The structural parameter of spin states of C 1-symmetric four-coordinate cobalt complexes: D 4.

Herein, we reveal the correlation between structure and spin-states for C 1-symmetric four-coordinate cobalt complexes. A series of C 1-symmetric four-coordinate cobalt complexes with various steric, electronic, anions and chelation modes were synthesized and characterized. X-ray diffraction studies revealed a structural distortion from square-planar to distorted tetrahedral pyramidal geometry. Combining paramagnetic nuclear magnetic resonance (pNMR), magnetic measurement (SQUID), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT), the electronic structure with a cobalt(ii) (S Co = 1/2 to 3/2) ion antiferromagnetically coupled to a radical anion ligand (S Ligand = 1/2) was established. A new structural parameter, D 4, was introduced as an improved parameter for quantitatively assessing the spin state in four-coordinate complexes.