cyclo-Tetrakis{μ-2,2′-dimethyl-1,1′-[2,2-bis(bromomethyl)propane-1,3-diyl]di(1H-benzimidazole)-κ2 N 3:N 3′}tetrakis[bromidocopper(I)]

The title compound, [Cu4Br4(C21H22Br2N4)4], features a macrocyclic Cu4 L 4 ring system in which each CuI atom is coordinated by one bromide ion and two N atoms from two 2,2′-dimethyl-1,1′-[2,2-bis(bromomethyl)propane-1,3-diyl]di(1H-benzimidazole) (L) ligands in a distorted trigonal–planar geometry. The L ligands adopt either a cis or trans configuration. The asymmetric unit contains one half-molecule with the center of the macrocycle located on a crystallographic center of inversion. Each bromide ion binds to a CuI atom in a terminal mode and is oriented outside the ring. The macrocycles are interconnected into a two-dimensional network by π–π interactions between benzimidazole groups from different rings [centroid–centroid distance = 3.803 (5) Å.

The title compound, [Cu 4 Br 4 (C 21 H 22 Br 2 N 4 ) 4 ], features a macrocyclic Cu 4 L 4 ring system in which each Cu I atom is coordinated by one bromide ion and two N atoms from two 2,2 0 -dimethyl-1,1 0 -[2,2-bis(bromomethyl)propane-1,3-diyl]di-(1H-benzimidazole) (L) ligands in a distorted trigonal-planar geometry. The L ligands adopt either a cis or trans configuration. The asymmetric unit contains one half-molecule with the center of the macrocycle located on a crystallographic center of inversion. Each bromide ion binds to a Cu I atom in a terminal mode and is oriented outside the ring. The macrocycles are interconnected into a two-dimensional network byinteractions between benzimidazole groups from different rings [centroid-centroid distance = 3.803 (5) Å . (L), and copper (II) bromide to obtain the title compound in which copper (II) was reduced to copper (I) under hydrothermal conditions.

Related literature
In the crystal structure of the title compound, each copper (I) atom is coordinated by one bromide ion, and two N atoms from two ligands L, resulting in a trigonal planar geometry. The Cu-N distances range from 1.932 (8) to 2.003 (8) Å, while the distances of Cu1-Br3 and Cu2-Br6 are 2.381 (2) and 2.316 (3) Å, respectively. Two Cu1 atoms and two Cu2 atoms are linked by eight N atoms from four organic ligands L in an alternative cis-/trans-configuration, resulting in a centrosymmetric Cu 4 L 4 ring. Only one half of the molecule is observed in the asymmetric unit, and there is a crystallographic center of inversion in the center of the macrocyclic molecule. Each bromide ion connects a copper (I) atom in a monodentate mode, oriented outside the ring (Fig. 2). The pitches of Cu1-Cu2 and Cu1-Cu2A are 12.738 (4) and 9.939 (4) Å, respectively.
The rings are further interconnected to a two-dimensional network by π-π interactions. Around the ring, benzimidazol groups connected to N3 and N4, and benzimidazol groups based on N1 and N2, are stacked with a distance of 3.803 (5) Å (red dashed) and 3.613 (4) Å (black dashed), respectively (Fig. 2).

Experimental
The organic ligand (L) was synthesized according to a previously reported procedure (Bai et al. 2010). A mixture of CuBr 2 (22.365 mg, 0.1 mmol), and L (49.023 mg, 0.1 mmol) was dissolved in 10 mL of water of pH = 6. The resulting mixture was then transferred to a 25 mL Teflon-lined stainless steel reactor, and heated to 438 K for three days. After the reactor was slowly cooled to the room temperature yellow block-shaped crystals were obtained with a yield of 53 %.

Refinement
Anisotropical displacement parameters were applied for all non-hydrogen atoms. Hydrogen atoms were positioned geometrically and refined in a riding model with C-H distances of 0.96, 0.97 and 0.93 Å for methyl groups, methylene groups and benzene rings and with U iso (H)=1.5U eq (CH 3 ), U iso (H)=1.2U eq (CH 2 ), U iso (H)=1.2U eq (CH), respectively.  Fig. 1. Crystal structure of the title compound (30% probability ellipsoids). All hydrogen atoms are omited for clarity. Fig. 2. Two-dimensional layered structure constructed from different eight-membered Cu 4 L 4 ring by π-π stacking interactions (dashed lines). All hydrogen atoms were omitted for clarity.

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.
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 > 2sigma(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.