Crystal structure of tetrakis[μ2-2-(dimethylamino)ethanolato-κ3 N,O:O]di-μ3-hydroxido-dithiocyanato-κ2 N-dichromium(III)dilead(II) dithiocyanate acetonitrile monosolvate

The crystal structure of the novel Pb/Cr heterometallic complex with 2-(dimethylamino)ethanol prepared by direct synthesis is reported.


Chemical context
There is considerable interest in polynuclear heterometallic complexes as a result of their potential for interesting physicochemical properties such as magnetic (Gheorghe et al., 2010), catalytic (Trettenhahn et al., 2006) and useful lightand/or redox-induced functions (Balzani et al., 2009). The interest currently paid to the synthesis of polynuclear transition metal complexes is stimulated, in particular, by attempts to design and construct multicomponent systems. Despite of a lot of work already done in this field, a limited number of synthetic strategies have been developed to date. Spontaneous self-assembly of Schiff base ligands or rigid building blocks appears to be an extremely powerful tool for the construction of novel polynuclear assemblies incorporating metal atoms by utilizing the various coordination modes of small and flexible ligands (Buvaylo et al., 2005;Kirillov et al., 2005). Metal powders have been successfully applied in direct synthesis of coordination compounds to yield a number of novel monometallic (Babich et al., 1996) and heterometallic complexes (Buvaylo et al., 2005) of various composition, nuclearities and dimensionalities. This work is a continuation of our investigations in the field of direct synthesis of heterometallic coordination compounds based on spontaneous self-assembly, ISSN 2056-9890 in which one of the metals is introduced as a powder (zerovalent state) and oxidized during the synthesis (Nesterov et al., 2011), in particular the application of Reinecke's salt in direct synthesis of heterometallic complexes (Nikitina et al., 2008).

Structural commentary
The complex cation with a distorted seco-norcubane Pb 2 Cr 2 O 6 framework is centrosymmetric, as shown in Fig. 1. The two crystallographically independent dimethylaminoethanol ligands form five-membered chelate rings with the Cr III and Pb II ions. The Cr III ion adopts a distorted octahedral coordination environment with one N atom and two 2 -O atoms from the dimethylaminoethanol ligands and one 3 -O atom from the hydroxide ion in the equatorial plane, and one N atom of the thiocyanate ion and one 3 -O atom of the second hydroxide ion in the axial positions. The Cr-O and Cr-N bond lengths are 1.950 (3)

Supramolecular features
In the crystal, the tetranuclear complex cations are linked through thiocyanate anions with the above-mentioned intermolecular PbÁ Á ÁS interactions and by an O-HÁ Á ÁN hydrogen bond (Table 1) into chains along the c axis (Fig. 2). The chains are further linked together by an SÁ Á ÁS sigma-hole bond [S1Á Á ÁS2 3.585 (2) Å ], where atom S2 acts as a lone-pair donor. The molecular structure of the title compound, shown with 30% probability displacement ellipsoids. O-HÁ Á ÁN hydrogen bonds are shown as dashed lines. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
Crystal packing diagram of the title compound, viewed along the b axis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were placed in idealized positions and refined as riding, with U iso (H) = 1.2U eq (C) or 1.5U eq (C,O) for methyl and hydroxyl groups.
During the refinement, several isolated electron density peaks were located, which were assignable to a solvent acetnitrile molecule(s) from the IR data and elementary analysis. Satisfactory results (R 1 = 0.045) were obtained modeling the disordered C and N atoms, but very large displacement parameters for them were observed. The SQUEEZE (Spek, 2015) procedure in PLATON (Spek, 2009) indicated solvent cavities of volume 118 Å 3 centered at (0.5, 0, 0.25), (0.5, 0, 0.75), (0, 0.5, 0.75) and (0, 0.5, 0.25), each containing approximately 18 electrons. In the final refinement, this contribution was removed from the intensity data, producing better refinement results. We assumed full occupancy of the solvent molecule for each cavity, although the estimated 18 electrons are fewer than the 22 electrons expected for full occupancy. The solvent molecule is included in the reported molecular formula, weight and density.  (Spek, 2009).

Tetrakis[µ 2 -2-(dimethylamino)ethanolato-κ 3 N,O:O]di-µ 3 -hydroxido-dithiocyanato-κ 2 N-dichromium(III)dilead(II)
dithiocyanate acetonitrile monosolvate where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.00 e Å −3 Δρ min = −0.69 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.