Cobalt(II) chloride complexes with 1,1'-dimethyl-4,4'-bipyrazole featuring first- and second-sphere coordination of the ligand.

In catena-poly[[dichloridocobalt(II)]-μ-(1,1'-dimethyl-4,4'-bipyrazole-κ(2)N(2):N(2'))], [CoCl2(C8H10N4)]n, (1), two independent bipyrazole ligands (Me2bpz) are situated across centres of inversion and in tetraaquabis(1,1'-dimethyl-4,4'-bipyrazole-κN(2))cobalt(II) dichloride-1,1'-dimethyl-4,4'-bipyrazole-water (1/2/2), [Co(C8H10N4)2(H2O)4]Cl2·2C8H10N4·2H2O, (2), the Co(2+) cation lies on an inversion centre and two noncoordinated Me2bpz molecules are also situated across centres of inversion. The compounds are the first complexes involving N,N'-disubstituted 4,4'-bipyrazole tectons. They reveal a relatively poor coordination ability of the ligand, resulting in a Co-pyrazole coordination ratio of only 1:2. Compound (1) adopts a zigzag chain structure with bitopic Me2bpz links between tetrahedral Co(II) ions. Interchain interactions occur by means of very weak C-H...Cl hydrogen bonding. Complex (2) comprises discrete octahedral trans-[Co(Me2bpz)2(H2O)4](2+) cations formed by monodentate Me2bpz ligands. Two equivalents of additional noncoordinated Me2bpz tectons are important as `second-sphere ligands' connecting the cations by means of relatively strong O-H...N hydrogen bonding with generation of doubly interpenetrated pcu (α-Po) frameworks. Noncoordinated chloride anions and solvent water molecules afford hydrogen-bonded [(Cl(-))2(H2O)2] rhombs, which establish topological links between the above frameworks, producing a rare eight-coordinated uninodal net of {4(24).5.6(3)} (ilc) topology.