Di-μ-bromido-bis({2-[(4,6-dimethylpyrimidin-2-yl)disulfanyl]-4,6-dimethylpyrimidine-κ2 N 1,S 2}copper(I))

The title dinuclear complex, [Cu2Br2(C12H14N4S2)2], is located about an inversion center. The CuI ion is coordinated in a distorted tetrahedral geometry by two bridging Br atoms in addition to an N and an S atom from the 2-[(4,6-dimethylpyrimidin-2-yl)disulfanyl]-4,6-dimethylpyrimidine ligand. In the crystal, π–π stacking interactions are observed with a centroid–centroid distance of 3.590 (2) Å.


Ruthairat Nimthong, Chaveng Pakawatchai and Yupa Wattanakanjana Comment
The studies of cooordination multidentate ligands such as heterocyclic thioamides, in complexes of closed-shell d 10 metal ions, have been shown attention from a number of researchers (Saxena et al., 2009;Cox et al., 2006;Falcomer et al., 2006) because of their interesting biochemical properties and presence in active sites of many metalloproteins (Holm & Solomon, 1996;Battistuzzi & Peyronel, 1981). Particularly, the formation of disulfide bonds is an essential step in the folding and assembly of the extracellular domains of many membrane and secreted proteins which are important features of the structure of many proteins (Sevier & Kaiser, 2006).
The molecular structure of the title compound is shown in Fig. 1. The complex is dinuclear in which the Cu I ions adopt distorted tetrahedral geometries. There is a binuclear µ,µ′-dibromobridged CuBr 2 Cu core. The Cu-S and Cu-N distances are similar to those reported for other thioamide containing complexes (Aslanidis et al., 2004;Lemos et al., 2001) and the disulfide bond distances is shorter than that reported in a related compound with a disulfide bond (Freeman et al., 2008). The 'bite′ angle S-Cu-N angle is 90.77 (7)°. The molecule lies on a crystallographic inversion center which is at the center of the CuBr 2 Cu core with a Cu···Cu separation of 2.7802 (7) Å. This value is close the sum of the van der Waals radii for two Cu atoms (2.8 Å). In the crystal π-π stacking interactions with a centroid to centroid distance of 3.590 (2) Å are observed (Fig. 2). In addition, fairly short C(sp 3 )-H···N intermolecular distances (H···N = 2.67 Å, C(sp 3 )-N = 3.41 Å and C(sp 3 )-H···N = 134.2°) are observed (Fig. 3).
Experimental 4,6-Dimethyl-2-pyrimidinethiol, dmpymtH, (0.07 g, 0.50 mmol) was dissolved in 30 cm 3 of methanol at 343-348K. CuBr (0.1 g, 0.70 mmol) was added and the mixture was stirred for 5 h. The resulting clear solution was filtered off and left to evaporate at room temperature. The crystalline complex, which was deposited upon standing for several days, was filtered off and dried in vacuo (yield 75%).

Refinement
The H atoms bonded to C atoms were constrained with a riding model of C-H = 0.93-0.96 Å and with U iso (H) = 1.2U eq (C). The DELU instruction in SHELXL (Sheldrick, 2008) was used without any further parameters. This sets up 'rigid bond′ restraints for all non-hydrogen atom. The dafault standard deviation values are 0.01 and 0.01. This appears to have little effect but it does affect the no of restraints (55) listed in the CIF.

Figure 2
Part of the crystal structure with π-π stacking interactions shown as dashed lines.  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. N1A-C1A-N2A 127.9 (3) C3B-C4B-C6B 122.1 (3) N1A-C1A-S1A 110.3 (2) C2B-C5B-H2B 109.5 N2A-C1A-S1A 121.7 (2) C2B-C5B-H4B 109.5