Reversible thermo-induced spin crossover in a mononuclear cis-dicyanamido-cobalt(ii) complex containing a macrocyclic tetradentate ligand

Abstract

We present a unique investigation of a mononuclear cis-dicyanamido-cobalt(II) complex, [Co(L)(N(CN)₂)₂] (1) (L = N,N′-di-tert-butyl-2,11-diaza[3,3](2,6)pyridinophane), which displays a reversible thermo-induced HS (S = 3/2) to LS (S = 1/2) Spin Crossover (SCO) with a T_1/2 value of around 238 K. The appropriate ligand field strength around the CoN₆ coordination environment is obtained using a tetradentate ligand and two dicyanamide [N(CN)₂]⁻ coligands at the cis position. Variable temperature XRD and several spectroscopic studies have been performed, which confirm the SCO behavior of 1. Interestingly, complex 1 pronounces redox stimulus responsive reversible spin-state switching from HS Co(II) to LS Co(III). These findings represent a rare example of the successful use of pseudohalide to design and synthesize a SCO cobalt(II) complex.