Synthesis, spectral and magnetical characterization of monomeric [Cu(2-NO 2 bz) 2 (nia) 2 (H 2 O) 2 ] and structural analysis of similar [Cu(RCOO) 2 (L–N) 2 (H 2 O) 2 ] complexes P. Stachova ´ a , M. Melnı ´k a , M. Korabik b , J. Mrozinski b , M. Koman a , T. Glowiak b , D. Valigura a, * a Department of Inorganic Chemistry, Slovak Technical University, Radlinske ´ho 9, 812 37 Bratislava, Slovakia b Faculty of Chemistry, University of Wroclaw, 50-383 Wroclaw, Poland Received 8 February 2006; received in revised form 22 June 2006; accepted 16 August 2006 Available online 26 August 2006 Abstract A new complex of composition [Cu(2-NO 2 bz) 2 (nia) 2 (H 2 O) 2 ](1) (nia = nicotinamide, 2-NO 2 bz = 2-nitrobenzoate) has been prepared and its composition and stereochemistry as well as coordination mode have been determined by elemental analysis, electronic, infrared and EPR spectroscopy, magnetization measurements over the temperature range 1.8–300 K, and its structure has been solved, as well. The complex structure consists of the centrosymmetric molecules with Cu(II) atom monodentately coordinated by the pair of 2-nitro- benzoato anions and by the pair of nicotinamide molecules, forming nearly tetragonal basal plane, and by a pair of water molecules that complete tetragonal–bipyramidal coordination polyhedron about the copper atom. The complex 1 exhibits magnetic moment l eff = 1.86 B.M. at 300 K which decreases to l eff = 1.83 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie–Weiss law with Curie constant of 0.442 cm 3 K mol 1 and with Weiss constant of 1.0 K. EPR spectra at room temperature as well as at 77 K are of axial type with g ^ = 2.065 and g i = 2.280 and exhibit clearly, but partially resolved parallel hyperfine splitting with A II = 160 G, that is consistent with the determined molecular structure of 1. In order to analyze the factors influencing the degree of tetragonal distortion of coordination polyhedron, the dataset of 72 structures similar to that of 1 was extracted from CCD and analyzed. A significant correlation between the average Cu–O ax bond length and tetragonality parameter s which was found as a consequence of the Jahn–Teller effect. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Copper; Carboxylate complexes; Crystal structure; Spectral properties; Magnetic properties; Nicotinamide 1. Introduction Crystal engineering, a subdiscipline of supramolecular chemistry, represents an important and rapidly developing area of chemical research. Metal-containing supramolecu- lar systems constructed from intermolecular forces by weak, as well as strong, hydrogen bonds and also hydro- phobic and electrostatic forces and covalent bonds, have potential applications in heterogeneous catalysis and molecular electronics and in magnetic nonlinear optical and nanoporous material [1]. Interesting, metal-containing supramolecular systems consist of coordination and orga- nometallic complexes connected by strong hydrogen-bond- ing motifs [2,3]. The coordination sphere of Cu(II) octahedral complexes, in contrast to most other central atoms, clearly demon- strates some pronounced properties of non-rigidity (plastic- ity). These plasticity properties are shown to be due to the Jahn–Teller effect [4]. Because of its electronic configura- tion, the Cu(II) atom is an ideal candidate for deformation studies of its coordination polyhedron. First of all, it has only one outermost electron which simplifies theoretical considerations. Secondly, if the ligand atoms around the 0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.08.019 * Corresponding author. Tel.: +421 2 59325726; fax: +421 2 52493198. E-mail address: dusan.valigura@stuba.sk (D. Valigura). www.elsevier.com/locate/ica Inorganica Chimica Acta 360 (2007) 1517–1522