Linkage isomerism in exchange coupled dinuclear Ni(II) complexes with three azide bridges; tris(μ-1,1-azido) versus tris(μ-1,3-azido) binding. Crystal structures of [L 2Ni 2(μ-1,1-N 3) 3]ClO 4 and [L 2Ni 2(N 3) 2-(μ-1,3-N 3) 2] (L = 1,4,7-trimethyl-1,4,7-triazacyclononane)

Abstract

Two linkage isomers of Ni(II), [L 2Ni 2(N 3) 3]ClO 4, containing either three end-to-end (μ-1,3-azido) 1, or three end-on (μ-1,1-azido) 2 bridging azide ligands and 1,4,7-trimethyl-1,4,7-triazacyclononane (L) as the capping ligands have been reported. The compounds have been characterized on the basis of IR, UV-Vis spectroscopy and variable-temperature (2–290 K) magnetic susceptibility measurements. The crystal structure of 1 has been reported earlier ( J. Chem. Soc., Chem. Commun., (1985) 1618). 2 crystallizes in the monoclinic space group P2 1/ c with cell constants a=14.989(1), b=14.610(2), c=14.756(2) A ̊ , β=111.12(1)°, V=3014.5 A ̊ 3 and Z=4 . The structure of 2 consists of a six-coordinated dinickel(II) center with three azide ions linking two Ni(II) ions adopting the end-on coordination mode. Analysis of the susceptibility data yields a moderately strong antiferromagnetic interaction between nickel centers in 1, but a ferromagnetic interaction in 2. The crystal structure of [L 2Ni 2(N 3) 2(μ-1,3-N 3) 2] ( 3) has been determined at 193 K. Crystals of 3·CH 3OH have the following cell parameters: monoclinic, C2/c; a=24.302(2), b=11.276(1), c=11.437(1) A ̊ ; β=109.70(1)°; V=2950.8; Z=4 . The structure of 3 consists of a six-coordinated dinickel(II) center with two end-to-end azide ions linking two Ni(II) ions. Magnetic susceptibility measurements have shown the existence of antiferromagnetic exchange interaction between the nickel centers (2 J = −72.8 cm −1). The magnetic behavior of 1,2 and 3 together with other related complexes is discussed to show the difficulty of rationalizing the magnetostructural trends.