Bis[2,6-bis(1H-pyrazol-1-yl)pyridine]decakis(μ2-3-nitrobenzoato)bis(3-nitrobenzoato)tetradysprosium(III): a linear tetranuclear dysprosium compound based on mixed N- and O-donor ligands

The title compound, [Dy4(C7H4NO4)12(C11H9N5)2] or Dy4(L1)12(L2)2, where HL1 = 3-nitrobenzoic acid and HL2 = 2,6-bis(1H-pyrazol-1-y1)pyridine, is a linear tetranuclear complex possessing inversion symmetry. The two central inversion-related DyIII atoms are seven-coordinate, DyO7, with a monocapped triangular-prismatic geometry. The outer two DyIII atoms are eight-coordinate, DyO5N3, with a bicapped triangular-prismatic geometry. The outer adjacent DyIII atoms are bridged by three L1− carboxylate groups, while the inner inversion-related DyIII atoms are bridged by four L1− carboxylate groups. The L2 ligands are terminally coordinated to the outer DyIII atoms in a tridentate manner. In the crystal, molecules are linked via C—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (001). Two carboxylate O atoms, and N and O atoms of three nitro groups, are disordered over two positions, with a refined occupancy ratio of 0.552 (6):0.448 (6).

Mn II -based SMMs were the first to be fully investigated, whereas recently 4f-or 5f-based compounds, especially Dy IIIbased compounds, have been investigated because of their potential significant magnetic anisotropy and large energy barriers . A number of multinuclear Dy-based compounds have been synthesized, for example, Dy 2 (Xu et al., 2010), Dy 3 (Hussain et al., 2009), Dy 4 (Abbas et al., 2010), Dy 5 (Blagg et al., 2011), and Dy 8 (Tian et al., 2012). In line with our interest in designing multinuclear Dy-based compounds, we report herein on the synthesis and crystal structure of a new and novel linear tetranuclear dysprosium compound, which is based on mixed N-donor and O-donor ligands.
The molecular structure of the title compound is illustrated in Fig. 1. It possesses inversion symmetry and the asymmetric unit is composed of two crystallographic independent Dy III ions, six crystallographic independent 3-nitro benzoate L1ligands, and one crystallographic independent 2,6-di(1H-pyrazol-1-y1)pyridine L2 ligand. Although the ligand 2,6-di(1H-pyrazol-1-y1) pyridine is extensively used to construct metal-organic compounds, it has rarely been used in combination with lanthanide ions, and there is no precedent of a cluster compound containing a lanthanide ion and the ligand 2,6-di(1H-pyrazol-1-y1)pyridine. The title compound is the first such compound to be synthesized and is a promising way to target multinuclear lanthanide clusters.
Moreover, in the literature, there is only one other report of a linear tetranuclear Dy III complex (Lin et al., 2012), [Dy 4 (L) 2 (C 6 H 5 COO) 12 (MeOH) 4 ] (L = 2,6-bis((furan-2-ylmethylimino)methyl)-4-methyl-phenol), where the Dy III sites are fully coordinated by O atoms, rather than being coordinated by both O and N atoms as observed in the title compound.
Interestingly the metal-to-metal distances (4.24 (2) Å and 4.06 (2) Å) reported there are slightly shorter than those observed in the title compound.

Refinement
The NH H atoms could be located in a difference  The coordination environment of the Dy III ions in the title compound, with atom labelling of heteroatoms only.

Figure 2
A view of the simplified tetranuclear structure of the title compound.

Figure 3
The polyhedral view of the tetranuclear structure of the title compound.

Bis[2,6-bis(1H-pyrazol-1-yl)pyridine]decakis(µ 2 -3-nitrobenzoato)bis(3-nitrobenzoato)tetradysprosium(III)
Crystal data Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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 > 2sigma(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.