Reversible Solid-State Phase Transitions between Au-P Complexes Accompanied by Switchable Fluorescence

Six complexes {(3-bdppmapy)(AuCl)₂} (1-6; 3-bdppmapy = N,N'-bis(diphenylphosphanylmethyl)-3-aminopyridine and tht = tetrahydrothiophene) were simultaneously formed by the reaction of Au(tht)Cl and 3-bdppmapy in CH₂Cl₂ followed by infusion with hexane. Complexes 4-6 could be produced independently by volatilizing solvent in air, solid-state heating, or solvothermal reaction. The PPh₂-Au-Cl moieties extended in different directions, forming Au-Au and Au-Au-Au interactions. Complex 4 could be converted to 5 by heating to 130 °C, with the cleavage of one Au-Au bond, while 5 reverted back to 4 upon exposure to CH₂Cl₂ vapor over 11 h. This solid-state phase transition could be recycled and was accompanied by a change in solid-state fluorescence, without obvious intensity decay over five cycles. The reason for both the phase transition and difference in photoluminescence is related to the different numbers and strengths of aurophilic interactions in each complex that could be modeled by density functional theory calculations.