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The mixed cation salts, (dimethylammonium)(3,5-dimethylpyridinium)CuX4 (X = Cl, Br), henceforth (DMA)- (35DM P)CuX4, are new examples of spin-ladders based on nonbonded halide…halide interactions between CuX42- anions. In these structures, double rows of the CuX42- anions are sheathed by the 35DMP+ cations, while the edges are capped by the DMA+ cations. For the Br salt, the Br…Br contacts that define the rungs of the ladder are 4.017 Å in length, while those that define the rails are 3.983 Å. For the Cl salt, the corresponding lengths are 3.967 and 4.045 A. The susceptibility data for the Br salt exhibits a maximum at ~5.5 K, and fitting the data to the spin ½ antiferromagnetic ladder model yields 2J(rail)/k = -7.95 K and 2J(rung)/k = -4.07 K. The exchange coupling is much weaker in the Cl salt, no maximum in χ is observed down to 1.8 K, and the corresponding exchange constants are -1.59 and -1.25 K, respectively. An analysis is made of the structural factors involved in the J(rung) pathway. [ABSTRACT FROM AUTHOR]

Abstract: The structural and magnetic properties of the planar dimers in the (morpholinium)2Cu2Cl6− x Br x salts are investigated. The salt is triclinic, space group , a =7.408(7), b =10.458(10), c =11.933(12) Å, α =82.26(2), β =88.35(2), and γ =77.22(2)° with Z =2, while the salt is monoclinic, space group P21/c, a =14.148(6), b =10.814(4), c =14.298(6) Å and β =117.108(7)° with Z =4. The mixed halide salts are all isomorphous with the salt. Structurally, the compounds contain isolated dimeric species due to the weak coordination of the morpholinium cations to the copper ions via semi-coordinate Cu⋯O bonds. This is in contrast to other such dimer systems, where semi-coordinate Cu⋯X bonds link the dimers together into stacks or chains. In the morpholinium salts, hydrogen bonding ties the molecular units into a layered structure. These N–H⋯X hydrogen bonds force short X⋯X contacts between dimers with X⋯X distances of 3.92–4.07 Å. In this manner, magnetic chains with alternating exchange pathways exist: the intradimer exchange coupling and the X⋯X (2H) pathway. Magnetic studies indicate that these systems behave as alternating AFM chains, demonstrating that the halide⋯halide contacts are effective exchange pathways. The magnetic studies show that the AFM coupling increases monotonically as the bromide content increases. The values for the salt are J 1/k =−41.6(1) K and J 2/k =−26(2) K, while those of the salt are −149.5(5) and −59(2) K. Comparison with other systems suggests that J 1 value for the chloride salt corresponds to the intradimer coupling while the J 2 value is assigned to the two-halide pathway, while the assignments are reversed for the bromide containing salts. [Copyright &y& Elsevier]

The crystal structure of bis(cyclopentylammonium)tetrabromocuprate(II) has been determined at room temperature and at -70 °C. The room temperature structure is orthorhombic, space group Pn21a, with a = 12.092(6) Å, b = 8.134(4) Å, and c = 18.698(10) Å. The Iow temperature structure is also orthorhombic, space group Pna21, with a = 24.111(5) Å, b = 8.089(2) Å, and c = 18.448(4) Å. DSC studies reveal the presence of a weak endotherm at -13 °C. The structures of the two phases are very similar, differing only in the relative orientations of the cyclopentyl rings of the organic cations and slight displacements of the anionic tetrahedra. The CuBr42- anions in the Iow temperature phase are arranged to define a spin ladder system through Cu-Br···Br-Cu two-halide exchange pathways. Magnetic susceptibility data have been analyzed and yield antiferromagnetic exchange strengths 2Jrail/k = 11.6 K and 2Jrung/k = -5.5 K with a singlet-triplet gap energy Δ/kB = 2.3 K. This is the first report of a spin ladder with a stronger interaction along the axis of the ladder than along the rungs. [ABSTRACT FROM AUTHOR]

The structures of three hybrid organic/inorganic halometalate salts are reported, and the layer structures developed are contrasted. Crystal structures of the isostructural N-methylethylenediammonium (MEDA²+) and N-ethylethylenediammonium (EEDA²+) salts of copper(I) bromide are both triclinic, space group P&1macr;, with lattice constants a = 6.284(7), b = 7.842(6), and c = 12.03(1) Å, α = 84.84(3), β = 83.08(2), and γ = 88.00(3)°, and V = 586(1) ų with Z = 2 for (MEDA)Cu2Br4 while (EEDA)Cu2Br4 has lattice constants a = 6.27(2), b = 7.78(2), and c = 13.12(3) Å, α = 84.69(4), β = 78.18(3), and γ = 88.17(7)°, and V = 623(3) ų with Z = 2. The dominant inorganic feature in both salts is anionic (CuBr2)nn− chains of edge-shared CuBr4 tetrahedra. The diammonium cations hydrogen bond these chains together into a unique double layer structure. For comparison purposes, the crystal structure of (CHA)PbBr3 (CHA+ = cyclohexylammonium)is reported (monoclinic, space group P21/n, a = 8.088(2) Å, b = 7.912(2) , Å, and c = 19.572(4) Å, β = 96.98(4)°, and V = 1243.2(4) ų with Z = 4). This contains (PbBr3)nn− halometalate chains, this time of face-shared PbBr6 octahedra. However, here the organic cations tie the chains together into the more common single layer structure. [ABSTRACT FROM AUTHOR]

Discusses polymorphism in bis(4-dimethylaminopyridinium)tetrachlorocuprate(II). Cocrystallization of two isomorphs of the compound from solution at room temperature; Absence of disorder of the organic cation in either phase; Differences in packing arrangements in the isomorphs.

Examines the bromination of 3-chloroanilinium cation. Reactions of 3-chloroaniline with copper bromide in HBr solution; Stoichiometry in resulting crystalline compounds; Reduction of copper ions in bromination process.

The compound (Me4P)2ZnBr4, a member of the β-K2SO4 structure class, undergoes a phase transition at 84°C from the room temperature space group P121/c1 to the parent Pmcn structure. The room temperature structure corresponds to a ferrodistortive transition of B1g symmetry at the zone center. At room temperature, the compound has lattice constants a=9.501(1), b=16.055(2), c=13.127(2) A˚ and β=90.43(1)°. For the high temperature phase, the orthorhombic cell has dimensions a=9.466(2), b=16.351(3) and c=13.284(2) A˚. The structures consist of two crystallographically independent Me4P+ cations and the ZnBr42− anions. In the room temperature phase, all three ionic species show substantial displacement from the mirror plane perpendicular to the a-axis that exists in the high temperature phase, as well as rotations out of that plane. The thermal parameters of the cations are indicative of substantial librational motion. Measurements of lattice parameters have been made at 2–5°C intervals over the temperature range 40–140°C. The changes in the lattice constants appear continuous at Tc (within experimental limits) indicating that the phase transition is likely second-order. The a lattice constant shows an anomalous shortening as Tc is approached. Thermal expansion coefficients are calculated from this data. An application of Landau theory is used to derive the temperature dependencies of spontaneous shear strain and corresponding elastic stiffness constants associated with the primary order parameter. [Copyright &y& Elsevier]

The synthesis, structure, and magnetic properties of a novel oxalate-based bimetallic magnet obtained by using the chiral (S)-trimethyl-(1-phenyl-ethyl)-ammonium, ((S)-[PhCH(CH3)N(CH3)3]+), cation as template is reported. This compound can be formulated as [(S)-[PhCH(CH3)N(CH3)3]][Mn(CH3CN)_Cr(ox)3] (CH3CN)_(solvate), and it crystallizes in the chiral trigonal space group P3. It shows a distorted two-dimensional honeycomb structure formed by MnIII and CrIII ions connected through oxalate anions with [(S)-[PhCH(CH3)N(CH3)3]+ cations and solvent molecules intercalated between the oxalate layers. Two-thirds of the MnII ions of the honeycomb anionic network are heptacoordinated. This compound behaves as a soft ferromagnet with an ordering temperature of 5.6 K. [ABSTRACT FROM AUTHOR]