Dichlorido(N,N-diethyl-4-{[(quinolin-2-yl)methylidene]amino-κ2 N,N′}aniline)mercury(II)

In the mononuclear title complex, [HgCl2(C20H21N3)], synthesized from the quinoline-derived Schiff base N 1,N 1-diethyl-N 4-(quinolin-2-ylmethylidene)benzene-1,4-diamine (QMBD), the coordination geometry around the Hg2+ atom is distorted tetrahedral, comprising two Cl atoms [Hg—Cl = 2.3654 (19) and 2.4394 (18) Å] and two N-atom donors from the QMBD ligand, viz. one imine and quinoline [Hg—N = 2.334 (5) and 2.340 (5) Å, respectively]. In the crystal, weak C—H⋯Cl hydrogen bonds and weak π–π aromatic ring stacking interactions [minimum ring-centroid separation = 3.680 (4) Å] give an overall three-dimensional network.


Comment
Mercury is one of the most prevalent toxic metals in the environment and gains access to the body orally or dermally, causing cell dysfunction that consequently leads to health problems (Mandal et al., 2012). Quinolyl derivatives of Schiff bases are important building blocks for many important compounds widely used in biological applications such as antioxidative, anticancer, fluorescent probe agents in industry, in coordination chemistry and in catalysis (Motswainyana et al., 2013;Das et al., 2013;Song et al., 2011;Jursic et al., 2002). The synthesis of a complex of mercury(II) using the quinoline aldehyde derivative of the Schiff base N 1 ,N 1 -diethyl-N 4 -(quinolin-2-ylmethylene-1,4-diamine (QMBD) has not previously been reported. The title Hg II complex with QMBD, [Hg(C 20 H 21 N 3 )Cl 2 ] has now been synthesized and the structure is reported herein.

Experimental
The iminoquinolyl compound N 1 ,N 1 -diethyl-N 4 -(quinolin-2-ylmethylidene)benzene-1,4-diamine (QMBD) was prepared by reacting 2-quinolinecarboxaldehyde with a substituted aniline and was obtained in very good yields. This compound was characterized by FT-IR, NMR and ESI-Mass spectroscopy. A mixture of QMBD (0.10 g, 0.33 mmol), mercury(II) chloride (0.09 g, 0.33 mmol) and ethanol (5 ml) were stirred vigorously for 1 h, after which the precipitate was filtered off and redissolved in dimethylformamide. Crystals of the title complex suitable for X-ray analysis was obtained within 3 days by slow evaporation of the DMF solvent.

Refinement
All H-atoms were positioned geometrically and refined using a riding model with C-H = 0.90-0.93 Å (aromatic), 0.97 Å (methylene) or 0.96 Å (methyl) and with U iso (H) = 1.2U eq (C) or 1.5U eq (C) (methyl). A large residual electron density peak (1.78 eÅ -3 ) located 1.47 from C19 of one of the ethyl goups suggested minor methyl group orientational disorder but this was not modelled.  The molecular conformation and atom-numbering scheme for the title complex with non-H atoms drawn as 30% probability displacement ellipsoids.  The one-dimensional weak interactive chain structure in the title complex extending along the approximate c-cell direction, with associations shown as dashed lines.

Figure 4
The structure viewed along the a-cell direction.

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.