摘要:

J. CHEM. SOC. DALTON TRANS. 1991 1167Sexidentate Co-ordination of the Pendant-arm Macrocycle6,13-Dimethyl-l,4,8,1 I -tetraazacyclotetradecane-6,13-diamine (L1) to Zinc(ii). Crystal Structure of[ZnL1][CI0,12.H20 tPaul V. Bernhardt/ Geoffrey A. Lawrance,*#a Marcel Maeder,8 Monica Rossignoli aand Trevor W. Hambleyba Department of Chemistry, The University of Newcastle, New South Wales, 2308, AustraliaSchool of Chemistry, The University of Sydney, New South Wales, 2006, AustraliaThe pendant-arm macrocycle 6,13-dimethy1-1,4,8,11 -tetraazacyclotetradecane-6,13-diamine ( L1)co-ordinates as a sexidentate ligand t o zinc(l1) in neutral aqueous solution. The complex [ZnL1]-[CIO,],~H,O crystallises in the monoclinic space group P2,/c, a = 9.488(4), b = 14.736(9), c =16.037(4) A, p = 97.95(3)' and Z = 4.The Zn-N bond lengths in [ZnL1I2+ are, on average, theshortest known for a hexaaminezinc(l1) complex. The stability constant for formation of [ZnL1I2+ wasdetermined to be log K 15.0 f 0.1, from potentiometric titrations. Five of the six successiveprotonation constants for the hexaamine L1 were measured similarly and values pK, 2.9, 5.5, 6.3,9.9 and 11 .O found.In earlier papers, we reported that sexidentate complexes ofthe pendant-arm macrocyclic hexaamine 6J3-dimethyl-1,4,8,1 l-tetraazacyclotetradecane-6,13-diamine (L') withchromium(m),' iron(m),' cobalt(111),~ rhodium(111)~ andnickel(11)~ exhibit the shortest metal-nitrogen bond lengths for ahexaamine complex of their particular series.H A HL'Although zinc(r1) complexes are essentially 'silent' withrespect to electronic, electrochemical and magnetic studies,structural properties obtained from their complexes can bequite informative.No ligand-field stabilisation energy isoperative upon complexation of the d" metal ion, and hencethere is no particular preference for octahedral over tetrahedralgeometry in zinc(I1) complexes. This is evident from theexistence of structures of both tetrahedral [Zn(en),]' + andoctahedral [Zn(en),] + (en = ethane- 1,2-diamine) complexesin the l i t e r a t ~ r e . ~ , ~ The resultant geometry of the sexidentatezinc(I1) complex of L' must therefore be dictated solely by stericfactors. The sexidentate hexaamine complex of zinc(r1) with theligand L' is reported herein with its stability constant, whichhas been determined from a potentiometric titration of L' andzinc(I1).The protonation constants of the free ligand are alsoreported.ExperimentalSyntheses.-The ligand 6,13-dimethyl-1,4,8,1 l-tetraaza-cyclotetradecane-6,13-diamine, as the hexahydrochloride salt( L1*6HC1), was prepared as described previ~usly.~(6,13-Dimethyl-1,4,8,11 -tetraazacyclotetradecune-6,13-di-t Supplementary data atjailable: see Instructions for Authors, J. Chem.Soc., Dalton Trans., 1991, Issue 1 , pp. xviii-xxii.amine)zinc(lr) perchlorate hydrate, [ZnL1][C104],~H,0. Asolution of anhydrous zinc@) chloride (0.13 g) and L'=6HCl (0.5g) in sodium perchlorate solution (20 cm3, 1 mol dm3) wasneutralised (pH 7-8) with dilute sodium hydroxide solution.Onstanding for 24 h, colourless crystals suitable for X-ray analysisformed which were collected by filtration and air dried. Severalcrops were obtained and the yield was quantitative. The productwas not washed with ethanol since this resulted in dehydrationand powdering of the crystals (Found: C, 26.8; H, 6.2; N, 15.5.Calc. for Cl2H3,C1,N,O9Zn: C, 26.7; H, 6.0; N, 15.6%). NMR(D,O): 'H, 6 1.19 (s, 6 H); 2.50,3.20 (q,8 H); 2.60, 3.30 (q,8 H);13C, 6 28.1,54.5,58.3 and 62.5 ppm.Physical Methods.-NMR spectra were recorded on a JEOLFX90Q FT spectrometer, using sodium [2H4]trimethylsilyl-propionate and 1,4-dioxane as internal standards for 'H and ' 3C spectra respectively, although I3C chemical shifts are citedversus tetramethylsilane.Infrared spectra were recorded usingan Hitachi 260- 10 spectrophotometer with compounds beingdispersed in potassium bromide discs. Potentiometric titrationswere performed with a Metrohm 605 digital pH meter, aMetrohm 665 digital burette and Metrohm combined glasselectrodes. All measurements were under the control of an IBMclone computer.* Titrations were performed at 298 K and anionic strength of 0.5 mol dm-3 KCl. Acidic solutions of0.6 x mol dm-3 L1*6HCl alone and in the presence of 0.9equivalent of zinc(I1) ion were titrated with 1 x dmP3increments of 0.4 mol dm-3 sodium hydroxide solution. Datareduction was performed using a TURBO BASIC version ofthe program TITFIT.9Structure Determination.-Crystal data. [ZnL'][ClO,],-H20, C12H32C12N609Zn, A4 = 540.6, monoclinic, spacegroup P2,/c, a = 9.488(4), b = 14.736(9), c = 16.037(4) A,p = 97.95(3)", U = 2220.7 A3, D, (2 = 4) = 1.617 g cmP3,F(OO0) = 1128, pMo = 14.19 cm-'.Specimen: colourless prisms,0.46 x 0.21 x 0.19 mm. A*,i,,max 0.74, 0.79; N = 4153, No =2446, range of hkl - 11 to ll,O-17, O-19. R = 0.044, R' = 0.048,w = k/[02(Fo) + gFo2] where k and g are 2.64 and 1.54 x 10-4,residual extrema f 0.5 eData collection. Cell constants were determined by a least1168 J. CHEM. SOC. DALTON TRANS. 1991Table 1CClO4I ,*H,ONon-hydrogen positional parameters ( x lo4) for [ZnL'I-A2318(1)662(5)3905(5)2311(6)3991(5)739(5)2350(5)1051(7)23 57(6)3778(8)523 7(6)5282(6)2359( 10)3 8 8 7( 7)2479(6)1190(8)- 575(6)- 608(6)2521(8)1501(2)276(5)134 l(7)2564(7)1994(9)2843( 2)2470(6)3986(7)3265( 1 1)1776(8)5034( 10)Y7220(1)6309(4)6290(3)639 l(3)8115(3)8195(4)8033(3)5442(5)5501(4)5504(4)6804(5)471 6(5)888 8( 5)8924(4)7776(6)6773( 6)97 14( 5)21 38( 1)1623(4)2930(4)1603(5)2429(4)91 59(1)8607(5)9726(6)8652(7)1529(8)7544(5)9049(5)9607(4)Z4068( 1)4192(3)453 l(3)2927( 3)39 14( 3)3685(3)5242(3)3823(5)3353(4)3955(4)4654(5)4015(5)2751(6)4835(4)4153(5)3898(5)3732(5)5460( 5)3780( 1)3652(4)43 12(4)4217(5)3061(3)1739( 1)985(3)1641(5)2379(4)1950(6)3059(5)4477(5)PAFig. 1 ORTEP drawing of the [ZnL']2+ cationsquares fit to the setting parameters of 25 independentreflections. Data were measured on an Enraf-Nonius CAD4-Fdiffractometer within the limit 1 < 8 < 25", with Mo-Ksrradiation, h = 0.71069 A, graphite monochromator, andoperating in the 0-8 scan mode.Independent reflections withI > 2.50(1) were considered observed and used for solution ofthe structure. Data were reduced and Lorentz, polarisation anddecomposition corrections were applied using the Enraf-NoniusStructure Determination Package.Structure solution. The structure was solved by PattersonTable 2 Bond lengths (A) and angles (") for [ZnL'][C104]2*H,0N(2)-Zn-N( 1 )N(3)-Zn-N(2)N(4)-Zn-N(2)N(5)-Zn-N( 1)N( 5)-Zn-N( 3)N(6)-Zn-N( 1)N(6)-Zn-N( 3)N(6)-Zn-N( 5)C(l 1)-N(1)-ZnC( 3)-N(2)-ZnC(5)-N(4)-ZnC( lO)-N(S)-ZnC(8)-N(6)-ZnC(4)-N(2)-C(3)C(7)-"4)-C(5)C( ltW)-N(3)C(3tC(P-C( 1C(6)-C(2)-C(l)C(2)-C( 3)-N(2)C(4)-C( 5)-N(4)C(7)-C(8)-N(6)C(9)-C( 8)-C( 7)C( 12)-C(8)-C(7)C(8)-C(9)-N(5)C( lO)-C( 1 1)-N( 1)O( 13)-C1( 1)-O( 1 1)O( 14)-C1( 1)-O( 1 1)O( 14)-C1( 1 )-O( 1 3)O( 23)-C1( 2)-O( 2 1)0(24)-C1(2)-0(2 1)0(24)-C1(2)-0(23)2.097( 5)2.200( 5)2.105(5)1.475(8)1.476(7)1.477(7)1.465(8)1.474(8)1.539(8)1.507(9)1.526(8)1.532(8)1.380(5)1.391(6)1.38 l(5)1.340( 7)9 3.3 (2)8 1.4(2)86.3(2)87.3(2)102.5(2)100.8(2)178.6(2)78.8(2)103.0(4)107.4(3)119.0(5)104.9(4)120.1(5)103.8(4)95.5(3)107.6(5)1 12.7(5)110.1(5)112.5(4)112.8(5)105.4(5)1 12.9(6)109.1 (5)11 3.6(5)11 1.6(6)107.4(4)1 15.2(4)107.0( 5)112.7(5)112.1(5)108.1(6)N(3)-Zn-N( 1)N(4)-Zn-N( 1)N(4)-Zn-N(3)N(5)-Zn-N(2)N(SFZn-N(4)N(6)-Zn-N(2)N(6)-Zn-N(4)C( 1 )-N( 1 )-ZnC(4kN(2)-ZnC(2)-N(3)-ZnC(7)-N(4)-ZnC(9)-N(5)-ZnC(11)-N(1kC(1)C( 10)-N(5)-C(9)C(2tC( 1 FN( 1)C( 3 F C (2l-N 3 1C(6)-C(2tN(3)C(6)-C(2tC(3)C(5)-C(4tN(2)C(8)-C(7)-N(4)C(9tC(8tN(6)C( 12)-C(8)-N(6)C( 12)-c(8)-c(9)0(12)-Cl(l)-O(ll)0(22)-C1(2)-0(2 1)C(l l)-C(lO)-N(5)O( 13)-C1( 1 )-O( 12)O( 14)-C1( 1)-O( 12)0(23)-C1(2)-0(22)0(24)-C1(2)-0(22)2.09 5( 4)2.104(5)2.228( 4)1.49 1 (8)1.464(7)1.477(7)1.497(9)1.480(7)1.545(8)1.501(9)1.53 5(8)1.500( 10)1.466(5)1.37 l(6)1.382(6)1.339(7)78.9(2)178.4(2)99.6(2)176.1(2)93.2(2)97.3(2)80.8(2)10633)1 15.4(6)105.9(4)96.4(3)107.4(4)106.5(4)115.4(5)114.3(5)104.7(4)112.8(5)108.9( 5)113.0(5)113.4(5)108.3( 5)1 12.4( 5)108.8( 5)11 1.7(5)11 1.8(4)1 06.5(4)108.4(4)107.0(4)107.4(6)109.4(6)techniques and refined by full-matrix least-squares analysis withSHELX 76." All non-hydrogen atoms were refined aniso-tropically, whereas hydrogen atoms were located and refinedwith isotropic thermal parameters.Scattering factors andanomalous dispersion coefficients for Zn were taken from ref. 11and for all other atoms the values supplied in SHELX 76 wereused. Absorption correction was by numerical integration.Non-hydrogen atom coordinates are listed in Table 1. Theatomic nomenclature is defined in Fig.1, drawn with ORTEP.'A list of non-hydrogen interatomic distances appears in Table 2.Additional material available from the Cambridge Crystallo-graphic Data Centre comprises H-atom coordinates andthermal parameters.Results and DiscussionComplexation of zinc(i1) by L' was found to be facile andwas achieved rapidly by neutralising an aqueous solution ofequimolar quantities of zinc(i1) and ligand, followed by crystal-lisation as the perchlorate salt. The infrared spectrum of [ZnL'I-[C104] displayed resonances common to other sexidentatecomplexes of L1,'-' with a strong primary amine vibratioJ. CHEM. SOC. DALTON TRANS. 1991 1169'O0R3 5 7PH9Fig. 2 Calculated distribution of the species Zn2+ (O), [Zn(H2L')-(OH2)J4+ (+), [Zn(HL')(OH2)]3+ (M) and [ZnL']2+ ( 0 ) as afunction of pH[G(NH2)] appearing at 1600 cm-' being indicative of co-ordination by both pendant groups.This is in contrast to thespectrum of trans-[Zn(H2L')(OS0,S0,)2], where protonationof both pendant amines was defined by the appearance ofresonances at 1630 and 1500 cm-' characteristic of primaryammonium g r o ~ p s . ' ~ The 'H NMR spectrum of [ZnL'I2+displayed two overlapping AB quartets and a low-field singletcorresponding to the two sets of methylene protons (in the five-and six-membered rings of the macrocycle) and the equivalentmethyl groups respectively. The proton-decoupled 13C NMRspectrum of [ZnL1l2 + displayed four resonances consistentwith the anticipated CZh geometry of the complex cation.Although strong evidence for sexidentate co-ordination of L' tozinc(I1) was obtained from the NMR and IR spectra, conclusiveproof was provided by the X-ray crystal structure of [ZnL'I-Unlike all other sexidentate complexes of L', the [ZnL1I2+cation was not located on a crystallographic centre of sym-metry, but instead was found on a general site, as were the twoperchlorate anions and a single water molecule.The five-membered ethylenediamine chelate rings adopt like conform-ations (both s), which removes the centre of symmetry at themetal, which has otherwise been found to exist in all otherstructures of sexidentate complexes of L'. The trans axialZn-N(primary bond lengths are inequivalent, but both areby far the largest axial elongation of M-N bond lengths in the[ML']"' series so far.There is not a large amount of dataavailable for comparison with [ZnL'I2+ but it is clear thatthe Zn-N bond lengths, particularly the equatorial Zn-N(secondary) bonds (Table 2), are much shorter than thosereported for other hexaaminezinc(I1) complexes. For com-parison, the average Zn-N bond lengths in Zn(en),12+ andExamination of Table 2 shows considerable distortion of theZnN, octahedron, with the N(3)-Zn-N(6) axis being tilted[C104]2*H20.more than 0.1 A longer than the equatorial Zn-N bonds. This is[Zn(H2L2)I4' were found to be 2.22 and 2.19 SF respecti~ely.~"~INH2L2 L3toward the atoms C(2) and C(8). That is, the N-Zn-N anglesin the five-membered rings formed by co-ordination of thependant amines are all close to 80".There is considerable strainin the angles C(3)-N(2)-C(4) and C(5)-N(4)-C(7), both beingclose to 120". It can be seen that this is a direct result of co-ordination of the pendant primary amines which 'pulls' the C(3)and C(7) atoms toward the metal centre and hence opens theangles at the co-ordinated secondary amines. There is less strainin the opposite five-membered chelate ring, which adopts adifferent conformation with respect to the rest of the molecule(although it is also a 6 conformer). The angles formed at thependant primary amines, C(2)-N(3)-Zn, 96.4(3)", and C(8)-N(6)-Zn, 95.5(3)", are both quite small compared with an idealtetrahedral geometry. To relieve this strain, either the axialZn-N bond must be shortened or the N(3)-Zn-N(1,2) andN(6)-Zn-N(4,5) angles contracted even more than theyalready have been.It is well known that bond compressionrequires more energy than bond angle deformation and thatintraligand non-bonded interactions may dominate both ofthese factors.16 In this case it is apparent that deformation ofthe C(2)-N(3)-Zn and C(8)-N(6)-Zn angles results in thesmallest increase in strain energy, although it appears that thisstrain is also shared to some degree by a reduction of the cisN-Zn-N angles.The metal centre and the four secondary amine nitrogens arenot coplanar. Calculation of the least-squares plane defined bythese atoms indicates that one pair of trans secondary aminenitrogens "(1) and N(4)] lies on the opposite side of the least-squares plane to the atoms N(2) and N(5).This is related to thestaggered conformations of the ethylenediamine chelates, whichdistort the ZnN, plane. The metal centre lies on the same sideof the plane as the N(l) and N(4) pair, as does N(3), whichindicates why the Zn-N(3) bond length is shorter than theZn-N(4) bond. It is also worth noting that the single watermolecule in the structure links complex cations via hydrogenbonds with the amine hydrogens on N(3) and N(6). The wateroxygen, 0(3), approaches N(3) somewhat more closely[HN(3)=..0(3) 2.23 6;] than the trans amine hydrogens[HN(6) O(3) 2.68 A]. This may also be entwined with thediscrepancy between the Zn-N(3) and Zn-N(6) bond lengths.A potentiometric titration of the ligand (H6L1)6 + identifiedfive of the six successive amine protonation constants: pKa 2.9,5.5, 6.3, 9.9 and 11.0.The first deprotonation step was not ableto be determined (pK, < 2). The pKa values of 5.5 and 6.3 areassigned to the deprotonation of the pendant amines and theremaining values to deprotonation of the macrocycle nitrogens.The deprotonation steps of the secondary amines compare wellwith those determined for L3 (pK, 1.5, 10.5 and 11.49).17 Theorder of titration was confirmed by the recent isolation andX-ray crystal structure of L'*2HClO4*2H2O, where the sites ofprotonation were found to be a pair of trans secondary-aminenitrogens.'* An earlier structure l 4 of the tetraprotonated ligandL'*4HC104-6H20, revealed that the four protonated sites werea pair of trans secondary-amine nitrogens and the pair ofpendant primary amines.Titration of an acidic solution ofzinc(1r) and L' yielded a stability constant for complexformation log K of 15.0 & 0.1 which is comparable with thevalue reported for [ZnL3I2+ (log K 15.34)." A furtherobservation was the stepwise deprotonation and co-ordinationof the pendant primary amines following insertion of the metalion into the macrocyclic cavity. A distribution of the threecoinplexed species [Zn(H L ')(OH 2)2]4 + (both pendants u nco-ordinated), [Zn(HL')(OH2)]3 + (one pendant co-ordinated)and [ZnL'I2+ as a function of pH is shown in Fig. 2.Intersections on the [Zn(HL')(0H2)l3 + curve yield pKa valuesof 5.9 and 7.0 for the two primary amine groups, compared withcorresponding values of 5.5 and 6.3 from titration of thefree ligand.It is apparent that the slight differences in pK,values determined from the two titrations are the result of aweaker inductive effect of the dipositive metal centre in[Zn(H2L')(OH,)J4+ on the protonated pendant amin1170 J. CHEM. SOC. DALTON TRANS. 1991groups compared with the two additional protons bound to thesecondary amines in (H4L1)4+.It is clear that sexidentate co-ordination of the macrocycle L1to zinc(rr) results in particularly short Zn-N bond lengths whencompared with other hexaaminezinc(rr) complexes that havebeen structurally characterised. However, it is most importantto realise that the Zn-N bond lengths in [ZnL1I2+ are notexceptionally short by comparison with, for example, diacido-tetraaminezinc(1r) complexes. To illustrate this, the crystalstructure of trans-[Zn(H, L1)(OS02S03)2 J revealed Zn-Nbond lengths of 2.096( 1) and 2.082(2) similar bond lengthswere reported for the structure of trans-[ZnL3(NCS), 1.'" Thenecessity of comparing similar systems (hexaamine complexes)is then seen.A similar observation was made when thestructures of [NiL'], + and trans-[NiL'(NCS),] were com-pared.5 The Ni-N bond lengths in the sexidentate nickel(@complex, although the shortest for a hexaaminenickel(rr) ion,were not shorter than those found in trans-[NiL'(NCS),].The origins of these apparent anomalies may be found byexamining the relative conformations of sexidentate andquadridentate complexes of L'.When the macrocycle co-ordinates as a sexidentate, the six-membered chelate rings mustform boat conformers, rather than the less strained chairconformers. Quadridentate co-ordination of the ligand allowsthe six-membered rings to adopt their most sterically favourableorientation, and in all quadridentate complexes of L1 reportedso far, this has indeed been the chair c ~ n f o r m e r . ' ~ , ~ ~ - * ~ Theadditional steric strain introduced by the boat conformer in[ZnL1I2+ compared with tran~-[Zn(H,L')(0SO,S0~)~] evi-dently results in an extension of the Zn-N(secondary) bondlengths. Perhaps related to this, intramolecular non-bondedH H interactions in the sexidentate complex are necessarilygreater than in the quadridentate complex.The more severeinteractions are expected to occur between the pendant aminehydrogens and the methylene hydrogens in the 'ethylenediamine'residues. These interactions are obviously unimportant instructures such as trans-[Zn(H2L')(OS02S03)2] and theZn-N bond lengths may be shorter in the absence of axialamino groups. The axial dithionato ligands in trans-[Zn(H2L1)(OS02S03),] are more sterically efficient donorsthan primary amines, and may also pivot about the Zn-0 axisso as to minimise steric clashes with the macrocycle hydrogens.The chelated pendant amines clearly do not enjoy the samefreedom of movement.References1 P. V. Bernhardt, P. Comba, N. F. Curtis, T. W.Hambley, G. A.Lawrance, M. Maeder and A. Siriwardena, Inorg. Chem., 1990, 29,3208.2 P. V. Bernhardt, T. W. Hambley and G. A. Lawrance, J. Chem. Soc.,Chem. Commun., 1989,553.3 P. V. Bernhardt, G. A Lawrance and T. W. Hambley, J. Chem. Soc.,Dalton Trans., 1989, 1059.4 P. V. Bernhardt, G. A. Lawrance and T. W. Hambley, J. Chem. Soc.,Dalton Trans., 1989,983.5 N. F. Curtis, G. J. Gainsford, T. W. Hambley, G. A. Lawrance, K. R.Morgan and A. Siriwardena, J. Chem. SOC., Chem. Commun., 1987,295.6 T. Fujita, T. Yamaguchi and H. Ohtaki, Bull Chem. SOC. Jpn., 1979,52, 3539.7 J. Cernak, J. Chomic, M. Dunaj-Jurco and C. Kappenstein, Inorg.Chim. Acta, 1984,85,219.8 H. Gampp, D. Haspra, M. Maeder and A. D. Zuberbuhler, Inorg.Chem., 1984,23,3724.9 A. D. Zuberbuhler and T. A. Kaden, Talanta, 1982,29,201.10 G. M. Sheldrick, SHELX 76, A Program for X-ray Crystal StructureDetermination, University of Cambridge, 1976.11 D. T. Cromer and J. T. Waber, International Tables for X-RayCrystallography, Kynoch Press, Birmingham, 1974, vol. 4.12 P. Coppens, L. Leisorwitz and D. Rabinovich, Acta Crystallogr.,1965,18,1035.13 C. K. Johnson, ORTEP, A Thermal Ellipsoid Plotting Program, OakRidge National Laboratory, TN, 1965.14 P. V. Bernhardt, T. W. Hambley and G. A. Lawrance, Aust. J. Chem.,1990,43,699.15 P. Comba, A. M. Sargeson, L. M. Engelhardt, J. M. Harrowfield,A. H. White, E. Horn and M. R. Snow, Inorg. Chem., 1985,24,2325.16 R. D. Hancock, Prog. Inorg. Chem., 1989,36,187.17 Critical Stability Constants, eds. R. M. Smith and A. E. Martell,18 P. V. Bernhardt, G. A. Lawrance, B. W. Skelton and A. H. White,19 T. Ito, M. Kato and H. Ito, Bull. Chem. Soc. Jpn., 1984,57,2634.20 G. A. Lawrance, B. W. Skelton, A. H. White and P. Comba, Aust. J.Chem., 1986,39,1101.21 P. Comba, N. F. Curtis, G. A. Lawrance, A. M. Sargeson, B. W.Skelton and A. H. White, Inorg. Chem., 1986,25,4260.22 P. V. Bernhardt, G. A. Lawrance, N. F. Curtis, A. Siriwardena, W. C.Patalinghug, B. W. Skelton and A. H. White, J. Chem. SOC., DaltonTrans., 1990,2853.Plenum Press, New York, 1989, vol. 6.unpublished work.AcknowledgementsSupport of this work by the Australian Research Council isgratefully acknowledged. Received 15th October 1990; Paper 0/04636

ISSN:1477-9226    

DOI:10.1039/DT9910001167

出版商:RSC    

年代:1991

数据来源: RSC