A pyridine-substituted diiron dithiolate complex (mu-dmedt)Fe-2(CO)(5)Py 1 was prepared as a biomimetic model for the active site of [FeFe]-hydrogenase by CO-substitution of all carbonyl complex (mu-dmedt)[Fe(CO)(3)](2) [dmedt = 2,3-butanedithiol] with pyridine, which has been determined by IR, (HNMR)-H-1, elemental analysis and X-ray crystallography analysis. Electrochemical and IR investigation of the complex 1 in MeCN-[NBu4][PF6] under N-2 and under CO has demonstrated that the reversible transformation reaction between the complex 1 and the acetonitrile-substituted species (mu-dmedt)Fe-2(CO)(5)(NCCH3) 2. As in reverse transformation, a pyridine ligand is coordinated to a Fe-I centre, and can be replaced by a solvent molecule under appropriate conditions, which could mimic the function of the flexible coordination site in the H(2)ase enzymes. Electrochemical studies also show complex 1 can catalyze hydrogen evolution from HOAc and aqueous media at -1.26 V. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.