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 = 1,10-phenanthroline, 4,4′-diethyl-2,2′-bipyridyl, N-methyl-2-(pyridin-2-yl)imidazole (pymim), bis(pyridin-2-yl)methane [(py)₂CH₂], or bis(N-methylimidazol-2-yl)methanol [(mim)₂CHOH]}, [TIMe₂(terpy)]NO₃·H₂O (terpy = 2,2′:6′,2″-terpyridyl), and [(TIMe₂)₃(Et₃terpy)₂][NO₃]₃(Et₃terpy = 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 2 739, 3 000, and 1 547 independent ‘observed’ reflections, respectively. The complexes have linear orislightly bent C–TI–C groups, with weak TI ⋯ N and/or TI ⋯ O 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 ⋯ O 2.770(9)–2.915(10)Å, and C–TI–C 171.7(5)°, opposite (py)₂CH₂. The terpy complex has a tridentate ligand [TI ⋯ N 2.620(10)–2.650(9)Å] with a water molecule and nitrate ion 2.932(12) and 3.250(19)Å from thallium, and is thus formulated as [TIMe₂(terpy)(H₂O)] NO₃, with a ‘TIC₂N₃O₂’ 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)Å] linked by a ‘TIMe₂(NO₃)₃’ group [linear C–TI–C, TI ⋯ O 2.72(2)–2.85(3)Å] to give the molecule [(TIMe₂)₃(Et₃terpy)₂(NO₃)₃] possessing a two-fold axis and ‘TIC₂N₃O₂’ and ‘TIC₂O₆’ co-ordination environments. Crystal data: [{TIMe₂[(py)₂CH₂](NO₃)}₂] monoclinic, space group P2₁/c, a= 8.923(3), b= 22.535(8), c= 7.527(3)Å, β= 96.78(3)°, and Z= 2; [TIMe₂(terpy)(H₂O)]NO₃ monoclinic, space group P2₁/c, a= 9.779(3), b= 13.290(3), c= 14.380(4)Å, β= 93.95(2)°, and Z= 4; [(TIMe₂)₃(Et₃terpy)₂(NO₃)₃] tetragonal, space group I4₁/a,a= 1 5.71 5(6), c= 45.21 (1)Å, and Z= 8.