Zeolites with varying Si/Al ratio, were synthesized using silica and alumina powder and by matching the XRD patterns with those given in the JCPDS files their chemical formula and crystal structure were determined. In order to make these into bipolar zeolite exchangers, they were modified (called Z(2) zeolite) using a gas-phase reaction with NO, at 225degreesC and the formation of the oxynitride groups was confirmed with FTIR, ESCA and the elemental analysis. The XRD patterns of the modified zeolites were found to have changed and did not match with any of the patterns given in the JCPDS files. For these modified zeolites, we have determined the crystal structures and these were found to change from cubic for the unmodified to orthorhombic for the modified zeolites with SUM less than or equal to 1.2 and to the tetragonal for SUM > 1.2.The oxynitride covalent bond in Z(2) zeolites could be reduced by reacting with hydrazine hydrate to give bipolar zeolite exchangers (denoted as Z(3) zeolite) containing imine groups, thus making the zeolite bipolar in nature. The cation exchange capacities were determined and found to have the same order of magnitude as reported in the literature. The elemental analysis of the modified zeolites was carried out and the experimentally determined nitrogen value of 3.85 wt% gives 0.9-1.2 oxynitride group per formula unit of the material. The experimentally determined anion exchange capacity of the Z(3) zeolites (1.72 meq/dry g for sample Al) suggests that for this value of exchange capacity, about two out of three formula units have an imine group. The difference between these two independent experiments suggests that not all imine groups participate in the anion exchange phenomena due to their non-availability. We found that Z(3) zeolite responds to organic reactions, and can be reacted with dichloroethane and subsequently quartemized with trimethylamine. Their anion exchange capacity is found to increase significantly. (C) 2003 Elsevier Ltd. All rights reserved.