Reversible Spin-State Switching and Tuning of Nuclearity and Dimensionality via Nonlinear Pseudohalides in Cobalt(II) Complexes

The self-assembly of a macrocyclic tetradentate ligand, cobalt(II) tetrafluoroborate, and nonlinear pseudohalides (dicyanamide and tricyanomethanide) has led to two cobalt(II) complexes, {[Co( L )(μ 1,5 -dca)](BF 4 )·MeOH} n ( 1 ) and [Co 2 ( L ) 2 (μ 1,5 -tcm) 2 ](BF 4 ) 2 ( 2 ) ( L = N , N '-di- er -butyl-2,11-diaza[3,3](2,6)pyridinophane; dca - = dicyanamido; tcm - = tricyanomethanido). Both complexes were characterized by single-crystal X-ray diffraction, spectroscopic, magnetic, and electrochemical studies. Structural analyses revealed tha 1 displays a one-dimensional (1D) coordination polymer containing [Co( L )] 2+ repeating units bridged by μ 1,5 -dicyanamido groups in cis positions, while 2 represents a discreate dinuclear cobalt(II) molecule bridged by two μ 1,5 -tricyanomethanido groups in a cis conformation. Both complexes have a CoN 6 coordination environment around each cobalt center offered by the tetradentate ligand and cis coordinating bridging ligands. Complex 1 exhibits a high-spin ( S = 3/2) state of cobalt(II) in the temperature range of 2-300 K with a weak ferromagnetic coupling between two dicyanamido-bridged cobalt(II) centers. Interestingly, complex 2 exhibits reversible spin-state switching associated with spin-spin coupling. Complexes 1 and 2 also exhibit interesting redox-stimuli-based reversible paramagnetic high-spin cobalt(II) to diamagnetic low-spin cobalt(III) conversion, offering an additional way to switch magnetic properties. A detailed theoretical calculation was consistent with the stated results.