Triangular, Ferromagnetically-Coupled CuII3-Pyrazolato Complexes as Possible Models of Particulate Methane Monooxygenase (pMMO)

Magnetic susceptibility and EPR studies show that trinuclear CuII-pyrazolato complexes with a Cu3((mu)3-X)2 core (X = Cl, Br) are ferromagnetically coupled: JCu-Cu = +28.6 cm^-1 (X = Cl), +3.1 cm^-1 (X = Br). The orderly transition from an antiferromagnetic to a ferromagnetic exchange among the Cu centers of Cu3((mu)3-X) complexes, X = O, OH, Cl, Br, follows the change of the Cu-X-Cu angle from 120° to ~80°. The crystal structures of [Bu4N]2 [Cu3((mu)3-Br)2((mu)-pz*)3Br3] (pz* = pz (1a) or 4-O2N-pz (1b), pz = pyrazolato anion, C3H3N2^1-) are presented.