Secondary Interactions versus Intramolecular π–π Interactions in CuII–Diradical Complexes

Abstract

Two new non‐innocent ligands, H2LOPh and H2LSPh, were synthesized. Both ligands reacted with 0.5 equiv. of CuCl2·2H2O to provide the corresponding mononuclear diradical‐containing CuII complexes [Cu(LOPh(SQ))2] (1) and [Cu(LSPh(SQ))2] (2). Both complexes were characterized by single‐crystal X‐ray diffraction measurements. Molecular structure analyses indicated that, in complex 1, the two –OPh groups of two [LOPh(SQ)]– ligands are situated trans to each other, while in complex 2, the two –SPh groups of two [LSPh(SQ)]– ligands were found to maintain a cis relationship. In complex 1, Cu–CPh interactions as well as two π–π interactions were observed between –OPh‐group‐containing C6 phenyl rings and the radical‐containing coordinated chelate rings. In complex 2, Cu–CPh interactions were absent, although intramolecular π–π interactions within one of the two coordinating ligands were present. The π–π interactions were between the C6 phenyl ring of an –SPh group and the 3,5‐di‐tert‐butyl‐amidophenolate unit. Variable‐temperature magnetic susceptibility measurements indicated that both complexes acquire an S = 1/2 ground state. X‐band EPR measurements confirmed that the unpaired electron is on the CuII center in both complexes. This implies that the expected CuII–S secondary interactions in complex 2 are suppressed by the dominating π–π stacking interactions, and the ground‐state electronic configuration was found to be (↑↑↓) instead of the expected (↑↓↑).