Crystal structure of bis(thiocyanato-κS)bis(thiourea-κS)mercury(II)

In the title complex, [Hg(NCS)2(CH4N2S)2], the HgII atom is four-coordinated having an irregular four-coordinate geometry composed of four thione S atoms of two thiocyanate groups and two thiourea groups. The S—Hg—S angles are 172.02 (9)° for the trans-thiocyanate S atoms and 90.14 (5)° for the cis-thiourea S atoms. The molecular structure is stabilized by an intramolecular N—H⋯S hydrogen bond, which forms an S(6) ring motif. In the crystal, molecules are linked by a number of N—H⋯N and N—H⋯S hydrogen bonds, forming a three-dimensional framework. The first report of the crystal structure of this compound appeared in 1966 [Korczynski (1966 ▸). Rocz. Chem. 40, 547–569] with an extremely high R factor of 17.2%, and no mention of how the data were collected.


S1. Synthesis and crystallization
A mixture of thiourea, ammonium thiocyanate and mercury (II) chloride were dissolved in aqueous solution in the molar ratio 2:2:1 and thoroughly mixed for 1 h to obtain a homogeneous mixture. The solution was allowed to evaporate slowly at ambient temperature. Colourless block-like crystals were obtained in a week.

S2. Refinement
All the H atoms were positioned geometrically with N-H = 0.86 Å and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (N).

S3. Comment
This work is part of a research project concerning the investigation of thiourea (N 2 H 4 CS) and thiocyanate (SCN) based metal organic crystalline materials and their derivatives (Ramesh et al., 2012;Shihabuddeen Syed et al., 2013). Transition metal thiourea and thiocyanate coordination complexes are candidate materials for device applications including their nonlinear optical properties. As ligands, both thiourea and thiocyanate are interesting due to their potential formation of metal coordination complexes as they exhibit multifunctional coordination modes due to the presence of ′S′ and ′N′ donor atoms. With reference to the hard and soft acids and bases) concept (Ozutsumi et al., 1989;Bell et al., 2001), the soft cations show a pronounced affinity for coordination with the softer ligands, while hard cations prefer coordination with harder ligands. Several crystallographic reports about mercury(II) complexes usually consist of discrete monomeric molecules with tetrahedral (somewhat distorted) coordination environments around mercury(II) (Nawaz et al., 2010).
Herein, we report on the synthesis and crystal structure of the title complex.
In the crystal, molecules are connected via N-H···N hydrogen bonds, involving the thiourea NH 2 H atoms and the thiocyanate N atom ( Fig. 2 and Table 1). This gives rise to the formation of a three-dimensional framework which is supporting information sup-2 Acta Cryst. (2015). E71, m28-m29 reinforced by N-H···S hydrogen bonds ( Fig. 2 and Table 1).
The first report of the crystal structure of the title compound appeared in 1966 (Korczynski, 1966) with an extremely high R factor of 17.2 %, and no mention of how the data were collected.

Figure 1
A view of the molecular structure of the title complex, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intramolecular N-H···S hydrogen bond is shown as a double dashed line (see Table 1 for details).

Figure 2
The crystal packing of the title complex, viewed along the a axis. Hydrogen bonds are shown as dashed lines (see Table 1 for details).

Bis(thiocyanato-κS)bis(thiourea-κS)mercury(II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.44 e Å −3 Δρ min = −1.02 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0082 (3) Absolute structure: Flack (1983), 1149 Freidel pairs. Absolute structure parameter: 0.034 (12) Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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.