Diaquabis(4-bromobenzoato-κ2 O,O′)zinc(II)

The monomeric title ZnII complex, [Zn(C7H4BrO2)2(H2O)2], contains two 4-bromobenzoate (BB) ligands and two coordinated water molecules around a ZnII atom on a twofold rotation axis. The BB ions act as bidentate ligands, with two very dissimilar coordination distances. The sixfold coordination around the ZnII may be described as highly distorted octahedral, with the two aqua ligands arranged cis. Hydrogen bonding involving the carboxylate O atoms has an effect on the delocalization in the carboxylate groups. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link the molecules into chains parallel to the c axis and stacked along the b axis.

The monomeric title Zn II complex, [Zn(C 7 H 4 BrO 2 ) 2 (H 2 O) 2 ], contains two 4-bromobenzoate (BB) ligands and two coordinated water molecules around a Zn II atom on a twofold rotation axis. The BB ions act as bidentate ligands, with two very dissimilar coordination distances. The sixfold coordination around the Zn II may be described as highly distorted octahedral, with the two aqua ligands arranged cis. Hydrogen bonding involving the carboxylate O atoms has an effect on the delocalization in the carboxylate groups. In the crystal structure, intermolecular O-HÁ Á ÁO hydrogen bonds link the molecules into chains parallel to the c axis and stacked along the b axis.

Comment
Transition metal complexes with biochemical molecules show interesting physical and/or chemical properties, through which they may find applications in biological systems (Antolini et al., 1982). Some benzoic acid derivatives, such as 4aminobenzoic acid, have been extensively reported in coordination chemistry, as bifunctional organic ligands, due to the varieties of their coordination modes (Chen & Chen, 2002, Amiraslanov et al., 1979Hauptmann et al., 2000).
The structure-function-coordination relationships of the arylcarboxylate ion in Zn II complexes of benzoic acid derivatives may also change depending on the nature and position of the substituted groups on the benzene ring, the nature of the additional ligand molecule or solvent, and the pH and temperature of synthesis, as in Co II complexes (Shnulin et al., 1981;Antsyshkina et al., 1980;Adiwidjaja et al., 1978). When pyridine and its derivatives are used instead of water molecules, the structure is completely different (Catterick et al., 1974).
The structure determination of the title compound, (I), a zinc complex with two bromobenzoate (BB) ligands and two water molecules, was undertaken in order to determine the ligand properties of (BB) and also to compare the results obtained with those reported previously.
In the monomeric title complex, [Zn(C 7 H 4 O 2 Br) 2 (H 2 O) 2 ], (I), the Zn atom lies on a on a twofold rotation axis and is surrounded by two 4-bromobenzoate (BB), acting as bidentate ligands, and two coordinated water molecules (Fig. 1).
The Zn coordination polyhedron is formed by four clear basal bonds and two close contacts of the symmetry related O2 and O2 i atoms, [(i) 2 -x, y, 1/2 -z, Zn···O2 = 2.468 (5) Å, in double dashed lines in Fig. 1] occupying apical positions and completing the six-coordination; this distance is greater than the sum of the corresponding ionic radii (2.14 Å; Day & Selbin, 1969)

Experimental
The title compound, (I), was prepared by the reaction of ZnSO 4 (1.61 g, 10 mmol) in H 2 O (100 ml) and p-bromobenzoate (4.00 g, 20 mmol) in H 2 O (100 ml). The mixture was filtered and set aside to crystallize at ambient temperature for several days, giving colorless single crystals.

Diaquabis(4-bromobenzoato-κ 2 O,O')zinc(II)
Crystal data [Zn(C 7  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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )