Reversible ferroelastic phase transition of N-chloromethyl-1,4-diazabicyclo[2.2.2]octonium trichlorobromoaquo copper(II)

A novel mononuclear metal-organic compound, N-chloromethy1-1,4-diazabicyclo-[2.2.2]octonium trichlorobromoaquo copper(II), Cu(LCH2Cl) (H2O) Br2.75Cl0.25 (1) (L + CH2Cl= N-chloromethy1-1,4-diazabicyclo[2.2.2] octonium ion) was synthesized. Differential scanning calorimetry (DSC) results showed that this compound underwent a reversible phase transition at ca. 190 K with a hysteresis of 11 K width and single crystal X-ray diffraction data suggested that there was a transition from a room-temperature phase with the space group of Pnma (a = 17.790(2)angstrom, b = 9.0000(12)angstrom, c = 8.2263(11)angstrom, V = 1317.1(3)angstrom(3) and Z = 1) to a low-temperature one with the space group of P2(1)/n (a = 8.184(4)angstrom, b = 17.681(8)angstrom, c = 8.941(4)angstrom, beta = 91.218(6)degrees, V = 1293.5(10)angstrom(3) and Z = 1). Symmetry breaking occurred with the Aizu notation of mmmF2/m. The ordering of twisting motions of 1,4-diazoniabicylo[2,2,2]octane ring may drive the phase transition. (C) 2014 Elsevier B.V. All rights reserved.