Bis(3-acetyl-6-methyl-2-oxo-2H-pyran-4-olato)bis(dimethyl sulfoxide)nickel(II)

In the title compound, [Ni(C8H7O4)2{(CH3)2SO}2], the NiII atom is located on a crystallographic centre of symmetry and has a distorted octahedral coordination geometry of type MO6. The bidentate dehydroacetic acid (DHA) ligands occupy the equatorial plane of the complex in a trans configuration, and the dimethyl sulfoxide (DMSO) ligands are weakly coordinated through their O atoms in the axial positions.

In the title compound, [Ni(C 8 H 7 O 4 ) 2 {(CH 3 ) 2 SO} 2 ], the Ni II atom is located on a crystallographic centre of symmetry and has a distorted octahedral coordination geometry of type MO 6 . The bidentate dehydroacetic acid (DHA) ligands occupy the equatorial plane of the complex in a trans configuration, and the dimethyl sulfoxide (DMSO) ligands are weakly coordinated through their O atoms in the axial positions.

Bis(3-acetyl-6-methyl-2-oxo-2H-pyran-4-olato)bis(dimethyl sulfoxide)nickel(II)
A. Djedouani, S. Boufas, A. Bendaas, M. Allain and G. Bouet Comment 3-Acetyl-4-hydroxy-6-methyl-2-oxo-2H-pyran (dehydroacetic acid) (Arndt et al., 1936) is a versatile starting material for the synthesis of a wide variety of heterocyclic ring systems (Tan & Ang, 1988). It has been shown to possess modest antifungal properties (Rao et al., 1978). The importance of similar pyrones as potential fungicides is reinforced by the existence of several natural fungicides possessing structures analogous to 5,6-dihydrodehydroacetic acid, such as alternaric acid (Bartels-Keith, 1960), the podoblastins (Miyakado et al., 1982) and lachnelluloic acid (Ayer et al., 1988). Also, it has been shown that the complexes of DHA with copper and with several other transition metal cations are fungistatic (Rao et al., 1978). This has motivated our study of the structural characterization of complexes of dehydroacetic acid. The complex of DHA with nickel was previously reported by Casabò et al. (1987), but their characterization of the compound was based only on thermal and elemental analysis, and on IR and NMR spectroscopy.
We present here the crystal structure determination of the title complex, [Ni(DHA) 2 .2(DMSO)], (I) (DMSO = dimethylsulfoxide). The nature of the title compound, (I), was established by an X-ray structure determination and is shown in Fig. 1 The Ni atom lies on a crystallographic centre of symmetry with the ligands bonded to nickel in an all-trans fashion.  (Zhang et al., 2007).
The coordination polyhedron around the Ni atom is a slightly distorted octahedron (Table 1) (Table   2) which form a three-dimensional network (Fig. 2).

Experimental
Compound (I) was prepared by the reaction of dehydroacetic acid with nickel (II) chloride hexahydrate in the presence of sodium acetate (Casabò et al. 1987). Crystals of (I) were grown by slow evaporation of a dimethylsulfoxide solution..

Refinement
H atoms were positioned geometrically and treated as riding, with C-H = 0.93 Å with U iso (H) = 1.2Ueq(C). The methyl H atoms were constrained to an ideal geometry (C-H = 0.96 Å) with U iso (H) = 1.2U eq (C), but were allowed to rotate freely about the C-C bonds.  Fig. 1. The independent components of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. Fig. 2. The crystal packing of (I); Hydrogen atoms have been omitted for clarity.