Crystal structure of a mixed-ligand dinuclear Ba—Zn complex with 2-methoxyethanol having triphenylacetate and chloride bridges

In a new Ba–Zn dimeric coordination complex which has 2-methoxyethanol as well as triphenylacetate and chlorido ligands, the BaO8Cl and ZnO2Cl2 complex centres are separated by 3.9335 (1) Å and are connected through two carboxyl O,O1 bridges and one bridging chloride anion.


Structural commentary
In the structure of (I), the asymmetric unit contains one dinuclear complex of [BaZn(Ph 3 CCOO) 2 (CH 3 OCH 2-CH 2 OH) 4 Cl 2 ] (Fig. 1), in which the dinuclear [BaZn] 4+ cationic core is bridged by two carboxylate arms of the triphenylacetate ligands in a 1 : 1 : 2 coordination mode and by one bridging chlorine atom ( 2 -Cl). The BaÁ Á ÁZn distance in the dinuclear complex is 3.9335 (11) Å . Oxygen atoms have the largest contribution to the filling of the coordination sphere of barium  (2) Å ; Table 1]. Barium is bonded to one bridging chloride atom ( 2 -Cl), two O-atoms of two carboxylate groups and also to six O atoms from the 2-methoxyethanol ligands (four from two bidentate O,O 1 -chelate interactions and two from monodentate interactions). 2-Methoxyethanol is coordinated only to the Ba 2+ cation. The coordination mode is achieved in two different ways. Two terminal molecules representing an 1 : 1 mode form two five-membered rings completed by the barium atom. Two other molecules of 2methoxyethanol coordinate to Ba only through the hydroxyl O atoms.
Zinc is four-coordinated with a distorted tetrahedral ZnO 2 Cl 2 stereochemistry (Table 1), with Zn-Cl1 (bridging) = 2.2595 (10) Å and Zn-Cl2 (monodentate) = 2.2653 (9) Å and Zn-O (both from the bridging triphenylacetate groups = 1.96817 (2) and 1.9683 (18) Å ). A comparison with other structurally characterized mixed-metallic zinc-barium complexes reveals that the Zn-Cl-Ba linkage has been observed for the first time in the present compound. There are only a few compounds containing both of these metals and only one is a dimeric structure, with a distance between the atoms of 3.629 (2) Å , significantly shorter than in the title complex [3.9335 (11) Å ], but zinc and barium are connected only via bridging oxygen atoms ( 2 -O) from organic ligands (Van Veggel et al., 1989). Also, in other structures without carboxylate bridges, the ZnÁ Á ÁBa distances are often much shorter than in the title complex with values in the range 3.4325 (5) to 4.850 (3) Å (Westerhausen et al., 2001(Westerhausen et al., , 2006Baggio et al., 2004;John et al., 2008). In those cases where the oxygen atom ( 2 -O) and also carboxylates connect zinc and barium, the ZnÁ Á ÁBa distance is not longer than 3.638 (1) Å (Akine et al., 2006(Akine et al., , 2009(Akine et al., , 2010. In a polymeric structure where zinc and barium cations are bridged via two carboxylate arms and also via one molecule of water, the distance between them is 4.0208 (5) Å (Zhang et al., 2012).

Supramolecular features
In the crystal, there are intramolecular O-HÁ Á ÁO hydrogen bonds (Table 2). One is formed between a hydroxyl group O1I and an O-atom acceptor from the ether atom (O2H) of a 2-methoxyethanol ligand, the second is formed between a hydroxyl group O1H and an O-atom acceptor from a carboxyl group (O3) of a Ph 3 CCOO À ligand (Fig. 1). The presence of electronegative atoms (oxygen and chlorine) also leads to the occurrence of intermolecular hydrogen bonds in the crystal structure.

Figure 1
The molecular structure of the title complex, with displacement ellipsoids drawn at the 50% probability level. Dashed lines represent intra-complex hydrogen bonds. C-bonded H atoms have been omitted for clarity.
bonds. The first one occurs between the hydroxyl group O1G and an ether O-atom acceptor O2I i , the second occurs between the hydroxyl group O1J and the terminal chlorine atom Cl2 iii . In the third interaction, the H-donor atom is from a 2-methoxyethanol carbon (C2I), with the bridging chlorine atom (Cl1I) ii acting as the H-atom acceptor (for symmetry codes, see Table 2). A two-dimensional network structure is generated (Fig. 2), lying parallel to (001).

Synthesis and crystallization
For the preparation of Ba(Ph 3 CCOO) 2 , a mixture of metallic barium (0.521 g, 3.8 mmol), triphenylacetic acid (2.209 g, 7.66 mmol), C 6 H 5 CH 3 (50 ml) and THF (10 ml) was stirred at 363-373 K for 24 h until all the metal had reacted. The solu-tion, which included a white precipitate, was concentrated to about 20 ml and then hexane (50 ml) was added while stirring, which led to further precipitation. The product was filtered on a Schlenk flask (yield: 2.520 g, 93.26% Part of the crystal structure of the complex. Dashed lines represent intra-and intermolecular hydrogen bonds. C-bonded H atoms not involved in hydrogen bonding have been omitted for clarity. For symmetry codes, see Table 2. Table 2 Hydrogen-bond geometry (Å , ).