Synthesis and characterization of cobalt(iii) cyanide complexes: cobalt participation in the decomposition of radical anion of TCNQ

Abstract

Reaction of Co(CH₃COO)₂·4H₂O, KTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) with the racemic or chiral H₂salency (N,N′-bis(salicylidene)-1,2-cyclohexanediamine) ligand afforded three Co(III) complexes K[Co(salency)(CN)₂]·CH₃OH (1), K[Co(S,S-salency)(CN)₂]·H₂O (1S) and K[Co(R,R-salency)(CN)₂]·CH₃OH (1R), which have been fully characterized. The cyanide groups in these three complexes are generated from the in situ decomposition of the radical anion of TCNQ with the participation of cobalt(II). Single-crystal X-ray diffraction analysis reveals that complex 1 exhibits an infinite double stair-like chain structure. However, the chiral complexes 1S and 1R show chain structures consisting of two independent sub-chains. All of these chains are bridged by the K⁺ ions, with the cyanides interacting with K⁺ in the end-on and unusual side-on π-type mode. Second-order nonlinear optical effect studies in the solid state revealed that 1S and 1R are SHG active.