Five neutral nickel(II) bimetallic models of the active site of [NiFe]-hydrogenase supported by tridentate sulfur-rich RNS 2 ligands, were synthesized and tested as electrocatalysts for proton (H + ) reduction. Complexes were classified according to the À NR substituent (1: 1-methylpyrene; 2: 2-methylthiophene; 3: phenyl) and as type a for those without bulky substituents and type b for the analogues with voluminous groups. Solid state structures were determined for three dimers, revealing [Ni 2 (μ-SAr) 2 ] frameworks, in which the two coordination planes around the Ni centres define a dihedral angle (θ) that is influenced by the substituents on the ligands (2 a:Using CF 3 COOH as H + source, 1 b and 2 b exhibit catalytic activity at À 1.72 V (i cat /i p � 2.40) and À 1.80 V (i cat /i p � 2.89) vs the ferrocenium/ferrocene couple (Fc + / Fc), respectively. In contrast, type a complexes were not viable catalysts. This behaviour suggests a relationship between the dimer conformation and its activity, due to a Ni ••• Ni cooperative effect, which is favoured in angular molecules and appears to assist during electrocatalytic H + reduction.