Di-μ-bromido-bis{[N,N-dimethyl-N′-(thiophen-2-ylmethylidene)ethane-1,2-diamine]copper(I)]}

In the crystal structure of the title compound, [Cu2Br2(C9H14N2S)2], the molecule resides about a crystallographic inversion center. The coordination sphere around each copper ion has a distorted tetrahedral geometry, with ligation by two bridging bromide ions, an amine N atom and an imine N atom. The thiophene ring is disordered over two sites, with occupancies of 0.719 (3) and 0.281 (3). Weak C—H⋯π interactions feature in the crystal packing.

In the crystal structure of the title compound, [Cu 2 Br 2 -(C 9 H 14 N 2 S) 2 ], the molecule resides about a crystallographic inversion center. The coordination sphere around each copper ion has a distorted tetrahedral geometry, with ligation by two bridging bromide ions, an amine N atom and an imine N atom. The thiophene ring is disordered over two sites, with occupancies of 0.719 (3) and 0.281 (3). Weak C-HÁ Á Á interactions feature in the crystal packing.

Jasinski Comment
Copper complexes of ligands containing hetero-aromatic and amine donor moieties have found multiple applications in metal catalyzed processes. Examples include catalysts for polymerizations and organic transformations (Perrier et al., 2002;Cristau et al., 2005), and model complexes in the biomimetic study of copper proteins (Lee et al., 2010). Our group has been interested in the use of neutral tridentate hetero-aromatic-amine ligands in metal-mediated atom transfer radical polymerizations (ATRP) (Matyjaszewski & Tsarevsky, 2009).
Here we report the synthesis and structure of a doubly bromide bridged dinuclear copper(I) complex with the ligand Fig. 1). A crystallographic inversion center generates the complete molecule from the asymmeric unit. The coordination sphere around each copper ion is arranged in a distorted tetrahedral geometry, with ligation by two bridging bromide ions, an amine nitrogen and an imine nitrogen. The thiophene ring is disordered (occupancy 0.719:0.281). The distances for the metal-amine bond (2.008 (2) Å) and the metal-imine bond (2.240 (2) Å) are within expected ranges (Allen et al., 1987).
As a result of the chelate ring formation the N(am)-Cu-N(im) angle of 85.27 (8)° is significantly smaller than the tetrahedral angle leading to appreciable distortion of the tetrahedral geometry and a large N(im)-Cu-Br angle of 132.01 (6)°. The N1/C7/C6/N2 torsion angle is 58.7 (3)°. The thiophene ring and imine group are near planar, with the sulfur oriented towards the copper atoms. However, Cu-S distances of 3.20 (6) Å make interactions unlikely. The Cu 2 Br 2 bridging unit forms a planar rhomboid arrangement, with an inversion center in the center. Related structures with a Cu 2 Br 2 core are published (Ball et al., 2001;Skelton et al., 1991;Churchill, et al., 1984). Cu1 possesses one short (2.4241 (4) Å) and one long (2.4805 (4) Å) Cu-Br bond, and a Cu-Cu distance of 2.980 (0) Å, outside the sum of the van der Waals radii of copper. The arrangement of the bromide bridging unit is asymmetrical: the Cu-Br-Cu bridging angle is 74.829 (13)°, close to the mean value of 74.(9)° found in structural units of this kind in the Cambridge Structural Database (Bruno et al., 2002). Weak C-H···Cg π-ring intermolecular interactions contribute to molecular packing in the crystal (Table 1, Fig. 2).

Experimental
The title compound was synthesized under a dinitrogen atmosphere by reacting a light green suspension of 233 mg of isolated as orange crystals suitable for X-ray analysis. A second crop was obtained by further addition of diethyl ether and storage at -25°C for 4 days to yield a combined crop of 440 mg of crystalline product (84% yield).

Refinement
All of the H atoms were placed in their calculated positions and then refined using the riding model with C-H lengths of 0.93 Å (CH), 0.97 Å (CH 2 ) or 0.96 Å (CH 3 ). The isotropic displacement parameters for these atoms were set from 1.19 to 1.22 (CH, CH 2 ), or 1.49 10 to 1.53 (CH 3 ) times U eq of the parent atom.

Computing details
Data collection: CrysAlis PRO (Oxford Diffraction, 2010); cell refinement: CrysAlis PRO (Oxford Diffraction, 2010); data reduction: CrysAlis RED (Oxford Diffraction, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).  Packing diagram of the title compound viewed along the b axis. Only the major component (S1A/C1A/C2A/C3A/C4A) of the disordered thiophene ring (occupancy: 0.719) is displayed. The hydrogen atoms have been removed for clarity. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.50 e Å −3 Δρ min = −0.51 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0021 (6) 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (