Diaquabis(cinnamato-κ2 O,O′)cadmium

The title complex, [Cd(C9H7O2)2(H2O)2], was obtained as an unintended product of the reaction of cadmium nitrate with hexamethylenetetramine and cinnamic acid. The CdII ion lies on a twofold rotation axis and is coordinated in a slightly distorted trigonal–prismatic environment. In the crystal, the V-shaped molecules are arranged in an interlocking fashion along [010] and O—H⋯O hydrogen bonds link the molecules, forming a two-dimensional network parallel to (001).

The title complex, [Cd(C 9 H 7 O 2 ) 2 (H 2 O) 2 ], was obtained as an unintended product of the reaction of cadmium nitrate with hexamethylenetetramine and cinnamic acid. The Cd II ion lies on a twofold rotation axis and is coordinated in a slightly distorted trigonal-prismatic environment. In the crystal, the V-shaped molecules are arranged in an interlocking fashion along [010] and O-HÁ Á ÁO hydrogen bonds link the molecules, forming a two-dimensional network parallel to (001).

Comment
The title compound was obtained as an accidental product of the reaction of cadmium nitrate with hexamethylenetetramine and cinnamic acid in ethanol in an attempt to synthesize a potentially interesting framework compound of the metal with both tetraamine and carboxylic acid groups. The potentially bridging hexamethylenetetramine ligand may have acted as a linker between cadmium ions; however, it was not incorporated into the material. A mononuclear cadmium complex with water and cinnamate ligands was the product formed in 75% yield, from an ethanolic solution.
The structure of diaqua-bis(cinnamato)-cadmium(II) had been previously recorded and was presented at the 1983 meeting of the American Chemical Society, but complete structural details are not available (Amma et al., 1983). In the Cambridge Structural Database (Version 5.35, with updates up to May 2013;Allen, 2002) [REFCODE: BUYTUK] only the data collection temperature (room temperature), unit cell parameters and space group, and the R value (10.4%) are reported but no atomic coordinates are available. Given the relatively poor precision of the previously reported structure and the lack of three-dimensional coordinates, we herein report the crystal structure of the title compound at 100 K.
The Cd II lies on a two-fold rotation axis and is coordinated by two cinnamate ligands and two water molecules (Fig. 1).
The carboxylate groups are bidentate-chelating, the water molecules monodentate and non bridging. The two oxygen atoms of each carboxylate group take coordination sites, the overall coordination environment of the metal center is best described as distorted trigonal prism, with angles varying between 92.86 (11)° (between the O atoms of the two water molecules), and 116.30 (8)° (for the angle between a water molecule O atom and a neighboring carboxylate group, using the carboxylate carbon atom as a substitute for the average of the two oxygen atoms).
The Cd-O bond distances are in the expected ranges. The bonds involving the water O atoms are 2.208 (2) Å , which compares well with those in similar Cd(II) complexes (O′Reilly et al., 1984, Mak et al., 1985. The Cd-O bond distances involving the two carboxylate O atoms are longer than those involving the water molecules, as would be expected due to the chelating coordination mode of the cinnamate ligand. The actual bond distances are 2.330 (2) and 2.375 (2) Å for Cd-O1 and Cd-O2, respectively. The similarity of the two Cd-O distances indicates an essentially symmetric coordination and a delocalization of the negative charge of the cinnamate carboxylate group. This is confirmed by the C-O bond distances within the carboxylate groups, which are also the same within experimental error, with values of 1.276 (3) and 1.269 (3) Å for O1-C9 and O2-C9, respectively.
In the crystal, the V-shape of the molecule results in a linear arrangement along [010] with the Cd(OH 2 ) 2 part of one molecule oriented towards the V-shaped part of a symmetry related molecule (Fig. 2). In addition, intermolecular O-H···O hydrogen bonds connect molecules forming a two-dimensional network parallel to (001) (Fig. 3).

Experimental
To a stirred colorless solution of Cd(NO 3 ) 2 ·4H 2 O (0.3084 g, 1 mmol) in 10 mL of water was added hexamethylenetetramine (0.2802 g, 2 mmol) in 5 mL of water to give a colorless solution. Then, cinnamic acid (0.2962 g, 2 mmol) in 20 mL of ethanol was added to a give a colorless solution. The solution was stirred at room temperature for 6 h, was filtered and then left to evaporate at room temperature. After several days, colorless needle shaped crystals suitable for Xray analysis were obtained in 75% yield. A single-crystal was isolated while suspended in mineral oil, was mounted with the help of a trace of mineral oil on a Mitegen micromesh mount and flash frozen to 100 K on the diffractometer.

Refinement
Reflection 0 0 1 was affected by the beam stop and was omitted from the refinement. All H atoms positions were refined.

Positions of carbon bound H atoms were freely refined, O bound H atoms were refined with an O-H distances restrained
of 0.84 (2) Å. All U iso (H) values were refined.