Tetrakis(5,7-dimethylquinolin-8-olato-κ2 N,O)hafnium(IV) dimethylformamide disolvate

In the title compound, [Hf(C11H10NO)4]·2C3H7NO, the HfIV atom is coordinated by four N,O-donating bidentate 5,7-dimethyl-8-quinolinolate (Ox−) ligands arranged to give a distorted square-antiprismatic coordination polyhedron. The average Hf—O and Hf—N distances are 2.098 and 2.298 Å, respectively, and the average O—Hf—N bite angle is 70.2°. The crystal packing is controlled by π–π interactions between Ox− ligands of neighbouring molecules, giving rise to a three-dimensional supramolecular grid network. The interplanar distances vary from 3.441 (1) to 3.509 (1) Å, while the centroid–centroid distances vary from 3.688 (2) to 3.759 (12) Å. A non-classical C—H⋯O hydrogen bond is observed between the complex and one of the solvate molecules.

Financial assistance from the Department of Science and Technology (DST) of South Africa and the Advanced Metals Initiative (AMI) as well as the New Metals Development Network (NMDN) and the South African Nuclear Energy Corporation Limited (Necsa) and the University of the Free State is gratefully acknowledged. et al., (2008, 2009a, 2009b, 2010a, 2010b). If hafnium and zirconium show differences in their chelating behaviour, either by reaction rates, solubilities, coordination modes, equilibrium behaviour, etc., it could possibly be exploited as a novel separation technique for the two metals. The introduction of N,O-bidentate ligands with the oxine or aminovinylketone backbones significantly influences both steric and electronic properties of transition metals as illustrated by literature examples (Graham et al., 1991;Mtshali et al., 2006;Roodt et al., 2011;Schutte et al., 2008;Steyn et al., 1997;Van Aswegen et al., 1991;Van der Westhuizen et al., 2010).
Red parallelepiped-like crystals of the title compound crystallize with two dimethylformamide solvent molecules in the asymmetric unit ( Figure 1). The structure of the title compound is composed of an eight-coordinate Hf(IV) atom in which the four N,O-donating bidentate ligands, 5,7-dimethyl-8-hydroxyquinoline (Ox -), are arranged around the metal atom to give a distorted square antiprismatic geometry. The Hf-O and Hf-N bond lengths vary from 2.094 (2) to 2.1036 (19) Å and 2.377 (2) to 2.413 (2) Å, respectivily, and the O-Hf-N bite angles vary from 69.58 (8) to 70.87 (1)°. Only one C-H···O hydrogen bonding interaction is observed between a solvent molecule and one of the oxygen atoms in the complex molecule (Table 1). The molecular units of the title compound are stablilized by π-π interactions between different Oxligands of neighbouring molecules, producing a three dimensional supramolecular grid network, with interplaner distances varying between 3.441 (1) and 3.509 (1) Å and centroid-to-centroid distances from 3.668 (2) to 3.759 (2) Å ( Figure 2).

Experimental
Chemicals were purchased from Sigma-Aldrich and used as received. HfCl 4 (206 mg, 0.64 mmol) was dissolved in a minimal amount of DMF. While stirring this solution at room temperature, another solution of 5,7-dimethyl-8-quinolinol (OxH, C 11 H 11 NO) (445 mg, 2.5 mmol) was dissolved in a minimal amount of DMF and slowly added to the HfCl 4 solution, resulting in the formation of a bright yellow solution. The solution was left to stand for ca a week for reddish crystals to form.

Refinement
The aromatic, methine, and methyl H atoms were placed in geometrically idealized positions (C-H = 0.93-0.98) and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C) for aromatic and methine, and U iso (H) = 1.5U eq (C) for methyl protons. The highest residual electron density was located 1.34 Å from H33 and was essentially meaningless.
supplementary materials sup-2 Figures Fig. 1. Representation of the molecular title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius. Fig. 2. Graphical illustration of π-π interaction and stacking between different Ox --ligands of neighboring molecules to form a three-dimensional network (displacement ellipsoids are drawn at the 50% probability level). Hydrogen atoms and solvent water molecules were omitted for clarity.