Crystal structure, spectroscopic and magnetic properties of two unusual compounds: [Cu(terpy)(N3)Cl] and [{Cu0.75Ni0.25(terpy)(N3)2}2]·2H2O (terpy = 2,2′ : 6′,2″-terpyridine)

Abstract

The crystal structures of two unusual complexes [Cu(terpy)(N₃)Cl]1 and [(Cu_0.75Ni_0.25(terpy)-(N₃)₂}₂]·2H₂O 2(terpy = 2,2′:6′,2″-terpyridine) have been determined at room temperature: 1. space group P2₁c. a= 10.586(5), b= 8.572(1), c= 16.396(3)Å, β= 100.69(3)°, Z = 4, R=R′= 0.036, for 2818 reflections with I 3σ(I); 2, space group P2₁/c, a= 10.195(5), b= 9.996(3), c= 15.866(8)Å, β= 91.10(5)°, Z= 4, R=R′= 0.055 for 3134 reflections with I 3σ(I). Complex 1 possesses the first known co-ordination polyhedron including both halide (Cl) and pseudohalide (N₃) ligands. It shows a square-pyramidal topology for the copper(II), with the three nitrogen atoms of the terpy ligand and one terminal nitrogen atom of the azide group in the basal positions while the chloride atom is in the apical one. Compound 2 contains 25% of [{Ni(terpy)(N₃)₂}₂]·2H₂O and 75% of [{Cu-(terpy)(N₃)₂}₂]·2H₂O enclosed in the global lattice. It possesses (end-on) azide bridges and terminal azide ligands. The co-ordination polyhedron of the metal ion is a slightly distorted octahedron with the nitrogen atoms of the terpy ligand and a nitrogen atom of one of the azide bridging groups in the equatorial positions, while the nitrogen atoms of both the bridge and terminal azide groups occupy the axial positions. The pure copper phase related to compound 2 exhibits a discrete molecular topology; however, the pure nickel phase shows the same dimeric structure, which is useful for comparison. The magnetic properties of compound 2 can be explained by contributions from the isolated Cu₂ and Ni₂ entities, giving rise to global ferromagnetic interactions characterised by the parameters J= 20.1 cm^–1, D=–12.5 cm^–1, g_Ni= 2.26 and ρ= 0.76 corresponding to the copper proportion. The EPR measurements for both compounds reveal rhombic symmetries for the g tensors. Single-crystal EPR measurements on 2 show the presence of two magnetically different copper entities, with an antiferrodistortive ordering, in the lattice.