Structure and magnetic properties of a linear oximato-bridged tetranuclear copper(II) complex

Abstract

The tetranuclear copper(II) complex of formula [Cu 2(dmg)(Hdmg)(terpy)] 2(ClO 4) 2 ( 1) (H 2dmg = dimethylglyoxime and terpy = 2,2′:6′,2″-terpyridine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the triclinic system, space group P(−1), with a = 14.382(3), b = 13.728(3), c = 8.979(2) Å, α = 96.99(2), β = 111.85(2), γ = 111.22(3)°, V = 1465.0(9) Å 3, Z = 1, D c = 1.607 g cm −3, M r = 1418.0, F(000) = 719, λ(Mo K α) = 0.71073 Å, μ(Mo K α) = 16.61 cm −1 and T = 298 K. A total of 4891 reflections were measured over the range 2 ≤ θ ≤ 25° and 4393 of them were unique ( I > 2.5 σ( I) and used in the structural analysis. The structure of 1 may be described as two dimeric [Cu 2(dmg)(Hdmg)(terpy)] + units linked by relatively long out-of-plane oxime bonds building a cationic centrosymmetric tetrameric entity with a linear Cu 4(NO) 8 core, and uncoordinated perchlorate anions. Within each dinuclear unit, the partially deprotonated [Cu(dmg)(Hdmg)] − complex unit coordinates to the [Cu(terpy)] 2+ fragment through in-plane oxime bonds in an asymmetric fashion. The coordination geometry around both copper atoms is square pyramidal. The intra- and interdimer copper separations within the tetranuclear complex are 3.674(5) and 3.994(6) Å, respectively. Variable-temperature magnetic susceptibility measurements (4.2–300 K) have been interpreted on the basis of the tetranuclear nature of the compound. The nature and magnitude of the magnetic couplings are discussed on the basis of the structural features and compared with that of related oximato-bridged copper(II) dinuclear complexes.