Pyrazolate-supported Cr3(μ3-O) cores; homovalent Cr III3 and mixed-valent Cr III2CrIV

Abstract

The thermally assisted reaction of Cr(NO₃)₃·9H₂O, 4-Cl-pzH, and Et₃N yielded electrochemically active trinuclear Cr^III–oxo–pyrazolate complexes with formula (Ph₄P)₂[Cr₃(μ₃-O)(μ-4-Cl-pz)₆X₃], X = Cl (1) and Br (2). Magnetic susceptibility measurements and EPR spectroscopy show that 1 has an antiferromagnetically coupled Cr₃O-core with an S = 1/2 ground state and isotropic exchange of J = −12.7 cm⁻¹. (H_ex = −2JS₁S₂). Cyclic voltammetry reveals a facile reversible oxidation to the formally Cr^III₂Cr^IV analogue of 1. The UV-Vis-NIR spectra of Cr^III₃ and Cr^III₂Cr^IV species have been assigned with the help of DFT calculations.