Crystal structure of [3-(4,5-dihydro-1,3-thiazolin-2-yl-κN)-1,3-thiazolidine-2-thione-κS 2](1,3-thiazolidine-2-thione-κS 2)copper(I) nitrate

In the mononuclear complex title salt, all of the non-H atoms of the cation lie on a mirror plane, as do the N and one O atom of the nitrate anion, such that the planes of the cation and anion are mutually orthogonal. In the crystal, layers parallel to (010) are generated by N—H⋯O hydrogen bonds, supported by short S⋯O [3.196 (4) and 3.038 (3) Å] and S⋯S contacts [3.4392 (13) Å].


Chemical context
1,3-Thiazolidine-2-thione (tzdSH: C 3 H 5 NS 2 ), is a well known heterocyclic thione/thiol ligand. Crystallographic studies and investigations of its modes of coordination have been reported (Raper et al., 1998;Ainscough et al., 1985;Kubiak & Głowiak, 1987;Cowie & Sielisch, 1988;Ballester et al., 1992;Fackler et al., 1992;Saithong et al., 2007). We are interested in the coordination behaviour and structure of tzdSH complexes with Cu II cations. We have normally used Cu(NO 3 ) 2 Á3H 2 O as the starting material with the possibility that the NO 3 À anions could function as simple counter-ions to balance the charge on the metal or alternatively act as a ligand to the metal ion (Ferrer et al., 2000;Pal et al., 2005;Khavasi et al., 2011). However, the tzdSH ligand could also act as a reducing agent during the reaction, converting Cu II to Cu I and forming 3-(2thiazolin-2-yl)thiazolidine-2-thione [tztzdt or C 6 H 8 N 2 S 3 ] in the process. A similar reduction reaction was described previously by Ainscough et al. (1985). Complexation of the resulting Cu I cation to both the tztzdt ligand thus formed, and to tzdSH generates the title compound.

Structural commentary
The title compound is a mononuclear Cu I complex and its structure is shown in Fig. 1. The Cu I atom has a distorted trigonal-planar coordination geometry and is chelated by the exocyclic S3 atom and the N3 atom of the thiazolidine ring of the tztzdt ligand, forming a six-membered chelate ring. The trigonal coordination sphere is completed by the exocyclic S1 atom of the tzdSH ligand. The NO 3 À acts solely as counter-ion. The complex molecule is strictly planar as all non-hydrogen atoms of the complex lie on a mirror plane. Atoms N4 and O1 of the nitrate counter-ion also lie on a mirror plane, such that the mirror plane of the cationic complex is perpendicular to that of the NO 3 À anion. The Cu1-S1 [2.1774 (9) Å ], and Cu1-N3 [1.956 (3) Å ] bond lengths are not unusual in comparison with the mean values [Cu-S = 2.21 (3) and Cu-N = 1.99 (3) Å ] found in the Cambridge Structural Database. In contrast, the Cu1-S1 distance of 2.1774 (9) Å is somewhat shorter than those previously reported for other Cu I complexes of tzdSH [mean Cu-S = 2.33 (1) Å ].

Figure 2
Two-dimensional sheets of molecules parallel to (010). Hydrogen bonds are drawn as dashed lines and H atoms not involved in hydrogen bonding have been omitted for clarity. stacking interactions between molecules. Centroid-centroid and unusual Cu1-centroid contacts are drawn as dotted lines with the centroids shown as coloured spheres. Hydrogen bonds are drawn as dashed lines and H atoms not involved in hydrogen bonding have been omitted for clarity.

Figure 4
The overall packing of the title compound. Hydrogen bonds are drawn as dashed lines and H atoms not involved in hydrogen bonding have been omitted for clarity.

Database survey
Only four discrete reports are given of transition-metal complexes with the metal atom chelated by the tztzdt ligand. All are copper complexes, three of Cu I (Lobana et al., 2013) and the fourth a Cu II coordination polymer (Ainscough et al., 1985). Complexes of tzdSH are more plentiful with 29 unique entries, ten of which involve Cu I cations (see, for example: Lobana et al., 2013;Raper et al., 1998).

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 al data will be even larger.