supplementary materials

It is widely known that diverse coordination architectures can be constructed by coordinative bonds using metal ions to combine with multifunctional ligands (Moulton & Zaworotko, 2001). Aside from that, supramolecular interactions such as hydrogen bonding and aromatic stacking are usually used as the assistant tools to extend or sustain the resultant structures (Roesky & Andruh, 2003; Ye et al., 2005; Du et al., 2007). It has been reported that 1,2,4-triazole a is stronger σ-donor and weaker π-acceptor than 2,2'-bipyridine and their derivatives have gained considerable interest in recent years in the development of polypyridyl transition metal complexes (Haasnoot, 2000). Recently, one triazole derivative, 4-amino-3,5-di-2-pyridyl-1,2,4-triazole (2-bpt) has attracted our interest because of its potential ability for providing multi-coordination modes and generating hydrogen-bonding and/or aromatic stacking interactions (Van Koningsbruggen et al., 1998; Moliner et al., 2001; García-Couceiro et al.,2004; Peng et al., 2006). With respect to the Ni^II-2-bpt complexes, mononuclear and binuclear molecules have been reported (Keij et al., 1984; Tong et al., 2007), in which anions such as Cl^- and N₃^- are existent, coordinating to the metal ion or serving as lattice entity to charge compensate. Here we report a new mononuclear Ni^II-2-bpt complex [Ni(2-bpt)₂(H₂O)₂](ClO₄)₂ (I), in which 2-bpt acts as a chelating reagent and supramolecular interactions such as hydrogen bonds and aromatic stacking can extend the mononuclear molecule into a three-dimensional architecture.

The molecular structure of (I) reveals a neutral centrosymmetric mononuclear complex, with the asymmetric unit of which comprising a half-occupied Ni^II atom, one 2-bpt molecule, one water ligand as well as one lattice ClO₄^- anion. As depicted in Fig. 1, the distorted octahedral Ni^II center, which is located on a crystallographic inversion center, is defined by two pairs of chelating nitrogen donors from two individual 2-bpt molecules as well as two water ligands. The axial Ni—N distances [2.037 (3) Å] are significantly shorter than those of the Ni—O and Ni—N equatorial lengths [2.101 (3) and 2.111 (3) Å]. In the structure, 2-bpt molecule exhibits trans-conformation and intramolecular N5—H5B···N6 hydrogen bond (Table 2) can be detected between the adjacent amino and pyridyl groups. Along the [011] plane, such mononuclear units related by 2-fold screw operation are interlinked by intermolecular O1—H1B···N6 interactions (Table 1) involving water ligands and pyridyl rings of 2-bpt to generate a 2-D net with simple (4,4) topology, (Batten et al., 1998) as shown in Fig. 2. The dimension of the large grid of the net is 9.8005 * 9.8005 Ų. Furthermore, the hydrogen-bonded 2-D nets are interdigitated and interlayer π···π stacking interaction can be observed between the nearly parallel pyridyl of the 2-bpt molecules as expected, which can extend the structure to a 3-D supramolecular architecture (Fig. 3). The center-to-center and center-to-plane separations of the pyridyl groups are 3.809 and 3.499/3.294 Å (with a dihedral angle of 6.9°), respectively. What's more, the lattice ClO₄^- anions are located in the interlayer space [a volume of 308.9 Å, 20.2% of the unit-cell volume as evaluated by PLATON (Spek, 2009)] and also hydrogen bonded to the 3-D aggregate via multiple O_water—H···OClO₄^- and N_amino—H···OClO₄^- interactions (Table 1).