catena-Poly[[dichloridomercury(II)]-N′-nicotinoylnicotinohydrazide]

The title complex, [HgCl2(C12H10N4O2)]n, is composed of one HgII ion, one nnh ligand (nnh = N′-nicotinoylnicotinohydrazide) and two coordinated chloride ions. The HgII ion shows a distorted tetrahedral geometry, being surrounded by two N atoms from two nnh ligands and two chloride ions. Due to the bridging role of nnh, the HgII atoms are connected into polymeric chains along the c axis, which are further interlinked via N—H⋯O and C—H⋯Cl hydrogen-bonding interactions, forming a three-dimensional network.

The title complex, [HgCl 2 (C 12 H 10 N 4 O 2 )] n , is composed of one Hg II ion, one nnh ligand (nnh = N 0 -nicotinoylnicotinohydrazide) and two coordinated chloride ions. The Hg II ion shows a distorted tetrahedral geometry, being surrounded by two N atoms from two nnh ligands and two chloride ions. Due to the bridging role of nnh, the Hg II atoms are connected into polymeric chains along the c axis, which are further interlinked via N-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen-bonding interactions, forming a three-dimensional network.

Teng Ma, Yuanlu Wang, Fengliang Wang and Fei Li Comment
Flexible ligands containing N-donor heterocyclic groups, such as pyridyl, pyrazinyl, and triazolyl (see: Zhang et al., 2010;Ma et al., 2005;Tao et al., 2010), have been widely studied in the realm of metal-organic coordination assemblies.
With regard to this, N′-nicotinoylnicotinohydrazide (nnh), an interesting ligand with flexible spacer and multiple binding sites, has attract our attention. Herein, we report the title complex [Hg(nnh)Cl 2 ] n , which crystallizes in the monoclinic space group P2/c, and shows a one-dimensional polymeric array and H-bonding supramolecular network.
As shown in Fig.1, the asymmetric unit of the complex is provided by a Hg II center, one nnh ligand and two chloride ions. The Hg II ion is tetra-coordinated to two nitrogen atoms from two nnh ligands with the Hg-N distance of 2.475 (2) Å, as well as two chloride ions with the Hg-Cl distance of 2.3405 (9) Å. The adjacent Hg centers are bridged by the nnh ligands to afford a one-dimensional zigzag chain with the Hg···Hg separation of ca 12.8371 (6) Å (see Fig. 2).
Notably, H-bonding interactions do play a decisive role in the crystal packing arrangement. As shown in Fig. 3, the adjacent one-dimensional arrays are linked to form a two-dimensional layer via N2-H2A···O2 i [symmetry operation (i) = x, 1 + y, z] hydrogen bonding between the nnh ligands from different chains. Furthermore, such two-dimensional layers are interlinked by the weak hydrogen bonds C3-H3···Cl ii [symmetry operation (ii) = -1 + x, -1 + y, z] to generate a threedimensional supramolecular network (see Fig. 4).

Experimental
A CH 3 OH solution (10 ml) of nnh (24.2 mg, 0.1 mmol) was carefully layered onto an aqueous solution of HgCl 2 (27.1 mg, 0.1 mmol) in a straight glass tube. After evaporating the solvents slowly for ca one month, suitable yellow block single crystals for X-ray analysis were produced.

Figure 2
View of the one-dimensional chain.

Figure 3
View of the two-dimensional layer via N-H···O hydrogen bonds (red dashed lines).  View of the three-dimensional network via C-H···Cl hydrogen bonds (green dashed lines).

catena-Poly[[dichloridomercury(II)]-N′nicotinoylnicotinohydrazide]
Crystal data Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq