title: Unusual magnetic properties of one-dimensional molecule-based magnets associated with a structural phase transition.
abstract: Three ion-pair complexes, [RbzPy](+)[Ni(mnt)(2)](-) (mnt(2)(-) = maleonitriledithiolate; [RbzPy](+) = 4-R-benzylpyridinium; R = Br (1), Cl (2), and NO(2) (3)), with unusual magnetic properties have been synthesized and characterized. The crystal structures of 1 and 2 have been solved. The two complexes belong to the P2(1)/c space group with Z = 4 and C(20)H(11)BrN(5)NiS(4), a = 12.0744(17) A, b = 26.369(4) A, c = 7.440(3) A, and beta = 102.63(3) degrees for 1 and C(20)H(11)ClN(5)NiS(4), a = 12.105(2) A, b = 26.218(4) A, c = 7.374(2) A, and beta = 102.55(2) degrees for 2, respectively. The [Ni(mnt)(2)](-) anions in 1-3 form uniformly spaced one-dimensional (1-D) magnetic chains of s = 1/2 at room temperature. The temperature dependences of the susceptibility for 1-3 show that they undergo phase transitions. All three complexes are paramagnetic in their high-temperature (abbreviation HT) phase and diamagnetic in the low-temperature (abbreviation LT) phase because of strong dimerization along the stacking direction. The results of thermal analysis (DSC) further confirm that the phase transition for 1 and 2 is first-order but maybe second-order for 3. The phenomena observed in this study are similar to those of the 1-D radical systems.
authors.affiliation: Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P.R. China.
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Ren
authors.forename: Qingjin
authors.initials: Q
authors.lastname: Meng
authors.forename: You
authors.initials: Y
authors.lastname: Song
authors.forename: Changsheng
authors.initials: C
authors.lastname: Lu
authors.forename: Chuanjiang
authors.initials: C
authors.lastname: Hu
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Chen