Geometric Control of Ground State Multiplicity in a Copper(I) Bis(verdazyl) Complex

A copper(I) complex of a 3-(6′-isopropylpyridyl)-substituted verdazyl was synthesized and characterized by X-ray crystallography and magnetic susceptibility. The complex crystallizes in the monoclinic space group C2/c with cell dimensions a = 22.544 Å, b = 11.576 Å, c = 17.157 Å, β = 123.907°, V = 3716.2 Å3. The coordination geometry at copper is distorted tetrahedral, with the two ligand planes separated by 75°. Magnetic susceptibility measurements indicate that the ground state of the diradical is a triplet at this geometry. Fitting to a simple Heisenberg Hamiltonian (H = −JS1·S2) gave J = 47(1) cm−1. The triplet ground state results from exchange mediated by the copper ion; in particular, the direction of the distortion from tetrahedral geometry appears to be essential to maintain the high-spin ground state.