Crystal structure and magnetic properties of two two-dimensional sheet-like polynuclear copper complexes with bridging trans-oxamidate and 4,4′-bipyridine or pyrimidine

Abstract

Two two-dimensional complex polymers [Cu₂L(4,4′-bipy)₂]_n[ClO₄]_2n1 and [Cu₂L′(pym)₂]_n[ClO₄]_2n2, where H₂L =N,N′-bis(2-aminoethyl)oxamide, H₂L′=N,N′-bis(2-aminopropyl)oxamide, 4,4′-bipy = 4,4′-bipyridine and pym = pyrimidine, have been synthesised, and characterized by crystallographic, spectroscopic and magnetic methods. Both compounds crystallize in the monoclinic system, space group P2₁/c and Z= 4, with a= 6.859(1), b= 20.085(4), c= 11.860(4)Å and β= 93.56(2)° for 1, and a= 8.721(2), b= 8.679(2), c= 16.741(2)Å and β= 98.59(1)° for 2. The structures of the two compounds consist of layers of two-dimensional networks along the a-axis. Within each layer, trans-oxamidato-bridged copper(II) dimers asymmetrically connected by 4,4′-bipyridine or pyrimidine extend along bc plane to form an infinite network. The copper(II) has a square-pyramidal co-ordination geometry with N₃O atoms forming the basal plane and a nitrogen atom from 4,4′-bipyridine or pyrimidine occupying the apical position. Both compounds exhibit strong antiferro-magnetic coupling with J=–335 for 1 and –560 cm^–1 for 2, owing to the efficiency of the oxamidato bridges in facilitating such coupling between copper(II) ions which are separated by more than 5.2 Å.