Copper(II) halide coordination complexes and salts of 3-halo-2-methylpyridines: Synthesis, structure and magnetism Mahmoud Abdalrahman a , Christopher P. Landee b , Shane G. Telfer c , Mark M. Turnbull a,⇑ , Jan L. Wikaira d a Carlson School of Chemistry and Biochemistry, Worcester, MA 01610, United States b Dept. of Physics, Clark University, 950 Main St., Worcester, MA 01610, United States c MacDiarmid Institute for Advanced Materials and Nanotechnology, Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand d Dept. of Chemistry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand article info Article history: Available online 7 February 2012 Dedicated to Prof. Jon Zubieta Keywords: Copper halides Crystal structures Magnetic measurements Halopyridine complexes abstract Two families of compounds have been prepared from the reaction of 3-X 0 -2-methylpyridine with CuX 2 (X, X 0 = Cl, Br) in the presence or absence of HX. Four salts, (3-X 0 -2-methylpyridinium) 2 CuX 4 were prepared, three of which crystallize in the orthorhombic space group Pbcn while the fourth (X = Br and X 0 = Cl) crys- tallizes in the monoclinic space group C2/c. All four neutral compounds of formula (3-X 0 -2-methylpyri- dine) 2 CuX 2 crystallize in the space group P  1. Of these, three form weakly bridged chains via long CuX contacts, while the fourth (X = X 0 = Cl) forms centrosymmetric dimers. Most of the complexes exhibit only very weak antiferromagnetic interactions and can be modeled as weak uniform chains. Com- pound 4, (3-Cl-2-methylpyridinium) 2 CuBr 4 , shows behavior that models an isolated 2D-Heisenberg anti- ferromagnetic layer with J = 5.09(2) K, while compound 7, (3-Cl-2-methylpyridine) 2 CuCl 2 , crystallizes as a bichloride bridged centrosymmetric dimer with J = 29.31(6) K. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The bulk magnetic properties of transition metal complexes are dependent upon chemical connectivity, local geometry, and non- bonding contacts between magnetic species in the crystalline lat- tice. We have been studying magneto-structural correlations in copper(II) halide coordination complexes and salts in an attempt to understand the factors that affect the magnetic superexchange pathways in the compounds and to derive quantitative structure/ function relationships. There are two common superexchange pathways in cupric halides:bihalide bridges, where a pair of halide ions bridge a pair of Cu(II) ions, and the two-halide pathway (Cu– XX–Cu) where non-bonding overlaps between the halide ions mediate the magnetic exchange. In both cases, there are multiple bond lengths, angles, dihedral angles, geometric distortions, etc. that may contribute to the overall pathway [1]. Correlations be- tween the magnetic properties and the structure of compounds have continually been drawn [2]. Given the large number of poten- tial controlling factors, a similarly large number of compounds are necessary to provide the data needed to attempt any degree of quantitative correlation. To that end, we have been studying fam- ilies of Cu(II) coordination complexes and salts of substituted pyr- idines with the general formulae (AH) 2 CuX 4 or (A) 2 CuX 2 where A is the substituted pyridine which serves as an organic base or ligand, and X is bromide or chloride. For both the salts and neutral complexes, the size, shape and location of substituents on the pyridine rings has a major effect on the crystal packing. Systems with magnetic interactions that form dimers [3], chains [4], ladders [5], layers [6] and three-dimensional systems [7] have all been isolated. We have recently reported work involving the complexes of CuX 2 with 2-X-3-methylpyridine (X = Cl, Br) where the magnetic behavior of the compounds was success- fully fit to models for dimers or chains [8]. In the present work, the relative positions of the halogen and methyl group have been reversed and we report here the synthesis, structure, and magnetic behavior of the compounds (3-X 0 -2-methylpyridinium) 2 CuX 4 (1, X = Cl, X 0 = Br; 2, X=X 0 = Br; 3, X=X 0 = Cl; 4, X=Br, X 0 = Cl) and (3-X 0 -2-methylpyridine) 2 CuX 2 (5, X = Cl, X 0 = Br; 6, X=X 0 = Br; 7, X=X 0 = Cl; 8, X = Br, X 0 = Cl). 2. Experimental 3-Bromo-2-methylpyridine was purchased from AK Scientific, Inc. and 3-chloro-2-methylpyridine was purchased from Synchem OHG and used without further purification. Copper chloride, cop- per bromide, HCl and HBr were obtained from VWR and used with- out further purification. IR spectra were recorded on a Perkin Elmer Spectrum 100 spectrometer. Elemental analyses were carried out by Marine Science Institute, University of California, Santa Barbara, CA 93106, USA. 0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2012.01.050 ⇑ Corresponding author. E-mail address: mturnbull@clarku.edu (M.M. Turnbull). Inorganica Chimica Acta 389 (2012) 66–76 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica