Molecular mechanics for multiple spin states of transition metal complexes
UNSPECIFIED. (2003) Molecular mechanics for multiple spin states of transition metal complexes. DALTON TRANSACTIONS (20). pp. 3949-3955. ISSN 1477-9226Full text not available from this repository.
Official URL: http://dx.doi.org/10.1039/b305868a
Empirical Ligand Field Molecular Mechanics (LFMM) parameters for Co-III-F and Co-III-CN bonds are developed from Density Functional Theory (DFT) calculations on octahedral [CoF6](3-) and [Co(CN)(6)](3-). In addition to the T-5(2g) and (1)A(1g) ground states of [CoF6](3-) and [Co(CN)(6)](3-) respectively, DFT can also access the low-spin form of [CoF6](3-) and the high-spin form of [Co(CN)(6)](3-) as well as the averaged d configuration (ADC) state corresponding to a t(2g) (3.6)e(g) (2.4) configuration in which the ligand field stabilisation energy is formally zero. DFT orbital energies are used to estimate the dependence of Delta(oct) on the Co-L distance which, when used in conjunction with the relation that the DFT spin state energy difference DeltaE(spin)(T-5(2g)-(1)A(1g))=2Delta(oct)-(5B+8C), provides a measure of the interelectron repulsion energy. Finally, the ratio of e(sigma) to e(pi) ligand field parameters is obtained via fitting the DFT orbital energies of hypothetical square planar [CoF4](-) and [Co(CN)(4)](-) complexes using an ADC corresponding to a b(1g) (1.2)b(2g) (1.2)a(1g) (1.2)e(g) (2.4) configuration. The LFMM parameters are derived solely from the homoleptic systems but are nevertheless able to reproduce the structures and spin-state energies of the eight mixed-ligand systems in between. The latter are estimated theoretically since no experimental data exist. The high-spin and low-spin structures have Co-L rms errors of 0.06 and 0.03 Angstrom, respectively. Explicit recognition of d-d interelectron repulsion energies provides a common reference for both spin states which facilitates a direct LFMM calculation of the spin-state energy difference. Both LFMM and DFT predict: (i) a change from high to low spin after replacement of a single fluoride ligand; (ii) the difference increases with each subsequent replacement and (iii) (1)A(1g) is relatively more stable than T-5(2g) for cis and mer compared to trans and fac, respectively. The spin-state energy difference rms error is similar to7 kcal mol(-1) but there is a systematic overestimation for the mixed-ligand systems since the LFMM does not fully capture the cis and trans influences.
|Item Type:||Journal Article|
|Subjects:||Q Science > QD Chemistry|
|Journal or Publication Title:||DALTON TRANSACTIONS|
|Publisher:||ROYAL SOC CHEMISTRY|
|Number of Pages:||7|
|Page Range:||pp. 3949-3955|
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