Journal of Solid State Chemistry 178 (2005) 100–105 Synthesis, crystal structure and magnetic property of a new 1D molecular material [1-(4 0 -chlorobenzyl)–4-aminopyridinium](+) bis(maleonitriledithiolato)nickel(–) Chunlin Ni a , Dongbin Dang a , Yizhi Li a , Song Gao b , Zhaoping Ni a , Zhengfang Tian a , Qingjin Meng a,Ã a State Key Laboratory of Coordination Chemistry, Department of Chemistry, Coordination Chemistry Institute, Nanjing University, Hankou Road, Number 22, Nanjing city, Jiangsu province 210093, People’s Republic of China b State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, 100 871 Beijing, People’s Republic of China Received 23 May 2004; received in revised form 22 June 2004; accepted 1 November 2004 Abstract A new ion-pair complex, [1-(4 0 -chlorobenzyl)–4-aminopyridinium](+)bis(maleonitrile-dithiolato)nickel(),[ClbzPyNH 2 ] [Ni(mnt) 2 ](1), has been prepared and characterized. X-ray single crystal structure conforms that the Ni(mnt) 2  anions and [ClbzPyNH 2 ] + cationsof 1 formcompletelysegregateduniformstackingcolumnswiththeNi?Nidistance3.944A ˚ intheNi(mnt) 2  stacking column. The temperature dependence of the magnetic susceptibility reveals that 1 undergoes a magnetic transition, and exhibits ferromagnetic interaction in the high-temperature phase and spin gap system in the low-temperature phase. r 2004 Elsevier Inc. All rights reserved. Keywords: 1-(4 0 -Chlorobenzyl)–4-aminopyridinium; Bis(maleonitriledithiolate)nickelate(III) complex; X-ray structure; Ferromagnetic interaction; Spin gap 1. Introduction Transition metal complexes of 1,2-dithiolenes are currently of extensive interest owing to their application aspotentiallybuildingblocksinmolecular-basedmateri- als showing magnetic, superconducting, and optical properties [1–3]. The complexes containing [M(mnt) 2 ]  (mnt 2 ¼ maleonitriledithiolate, M ¼ Ni(III) or Pt(III)) ions) have attracted much attention because they show novel magnetic properties [4–11]. Especially, the discovery of the ferromagnetic complex containing Ni(mnt) 2  ion, NH 4 ?Ni(mnt) 2 ?H 2 O, in 1996, strongly stimulated the study on Ni(mnt) 2 complexes as building blocks for new molecular magnets [12]. One of the current interests in our laboratory has been developed new class of complexes [RbzPy] + [M(mnt) 2 ]  ([RbzPy] + ¼ benzylpyridinium derivative), and found that these ion-pair complexes exhibit versatile magnetic properties such as ferromagnetic ordering at low temperature [13],magnetictransitionfromferromagnetic coupling to diamagnetism [14], meta-magnetism [15] and spin-Peierls-like transitions [16–18]. In these ion-pair complexes, the prominent structural feature is that the Ni(mnt) 2  ions and [RbzPy] + cations stack into well- segregated columns in the solid state. In our continuing researchwith[M(mnt) 2 ]  complexes,wehavefocusedon thefollowingtwostrategies.Oneistofindmoresuitable multifunctional organic cations to tune the crystal stacking structure of [M(mnt) 2 ] anion with a view to obtaining ideal molecular magnets. The second strategy is to establish a relationship between the magnetic interactions and the stacking pattern of anions or cations. Herein, we report the crystal structure and magnetic property of a novel 1D molecular material [1-(4 0 -chlorobenzyl)–4-aminopyridinium][Ni(mnt) 2 ](1) ARTICLE IN PRESS www.elsevier.com/locate/jssc 0022-4596/$-see front matter r 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jssc.2004.11.002 Ã Corresponding author. Fax: +862583314502. E-mail address: njuchem1024@163.com (Q. Meng).