Structure and magnetic susceptibility of (PhCH 2 NEt 3 ) 2 Cu 2 Br 6 : Unprecedented similarity to the Haldane state with potential competing interactions

Abstract

Abstract The synthesis, crystal structure and magnetic susceptibility of a new binuclear Cu(II) complex templated by benzyltriethylammonium as a counterion, are reported. The X-ray crystal structure reveals that this compound is composed of an anionic dimer and organic cation. The complex, (PhCH2NEt3)2Cu2Br6 crystallizes in the triclinic space group P 1 ¯ with two molecules in the unit cell. In the crystal structure, the inorganic layer, built up by the independent anionic binuclear moiety [Cu2Br4-(μ-Br)2]2−, is connected to the organic layers through C H⋯Br hydrogen bonding to build a three-dimensional network. Each copper ion exhibits an intermediate geometry between square planar and tetrahedral. The Cu2Br2 structural core is characterized by a bridging Cu Br Cu angle of 91.335° and a short Cu Cu separation of 3.487 A. Magnetic interactions in the binuclear copper(II) material were studied with the aim of elucidating magneto-structural correlations. The magnetic susceptibility data (1.8–300 K) show a maximum in χ near 8 K with a significant decrease in susceptibility at lower temperatures. The best fit was obtained using the strong-rail ladder model which resulted in exchange values of −14.2(1) K for the rail and +3.6(2) K for the rung. The existence of ferromagnetic exchange across the rungs of this system may induce a transition from an S = ½ ladder-like system to an S = 1 Haldane system at low temperatures.