Crystal structure of aquatris(isonicotinamide-κN)bis(thiocyanato-κN)cobalt(II) 2.5-hydrate

In the crystal structure of the title compound, the CoII cations are coordinated by two terminal N-bonded thiocyanate anions, three isonicotinamide ligands and one water molecule into discrete octahedral complexes that are connected by classical and non-classical hydrogen bonding into a three-dimensional network.

The asymmetric unit of the title compound, [Co(NCS) 2 (C 6 H 6 N 2 O) 3 (H 2 O)]Á-2.5H 2 O, comprises one Co II cation, three isonicotinamide ligands, two thiocyanate anions, one aqua ligand and two water solvent molecules in general positions, as well as one water solvent molecule that is located on a twofold rotation axis. The Co II cations are octahedrally coordinated by two terminally N-bonded thiocyanate anions, one water molecule and three isonicotinamide ligands, each coordinating via the pyridine N atom. The discrete complexes are linked by intermolecular O-HÁ Á ÁO, N-HÁ Á ÁO and N-HÁ Á ÁS hydrogen bonding into a three-dimensional network that contains cavities in which the solvent water molecules are located. The latter are linked by further O-HÁ Á ÁO hydrogen bonds to the network. There are additional short contacts present in the crystal, indicative of weak C-HÁ Á ÁS, C-HÁ Á ÁO and C-HÁ Á ÁN interactions.

Chemical context
The synthesis of new coordination polymers with cooperative magnetic properties is still a major field in coordination chemistry. In this context, compounds that show a slow relaxation of the magnetization, such as, for example, single chain magnets, are of special interest because of their potential for future applications (Dhers et al., 2015;Caneschi et al., 2001;Liu et al., 2010). To trigger such behavior, cations of large magnetic anisotropy, such as, for example, Mn II , Fe II or Co II , must be linked by ligands into chains that can mediate a magnetic exchange. Therefore, we are generally interested in the synthesis and the magnetic properties of Co-and Fecontaining thio-and selenocyanate coordination polymers (Werner et al., 2014(Werner et al., , 2015aBoeckmann et al., 2012;Wö hlert et al., 2014). This also includes the synthesis of discrete complexes with a terminal coordination because such compounds can be transformed into the desired polymeric compounds by thermal decomposition reactions (Nä ther et al., 2013). In the course of our investigations, we attempted to prepare Co-containing thiocyanate coordination compounds with isonicotinamide as ligand and obtained crystals of the title compound, [Co(NCS) 2 (C 6 H 6 N 2 O) 3 (H 2 O)]Á2.5H 2 O. However, this phase could not be prepared as a pure phase. To identify these crystals, a single crystal structure analysis was performed and the results are reported herein.

Structural commentary
The asymmetric unit comprises one cobalt(II) cation, two thiocyanate anions, three isonicotinamide ligands and three ISSN 2056-9890 water molecules (one as a ligand and two as solvent molecules) that occupy general positions as well as one water solvent molecule that is located on a twofold rotation axis (Fig. 1). The Co II cation is coordinated by one water molecule, two terminal N-bonded thiocyanate anions and three terminal isonicotinamide ligands bonded through the pyridine N atom. The Co-N distances to the negatively charged anionic ligands of 2.0746 (1) and 2.0834 (17) Å are shorter than that to the neutral isonicotinamide ligands [Co-N: 2.1725 (16)-2.2059 (15) Å ]. The bond angles around the Co II atom deviate slightly from the ideal values [cis angles: 85.81 (6)-92.60 (7) ; trans angles: 173.17 (7)-177.74 (6) ]. The resulting coordination polyhedron can be described as a slightly distorted octahedron (Fig. 1) .

Supramolecular features
In the crystal structure, four symmetry-related complexes are linked by intermolecular O-HÁ Á ÁO hydrogen bonding between the water H atoms of the coordinating water molecules of two complexes and the carbonyl O acceptor atoms of two additional complexes into eight-membered rings that are located on centres of inversion (Fig. 2). These tetramers are further connected by intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonding between water molecules and amide H atoms, respectively, and the carbonyl as well as water acceptor-O atoms into a three-dimensional network (Fig. 2). There are additional hydrogen bonds between the amide H atoms and the S atoms of the anionic ligands. The N-HÁ Á ÁS angles deviate only slightly from 180 . Within this network cavities are formed, in which additional water molecules are embedded. These solvent molecules are linked by (water)O-HÁ Á ÁO(water) hydrogen bonding into chain-like aggregates that consist of five water molecules each, whereby the aggregates are located on twofold rotation axes. These water aggregates are linked by additional O-HÁ Á ÁO hydrogen bonds involving the carbonyl O acceptor atoms of the isonicotinamide ligands to the network. Finally, there are several short contacts indicative of weak C-HÁ Á ÁS, C-HÁ Á ÁO and C-HÁ Á ÁN interactions. Numerical values of the hydrogenbonding interactions are collated in Table 1.

Database survey
Some metal compounds based on isonicotinamide ligands and thiocyanates anions are reported in the Cambridge Structure Database (Version 5.37, last update 2015; Groom et al., 2016). Two Ni-clathrates, one with 9,10-anthraquinone and the other with pyrene, in which Ni II cations are connected by -1,3bridging thiocyanate ligands into coordination polymers (Sekiya et al., 2009) and one very similar cadmium compound with 9,10-dichloroanthracene as clathrate molecule (Sekiya & Nishikiori, 2005). Moreover, one compound comprising a three-dimensional coordination network based on Cd(SCN) 2 (Yang et al., 2001) and a compound built up of Cu-NCS layers are also reported (Ðaković et al., 2010). Very recently we reported two discrete complexes with isonicotinamide as coligand, one of which is based on Zn(NCS) 2 with the Zn II cation in tetrahedral coordination (Neumann et al., 2016a) while the other is based on Co(NCS) 2 in which the Co II cation is octahedrally coordinated (Neumann et al., 2016b).

Synthesis and crystallization
Cobalt thiocyanate and 4-isonicotinamide were obtained from Alfa Aesar and were used without any further purification. Crystals suitable for single crystal structure analysis were obtained from a mixture of 26.3 mg Co(NCS) 2 (0.15 mmol) and 73.3 mg 4-isonicotinamide (0.6 mmol) in demineralized water (1.5 ml) within three days. The title compound could not be prepared as a single phase and was always contaminated with a second crystalline phase which could not be identified so far.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-H and N-H hydrogen atoms were positioned in calculated positions with U iso (H) = 1.2U eq (C, N) using a riding model with C-H = 0.95 Å for aromatic and N-H = 0.88 Å for amide H atoms. The water hydrogen atoms were located in a difference map, and their bond lengths were constrained to O-H = 0.84 Å and with U iso (H) = 1.5U eq (O). Table 1 Hydrogen-bond geometry (Å , ).

Aquatris(isonicotinamide-κN)bis(thiocyanato-κN)cobalt(II) 2.5-hydrate
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.