An interesting magnetic behavior in molecular solid containing one-dimensional Ni(III) chain Chunlin Ni a , Dongbin Dang a , You Song a , Song Gao b , Yizhi Li a , Zhaoping Ni a , Zhengfang Tian a , Lili Wen a , Qingjin Meng a, * a State Key Laboratory of Coordination Chemistry, Department of Chemistry, Coordination Chemistry Institute, Nanjing University, Hankou Road 22, Nanjing, Jiangsu 210093, PR China b State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, Beijing 100871, PR China Received 26 June 2004; in final form 16 August 2004 Abstract The preparation, crystal structure and magnetic properties of a new ion-pair complex, [BrFBzNH 2 Py][Ni(mnt) 2 ] (1) [BrFBzNH 2 Py + = 1-(4 0 -bromo-2 0 -flurobenzyl)-4-aminopyridinium, mnt 2 = maleonitriledithiolate] are reported. The NiðmntÞ  2 ani- ons and [BrFBzNH 2 Py] + cations of 1 form completely segregated uniform stacking columns. The intrachain NiNi separation is 4.045 A ˚ in the NiðmntÞ  2 stacking column. Magnetic susceptibility measurements for 1 in the temperature range 2.0–300 K show the occurrence of significant ferromagnetic interaction in the high-temperature phase (HT), spin gap in the low-temperature phase (LT) and weak ferromagnetism due to spin canting below 5 K. Ó 2004 Elsevier B.V. All rights reserved. 1. Introduction The design of new molecule-based magnets with higher critical temperatures T c has been one of the ma- jor challenges in magneto-chemistry [1,2]. Recently, bis-1,2-dithiolene transition metal complexes have at- tracted intensive interest because of their attractive properties and application in many fields [3,4]. The ion-pair complexes which are comprised of organic or inorganic cations and anions have a unique position in this field. One class of these complexes is exemplified by [Ni(mnt) 2 ] complexes [5–7]. Especially, the discovery in 1996 of the ferromagnetic complex containing NiðmntÞ  2 ion, NH 4 Æ Ni(mnt) 2 Æ H 2 O, revived the inter- est in Ni(mnt) 2 complexes as building blocks for new molecular magnets [8]. Recently, much of our attention has been directed at a new class of ion-pair complexes [RbzPy] + [Ni(mnt) 2 ]  ([RbzPy] + = derivatives of ben- zylpyridinium). These efforts are motivated by the de- sire to tune the stacking pattern of NiðmntÞ  2 complexes, and modulate the magnetic properties by the molecular conformation of the attractive RbzPy + cation. Versatile magnetic properties, such as magnetic transition from ferromagnetic coupling to diamagnet- ism, meta-magnetism, ferromagnetic ordering at low temperature, and Spin-Peierls-like transitions, had been founded in our pervious Letters [9,10]. With the view to further determine the structure-function relationship for this new class of magnetic materials, in this contri- bution we wish to report the synthesis, crystal struc- ture, and magnetic properties of a novel ion-pair complex [BrFBzNH 2 Py][Ni(mnt) 2 ](1) which exhibits a complicated magnetic transition from ferromagnetic interaction to spin gap, then to spin canting, as the temperature is lowered. 0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.08.060 * Corresponding author. Fax: +86 25 83314502. E-mail address: njuchem1024@163.com (Q. Meng). www.elsevier.com/locate/cplett Chemical Physics Letters 396 (2004) 353–358