Poly[[μ4-bis(4-pyridylcarbonyl)piperazine-κ4 N:N′:O:O′]bis(thiocyanato-κN)cobalt(II)]

In the title compound, [Co(NCS)2(C16H16N4O2)]n, the octahedrally coordinated CoII ion lies on a crystallographic inversion center, with trans isothiocyanate ligands. Pyridyl N-donor atoms and formyl O-donor atoms from exotetradentate bis(4-pyridylcarbonyl)piperazine (4-bpfp) ligands link the Co(NCS)2 units into a [Co(NCS)2(4-bpfp)]n coordination polymer layer that is oriented parallel to (101). The layers stack along [010] to construct the pseudo-three-dimensional structure.

We gratefully acknowledge the donors of the American Chemical Society Petroleum Research Fund for funding this work. ZMW thanks Dr Richard Staples for instruction in the use of the crystallographic software.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HY2308).
of hydrogen-bond accepting formyl oxygen atoms in a similar ligand, we attempted to prepare a cobalt phthalate coordination polymer containing bis(4-pyridylcarbonyl)piperazine (4-bpfp). Use of cobalt(II) thiocyanate as the metal precursor afforded pink plates of the title compound.
The title compound crystallizes in the centrosymmetric triclinic space group with an asymmetric unit consisting of a Co II ion on a crystallographic inversion center, one isothiocyanate ligand bound via its N atom, and one-half of a 4-bpfp molecule.
The coordination environment at Co is a slightly distorted [CoN 4 O 2 ] octahedron ( Fig. 1), with trans isothiocyanate ligands, trans pyridyl N atom donors from two 4-bpfp ligands, and trans formyl O atom donors from two other 4-bpfp ligands.
Each 4-bpfp ligand is exotetradentate, ligating to Co atoms through both pyridyl N atoms and both formyl O atoms. As a result, [Co(NCS) 2 (4-bpfp)] n coordination polymer layers are formed (Fig. 2), which are oriented parallel to the ac crystal planes. Fourteen-membered [CoOC 4 N] 2 circuits, whose centroids rest on crystallographic inversion centers, are evident within the layer motifs. The Co···Co distances across these circuits denote the a lattice parameter. The through-ligand Co···Co distances across the full span of the 4-bpfp ligands measure 16.471 (4) Å.
Adjacent [Co(NCS) 2 (4-bpfp)] n layers stack in an AAA pattern along the b direction (Fig. 3), with the isothiocyanate ligands projecting above and below the layer planes. Crystal packing forces cause aggregation of the layer motifs into pseudo three-dimensional crystal structure of the title compound.

Experimental
All starting materials were obtained commercially, except for 4-bpfp, which was prepared by a published procedure (Hou et al., 2003). Cobalt(II) thiocyanate (130 mg, 0.74 mmol), phthalic acid (123 mg, 0.74 mmol) and 4-bpfp (110 mg, 0.37 mmol) were placed into 10 ml H 2 O in a 23 ml Teflon-lined Parr acid digestion bomb. The bomb was heated at 393 K for 48 h and was then allowed to cool to room temperature. Pink plates of the title compound were obtained along with a white powdery solid.

Refinement
All H atoms bound to C atoms were placed in calculated positions, with C-H = 0.93 (CH) and 0.97 (CH 2 ) Å, and refined in a riding mode with U iso (H) = 1.2U eq (C).