The structural systematics of protonation of some important nitrogen-base ligands. III. Some (univalent) anion salts of some hindered unidentate nitrogen bases

Abstract

Recent structural studies of salts of the 2,2,6,6-tetramethylpiperidinium cation [tmpH]+ (chloride, bromide; thiocyanate) present as interesting dimeric or polymeric associations linked by pairs of directional hydrogen-bonds from the cationic = NH2+ moieties to two-coordinate anions. Present single crystal X-ray studies have characterized the iodide, perchlorate, nitrate and trifluoroacetate complexes, all, like those of the preceding studies, of composition [tmpH]+X- (anhydrous). A variety of forms are found: the nitrate compound is dimeric [[tmpH](O·NO·O)2[Htmp]], the trifluoroacetate compound being similar in form while the iodide and perchlorate salts are mixtures of dimers (with the anions essentially single atom bridges) and single-stranded helical polymers, the stoichiometric ratio of these being 1:1 and 2:1 in terms of [tmpH]X formula units, respectively. A study of 4-keto-2,2,6,6-tetramethyl-piperidinium thiocyanate shows it to be a dimer [[OtmpH](SCN/NSC)[HtmpO]] unlike its previously studied chloride analogue which is a cyclic tetramer. A new P21/n phase of di-isopropylammonium chloride, derivative of the previously described P212121 and P21 forms, is reported, together with descriptions of protonated salts of the other hindered unidentate bases 2,6-lutidine (as the chloride salt), quinoline (as the perchlorate, trifluoroacetate, hexachlorostannate and bisulfate salts) and 2-quinaldine (as the chloride (anhydrous and monohydrate) and hexachlorostannate salts), all displaying arrays derivative of ion-pair formation (extended by anion-anion hydrogen-bonds as well in the bisulfate salt) and, in the case of the aromatic bases, dominated by parallel stacking.