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A Theoretical Rationale for the Formation, Structure and Spin State of Pentacyanochromate(II)
Author(s) -
Deeth Robert J.
Publication year - 2006
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200600137
Subject(s) - chemistry , homoleptic , spin states , density functional theory , solvation , ground state , ligand field theory , octahedron , hexacoordinate , spin crossover , computational chemistry , ligand (biochemistry) , spin (aerodynamics) , aqueous solution , crystallography , inorganic chemistry , atomic physics , molecule , ion , organic chemistry , thermodynamics , crystal structure , biochemistry , receptor , silicon , metal , physics
The pentacyanochromate(II) complex is unusual in two respects. Firstly, it is one of the few homoleptic cyanide species with a high‐spin ground state. Secondly, it was synthesised during an attempt to make the hexacoordinate complex. A combination of qualitative ligand field theory and quantitative density functional theory including solvation effects is applied to rationalise these observations. The spin state depends on the d orbital energy differences and how the promotion energy, PE, associated with a change in spin state compares to the d–d spin pairing energy, SPE. The calculations show that PE > SPE for octahedral [Cr II (CN) 6 ] 4– , hence it has a spin triplet S = 1 ground state, while PE < SPE for [Cr II (CN) 5 ] 3– , hence it is high spin with S = 2. The hexacyanide is stabilised in aqueous solution by solvation. In less polar solvents such as acetonitrile, the unfavourable electrostatic interactions dominate and the reaction stops at the pentacyano complex. In both complexes, the cyanide behaves as a strong‐field ligand and is both a good σ donor and π acceptor.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)