Dirhenium Paddlewheel Compounds Supported by <i>N</i>,<i>N</i><i>‘</i>-Dialkylbenzamidinates: Synthesis, Structures, and Photophysical Properties

Dirhenium(III,III) compounds Re2(DMBA)4Cl2 (1, DMBA = N,N‘-dimethylbenzamidinate) and Re2(DEBA)4Cl2 (2, DEBA = N,N‘-diethylbenzamidinate) were synthesized via molten reactions between Re2(OAc)4Cl2 and the corresponding amidine. Re2(DMBA)4(NO3)2 (3) was obtained through reacting Re2(DMBA)4Cl2 with AgNO3. Single crystal X-ray diffraction studies revealed that the Re−Re distances in compounds 1−3 are 2.212(1), 2.217(1), and 2.173(1) Å, respectively, which are consistent with the presence of a Re−Re quadruple bond. Voltammetric studies revealed that compound 2 exhibits two quasireversible couples, an oxidation and a reduction, and an irreversible reduction, while compound 1 displays irreversible couples at similar potentials. The three complexes exhibit 1δδ* absorption as a shoulder at ∼440 nm (ε ∼1500 M-1 cm-1). Upon excitation of solid samples or CH2Cl2 solutions of 2 with visible light, emission is observed at 824 nm (77 K) and 833 nm (298 K), respectively. The luminescence is assigned as arising from the 3δδ* excited state.