Azido bridged two new ferromagnetic Cu(II) chains: synthesis, structure and magnetic behaviour Sudipta Dalai a , Partha Sarathi Mukherjee a , Michael G.B. Drew b , Tian-Huey Lu c , Nirmalendu Ray Chaudhuri a, * a Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India b Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK c Department of Physics, National Tsing Hua University, Hsinchu 300, People’s Republic of China Received 25 October 2001; accepted 30 January 2002 Abstract Two new polynuclear copper(II) complexes, derived from the end-to-end azido bridging ligand and two tridentate (NNN-donor) Schiff base ligands have been synthesised and their single crystal structures have been determined. They are single azido bridged chains, [Cu(L1)(m-1,3-N 3 )] n (ClO 4 ) n (1) and [Cu(L2)(m-1,3-N 3 )] n (ClO 4 ) n (2) where L1 and L2 are two different tridentate Schiff bases obtained from the condensation of pyridine-2-aldehyde with N, N, 2, 2-tetramethylpropane-1, 3-diamine and 1-dimethylamino-2- propylamine, respectively. Structural analyses reveal that each copper(II) centre in both the complexes are in square pyramidal geometry. The azido ligand is bridged in such a fashion that one of the nitrogens of the bridging azide is linked to equatorial of one copper(II) while the other in the axial of the neighbouring copper(II). Low temperature magnetic susceptibility data show weak intrachain ferromagnetic interaction through end-to-end azido pathway in both the complexes. The magnetic data are fitted to a high temperature series expansion for 1D system with S /1/2 local spin based on the Hamiltonian H //J SS i S i  1 , giving the parameters J /2.69 cm 1 , g /2.10 for (1) and J /2.02 cm 1 , g /2.02 for (2). # 2002 Elsevier Science B.V. All rights reserved. Keywords: Schiff base; Cu(II) complexes; End-to-end azido (m-1,3-N 3 ); Magnetic behaviour 1. Introduction Recently there has been a growing interest in design and elaboration of polynuclear molecular system with extended structures and predictable properties, mainly molecule-based magnets [1]. Coordination complexes with novel magnetic properties which may have poten- tially useful application in materials science, have focussed attention on superexchange bridges with the ability to propagate ferromagnetic coupling between paramagnetic transition metal centres [2]. The prime strategy for designing these molecular materials is assembling the paramagnetic metal centres using suita- ble bridging ligand that determines the nature of magnetic interaction. The azido ligand is an efficient superexchange path- way for propagating magnetic interaction between the paramagnetic centres, giving dinuclear, tetranuclear, 1D, 2D and 3D complexes [3 /8]. The versatility of this ligand is due to its diverse binding modes lead to variation in magnetic properties that depend on its orientation with respect to the magnetic centres [9]. The flexidentate azide ligand can bridge two metal centres in two different ways i.e. m-1, 1 and m-1, 3-fashion [10,11]. In 1,1-mode the magnetic role depends in large measure on the angle it subtends at the two metal centres [12 /16]. For dicopper(II) system with small angles ( B/1088) ferromagnetic interaction dominates while for larger angles the azido has been shown to propagate anti- ferromagnetic exchange. But in 1,3-mode, superex- change is generally antiferromagnetic in nature with the exception of only a few systems reported recently showing weak ferromagnetic interaction through 1,3- azido pathway [17]. Recently this laboratory first reported the observation of a ferromagnetic interaction * Corresponding author. Tel.: /91-33-473 4971; fax: /91-33-473 2805. E-mail address: icnrc@mahendra.iacs.res.in (N.R. Chaudhuri). Inorganica Chimica Acta 335 (2002) 85 /90 www.elsevier.com/locate/ica 0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0020-1693(02)00815-0