Several new lanthanide complexes of the types, (N2H5)(2)[Ln(C6H4(COO)(2))(2.5)], A, where Ln is La-Eu except Pm, and N2H5[Ln(C6H4(COO)(2))(2)(H2O)(3)]. H2O, B, where Ln is Eu-Dy, have been prepared by crystallisation from concentrated aqueous solutions containing the metal nitrates and dihydrazinium phthalate in 1:6 molar ratio. The aqueous solutions of the compounds are acidic and exhibit high values of molar conductance. The complexes were characterised by analytical, magnetic, spectral, thermal and X-ray studies. The OCO- groups of phthalate bridge in both mono- and bidentate fashion as evidenced by IR data. The N-N stretching frequency in the region 960-965 cm(-1) supports the non-coordination of N2H5+ ions. Both IR and thermal data confirm the presence of three coordinated and one lattice water molecules in the B complexes. Based on the results obtained, a nine-coordination for the lanthanide ions is proposed. Simultaneous TG-DTA of the complexes shows that they are thermally less stable and give metal oxides as the final product. X-ray powder patterns show isomorphism among the A and B complexes but not between them.