1306. l8 E. R. S. Winter, J. Chem. SOC., 1964, 5781. l9 A. V. Vorontsov and L. A. Kasatkina, Kinet. Katal., 1980, 21, 1494. 2o K. P. DeJong, J. W. Geus and J. Joziasse, J. Catal., 1980, 65, 437. 21 R. M. Dell, F. S. Stone and P. F. Tiley, Trans. Faraday SOC., 1953, 49, 201. 22 J. J. F. Scholten and J. A. Konvalinka, Trans. Faraday SOC., 1969, 65, 2465. 23 A. Kazusaka and J. H. Lunsford, J. Catal., 1976, 45, 25. (PAPER 4/0 12)

ISSN:0300-9599    

DOI:10.1039/F19848003245

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

J . Chem. SOC., Faraday Trans. I, 1984, 80, 3257-3274 Vibrational Study of the Methyl Viologen Dication MV2+ and Radical Cation MVo+ in Several Salts and as an Intercalate in Some Layered MPS, Compounds BY OLIVIER POIZAT* Laboratoire de Spectrochimie Infrarouge et Raman, CNRS, 94320 Thiais, France AND CLAUDE SOURISSEAU Laboratoire de Spectroscopie Infrarouge, LA 124, Universite de Bordeaux I, 33405 Talence, France AND YVES MATHEY Laboratoire de Physicochimie Minerale et ERA 672, Universite Paris-Sud, 91405 Orsay, France Received 8th February, 1984 Infrared and Raman spectra (1 800-200 cm-l) of methyl viologen (1,l’-dimethyl-4,4’- blpyridyl dication or MV2+) ([lH8] and [2H,] derivatives) have been recorded for the chloride, iodide and palladate salts and for the intercalated compounds of formula Ma.,, PS,-(MV),, 16 (with M = Mn and Cd), FePS,-(MV),.,, and Zn,,,, PS,-(MV),,,,.Complete assignments have been proposed for all these species. The methyl viologen appears to be intercalated in its dicationic form and is weakly interacting with the host lattice. In the ZnPS, system the MV2+ pyridyl rings are twisted while in MnPS,, CdPS, and FePS, the cation rings are coplanar and parallel to the sulphur layers. From these results, a model of packing of MV2+ in the MPS, host lattices has been established which accounts for the different intercalation rates. Finally, the reduced product, MV’+, has been studied in both the chloride salt and the CdPS, intercalation compound; in the latter case the radical cation behaves as though diluted and trapped inside an inert matrix, demonstrating unexpected stability.Extensive studies of the methyl viologen cation, (CH,-NC,H,-C,H,N-CH,)i+, have been reported over the last decade in relation to its ability to be photoreduced by transition-metal complexes, which is an important primary process for the splitting of water and the evolution of hydrogen.l-, Other studies have been devoted to the layered metal phosphorus trichalcogenides MPS,, where MI1 is a transition metal, because of the ability of these two-dimensional phases to intercalate reversibly different ions or metal complexes in the van der Waals For instance, we have recently reported an infrared, Raman and resonance Raman study of the Ru(2,2’- dipyridyl)z+ cation intercalated in MnPS,. This work is thus part of a general vibrational investigation of layered MPS, systems intercalated with various molecular entities.In recent studies we have shown that structural, dynamic and electronic information concerning the guest species can be obtained usinginfrared, Raman and neutron-scattering It thus appeared interesting to focus our attention on the potentially reactive 1,l ’-dimethyl-4,4’-dipyridyl cation or methyl viologen (abbreviated hereafter as MV2+) with the aim of under- standing the changes in its photophysical and electronic properties which occur upon 106 3257 FAK 13258 VIBRATIONAL STUDY OF MV2+ AND MV.+ intercalation. We were also concerned with the stabilization of the radical cation MV'+ inside the van der Waals gaps. The vibrational spectra of MV2+ halides have already been analysed.12-14 Recently, Hester and Suzuki15 have performed a normal-mode calculation for the in-plane vibrations of both MV2+ and MV'+. However, all these previous studies are incomplete because of the lack of data on isotopic derivatives. We have thus prepared [lH,] and [,H,] samples of MVCl,, MVI, and MVPdC1, compounds and carried out a complete vibrational investigation of these salts. It is now established that the conformation of MV2+ depends on the nature of the counter ion: the two pyridyl rings of the dication are coplanar in the halide salts16 and twisted (8 = 50") in the palladate c0mp1ex.l~ We have thus been looking at modifications of the charge-transfer strength when changing the anions. Moreover, we have carried out the intercalation of MV2+ uia either the 'metal-vacancies-creation ' route4? for the MnPS, CdPS, and ZnPS, lattices, or the 'direct' route6 for the FePS, system.In the former cases new compounds of general formula M,-,PS, (MV, nH,Q),, where x = 0.16 for M = Mn, Cd and x = 0.29 for M = Zn, were obtained, while in the latter case FePS, (MV, nH,Q),. 15 was prepared. The corresponding vibrational spectra have been carefully analysed in order to determine the structural conformation and packing of MV2+ in the gaps and to estimate the interactions occurring between the guest cation and the host lattices. Finally, the radical cation MV'+ ([lH,] and [,H,] derivatives), in both the chloride salt and the intercalated CdPS, compound, has been generated. The Raman spectra were recorded in order to evaluate the extent to which the electronic and photophysical properties of this radical cation are perturbed upon intercalation.EXPERIMENTAL MATERIALS The [IH,] and [,HE] derivatives of methyl viologen dichloride, MVCl,, were synthesized as follows: 4,4'-bipyridyl ([lH,] or [,HE] derivative) ( lo-, mol) prepared from pyridyl ([lH5] or [,HJ derivative) according to the literature method,', was added to a solution of 6 cm3 CH,Cl in 5 cm3 H,O and heated at 130 "C for 8 h in an evacuated ampoule. The excesses of CH,Cl and H,O were evaporated and the quaternized salt (C,H,N-CH,),Cl, [or (C,D,N-CH,),Cl,] was recrystallized several times from methanol. Anhydrous salts were easily obtained by gently heating (ca. 60 "C) powder or crystal samples for 20 min; water is reabsorbed as soon as the complex is left under an ambient atmosphere.MVI, (['H,] or [,HE] derivative) was obtained from MVCl, by halogen exchange.lg MVPdCl, ([lH,] derivative) was prepared by mixing hot solutions of MVCl, ( lo-, mol) and Na,PdCl, (1 O-, mol) in 6 mol dm-, HCl(1 cm3) and allowing them to cool slowly. Brown crystals of MVPdCl, were isolated and washed. Finally the free radical [lH,] or [,HE] MV'+ was obtained by direct sublimation from the chloride MV2+ salt. The layered MPS, system with MI1 = Mn, Cd, Fe and Zn, were synthesized according to previously described procedures20- and were characterized by X-ray powder diffraction and chemical analysis. Intercalation in MnPS,, CdPS, and ZnPS, was performed by treating the pure materials (powder or platelet) with lo-, mol dm-, aqueous solutions of methyl viologen chloride ([IH,] and [,HE] derivatives) at 60 "C for 15 days.After washing and drying, intercalates of general formula MI-,PS,(MV, nH,O), with x = 0.16 for MI1 = Mn, Cd and x = 0.29 for MI1 = Zn were obtained. The value of n was 4 for the Cd compound. This intercalation route requires the creation of M2+ intralamellar vacancies in the and corresponds to the following reaction : MPS, + XMVE; + M,-,PS, (MV, nH,O), + xM::. Intercalation in FePS, was carried out in presence of sodium dithionite as reducing agent and led to the compound FePS, (MV, nH,O),,,,. This last intercalation route has been described0. POIZAT, C. SOURISSEAU AND Y. MATHEY 3259 as the ‘direct’ or ‘reduction’ route;6 it corresponds to the reaction FePS, + xMVt: + 2xe- -+ FePS, (MV, nH,O), then 2x electrons are accommodated by the FePS, lattice. All these compounds were charac- terized by chemical analysis and powder X-ray diffraction.The sets of (001) lines observed in the X-ray diffraction patterns indicate increases of 3.3 A in the basal spacing upon intercalation in MnPS,, CdPS, and FePS, and an increase of 3.7 A in ZnPS, The following analyses were obtained. Mn,,,,PS,(MV),~,,, calc. : Mn 17.55; P, 1 1.91 ; S, 36.93; C, 8.80; N, 1.63; found: Mn, 17.51; P, 11.87; S , 37.14; C, 8.92; N, 1.68. Cd,.,,PS,(MV, 4H20)0,16, calc.: Cd, 35.87; P, 11.91; S, 36.92; C, 8.80; N, 1.63; H, 1.34; found: Cd, 35.84; P, 11.80; S, 37.10; C, 8.75; N, 1.57; H, 1.30. Zn,.~,,PS,(MV),,,,, calc.: Zn, 17.98; P, 11.89; S, 36.92;C, 16.24;N,2.84;found:Zn, 17.71;P, 11.84;S,38.41;C7 16.12;N72.85.FePS,(MV),.,,, calc.: Fe, 20.43; P, 10.73; C, 7.61; found: Fe, 20.47; P, 10.74; C, 7.39. The reduction of the already intercalated MV2+ was performed by treating a powder sample of Cd,,,,PS,(MV),,,, with a tetrahydrofuran solution of butyl-lithium. The formation of intercalated MV+ is well characterized by its deep blue colour and its Raman spectrum, and charge neutrality is maintained because of the concomitant intercalation of Lif ions. The radical cation appears to be quite stable in air since, from repetitive Raman measurements, a half-life of more than three weeks has been estimated. SPECTRA Infrared spectra were recorded on Perkin-Elmer 225 and 180 spectrometers.Polycrystalline samples were dispersed in Nujol and Fluorolube and spectra of oriented platelets (ca. 2 x 2 x 0.03 mm) were obtained using a beam condenser. Raman spectra were recorded on a Dilor RTI triple monochromator equipped with a krypton laser (6471 A) and an ionized argon laser (5145 A). In order to minimize any local heating effects, Raman spectra of absorbing compounds were measured by means of the rotating sample technique and using low incident laser power (I d 50 mW). Inelastic neutron scattering (INS) spectra were obtained from powdered samples contained in flat thin-walled aluminium alloy cans using a beryllium filter detector spectrometer at the Institut Laue-Langevin (Grenoble, France). RESULTS AND DISCUSSION MV2+ SALTS The band wavenumbers and proposed assignments corresponding to the infrared and Raman spectra (1700-200 cm-l) of the anhydrous and hydrated MVCl, ([‘HJ and [2H8] derivatives) and of the MVPdC1, ([lH,] derivative) complexes in the solid state are presented in table 1.Inelastic neutron-scattering results for anhydrous MVCl, ([lH8] and [2H8] derivatives) are also included. Some related vibrational spectra are shown in fig. 1. SYMMETRY AND METHOD OF BAND ASSIGNMENT The MV2+ cation is planar in its various dihalide salts16 and belongs to the Dzh symmetry group. In contrast, in the PdCli- salt the two pyridyl rings are twisted1’ in such a way that the symmetry is lowered to D,. For the sake of convenience, we have used the notation already employed for the vibrational modes of pyridine22 and N-methylpyridinium 24 The correlation table between the C,, symmetry group of the methylpyridinium cation and the D,, or D, groups of MV2+ is presented in table 2.Moreover, site and intermolecular effects are expected in the solid compounds; however, they must be negligible since the vibrational spectra of MVCl, in the solid state and in ~ o l u t i o n ~ ~ , ~ ~ are quite similar. The only reported changes have been explained by a lowering of the symmetry of MV2+ in solution because of a loss of 106-2w Table 1. Infrared and Raman band wavenumbers (cm-l) and assignments for chloride and palladate salts of MV2+ ([lH8] and [2Hg] derivatives) and inelastic neutron-scattering wavenumbers for anhydrous MVCl, ['H,]MVCl, [2H,]MVC12 anhydrous hydrate anhydrous hydrate ['H,]MVPdCI, Raman i.r.neutron Raman i.r. Raman i.r. neutron Raman i.r. Raman i.r. assignmentb 1655 br - - - - 1650 br 1619sh - - 1603m - 1610 m) 1649s - 1599s - 1628 m - - 1602 s - 1654 s 1654 s 1651 s 1643 s - - 1563 m 1634 s - 1623 vw 1584 vw - 1577 vw - - 1575 vw - - - - - - 1573m - 1530m - - 1534 m - ET) - 1 4 8 6 ~ - - 1458m - - - - - - ( 1516m - 1459m - 1435sh - 1 4 2 0 ~ 1447sh 1 4 5 0 ~ - - - 1436 m 1372 sh - 1366m - 1425m 1430br - 1430 sh 1335s - - 1343 s 1284m - - 1287 m - - - - - - - - - - - - - - - - - - - - - 1290 w - 1221 s - - 1 2 8 0 ~ - 1211 vs - - - - 1558 w 1554 w 1531 m 1514 m 1465 sh 1445 m 1418 vw 1368 sh 1357 m ) - - - 1492 vw 1446 vw 1428 vw 1363 vw - - - 1490 vw - 1420 s 1370 br - 1427 vw 1340 w 1328 w - 1418 vw) - BCH, 1326 s 1299 s 1278 w 1266 sh - - 1291 s 1281 sh 1303 s 1285 w 1264 vw - 1270 m 1242 m - - - 1274 w - 1134s - - 1140 s 1240m - 1 1 5 2 ~ - - 1 1 3 8 ~ - - 1224 m 1220 sh - 1233a w- 1189m 1143 m 1086 vw I - - 1040 vw 972 w - - - - - - - 884 vw - - - 825 s - - - - 790 sh - - 710 w - - 669 w - - 1190 s 1153 s - - - - 1057 w 1037 vw - - - - - - - - - 873 w 840 s - - - - - 813 vw 793 w - - 720 vw - - 672 vw 661 m - rCH3 3 BCD + Vring 5 YCH + rring m 0 C 6b Aring + Vringw h, m h, Table 1.(cont.) ['H,]MVCl, [2H8]MVC12 anhydrous hydrate an hydrous hydrate [ 'H,]MVPdCl, Raman i.r. neutron Raman i.r. Raman i.r. neutron Raman i.r. Raman i.r. assignmentb - - - 561 w - - 485m - - - 468 sh 470 w - 405w 410s 4oovw - 345vw - 348 w - - - - - - - - - - 278vw 278 w 280s - 217 vs - - 531 vw - 5 2 6 ~ - 5 0 2 ~ ~ - 482 w - - 475m - 430 sh 430 sh, w - 464m - 418s - - - - - - - - - - - - - - - 3 9 2 ~ ~ 402s - - - - - 400aw - 3 4 0 ~ ~ - 331 w - 332w 324vw - - - - 3 5 0 ~ ~ - - - - - - - - - - - - - 282 w - 273 w - 274s 278 w - - - 2 1 3 ~ ~ - - - 5 2 4 ~ ~ - 424s - '468 vw I 392vw 429vw - - 353vw - 308 vs - 283vs F1'] - - - 268 s - a Bands observed only in the spectra of the solution. v = stretch; d,A = in-plane deformations; y, = out-of-plane deformations; r = rocking.0.POIZAT, C. SOURISSEAU AND Y. MATHEY 3263 I I I I I I I 1600 12 00 800 4 00 wavenumber/cm -' Fig. 1. Infrared and Raman spectra (A, = 6471 A), in the 1700-200 cm-l region, of anhydrous MVCl, {(a) ['H,] and (b) [2H,]} and of MVPdC1, ( c ) in the solid state. cation ~1anarity.l~ In agreement with the expected selection rules, the vibrational spectra of MVC1, and MVI, are quite simple and show complete exclusion between infrared and Raman wavenumbers, while band splittings and infrared-Raman coincidences are observed for many modes with the palladate complex.Our band assignments were established using isotopic data (table 2) and by comparison with previous vibrational results for pyridine,,, p i c ~ l i n e , ~ ~ biphenyl,26 2,2'-di~yridyl,~~ 4,4'-dip~ridyl,~~ 1,l 'dimethyl-4,4'-dipheny128 and N-methylpyr- i d i n i ~ m . ~ ~ ? 24 In fact, very characteristic group-frequency sequences are commonly encountered in these six-membered aromatic molecules. In particular a very close analogy is noted between MV2+ and methylpyridinium data.This behaviour has beenw h) o\ P Table 2. Correlation diagram and selection rules for the MV2+ cation in both the planar and the twisted conformations, from the methylpyridinium ion symmetry (v = stretch; 6, A = in-plane bends; r = rocking; t = torsion; y, r = out-of-plane bends) planar methyl viologen, Dzh twisted methyl viologen, D, methyl- pyridinium, CH, activity symmetry C,,,: symmetry activity ring CH CH, ring- N- ring CH, symmetry ring CH, ring ring- N- CH 3v+2A w v 3v+lA A A 2 r r r i r r - ir - - 2 r r r 3v+lA A A 3 ~ + 2 A - v 2v+ 26 2v+ 26 2Y 2Y 2Y 2Y 2v + 26 2v+26 lv+16 R(p) lv+16+lr R lv+lG+lr R It R It - I v + 16+ Ir i.r. I v + 16+ Ir i.r. lv+ 16 1.r. R(p) 3 v + 2 A + l r o+T v 2~+26+2y lu+16+lt R,i.r. 3v+2A+lr - v 2v+26+2y lv+IG+lt R, i.r.3v+ l A + 2 r A+T A+T 2v+26+2y lv+ 16+2r R , i . r . 3v+lA+2r A + r A+T 2v+26+2y lv+16+2r + B,,0. POIZAT, C. SOURISSEAU AND Y. MATHEY 3265 Table 3. Comparison of the band wavenumbers (cm-l) corresponding to the YCH,CD (vll), v ~ - ~ ~ ~ and ~ 5 % ~ ~ modes for various MV2+ complexes and intercalation compounds MVCl, i anhydrous 1 hydrated MVI, MVPdCl, MV2+ in CdPS, MV2+ in MnPS, MV2+ in FePS, MV2+ in ZnPS, 825 850 810 848 813 816 814 675 1242 688 1240 668 1229 1220 - (1224 668 1224 670 1224 - 1223 1216 - 1226 - 1134 (:it; 1425 1436 1430 1140 (:ili 1128 1352 1412 - 1326 - 1332 1144 1344 1144 1340 1345 - 1331 - 1335 - of great help as a reliable assignment is known for the methylpyridinium, supported by a valence force-field calculation performed using the four derivatives C,H,N-CH,, C,D4N-CH,, C,H,N-CH, and C,D,N-CD,.28 Finally the assignments of the CH,-group deformations have been confirmed by comparison of the inelastic neutron-scattering spectra of the [lH,] and [2H,] derivatives, where these modes give rise to the most intense signals.VIBRATIONAL RESULTS The experimental results allow us to propose new assignments for several modes in disagreement with previous studies. In particular, we assign the strong absorption band at ca. 850 cm-l to the in-phase out-of-plane CH deformation (BEH, vll), which generally leads to the most intense infrared band in aromatic mo1ecules.22-28 This band cannot be connected with the almost coincident Raman peak at 842 cm-l, which corresponds to a typical in-plane vibration.This precision is supported by the spectra of deuterated MV2+, where the absorption shifts to ca. 675 cm-l (pPHID = 1.26) while the Raman band shifts to 808 cm-l (pH,,, = 1.05). A second major remark concerns the two infrared bands observed at 1459 and 1145 cm-l ([lH,] derivative), which have been omitted in the normal-mode calculation of Hester and Suzuki.', We assign the former band to the ring vibration vlgb by analogy with the results for various aromatic m01ecules.~~-~~ The latter band, whose intensity depends on the degree of hydration of the complex (see table l), corresponds to a strong signal on the inelastic neutron-scattering spectrum and it is thus assigned to a CH, rocking mode. The frequencies of three infrared-active vibrations, namely v,, (yCH), vN-cH, and d$H,, are remarkably sensitive to modifications of the surroundings (hydration rate, nature of the counter ion and twist-angle between the two pyridyl rings) of the MV2+ cation (see table 3).This behaviour is due partly to variations of the charge-transfer strength, which occur when the molecular conformation and the counter-anion are modified. vN-CH, and BEH, modes have frequencies which are dependent on the electronic charge of the nitrogen atom. Such specific perturbations indicate that the charge transfer is mainly localized on the N atoms. This conclusion is strengthened3266 VIBRATIONAL STUDY OF MV2+ AND MV.+ by a comparison of the vibrational spectra of MV2+ and of the isoelectronic molecule 1,l '-dimethyl-4,4'-diphenyl: in agreement with the quasi-similarity of their atomic masses and molecular geometries, their Raman spectra are almost identical.In contrast, their infrared spectra are different and reveal important variations of the dipole moments in these molecules. This confirms the localized character of the charge-transfer mechanism in MV2+ salts. In addition, MVPdCl, vibrational spectra exhibit several characteristics of the non- planarity of the cation: first, the two absorption bands for out-of-plane ring deformations (v, and 1'16) and previously situated at ca. 468 and 485 cm-l (halide salts) are now observed at 534 and 561 cm-l, respectively. A second typical shift occurs for the in-phase ScH3 absorption band, observed in the 1365-1 340 cm-l range for planar MV2+ and lowered to 1326 cm-l in MVPdCl,.Similar behaviour has been observed with MV2+ intercalation products of mica-type ~ i l i c a t e s : ~ ~ while planar in mont- morillonite, the cation is twisted in vermicullites and the vibration is shifted from 1354 to 1332 cm-l. Finally, the non-planarity of the MV2+ cation is characterized by the presence of a Raman component of the vNPcH, mode; situated at 1224 cm-l for MVPdCl,, this mode is also observed at 1233 cm-l in the Raman spectrum of MVCl, in solution. Note that most of the in-plane ring vibrations, which are expected to be sensitive to the electronic delocalization within the rings, do not show significant frequency variations. In contrast the frequency increase of the r ring modes indicates strengthening of the ring-deformation constraints, which may be caused by crystal packing effects.INTERCALATED MV2+ COMPOUNDS Infrared and Raman spectra (1 700-200 cm-l) of ZnPS, and MnPS, intercalated with MV2+ are shown in fig. 2. The corresponding band wavenumbers and proposed assignments are reported in table 4, together with the infrared data for the intercalated FePS, analogue. No Raman spectra were obtained for this last compound because of its opacity. Some infrared results obtained with polycrystalline samples and quasi-monocrystalline platelets of intercalate MnPS, are compared in fig. 3. These spectra seem to arise from the superposition of bands characteristic of the host lattices and those of the MV2+ cation. However, some changes are noted in the MPS, vibrations [splittings of the vdps3 and SS,,, modes and the presence of new low-frequency i.r.bands] with respect to the pure lattice spectra. Similar results have already been reported for the CoCp: and CrBz: intercalates in the corresponding host structures.89 lo, l1 We can thus easily compare the spectra of Mn,~,,PS,(CoCp,),,,, with those of Mno~,,PS,(MV)o~16 on the one hand, and the spectra of Zn,,,,PS,(CoCp,),~,, with those of Zn,~,lPS,(MV),~,g on the other hand, despite the fact that the CoCp: intercalation induces a larger increase in the basal spacing (ca. 516 A) than the MV2+ intercalation (ca 3.3 A). Vibrational spectra thus appear to be more sensitive to the nature of the host system, i.e. the nature of the MI1 transition metal constituting the lattice, than to the amount and geometry of the intercalated species. MV2+ INTERCALATES OF MnPS,, CdPS, AND FePS, In all cases, the MV2+ intercalated species ([lH,] and [2H,] derivatives) are well characterized by vibrational bands whose frequencies and relative intensities are close to those observed for the halide salts.This indicates that in these compounds the two pyridyl rings are again coplanar and that the cations interact only weakly with the host lattices, which behave as regular counter-ions. However, some frequency shifts are noted for the above mentioned three vibrations yCH, vN-CH, and SCH3 for their energy dependence on the cation surroundings (see table 3).0. POIZAT, C. SOURISSEAU AND Y. MATHEY 3267 / r L V I I I 1 I 1 1 1 1600 1200 800 400 Fig. 2. Infrared and Raman spectra (A, = 6471 A), in the 1700-200 cm-l range, of the MV2+ cation intercalated in (a) MnPS, and (b) ZnPS, host lattices. w avenumberlcm-’ For the polarized infrared spectra (EHlayer planes) of platelets of the Mn and Cd compounds (fig.3), the vp-p (ca. 450 cm-l) and C ~ S , , ~ (ca. 317 cm-l) bands are extinguished, as expected from geometric lo Similarly, bands corre- sponding to the two characteristic out-of-plane MV2+ vibrations, yCH(vl1) and rring (v16a)7 at 813 and 475 cm-l and at 668 and 424 cm-’, respectively, for the [lH,] and [2Hg] derivatives of MV2+ in CdPS,, nearly disappear. We conclude that the two coplanar pyridyl rings are parallel to the host layer planes. A schematic picture of such a cation lying in the interlamellar spacing and undergoing van der Waals interactions with the sulphur atoms of the lattice is represented in fig.4. The interlamellar distance estimated from this representation is nearly 3.3 A, in agreement with the value obtained from powder X-ray diffraction data. This confirms the validity of the proposed structural model. According to the calculated values of the area of a flat MV2+ on the one hand and of the layer plane area per primitive cell on the other hand, we can deduce that an intercalation rate of x z 0.16 corresponds satisfactorily to maximum filling of the available interlayer space; nevertheless, there are still empty regions, around the nitrogen atoms, able to accommodate up to four water molecules between the cations. The MV2+ intercalates of MnPS,, CdPS, and FePS, reach the same intercalation rate with x = 0.16 & 0.01 ; hence, whatever the intercalation route (‘direct’ route or ‘metal-vacancies-creation’ route) the reactions are likely to be limited3268 VIBRATIONAL STUDY OF MV2+ AND MV.+ Table 4.Infrared and Raman band wavenumbers (cm-l) and assignments for the MnPS,, ZnPS, and FePS, compounds intercalated with the methyl viologen (MV2+) cation MV2+ in MnPS, MV2+ in ZnPS, MV2+ in FePS, Raman 1.r. Raman i.r. i.r. assignmentsa - 1640 s 1620 m 1570 m 1507 m 1436 m 1340 w - - - - - 1278 m 1224 w - - 1194 m 1052 vw - - - - - - - - 816 s 798 sh 694 w - - 606 vs - - - - 557 vs - I 475 w 467 sh 451 m 380 w - 1649 s - - - 1530 m - - 1352 w (:E m) 1298 s 1290 sh - - 1226 w 1188 s 1154 vw 1064 vw 1038 vw - - - - 873 vw - - 837 m - - 705 w 678 vw 657 m 625 w - - - 573 sh 563 m 554 sh - - 473 m - - - 1635 s 1601 m 1560 m 1499 m 1440 m 1350 sh 1331 m - - - 1273 m 1267 sh 1226 w 1216 m 1188 sh 1185 m 1065 vw 1038 vw 979 vw 950 vw 872 w 863 vw 847 w 837 vw - (K 3 G: 3 793 vw - - 625 s 605 vs 596 vs 583 vs 573 vs 558 sh 518 w 506 w 450 s 380 vw - - - 1640 s 1620 br 1507 m 1436 m 1345 w} - - - - 1276 m) 1192 m 1055 vw 1032 vw - - - - 698 m 614 sh 604 vs - 480 sh} 468 m 446 s 414 m 380 w 8a H2O 19a 8a 19 b &Ha C’ 3 ‘N-CHa 9a 9b 18 a 5 17a ‘CH3 YCH ‘d’ YCH 6a 6b VdPSa ‘e’ 4+16a CPS3 VSPS30.POIZAT, C. SOURISSEAU AND Y. MATHEY 3269 Table 4. (con?.) MV2+ in MnPS, MV2+ in ZnPS, MV2+ in FePS, Raman i.r. Raman i.r. i.r. assignmen tsa - - 330 s __ 298 m 300 s - - - 317 m 306 s 306 s 307 s) 6% - - 272 s - - 286 s 273 vs (276 sh - - - - 257 sh 239 vs - 219 m - TiY+RiY 222 s - 240 s 237 229 s s 230 m - ,,,q (PS,) - - - a v = stretch; 6, y = in-plane and out-of-plane deformations; r = rocking; T', R' = external translation and rotation.mainly by the steric constraints of the cations in the gap. Similarly the intercalation of organometallic species in various MPS, systems*q lo, l1 led to the common formula M,-,,,PS, (cation),, with x = 0.35 k0.05 for CoCpz and x = 0.30+0.03 for CrBzi; note that these intercalation rates are approximately twice those reached with the MV2+ intercalates, in agreement with the fact that the organometallic cations occupy roughly half the area of MV2+. MV2+ INTERCALATE OF ZNPS, In contrast to the preceeding intercalated systems, i.r. and Raman bands of MV2+ intercalated in ZnPS, (fig.2) are comparable to those recorded with the palladate salt: they exhibit infrared and Raman coincidences, complex structure and numerous vibrational components. In addition, several vibrational frequencies are shifted with respect to the frequencies observed with the intercalates of MnPS,, CdPS, and FePS,. These shifts are similar to those mentioned above for the palladate salt: the Tring(v4,v16) and B&, modes are situated at 506/518 cm-l and at 1331 cm-l, respec- tively, and the v ~ - ~ ~ , vibration leads to a Raman peak at 1226 cm-l (see table 3). We thus conclude that the pyridyl rings of the MV2+ cation intercalated in ZnPS, are likely to be twisted as in the PdCli- salt. Note that in this case an important sharpening of most infrared and Raman bands is also observed.In agreement with the high rate of intercalation (x = 0.29) found with this host system, all these results are indicative of the high order and compactness of the cations in the ZnPS, gap. The non-planarity of the MV2+ pyridyl groups leads to a possible partial overlap of the cations and consequently allows more compact arrangement in this interlayer space than in the MnPS,, ZnPS, and FePS, gaps. ' FREE ' AND INTERCALATED MV' -k RADICAL Raman spectra (1800-180 cm-l) of the MV'+ radical ([lH,] and [2H,] derivatives) intercalated in CdPS,, recorded using the 6471 A excitation line, are shown in fig. 5. 'The corresponding band wavenumbers are reported in table 5 and compared with those of the 'free' species generated from the chloride salts.Tentative assignments are also given.3270 VIBRATIONAL STUDY OF MV2+ AND MV.+ 80 0 600 400 750 550 3 50 wavenum berlcm -' Fig. 3. Infrared spectra of the (a) ['H,] (900-400 cm-l) and (b) [2Hg] (760-340 cm-l) derivatives of MV2+ intercalated in CdPS,. Upper traces, polycrystalline samples ; lower traces, platelets @//lattice layers). 5. --- gap 3.3 A C a d 0 5 A Fig. 4. Packing model for a planar methyl viologen cation inside the interlayer spacing of the MPS, host lattice, as viewed along the b direction. MV2+ van der Waals contours and sulphur atom van der Waals radii are represented to point out the interaction between the guest species and the host lattice.0. POIZAT, C. SOURISSEAU AND Y. MATHEY 327 1 * 1600 1200 8 00 wavenumberlcm-' 400 Fig.5. Resonance Raman spectra (A, = 6471 A) of the (a) ['H,] and (b) [2H,] MV" species intercalated in CdPS, (asterisks indicate bands from the host lattice). The MV'+ radical exhibits a strong electronic absorption band30 centred at ca. 605 nm which accounts for the resonant character of the Raman spectra.14 Hence, as pointed out by Forster et aZ.,14 the observed Raman peaks correspond to vibrations mainly involved in the electronic transitions responsible for this absorption band : only those modes which contain high contributions from the chromophore coordinates (ring and N-CH, stretches and bends) are expected to be enhanced and thus to be observed. Our assignments are in agreement with this assumption and have been established according to the experimental isotopic shifts and comparison of the MV2+ and MV'+ data.These assignments roughly correspond to the potential-energy description computed by Hester and Suzuki.15 The main difference comes from the observation of several new bands, which precludes an assignment of all the bands to only totally symmetric modes. In any case, the great complexity of the excitation profiles obtained by Forster et all4 for the MV'+ Raman peaks, in the contour of the visible electronic band, indicates that this absorption results from the overlap of several electronic transitions. As the nature and the symmetry of these transitions are not yet established, it is not possible to determine the resonance Raman scattering mechanism. However, since our results show that both totally symmetric and non-symmetric modes are enhanced, we believe that this mechanism is more complex than previously suggested and is probably caused by interfering phenomena.,l Moreover, it is evident from table 5 that the 'free' and intercalated MV'+ spectra are very similar in wavenumbers, relative intensities and enhancement factors.We conclude that, in both the chloride salt and the CdPS, intercalation system, the3272 VIBRATIONAL STUDY OF MV2+ AND MV.+ Table 5. Raman band wavenumbers (cm-l) and assignments of the MV'+ chloride salt and of the reduction product of MV2+ intercalated in CdPS, [IHJ MV'+ [,H,] MV'+ chloride in CdPS, chloride in CdPS, assignmen tsa 1660 m 1656 sh 1534 s 1430 w - - 1357 m 1250 w 1210 vw 1046 sh 1028 m 818 vw 682 w - - 554 vw 430 vw 385 vw 282 w - - - - 1652 m 1528 s 1427 vw 1373 sh 1365 vw 1349 m 1245 vw 1038 sh 1022 m 682 w 562 vw - - - - - - - 381 m 281 w 273 w 269 sh 243 vw 1623 w 1603 sh 1475 s 1432 w - - - - - 866 m 920 w 794 vw 669 vw 615 vw - - - - - ,2w1 - - 1618 m 1475 s 1429 w - - - - - - 861 m 924 w 668 vw 562 vw - - - - 381 m 272 m 242 w ' c ' Vring-ring 'N-CH3 9a + Vring 18a ~ C H + Vriy 1 ring breathing 'd' (ring) 6b Aring CdPS, lattice ' e ' (ring) AN-CH~ + A r i n g AN-CH3 - CdPS, CdPS, CdPS, a v = stretch; 6, A = in-plane deformation; r = out-of-plane deformation.reduction of MV2+ induces identical electronic perturbations in the intramolecular bonds. Hence, the structural and electronic properties of the radical cation are not markedly changed upon intercalation.Finally, the half-life of the radical species in the atmosphere has been estimated by measuring the intensity decay of the MV'+ Raman spectrum with time. Such kinetic measurements have been carried out under identical experimental conditions with the free chloride salt and with the intercalate of CdPS,. A half-life as long as three weeks is estimated for the intercalated MV'+ species, in contrast with the very short lifetime (less than one second under ambient laboratory conditions) of the free-radical cation. Such stability reveals that no electron transfer occurs between the guest species and the host lattice, and confirms once more the absence of strong electronic interaction. Under these conditions it appears that the radical cation has the appearance of a diluted and trapped species inside an inert matrix.This material thus provides an adequate starting system for performing interlamellar photochemical studies, and work towards this goal is in progress.3273 0. POIZAT, C. SOURISSEAU AND Y. MATHEY CONCLUSIONS In this spectroscopic study, the assignment for the vibrational modes of the methyl viologen cation (MV2+) has been improved owing to new data from deuterated molecules. The frequencies of three i.r.-active vibrations, namely yEH (v,,), v ~ - ~ ~ , and &,, are particularly sensitive to modifications of the external environment of the cation, and several characteristic band structures and frequency shifts provide convincing evidence for a transformation from planar to twisted MV2+ structural conformation.Spectra of the intercalated compounds nearly correspond to the superposition of those of the host lattice and of the guest species; this suggests that the intercalated cation interacts only very weakly with the host systems, which behave as regular counter-ions. The orientation and conformation of the guest molecules in the different lattices have been inferred from polarized infrared results and thus can account for the different observed intercalation rates. In the ZnPS, host system the MV2+ pyridyl groups appear to be twisted, while in the MnPS,, CdPS, and FePS, lattices the cation is planar and parallel to the layers. Finally, chemical reduction of the guest MV2+ cation in CdPS, leads to the intercalated MV'+ radical cation, whose vibrational properties are similar to those of the 'free' radical (chloride salt).However, the radical cation trapped inside the interlamellar space possesses a substantially longer lifetime. This last result may be of great interest in the field of electron-transfer processes involving the MV2+/MV'+ redox couple, e.g. in the photochemical reduction of water, especially if we consider intercalation of the Ru(bipy)i+ cation, which is an oxidizing agent commonly associated with MV2+ in such photoreduction reactions. Therefore additional experi- ments are currently in progress with the aims of co-intercalating both these reactive entities and then performing photochemistry inside these layered compounds. We thank Mrs J. Belloc for technical assistance in the synthesis, Dr H.Jobic for the inelastic neutron-scattering data and Dr R. Clement for helpful discussions. D. Meisel, W. A. Mular and M. S. Matheson, J. Phys. Chem., 1981, 85, 179. P. A. Brugger, P. P. Infelta, A. M. Braun and M. Gratzel, J . Am. Chem. SOC., 1981, 103, 320. R. Clement and M. L. H. Green, J . Chem. Soc., Dalton Trans., 1979, 1566. R. Clement, J. Chem. Soc., Chem. Commun., 1980, 647. R. Clement, 0. Garnier and Y . Mathey, Nouv. J. Chim., 1982, 6, 13. Y. Mathey, R. Clement, C. Sourisseau and G. Lucazeau, Znorg. Chem., 1980, 19, 2773. C. Sourisseau, Y. Mathey and C. Poinsignon, Chem. Phys., 1982, 71, 257. lo C . Sourisseau, J. P. Forgent and Y. Mathey, J. Solid State Chem., 1983, 49, 134. C. Sourisseau, J. P. Forgerit and Y. Mathey, J. Phys. Chem. Solids, 1983, 44, 119. I s R. Haque and S. Lilley, J . Agr. Food Chem., 1972, 20, 57. A. Regis and J. Corset, J . Chim. Phys., 1981, 78, 687. M. Forster, R. B. Girling and R. E. Hester, J . Raman Spectrosc. 1982, 12, 36. R. E. Hester and S.Suzuki, J . Phys. Chem., 1982, 86, 4626. C. K. Prout and P. Murray-Rust, J . Chem. Soc. A , 1Y6Y, 1520. '' M. Gratzel, Ace. Chem. Res., 1981, 14, 376. ' 0. Poizat and C. Sourisseau, J . Phys. Chem., 1984, 88, 3007. l6 J. H. Russell and S. C. Wallwork, Acta Crystallogr., Sect. B, 1972, 28, 1527. In F. J. Marshall, J . Am. Chem. SOC., 1956, 78, 3696. l9 A. J. MacFarlane and R. J. P. Williams, J . Chem. Soc. A, 1969, 1517. W. Klingen, R. Ott and H. Hahn, Z . Anorg. Allg. Chem., 1973, 396, 271. 21 G. Ouvrard, R. Brec and J. Rouxel. C.R. Acad. Sci., Ser. C, 1982, 294, 971. D. A. Long, F. S. Murfin and F. L. Thomas, Trans. Faraday SOC. 1963, 59, 12.3274 VIBRATIONAL STUDY OF MV2+ AND MV. -t 23 R. Foglizzo, Thesis (Universite de Paris 6, 1970). 24 E. Spinner, A m . J . Chem., 1967, 20, 1805. 25 D. A. Long and W. 0. George, Spectrochim. Acta, 1963, 19, 1777. 26 G. Zerbi and S. Sandroni, Spectrochim. Acta, Part A , 1968, 24, 483. 27 N. Neto, H. Munitz-Miranda, L. Angeloni and E. Castellucci, Spectrochim. Acta, Part A , 1983, 39, 97. 0. Poizat, unpublished results. 29 M. Raupach, W. W. Emerson and P. G. Slade, J. Colloid Interface Sci., 1979, 69, 378. 30 E. M. Kosower and J. L. Cotter, J. Am. Chem. SOC., 1964, 86, 5524. 31 W. Siebrand and M. Z. Zgierski, in Excited States (Academic Press, New York, 1979), vol. 4. 32 R. Clement, J. Am. Chem. Soc., 1981, 103, 6998. (PAPER 4/226)

ISSN:0300-9599    

DOI:10.1039/F19848003257

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I , 1984,80, 3275-3284 Stability Constants of Complexes of Monensin and Lasalocid with Alkali-metal and Alkaline-earth-metal Ions in Protic and Polar Aprotic Solvents BY BRIAN G. Cox* AND NGUYEN VAN TRUONG Chemistry Department, University of Stirling, Stirling FK9 4LA AND JADWIGA RZESZOTARSKA Chemistry Department, Warsaw University, 02-093 Warsaw, Poland AND HERMANN SCHNEIDER* Max-Planck-Institut fur biophysikalische Chemie, D-3400 Gottingen, West Germany Received 17th February, 1984 Measurements have been made of the stability constants of complexes of the anionic ionophores monensin and lasalocid with alkali-metal cations, alkaline-earth-metal cations and Ag+ in several solvents, both protic and polar aprotic. The complexes of monensin are very stable and show a sharp stability maximum among the alkali-metal cations for the Na+ complex in all solvents.Compared with complexes of various neutral ionophores, the stability constants of monensin complexes are relatively much higher in aprotic than protic solvents. This may be attributed to a loss of solvation altering the free energy and conformation of the monensin anion on transfer from protic to aprotic solvents. Complexes of the smaller lasalocid ion are less stable, less sensitive to solvent variation and show a different selectivity pattern to those of monensin. Structural features of the two ligands responsible for the different complexing properties are discussed. The Nigericin group of antibiotic ionophores is a subclass among the ion-carrier antibiotics, which are distinguished by their ability to form electrically neutral 1 : 1 or 2: 1 ligand-cation complexes.These compounds contain tetrahydrofuran and/or tetrahydropyrane rings and a carboxy function which is dissociated at physiological pH values,I as in monensin [MonH, structure (I)] and lasalocid [X-537A, LasH, structure (191. They are known to induce exchange of M+ and HS via the electrically neutral complexed or protonated species,2 but evidence from membrane bilayer conductance measurements3 suggests that charged, dimeric species of the form (HL& and (CaHL,)+, where L- represents the antibiotic anion, may also be important. * OH COOH (1) CH2 32753276 STABILITY CONSTANTS OF MONENSIN AND LASALOCID COMPLEXES X-ray analyses of the ionophores and their cation complexes reveal a macrocyclic structure stabilised by hydrogen-bond formation between the -CO,H (or -CO;) group and appropriate -OH groups within the molecule.The Ag+ and Na+ complexes of monensin involve coordination by six oxygen atoms, as indicated by an asterisk in structure (I);4* the general structure of MonH is similar to that of the metal com~lexes,~ although the detailed hydrogen-bonding pattern is different. Crystallo- graphic studies of complexes of lasalocid, the smallest member of the Nigericin group, show the existence of dimeric structures, e.g. (AgLas),, (NaLas), and Ba(Las),, in which the cation is coordinated to five oxygen atoms from one lasalocid molecule [asterisk in structure (II)] and a sixth from the second lasalocid.6-8 Several studies of the stabilities of monensin9-14 and lasalocidl2.1 5 7 l6 complexes have been reported, all of them involving methanol or ethanol as solvent. Earlier work on natural synthetic ionophores such as crown ethers1’ and crypfandsl8 has shown the stability constants of M+ and M2+ complexes to be very sensitive to solvent variation; similar effects might be expected for complexes of monensin and lasalocid. For example, partitioning experiments on the H,O+ hexane system for lasalocid complexes, reported by Degani and Friedman,15 indicate that shielding of M+ by Lass from the solvent is incomplete and that residual ion-solvent interactions in the complexes may quite strongly influence their complexing properties. In addition to cation-solvent and cationdonor interactions, hydrogen-bond formation clearly plays an important role in determining the structures of the free ligands and the complexes.This suggests that it would be of some interest to compare the stabilities of complexes in protic solvents, such as methanol and ethanol, with those of aprotic solvents, such as dimethylformamide and dimethylsulphoxide. Some indication of the influence of hydrogen-bond formation on both the stabilities and kinetics of complex formation was obtained recently in a study of silver monensin complexes in various non-aqueous solvents. l9 In the paper we report a study of the solvent dependence of the stabilities of the lasalocid and monensin complexes of alkali-metal, alkaline-earth-metal and Ag+ cations. The solvents used include methanol, ethanol, dimethylformamide (DMF), dimethylsulphoxide (DMSO), propylene carbonate (PC) and acetonitrile (AN).EXPERIMENTAL MATERIALS The purification of the solvents and tests for their purity and water content have been described previously. 2o The following reagents were used: LiClO,, NaClO,, AgClO,, AgNO,, KClO,, KF, RbClO,, RbF, CsClO,, CsF, Ca(NO,), 4H20, Ca(C10,), - 4H20, Sr(NO,),, Sr(CIO,), 6H,O, Ba(ClO,), - 3H20, Et,NClO,, Et,NOH and Bu,NOH (as an aqueous solution). All were high-purity commercial samples, except for Et,NC10, which was prepared from NEt,OH (Aldrich, 20% solution in water) and HClO, and purified by several recrystallisations from water, followed by drying under vacuum. Solutions of hydrated salts were normally dried over molecular sieves, type 5A, although at the electrolyte concentrations used (vide infra) the amount of water introduced in this way was negligible.Sodium lasalocid (Sigma) and sodium monensin (Sigma, or a gift from Eli Lilly Corp.) were dissolved in hot methanol and the hot solution filtered. The complexes were then reprecipitated by the addition of water to the cooled methanolic solution. This procedure was repeated twice in order to rid the commercial salts of an unidentified yellow impurity. The white salts obtained were dried under vacuum for several hours and were then converted successively into the free acids (MonH, LasH) and the tetraethyl- or tetrabutyl-ammonium salts, as described previously.21 It had been shown earlier that NEtt and Bu,N+ have no effect on the com-B.G. COX, N. VAN TRUONG, J. RZESZOTARSKA AND H. SCHNEIDER 3277 plexing properties of Mon- other than a normal ionic-strength effect,21 and these salts may be used for the study of a variety of metal-ion complexes. STABILITY-CONSTANT MEASUREMENTS The stability constants of the Ag+ complexes where L is Mon or Las, were determined by direct titration of Ag+ solutions with an excess of Et,NL using pAg+ potentiometry with a three-compartment cell, as described previously for cryptate stability-constant determinations.22 As both monensin14 and lasalocid15 are weak acids in methanol (pK, = 10.3 and 7.6, respectively), and presumably in ethanol, checks were made for possible effects from solvolysis of Las- and Mon- in these solvents (ROH + L- + LH + RO-) by adding known small amounts of LH to the solution. Stability constants calculated according to eqn (2) were independent of the ratio L-/LH, although at higher concentrations of LH complexes of the form AgLH+ are known to exist.’, Total Ag+ concentrations were in the range (1.5-5) x lop4 mol dm-3 and L- in the range (0.4-2) x mol dm-3.Activity coefficients, which refer to infinite dilution in the solvent in question, were calculated according to the Davies equation23 where I is the ionic strength and A [= 1.825 x 106/(~T)3’2] is the Debye-Huckel function. At the low ionic strengths used, corrections were small (< 0.1 in logK,). The stability constants of the alkali-metal and alkaline-earth-metal complexes were determined by disproportionative reaction of the cations with the corresponding Ag+ complex log y+ = - Z2AP’2/( 1 + P’2) + Z2A1/3 (3) Ke AgL + M+ ;t ML + Ag+ (4) Ke AgL+M2+eML++Ag+ ( 5 ) as described earlier for cryptate complexes.22 Eqn (4) should be independent of ionic strength, but corrections are required for eqn (5).For the competitive equilibria, concentrations used were 1 x and 1.5 x lo-* d [Ag+]/mol dm-3 < 5 x lop4. As the reactions always involved an excess of metal ion (Ag+, Mn+) over L-, the concentrations of uncomplexed L- were very low, so that solvolysis (to give LH) or formation of 2: 1 species such as NaL,, CaL, etc. was negligible, i.e. complexation equilibria refer to the 1 : 1 complexes for both M+ and M2+ cations. Activity-coefficient corrections are larger (up to 0.4 log units) for M2+ systems because of the higher ionic strengths involved ( I d 0.015 mol dm-3).The possible influence of ion-pair formation involving the uncomplexed M2+ cations should also be considered. However, although ion-pair formation constants of alkaline-earth-metal halides in, for example, methanol are of the order of lO(r-400 dm3 m 0 1 - l ~ ~ ~ values for NO; and Cloy salts as used in the present study are considerably Thus we have assumed that all of the salts are fully dissociated. For the Na+ complexes it was also possible to use the purified NaL directly, rather than NEt,L. The results obtained in both cases agreed within experimental error. < [Mn+]/mol dm-3 < 5 x lop3, 4 x lo-, < [L-]/mol dmP3 G 1 x RESULTS The stability constants of the various monensin and lasalocid complexes at 25 “C are listed in tables 1 and 2, respectively. It is possible in some cases to compare these results with values obtained in earlier studies.The most comprehensive set of values is for alkali-metal complexes of monensin in methanol. Earlier values of log& (MMon) are as follows: Li+, 3.3;13 Na+, 5.9,9 6.1,11 4.912 and 6.72;13 K+, 4.6,1° 4.7,93278 STABILITY CONSTANTS OF MONENSIN AND LASALOCID COMPLEXES Table 1. Stability constants of monensin complexes with monovalent and divalent cations in various solventsa at 25 "C log (Ks/dm3 mol-l)b cation MeOH EtOH DMF DMSO PC AN Ag+ Li+ 7.86 3.6, 8.95" 5.3 1" 10.0, 5.9, 5.8, 15.1, 8.5, 3.7, 11.4, 2 10.3 5.7, 12.0, (1 2.6)d (12.l)d (5.72)e (1 1 .9,)' 5.0, 9.1, 2 9.3 (9.7)d 4.3, 7.3, 7.9, 3.2, 5.5, 6.0, 5.4, 12.6, 5.6, 11.9, 5.1, 14.0, 5.1, 14.0, Na+ 6.3, (6-4,Y 4.9, 8-80' 8.9, (9.02 7.3, K+ 7.2," Rb+ Cs+ Mg2+ Ca2+ Sr2+ Ba2+ 4.2, 3.5, 4.4, 5.9, 5.2, 7.1, 6.2,c 5.1," 9.1, 6.7, 9.4 9.9 6.2, 4.6, 6.8, 6.0, 6.2, 7.0, a Abbreviations: DMF, N,N-dimethylformamide; DMSO, dimethylsulphoxide; PC, propy- log K, values, 0.1 for M+ systems, & 0.2 for M2+ systems, Values estimated from log& in PC, assuming a constant Value obtained lene carbonate; AN, acetonitrile.corrected to I = 0. " Ref. (21). difference between complexes of alkali-metal cations in PC and AN.,Op 39-41 using NaMon in potentiometric titration, see text. Table 2. Stability constants of lasalocid complexes with monovalent and divalent cations in various solventsa at 25 "C log (K,/dm3 mol-l)* cation MeOH EtOH DMF DMSO PC AN Ag+ Li+ Na+ 4.1, 2.8, 2.1, 4.8, 2.8, 4.1, 4.1, 3.1, 2.1, 2.5, 8.3, 3.4, - 4.9, - - 5.2, 5.8," - 5.1, (5.40)~ - 4.5, - 7.7, - 6.4, - 4.1, 2 8.8 - K+ Rb+ cs+ Mg2+ Ca2+ Sr2+ 3.6, 3.6, 3.6, 3.9, 4.6, >, 5.6 (5.6)" >, 5.6 (6.6)e 4.7, 4.4, 4.5, 4.6, 6.2, >, 6.4 4.0, 3.9, 3.7, 3.3, 3.1, 2.7, 2 6.5 4.1, - >, 9.1 Ba2+ a Abbreviations as in table 1.complexes, corrected to I = 0. " Value obtained using Na-glass electrode. using NaMon, see text. Ref. (15). log& values, kO.1 for M+ complexes, k0.2 for M2+ Value obtainedB. G. COX, N. VAN TRUONG, J. RZESZOTARSKA AND H. SCHNEIDER 3279 4.S2 and 5.18;13 Rb+, 4.212 and 4.58;13 Cs+, 3.712 and 3.75;13 Ag+, 8.2.13 The agreement with the values in table 1 is generally very good, although the results obtained in the careful study of Hoogerheide and POPOV~~ are consistently a little higher than the present values.The differences most probably arise from the fact that their measure- ments were made at an ionic strength of 0.15 and very large corrections to zero ionic strength were required ( y + = 0.42 was used).13 Given the combined experimental errors and the uncertainty in activity-coefficient corrections at high ionic strengths in low dielectric media, the agreement is quite reasonable. Stability constants are also available for lasalocid complexes inmethanol, using fl~orescencel~ and potentiometric16 methods: Li+, 1.6815 and 1.44;16 Na+, 2.57,15 2.6116 and 2.83 (conductimetric determination);26 K+, 3.5815 and 3.45;16 Rb+, 3.5615 and 3.39;16 Cs+, 3.4315 and 3.36;16 Ca2+, 4.5715 and 4.88;16 Sr2+, 5.4715 and 5.60;16 Ba2+, 6.4615 and 6.58.16 The values from ref.(16) refer to I = 0.10 mol dm-3, but again there is quite reasonable agreement with the present values. We have earlier also reported the stability constants of AgMon in several ~ o l v e n t s , ~ ~ determined by competitive reaction of AgMon with the cryptand (2,2,2). Except for AgMon in DMSO (log K, = 5.38), the agreement with the present values is within experimental error. The reasons for the differences between the values in DMSO are not clear. Attempts were made to study some of the complexes in water, as the Et,NL salts are relatively soluble, but the low solubility of ML made this impossible. A pH titration of Et,NLas and Bu,NMon in water (initial concentration 1.5 x mol dmP3) was carried out and analysed according to PH = PK, + log([L-I/[HLl,,) = - log(K, KSOJ + log[L-l.(7) Precipitation was observed after only 1 % neutralisation and the results gave log(Ka Ksol) = - 10.75( & 0.05) and - 9.43( f 0.04) for MonH and LasH, respectively. If the pK, of the acids in water are similar to those of a normal aliphatic carboxylic acid for MonH (pKa = 4.75)27 and salicylic acid for LasH (pK, = 2.76)28 then the solubilities of MonH and LasH in water must be ca. and 2 x lop7 mol dm-3, respectively. These estimated solubilities should be reasonable, at least as an order of magnitude, as, for example, the pK, of the acids in m e t h a n 0 1 ~ ~ ~ ~ ~ are similar to those of simple model compounds.28 The low solubilities in water should ensure almost quantitative partitioning of LH (and presumably ML) into the phospholipid bilayers in biological membrane systems.DISCUSSION If we consider first the alkali-metal complexes, it is clear that there are significant differences between monensin and lasalocid complexes in terms of the absolute stabilities, the selectivities and the solvent-dependence of the stability constants. The complexes of monensin are very stable and show a sharp stability maximum for the Na+ complex. In terms of the ring size and number of coordinating oxygen atoms, the hydrogen-bonded cyclic structure adopted by monensin in the complexeslT is similar to that of 18-crown-6 (18-C-6), and this might be expected to be reflected in the stability constants.In fact, the K, values in methanol of monensin and 18-C-629 complexes of Cs+, Rb+ and K+ are similar, but those of NaMon and LiMon are much larger than the corresponding 18-C-6 values. The result is that the stability maximum shifts from K+ for 18-C-6 complexes to Na+ for Mon- complexes. This is unlikely3280 STABILITY CONSTANTS OF MONENSIN AND LASALOCID COMPLEXES to be a simple ring-size effect, as even for the much smaller 15-C-5 ligand, K+ forms the most stable complex.29 The differences can be attributed to the presence of the negative charge on Mon-, which will introduce additional direct electrostatic stabilisation, the magnitude of which will increase with decreasing cation size. This negative charge may also be very important in determining the solvent dependence of the stability constants (vide infra).The neutral naturally occurring macrocyclic ionophores such as valin~mycin,~~~ 31 the macrotetralides (e.g. monactin and t r i n a ~ t i n ) ~ ~ and the e n n i a t i n ~ ~ ~ in methanol have different complexing properties from those of monensin. They show typical plateau selectivities (K, values for K+, Rb+ and Cs+ complexes are similar and considerably higher than those for Na+ and Li+ complexes). The maximum K, values are also lower than that of NaMon. Similar behaviour is also observed for the larger crown ether 21-C-7, for which Cs+ forms the most stable complex. These neutral ionophores, which have much larger ring sizes than Mon-, presumably have difficulty in adopting conformations to interact effectively with the smaller cations and do not have the compensating stronger electrostatic interactions for Na+ and Li+ exhibited by the monensin anion.Complexes of the smaller lasalocid anion also show plateau selectivity, with maximum stabilities (in methanol) for K+-Cs+ complexes. The crystal structures of lasalocid complexesg-8 may provide a clue to this behaviour. The structures adopted suggest that in the solid state the cations interact readily only with five of the lasalocid oxygen atoms [asterisk in structure (II)] and not directly with the salicylic acid group. It is possible, then, that in solution Li+ and Na+ are involved in fairly weak complexation with only five oxygen atoms, but that the ligand can adopt conformations in which the salicylic group can interact with the larger cations.Several spectroscopic investigations of lasalocid complexes in solution have been re~0rted.l~’ 33-35 Precise interpretation of spectral effects is difficult, but they suggest the existence of both open-chain conformations [for LasH, Las- and (partly) NaLas in hydroxylic solvents] and cyclic forms with varying degrees of hydrogen-bond formation (for complexes of the larger cations in all solvents and for Lass and LasH in aprotic solvents). Circular dichroism studies of LiLas indicate that this complex has a special conformation quite different from that of complexes of the larger cations, probably because of the small size of Li+. The stability constants of alkaline-earth-metal complexes refer to the 1 : 1 species, as they were measured in the presence of an excess of metal ion.However, lasalocid and related ligands are known to form electrically neutral ML, complexes in the presence of an excess of ligand.16 In almost all cases studied here, the ML+ stabilities pass through a minimum for Ca2+ complexes. By analogy with 18-C-6,29 diaza- 18-cr0wn-6~~ and cryptand (2,2,1) complexes, considerations based on ligand cavity size alone would predict a steady increase in stability from the complexes of the smaller cations to those of Sr2+ and Ba2+. However, electrostatic interactions, which should be strong for complexes of the M2+ cations, vary in the opposite direction and may account for the increase in stability observed on going from Ca2+ to Mg2+. Some care should be exercised in interpreting these values as the stabilities arise from small differences between the very large energies of interaction of the cations with solvent and ligand.The stabilities of the monensin complexes are strongly dependent upon the solvent, especially for the smaller M+ and the M2+ cations. A striking difference between the monensin complexes and those of the neutral cryptand [e.g. (2,2, 37] and the crown ether (e.g. dibenzo- I 8-C-638) ligands is the variation in stability constants on transfer from the protic solvents, MeOH and EtOH, to the aprotic solvents. Fig. 1 illustratesB. G. COX, N . VAN TRUONG, J. RZESZOTARSKA AND H. SCHNEIDER 328 1 .U 8' I l i 8.0 6.0 4.0 h 4 I - z 8.0 rn E 5 6.0 a M - 4.0 0.4 0.8 1.2 1.6 0.L 0.8 1.2 1.6 r i t /A -1 r ,! J A-1 Fig.1. Stability constants of alkali-metal-cation complexes in methanol (MeOH) and propylene carbonate (PC): (a) monensin in MeOH (a) and PC (D); (b) (2,2,1) in MeOH (0) and PC (m) and 18-crown-6 in MeOH (0) and PC (0). stability constants of complexes of the three ligands in methanol and propylene carbonate; a similar picture emerges from a consideration of the M2+ complexes. The difference between the stability constants in the two solvents is much larger for monensin complexes, especially when compared with the structurally related crown ether complexes. Similar differences are apparent for transfer from methanol to DMF. Monensin complexes are less stable in DMF by ca. 2 orders of magnitude, whereas the reverse is true for cryptand and crown ether complexes. However, the stability constants for complexes of all three ligands change by almost the same amount on transfer between any two aprotic solvents (e.g. DMF or PC).Qualitatively this seems most likely to be related to a loss in solvation of the monensin anion on transfer from protic to aprotic solvents (vide infra). This effect should be much smaller for lasalocid complexes, as the lasalocid anion, by analogy with the salicylate anion, should be strongly stabilized by an intramolecular hydrogen bond, this being reflected in the stability constants of MLas and MLas+ (table 2). The sensitivity of the stability constants to solvent variation will depend upon the effect of solvent on the free energies of the species involved in the complexing equilibria.This may be expressed quantitatively by (8) for solvents S1 and S2, where Ks(ML) is the stability constant of complex ML and AG,, represents the free energy of transfer from S 1 to S2. An analogous equation may be written for complexes involving M2+ cations, but here we restrict the discussion primarily to alkali-metal and Ag+ complexes, because of the much greater amount of data available on the thermodynamic properties of salts of these cations. Values of AG,,(M+), based on the convention that AGt,(Ph,As+) = AGtr(BPh;),3g RT[ln Ks(ML)s2 -In K,(ML),,] = AG,,(M+)+ AGtr(L-) - AG(ML)3282 STABILITY CONSTANTS OF MONENSIN AND LASALOCID COMPLEXES are available for the M+ cations in all of the solvents studied h e ~ e . ~ ~ - ~ l These may be used in conjunction with eqn (8) in two ways. Taking, for example, methanol as reference solvent (Sl), values of AGtr(L-) - AG,,(ML) may be calculated for transfer to a given second solvent, S2, using the stability constants from tables 1 and 2.Then for complexes of monensin (say), variations in AGtr(L-) - AG,,(ML) within a solvent for different M+ provide a direct measure of the dependence of the solvation of ML upon the cation contained in the complex, independent of any convention or assumption used to determine AG,,(M+) values. In addition to this, variations in absolute values of AGtr(L-) - AG,,(ML) with solvent may provide information on the solvation of L- and ML. The validity of this approach, however, will depend upon the reasonableness or otherwise of the AG,,(M+) values used.It is also of interest to compare the results so obtained for monensin and lasalocid complexes with corres- ponding values for complexes (MC+) of the neutral crown ethers or cryptands derived from RT[ln Ks(MC+),, -In K,(MC+),,] = AG,,(M+) + AG,,(C) - AG,,(MC+). (9) Table 3 lists values of AGtr(L-) - AG,,(ML) and AGtr(C) - AG,,(MC+) for transfer from methanol to three representative solvents : EtOH (protic solvent), DMF (aprotic solvent with favourable cation-solvent interactions) and PC (aprotic solvent with relatively weak cation-solvent interaction^).^' With a few exceptions the AG,,(ML) or AG,,(MC+) (especially LiLas in DMF and PC) values in a given solvent are independent of M+, considering the combined experimental uncertainties in the stability constants and AG,,(M+) values [ca._+ 2 kJ mol-l, based on _+ 0.1 in individual log& values and f0.8 kJ mol-1 in AG,,(M+) values]. This suggests that in the complexes the cations are well shielded from the solvent by the ligands, at least from any strong specific interactions. This is at variance with the conclusion reached by Degani and Friedman15 from partitioning experiments with lasalocid complexes between water and hexane. Combining the partitioning results with measured stability constants in methanol they concluded that there is a systematic trend with cation size in AG,,(MLas) from methanol to hexane. However, the total spread of values from Li+ to Cs+ complexes was only 6 kJ rnol-l, which is not much larger than the overall scatter obtained for the lasalocid system in this work.The absolute values of AG,,(Mon-)-AG,,(MMon) in table 3 depend upon the assumption used to determine the AG,,(M+) values, as mentioned above. Nevertheless the values are sufficiently large and positive for transfer to DMF and PC (also to AN and DMSO) from MeOH (and EtOH) to suggest a significant effect attributable to loss of solvation or change in conformation of Mon- on transfer from protic to aprotic solvents. This is further emphasised by the fact that preliminary solubility studies show much higher solubilities of MMon in methanol than in the aprotic solvents, i.e. AGtr(L-) to aprotic solvents are even more positive than the AGtr(L-) - AG,,(ML) values given in table 3. Carboxylate anions appear normally to be much more strongly solvated in protic than aprotic s o l ~ e n t s , ~ ~ - ~ ~ which may be sufficient to explain these AG,, values and hence the greater sensitivity of MMon compared with MC+ complexes to solvent transfer shown in fig.1. The AG,,(L-) - AG,,(ML) values may be discussed more specifically in terms of a proposed complexation K,* L * - + M + e M L *B. G . COX, N. VAN TRUONG, J. RZESZOTARSKA AND H. SCHNEIDER 3283 Table 3. Difference in free energies (in kJ mol-l) of transfer between macrocyclic complexes and the free ligands [AG,,(L-) -AG,,(ML)] from methanol to various solventsaq * at 25 "C cation EtOH DMF PC cation EtOH DMF PC Li+ Na+ K+ Rb+ cs+ Ag+ average Li+ Na+ K+ Rb+ cs+ Ag+ average monensin 6.3 26.3 8.8 33.0 7.2 32.8 7.9 29.8 5.1 24.5 8.4 37.4 6.9 30.7 (k1.3) (k4.8) cryptand (2,2,1) - 3.4 7.9 - 0.6 8.1 - 4.8 7.5 - 2.6 10.8 - 1.5 14.3 - 2.2 12.0 -2.5 10.1 (+ 1.5) (42.7) 28.9 28.4 29.1 25.7 20.6 32.8 27.7 (44.1) 8.5 9.6 13.1 10.2 12.9 12.8 11.1 (k 2.0) lasalocid Li+ 0.8 13.1 0.0" Na+ 3.5 19.3 9.0 K+ 1.3 20.1 14.0 Rb+ 1.3 20.8 13.9 Cs+ 1.7 19.1 12.4 Ag+ 6.1 24.4 14.8 average 2.5 19.6 12.9 (k2.0) (k3.7) (k2.1) crown ether dibenzo- 18-C-6 Li+ Na+ 8.9 3.3 K+ 5.7 8.9 Rb+ 6.6 9.7 Cs+ 6.9 11.0 3.7 Ag+ average 7.0 7.3 - (+ 1.4) (f3.6) a Abbreviations as in table 1.* Values obtained using eqn (8) and (9) with AG,,(M+) taken Not included from ref. (39)-(41), based on the convention that AG,,(BPh;) = AG,,(Ph,As+). in the average value. in which the free ligand can assume a certain conformational state (L*-) which is the same in terms of solvation as that adopted by the ligand in the metal complex (ML*), except for a small Born term, SBorn.The proportion of ligand molecules with conformation L*- to the total number of ligand molecules L- is given by Kconf. = [L*-]/[L-1, and it may be shown that the difference in AGtr between the complex and the ligand is given by40 AGtr(L-) -AGtr(ML) = RT In (Kconf. SzlKconf. SA + b o r n . (12) For monensin, as L*- will almost certainly be a cyclic conformation involving an intramolecular hydrogen-bond, Kconf. should be much higher in aprotic solvents than in protic solvents, where competing intermolecular hydrogen-bonding of the -CO; group by the solvent would tend to favour acyclic conformations of L-. Among the aprotic solvents, however, values of Kconf.may be relatively constant, as the dominant conformational influence should be intramolecular hydrogen-bond formation invol- ving the poorly solvated -CO, group. These general considerations are supported by the results for the two neutral ligands and lasalocid shown in table 3. For the neutral ligands, with preformed cyclic structures, hydrogen-bond donation by MeOH and EtOH might influence the conformation (and stability) of the free ligand relative to the complexed ligand in which the donor atoms are interacting with the enclosed cations, but to a much lesser extent than for Mon-. Thus AG,,(C) - AG,,(MC+) values are considerably smaller. Similarly the structure of Las- should be less influenced by solvent than that of Mon-, because of the possibility of intramolecular hydrogen-bond formation with the hydroxy function of the salicylic acid group.However, the solution spectroscopic3284 STABILITY CONSTANTS OF MONENSIN AND LASALOCID COMPLEXES studies do provide evidence for open-chain conformations of Las- in methano1,15 and AGtr(L-) - AG,,(ML) values for transfer to aprotic solvents, especially to DMF, are still relatively large. We thank the S.E.R.C. for a research grant and Ely Lilly Corp. for a gift of monensin. J.R. thanks the University of Warsaw for study leave at Stirling University. W. Burgermeister and R. Winkler-Oswatitsch, Top. Curr. Chem., 1977, 69, 91. E. Racker, Acc. Chem. Res., 1979, 12, 338. H. Celis, S. Estrada and M. Montral, J. Membr. Biol., 1974, 18, 187. W. K. Lutz, F. K. Winkler and J.D. Dunitz, Helu. Chim. Acta, 1971, 54, 1103. W. L. Duax, G. D. Smith and P. D. Strong, J. Am. Chem. Soc., 1980, 102, 6725. C. A. Maier and I. C. Paul, Chem. Commun., 1970, 181. S. M. Johnson, J. Herrin, S. J. Liu and I. C. Paul, Chem. Commun., 1970, 72. P. G. Schmidt, A. H-J. Wang and I. C. Paul, J. Am. Chem. Soc., 1974,%, 6189. W. K. Lutz, H. K. Wipf and W. Simon, Helv. Chim. Acta, 1970,53, 1741. lo P. U. Fruh, J. T. Clerc and W. Simon, Helv. Chim. Acta, 1971, 54, 1445. l1 W. K. Lutz, P. U. Fruh and W. Simon, Helv. Chim. Acta, 1971, 54, 2767. l2 G. Cornelius, W. Gatner and D. H. Haynes, Biochemistry, 1974, 13, 3052. l3 J. G. Hoogerheide and A. I. Popov, J. Solution Chem., 1978, 7 , 357. l4 J. G. Hoogerheide and A. I. Popov, J. Solution Chem., 1979, 8, 83. l5 H.Degani and H. L. Friedman, Biochemistry, 1974, 13, 5022. l6 J. Bolte, C. Demuynek, G. Jeminet, J. Juillard and C. Tissier, Can. J. Chem., 1982, 60, 981. l7 C. J. Pedersen, J. Am. Chem. Soc., 1967, 89, 7017. lS J. M. Lehn, Struct. Bonding (Berlin), 1973, 16, 1. l9 J. Garcia-Rosas, H. Schneider and B. G. Cox, J. Phys. Chem., 1984, 88, 996. 2o B. G. Cox, J. Garcia-Rosas and H. Schnieder, J. Am. Chem. Soc.. 1981. 103, 1384. 21 B. G. Cox, Ng. van Truong, J. Rzezotarska and H. Schneider, J. Am. Chem. Soc., 1984, in press. 22 B. G. Cox, H. Schneider and J. Stroka, J. Am. Chem. Soc., 1978, 100,4746. 23 C. W. Davies, Zon Association (Butterworths, London, 1962), eqn (3.14). 24 W. H. Lee and R. J. Wheaton, J. Phys. Chem., 1978, 82, 605. 25 R. M. Farmer and A. I. Popov, Inorg. Nucl. Chem. Lett., 1981, 17, 51. 26 J. Garcia-Rosas and H. Schneider, Inorg. Chim. Acta, 1983, 70, 183. 27 G. Kortum, W. Vogel and K. Andrussow, Dissociation Constants of Organic Acidr in Aqueous Solution 28 B. W. Clare, D. Cook, E. C. F. KO, Y. C. Mac and A. J. Parker, J. Am. Chem. Soc., 1966,88, 191 1. 29 J. D. Lamb, R. M. Izatt, C. S. Swain and J. J. Christensen, J. Am. Chem. Soc., 1980, 102,475. 30 E. Grell, Th. Funk and F. Eggers, in Molecular Mechanisms on Antibiotic Action on Protein Biosynthesis and Membranes, ed. E. Monoz, F. Garcia-Ferrandiz and D. Vazquez (Elsevier, Amster- dam, 1972), p. 646. (Butterworths, London, 1961). 31 H-K. Wipf, L. A. R. Pioda, Z. Stefanac and W. Simon, Helv. Chim. Acta, 1968, 51, 377. 32 P. B. Chock, F. Eggers, M. Eigen and R. Winkler, Biophys. Chem., 1977, 6, 239 33 S. R. Alpha and A. H. Brady, J. Am. Chem. Soc., 1973,95, 7043. 34 F. S. Richardson and A. D. Gupta, J. Am. Chem. Soc., 1981, 103, 5716. 35 G. D. J. Phillies and H. E. Stanley, J. Am. Chem. SOC., 1976, 98, 3892. 36 B. G. Cox, P. Firman and H. Schneider, Znorg. Chim. Acta, 1983, 69, 161. 37 B. G. Cox, Ng. van Truong and H. Schneider, J. Am. Chem. SOC., 1984, 106, 1273. 38 I. M. Kolthoff and M. K. Chantooni, Anal. Chem., 1980,52, 1039; Proc. Natl Acad. Sci. USA, 1980, 3g B. G. Cox, G. R. Hedwig, A. J. Parker and D. W. Watts, Aust. J. Chem., 1974, 27, 477. 40 B. G. Cox, Annu. Rep. Prog. Chem., Sect. A, Phys. Inorg. Chem., 1973, 70, 249. 41 B. G. Cox and W. E. Waghorne, Chem. SOC. Rev., 1980, 9, 381. 42 B. G. Cox, P. Firman, J. Garcia-Rosas and H. Schneider, Tetrahedron Lett., 1982, 23, 3777. 77, 5040. (PAPER 4/274)

ISSN:0300-9599    

DOI:10.1039/F19848003275

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. 1, 1984,80, 3285-3293 Kinetics of Ligand-exchange Reactions of Macrobicyclic Cryptands BY BRIAN G. COX* AND NGUYEN VAN TRUONG Chemistry Department, University of Stirling, Stirling FK9 4LA AND HERMANN SCHNEIDER* Max-Planck-Institut fur biophysikalische Chemie, D-3400 Gottingen, West Germany Received 17th February, 1984 The rate constants for exchange reactions between metal cryptate complexes, MCryy+, and a free cryptand, Cry,, have been determined in several solvents. Two mechanisms could be distinguished : a reaction proceeding via the free metal cation following dissociation of MCryy+, and a direct, bimolecular cation exchange between the two ligands. In solvents such as water, dimethylsulphoxide and dimethylformamide, which interact strongly with cations, the former pathway predominates for alkali-metal and alkaline-earth-metal cryptates.In poorly solvating media such as methanol and propylene carbonate, where dissociation rate constants are very low, bimolecular pathways make an important contribution to the overall exchange pathway. Exchange reactions of Ag+ cryptates show ligand-dependent rates and strong saturation effects in both methanol and dimethylsulphoxide. Carrier-mediated ion transport through artificial and biological membranes occurs by two principal modes: a carrier or carrier-relay mechanism and a channel mechanism.l Among the mobile carriers are the naturally occurring macrocyclic antibiotics such as valinomycin, the macrotetralides, the enniatins etc.l and synthetic ionophores such as the crown ethers2 and crypt and^,^ while the channel-forming ionophores include the gramicidins and alamethicin.Common to both transport mechanisms are the formation and dissociation steps of the complexes, involving the ligand and the free, solvated cation. It has also been shown by Simon and c o ~ o r k e r s , ~ using 14C-labelled valinomycin and macrotetralides, that for transport by mobile carriers, exchange of ligand occurs during passage through the membranes (carrier-relay mechanism). Thus it appears that both the carrier and ion-conduction transport processes involve the transfer of cations between different groups of donor atoms. A considerable amount of information is now available on the kinetics of complexation-decomplexation reactions of naturally occurring and synthetic macro- cyclic ionophores.l* 5-11 A general conclusion from the results is that the formation rate constants are high and relatively independent of the nature of the ligand, solvent or cation (although M2+ cations react more slowly than M+ cations).ll On the other hand, the dissociation rates are very sensitive to all three factors and are largely responsible for the selectivity of the ligands in complex formation.In particular, the dissociation rates become very slow in poorly solvating media81 11* l2 and it is clear, therefore, that efficient cation transport by carrier relay or conduction in channels cannot involve any substantial loss of the interaction of cations with donor atoms. To date very little has been reported on the exchange of cations between two 32853286 LIGAND-EXCHANGE REACTIONS OF CRYPTANDS different (macrocyclic) ligands, despite the importance of this in relation to cation- transport processes.Lehn13 has presented evidence of an intramolecular cation- exchange process between two complexing sites within a cylindrical macrotricyclic ligand. We have also investigated the exchange of Ca2+, Tl+ and Pb2+ between two different cryptand (Cry) ligands in water and methanol, as in14 ke MCry,"+ + Cry, --+ MCry;+ +Cry,. (1) The exchange rates of Pb2+ in methanol were found to be too fast to be attributed to a mechanism involving initial dissociation of PbCryf+ and a direct bimolecular exchange mechanism was proposed. In this paper we report a more systematic study of exchange of alkaline-earth-metal and Ag+ cations between the benzo-substituted cryptands (2,9272) and (2,72,,2) and the unsubstituted cryptands (2,2,1) and (2,2,2) in the solvents water, methanol, dimethylsulphoxide (DMSO), dimethylformamide (DMF) and propylene carbonate (PC).Two mechanisms could be distinguished : a reaction proceeding via the free metal cation following dissociation of MCryy+ and a direct, bimolecular cation exchange between the two ligands. As expected, the latter pathway becomes more important as the solvating power of the solvent decreases. (2,,2,,2) (2,2,1), a = 0 (2,2,2), a = 1 EXPERIMENTAL MATERIALS Cryptands (2,2, I), (2,2,2), (2,,2,2) and (2B,2,,2) were purchased from Merck and used without further purification. The purification of solvents has been described previo~s1y.l~ The inorganic salts used were Ca(NO,), -4H,O (Fisons, SLR), Sr(NO,), (B.D.H., LR), Ba(C10,), * 3H,O (Koch-Light, puriss.), AgNO, (Fisons, AR), AgClO, (Fisons, SLR) and Pb(C10,), (Aldrich, hydrated).Solutions of the hydrated salts in non-aqueous solvents were normally dried with molecular sieves (type 5A) prior to use, although at the metal-ion concentrations used (uide i n m ) the amount of water introduced by the salts has a negligible effect on the kinetics." KINETIC MEASUREMENTS The kinetics of the cation-exchange reactions [eqn (1) with Cry, = (2,,2,2) or (2B,2B72)] were determined spectrophotometrically. This was possible because of the spectral shifts in the U.V. region (A = 265-290) between the free and complexed benzo-substituted cryptands.Neither the cryptands (2,2,1) and (2,2,2) nor their metal complexes absorb in this region. Reactions were monitored using a Gilford 2400 S or Unicam SP 8300 spectrophotometer for slower reactions, or a Durrum-Gibson stopped-flow apparatus. All measurements were made at 25 f 0.2 "C. In all cases the incoming ligand forms a complex with the cation which is more stable than that of the displaced ligand,". l5 this, combined with use of a large excess of Cry,, ensuring that the reactions went to completion, as indicated in eqn (1). In the presence of a large excess of the incoming ligand, Cry,, pseudo-first-order kinetics were observed in all cases. The stopped-flow data were digitised in the form of 1024 eight-bit integers and transferred to a commodore PET 3016 microcomputer, which performed a linear least-squares fit to a standardB.G. COX, N. VAN TRUONG AND H. SCHNEIDER 3287 first-order rate expression to calculate the pseudo-first-order rate constant, k,. Data from the slower reactions were either collected directly using an Apple I1 microcomputer (for the Unicam SP 8300) or read from a chart recording. The exchange reactions were measured as follows in the various solvents. WATER The rates of the cation-exchange reactions were followed at R = 277-281 nm for Ca2+, Sr2+ and Ba2+ cryptands. The incoming cryptand was (2,2,1) for Ca2+ and Sr2+ cryptates and (2,2,2) for Ba2+ cryptates. The concentrations of MCry:+, where Cry, = (2,9272) and (2&&,2), were in the range (1-2) x mol dm-3 and [Cry,] in the range from 5 x to 1.6 x lo-, mol dm-3.Solutions of MCry:+ were prepared with a slight excess of Cry, (in all solvents). N,N-DIMETHY LFORMAMIDE The exchange reactions were measured at R = 285 nm for the metal cations Sr2+ and Ba2+. The incoming ligands used were as in H,O. The concentrations of MCry:+ were in the range (2-2.5) x 10 -4 mol dm-3 and [Cry,] in the range from 4 x to 7 x mol dm-3. DIMETHY LSULPHOXIDE The cation-exchange reactions of Sr2+, Ba2+ and Ag2+ between two cryptands were followed at R = 283 nm for M2+ cations and A = 265-270 and 291 nm for Ag+. The incoming cryptand (2,2,1) was used for SrCry:+ and (2,2,2) for BaCry:+, while for Ag+ exchange reactions both (2,2,1) and (2,2,2) were used. The concentrations of MCryT+ were in the range (1.2-1.9) x rnol dm-3 and [Cry,] in the range from 4 x to 1 x lo-, rnol dm-3.METHANOL The kinetics of cation-exchange reactions were monitored at R = 281-284 nm for alkaline- earth-metal cations and at R = 267-274 nm for Ag+. The cryptand (2,2,1) was used as the incoming ligand, Cry,, for SrCry:+ and (2,2,2) for BaCryy+. For Ca2+ and Ag+ exchange reactions both (2,2,1) and (2,2,2) were used for Cry,. The concentrations of MCryy+ were in the range (1-3) x mol dmP3 and [Cry,] in the range from 3 x to 1 x lo-, mol dmP3. PROPYLENE CARBONATE The kinetics of Ca2+ and Pb2+ exchange reactions were determined at ;1 = 285 nm. Both cryptands (2,2,1) and (2,2,2) were used as incoming ligands. The concentrations of MCryt+ were in the range (1.7-2.5) x mol dm-3 and [Cry,] in the range from 2 x to 3 x lop2 mol dm-3.RESULTS AND DISCUSSION Three distinct behaviour patterns were observed among the various exchange reactions : (i) the exchange rate constant was independent of the concentration of the incoming ligand, with a rate constant equal to that for the dissociation of MCryr+ (reactions of Ca2+, Sr2+ and Ba2+ cryptates in H20, DMSO and DMF), (ii) the exchange rate constants increased linearly with the concentration of incoming ligand (reactions of M2+ cryptates in MeOH and PC) and (iii) the exchange rate constants increased linearly with [Cry,] at low [Cry,] but levelled off to a maximum rate at higher concentrations (Ag+ cryptates in DMSO and MeOH). Reactions whose rate constants were independent of the concentration of incoming ligand may be discussed in terms of "h k! MCryr+ f Mn+ +Cry, (2) "I Mn+ + Cry, --+ MCry;+ (3)3288 LIGAND-EXCHANGE REACTIONS OF CRYPTANDS Table 1.Kinetics of alkaline-earth-metal cryptate exchange reactions in water, dimethylformamide and dimethylsulphoxide at 25 "C MCryt+ Cry, [Cry,]/mol dmV3 kea/s-l k i b / ~ - l H2O 1 x 1OP3-8.2 x 3 x 1OP3-1.6 x 5 x 10-3-1.6 x lop2 4 x 10-4-1 x 10-3 6 x 10-4-4 x lov3 4 x 1 0-4-7 x lop3 4 x 1OP4-5 x loe3 3 x 10-4-6 x DMSO 6 x 10-4-2 x 6 x lOP4-2.2 x DMF 4 x 10-4-4 x 10-3 2 x 10-3-1 x 10-2 0.54 0.24 3.0 x 10-4 5.56 x 10-4 1.42 x 10-4 4.5 x 10-3 7.9 x 10-3 2.3 x lo-, 0.27" 8 . o ~ 10-3 8.5 x 10-3 9 . 0 ~ 0.50 0.20 2.9 x 10-4 5.5 x 10-4 1.44 x 10-4 4.5 x 10-3 8.9 x 10-3 2.2 x 10-2 0.24 8.2 x 10-3 8.95 x 10-3 9.0 x lop2 a The observed rate constants were independent of [Cry,]; k, values f 5 % .ki values from ref. (11). k, k0.05 s-l. where, in the presence of an excess of Cry,, the dissociation reaction of MCryf+ may be neglected, as discussed above. Application of the steady-state approximation to [Mn+] leads to - d[MCryr+]/dt = k,[MCryy+] (4) where ke = k:, ~,2[CrY,l/(k,l[CrYll +kW-Y,l). ( 5 ) The reactions were measured in the presence of an excess of Cry, and, because the formation rate constants of (2,2,1) and (2,2,2) complexes are also normally higher than those Of (2,7292) and (2B92B,2),117 l6 k,2[Cry2] $ k,"Cry,]. Thus eqn (5) simplifies to k, = ki. (6) Table 1 lists observed rate constants for systems exhibiting this type of kinetic behaviour and fig. 1 shows examples of typical results. Such a mechanism will always be open to an exchange system, but other, more favourable pathways involving directly the incoming ligand may also be present. One such reaction scheme, which can accommodate all of the remaining results, is Kass MCryr+ + Cry, =(Cry, - M - Cry,)%+ (7) k (Cry,MCry,)"+ - Cry, + MCry, where (Cry,MCry,)n+ is an intermediate species formed during reaction.If (Cry,MCry,)n+ is in rapid equilibrium with MCry, and Cry,, then the observed kinetic behaviour will be d[MCry;+]/dt = - d[MCry:+],/dt = kL[MCryr+], (9)B. G. COX, N. VAN TRUONG AND H. SCHNEIDER 3289 t 8-a Table 2. Kinetics of cryptate exchange reactions in methanol and propylene carbonate at 25 "C kKassav MCry;+ Cry, /dm3 mol-1 s-l kiul b / ~ - l ki c/s-l MeOH (2,2,1) 6.9 x lo-, (2,2,2) 6.4 x (2,2,2) 6.0 x lop2 (2,2,2) 2.4 x lo-, (2,2,1) 2.7 x lop2 (2,2,1) 1.9 x 10-4 PC (2,2,2) 2.1 x 10-1 (2,2,1) 3.3 x 10-1 7.0 x 10-4 7.6 x 10-4 2.9 x 10-4 8.8 x 5.1 x 10-6 d d d 5.ox 10-4 5.0 x 10-4 4.7 x 10-4 2.9 x 10-4 4.3 x 10-6 1.4 x 10-5 1.1 x 10-5 1.4 x 10-5 Ca(2B,2B,2)2+ (2,272) 1.3 d 1.1 x 10-5 Pb( 2,, 2, 2), + (2,2,1) 2.0 x 10-3 d 10-Ge Pb(2,,2B,2)2+ (2,2,1) 5.0 x lop2 d 1 0-6 Pb(2B,2B,2)2+ (2,2,2) 2.5 x loF2 d a kK,,, and ki from eqn (12).10%. kK,,,, k; 20% for Ca2+ complexes in MeOH, otherwise Intercepts [eqn (12)] too low to allow k, values from ref. (11) and (17). determination of k i . Estimated from dissociation rates in acid solution. 107 FAR 13290 8'- 6- - I P 2 . 4- *" 2- LIGAND-EXCHANGE REACTIONS OF CRYPTANDS /@' ( b ) /@' / @ zt /@ ,.- a/. / I I I I - 4 8 12 16 I [(2,2,1>]/10-3 mol dm-3 where kL = kKass[Cr~zl/(l+ Kass[Cr~zI) (10) and [MCry;+IT = [MCry;+] + [(Cry,MCryz)n+] is the total concentration of MCryr+ present.It is clear that if K,,, is sufficiently small such that Ka,,[Cry,] 4 1, eqn (1 0) (1 1) reduces to with the observed rate constant for the total exchange reaction, k,, being given by (12) Note that a direct bimolecular exchange which does not involve a stable intermediate, but rather a transition state of the type shown in eqn (7), will also lead to a rate expression of the form given in eqn (12). It is not possible to distinguish between these possibilities for the reactions of M2+ cryptates in MeOH and PC studied here, but we report the rate constants as k i and kKa,, values.Table 2 lists rate constants obtained for M2+ systems in MeOH and PC, together with earlier reported k: valuesllq l7 and fig. 2 shows typical examples of the results obtained. As illustrated in fig. 2(b), the intercepts of k, against [Cry,] plots in PC were too small to allow independent determination of k i . The exchange reactions of Ag+ cryptates showed distinct saturation phenomena. G = k~a,,[CrYzl ke = ki + kKas,[Cryz].Fig. 3. Rates of I I I I 1 I I 5 B. G. COX, N. VAN TRUONG AND H. SCHNEIDER 329 1 C L 3 5- 4 - /+- 2 - #/< ( b ) #'* 3 - I I I 1 I I , 1 2 3 4 5 6 7 [(2,2,1)]/10-3 mol dm-3 silver cryptate exchange reactions at 25 "C : (a) Ag(2,,2R,2)2+ + (2,2,1) in methanol and (b) Ag(2~,2~,2)+ + (2,2,1) in dimethylsulphoxide. These could be accounted for quantitatively by eqn (lo), combined with ka values for exchange via the free metal cation. This is illustrated in fig.3, which shows examples of the kinetic behaviour in DMSO and MeOH. In both cases the solid lines represent the best fit to eqn (10). The ki values (i.e. the intercept at [Cry,] = 0) were determined independently in DMSO using dichloroacetic acid as a scavenger for Cry,, according to a procedure described in detail previously.* The best-fit values of k and K,,,, together with ki values for the various systems studied, are listed in table 3. Considering first the exchange reactions of alkaline-earth-metal cryptates in H,O, DMF and DMSO, it is clear that exchange occurs via reaction of the incoming cryptand with the free cation.The excellent agreement between the exchange rate constants and the previously determined dissociation rate constants shown in table 1 confirms that the rate-determining step is the dissociation of MCryt+. This is not surprising as all three solvents interact strongly with cations and this facilitates dissociation of the cations from the complex. The kd values for M2+ cryptates in water are on average approximately one order of magnitude lower than those in DMSO and DMF, which would tend to make alternative bimolecular pathways easier to observe in water. However, the stronger solvation of the free cryptands in water,l5? la presumably by hydrogen-bond formation with the ligand donor atoms, counteracts this. 107-23292 LIGAND-EXCHANGE REACTIONS OF CRYPTANDS Table 3.Kinetics of silver cryptate exchange reactions in methanol and dimethysulphoxide at 25 "C MeOH (2,2,1) 0.68( f 0.02) (2,2,2) 0.47( f 0.02) (2,2,1) 0.43( f 0.01) (2,2,2) 0.39( f 0.01) DMSO (2,2711 6.9( f 0.4) (2,272) 6.9( f 0.4) (2,2,1) 5.5( 0.4) (2,292) 3.0( f 0.4) 5.5(f0.9) x lo3 3.7( f 1 .o) x 103 4.6( f 0.4) x lo3 3.5(+0.5) x lo3 5 x 10-3b 5 x 10-36 5 x 10-4b 5 x 10-4b 3.89( f0.68) x lo2 0.20( f0.03)c 3.22(_+0.53) x lo2 0.20(f0.30)c 5.44( & 0.90) x lo2 0.30( f 0.03y 1.39( f 0.25) x lo2 0.30( & 0.03)c a From eqn (12). Estimated from the stability constant of AgCry, assuming Obtained using dichloroacetic acid as a scavenger k, = lo9 dm3 mol-1 s-l [ref. (8) and (15)l. (N. van Truong, unpublished results). In more poorly solvating media, such as MeOH and PC, the normal dissociation rate constants are reduced drastically relative to those in DMSO and DMF (lo3-lo4 times in MeOH and 104-105 times in PC).ll In these solvents a bimolecular reaction involving direct interaction with the incoming cryptands makes an important contribution to the overall exchange process (table 2 and fig.2). An intermediate in which the cation is shared between donor atoms from both ligands [eqn (7) and (8)] is not unreasonable in view of the known ability of cryptands and crown ethers to form 2 : 1 (ligand :cation) complexes when the cation is too large to fit completely into the ligand cavity.l99 2o Such complexes are also well known for several of the naturally occurring ionophores.21 The rates of bimolecular pathways are not expected to vary in the same way with solvent as those of the normal dissociation reaction.They will depend upon the solvation of MCry?+ and Cry,, whereas k, values depend strongly on the solvation of the free cation, M2+. Indeed it may be noted that kK,,, values in PC are similar to or higher than those in MeOH, whereas k, values in MeOH are normally at least an order of magnitude higher than in PC." This means that in very poorly solvating media, such as in membranes, cation transfer between ligslnds during transport or movement in conduction channels may be relatively rapid, despite the very slow dissociation rates of complexes in such media. The exchange reactions of Ag+ cryptates are different in that they show strong saturation effects, and ligand-dependent rates are observed in DMSO as well as in MeOH.Again the general behaviour can most readily be interpreted in terms of the association-exchange mechanism depicted in eqn (7) and (8), but with rather larger Kass values than those of the alkaline-earth-metal cryptates. The data in all cases show an excellent fit with eqn (10) (e.g. fig. 3). It does seem surprising that the k values, corresponding to transfer within the association complex, differ by a factor of 10 for reactions in MeOH and DMSO. This difference, however, is considerably smaller than that between the uncatalysed dissociation reactions ( 102-103 fold). A kinetically equivalent alternative scheme would be one involving formation of an association complex which is not on the reaction path for the exchange process, viz.K k S S k' (CrylAgCry,)+ AgCry: + Cry, - AgCryi + Cry,.B. G. COX, N. VAN TRUONG AND H. SCHNEIDER 3293 Such a complex could, for example, involve interaction between Ag+ and a lone pair of one of the cryptand nitrogens in an exo conformation. This could account for the different behaviour of Ag+ relative to the alkaline-earth-metal cations, as Ag+ is known to form very strong complexes with nitrogen donors. It is also unlikely that this type of complex would lie on the reaction path for the exchange reaction, as entry of Ag+ into the cavity of Cry, would require dissociation of Ag+, followed by inversion of the nitrogen and recomplexation. The present study does not provide much information on the influence of ligand structure on the exchange rates because of the rather limited range of ligand structures involved.The flexibilities of the ligands would be expected to be an important factor in determining rates of cation exchange and some evidence of this may be discerned from the results. It is noticeable that for Ag+ exchange, k values for (2,,2,2) cryptates are larger than those for (2B,2,,2) cryptates, whereas the normal dissociation rates are in the opposite direction. This may be a reflection of the greater flexibility of (2B,2,2) relative to (2,,2,,2). Similarly in alkaline-earth-metal exchange reactions, the more flexible incoming ligand (2,2,2) showed higher values of kK,,, than (2,2,1) for a given MCryy+; however, for Ag+ exchange, Kass values were slightly larger for (2,2,1). In order to look at the effect of ligand structure more carefully we are presently extending this work on cation-exchange reactions to include the much more flexible open-chain antibiotic ionophores of the Nigericin group, such as monensin.,, We thank the S.E.R.C.for a research grant. W. Burgermeister and R. Winkler-Oswatitsch, Top. Curr. Chem., 1977, 69, 91. C. J. Pedersen and H. K. Frensdorf, Angew. Chem., Int. Ed. Engl., 1972, 11, 16. J. M. Lehn, Struct. Bonding (Berlin), 1973, 16, 1. H. K. Wipf, A. Oliver and W. Simon, Helv. Chim. Acta, 1970, 53, 1605. Th. Funk, F. Eggers and E. Grell, Chimia, 1972, 26, 632. P. B. Chock, F. Eggers, M. Eigen and R. Winkler, Biophys. Chem., 1977, 6, 239. 1978, 82, 647. B. G. Cox, J. Garcia-Rosas and H. Schneider, J . Am. Chem. Soc., 1981, 103, 1054. B. G. Cox, Annu. Rep. Chem. SOC., Sect. C, 1981, 3 . E. Schmidt and A. I. Popov, J . Am. Chem. SOC., 1983, 105, 1873. ’ L. J. Rodriguez, G. W. Liesegang, M. M. Farrow, N. Purdie and E. M. Eyring, J. Am. Chem. SOC., l 1 B. G. Cox, Ng. van Truong and H. Schneider, J. Am. Chem. SOC., 1984, 106, 1273. l2 W. Burgermeister, T. Wieland and R. Winkler, Eur. J. Biochem., 1974, 44, 31 1. l 3 J. M. Lehn, Pure Appl. Chem., 1980, 52, 2441. l4 B. G. Cox, J. Garcia-Rosas and H. Schneider, J . Am. Chem. SOC., 1982, 104, 2434. l5 B. G. Cox, J. Garcia-Rosas and H. Schneider, J. Am. Chem. Soc., 1981, 103, 1384. l7 B. G. Cox, Ng. van Truong, J. Garcia-Rosas and H. Schneider, J . Phys. Chem., 1984,88, 996. B. G. Cox, P. Firman, I. Schneider and H. Schneider, Inorg. Chim. Acta, 1981,49, 153. M. H. Abraham, A. F. Danil de Namor and R. A. Schultz, J. Chem. SOC., Faraday Trans. I , 1980, 76, 869. J. M. Lehn and J. P. Sauvage, J . Am. Chem. SOC., 1975,97, 6700. 2o E. Mei, J. L. Dye and A. I. Popov, J . Am. Chem. SOC., 1976,98, 1619. 21 J. Bolte, C. Demuynke, G. Jeminet, J. Juillard and C. Tissier, Can. J. Chem., 1982, 60, 981. 22 A. Agtarap, J. W. Chamberlin, M. Pinkerton and L. Steinrauf, J. Am. Chem. SOC., 1967, 89, 5737. (PAPER 4/275)

ISSN:0300-9599    

DOI:10.1039/F19848003285

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I, 1984,80, 3295-3305 Capillary Phenomena Part 25.-Thermodynamic Equilibrium and Stability of Capillary Systems in a Gravitational Field BY ERNEST A. BOUCHER School of Chemistry and Molecular Sciences, University of Sussex, Brighton BN1 9QJ Received 17th February, 1984 A unified analysis is given of the thermodynamics of systems in a gravitational field, appropriate for sessile and pendent drops and fluid bridges, as well as for fluids in porous media, solids detaching from surfaces and liquid lenses. Mechanical and physicochemical phenomena are described. Stability criteria as well as equilibrium changes are discussed. By permitting transport of substances between phases and compression effects a scheme is presented which can deal with a wide range of systems, including those in various gravitational fields.Examples, mainly using certain of the mechanical aspects, e.g. for solids at surfaces, for pendent drops and for fluid bridges, have been given separately. There are three theoretical approaches to the analysis of the equilibrium and stability of capillary systems such as pendent drops beneath a solid, fluid bridges between two solids or fluid/fluid interface displacement within a porous solid: (i) the phenomenological approach where, instead of experimental observations, one interprets the results of numerical computation starting with the equilibrium fluid/fluid interface shapes, (ii) the thermodynamic approach entailing more explicit quantities such as interfacial areas in free-energy expressions, with general criteria applied to detect the onset of instability, and (iii) the variational approach where selected (arbitrary, but convenient) perturbations from an equilibrium configuration are examined as a test for instabilities. These divisions are arbitrary, but they broadly reflect aspects of recent studies : they should lead to consistent conclusions and all three are thermodynamic in nature.Fluid/fluid displacement can also be dealt with by model computer simulation and by the application of network models and percolation the0ry.l. The phenomenological approach has been used extensively and successfully in recent years, especially for systems having axially symmetric fluid/fluid interface shapes in the presence of a gravitational The reasons for this success are (a) that second-order differential equations analogous to those solved numerically to give interface meridians by Powalky for the Bashforth and Adams monograph6 of a hundred years ago can now be solved rapidly and with ease and (b) that the data from this method are often amenable to self-evident interpretation. The thermodynamic approach is capable of showing explicitly how quantities such as the gravitational free energy and the surface free energy contribute to the overall beha~iour.~ The variational approach has proved itself of value in testing for stability limits (onset of irreversible changes of a large-scale nature such as pendent-drop detachment) or more precisely for confirming stability limits deduced otherwise,8 since alone the method is difficult to apply.g Even more difficult to use is the rigorous method of testing 32953296 CAPILLARY THERMODYNAMICS configurations neighbouring one known to be at equilibrium. lo The variational method has the advantage that the stability of a configuration can be tested with respect to symmetrical and unsymmetrical perturbations, but in practice this distinction of type cannot be made.The present study is based on the premise that a thermodynamic analysis should be capable of describing thermodynamic systems in a unified manner, leading to quantities relating to an equilibrium path and criteria for instabilities, either concerning fluid flow or displacement, or with respect to the physicochemical phenomena of condensation (evaporation) and the diffusion of chemical species across an interface.With all except simple systems some numerical computation will be needed to evaluate quantities, i.e. as an extension of the original phenomenological studies. Additional unification of approach has been provided by giving an analysis applicable to gravity-free systems as well as those subjected to the terrestrial gravitational field or to varied field strengths.ll In manipulating a capillary system it is important to acknowledge the nature of the mechanical device as well as the intrinsic properties of the capillary system in isolation. l2 The analysis and techniques developed in this paper can in principle be extended to deal with systems in a centrifugal field. Note that many other capillary systems can be treated in the manner described: only a few examples are given.The aims of this paper are to give a thermodynamic account of equilibrium and stability in terms relevant to a variety of capillary systems. In particular, compression of phases, condensation and transfer of matter between phases are permitted with systems in a gravitational field. The ensuing free-energy expressions contain terms in surface areas, centres of mass and phase volumes which are discussed as they relate to mechanical and physical processes. Axial symmetry is not assumed, although this has made it possible to compute interface shapes and attendant quantities for the examples cited, e.g. pendent drops and fluid bridges. The dependence of stability limits on the mechanical properties of the device used to manipulate capillary systems is an important aspect to emerge from these studies.BASIC MECHANICAL MODELS Fig. 1 shows a schematic model enabling the fluid-bridge configuration to be altered by a controlled movement by means of mechanical links to external forces applied to the pistons or to the upper solid. Constraining solids could more generally be subjected to an applied torque13 as well as to a tensile force. Clearly similar arrangements could be used to produce pendent and sessile drops or other large-scale capillary systems. The fluid bodies have an axis of symmetry about which rotation of the meridian curve generates the fluid/fluid interface configuration. Many of the thermodynamic relationships already developed4* 7 7 l4 are applicable to fluids con- strained by irregular solids.We begin with the more abstract arrangement, without implied symmetry, shown in fig. 2. The boundary of the thermodynamic system can be assigned convenient properties. For the present it will be assumed to be rigid and impermeable but capable of permitting heat transfer to keep the temperature constant and of permitting the mechanical linkages to manipulate the phases. Fig. 3 shows three representative types of horizontal zone which could exist. A zone is a horizontal element of the system at gravitational potential v/ = gz, of height dz and volume dv. Zone 3(a) consists of two fluid phases a and /I, of volume dva and d d , which when the system is manipulated by incremental external displacements undergo changes 6ua and BUD. A sensibly chosen Gibbs dividing surface of area dAaP and tension yap separates a and /I within dv.E.A. BOUCHER 3297 mechanical l i n k c y l i n d e r and p i s t o n p cylinder and p i s t o n a Fig. 1. Idealized representation of a system of springs and pistons for manipulating fluid bridges and other capillary systems. I - - - I I 1 I I 1 I I I I I I I I I I I I I I I I I I I . . . . . . . . . . . . . . . . . . . . . bv . I f Ppring Z* . 4: m e c h a n i c a l l i n k . . . . . . . . . . . . . . . . . . . . . I I Fig. 2. Representation of a horizontal zone dz at position z relative to a fluid supply and mechanical link at position zt . The capillary system is bounded by the fence denoted ( . . . ) and the springs are within the boundary denoted (---).3298 CAPILLARY THERMODYNAMICS \ Fig.3. Types of horizontal zone in a capillary system: (a) consisting only of fluid phases a and p, (b) consisting of fluids a and p within a porous solid s with the alp interface making edge contact and contact with a smooth solid and (c) a representation of three fluids a, p and E meeting as in a liquid lens (the horizontal scale is distorted). Suppose fluids a and p in cylinders at a height where the gravitational potential is y/t undergo incremental volume changes Dva.t and D&t. It is assumed here that only one fluid phase exists in a cylinder and that new phases are not nucleated: in the most straightforward example, condensation involves a single component. A portion 6va7 t and Sd. 7, of each phase displacement, is associated with the change within du.A change can severally or collectively involve: (i) pure displacement (disp) of the alp interface, with or without area change 6A@, e.g. for incompressible liquids a and /I, (ii) displacement of the a/p interface because of condensation and/or evaporation (cond) of one or more components of a phase, (iii) displacement of the alp interface accompanied by compression or expansion (comp) or (iv) changes because of transfer by diffusion (dim of chemical components from one phase to another so as to attain and maintain physiochemical equilibrium. Since dv is constant, all changes are subject to 6va+6@ = 0 (1) and changes caused by condensation and evaporation, or compression and expansion, can be identified by the abbreviations above with the sign of the change indicating which of the pair is involved.Generally, for cases (ii)-(iv), 6va9 7 # Sva and Sd. 7 # dvp; only for change (i) will these volume changes at zt and z be equal. However, the corresponding mass changes are necessarily equal, e.g. Smayt = 6ma. In general 6v = Gu(disp) +dv(cond) + Sv(comp) + &(dim (2) where the right-hand terms apply to a zone. We shall for the moment neglect adsorption phenomena and will not specifically account for diffusion of components between phases. The abbreviation disp is used for the sum of all contributions to interface displacement. The external work Dw done on the system by moving pistons located at height zt is Dw(ext) = - F t D u a ~ t -Pp>tD&t. (3) A portion of this given by dwt = - p , t & a , t -pP,tg,P,t (4) is associated with changes within zone dz where the hydraulic pressures are pb[ andE.A. BOUCHER 3299 Pp and the gravitational potential is w. Within the zone, the work done on the system is dw = (p" - PB) dvyllsp) - P"[SV"~ t + Guy*)] - P ~ [ ~ V B ? t + dvP(d@)] + (w - v/t) (6ma. + + 6mp.t). ( 5 ) In deriving eqn (5) it has been assumed that dua(disp) = -Gva(disp), but dwayt and 6vB7t are not of equal magnitude, except for incompressible fluids in the absence of condensation and inter-phase diffusion. Little error will usually ensue from assuming densities pa and fl to be constant in the vertical direction, but an equation of state might be needed for compressible phases in some circumstances. When 6va9 7 = - t , and the only change is due to pure interface displacement, i.e.dva9t = -dva, 6w = (P- PB) dva+ (w - v/t) (dma +dmQ (6) where all quanitities except the arbitrarily chosen y/t pertain to a horizontal zone dz. An equivalent expression was derived previously15 for pendent-drop growth for incompressible phases. De Donder extended the thermodynamic methods of Gibbs by using the concept of entropy production and by introducing a state function called the affinity (see Prigogine and DefaylG and Sanfeld17). Clausius used the term uncompensated heat and Rayleigh recognized entropy production caused by viscosity effects. If 6,s is the entropy received from the surroundings and diS is the entropy produced within the (7) system, dS = d,S+diS; 6,s = dq/T,d,S 3 0. For a zone, the Helmholtz free energy d F undergoes a change 6F.From the first and second laws of thermodynamics d F = dw-TdiS-SdT (8) where d w is the work expended in forming the unperturbed state within the zone. Then the change 6F is given by The zones are thin enough that the Helmholtz free energy for the whole capillary system of volume u allows the summation over all zones to be replaced by integration, F = JvdF, and the change for the whole system is dF=dw-TdiS-SdT. (9) D F = [(dF+dq-dl;] = 6F. (10) zones sv We can write eqn (5) in the slightly simpler form dw = (P" - PB) Sva(t€i@) - ~ a d v ~ - Ppdvp + ( I+Y - v/t) (ha + dmB) d~ = (P" - PB) d~~(il@) - P"GV~ - P@UB + ( t , ~ - I,v~) (dma + 6,B) - ~6~ s (1 1) ( 1 2) so that, from eqn (9) and (1 1) at constant temperature, for a zone whence the complete differential of the Helmholtz free energy of the entire system is D F = (P" - PB) Gva(*) - sp"dua - sPp6vB+ [ ( v f - w ) (6ma + dms) - TD, S.(13) On integrating some of the terms in eqn (13) in the vertical direction to include the whole system we obtain D F = - P d v a - P@vB+ (P" - PB) dva(disp) + (yo- v/t) D(ma - mB) s -(rna+mB)D(v/*-t,vt)- 7'DiS. (14) sss3300 CAPILLARY THERMODYNAMICS The first two terms are only important when compression of one or other phase occurs. The potential rym is that at the centre-of-mass of the appropriate phase. The term representing integration over the pressure difference across the interface with respect to the volume displaced by movement of the alp interface will be simplified later. GIBBS MODEL We now suppose that there are present in the capillary system phases a, p, .. ., a, components 1,2, . . . , c and interfaces aB, . . ., au, between different adjacent phases. The Helmholtz free energy is then supposed to be completely described by (15) We adopt but extend the suggestion of Guggenheim18 for dividing a system into horizontal ‘phases’ of uniform gravitational potential ry (nothing to do with his sandwich model of adsorption), noting that several conventional phases can exist within a zone at potential ry, and in particular that F = F(T, Va, Va, . . . Vw, A@. . .AaW, n:. . .ny, . . ., nz.. .np). dF= d P + d p + d F etc. (16) where t~ refers to the interface(s). Consequently, from eqn (1 5), for a zone a a8 + c , z [P:+(ry-ryt)M,ldn: (17) phases components a C where Mc is the molar mass of component c and dn: is the incremental change in the number of moles of component c: as far as the chemical potential ,@ is concerned it does not matter where this substance came from, but in the gravitational term an arbitrary source position of potential ryt has been chosen.From eqn (17), for two phases a and p consisting of pure components of molar mass Ma and MB, d F = -SdT-Pdva-PBdvb+yafidAaB + + (ry - ryt ) Ma] dna + ha+ (ry - yt ) Mq dnb. (1 8) Some of the consequences of taking the gravitational field into account can be deduced. The gravitational field does not affect the partial differential quantities for component i, aPi/ap = av/ani; api/dT = -as/an, = V i - - -si. (19) One component, i, can achieve physiochemical equilibrium at constant temperature, volume and area within this gravitational zone, i.e.where d(dF),, v a , ~ , A a ~ = 0, as follows : (i) within two conventional phases at the same gravitational potential P9 = P& v(a) = wco> (20) (ii) within the same conventional phase at two different gravitational potentials y’ and pf( ry’) + Mi y’ = pf( ly”) + Mi ry” ryff or the equivalent dpf+Midry = 0E. A. BOUCHER 3301 and (iii) within two different phases a and /3 located at two different chemical potentials ry' and ry" Because we are dealing with capillary systems, the applied pressures in two conventional phases at the same gravitational potential will not usually be equal. Finally, from this line of reasoning a form of Pascal's laws of hydrostatics can readily be deduced, since at constant temperature eqn (19) and (22) give1* ,u: + Mi v'( a) = pf + Mi ~"(p).(23) a P p y = - p i ; pi = Mi/Vi. (24) Returning to the free-energy expression, it would for some purposes be sufficient to use only eqn (17), but we now investigate the nature of the incremental variation 6(dF) in dF, using the two-phase system of pure components for which at constant temperature 6(dF) = - P d v a - Ppdvp+ y@dA@+(ry- ryt) drna+(y- v/t) drnp+paSna+p~6np (25) where ama = Madnu etc. Eqn (25) still applies only to a horizontal zone. It is seen that eqn (12) was obtained by doing mechanical work on the system. If it is supposed that eqn (25) should be its equivalent then this expression alone accounts for physicochemical effects through the presence of the chemical potentials of the components. The dva and dub terms in eqn (25) are associated with the work done on compression of the phases.Equating eqn (1 2) and (25) T6, S = (P - P9 6 v a ( G ) - ya@dAap - padnu - ppdnp. (26) If in the zone dz the pressure difference across the a/P interface is given by the Laplace equation in terms of the mean surface curvature J where the potential is ry, we can write eqn (26) as Td, S = yapJSva(*) - yap6Aap - pa6na - pp6np. (27) When the change within zone dz involves condensation of a to p, i.e. both phases are of the same component, dna = -6np and in the absence of compression duo! = -6vp, giving Everett and Hayneslg derived an exactly analogous expression for vapour adsorption in a porous solid, regarded as overall gravity free.The same equation was later usedz0 to deduce the criteria for the mechanical and physicochemical equilibrium and stability of fluid/fluid displacement in porous solids. A thin horizontal zone behaves as though it were gravity free. Tdi S = yJdva - y6Aap+ - p 9 ana. (28) EQUILIBRIUM AND STABILITY CONDITIONS We continue to examine equilibrium and stability conditions using the system of two fluid phases, rather than the more general system to which eqn (1 7) applies. At constant temperature the complete differential of the Helmholtz free energy for the whole system is given by integrating eqn (25): DF = - [ P d v a - [P&bp + yamAaD J J3302 CAPILLARY THERMODYNAMICS from which DF = - P d v a - PbduB + yaSDAaB i s + (yo - v/t) D(ma + mB) - (ma + mB) D( yo - v/t) + [paGna + [p@nb.(30) J J On the supposition that eqn (14) and (30) should be compatible for capillary system, the entropy production by irreversible processes can be as TD, S = s(P - PB) dva(d@) - yaBDAaB- Jpadna - spbd.8. the entire expressed (31) Assuming that within each zone the local pressure difference (P - PB) across the a//? interface satisfies the Young-Laplace principle, eqn (3 1) can be written with integration over the local mean surface curvature J for each zone dz: Entropy production in the system can occur by the flow of phases a and /? to achieve overall equilibrium, not just local equilibrium, by area changes (generalized below) and by the transport of substances between phases by condensation (or evapora- tion) and diffusion so that the chemical potentials pa and become equal, eqn (20), when overall physicochemical equilibrium is attained.To see more clearly the implications for achieving local and overall equilibrium we write eqn (31) in a less concise form without simplifying terms in dna and dnb: n + [(v/ - v/t) D(ma +mB) - (ma +mB) D(y/ - v/f)] r r We have assumed sufficient symmetry that separate potentials $(a) and yo@ are not required. The most general equilibrium condition is that DiS = 0. However, it will usually be found convenient to examine a system separately for equilibrium and for the stability of that equilibrium with respect to mechanical and physicochemical pheno- mena. The stability of a system can be decided by the requirement that DiS > 0 as equilibrium is attained.Conversely, one can formally identify the condition DiS < 0 as signifying that the system being perturbed from equilibrium is stable. PHYSICOCHEMICAL AND MECHANICAL FEATURES Often mechanical and physicochemical effects are not only separated by their involving different thermodynamic quantities, but by the timescale of events. Fluid flow can be very rapid, whereas diffusion of components of the same system can occur relatively very slowly. One must of course realize that these phenomena affect one another, and that in a practical system judgements must be made about the magnitude of effects and the timescales involved. Included in the category of physicochemical phenomena are the adsorption of chemical components at interfaces, the influence of adsorption on interfacial tensions and therefore on spreading pressures being wellE. A.BOUCHER 3303 recognized. Furthermore it is tacitly assumed that no electrostatic effects are involved which might modify interface shapes. One of the most commonly discussed physicochemical effects in capillarity is the vapour pressure of component one, say, of a phase separated from a liquid phase by a curved surface. The chemical potential of component one in the liquid phase pi( T, v / ) will equal that, &'(T,p*), in the vapour phase where p* is the fugacity. The vapour pressure p relative to that p o above a plane surface at the same temperature is given for an incompressible liquid, with vapour imperfection represented by the virial coefficient B, by4 RTln @ / P O ) = - (pl -pv)gzv: + (p -po) (0: - B) (34) where liquid and vapour densities are p1 and pv and v: is the partial molar volume of one in the liquid phase.The vapour pressure p(z) over a curved surface in a gravitational field, e.g. up the side of a pendent drop, varies with z in exactly the same way as that above a plane liquid surface varies with height in the absence of a capillary system. Eqn (17) contains the sum of terms of the type yaPdAaP, but for simplicity other interfacial areas did not appear in subsequent equations. Many systems involve two fluid phases and one or two solids. Interfacial area changes can be combined into a quantity called the effective area Aeff,14 provided Young's equation of wetting is (35) accepted : ysB = ysa + yap cos 8 where 8 is the contact angle between the a/P interface and the solid taken through the a fluid phase, the denser.The general acceptance of eqn (35) is not being advocated since in some practical circumstances it might be advisable to avoid, if possible, problems of contact-angle hysteresis and controversy over microscopic as opposed to macroscopic contact angles. The surface free-energy change for a system consisting of solids s, and s,, and fluid phases a and p, and with contact angles 8, and 8,, can be written as (36) D P = y@DAaP+ yaslDAasl + y&DA& + yaS2DAaS2 + akDAPS2. Defining the effective area as Aeff = I"/y@, noting that one is usually justified in writing DAaP1 = -DAaS1 with a similar expression for s,, the application of eqn (34) for each solid gives ~ ~ e f f = D A ~ P - DAQS~ cos 8, - DA~S, cos 8,.(37) It will usually be convenient to use reduced or dimensionless rather than actual quantities, e.g. by dividing actual quantities of dimension I" by av where a2 = 2yaB/Apg: Ap = p a - / . To evaluate the ensuing reduced quantities involves the separate task of numerical computation which has recently included examples of pendent drops subjected to variation in the gravitational field,119 21 the detachment of rods from liquid surfaces and fluid drainage22 and the properties of fluid bridges between Detailed examples will not be discussed here: the present treatment unifies the accounts just cited and provides a framework for extensions while showing the basic assumptions of the model. However, attention is drawn to additional features revealed by consideration of examples.A pendent drop of liquid a at rest will according to eqn (33) satisfy ya'BDAaP = - maD( v/ - v/t) (38) since the equilibrium condition is that Di S = 0 and the phases are at constant volume3304 CAPILLARY THERMODYNAMICS Fig. 4. (i) Indirect area change accompanying condensation of vapour phase into a droplet of liquid phase and (ii) the extension of area A" by a directly linked forcef. and composition. When subjected to a change dc in the gravitational field denoted by [g, eqn (38) becomes in reduced terms (39) aAa@ - -2vyC7(z'--zt) 1 - ac ac V , T since ry' = 2% and vapa = ma. By the above stability criteria, the change signified by eqn (39) will be stable if The advantage of introducing the variable gravitational field, permitting a unified treatment of systems subjected to terrestrial- and micro-gravity, has been dis- cussed.ll9 21 It is also now clear from eqn (14) and (30) that a distinction has been made between mass transfer in a gravitational field and volume changes.Previ0usly,~3 systems were in effect at a constant total volume. An explicit distinction can also be made between two types of area change. Fig. 4(i) and (ii) show, respectively, the condensation of liquid into a droplet with concomitant area change and an area change for a planar interface. In the case of condensation the equilibrium change (P" - P) do" is exactly balanced by the work done in areal extension ydA. There is no analogous volume change when the plane interface is extended and the work done requires direct coupling to an externally applied force.FREE-ENERGY CHANGES The work done on a capillary system or the finite Helmholtz free-energy difference AFaccompanying a change from state I to state I1 can be broken down in the following manner : A F = J;*DF' (41) is given by integrating eqn (30) along an equilibrium path. When there is no transfer of substance between phases and no overall volume changes A F = ya@AAa@ + A[(ty ' - tyt) (ma + mq]. (42) An interesting relationship is obtained by expressing the (often ficticious) mean surface curvature J t at zt to that, J ' , at the centre of mass, z', of say phase a: ya@Jf = yaBJ'+@a-#)g(z'-~t) (43) and using the simplifying conditions D(ma-mmP) = (pC'--pp) Doa, Dua,t = -Do@,+ and Dua.t = Doa (44)E.A. BOUCHER 3305 the differential equivalent of eqn (42) leads directly to a condition for an equilibrium displacement4 (45) CONCLUDING REMARKS The overall effect of doing work on a capillary system will be that the existing a phase changes position dz' with an energy change pavagdz', and that the new material has been moved vertically a distance (z'-zt) with an energy change paduag(z'-zt), accompanied by changes to p in the opposite sense, in addition to which there has been an area change dAeff with energy change yaBdAeff, and energy changes may have occurred because of volume changes (e.g. by compression) to the a and /3 phases. The necessary distinction between methods used to manipulate systems, leading to ideal extremes of stress and strain control, with intermediate cases depending on the effective mechanical stiffness, has led to a demonstration of the value of considering the entire system.22 For example, the raising of a rod with its lower edge contacting a surface by pulling on a spring attached to the upper end of the rod, fig.1 and 2, would introduce the energy stored in the spring for a displacement into the free-energy expressions. Instability, i.e. rod detachment, depends on the spring constant and is signified in a cusp in a plot of AFtot against displacement. It is clear that one could relate the isolated cases so far examined to catastrophe theory. It is also evident that we have found mechanical instability criteria which are exactly analogous to those described by Thompson24 for mechanical structures.The majority of this analysis was carried out while the author was Visiting Professor at Carnegie-Mellon University, Pittsburgh. Support of the Universities and the encouragement of colleagues during that period, 198 1-82, is gratefully acknowledged. J. Koplik, J . Fluid Mech., 1982. 119, 219. R. Chandler, J. Koplik, K. Lerman and J. F. Willemsen, J. Fluid Mech., 1982, 119, 249. J. F. Padday, Pure Appl. Chem., 1976,48,485. E. A. Boucher, Rep. Prog. Phys., 1980. 43, 497. S. Hartland and R. Hartley, Axisymmetric FluidlLiquid Interfaces (Elsevier, Amsterdam, 1976). F. Bashforth and J. C. Adams, An Attempt to Test the Theories of Capillary Action (Cambridge University Press, Cambridge, 1983). D. H. Michael, Annu. Rev. Fluid Mech., 1981, 13, 189. E. Pitts, J. Fluid Mech., 1976, 76, 461. ' E. A. Boucher, Proc. R. Soc. London, Ser. A, 1978, 358, 519. lo D. C. Dyson, Prog. Surf. Membr. Sci., 1978, 12, 479. l 1 E. A. Boucher and T. G. J. Jones, J. Chem. Soc., Faraday Trans. I , 1982, 78, 2643. l 2 E. A. Boucher and H. J . Kent, J. Chem. Soc., Faraday Trans. 1, 1978,74, 846. l 3 J. W. Cahn and R. B. Heady, J . Am. Ceram. Soc., 1970,53, 406. l 4 E. A. Boucher, 2. Phys. Chem., N.F., 1978, 113, 125. l5 E. A. Boucher, M. J. Evans and H. J. Kent, Proc. R . Soc. London, Ser. A, 1976, 349, 81. l6 I. Prigogine and R. Defay, Chemical Thermodynamics, translated and revised by D. H. Everett (Wiley, New York, 1954). A. Sanfeld, in Physical Chemistry, Volume 1 : Thermodynamics,ed. W. Jost (AcademicPress, New York, 1971), chap. 2. E. A. Guggenheim, Thermodynamics (North-Holland, Amsterdam, 4th edn, 1959), chap. 10. D. H. Everett and J. M. Haynes, 2. Phys. Chem., N.F., 1972, 82, 36. 2o D. H. Everett, J. Colloid Interface Sci., 1975, 52, 189. 21 E. A. Boucher and T. G. J. Jones, J. Colloid Interface Sci. 1983, 91, 301. 22 E. A. Boucher and T. G . Jones, J. Chem. SOC., Faraday Trans. I , 1983, 79, 2529. 23 E. A. Boucher and M. J. B. Evans, J. Chem. Soc., Faraday Trans. 1 , in press. 24 J. M. T. Thompson, Philos. Trans. R . Soc. London, Ser. A, 1979, 292, 1. (PAPER 4/276)

ISSN:0300-9599    

DOI:10.1039/F19848003295

出版商:RSC    

年代:1984

数据来源: RSC