Abstract

The complex NaBi(cit)middle dot7HO (Hcit = 3-carboxy-3-hydroxypentane-1{,}5-dioic acid) crystallized during reactions of the antiulcer drug ranitidine bismuth citrate with the tripeptide glutathione (gamma--Glu--Cys-Gly) at low pH. X-Ray analysis showed one Bi(cit) fragment per asymmetric unit with Bi chelated to a terminal carboxylate group; citrate also binds{,} in tridentate mode{,} to the bismuth of an equivalent Bi(cit) unit (related to the first by a axis) one oxygen donor from each of the remaining two carboxylate groups and the alkoxy group. Both ends of the resultant dimeric anion {Bi(small micro-cit)Bi} bind to adjacent dimers{,} related by -glide plane symmetry{,} double carboxylate bridges{,} to form a continuous polymeric anionic chain {Bi(small micro]-cit)Bi}] running throughout the crystal. In this way each bismuth atom achieves six-co-ordination Bi-O 2.210(10)-2.505(10)A with a -pentagonal-bipyramidal geometry{,} the vacant axial site providing evidence for a stereochemically active lone pair and the second axial site being occupied by the alkoxy donor. The parallel polyanionic chains are linked by anion-cation interactions Na O (cit) 2.37-2.50 A and by bonds of largely ionic character (Bi O 3.003-3.095 A) to give the overall three-dimensional solid-state structure which incorporates seven water molecules per dianionic subunit. The solid-state cross-polarization magic angle spinning C NMR spectrum of this complex is assigned with the aid of dipolar-dephasing and inversion-recovery cross-polarization experiments{,} and compared to those of ranitidine bismuth citrate and bismuth citrate Bi(Hcit). The IR and solid-state C NMR data suggested that the alkoxy group is protonated in Bi(Hcit) but deprotonated in ranitidine bismuth citrate{,} and that the latter contains similar dimeric units to NaBi(cit)middle dot7HO. The general modes of aggregration of dimeric {Bi(small micro]-cit)Bi}] units and the relevance to antiulcer activity are discussed.