Six new coordination compounds of Ni(II), Pd(II) and Cr(III) with chlorhexidine, 1,1′-hexamethylenebis [5-(4-chlorophenyl)biguanide], were prepared, characterized and examined for their potential as antimicrobial agents, as well as for their antioxidant activity. The metal complexes correspond to the formulas: [Ni(CHX)]Cl 2 ·2H 2 O, [Ni(CHX)]Br 2 ·2H 2 O, [Ni(CHX)](CH 3 COO) 2 ·C 2 H 5 OH, [Pd(CHX)][PdCl 4 ]·2H 2 O, [Pd(CHX)](CH3COO) 2 and [Cr(CHX)Cl 2 ](CH 3 COO), where CHX = chlorhexidine.

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... estigations on the in vitro antimicrobial activity of the complexes indicated that all have high activity against the tested bacteria, but are less active against fungi. Among the six complexes, those of Pd(II) showed the highest antibacterial activity, [Pd(CHX)][PdCl 4 ]·2H 2 O being more active against Gram-positive and Gram-negative bacteria than chlorhexidine diacetate. The antioxidant activity of the metal complexes was investigated by photochemiluminescence and the results showed that the palladium(II) complexes have high antioxidant activities. EXPERIMENTAL Materials and physicochemical analyses All the chemicals were of AR grade purchased from Sigma-Aldrich or Merck and used without further purification. Carbon, hydrogen and nitrogen analyses were performed with a Euro EA elemental analyser. The nickel and palladium contents were determined gravimetrically, by precipitation with dimethylglyoxime. The chromium content was also estimated gravimetrically, as Cr 2 O 3 . Thermogravimetric analysis was performed under a static air atmosphere, at a heating rate of 10 °C min -1 , using an STA 6000 Perkin Elmer derivatograph. The infrared spectra (in KBr pellets) were recorded on a BIORAD FTIR 135 spectrophotometer, in the range 4000-400 cm -1 . The UV-Vis diffuse reflectance spectra in the range 200-900 nm were measured on a UV-Vis Jasco 650 spectrophotometer. Magnetic susceptibility measurements were performed by the Faraday method, on a Gouy balance, at room temperature, using Hg[Co(SCN) 4 ] as the calibrant. The 1 H-NMR (300 MHz) and 13 C-NMR (75 MHz) spectra of chlorhexidine and its Ni(II) and Pd(II) complexes in DMSO-d 6 were recorded on a Gemini 300BB spectrometer using TMS as an internal standard. The total antioxidant capacity of the metal complexes was registered using a photochemiluminometer,