Masking of Lewis acidity trends in the solid-state structures of trichlorido- and tribromido(2,2′:6′,2′′-terpyridine-κ³N,N′,N′′)gallium(III)

Abstract

The molecular structures of trichlorido(2,2':6',2''-terpyridine-κ(3)N,N',N'')gallium(III), [GaCl3(C15H11N3)], and tribromido(2,2':6',2''-terpyridine-κ(3)N,N',N'')gallium(III), [GaBr3(C15H11N3)], are isostructural, with the Ga(III) atom displaying an octahedral geometry. It is shown that the Ga-N distances in the two complexes are the same within experimental error, in contrast to expected bond lengthening in the bromide complex due to the lower Lewis acidity of GaBr3. Thus, masking of the Lewis acidity trends in the solid state is observed not only for complexes of group 13 metal halides with monodentate ligands but for complexes with the polydentate 2,2':6',2''-terpyridine donor as well.

Hydrothermal synthesis of Group 13 metal trifluoride complexes with neutral N-donor ligands

“…The solutions decompose slowly forming F − or HF 2 − , qualitatively the indium complexes seem less stable in solution than those of the lighter metals. At 183 K, all six complexes show two resonances with relative intensities 1 : 2 in the 19 (Fig. 16) has been obtained previously as the [NMe 4 ] + salt, 32 and breaks up in solution to form [AlF 4 ] − , which was identified by a combination of 27 Al (δ = 48.7 (s)) and 19 F{ 1 H} NMR data (δ = -194.6, 6 lines, 1 J AlF = 38 Hz).…”

“…At 183 K, all six complexes show two resonances with relative intensities 1 : 2 in the 19 (Fig. 16) has been obtained previously as the [NMe 4 ] + salt, 32 and breaks up in solution to form [AlF 4 ] − , which was identified by a combination of 27 Al (δ = 48.7 (s)) and 19 F{ 1 H} NMR data (δ = -194.6, 6 lines, 1 J AlF = 38 Hz). 32 In the cases of the gallium and indium reactions, a few crystals of the same cation were obtained as the chloride salt, from traces of chloride in the reaction.…”

“…20 The limited number of structurally characterised complexes of the trifluorides limits detailed comparisons, but it seems that the metaldonor bond length may be very sensitive to the electronegativity of the donor atom, with little difference between Al-L and Ga-L with heavier donor ligands and halides, 21 but significant differences in the M-F bond lengths. The effects of solvent molecules and hydrogen bonding also complicates the interpretation of small differences in metal-donor bond lengths, 19,22 and these may be a significant factor in the extensively hydrogen bonded metal fluoride complexes. Interpretation of the spectroscopic properties (Experimental section) of the three terpy complexes is straightforward.…”

“…The complex, formed by dissociation of one fluoride from each gallium centre, followed by dimerisation, dissolves in CD 3 OD with decomposition and formation of a white precipitate. The 19 which means the neutral bipy ligand is trans to OH 2 /F ( Fig. 9 and 10).…”

“…Overall, the structural data reinforce earlier conclusions that trends in the bond lengths in comparable Al and Ga complexes often differ from those predicted on the basis of simple Lewis acidity in the gas phase; 22,[27][28][29] other factors, including the presence or absence of lattice solvent and hydrogen bonding also need to be considered. 13,19,21,22 The effects are less noticeable at indium, where corresponding bonds are typically ∼0.2 Å longer than for Ga, reflecting the increased radius of the metal centre.…”