Supramolecular hydrogen-bond structures and magnetic interactions in basal-apical, dinuclear, azide-bridged copper(II) complexes

Abstract

The synthesis, characterisation, X-ray single crystal structures and magnetic properties of three new basal-apical μ₂-1,1-azide-bridged complexes [CuL¹N₃]₂ (1), [CuL²N₃]² (2) and [CuL³N₃]₂ (3) with very similar tridentate Schiff-base blocking ligands {HL¹ = N-[2-(ethylamino)ethyl]salicylaldimine; HL² = 7-(ethylamino)-4-methyl-5-azahept-3-en-2-one; HL³ = 7-amino-4-methyl-5-azaoct-3-en-2-one} have been reported [complex 1: monoclinic, P2₁/c, a = 8.390(2), b = 7.512(2), c = 19.822(6) Å, β = 91.45(5)°; complex 2: monoclinic, P2₁/c, a = 8.070(9), b = 9.787(12), c = 15.743(17) Å, β = 98.467(10)°; complex 3: monoclinic, P2¹/n, a = 5.884(7), b = 16.147(18), c = 11.901(12) Å, β = 90.050(10)°]. The structures consist of neutral dinuclear entities resulting from the pairing of two mononuclear units through end-on azide bridges connecting an equatorial position of one copper centre to an axial position of the other. The copper ions adopt a (4+1) square-based geometry in all the complexes. In complex 2, there is no inter-dimer hydrogen-bonding. However, complexes 1 and 3 form two different supramolecular structures in which the dinuclear entities are linked by H-bonds giving one-dimensional systems. Variable temperature (300−2 K) magnetic-susceptibility measurements and magnetisation measurements at 2 K reveal that all three complexes have antiferromagnetic coupling. Magneto-structural correlations have been made taking into consideration both the azido bridging ligands and the existence of intermolecular hydrogen bonds.