Tuning of Spin Crossover Properties in a Series of Mononuclear Cobalt(II) Complexes Based on Macrocyclic Tetradentate Ligand and Pseudohalide Coligands
The three mononuclear cobalt(II) complexes, [Co(L)(NCX)2] (L = N,N'-di-tert-butyl-2,11-diaza[3,3](2,6)pyridinophane, and X = S (1), Se (2), and [C(CN)2] (3)), have been synthesized and characterized using variable temperature single-crystal X-ray crystallography, spectroscopic, magnetic, and electrochemical studies. All three complexes have a similar distorted octahedral CoN6 coordination geometry produced by the macrocyclic tetradentate ligand L, and two NCX- co-ligands in cis position. Complexes 1 and 2 have crystallized in monoclinic P21/n (Z = 4) space group, while complex 3 has isolated in monoclinic P21/c (Z = 4) space group. Interestingly, complexes 1 and 2 exhibit a reversible and gradual spin-crossover behavior between high-spin (S = 3/2) and low-spin (S = 1/2) state at ca. 168 K and 255 K respectively, however for complex 3, low-spin configuration persists up to 260 K, and it exhibits an incomplete and reversible spin crossover even at 400 K. Additionally, complex 1 display a reversible redox behavior indicating paramagnetic cobalt(II) to diamagnetic cobalt(III) conversion.
- This article is part of the themed collection: Dalton Transactions HOT Articles