Dimethyl(2,2′:6′,2′′-terpyridine-κ3 N,N′,N′′)zinc(II)

The title compound, [Zn(CH3)2(C15H11N3)], was synthesized by the addition of dimethylzinc to 2,2′:6′,2′′-terpyridine and was crystallized by the slow evaporation of THF. The pentacoordinate ZnII atom, lying on a twofold rotation axis, displays a distorted trigonal-bipyramidal geometry, with two terminal N atoms at the axial positions and the central N atom and two methyl C atoms at the equatorial positions.

The title compound, [Zn(CH 3 ) 2 (C 15 H 11 N 3 )], was synthesized by the addition of dimethylzinc to 2,2 0 :6 0 ,2 00 -terpyridine and was crystallized by the slow evaporation of THF. The pentacoordinate Zn II atom, lying on a twofold rotation axis, displays a distorted trigonal-bipyramidal geometry, with two terminal N atoms at the axial positions and the central N atom and two methyl C atoms at the equatorial positions.

Comment
The chelating ligand 2,2':6',2''-terpyridine coordinates to a variety of first-row transition metal Lewis acids. Specifically, it can coordinate to disubstituted zinc compounds, allowing for the formation of trigonal bipyramidal zinc(II) complexes (Harrison et al., 1986). The structure of terpyridine dichlorozinc(II) has been reported a number of times with different results (Corbridge & Cox, 1956;Einstein & Penfold, 1966;Vlasse et al., 1983). In addition to substituents on the zinc(II) center, substituents on the terpyridine are also known (Hou et al., 2004). The structure presented here is the first known structure in a class of terpyridine zinc(II) compounds with two alkyl groups bound directly to the metal center.
The title compound ( Fig. 1) was obtained by the reaction of dimethylzinc with 2,2':6',2''-terpyridine. It exhibits a distorted trigonal bipyramidal geometry about the metal center and has the two terminal N atoms in the axial positions, with a bond length of 2.3381 (12) Å (Table 1). The central N atom, coordinated to the zinc via the equatorial position, has a slightly smaller bond length, 2.2603 (16) Å, due to the size of the ligand, which is not able to wrap around the metal 180°. The N1-Zn-N1 i bond angle is 140.52 (6)° [symmetry code: (i) -x, y, 1/2-z], illustrating the degree to which the compound is distorted from a perfectly trigonal bipyramid. The Zn-C bond length is 2.0282 (15) Å, and the C1-Zn-C1 i bond angle is 133.21 (9)°: slightly greater than the expected 120° between equatorial atoms. Interestingly, the Zn-N bond lengths shown here are about 0.2 Å longer than those reported for similar terpyridine zinc(II) complexes, while the Zn-C length is expectedly shorter than the Zn-Cl and Zn-S lengths (Harrison et al., 1986;Hou et al., 2004;Vlasse et al., 1983).
However, the Zn-C bond length is similar to that reported for a bipyridine dimethylzinc(II) complex, characterized by Wessing et al. (1994). The terpyridyl N1-Zn-N1 i and N1-Zn-N2 bond angles are in agreement with those reported in the literature (Harrison et al., 1986;Hou et al., 2004;Vlasse et al., 1983).

Refinement
A suitable crystal was mounted in a nylon loop with Paratone-N cryoprotectant oil and data was collected on a Bruker APEXII CCD platform diffractometer. H atoms were included in calculated positions and were refined using a riding model, with C-H = 0.95 (aromatic) and 0.98 (methyl) Å and with U iso (H) = 1.2(1.5 for methyl)U eq (C).