|
111. |
Tetranuclear osmium complexes of tetracyanoquinodimethane [TCNQ, 2,2′-(cyclohexa-2,5-diene-1,4-diylidene)bis(propane-1,3-dinitrile)] and 1,2,4,5-tetracyanobenzene (TCNB). Synthesis, spectroelectrochemistry and magnetism † |
|
Dalton Transactions,
Volume 0,
Issue 22,
1997,
Page 4455-4460
Frank Baumann,
Preview
|
|
摘要:
DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 4455–4459 4455 Tetranuclear osmium complexes of tetracyanoquinodimethane [TCNQ, 2,29-(cyclohexa-2,5-diene-1,4-diylidene)bis(propane-1,3- dinitrile)] and 1,2,4,5-tetracyanobenzene (TCNB). Synthesis, spectroelectrochemistry and magnetism † Frank Baumann,a Wolfgang Kaim,*,a Jose A. Olabe,b Alejandro R. Parise b and Jeanne Jordanov c a Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany b Departamento de Química Inorgánica, Analítica y Química Física (Inquimae), Facultad de Ciencias Exactas y Naturales, UBA, Pabellón 2, Ciudad Universitaria, Buenos Aires, Capital Federal 1428, Republic of Argentina c Centre d’Etudes Nucléaires de Grenoble, DRFMC/SCIB/SCPM, 85 X, F-38054 Grenoble Cedex 09, France The new complexes [(m4,h4-TCNX){Os(PR3)2(CO)(H)Cl}4], R = isopropyl, TCNX = tetracyanoquinodimethane [TCNQ, 2,29-(cyclohexa-2,5-diene-1,4-diylidene)bis(propane-1,3-dinitrile)] or 1,2,4,5-tetracyanobenzene (TCNB), were studied by spectroelectrochemistry in the UV/VIS/NIR and IR regions and by EPR spectroscopy.Both compounds are reduced in two reversible steps and oxidized in a two-electron process (reversible for TCNQ, quasi-reversible for TCNB). In all oxidation states studied (2, 0, 21) the TCNQ complexes exhibited intense long-wavelength absorptions in the near IR region (lmax >1000 nm). The EPR spectra of the monoanionic forms exhibit hardly any g anisotropy and thus very little metal participation, suggesting an oxidation state formulation [(TCNX~2)(OsII)4].The dication of the TCNQ system is formulated as [(TCNQ)(Os2.5)4] with an intervalence transfer transition at lmax = 1245 nm (e = 50 000 M21 cm21). In the solid state, the neutral complexes show temperature dependent paramagnetism that could be fitted with a model implying two coupled S = ��� entities. The TCNX ligands {e.g. tetracyanoethene (TCNE), tetracyanoquinodimethane [2,29-(cyclohexa-2,5-diene-1,4-diylidene)bis- (propane-1,3-dinitrile)] (TCNQ) or 1,2,4,5-tetracyanobenzene (TCNB)} are very unusual 1 because of their variable coordination behaviour (s or p),1–3 their proven ability to bridge up to four metal centres,1,4–8 their tendency to form aggregates via p–p interaction (stacking 3,9) and their non-innocence, i.e.their facile reduction to the radical anionic or dianionic state.1,2,10–13 In the course of exploring the electron transfer and oligonucleation behaviour of the TCNX ligand family we have recently extended our previous studies on Group 6 and 7 organometallic 5,13–17 and pentaammineruthenium complexes 6 to organoosmium18 complexes [(mn,hn-TCNE){Os(PR3)2(CO)- (H)Cl}n], n = 1, 2 or 4; R = isopropyl.8 The ability to obtain a tetranuclear compound has prompted us now to study the related systems [(m4,h4-TCNX){Os(PR3)2(CO)(H)Cl}4], [(TCNX)(Osf)4], TCNX = TCNQ or TCNB.The 16 valence electron organoosmium fragments [Osf] = [Os(PR3)2(CO)(H)Cl] have been employed in the binding of O2 or H2 and in catalysis studies.19,20 Among the questions posed by the present investigation will be that of the proper oxidation state formulation with respect to the bridging ligand (TCNX0/~2/22) and the four metal centres.1,6,8 These questions pertain to the neutral state as well as to spectroelectrochemically accessible oxidized and reduced forms.We also address the magnetism of these materials since other tetranuclear complexes of the TCNX ligands with pentaammineruthenium or organomanganese fragments have exhibited peculiar and unique magnetic coupling behaviour.21,22 The observed paramagnetism is of particular interest as it involves heavy and/or organometallic transition-metal centres with † Non-SI units employed: mB ª 9.274 × 10224 J T21 and eV ª 1.602 × 10219 J.formal 18 valence electron configurations; few such examples are known in the literature.21–23 Results and Discussion Tetranuclear complexes of TCNQ or TCNB have hitherto only been obtained in a few cases.5–7 For the discrete complexes [(m4,h4-TCNQ){(C5Me5)(CO)2Mn}4] 5 and [(m4,h4-TCNX)- {(H3N)5Ru}4]81, TCNX = TCNQ or TCNB,6 it was demonstrated that these addition products of potentially tetradentate TCNX with four d6 metal components have a delocalized electronic structure where TCNX has acquired some charge from the electron-rich metals in the ground state.5,6 The preparation of the new tetranuclear compounds [(m4,h4-TCNX){Os(PR3)2- (CO)(H)Cl}4], TCNX = TCNQ or TCNB, is similar to that reported for the TCNE analogue.8 However, the TCNQ and TCNB compounds have greater solubility, thus allowing for spectroelectrochemical characterization (see below).To confirm C N [Osf] C N [Osf] C N [Osf] C N [Osf] C N [Osf] C N [Osf] C N [Osf] C N [Osf] [TCNQ][Osf]4 [TCNB][Osf]44456 J. Chem. Soc., Dalton Trans., 1997, Pages 4455–4459 Table 1 Proton and 31P NMR spectroscopic data a 1H NMR 31P NMR Compound [Osf] c [(TCNB)(Osf)4] c TCNBc [(TCNQ)(Osf)4] e TCNQe d(PCHCH3) 1.27, 1.20 1.35, 1.20 — 1.42, 1.25 — J(HH) 6.5 6.9 — 6.3 — d(PCHCH3) 2.83 2.73 — 2.75 — d(OsH) 231.92 22.44 — 22.78 — J(PH) 14 30 — 30 — d(CH)b — 8.27 d 8.10 7.80 d 7.52 d(PR) 47.3 23.9 — 24.0 — a Chemical shifts d in ppm, coupling constants J in Hz.b Protons of the TCNX ligand. c Solvent C6D6. d Broad. e Solvent CD2Cl2. the identity, co-ordination mode and electronic structure of the neutral complexes, we characterized both compounds by 1H and 31P NMR spectroscopy (Table 1), IR vibrational spectroscopy (nitrile and carbonyl stretching, Table 2), electrochemistry (Table 3), magnetic susceptibility measurements (Table 4), EPR spectroscopy of monoreduced forms (Table 5) and UV/VIS/NIR spectroscopy/spectroelectrochemistry (Table 6).The NMR spectroscopic results (Table 1) show the equivalence of the 1H and 31P nuclei in the four organoosmium fragments, thus confirming the symmetrically tetranuclear character of the compounds.Whereas the co-ordination of [Osf] causes a slight upfield shift of the 31P resonances after binding to TCNX, the CH protons of the TCNX ligands experience a marginal downfield shift. However, there is also a conspicuous broadening of the H(C) resonances of the co-ordinated TCNQ and TCNB molecules which indicates some degree of paramagnetism. Solid-state susceptibility measurements as described below confirm this interpretation. Significant effects with regard to intramolecular charge transfer and proper oxidation state formulation 1 are apparent from the vibrational data (Table 2) which also suggest a high symmetry arrangement even on the vibrational time-scale of about 10212 s.There are two low-energy shifted cyanide stretching bands for the TCNQ system which lie in the regions of oneand two-electron reduced TCNQ.1 Similarly, the broad n(CN) band of the TCNB complex 6 shows a shift to lower energies.Fig. 1 Cyclic voltammogram of [(TCNQ){Os(PR3)2(CO)(H)Cl}4] in 1,2-dichloroethane/0.1 M NBu4PF6, 100 mV s21 scan rate Table 2 Vibrational data (in cm21) from IR spectroscopy Compound [Osf] a TCNQb TCNQ~2b TCNQ22b [(TCNQ)(Osf)4] b TCNBb [(TCNB)(Osf)4] b [(TCNE)(Osf)4] b,c n(C]] ] O) 1886s — — — 1945s, 1892vs — 1946s, 1895vs 1930s, 1905vs n(Os]H) Not observed — — — 2099w — Not observed Not observed n(C]] ] N) — 2228 2197, 2166 2164, 2096 2180s, 2140s 2245 2185s (br) 2170w, 2110m a Solvent C6H6.b KBr pellet. c From ref. 8. On the other hand, the carbonyl stretching frequencies within the organoosmium fragment exhibit both a splitting and a highenergy shift, reflecting 5 partial oxidation and vibrational coupling through what appears to be a conjugated tetrametalla p system.5,6,8 Cyclic voltammetric measurements of compounds [(m4,h4- TCNX){Os(PR3)2(CO)(H)Cl}4], TCNX = TCNQ or TCNB, gave similar results to those observed for the complex ions [(m4,h4-TCNX){Ru(NH3)5}4]81.6 There are one (TCNB) or two (TCNQ, Fig. 1) reversible or at least quasi-reversible oneelectron reduction steps and one two-en oxidation wave, the latter occurring at rather low potential for both compounds (Table 3). The reduction potentials are quite close to those of the non-co-ordinated ligands (Table 3), implying an almost full compensation of the s donor effect (which by itself would facilitate reduction) by the p-back bonding interaction (the effect of which is a cathodic shift).1,13,14 Before looking at the nature of the electrogenerated ionic states by EPR and UV/VIS/NIR spectroelectrochemistry we address the small but evident paramagnetism of both compounds.The magnetic moments, meff, determined at 300 K are 1.44 mB for the TCNQ derivative and 1.83 mB for the TCNB analogue. Although this would be formally in agreement with an S = ��� state, the even electron count and the non-saturation behaviour of the magnetic susceptibility suggest otherwise.We therefore undertook a more detailed study.21,22 The temperature dependence between 5 and 300 K of cmT (cm = molar magnetic susceptibility and T = temperature) could be successfully analysed (Fig. 2) employing the model developed recently for Fig. 2 Temperature dependence of the magnetic behaviour of compounds [(TCNX){Os(PR3)2(CO)(H)Cl}4] and simulated responses according to the model described in the text Table 3 Electrochemical data a of ligands and complexes Compound TCNQ [(TCNQ)(Osf)4] TCNB [(TCNB)(Osf)4] E12/0 — 0.09 (50) — 0.18 (95) b E0/12 20.29 20.20 (65) 21.14 21.10 (66) < E12/22 20.88 20.94 (64) 22.23 22.3 a From cyclic voltammetry in dichloromethane/0.1 M NBu4PF6 at 100 mV s21.Potentials in V vs. Fe(C5H5)2 0/1; peak potential differences for complex in mV (in parentheses). b Quasi-reversible at 273 K.J. Chem. Soc., Dalton Trans., 1997, Pages 4455¡V4459 4457the pentaammineruthenium analogues,22 i.e.there is spin¡Vspincoupling between two S = moieties of the molecule, mostlikely two dimeric [Os2.5] mixed-valent subunits.22 This model isthe most straightforward and reasonable from a chemical andspectroscopic point of view; the best agreement betweenexperiment and calculation was obtained when axial zero-fieldsplitting was added to the isotropic exchange coupling betweenthe two S = spins. The Hamiltonian for this model is shown inequation (1).H = 2JS1S2 1 SDS 1 bSgB (1)Considering an axial symmetry the eigenvalues E becomeE1|| = 2(J/4) 2 [(2/3)D], E1^ = 2(J/4) 2 [(3b2/D)g2^B2], E2|| =2(J/4) 2 (D/3) 2 g||bB, E2^ = 2(J/4) 2 (D/3), E3|| = 2(J/4) 2(D/3) 2 g||bB, E3^ = 2(J/4) 2 (D/3) 1 [(3b2/D)g2^B2], E4|| =2(3/4)J, E4^ = 2(3/4)J.Combination of these eigenvalues withthe Van Vleck equation yields cm|| and cm^ which can be averagedto yield cm. Neglecting the g anisotropy (g^ = g|| = g) oneobtains 22 equation (2) (where TIP is the temperature independcmT=23Nb2kg2e2D/3kTe2D/3kT 1 2e2D/3kT 1 e2J/kT 16D/kT(1 2 e2D/3kT)1 1 2e2D/3kT 1 e2J/kT£»£»¢X1TIP ¡Ñ T (2)ent paramagnetism) which was used for curve fitting.The datafrom this analysis are summarized in Table 4 and comparedwith the results for the pentaammineruthenium species.22The data from the analysis of the paramagnetism of Ru andOs systems agree with respect to small positive J values andlarger D parameters, the numbers for the osmium systems beingsomewhat smaller in accordance with the diminished paramagnetismof the 5d system.The g values calculated by thefitting procedure are extremely small for the osmium compoundswhich confirms our previous statement 22 that thesenumbers reflect unaccounted contributions from the metalspin¡Vorbit coupling. Relative to the TCNQ analogues, thelarger J values of the TCNB complexes can be attributed tostronger coupling across this smaller bridging ligand.22 Thesmallest J values are thus found for the TCNQ systems, correlatingwith the largest sum of metal¡Vmetal distances.22 Similarcorrelations can be drawn using the sum of the numbers ofintervening bonds which is largest for TCNQ.Surprisingly, theTCNB ligand fits quite well into such correlations 22 althoughthe free ligand has a distinctly less stabilized p* acceptor level ascompared to TCNQ (Table 2). We therefore do not think itnecessary to consider TCNX-based spin in the description ofthe magnetic behaviour.21,22The positive sign of J is tentatively attributed to the metacoupling pattern (TCNB compound) or to a possible deviationfrom planarity in the TCNQ complex; the barrier towardsrotation around exocyclic C]C bonds is strongly diminished inreduced TCNQ.Table 4 Magnetic coupling data* for tetranuclear osmium andruthenium complexes with TCNX ligandsCompound[(TCNQ){Ru(NH3)5}4][(TCNB){Ru(NH3)5}4][(TCNE){Ru(NH3)5}4][(TCNQ)(Osf)4][(TCNB)(Osf)4]J3.24.08.22.64.0D13.79.342.18.68.5g1.811.471.100.670.59TIP1.9?10242.0?10234.4?10247.1?10241.3?1023Reference222222This workThis work* Determined by simulations of experimental cmT vs. T curves.Exchangecoupling constants J and zero-field splitting parameters D in cm21,temperature independent paramagnetism TIP in emu mol21 (1 emu =1023 A m2).Summarizing, the analysis of the magnetic data suggests thatintramolecular electron transfer can produce a situation whichmay be described in terms of two strongly coupled mixedvalentsites, i.e.dinitrilato-bridged OsIII¡VOsII entities (each withStotal = ) which can couple via an essentially diamagnetic bridgingligand.Whereas the neutral complexes with their even-electroncount exhibit ¡¥normal¡¦ NMR behaviour but no EPR signalsdown to 3.5 K despite the apparent paramagnetism, themonoreduced species could be characterized by EPR in fluidand frozen solution (Table 5). The small g anisotropy in thefrozen state and the little deviation of g factors from the freeelectron value of 2.0023 suggests 24 that these species have theunpaired electron in a predominantly ligand-based molecularorbital (MO), hyperfine contributions from TCNX nuclei (1Hor 14N)6b or from the metal fragment (189Os or 31P) 24,25 are notobserved and must lie within the linewidth (Table 5).In contrast,complexes exhibiting sizeable OsIII character are distinguishedby rapid relaxation and thus very broad EPR signalsas well as by considerable g anisotropy.26 Summarizing, theanionic states must be formulated with TCNX~2 ligands andeven-electron osmium(II) centres (5d6 configuration).Theslightly different giso values reflect the stabilized p* MO ofTCNQ in relation to TCNB. According to a well-establishedapproximation 1,27 the higher g of the TCNQ complex impliesthe presence of close-lying occupied MOs whereas the low gvalue of the TCNB analogue reflects the closeness of emptyorbitals.Additional information on the electronic structures of thecompounds can be obtained from UV/VIS/NIR spectroelectrochemistry.Fig. 3 shows the result of one such experiment. Table6 summarizes the data. A first conspicuous result is that allavailable states of the TCNQ complex exhibit very intensebands in the near infrared region, lmax >1000 nm. The neutraland monoanionic forms of the TCNB complexes, on the otherhand, show their long-wavelength absorptions only at muchhigher energies (Table 6).For the neutral species this result issimply a consequence of the much closer lying highest occupiedand lowest unoccupied molecular orbitals (HOMO and LUMOrespectively) in the case of the TCNQ system; the correspondingdifferences between redox potentials Eox 2 Ered are 0.29 Vfor the TCNQ and 1.28 V for the TCNB analogue (0.99 Vdifference, Table 3). The pertinent absorption maxima at 1170nm = 1.06 eV and at 673 nm = 1.84 eV, respectively, exhibit anapproximately similar difference of 0.78 eV, suggesting com-Table 5 EPR data *[(TCNQ)(Osf)4]~2[(TCNB)(Osf)4]~2298 Kg = 2.0124DHpp = 1.27 mTg = 2.0005DHpp = 0.86 mT110 Kg^ = 2.0160g|| = 2.0065g^,|| = 2.0004DHpp = 1.31 mT* Anions generated electrochemically in 1,2-dichloroethane/0.1 MNBu4PF6.DHpp peak-to-peak linewidth.Table 6 Absorption maximaa of complexes [TCNX][Osf]4 in differentoxidation statesComplex[(TCNQ)(Osf)4]21[(TCNQ)(Osf)4][(TCNQ)(Osf)4]12[(TCNB)(Osf)4][(TCNB)(Osf)4]12[(TCf)4]lmax/nm [log e(e/M21 cm21)]1245 (4.70, Dn2 1b = 3800 cm21)1170 (4.46, Dn2 1b = 3200 cm21), 697 (3.86)1430 (4.50, Dn2 1b = 1700 cm21), 1215 (sh), 875(3.90), 426 (4.31)673 (4.40, Dn2 1b = 4600 cm21), 471 (4.23)554 (sh), 461 (4.40)800ca From spectroelectrochemistry in 1,2-dichloroethane/0.1 M NBu4PF6.b Dn2 1bandwidth at half height. c In 1,2-dichloroethane, from ref. 8.4458 J. Chem. Soc., Dalton Trans., 1997, Pages 4455–4459 parably large Franck–Condon contributions from intra- and inter-molecular reorganization.28 On one-electron reduction of the TCNQ compound there is a new spectrum with a highintensity (e = 32 000 M21 cm21) and vibrationally structured (Dn = 1230 cm21) transition at very low energy (1430 nm = 0.87 eV) which can be identified as the bathochromically shifted long-wavelength band of TCNQ~2 (TCNQ~2: lmax = 842 nm and e = 43 300 M21 cm21; first vibrational spacing 1260 cm21).29 Also, a band at 426 nm intensifies which may be associated with the 420 nm feature of free TCNQ~2 (e = 24 300 M21 cm21).29 Obviously, the electronic absorption features confirm the [(TCNQ2I)(OsII)4] oxidation state formulation that had been deduced from EPR.We similarly attribute the spectrum of the reduced TCNB analogue to a [(TCNB2I)(OsII)4] state and assume a TCNX ligand-based p* orbital as the LUMO of the neutral complexes. As to access of the HOMO we have to take into account the two-electron nature of the electrochemical oxidation which, first of all, suggests a small interaction between the two sites involved.6 This observation is in agreement with metal-centred processes, as was also suggested by the analysis of the weak spin–spin coupling.Unfortunately, the oxidation of the TCNB complex was not sufficiently reversible on the spectroelectrochemical time-scale of a few minutes. On two-electron oxidation of [(TCNQ){Os(PR3)2(CO)(H)Cl}4] the NIR band intensifies (e = 50 000 M21 cm21) and shifts to lower energies (Table 6).No other significant bands are observed above 350 nm. Since we assume a non-reduced state for the bridging ligand in such a highly charged ion we have to invoke a delocalized mixed-valent formulation [(TCNQ0)(Os2.5)4] to account for the observed high intensity NIR transition. Such very intense features have been reported previously for efficiently coupled dinuclear OsIII–OsII systems, bridged by 1,2-diacylhydrazide- (22).26a This interpretation would also explain the two-electron nature of the oxidation (weak coupling across the benzo rings), the NIR absorption of, in effect, malonodinitrilato-bridged 5,6,30 mixed-valent [Os2.5]2 systems, and the metal to ligand chargetransfer (MLCT) character of the long-wavelength transitions in the neutral complexes.The peculiar paramagnetism of evenelectron species with formally 18 valence electron 5d metal centres merits further investigation, especially since both complexes, the one with the very strong (TCNQ) and the other with the less pronounced p acceptor ligand (TCNB) display rather similar behaviour.Experimental Materials Tetracyanoquinodimethane (TCNQ) and 1,2,4,5-tetracyanobenzene (TCNB) were used as commercially available. The Fig. 3 Spectroelectrochemical response for the reduction of [(TCNQ)- {Os(PR3)2(CO)(H)Cl}4] to the monoanion in 1,2-dichloroethane/0.1 M NBu4PF6 compound Os(PPri 3)2(CO)(H)Cl was prepared according to the literature procedure.31 All syntheses and spectroscopic manipulations were carried out under an argon atmosphere using dried and redistilled solvents.Synthesis [(Ï4,Á4-TCNQ){Os(PPri 3)2(CO)(H)Cl}4]. A solution of TCNQ (24 mg, 0.12 mmol) in toluene (25 cm3) was added slowly to Os(PPri 3)2(CO)(H)Cl (325 mg, 0.52 mmol), also dissolved in toluene (15 cm3). After stirring for about 12 h 20 cm3 of the solvent were evaporated. Addition of n-pentane (10 cm3), cooling to 228 8C, washing with toluene and n-pentane and vacuum drying yielded 185 mg (62%) of the green product (Found: C, 42.94; H, 7.14; N, 2.16.C88H176Cl4N4O4Os4P8 requires C, 42.20; H, 7.08; N, 2.24%). [(Ï4,Á4-TCNB){Os(PPri 3)2(CO)(H)Cl}4]. A solution of TCNB (8 mg, 0.04 mmol) in toluene (10 cm3) was added slowly to Os(PPri 3)2(CO)(H)Cl (111 mg, 0.19 mmol), also dissolved in toluene (5 cm3). After stirring for about 12 h 5 cm3 of the solvent were evaporated. Addition of n-pentane (5 cm3), cooling to 228 8C, washing with toluene and n-pentane and vacuum drying yielded 57 mg (53%) of the dark purple product (Found: C, 41.89; H, 7.11; N, 1.98. C86H174Cl4N4O4Os4P8 requires C, 41.64; H, 7.08; N, 2.26%).Instrumentation The EPR spectra were recorded in the X-band on a Bruker System ESP 300, equipped with a Bruker ER035M gaussmeter and a HP 5350B microwave counter; NMR spectra were recorded on a Bruker AC 250 spectrometer, infrared spectra on a Fourier-transform IR spectrometer Paragon 1000 PC.Absorption spectra in the UV/VIS/NIR regions were measured with a Bruins Instruments Omega 10 spectrometer. Cyclic voltammetry was carried out in 0.1 M NBu4PF6 in 1,2- dichloroethane (DCE) using a PAR M273 potentiostat and function generator and a three-electrode configuration (glassy carbon working electrode, platinum wire counter electrode, Ag– AgCl reference electrode). The ferrocene–ferrocenium couple served as an internal standard for the calibration of the redox potential.Spectroelectrochemical measurements were carried out using an optically transparent thin-layer electrolytic (OTTLE) cell,32 composed of CaF2 plates, an Ag reference, Pt working and counter electrodes. In all experiments described as reversible the spectral features of the initial state could be regenerated. Magnetic susceptibility measurements were performed using a Quantum Design SQUID magnetometer, equipped with a Quantum Design controller MPS 1822 and a digital bridge 1802, operating at 0.5 T magnetic field strength and variable temperature (5–300 K).Magnetization studies were carried out between 0.1 and 1 T at 6 K to determine the most suitable field (i.e. non-saturation conditions). Typical samples involved 15–25 mg of the compound; all data are corrected for effects from the sample holder and diamagnetic contributions. Simulations were performed on an IBM personal computer using the programs Microsoft Excel 4.0 and Microsoft Excel Solver. Non-linear minimization of R yielded the values of g, J, D and TIP given in equation (3).Different sets of starting values were used R = Si[(cmT)i exp 2 (cmT)i calc]2 Si[(cmT)i exp]2 (3) to avoid local minima. Being largely independent of the number of data points and the absolute values, R allows a comparison of the quality of fit between compounds with widely differing magnetic susceptibilities.22,33J. Chem. Soc., Dalton Trans., 1997, Pages 4455–4459 4459 Acknowledgements We thank the Gesellschaft für Technische Zusammenarbeit (GTZ) and the Franco–German exchange programme PROCOPE for financial support. Contributions from Deutsche Forschungsgemeinschaft, Volkswagenstiftung and Fonds der Chemischen Industrie are also acknowledged.References 1 W. Kaim and M. Moscherosch, Coord. Chem. Rev., 1994, 129, 157. 2 C. Panattoni, G. Bombieri, U. Belluco and W. H. Baddley, J. Am. Chem. Soc., 1968, 90, 798. 3 H. Braunwart, G. Huttner and L.Zsolnai, J. Organomet. Chem., 1989, 372, C23. 4 A. L. Crumbliss and F. Basolo, Inorg. Chem., 1971, 10, 1676. 5 R. Gross and W. Kaim, Angew. Chem., 1987, 99, 257; Angew. Chem., Int. Ed. Engl., 1987, 26, 251; R. Gross-Lannert, W. Kaim and B. Olbrich-Deussner, Inorg. Chem., 1990, 29, 5046. 6 (a) M. Moscherosch and W. Kaim, Inorg. Chim. Acta, 1993, 206, 229; (b) M. Moscherosch, E. Waldhör, H. Binder, W. Kaim and J. Fiedler, Inorg. Chem., 1995, 34, 4326. 7 F. A. Cotton and Y.Kim, J. Am. Chem. Soc., 1993, 115, 8511; C. Campana, K. R. Dunbar and X. Ouyang, Chem. Commun., 1996, 2427. 8 F. Baumann, M. Heilmann, W. Matheis, A. Schulz, W. Kaim and J. Jordanov, Inorg. Chim. Acta, 1996, 251, 239. 9 A. E. D. McQueen, A. J. Blake, A. Stephenson, M. Schröder and L. J. Yellowless, J. Chem. Soc., Chem. Commun., 1988, 1533. 10 S. E. Bell, J. S. Field, R. I. Haines, M. Moscherosch, W. Matheis and W. Kaim, Inorg. Chem., 1992, 31, 3269. 11 J. S. Miller, J.C. Calabrese, H. Rommelmann, S. R. Chittipeddi, J. H. Zhang, W. M. Reiff and A. J. Epstein, J. Am. Chem. Soc., 1987, 109, 769. 12 G. T. Yee, J. C. Calabrese, C. Vazquez and J. S. Miller, Inorg. Chem., 1993, 32, 377. 13 B. Olbrich-Deussner, R. Gross and W. Kaim, J. Organomet. Chem., 1989, 366, 155. 14 B. Olbrich-Deussner, W. Kaim and R. Gross-Lannert, Inorg. Chem., 1989, 28, 3113. 15 W. Kaim, B. Olbrich-Deussner, R. Gross, S. Ernst, S. Kohlmann and C. Bessenbacher, in Importance of Paramagnetic Organometallic Species in Activation, Selectivity and Catalysis, ed.M. Chanon, Kluwer Academic Publishers, Dordrecht, 1989, p. 283; B. Schwederski, W. Kaim, B. Olbrich-Deussner and T. Roth, J. Organomet. Chem., 1992, 440, 145. 16 W. Kaim, B. Olbrich-Deussner and T. Roth, Organometallics, 1991, 10, 410. 17 D. J. Stufkens, T. L. Snoeck, W. Kaim, T. Roth and B. Olbrich- Deussner, J. Organomet. Chem., 1991, 409, 189. 18 F. G. Moers and J. P. Langhout, J. Inorg.Nucl. Chem., 1977, 39, 591. 19 H. Werner and B. Juthani, J. Organomet. Chem., 1981, 209, 211; M. J. Macazaga, M. S. Delgado and J. R. Masaguer, J. Organomet. Chem., 1986, 299, 377; M. J. Macazaga, M. S. Delgado and J. R. Masaguer, J. Organomet. Chem., 1986, 310, 249; M. Bourgault, A. Castillo, M. A. Esteruelas, E. Oñate and N. Ruiz, Organometallics, 1997, 16, 636. 20 D. G. Gusev, R. L. Kuhlman, K. B. Renkema, O. Eisenstein and K. G. Caulton, Inorg. Chem., 1996, 35, 6775. 21 W. Kaim, T. Roth, B. Olbrich-Deussner, R. Gross-Lannert, J. Jordanov and E. K. H. Roth, J. Am. Chem. Soc., 1992, 114, 5693. 22 E. Waldhör, W. Kaim, M. Lawson and J. Jordanov, Inorg. Chem., 1997, 36, 3248. 23 M. A. D. Koeslag, B. K. Hunter, J. H. MacNeil, A. W. Roszak and M. C. Baird, Inorg. Chem., 1996, 35, 6937; M. E. Smith and R. A. Andersen, J. Am. Chem. Soc., 1996, 118, 11 119. 24 W. Kaim, Coord. Chem. Rev., 1987, 76, 187. 25 W. Kaim, R. Reinhardt and M. Sieger, Inorg. Chem., 1994, 33, 4453. 26 (a) W. Kaim and V. Kasack, Inorg. Chem., 1990, 29, 4696; (b) M. Heilmann, Ph.D. Thesis, Universität Stuttgart, 1997; (c) G. K. Lahiri, S. Bhattacharya, B. K. Ghosh and A. Chakravorty, Inorg. Chem., 1987, 26, 4324. 27 W. Kaim, Inorg. Chem., 1984, 23, 3365. 28 E. S. Dodsworth and A. B. P. Lever, Chem. Phys. Lett., 1985, 119, 61; 1986, 124, 152; E. M. Kober, K. A. Goldsby, D. N. S. Narayana and T. J. Meyer, J. Am. Chem. Soc., 1983, 105, 4303. 29 L. R. Melby, R. J. Harder, W. R. Hertler, W. Mahler, R. E. Benson and W. E. Mochel, J. Am. Chem. Soc., 1962, 84, 3374. 30 H. Krentzien and H. Taube, J. Am. Chem. Soc., 1976, 98, 6379; Inorg. Chem., 1982, 21, 4001. 31 M. A. Esteruelas and H. Werner, J. Organomet. Chem., 1986, 303, 221. 32 M. Krejcik, M. Danek and F. Hartl, J. Electroanal. Chem., Interfacial Electrochem., 1991, 317, 179. 33 S. W. Gordon-Wylie, E. L. Bominaar, T. J. Collins, J. M. Workman, B. L. Claus, R. E. Patterson, S. A. Williams, B. J. Conklin, G. T. Yee and S. T. Weintraub, Chem. Eur. J., 1995, 1, 528. Received 2nd June 1997; Paper 7/03824K
ISSN:1477-9226
DOI:10.1039/a703824k
出版商:RSC
年代:1997
数据来源: RSC
|
|