Proton Magnetic Resonance Coordination-Number Study of AlCl3 in Aqueous Mixtures of Acetone, N,N-Dimethylformamide, Dimethylsulfoxide, Dioxane, Tetrahydrofuran, and Tetramethylurea

Abstract

The coordination number of Al(III) in aqueous mixtures of acetone, dimethylformamide, dimethylsulfoxide, dioxane, tetrahydrofuran, and tetramethylurea was measured over a range of solvent concentrations by a proton magnetic resonance technique. At low temperatures, proton exchange is slowed to such an extent in these mixtures that separate resonance signals are observed for bulk water and water molecules in the Al(III) solvation shell. Coordination numbers were measured by direct integration of the two water signals. The measurements show that in aqueous mixtures of acetone and tetramethylurea, and over a small solvent concentration range, dioxane and tetrahydrofuran, only water solvates Al(III). This was indicated by the value of six molecules obtained for the contribution of water to the Al(III) solvation shell in these mixtures. In aqueous mixtures of dimethylformamide and dimethylsulfoxide, wherein separate signals were also observed for the nonaqueous components, both solvents contribute to the Al(III) solvation shell. No evidence for ion pairing was found in any of the mixtures.

Solvation of aluminum(III) ion in dimethyl sulfoxide-water solutions by proton magnetic resonance spectrometry

“…No particular complex appears to be favored as no other experimental ratio is appreciably different from the statistical value. The equilibrium constants are larger than initially expected based on the results of Fratiello et al (8). Our results do not show the enhanced solvating ability of DMSO nor the decreasing total coordination number with increasing A1(C104)3 concentration that these authors observed with AICI3.…”

Structure of the aluminate ion in solutions at high pH

“…Similar results have been obtained for AIm in aqueous mixtures of various solvents using proton magnetic resonance. 2,3 The nature of the aluminum species during the process of neutralization has been inferred from crystallographic studies of various basic salts. For example, Johansson4 described the structure of the [Ali304(0H)24-(H20)i2]7+ ion existing in certain basic aluminum salts as having the aluminum octahedrally surrounded by oxygens, some of which form oxo bridges to other Alm ions.…”

Transition metal hydroborate complexes. IV. Cyanotrihydroborate complexes of the Group Ib metals

“…This behavior parallels the results of solution conductivity studies (vide infra) and is consistent with results for coinage metal derivatives of the larger borane anions. 4 In LiH3BCN • diox, the C-N stretching band occurs at 2198 cm-1, which has been attributed to a Li-N interaction.8 An increased C-N stretching frequency (to 2206 cm-1) has also been reported for the [Ru(NH3)6-(NCBH3)]2+ cation, in which ruthenium-nitrogen bonding occurs.12 In the ruthenium(II) cation [Ru-(NH3)6(NCBH3)]+, however, the C-N band is at 2170 cm-1, demonstrating the ability of the cyanotrihydroborate ligand to accept -electrort density when coordinated to a strong -donor metal atom.12 Since the N-C stretching frequency in sodium isocyanotrihydroborate is 2070 cm-1,9 it seems unlikely that the ligand has isomerized in the L3M(NCBH8) compounds. The possibility of isomerization cannot be completely eliminated, however, since in (o-phen)2Fe(CNBHs)2, the C-N absorptions occur at 2165 and 2154 cm _ 1.13 The B-H stretching and BH2 deformation frequencies in the free and coordinated cyanotrihydroborate ligand are very similar (Table II).…”

“…As mentioned above, the lesser affinity of the cyanotrihydroborate ion for the triphenylphosphine-silver ion (Figure 1) is not unexpected in view of results for compounds containing larger borane anions. 4 Cyanotrihydroborate as a Bridging Ligand.-Since hydroborate ions are well known to coordinate to transition metals by forming multicenter, hydrogenbridged bonds,26 it was of interest to investigate the possibility that the NCBH3~ion might act as a bridging ligand. The tetrahydroborate ion, for example, is known to bridge two copper atoms in the { [(Ce-H5)3P]2Cu(BH4)Cu[P(CeH6)3]2}+ cation.27 From a chloroform solution containing triphenylphosphinecopper(I) in a 2:1 ratio, the compound of empirical formula [(C6H6)3P]2Cu(NCBH3) was isolated.…”