Temperature-induced reversible structural phase transition of N-chloromethyl-1,4-diazabicyclo[2.2.2]octonium trichloroaquo-manganese(II)

A novel mononuclear metal–organic compound, N-chloromethyl-1,4-diazabicyclo-[2.2.2]octonium trichloroaquomanganese (II), Mn(LCH2Cl) (H2O) Cl3 (1) (L + CH2Cl = N-chloromethyl-1,4-diazabicyclo[2.2.2]octonium ion) was synthesized. Differential scanning calorimetry (DSC) measurement detected that this compound underwent a reversible phase transition at ca. 187.5 K with a hysteresis of 1.5 K width, The single crystal X-ray diffraction data suggested that the phase transition undergoes from a room temperature paraelectric phase with a space group of Pnma (a = 18.219(1) Å, b = 8.945(6) Å, c = 8.191(5) Å, V = 1334.9(2) Å3 and Z = 4) to a low temperature paraelectric one with a space group of P21/n (a = 8.117(2) Å, b = 17.956(5) Å, c = 8.923(2) Å, β = 91.819(3)°, V = 1299.9(6) Å3 and Z = 4), and symmetry breaking occurred with an Aizu notation of mmmF2/m. The ordering of twisting motions of dabco ring may drive the phase transition.