Three new transition metal complexes, [Cu(L-cyst)(dmbpy)(H₂O)] (1), [Mn(dmbpy)₂(N₃)(Cl)] (2) and [Co(dmbpy)₃].[CoCl₄].Cl.7H₂O (3) with (L-cyst=L-cysteic acid, dmbpy=4,4’-dimethyl-2,2’-bipyridine, N₃=azide) have been synthesized and characterized by elemental analysis, thermal analysis (DTA/TGA), IR spectroscopy and single crystal X-ray diffraction (XRD). In the complex 1, the copper atoms are five-coordinated in a distorted square pyramidal site. It forms monomeric species, which are further connected into a three-dimensional supramolecular network through hydrogen bonding interactions. In the complex 2, the manganese atoms have a distorted octahedral environment with four nitrogen atoms of the two dmbpy, one nitrogen atom provided from azide ligand, the coordination sphere being completed by a chlorine atom. (2) is also a monomeric complex and the molecular structure of compound 2 is stabilized by non standard weak C-H…Cl hydrogen-bonds. The asymmetric unit of the complex 3 is built of two cobalt-containing fragments: the cationic [Co^II(dmbpy)₃]⁺² and the anionic (Co^IICl₄)⁻²groups. The molecular structure of compound 3 is stabilized by hydrogen bonds via O-H…O, O-H…Cl and C-H…Cl interactions. The thermal decompositions for 1 and 3 in the temperature range 30–1000°C has revealed that the Cu complex decomposes in three steps whereas Co complex decomposes in four steps and transforms into the corresponding metal oxide.