μ-Bromido-bis{μ-2,2′-[4,7-diazadecane-1,10-diylbis(nitrilomethanylylidene)]diphenolato}tricopper(II) bromide dimethylformamide disolvate

The complex molecule of the title compound, [Cu3Br(C22H28N4O2)2]Br·2C3H7NO, contains three copper atoms, two of which are five-coordinate within a square-pyramidal environment and linked by a bridging Br atom occupying the apical position in each square pyramid. The remaining Cu atom is four-coordinate but with considerable tetrahedral disortion [the dihedral angle between the two chelate planes is 69.21 (7)°]. There are two molecules of dimethylformamide (DMF) present as solvent molecules, one of which is disordered over two equivalent conformations with occupancies of 0.603 (5) and 0.397 (5). The amine H atoms are involved in both inter- and intramolecular hydrogen-bonding interactions with the Br and O atoms of the cation, as well as with the O atom of the ordered DMF molecule.


Related literature
For information concerning the parameter, see: Addison et al. (1984). For background to the use of multi-nuclear copper complexes in metallo-enzymes for catalyzing the four-electron reduction of oxygen to water, see: Yoon et al.
Cu(II) centers and is diagmagetic (Li et al. 2009). The role of Type (I) copper is to transfer electrons to the tri-nuclear unit in ascorbate oxidase for a simultaneous four-electron reduction of dioxygen (O 2 ) (Yoon et al. 2005). The tri-nuclear cluster of the enzymes is comprised of a Type (II) copper center and a Type (III) coupled binuclear site in relatively close proximity where oxygen reduction is effected (Yoon et al. 2005;Solomon et al. 1996;Chen et al. 2010;Lawton et al. 2009;Hakulinen et al., 2008). Generally, the multinuclear copper complexes that are in the group of metalloenzymes are used to catalyze the four-electron reduction of O 2 to H 2 O (Yoon et al. 2005;Mukherjee et al. 2003;Mirica et al. 2005;Augustine et al. 2010;Chaudhuri et al. 1992;Chen et al. 2010).
A number of researchers have synthesized or studied model complexes of multicopper oxidases. Paine et al. 2004 synthesized and characterized seven copper (II) complexes with a ligand 2,2'-selonobis(4,6-di-tert-butylphenol) (H 2 L). Two of the complexes were found to belong to the asymmetric tri-nuclear copper (II) complexes modeling the tri-nuclear copper site in multi-copper oxidases. Other researchers that have studied model complexes of multi-copper oxidases include, Cole et al. 1996et al. . Kataoka et al. 2009 studied the mechanism of the four-electron reduction of dioxygen by a multi-copper oxidase.
The title compound C 50 H 69 Br 2 Cu 3 N 10 O 6 is a mimic of the multi-copper enzymes such as ascorbate oxidase which is a tri-nuclear copper complex that is engaged in dioxygen (O 2 ) activation and subsequent substrate oxidation (Solomon et al. 1996). The complex consists of two copper (II) cations bridged by a bromide anion and is thus a model for the type III site and one distorted 4-coordinate copper center and thus a model for the type II site. Taken together this comprises a model for the multi-copper oxidases which consists of a type III and type II site in close proximity. In the present case the distances from type II model center, Cu1, to the two Cu's (Cu2 and Cu3) comprising a model for the type III site are respectively 5.915 (1) and 6.565 (1) Å. The type II copper center Cu(1) is considerably distorted from square planar coordination geometry with the dihedral angle between the two chelate planes being 69.21 (7)°. The two remaining Cu's are both square pyramidal with the bridging Br in the apical position in each coordination sphere (τ values are 0.0297 (2) and 0.0386 (2), respectively [Addison et al., 1984]).
There are two molecules of N,N-dimethylformamide (DMF) present as solvent molecules, one of which is disordered over two equivalent conformations with occupancies of 0.603 (5)   The synthesis of N,N-bis(3-aminopropyl)-ethylenediamine-bis(salicylaldimine) was accomplished by adding a solution of (5 g, 30.52 mmol) N,N-bis(3-aminopropyl)-ethylene-di-amine in 20 ml methanol drop-wise to the solution of (7.45 g, 61.04 mmol) salicylaldehyde. The mixture was refluxed overnight while stirring with a magnetic stirrer. Then the reaction mixture was evaporated under reduced pressure. An oily orange product was obtained which later solidified into yellow compound.
Synthesis of the complex C 50 H 70 Br 2 Cu 3 N 10 O 6 was achieved by adding a solution of (0.97 g, 6.76 mmol) CuBr in a mixture of 20 ml methanol and 25 ml ethanol to a solution of (1.17 g, 3.06 mmol) N,N-bis(3-aminopropyl)-ethylenediamine-bis(salicylaldimine) in 20 ml of CH 2 Cl 2 drop-wise while stirring. The reaction time was 24 h after which the reaction mixture was evaporated under reduced pressure. Dark greenish solids were obtained. These solids were then dissolved in DMF, filtered and layered with diethyl ether for crystallization. X-ray diffraction quality crystals were obtained.

Refinement
H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with a C-H distances of 0.93 to 0.99 Å and N-H distances of 0.93 Å and U iso (H) = 1.2U eq (C, N). Fig. 1