(2,2′-Bipyridine-κ2 N,N′)bis(4-formylbenzoato-κO 1)copper(II)

The title mononuclear CuII complex, [Cu(C8H5O3)2(C10H8N2)], is comprised of a CuII cation, two 4-formylbenzoate (L −) ligands and a 2,2′-bipyridine (bipy) ligand. The CuII ion and bipy ligand lie on a crystallographic twofold rotation axis; the CuII ion is coordinated by two N atoms from one bipy ligand and two O atoms from two different carboxylate groups of two L − ligands, exhibiting effectively a distorted square-planar geometry. The complex molecules are interlinked to generate two-dimensional supramolecular layers in the ab plane, formed by C—H⋯O hydrogen bonds, where the O acceptor is the O atom from the carboxylate group not involved in coordination to the CuII ion. The two-dimensional layers are stacked in a sequence via C—H⋯O hydrogen-bonding interactions where the formyl O atom acts as acceptor.

The title mononuclear Cu II complex, [Cu(C 8 H 5 O 3 ) 2 -(C 10 H 8 N 2 )], is comprised of a Cu II cation, two 4-formylbenzoate (L À ) ligands and a 2,2 0 -bipyridine (bipy) ligand. The Cu II ion and bipy ligand lie on a crystallographic twofold rotation axis; the Cu II ion is coordinated by two N atoms from one bipy ligand and two O atoms from two different carboxylate groups of two L À ligands, exhibiting effectively a distorted square-planar geometry. The complex molecules are interlinked to generate two-dimensional supramolecular layers in the ab plane, formed by C-HÁ Á ÁO hydrogen bonds, where the O acceptor is the O atom from the carboxylate group not involved in coordination to the Cu II ion. The twodimensional layers are stacked in a sequence via C-HÁ Á ÁO hydrogen-bonding interactions where the formyl O atom acts as acceptor.

Related literature
For general background on the use of transition metal complexes containing carboxylate ligands and secondary building units, see: Sun et al. (2002); Liu et al. (2006); Xu et al. (2011). For related structures using the same metal, similar ligands and with a similar coordination environment, see: Li et al. (2007).

Jin-li Qi and Wei Xu Comment
Transition metal complexes with carboxylic acids using various secondary building units (SBUs) frequently show interesting physical, chemical and/or biological properties (Sun et al., 2002, Li et al., 2007, Liu et al., 2006. Herein, we are interested in selfassemblies of Cu 2+ ions and 2,2′-bipydine (bipy) with 4-formylbenzoate, which led to the preparation The asymmetric unit contains a half Cu II cation, a half bipy ligand and one 4-formylbenzoate (L -= p-CHO-C 6 H 4 COO -) ligand. Both the Cu II ion and bipy ligand lie on a crystallographic twofold rotation axis. In the complex, two crystallographically equivalent Lanions function as monodentate ligands, while one bipy molecular functions as a terminal ligand adopting an expected chelating mode to coordinate with one Cu II ion, forming a mononuclear unit. The Cu II ion is coordinated by two nitrogen atoms (N and N #1 , #1 = 1 -x, y, 1.5 -z) of one bipy ligand and two oxygen atoms (O1, O1 #1 ) from two different carboxylic groups of two Lligands exhibiting essentially distorted square planar geometry  (Li et al., 2007).
Experimental 1 mL (1M) NaOH was added to an aqueous solution of CuCl 2 .2H 2 O (0.0852 g, 0.5 mmol) and Clanions were removed by repeated centrifugation with NaOH, then 5.0 ml H 2 O and 5.0 ml EtOH were subsequently added. The blue suspension above was added to an aqueous ethanol solution (5.0 ml and 5.0 ml) of 4-formylbenzoic acid (0.1501 g, 1.0 mmol), then another aqueous ethanol solution (5.0 ml and 5.0 ml) of 2,2′-bipyridine (0.0782 g, 0.5 mmol) was added and stirred continuously for 1 h to give another blue suspension. After filtration, the blue filtrate (pH = 4.8) was allowed to evaporate at room temperature for one week to give dark blue plate-shaped crystals.

Refinement
H atoms bonded to C atoms were placed in geometrically calculated position and were refined using a riding model, with U iso (H) = 1.2 U eq (C). After refinement there still remains one large residual peak 1.16 e.Å -3 high and located 2.36 Å from H10A. This was initially postulated as partly occupied water. However, the TG-DTA curve of the title complex shows no removal of a water molecula in the weight loss progress. We believe that the residual peak may be an artifact of poor crystal quality.

Figure 1
ORTEP view of the title compound, The dispalcement ellipsoids are drawn at 30% probability dispalcement ellipsoids.  the two-dimensional lay structure parallel to (001).

(2,2′-Bipyridine-κ 2 N,N′)bis(4-formylbenzoato-κO 1 )copper(II)
Crystal data 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 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.