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

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Abstract

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 PMo12O403-. 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.

Original languageEnglish
Pages (from-to)1-37
Number of pages37
JournalSolvent Extraction and Ion Exchange
Volume6
Issue number1
DOIs
StatePublished - Jan 1 1988

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