Magnetic canting or not? Two isomorphous 3D Co II and Ni II coordination polymers with the rare non-interpenetrated (10,3)-d topological network, showing spin-canted antiferromagnetism only in the Co II system{ Jian-Rong Li, a Qun Yu, a Ying Tao, a Xian-He Bu,* a Joan Ribas b and Stuart R. Batten c Received (in Cambridge, UK) 15th January 2007, Accepted 9th February 2007 First published as an Advance Article on the web 1st March 2007 DOI: 10.1039/b700569e The in situ solvothermal reaction of 3,4-dicyano-1,2,5-thiadia- zole with MCl 2 (M = Co, Ni) and NaOH afforded two isomorphous complexes, [M 2 (L) 2 (H 2 O) 2 ] n (L = 2,1,3-thiadia- zole-4,5-dicarboxylate), which exhibit a rare non-interpene- trated (10,3)-d (utp) network topology and interesting magnetic behaviors: spin-canted antiferromagnetism for the Co II com- plex, but simple antiferromagnetic coupling for the Ni II . Construction of metal–organic coordination polymers has attracted intense attention, owing to their intriguing network topologies and peculiar properties. 1 Intelligent ligand design and the proper choice of a metal center are the main keys to the design of such coordination polymers. In this context, some progress has been achieved in the construction of magnetic materials with extended structures by using multi-functional organic carboxylic acid ligands to assemble paramagnetic metal ions; however it still remains difficult to predict their structures and magnetic behaviors due to the diversity of coordination and the complicated nature of magnetic interactions. 2 Thus, the search for magnetic metal– organic framework structures has become a major challenge. As an example, imidazole-4,5-dicarboxylic acid has been used in this field, 3 whereas an analog of it, 2,1,3-thiadiazole-4,5-dicarboxylic acid (H 2 L, Chart 1S, ESI{), is still unexplored to date. Herein, we report the first crystallographically characterized metal complexes of H 2 L, [M 2 (L) 2 (H 2 O) 2 ] n (M = Co, 1; Ni, 2), which are isomorphous and exhibit a rare three-dimensional (3D) (10,3)-d (utp) network topology and unexpected magnetic behaviors: the Co II complex shows spin-canting, 4 whereas the Ni II complex shows only simple antiferromagnetic coupling. Complicated magnetic anisotropy has significant influence on the bulk magnetic properties. Indeed, Co II , owing to its single-ion anisotropy, is a good candidate for giving a spin-canted system, although the number of Co II complexes with this property is limited. It is known that a-CoSO 4 is a 3D canted antiferromagnet, 5 as well as a-Co(dca) 2 (dca = dicyanamide). 6 Recently, another 3D Co II complex showing spin canting was reported by Chen and co- workers. 7 With azide and 4,49-bipyridine, a 2D network structure has been reported with this behavior. 8 In fact, very few low- dimensional framework complexes with this behavior have been reported. 9 It is also worth mentioning that the first and extremely rare discrete molecule showing this magnetic ordering (3D by nature) was a Co II complex, {K 2 [CoO 3 PCH 2 N- (CH 2 CO 2 ) 2 ]} 6 ?xH 2 O. 10 The in situ solvothermal reaction of 3,4-dicyano-1,2,5-thiadia- zole (DCT) with CoCl 2 ?6H 2 O and NaOH in H 2 O–EtOH (1 : 1) gave brownish red crystals of 1 (Fig. 1),{ which have high thermal stability (decomposes above 300 uC, Fig. 3S, ESI{). Its phase purity was confirmed by XRPD (Fig. 1S, ESI{) and EA. It should be pointed out that in the solvothermal process the two nitriles of DCT have been converted to carboxylate groups, giving the ligand L 22 , which has been observed before. 11 Single-crystal X-ray diffraction§ of 1 indicates that it crystallizes in the chiral space group P2 1 and has a 3D framework structure. In the crystal- lographic asymmetric unit there each exist two unique but chemically similar Co II ions and L 22 ligands, and two coordinated H 2 O molecules (Fig. 1 and 4S, ESI{). Each Co II lies on a general position and shows a distorted octahedral geometry formed by three O and two N atoms of three distinct L 22 ligands and one H 2 O molecule. Two L 22 chelate one Co II ion in a kN,O-mode, while the third L 22 binds Co II in a monodentate mode via one carboxylate O atom. Thus each L 22 adopts a m 3 -kN,O:kN9,O9:kO0 a Department of Chemistry, Nankai University, Tianjin 300071, China. E-mail: buxh@nankai.edu.cn; Fax: +86-22-23502458 b Departament de Quı ´mica Inorga `nica, Universitat de Barcelona Diagonal, 647, 08028, Barcelona, Spain c School of Chemistry, Monash University, Victoria, 3800, Australia { Electronic supplementary information (ESI) available: Synthesis, characteristics, XRPD, IR, TG-DTA, X-ray crystallographic data and additional views of structures. See DOI: 10.1039/b700569e Fig. 1 Left: scheme showing the preparation of 1 and 2; right: local coordination geometries and H-bonding interactions (striped bonds) in 1. Co1 atoms are shown in light purple, Co2 as dark purple, and the two crystallographically distinct L have their N atoms depicted in different shades of blue. C are shown as green, O as red, S as yellow, and H as grey. COMMUNICATION www.rsc.org/chemcomm | ChemComm 2290 | Chem. Commun., 2007, 2290–2292 This journal is ß The Royal Society of Chemistry 2007