Diaquabis[5-(2-pyridyl)-1H-tetrazolato-κ2 N 1,N 5]cobalt(II)

In the title compound, [Co(C6H4N5)2(H2O)2], the Co atom is bonded to two water molecules and two bidentate 5-(2-pyridyl)tetrazolate ligands resulting in a slightly distorted octahedral CoN4O2 coordination geometry. The CoII cation is situated on a crystallographic center of inversion. The asymmetric unit therefore comprises one-half of the molecule. The four N atoms belonging to two bidentate 5-(2-pyridyl)tetrazolate ligands lie in the equatorial plane and the two associated water molecules are observed in the axial coordination sites. The crystal structure exhibits a three-dimensional supramolecular network assembled by intermolecular O—H⋯N hydrogen bonds.

In the title compound, [Co(C 6 H 4 N 5 ) 2 (H 2 O) 2 ], the Co atom is bonded to two water molecules and two bidentate 5-(2pyridyl)tetrazolate ligands resulting in a slightly distorted octahedral CoN 4 O 2 coordination geometry. The Co II cation is situated on a crystallographic center of inversion. The asymmetric unit therefore comprises one-half of the molecule. The four N atoms belonging to two bidentate 5-(2-pyridyl)tetrazolate ligands lie in the equatorial plane and the two associated water molecules are observed in the axial coordination sites. The crystal structure exhibits a threedimensional supramolecular network assembled by intermolecular O-HÁ Á ÁN hydrogen bonds.

Comment
The design of different kinds of paramagnetic metal coordination architectures with appropriate organic radicals and coligands has been an important subject during the last decade because of its potential usages for molecule-based magnetic materials and optical devices (Caneschi et al., 1989;Tsukuda et al., 2002;Vostrikova et al., 2000;Kuchar et al., 2003). If organic radicals such as the tridentate nitronyl nitroxide radical or the bidentate nitroxide radical are used as an integral part of a ligand system a large number of building blocks with various potentional applications may be achieved. In this paper, we report the structure of the title compound, (I).
The molecular structure of the title compound is shown in Fig. 1. The Co II atom (site symmetry 1) is bonded to two water molecules and two bidentate 5-(2-pyridyl)tetrazolato ligands resulting in a slightly distorterd octahedral CoN 4 O 2 coordination geometry. The Co II cation is situated on a crystallographic center of inversion. The asymmetric unit therefore comprises one half of the molecule. The four nitrogen atoms belonging to two bidentate 5-(2-pyridyl)tetrazolato ligands lie in the equatorial plane and the two associated water molecules are observed in the axial coordination sites. In the equatorial plane, the Co-N bond lengths are in the range of 2.142 (2)-2.173 (2) Å. The Co-O axial bond length is 2.093 (2) Å. It is also worth noticing that the three-dimensional supramolecular structure is assembled via complicated hydrogen bonds, shown in Fig. 2. The hydrogen bonds are listed in Table 1.

Experimental
A mixture of cobalt(II) dichloride hexhydrate (1 mmoL), 5-(2-pyridyl)tetrazolate (1 mmoL) in 20 ml mixed solvate(1:1) of methanol and water was refluxed for several hours. After cooling down the solution was filterated and the filtrate was kept in the ice box. One week later, red blocks of (I) were obtained with a yield of ca 56%. Anal. Calc. for C 12 H 12 CoN 10 O 2 : C 37.19, H 3.10, N 36.15%; Found: C 37.22, H 3.08, N 36.11%.

Refinement
All H atoms were placed in calculated positions with C-H = 0.93Å and refined as riding with U iso (H) = 1.2U eq (C). The H atoms of the water molecule were located from difference density maps and were refined with distance restraints of d(H-H)  Fig. 1. The molecular structure of (I), around Co II , displacement ellipsoids for the non-hydrogen atoms are drawn at the 50% probability level. Crystal data [Co(C 6  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.