Syntheses, crystal structures, magnetochemistry and catechol oxidase activity of a tetracopper(ii) compound and a new type of dicopper(ii)-based 1D coordination polymer

Abstract

This report describes the syntheses, crystal structures, electrospray ionisation mass spectra, catechol oxidase activity and magnetic properties of a tetracopper(II) cluster [Cu^II₄L₂(µ₃-OH)₂(NCO)₄]·2H₂O (1) and a one-dimensional (1D) coordination polymer [{{Cu^II₂L(µ_1,1-N₃)}₂(µ_1,1-N₃)₂}(µ_1,3-N₃)₂]_n (2) derived from a Schiff base ligand (HL; 1 : 2 condensation product of 4-ethyl-2,6-diformylphenol and 3-morpholinopropylamine). Compound 1 may be considered a dimer of two µ-phenoxo-µ₃-hydroxido dicopper(II) units, where the dimerisation takes place through the two µ₃-hydroxido moieties. Compound 2 is a µ-phenoxo-µ_1,1-azido dicopper(II)-based 1D polymer, where the dicopper(II) units are interlinked by two end-on azide bridges to form a dimer of dinuclear-type tetracopper(II) moieties, which, in turn, are self-assembled by end-to-end azide bridges. Magnetic investigations reveal a strong antiferromagnetic interaction in the dicopper(II) basic unit in both cases, with J values of −382 cm⁻¹ for 1 and −220 cm⁻¹ for 2. Both compounds have been found to be functional models for catechol oxidase activity in N,N-dimethylformamide (DMF) and acetonitrile, with K_cat values around 15 h⁻¹ for 1 and 13 h⁻¹ for 2. Interestingly, compound 2 is a unique example in which a dimer of a dinuclear metal unit is the node for a versatile and well-explored linker, azide, to generate a coordination polymer. It is also interesting that a coordination polymer, 2, has been identified as the functional model of catechol oxidase activity.