Bis(acetonitrile-κN)diaquabis(perchlorato-κO)copper(II)

In the title compound, [Cu(ClO4)2(CH3CN)2(H2O)2], the Cu2+ ion, located on a special position (site symmetry ), is coordinated by six monodentate ligands, viz. an N-coordinated acetonitrile, a perchlorate anion and a water molecule, and their symmetry-related counterparts. The perchlorate anion is disordered over two sets of sites with occupancies of 0.53 (2) and 0.47 (2). The crystal structure is stabilized by O—H⋯O hydrogen bonds involving the perchlorate ion and aqua H atoms.

In the title compound, [Cu(ClO 4 ) 2 (CH 3 CN) 2 (H 2 O) 2 ], the Cu 2+ ion, located on a special position (site symmetry 1), is coordinated by six monodentate ligands, viz. an N-coordinated acetonitrile, a perchlorate anion and a water molecule, and their symmetry-related counterparts. The perchlorate anion is disordered over two sets of sites with occupancies of 0.53 (2) and 0.47 (2). The crystal structure is stabilized by O-HÁ Á ÁO hydrogen bonds involving the perchlorate ion and aqua H atoms.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FI2110).

Comment
It was found (Tafeenko et al., 2009;Tafeenko et al., 2010) that the luminescent properties (emission energy) of the 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate (A)-based salts depend on the molecular environment around (A). To investigate the effect of transition metals, which act usually as fluorescence quenchers (Xu et al., 2005(Xu et al., , 2010, we made an attempt to synthesize (A)-based salts with Cu 2+ . Acetonitrile treatment of crude crystalline mass, obtained after evaporation of CuSO 4 + BaA 2 (equivalent amounts) mixture in water-ethanol (v/v=1/1) solution, and posterior evaporation of an acetonitrile solution in an air atmosphere at room temperature resulted in formation of (A)-based salts with Cu + . We saw several reasons for the reduction of Cu 2+ to Cu + : -iodide anion Ireduces Cu 2+ in water-ethanol solution, as it was detected that BaA 2 salt used for synthesis contained I -; -anion (A) exhibits of reducing properties; -acetonitrile-water mixture causes reduction of copper(II) to copper(I), as it was documented that i) copper(II) salt solution in acetonitrile-water mixture is a powerful oxidizer of organic molecules (Verma et al., 1979;Cox et al.,1988;Sumalekshmy et al., 2005;Ajayakumar et al., 2009); ii) acetonitrile can reduce Cu 2+ to Cu + (Drew et al., 1985).
To find out whether acetonitrile-water mixture can cause a reduction of Cu 2+ to Cu + , we prepared a Cu(ClO 4 ) 2 solution in a mixture of 99.5% CH 3 CN and 0.5% H 2 O (volume percentage) and evaporated this solution, which yielded crystals of the title compound, [Cu(CH 3 CN) 2 (H 2 O) 2 (ClO 4 ) 2 ]. No other phases could be detected using powder-XRD. The crystal and molecular structure of the title compound ( Fig.1) is presented in this paper.
The structure is composed of monomeric units built up around a Cu 2+ on a special position (site symmetry -1). The Cu 2+ cation is surrounded by six monodentate ligands, viz. an N-coordinated acetonitrile, a perchlorate anion and a water molecule, and their symmetry related counterparts. The perchlorate anion is disordered over two positions, with occupancies (0.53 (2) and 0.47 (2)), but it's O atoms displacement ellipsoids are still quite large, indicating possible rotational disorder, with the rotation axis passing through oxygen O1 of the perchlorate coordinated with Cu1 and Cl1. The complex adopts an elongated octahedral coordination geometry.
Besides ionic forces, the crystal structure is stabilized by hydrogen bonding interaction via the perchlorate and aqua H atoms (Fig. 2).
supplementary materials sup-2 In conclusion, we have to note that the structure of the title compound differs from reported by Inamo with co-workers (Inamo et al., 2001)

Refinement
During the refinement a difference maps showed peaks consistent with the perchlorate atoms Cl1,O2-O5 being unequally disorder over two interpenetrating sites. This was allowed for by use of the appropriate SHELXL SAME, EADP restraints.
The positions of the H atoms of the water molecule were determined from Fourier difference maps and refined freely; the positions of the H atoms of the methyl group were placed in calculated positions and allowed to ride on their parent atoms [C-H = 0.96 Å]. U iso (H) = xU eq (parent atom), where x = 1.5 for attached C atoms. Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. Only one of the two disordered positions of the perchlorate ion is shown. Symmetry code: (i) -x,1 -y, -z.