Diaquabis(8-chloro-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purinato-κN 7)copper(II) dihydrate

The title mononuclear copper(II) complex, [Cu(C7H6ClN4O2)2(H2O)2]·2H2O, based on 8-chlorotheophylline (HCt), has the Cu atom at a center of symmetry in a slightly distorted trans square-planar geometry coordinated by two N atoms of two deprotonated HCt ligands and two O atoms of water molecules. The crystal packing is stabilized by hydrogen bonds involving deprotonated HCt ligands, coordinated water molecules and uncoordinated solvent water molecules.

The title mononuclear copper(II) complex,  O 2 ) 2 (H 2 O) 2 ]Á2H 2 O, based on 8-chlorotheophylline (HCt), has the Cu atom at a center of symmetry in a slightly distorted trans square-planar geometry coordinated by two N atoms of two deprotonated HCt ligands and two O atoms of water molecules. The crystal packing is stabilized by hydrogen bonds involving deprotonated HCt ligands, coordinated water molecules and uncoordinated solvent water molecules.
The stucture of (I) is shown in Fig. 1. It is composed of a mononuclear entity [Cu(Ct) 2 (H 2 O) 2 ], together with two crystal water molecules; the copper II atom, lying in a center of symmetry, is bonded to the nitrogen atoms of two individual 8-Ct molecules and oxygen atoms from two water molecules (Table 1), forming a trans square-planar arrangement. It should be noted that the ligand is in its anionic form (8-Ct -) in order to achieve charge balance.
Selected bond distances and bond angles are given in Table 1. The Cu-N and Cu-O bond lengths and bond angles at Cu1 are similar to those reported in some tetra-coordinated copper complexs (Zhao et al., 2003;Okabe et al., 1993).
The 8-Ct molecule deviates slightly from planarity and the dihedral angle created by the least squares planes between the pyrimidine and imidazole ring is 1.2 (1) °.
The structure presents O-H···O, O-H···N intermolecular hydrogen bonds (Table 2). between 8-Cts and water molecules. The coordinated water molecule is a donor towards the pyrimidine O2 and the uncoordinated water O4, thus linking the complex units into a 2-dimentional structure along the b axis. Besides, the lattice water molecules acts as a donor towards the pyrimidine O1 and imidazole N4. These two hydrogen bonds serve to link the 2-D structures into a 3-D array along the c axis. Hydrogen atoms attached to carbon atoms were positioned geometrically and treated as riding, with C-H = 0.96 Å and U iso (H) = 1.2U eq (C). The water H atoms were located in a difference Fourier map, and were refined with a distance restraint of O-H = 0.82-0.84 Å and U iso (H) = 1.5U eq (O). The crystals are unstable outside the parental solution, for what the quality of the diffraction data was poor. This led to unrealistic displacement parameters for four C and one O atoms, which were accordingly restrained to be nearly isotropic. Fig. 1. The structure of (I), showing 30% probability displacement ellipsoids and the atom-labeling scheme. Diaquabis(8-chloro-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purinato-κN 7 )copper(II) dihydrate Crystal data [Cu(C 7

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 Rfactors(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.