Summary The complexes of the type [M(HDMBG)Cl3] ((1) M:Co; (2) M:Zn;) and [M(DMBG)Cl2] ((3) M:Pd; (4) M:Pt; DMBG: N,N-dimethylbiguanide) present in vitro antimicrobial activity. The modification evidenced in IR and 1H NMR spectra (in the case of complex (2)) was correlated with the presence of N,N-dimethylbiguanide ion as unidentate, coordinated through N3 and of N,N-dimethylbiguanide as chelate, coordinated through N1 and N4 respectively. The electronic reflectance spectrum showed the d-d transition for complex (1) characteristic for the tetrahedral surrounding while the spectra for complexes (3) and (4) have the characteristic pattern for square-planar stereochemistry. The cyclic voltammetric data show the characteristic waves for mononuclear complexes of the metallic ions presented below. The thermal analysis has evidenced the thermal intervals of stability and also the thermodynamics effects that accompany them. The different nature of the ligands generates a different thermal behaviour for complexes.