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A systematic investigation of the CuCl2/Mebta (Mebta = 1-methylbenzotriazole) reaction system is described, involving the determination of the influence of the Cu-II:Mebta ratio, the nature of solvent and the presence of counterions on the identity of the reaction products. As a consequence, complexes [Cu2Cl4(Mebta)(4)] (1), [CuCl2(Mebta)(2)] (2), {[Cu2Cl4(Mebta)(2)]}(n) (3), [Cu4OCl6(Mebta)(4)] . 0.25H(2)O (4 . 0.25H(2)O) and [Cu2Cl2(Mebta)(6)](ClO4)(2) (5) have been isolated and structurally characterized by single-crystal X-ray studies. Mebta behaves as a monodentate ligand binding through N(3). I is a dinuclear complex, the structure of 2 consists of discrete monomeric units, and that of 3 is composed of linear, well-separated polymeric chains of Cu-II atoms. The molecules of 4 . 0.25H(2)O have a central mu(4)-oxide ion surrounded tetrahedrally by four Cu-II atoms. In the cations of 5 the two Cu-II centres are asymmetrically bridged by two chloro ligands, with three Mebta molecules completing five coordination at each metal. Complexes were characterized by spectroscopic (IR, far-IR, solution UV/Vis) and thermal decomposition (TG, DTG, and DTA) techniques. Variable-temperature magnetic susceptibility data for 1, 3 and 5 showed intramolecular (1, 5) and intrachain (3) ferromagnetic exchange interactions. Estimates of the J parameters, experimentally derived, were in close agreement with a new magneto-structural criterion developed by us, holding for bis(mu-chloro) copper(II) dimers. A comparison between the CuCl2/Mebta and CuBr2/Mebta systems is also presented. (C) 2004 Elsevier B.V. All rights reserved. Inorganica Chimica Acta

The mercury(II) complexes [Hg(2)X(4)L(2)] (X=Cl,Br) and [HgI(2)L], where L is 2-(2'-pyridyl)quinoxaline, have been prepared and studied by; a combination of conductivity measurements and FT-IR and far-IR, Raman and H-1 NMR spectroscopy. The structures of the free ligand L and [Hg(2)Cl(4)L(2)] have been determined from three-dimensional X-ray data collected by counter methods. Compound L crystallizes in space group P2(1)/c with a=4.163(2), b=16.953(4), c=14.509(3) Angstrom, beta=94.79(2)degrees and Z=4. The complex [Hg(2)Cl(4)L(2)] crystallizes in space group P2(1)/n with a=7.627(3), b=15.617(4), c=11.099(4), beta=92.03(3)degrees and Z=2. In free L, the pyridine nitrogen and the nearest quinoxaline nitrogen are located on the opposite side of the carbon-carbon bond which connects the two rings; the reverse conformation has been observed on complexation. The structure of [Hg(2)Cl(4)L(2)] consists of two Hg(II) centres bridged by two chloro ligands, with a terminal chloride and a chelating molecule of L completing five-coordination at each metal. The geometry at mercury is a distorted trigonal bipyramid with the bridging chlorides occupying apical and equatorial sites of each Hg(II) atom. The bromo compound is isostructural with [Hg(2)Cl(4)L(2)], while a monomeric pseudotetrahedral structure is assigned for the iodo complex in the solid state. Inorganica Chimica Acta

The reaction of the unexpectedly formed ligand 2-(2'-pyridyl)quinoxaline (L) With CuCl2 in ethanol, followed by recrystallization from methanol, yields the dinuclear copper (II) complex [Cu2Cl4L2]. The crystal structure of this compound shows a bidentate chelating behaviour of L and different (terminal, asymmetric bridging) chloride coordination modes. Some properties of the dimer are also described. Polyhedron

An inorganic model approach to the corrosion inhibition of metals by benzotriazoles has been initiated. The preparation and characterization of monomeric cobalt(II) complexes of the types [CoX2(Mebta)2] (X = Cl, Br, NCS, NO3), (MebtaH)[CoCl3(Mebta)], (MebtaH)2[CoCl4], [Co(NCS)2(Mebta)4], [Co(NCS)2(MeOH)2(Mebta)2] and [Co(NO3)2 L2(Mebta)2] (L = H2O, MeOH), where Mebta = 1-methylbenzotriazole, are described. Four representative complexes have been structurally characterized by single-crystal X-ray diffraction studies; [CoCl2(Mebta)2] (1), trans-[Co(NCS)2(Mebta)4] (5), trans-[Co(NCS)2 (MeOH)2(Mebta)2] (6) and cis-[Co(NO3)2(Mebta)2] (8). Mebta acts as a monodentate ligand binding through N(3). The geometry about cobalt in 1 is tetrahedral, while complexes 5, 6 and 8 have octahedral stereochemistries. The new complexes were also characterized by elemental and thermogravimetric analyses, conductivity measurements, variable-temperature magnetochemistry and spectroscopic (IR, ligand field, low-temperature ESR) methods. The data are discussed in terms of the nature of bonding and known structures. Polyhedron