Synthesis, Spectroscopic, and Structural Studies of Dimethylthallium(III) Complexes containing Heterocyclic Nitrogen-donor Ligands, including 'TIC2N3O2' and 'TIC2O6' Geometries

Abstract

The complexes dimethyl[2-(pyridin-2-yl)imidazolato]thallium(III), (2,2'- bi-imidazolato)bis[dimethylthallium(III)], and their benzimidazolato-analogues are monomeric in chloroform. Dimethylthallium(III) nitrate forms complexes of stoicheiometry [TIMe2L]NO3 {L = 1,l0-phenanthroline, 4,4'-diethyl-2,2'-bipyridyl, N-methyl-2-(pyridin-2-y1)imidazole (pymim), bis-(pyridin-2-yl)methane [(py)2CH2], or bis(N-methylimidazol-2-yl)methanol [(mim)2CH0H}, [TIMe2(terpy)]NO3.H2O (terpy = 2,2':6',2"-terpyridyl), and [(TIMe2)3(Et3terpy)2][NO3]2 (Et,terpy = 4,4',4''-triethyl-2,2':6',2''-terpyridyl). Proton n.m.r. spectra of the nitrate complexes in methanol indicate co-ordination of the nitrogen-donor ligands to the dimethylthallium(III) cation. The structures of the (py)2CH2, terpy, and Et3terpy complexes have been determined by single-crystal X-ray diffraction at 295 K and refined by least-squares methods to R 0.048,0.061, and 0.071 for 2739, 3000, and 1547 independent 'observed' reflections, respectively. The complexes have linear or slightly bent C-TI-C groups, with weak TI...N and/or TI...0 interactions in approximate equatorial planes. The (py)2CH2 complex has a dimeric, centrosymmetric, structure with nitrate groups weakly linking two 'TIMe2{(py)2CH2}' groups to form [{TIMe2[(py)2CH2](NO3)}2] with 'TIC2N2O3' co-ordination having TI-N 2.658(9) and 2.666(9), TI-0 2.770(9)-2.915(10) A, and C-TI-Cl71.7I5) opposite (py)2CH2. The terpy complex has a tridentate ligand [TI-N 2.620(10)-2.650(9) A] with a water molecule and nitrate ion 2.932(12) and 3.250(19) A from thallium, and is thus formulated as [TIMe2(terpy) (H2O)]NO3, with a 'TIC2N302' environment having C-TI-C 169.6(6) opposite terpy. The Et3terpy complex has two 'TIMe2(Et3terpy)' groups [C-TI-C 166(1) opposite tridentate Et3terpy, TI-N 2.61 (3)-2.66(3) A] linked by a 'TIMe2(NO3)3' group [linear C-TI-C, TI-0 2.72(2)- 2.85(3) A] to give the molecule [(TIMe2)3(Et3terpy)2(NO3)3] possessing a two-fold axis and 'TIC2N3O2' and 'TIC2O6' co-ordination environments.