Crystal structure of catena-poly[bis(tetraethylammonium) [tetraaquatris(μ-dicyanamido-κ2 N 1:N 5)bis(dicyanamido-κN 1)dicobaltate(II)] dicyanamide]

The title structure comprises a cation-templated anionic CoII-dicyanamide network composed of μ 1,5-dicyanamide-bridged CoII chains inter-connected via μ 1,5-dicyanamide bridges.


Chemical context
Dicyanamide is a versatile ligand in the design and synthesis of coordination polymers due to its ability to coordinate to transition metal ions in a number of different modes involving some or all of its three nitrogen atoms (Batten & Murray, 2003). Reactions between transition metal ions and dicyanamide have mainly produced three types of coordination polymers, including the neutral binary systems of M II (dca) 2 (dca = dicyanamide), complexes derived from M II (dca) 2 by including a co-ligand, and cation-templated anionic [M II (dca) n ] (2-n) (n = 3,4) networks (Batten & Murray, 2003). These metal-dicyanamide coordination polymers exhibit a wide range of structures, from three-dimensional rutile-like structures for M II (dca) 2 to networks of reduced dimensions when a co-ligand or a counter-cation is included. Much of the interest in metal-dicyanamide coordination polymers has been focused on their structural diversities and their magnetic properties, particularly the long-range ferromagnetic ordering observed in some of the M II (dca) 2 networks (Kurmoo & Kepert, 1998). Compared to co-ligand-modified derivatives of M II (dca) 2 complexes, there are fewer examples of cationtemplated anionic [M II (dca) n ] (2-n) (n = 3,4) networks. We recently prepared the title compound, (N(C 2 H 5 ) 4 ) 2 [Co 2 -(H 2 O) 4 (C 2 N 3 ) 5 ](C 2 N 3 ), as a new example of a cationtemplated metal-dicyanamide coordination polymer. The title structure presents a unique single three-dimensional network of covalently linked chains rather than a two-dimensional structure as commonly observed in many other metal-dicyanamide coordination polymers. ISSN 2056-9890

Structural commentary
In the asymmetric unit of the title coordination polymer, there are two Co II ions, Co1 and Co2, linked by a 1,5 -bridging dicyanamide ligand (Fig. 1). Co2 is coordinated by three dicyanamide ligands via their terminal nitrogen atoms and two trans-positioned aqua ligands, forming an N 4 O 2 octahedral coordination sphere that is slightly elongated along the two Co-O bonds. Co1 is coordinated by one dicyanamide ligand via its terminal nitrogen atom and two trans-positioned aqua ligands. The likewise distorted octahedral N 4 O 2 coordination sphere around Co1 is completed by additional bonds to N20 ii and N15 xi [symmetry codes: (ii) x, 2 À y, À 1 2 + z; (xi) À 1 2 + x, 2 3 À y, À 1 2 + z] of two symmetry-generated dicyanamide ligands. The asymmetric unit also contains two tetraethylammonium counter-ions and a non-coordinating dicyanamide anion. Two nitrogen atoms, N3/N3 0 of one terminal ligand and N55/N56 of the anion, are disordered and were refined over two sets of sites.
In the crystal, a 1,5 -dca-bridged corrugated Co II chain can be seen parallel to the [101] direction and is composed of Co II ions generated by a c glide plane parallel to the ac plane. Among the four dca ligands on each Co II cation, three are in 1,5 -bridging mode with two bridging within the same chain and one bridging to another chain. The remaining fourth dca ligand [N1,C2,N3(N3 0 ),C4,N5 for Co1 and N21,C22,N23,C24, N25 for Co2] is mono-dentate non-bridging. In the chain, the distances between two neighboring Co II atoms linked by 1,5dca ligands alternate between 8.1484 (8) Å (Co1Á Á ÁCo2) and 8.5620 (8) 2005;Biswas et al., 2006). In the title structure, each chain is linked to four other chains generated by a c glide plane via the inter-chain 1,5 -dca ligands at each Co II site [Co1Á Á ÁCo2 ii , Co2Á Á ÁCo1 xii ; symmetry code: (xii) x, 2 À y, 1 2 + z; Co1 ix Á Á ÁCo2 v ; symmetry code: (ix) 1 2 + x, 2 3 À y, 1 2 + z, and Co2 ix Á Á ÁCo1 x ; symmetry code: (x) 1 2 + x, À 1 2 + y, 1 + z], resulting in a single three-dimensional network of covalently linked parallel chains. This is in contrast to the layered structures observed in a number of [M II (dca) n ] (2Àn) (n = 3, 4) networks that exhibit parallel sheets linked in the third dimension via 1,5 -dca ligands (Batten & Murray, 2003;Schlueter et al., 2005;Biswas et al., 2006). As a result of the mono-dentate nonbridging dca ligands in the title compound, the commonly observed (4,4) nets in other metal-dca networks are absent in its structure. However, channels extending along the b axis can   still be seen in the title structure and these are occupied by columns of tetraethylammonium cations (Fig. 2) and dca À anions. Similar to other cation-templated anionic [M II (dca) n ] (2Àn) (n = 3, 4) networks, interpenetration is not observed in the title structure due to the presence of tetraethylammonium cations in the void space, making these structures potential candidates for investigating their ability of storing guest molecules.

Supramolecular features
Hydrogen bonding is generally not observed amongst the neutral M II (dca) 2 networks. Upon introducing co-ligands or counter-ions, the derived M II (dca) 2 L n (L: co-ligand) and cation-templated [M II (dca) n ] (2-n) (n = 3,4) complexes display hydrogen bonding. In most of the M II (dca) 2 derivatives, the hydrogen bonds are of non-classical C-HÁ Á ÁX (X = N, O) types (Tong et al., 2003;Biswas et al., 2006;Rajan et al., 2013). In the title structure, hydrogen bonds are mainly of the classical O-HÁ Á ÁN type between OH groups of coordinating water molecules and nitrogen atoms of the non-coordinating dca À anion or the mono-dentate non-bridging dca ligands. Some hydrogen bonds in the title structure are bifurcated between two donor water molecules located on two neighboring chains stacked along the b axis and thus hold these chains in place along the b axis. Chains related by c glide-plane symmetry are primarily linked via single 1,5 -dca ligands as described in the previous section, but are further stabilized by hydrogen bonds across the non-coordinating dca À anions (N51 and N55/56) and by hydrogen bonds involving N1 and N25 of the mono-dentate non-bridging dca ligand. In addition to the O-HÁ Á ÁN hydrogen bonds, C-HÁ Á ÁN hydrogen bonds are also present in the title structure between C-H groups of the tetraethylammonium cations and dicyanamide amide nitrogen atoms (Fig. 2). The hydrogen-bond lengths and angles are summarized in Table 1.

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. Refinement. All H atoms were positioned geometrically ( C-H = 0.93/1.00 Å) and allowed to ride with U iso (H)= 1.2/1.5U eq (C). Methyl ones were allowed to rotate around the corresponding C-C. The asymmetric unit consists of a 2 Co units with each coordinated to four diamine ligand forming a square plane and two water ligands trans to each other.. The asymmetric unit also contains two tetraethylammonium counterions. Two nitrogen atoms, N3/N3′ and N55/N56, were disordered and refined in two parts each with their site occupation factors dependently refined. All of the water protons were obtained from a Difference Fourier map and refined freely.