Crystal structure of tetra-μ-acetato-bis[(5-amino-2-methylsulfanyl-1,3,4-thiadiazole-κN 1)copper(II)]

The reaction of 2-methylthio-5-amino-1,3,4-thiadiazole with copper(II) acetate monohydrate resulted in the formation of the title binuclear compound


Structural commentary
The title binuclear Cu II complex, (I) (Fig. 1), is arranged about a crystallographic inversion centre located at the midpoint of the CuÁ Á ÁCu-connecting line. The asymmetric unit comprises one half of the complex molecule, namely, one Cu atom, two acetate groups and one 2-methylthio-5-amino-1,3,4-thiadiazole molecule. The two Cu atoms in the dimer are held together by the four carboxylate groups. Each Cu atom is bound in a square-pyramidal configuration to four carboxylate O atoms and to the N atom of an Me-SNTD molecule.

Supramolecular features
The packing of (I) is shown in Fig. 2. The acetate group containing oxygen atoms O1 and O3 does not form any hydrogen bonds. However, the acetate group containing oxygen atoms O2 and O4 forms both intra-and intermolecular hydrogen bonds. Each binuclear complex molecule exhibits one intramolecular N3-H3Á Á ÁO2 i hydrogen bond, forming a six-membered ring. The dimers are connected through an intermolecular N3-H3Á Á ÁO4 ii hydrogen bond between the Part of the crystal structure with hydrogen bonds shown as dashed lines. For clarity, H atoms not involved in hydrogen bonding are omitted.

Database survey
A survey of the Cambridge Structural Database (CSD Version 5.4, update of February 2019; Groom et al., 2016) revealed that crystal structures have been reported for complexes of 1,3,4thiadiazole derivatives and OAc with a number of metal ions, including zinc, copper, nickel, manganese, cadmium, cobalt and palladium. Copper(II) acetate complexes of the general formula [Cu 2 (OAc) 4 L 2 ], where L is a ligand with an oxygen or nitrogen ligator atom, have been well explored. The structures of 2-methylthio-5-amino-1,3,4-thiadiazole and a complex of this molecule with cadmium have been deposited in the CSD [XUVPEK (Lynch, 2010) and JIZKEK (Soudani et al., 2014), respectively]. However, no mixed-ligand metal complexes containing both 1,3,4-thiadiazole derivatives and OAc have been documented in the CSD.

Synthesis and crystallization
Cu(OAc) 2 ÁH 2 O (0.218 g, 1 mmol) and 2-methylthio-5-amino-1,3,4-thiadiazole (0.147 g, 1 mmol) were dissolved separately in a mixture of methanol-dichloromethane (10 mL, 1:1 v/v), mixed together and stirred for 1.5 h. The green solid that precipitated was dissolved in methanol to form a green solution. Single crystals of the complex suitable for X-ray analysis were obtained by slow evaporation of the solution over a period of 10 d.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The restraint N-H = 0.86 AE (1) Å was applied. Methyl H atoms were positioned geometrically C-H = 0.96) and refined as riding with U iso (H) = 1.5Ueq(C).   Table 1 Hydrogen-bond geometry (Å , ).

Tetra-µ-acetato-bis[(5-amino-2-methylsulfanyl-1,3,4-thiadiazole-κN 1 )copper(II)]
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.