Two halide exchange in copper(II) halide dimers: (Morpholinium)2Cu2Cl x Br6− x

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]