Models for the trinuclear copper(II) cluster in the particulate methane monooxygenase from methanotrophic bacteria: Synthesis, spectroscopic and theoretical characterization of trinuclear copper(II) complexes

Abstract Three trinuclear Cu(II) complexes [Cu 3 (tacp)(μ 3 -Cl) 2 ](Cl) 4 ( 1 ), [Cu 3 (tacp)(μ 3 -Br) 2 ](Br) 4 ( 2 ) and [Cu 3 (tacp)(μ 3 -OH) 2 ](Cl) 4 ( 3 ) (tacp, 1,10,19-trioxa-4,7,13,16,22,25-hexaazacycloheptaeicosane) are synthesized to model the oxidized tricopper cluster implicated in the particulate methane monooxygenase from Methylococcus capsulatus (Bath) . In the enzyme, the three Cu(II) ions are coupled by weak ferromagnetic interactions. The Cu(II) ions in 1 and 2 are shown to be ferromagnetically coupled from magnetic susceptibility and electron paramagnetic resonance (EPR) measurements. EPR suggests anti-ferromagnetic interactions among the Cu(II) ions in 3 . Density functional theory calculations reproduce well the geometric, electronic and magnetic properties observed in these complexes and provide insights into the spin-coupling interactions mediated by the bridging ligands.