Five types of odd–even effect and crystal structure changes brought about by ω-phenylalkyl group in [Ni(dmit)2] complex salts

Abstract

A series of [Ni(dmit)₂] (dmit: 1,3-dithiole-2-thione-4,5-dithiolate) salts of ω-phenylalkyl-trimethylammonium (CnPh: n is the alkylene chain length; n = 2–5) have been prepared and characterized by X-ray crystallographic structural analysis. All complex salts are found to be composed of an alternating stack of [Ni(dmit)₂] anions and CnPh cations, whereas the crystal structures are different in each complex. Interestingly, this series exhibited five types of odd–even effects in the crystal structures: 1. [Ni(dmit)₂] anion length, 2. CnPh cation length, 3. orientation of the alkylene group against the terminal phenyl group, 4. relative orientation of the terminal phenyl group against [Ni(dmit)₂] anions, 5. structure of dimerized [Ni(dmit)₂] anions. The last odd–even effect led to an unusual vertical dimer structure. The vertical dimer is a unique structure in [M(dmit)₂] complex salts (M = transition metal) and has not been reported. The introduction of a terminal phenyl group is concluded to have increased the steric effect and led to a marked structural difference between odd and even-numbered complex salts, i.e. the odd–even effect.