The design and development of suitable biomimetic catalytic systems capable of mimicking the functional properties of enzymes continues to be a challenge for bioinorganic chemists. In this study, we report on the synthesis, X-ray structures, and physicochemical characterization of the novel isostructural [Fe^IIICo^II(BPBPMP)(μ-OAc)₂]CIO₄ (1) and [Ga^IIICo^II(BPBPMP)(μ-OAc)₂]CIO ₄ (2) complexes with the unsymmetrical dinucleating ligand H ₂BPBPMP (2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl) -(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol). The previously reported complex [Fe^III Zn^II(BPBPMP)(μ-OAc)₂]CIO ₄ (3) was investigated here by electron paramagnetic resonance for comparison with such studies on 1 and 2. A magneto-structural correlation between the exchange parameter J (cm^-1) and the average bond lengh of (Å) of the [Fe^III-O-M^II] structural unit for 1 and for related isostructural Fe^IIIM^II complexes using the correlation J = -10⁷ exp(-6.8d) reveals that this parameter is the major factor that determines the degree of antiferromagnetic coupling in the series [(BPBPMP)Fe^III(μ-OAc)₂M^II] ⁺(M^II = Mn, Fe, Co, Ni) of complexes. Potentiometric and spectrophotometric titrations along with electronic absorption studies show that, in aqueous solution, complexes 1 and 2 generate the [(HO)M ^III(μ-OH)CO^II(H₂O)] complex as the catalytically active species in diester hydrolysis reactions. Kinetic studies on the hydrolysis of the model substrate bis(2,4-dinitrophenyl)phosphate by 1 and 2 show Michaelis - Menten behavior, with 2 being 35% more active than 1. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal M^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst. In addition, the complexes show maximum catalytic activity in DNA hydrolysis near physiological pH. The modest reactivity difference between 1 and 2 is consistent with the slightly increased nucleophilic character of the Ga^III- OH terminal group in comparison to Fe^III - OH in the dinuclear M^IIICo ^II species.