Crystal structure of aqua-1κO-{μ-2-[(2-hydroxyethyl)methylamino]ethanolato-2:1κ4 O 1,N,O 2:O 1}[μ-2,2′-(methylimino)diethanolato-1:2κ4 O,N,O′:O]dithiocyanato-1κN,2κN-chromium(III)copper(II)

[Cr(μ-mdea)Cu(μ-Hmdea)(NCS)2H2O], (where mdeaH2 is N-methyldiethanolamine) is formed as a neutral heterometal CuII/CrIII complex whose molecular structure is based on a binuclear {CuCr(μ-O)2} core. In the crystal, the binuclear complexes are linked via two pairs of O—H⋯O hydrogen bonds to form inversion dimers, which are arranged in columns parallel to the a axis.


Chemical context
The search for heterometallic complexes has been stimulated by the general interest in combining different metal atoms within one assembly, since even the synthesis of such complexes often represents a non-trivial task. In addition, it was found that such compounds are potential novel magnetic materials (Gheorghe et al., 2010;Long et al., 2010;Visinescu et al., 2009;Amiri et al., 2010;Timco et al., 2008). Polydentate alkoxido ligands possessing versatile bridging modes were recognized as promising reagents for the synthesis of new heterometallic complexes. In particular diethanolamine and its N-alkyl derivatives are recognized N,O ligands that possess an interesting coordination chemistry and are thus often used for the design of various multimetallic cores and polymeric assemblies (Allen, 2002;Singh & Mehrotra, 2004;Verkade, 1993;Stamatatos et al., 2008;Beedle et al., 2008;Kirillov et al., 2008). Great interest in the synthesis and investigation of polynuclear chromium containing compounds dates from the late 90s, mostly due to the works of Winpenny and co-workers devoted to magnetic studies of high-nuclear cages and wheels (McInnes et al., 2005;Affronte et al., 2005). As has been shown in our previous publications, the synthetic approach named 'direct synthesis of coordination compounds' [Pryma et al., 2003;Nesterov et al., 2011Nesterov et al., , 2012Nesterova (Pryma) et al., 2004;Nesterova et al. 2005;Buvaylo et al., 2005] is an efficient method to obtain novel heterobi- (Buvaylo et al., 2005), heterotrimetallic (Nesterov et al., 2011), polymeric [Nesterova (Pryma) et al., 2004;Nesterova et al., 2005Nesterova et al., , 2008 and polynuclear (Nesterov et al., 2012) complexes. In a continuation of our investigations in the field of the ammonium salt route for direct synthesis (Pryma et al., 2003;Nikitina et al., 2008) the title compound [Cr(-mdea)Cu(-Hmdea)(NCS) 2 H 2 O] (where mdeaH 2 is N-methylethanolamine) was prepared using copper powder, Reineckes salt, ammonium thiocyanate and a non-aqueous solution of mdeaH 2 in air.

Structural commentary
The molecular structure of the title complex ( Fig. 1) is based on a binuclear {CuCr(-O) 2 } core. Each ligand (protonated and deprotonated) displays tridentate coordination by N and O atoms to a specific metal atom as well by a bridging O atom to the neighbouring metal atom. Thus the Cu II ion is pentacoordinated by the -oxygen (O1, O3) atoms of the protonated and deprotonated ligands, the N3 amino nitrogen atom of the mdea ligand and atom N1 of the thiocyanato ligand in the basal plane, and by the remaining oxygen atom (O4) of the Hmdea ligand in the apical site, and displays a distorted square-pyramidal coordination geometry. The apical oxygen atom is bound through the Cu1-O4 [2.259 (4) Å ] bond, which is typically elongated in comparison to those in basal sites, i.e. Cu1-O1 [1.994 (3) Å ] and Cu1-O3 [1.909 (4) Å ]. The coordination environment of the Cr III atom is completed in a distorted octahedral geometry by the additional coordination of atom O5 of the water molecule in an axial position trans to the N4 amino nitrogen atom of the ligand. The Cr-(O,N) bond lengths are within the range 1.912 (4)-2.118 (5) Å .
In general, all bonding parameters and the dimensions of the angles in the title complex are in good agreement with those encountered in related aminoalcohol complexes (Figiel et al., 2010;Kirillov et al., 2008;Gruenwald et al., 2009;Vinogradova et al., 2002).

Supramolecular features
In the crystal, the binuclear complexes are linked via two pairs of O-HÁ Á ÁO hydrogen bonds (Table 1)  The molecular structure of the title complex with 30% probability displacement ellipsoids Table 1 Hydrogen-bond geometry (Å , ).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms were located in difference Fourier maps and refined in a riding-model approximation with U iso = nU eq of the carrier atom (n = 1.5 for methyl group and n = 1.2 for other hydrogen atoms). Atoms C5, C6 and C7 were refined as disordered over two sets of sites with equal occupancies. The structure was refined as a twocomponent twin with a twin scale factor of 0.242 (1).