The Structural Systematics of Protonation of Some Important Nitrogen-base Ligands. II. Some Univalent Anion Salts of Singly Protonated Bis(2-pyridyl)amine

Abstract

Syntheses and single crystal X-ray structure determinations are recorded for a number of normal and 'acid' salts of bis(2-pyridylamine), 'dpa', with univalent anions, X, variously hydrated, i.e. [dpaH]X·nH2O, and [dpaH]X·HX·nH2O. The 'normal' salt arrays so characterized are for X = Br- (n = 2, isomorphous with the previously described chloride compound) and, I-, ClO4-, 'tca-' (≡Cl3CCO2)- (all n = 1); acid salt arrays are described for X = NO3- and tca (both n = 0). In all cases except those of X = ClO4-, NO3-, there is one independent formula unit devoid of crystallographic symmetry comprising the asymmetric unit of the structure. In all cases, the proton associated with the cation is 'chelated' by the pair of ring nitrogen atoms, disposed 'endo'; in the tca adducts and the nitrate salt, the total cation is disordered in each case by inversion about a real or putative inversion centre between the rings. In the perchlorate compound, the (ordered) cation lies on a crystallographic 2-axis, as does the water molecule, and the perchlorate ion, which is disordered about such an axis; in the nitrate compound, the acid hydrogen atom is modelled as disposed on a crystallographic inversion centre between a pair of symmetry-related nitrate groups, containing, like the Htca adduct, the [XHX]- moiety rather than a diprotonated cation.