Bis[N-(2-hydroxyethyl)-N-methylglycinato]copper(II)

The title compound, [Cu(C5H10NO3)2], was obtained unintentionally as the product of an attempted synthesis of a Cu/Cd mixed-metal mixed-anion complex using zerovalent copper, cadmium(II) oxide and two ammonium salts in the presence of 2-dimethylaminoethanol in acetonitrile, in air. The molecule is centrosymmetric with two monodeprotonated N-(2-hydroxyethyl)-N-methylglycines coordinated to the metal in a tridentate mode, giving a bicyclic chelate with two distorted five-membered rings. The CuII ion possesses a distorted octahedral geometry, with the N and the O atoms from the carboxylate groups in the equatorial plane. In the crystal structure, intermolecular O—H⋯O hydrogen-bonding interactions from the alkoxide functions of the ligand through the inversion centre form columns of molecules propagated along the a axis.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HK2547). In our previous studies, Cd(II) salts were found to react with zerovalent copper and 2-dimethylaminoethanol in solution in air affording tetra-, penta-and hexanuclear assemblies that demonstrated significant structural flexibility of heterometallic cores made up of Cu, Cd, halide ions or acetate groups with O atoms from the aminoalcohol (Vinogradova et al., 2002;Vinogradova et al., 2003). As the reaction systems studied have been so productive in generating new Cd/Cu structures and in attempting to extend this family by employment of two different anions, we have examined the reaction of zerovalent copper, cadmium(II) oxide and two ammonium salts in the presence of the aminoalcohol in a non-aqueous solution, in air:

Structure Reports Online
However, an attempt to isolate a desired Cu/Cd mixed-metal mixed-anion complex failed. A by-product of the interaction was crystallographically identified that appeared to be a low-dimensional copper complex with new ligand HL, N-(2-hydroxyethyl)-N-methylglycine, formed in situ. The compound with HL in a monodeprotonated form, Cu(MeN(CH 2 CH 2 OH)(CH 2 COO)) 2 , came as a surprise to us. To the best of our knowledge, neither the ligand nor its compounds with metals have been structurally characterized. The mechanism of the formation of the ligand is obscure, although it seemingly originates from 2-dimethylaminoethanol. It was reported that N-(2-hydroxyethyl)-N-alkylglycine derivatives could be conveniently prepared in high yields from N-alkylethanolamines and glyoxal (Farfán et al., 1987). The authors noted that the method could not be used with N-unsubstituted ethanolamines, but fully N-substituted analogues such as 2dimethylaminoethanol were not mentioned. We presume that in our case the conditions of the synthesis, namely the presence of zerovalent copper, could effect unknown organic reactions that led to the formation of HL.
In the title compound ( Fig. 1), the two L molecules are coordinated to the metal in a tridentate mode giving a bicyclic chelate with two distorted five-membered rings, where the N and the O atoms from the carboxylic and the alkoxide functions are bonded to the metal ion. The copper(II) ion, that is bonded to the six atoms in an all-trans configuration, possesses a distorted octahedral geometry with N1 and O2 atoms from the carboxylate group in the equatorial plane (Table 1). The Cu-O1 bond in the axial position is substantially elongated ( Table 1). The bond lengths (Table 1) are very similar to those observed in an analogous five-membered ring of bis(N,N-bis(2-Hydroxyethyl)glycinato)copper(II) (Thakuria & Das, 2007).
In the crystral structure, intermolecular O-H···O hydrogen-bonding (Table 2) interactions from the alkoxide functions of L through the inversion centre form columns of CuL 2 molecules propagated along the a axis (Fig. 2). The Cu···Cu separations in the crystal are larger than 6.6 Å.

Experimental
For the preparation of the title compound, copper powder (0.16 g, 2.5 mmol), CdO (0.32 g, 2.5 mmol), NH 4 SCN (0.38g, 5 mmol), NH 4 I (0.72 g, 5 mmol), acetonitrile (25 ml) and 2-dimethylaminoethanol (2 ml) were heated to 323-333 K and stirred magnetically for 8 h, until total dissolution of the copper was observed. A fine green powder that precipitated immediately supplementary materials sup-2 after cooling of the resulting solution was filtered off. The transparent blue solution was allowed to stand at room temperature and blue microcrystals suitable for X-ray analysis precipitated within 1 d. They were collected by filter-suction, washed with dry Pr i OH and finally dried in vacuo at room temperature (yield; 0.42 g). The crystals showed analytical data accounting for the presence of both Cu and Cd in the approximately 3Cu:Cd stoichiometry. However, the sample must has been a mixture as the X-ray structure investigation on a separate single-crystal conclusively established the identity of the compound as Cu(MeN(CH 2 CH 2 OH)(CH 2 COO)) 2 . We were not able to separate this mixture by manual separation due to the visual uniformity of the crystals.

Bis[N-(2-hydroxyethyl)-N-methylglycinato]copper(II)
Crystal data [Cu(C 5 H 10  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.