Electronic Structures of Mixed-Sandwich Complexes of Cyclopentadienyl and Hydrotris(pyrazolyl)borate Ligands with 3d Transition Metals
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- 作者：Tim J. Brunker ; Jennifer C. Green ; and Dermot O'Hare
- 刊名：Inorganic Chemistry
- 出版年：2003
- 出版时间：July 14, 2003
- 年：2003
- 卷：42
- 期：14
- 页码：4366 - 4381
- 全文大小：286K
- 年卷期：v.42,no.14(July 14, 2003)
- ISSN：1520-510X
文摘
The electronic and magnetic properties of a series of mixed-sandwich complexes MCpRTp (CpR = Cp or Cp*; Tp= hydrotris(pyrazolyl)borate; M = V, Cr, Fe, Co or Ni) have been studied and compared to their homolepticanalogues, MCpR2 and MTp2. Solid-state magnetic susceptibility measurements and EPR spectroscopic data indicatethat complexes with d3, d6, and d8 configurations are similar electronically to their metallocene analogues, exceptfor FeCp*Tp, which displays a spin equilibrium (S = 0 
S = 2) in solution which was investigated by variable-temperature NMR spectroscopy. The d2 complex [VCpTp]+ displays magnetic behavior consistent with an orbitallynondegenerate ground state. The d4 species CrCp*Tp has a high-spin (S = 2) ground state. The d7 speciesCoCpTp is high spin (S = 3/2) whereas its Cp* analogue and [NiCp*Tp]+ are both low-spin (S = 1/2) species. Theoptical spectra of the d3, d6, and d8 complexes were assigned in a fashion similar to the analogous metallocenesand ligand-field parameters (
1 = 
-
gap, 2 = -
gap for d-orbitals in axial symmetry) calculated. Theanalysis shows that for 15-electron species the total ligand-field splitting, TOT, is larger than for their metalloceneanalogues, whereas for the 18-electron case TOT is smaller and for 20-electron systems TOT is approximatelythe same. In all cases 2 is substantially reduced compared to the metallocenes, and in the majority of cases 1is markedly larger. DFT calculations were performed to investigate further the nature of the ligand environment onthe frontier orbitals in these complexes. Orbital energies and compositions were calculated and compared for aseries of homoleptic and mixed-sandwich complexes of Ni(II) and across the 1st transition series for MCpRTpspecies. The ability of Tp (vs Cp) to act as a -donor (with respect to the principal molecular axis) imparts significantligand antibonding character to the -orbitals and results in decreased 
- values compared to the metallocenesand an increased tendency toward high-spin complexes in the mixed-sandwich complexes. Structure calculationswere performed for CrCp*Tp, [VCpTp]+, and CoCp*Tp which show substantial distortions from ideal axial symmetryin their crystal structures. The origins of these distortions were confirmed to arise from unequal occupancy ofnear-degenerate - and -levels.
S = 2) in solution which was investigated by variable-temperature NMR spectroscopy. The d2 complex [VCpTp]+ displays magnetic behavior consistent with an orbitallynondegenerate ground state. The d4 species CrCp*Tp has a high-spin (S = 2) ground state. The d7 speciesCoCpTp is high spin (S = 3/2) whereas its Cp* analogue and [NiCp*Tp]+ are both low-spin (S = 1/2) species. Theoptical spectra of the d3, d6, and d8 complexes were assigned in a fashion similar to the analogous metallocenesand ligand-field parameters (1 = - gap, 2 = - gap for d-orbitals in axial symmetry) calculated. Theanalysis shows that for 15-electron species the total ligand-field splitting, TOT, is larger than for their metalloceneanalogues, whereas for the 18-electron case TOT is smaller and for 20-electron systems TOT is approximatelythe same. In all cases 2 is substantially reduced compared to the metallocenes, and in the majority of cases 1is markedly larger. DFT calculations were performed to investigate further the nature of the ligand environment onthe frontier orbitals in these complexes. Orbital energies and compositions were calculated and compared for aseries of homoleptic and mixed-sandwich complexes of Ni(II) and across the 1st transition series for MCpRTpspecies. The ability of Tp (vs Cp) to act as a -donor (with respect to the principal molecular axis) imparts significantligand antibonding character to the -orbitals and results in decreased - values compared to the metallocenesand an increased tendency toward high-spin complexes in the mixed-sandwich complexes. Structure calculationswere performed for CrCp*Tp, [VCpTp]+, and CoCp*Tp which show substantial distortions from ideal axial symmetryin their crystal structures. The origins of these distortions were confirmed to arise from unequal occupancy ofnear-degenerate - and -levels.