Luminescent Thermochromism in a Gold(I)–Copper(I) Phosphine–Pyridine Complex

The Au I complex [Au(Ph 2 PCH 2 py) 2 ]BF 4 ( 1 ) was prepared by mixing (tetrahydrothiophene)gold(I) chloride with 2‐[(diphenylphosphino)methyl]pyridine (Ph 2 PCH 2 py) in dichloromethane. The addition of [Cu(NCCH 3 ) 4 ]BF 4 to 1 produced green‐luminescent [AuCu(Ph 2 PCH 2 py) 2 (NCCH 3 ) 2 ](BF 4 ) 2 ( 2 ). When crystals of 2 were exposed to air, two acetonitrile molecules were lost to form crystals of yellow‐luminescent [AuCu(Ph 2 PCH 2 py) 2 ](BF 4 ) 2 ( 3 ). This simple solvent loss perturbs the environment around the Cu I center, and the Au ··· Cu distance shortens from 3.3 to 2.8 Å. Crystallization of 2 or 3 from dichloromethane produced the two‐coordinate Cu I –solvate complex, [AuCu(Ph 2 PCH 2 py) 2 ](BF 4 ) 2 · CH 2 Cl 2 ( 3· CH 2 Cl 2 ). Compound 3 exhibits temperature‐dependent emissions from 77 to 298 K (543 nm), 298 to 343 K (551 nm), and above 343 K (505 nm) that is reversed upon return to room temperature. The low‐temperature emission is typical of complexes with luminescent rigidochromic properties. However, based on differential scanning calorimetry, a phase change is responsible for the high‐temperature emission of 3 .