Trialkylammonium mixed salts in amine extraction systems. infrared study of the salts (R₃NH₃CPMo₁₂O₄₀] AND (R₃NH)C1 AND MIXED SALT (R₃NH₃LPMo₁₂O₄₀J].3(R₃NH)Cl

Infrared spectrophotometry has been used to compare the hydrogen-bonding (H-bonding) interactions in the set of solid trialkylammonium salts and double salts (R₃NH)₃[DMP], (R3NH)C1, and (R₃NH)₃[DMP]•3(R₃NH)Cl (A), where R represents a straight or methyl-branched alkyl group containing 8 to 13 carbons and DMP is the large dodecamolybdophosphate anion PMo₁₂O_403-. Through an examination of the characteristic heteropolymolybdophosphate vibrational bands of A and (R₃NH)₃[DMP], the complex anion is identified as α-DMP ad shown to be in an environment chemically similar to its tetrabutylammonium salt. A relatively weak H-bond in (R₃NH)₃[DMP] is indicated by small downward shifts in the N-H stretching frequencies vnh of the trialkylammonium cations from the hypothetical free-ion value. By contrast, large shifts in vnh induced by strong H-bonding occur in the salts (R3NH)C1. In the double salts A, the intermediate value of vnh suggests the existence of complex cations like [R₃NH•• •C1 ••• HNR₃]. The effect of amine structure on the infrared spectra is minor in all of the compounds studied except that methyl-branching increases the downward shift of the N-H stretching frequency of the salts (R₃NH)Cl; this is Interpreted as evidence that methyl branching strengthens the H-bond by decreasing the basicity of the parent amine. Density and unit-cell data are also reported for some of the DMP-containing compounds. Possible relationships between the present results and previously observed solubility patterns are discussed.