Three new complexes, namely [Cu(phen)(L)(H 2 O) 2 ]L·H 2 O 1, [M(phen) 2 (H 2 O) 2 ]2L·6H 2 O [M=Co(2), Ni(3)], where, HL=4-methylbenzenesulfonic acid and phen=o-phenanthroline, have been synthesized. The crystal structures were determined by X-ray diffraction method and refined by full-matrix least-squares methods to R=0.0535 and wR=0.1492 using 3567 reflections with I>2σ(I) for 1; R=0.0388 and wR=0.1223 using 3844 reflections with I>2σ(I) for 2; and R=0.0401 and wR=0.1222 using 3425 reflections with I>2σ(I) for 3. 1 Consists of cationic species [Cu(phen)(L)(H 2 O) 2 ] + , in which Cu(II) ion is five-coordinated by two nitrogen atoms of o-phenanthroline, two water molecules and one sulfonate oxygen atom. The cations and the non-coordinating sulfonate anions are linked by hydrogen bonds to form infinite chains. Complexes 2 and 3 are isostructral compounds. Each of them consists of cationic species [M(phen) 2 (H 2 O) 2 ] 2+ , in which metal ion is six-coordinated by four nitrogen atoms from two o-phenanthroline molecules and two water oxygen atoms. The sulfonate ions do not coordinate to metal ion. The cations, non-coordinating sulfonate ions and lattice water molecules are linked by hydrogen bonds to form infinite zigzag chains. CV, FT-IR, UV–Vis and TGA were also used to characterize these compounds.