Heterometallic Extended Metal Atom Chain Complexes with Carboxylate (O2CX) Axial Ligands

This work reports the preparation of Mo2Ni(dpa)4(O2CC6H4X)2 heterometallic extended metal atom chain complexes with a systematic series of substituted benzoate axial ligands (dpa = 2,2'-dipyridylamido). Here, X is the para substituent: CH3 (1_CH3), H (1_H), I (1_I), CN (1_CN), or CF3 (1_CF3). The synthetic route used to prepare these compounds builds upon our previous work on axial ligand substitutions with pseudohalides, as all compounds in series 1 are prepared in useful yields via the combination of the previously reported Mo2Ni(dpa)4(OTf)2 precursor with two equivalents of a [NEt4][O2CC6H4X] carboxylate salt. Crystallographic, spectroscopic, and magnetic measurements demonstrate that the compounds in series 1 possess similar structural and spectroscopic features and support an S = 1 Ni2+ paramagnetic center. Electrochemical studies show that the Mo24+/Mo25+ redox couple responds to the electronic characteristics of the axial benzoate para substituent (σp), with the E1/2 for the Mo24+/Mo25+ redox couple increasing with substituent σp. We also demonstrate that these synthetic methods are viable for ligands beyond the para-substituted benzoate series through the preparation and characterization of a Mo2Ni(dpa)4(O2CFc)2 complex, 2, where O2CFc = ferrocene carboxylate, a redox-active ligand.