Di-μ-chlorido-bis{[2-(benzyliminomethyl)pyridine-κ2 N,N′]chloridomercury(II)} dichloridomercury(II)

The HgII ion in the title centrosymmetric dinuclear complex, [Hg2Cl4(C13H12N2)2]·[HgCl2], adopts a distorted square-pyramidal geometry, being coordinated by the bis-chelating N-heterocyclic ligand, two bridging Cl atoms and one terminal Cl atom. One of the bridging Hg—Cl bonds [2.8428 (11) Å] is significantly longer than the other [2.5327 (10) Å]. In the crystal, there are weak π–π interactions [centroid–centroid distance = 3.630 (3) Å] between the aromatic rings of the discrete units. The HgCl2 adduct molecule is located on an inversion centre and has an Hg—Cl bond length of 2.2875 (11) Å.

The Hg II ion in the title centrosymmetric dinuclear complex, [Hg 2 Cl 4 (C 13 H 12 N 2 ) 2 ]Á[HgCl 2 ], adopts a distorted square-pyramidal geometry, being coordinated by the bis-chelating Nheterocyclic ligand, two bridging Cl atoms and one terminal Cl atom. One of the bridging Hg-Cl bonds [2.8428 (11) Å ] is significantly longer than the other [2.5327 (10) Å ]. In the crystal, there are weakinteractions [centroid-centroid distance = 3.630 (3) Å ] between the aromatic rings of the discrete units. The HgCl 2 adduct molecule is located on an inversion centre and has an Hg-Cl bond length of 2.2875 (11) Å .

Comment
Much attention has been paid to the design and synthesis of luminescent mercury compounds for the detection and extraction of the mercury (Elena et al., 2006;Durantaye et al., 2006), among which, Hg(II) complexes with pyridine-containing ligands are of importance for their high luminescent efficiency (Fan et al., 2009). In a previous report , we presented a structure of white Hg(II) complex with benzyl(2-pyridylmethylene)amine(bpma), (bpma)HgCl 2 , concerning its luminescence behavior He et al., 2008). The reported white crystals were obtained after recrystallization from methanol solution in a day. However, we could find another yellow crystals in 3-4 days in the same solution. Herein, we report the structure of separated yellow crystals, [(bpma)HgCl 2 ] 2 HgCl 2 .
In (I), Fig. 1, the Hg1 II ion is coordinated by two N atoms of heterocyclic ligand, two bridging Cl atoms and one terminal Cl atom. The angles around Hg1 atoms are in the range of 70.74 (12) -142.19 (9)°, suggesting the coordination geometry around the Hg1 atom is described as a distorted square pyrdmid with an apical position of Cl1 atom. One of the bridging Hg1-Cl bonds (2.843 (1) Å) is significantly longer than the other (2.533 (1) Å). The phenyl ring on the bpma ligand is twisted out of the pyridine plane, and form a dihedral angel of 81.21 (11)°. In the crystal structure, there are weak π-π interactions [centroid-centroid distance = 3.630 (3) Å] between the aromatic rings of the discrete units.

Experimental
Benzyl(2-pyridylmethylene)amine (bpma) was synthesized from the reaction of 2-pyridinecarboxylaldehyde and benzylamine. And bpma reacted with mercury dichloride in methanol to yield the titled complex. The yellow crystals were separated from white crystals in 3-4 days from methanol solution. The detailed synthetic method was previously reported .

Refinement
All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 -0.97 Å, and with U iso (H) = 1.2U eq (C). The maximum and minimum residual electron density peaks were located at 0.79 and 0.63 Å, respectively, from the Hg1 atom.