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

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 Xray 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 P211n phase of di-isopropylammonium chloride, derivative of the previously described P2(1)2(1)2(1) and P2(1) 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.