cis-Dichlorido[4,4,5,5-tetramethyl-2-(2-pyridyl)-2-imidazoline-1-oxyl]palladium(II) tetrahydrofuran hemisolvate

The asymmetric unit of the title complex, [PdCl2(C12H16N3O)]·0.5C4H8O, consists of one palladium complex in a general position and one half tetrahydrofuran (THF) solvent molecule, with the O atom lying on a twofold rotation axis. The PdII atom is bound to one chelating imino nitroxide radical through two N atoms, one from the pyridyl ring and the other from the imidazoline ring. The coordination of the metal centre is completed by two Cl atoms in a cis configuration, leading to a quasi-square-planar coordination of the metal centre. The four atoms that define the PdII coordination environment and the eight atoms that belong to the pyridylimine fragment are coplanar, with no deviation larger than 0.087 (5) Å. In the crystal structure, intermolecular interactions shorter than the corresponding van der Waals radii sum are observed only between PdII complexes, and no short contact is observed around the THF molecule. Weak C—H⋯O and C—H⋯Cl interactions yield a two-dimensional network of complexes in the (101) plane.


Comment
Organic nitronyl nitroxide radicals have attracted much attention for their magnetic properties in general and ferromagnetism in particular. Then several transition metal complexes with stable nitronyl nitroxide radical ligands have been prepared and extensively investigated (Ma et al., 2007;Xu et al., 2007;Ma et al., 2006;Ueda et al., 2005;Li et al., 2004;Ueda et al., 2003;Oshio et al., 1996;Caneschi et al., 1991). Our contribution in this field is the synthesis (see Scheme 1) and structure characterization of the title compound.
The molecular structure of the complex [Pd(IM 2 py)Cl 2 ] 0.5THF(I) is shown in Fig. 1 while selected geometric parameters are given in Table 1. Focusing the coordination square of Pd II , one can notice that Cl2 atom deviates significantly from the phane defined with atoms N3/N1/Pd1/Cl1 by 0.0843 (23) Å. The mean bond distance of Pd-Cl 2.277 Å is in agreement with the values observed in a similar complex while the average bond length of Pd-N 2.045 Å is slightly longer than seen previously (Fettouhi et al., 2003). Due to a chelation of the iminonitroxide radical with Pd II ion, the four atoms which define the Pd II coordination plane and the eight atoms which belong to both pyridyl ring and imino fragment are coplanar, the larger deviation to the plane is equal to 0.087 (5) and −0.064 (5) Å for O1 and N3 respectively. Only sp 3 carbon C7 and C8 from imino and methyl carbon C9, C10, C11 and C12 deviate significantly from the mean plane.
In the packing, one can notice that intermolecular interactions shorter than the corresponding van-der-Waals radii are only observed between Pd II complexes, no short contact are observed around THF molecule. Centrosymetric contacts take place between imino and pyridyl ring (O1-H4) of one neighbouring complex as well as contacts between chlorine Cl1 and H10B atom of methylene group (Table 1). These contacts yield a two-dimensional network of interacting complexes along the (101) plane (Fig. 2). Another short contact is observed between two adjacent 2-D networks thanks to a van-der-Waals interaction between two C1 atoms of pyridyl rings of two neighbouring molecules with C1-C1 3.393 (16) Å. The shortest distance between two palladium take place between ions from two adjacent planes (Pd1-Pd1 = 3.648 (2) Å), onto a plane, the shorter Pd1-Pd1 distance is 8.7834 (7) Å. THF solvent molecules are lying between two planes. A contact O1s-H1 of 2.7445 Å is observed with pyridyl ring.

Experimental
Dichlorobis benzonitrile palladium(II) PdCl 2 (PhCN) 2 and 2-(ortho-pyridyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl-3oxyde (NIT2Py) were synthesized according to literature method (Evans et al., 1968;Ullman & Holm, 1970;Davis et al., 1972). The complex Pd(IM 2 py)Cl 2 was synthesized as follows: The reaction was performed under a dry nitrogen atmosphere using standard schlenk technique. All solvents used were distilled under nitrogen. To a solution of PdCl 2 (PhCN) 2 (0.1 g;0.26 mmol) in 30 ml of toluene was added with stirring a solution of the radical NIT2Py (0.12 g;0.52 mmol) in 20 ml of toluene. After 2 h of stirring at room temperature, the mixture was filtered and the solvent removed under reduced supplementary materials sup-2 pressure. Parallelepipedic brown crystals of complex (I) suitable for x-ray crystallographic analysis were obtained by slow diffusion of hexane in THF solution of complex (I).

Special details
Experimental. Multiscan absorption correction methods did not yield a better refinement agreement, then no correction was applied. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.4332 (