Luminescent mononuclear copper(I) heteroleptic complexes with 6-cyano-2,2′-bipyridine

A new series of luminescent mononuclear Cu(I) heteroleptic complexes of 6-cyano-2,2′-bipyridine (cbpy), [Cu(cbpy)(PPh3)X] (X = I (1); Br (2)) and [Cu(cbpy)(PPh3)2](ClO4) (3), has been synthesized and characterized. It is revealed that phosphine in place of halide results in lengthening of the Cusingle bondP bond from 2.21 Å of 1 and 2.19 Å of 2 to 2.27 Å of 3. Complexes 1–3 display the weak low-energy absorption bands in the 350–600 nm region in dichloromethane, which are assigned to the Cu(I) to cbpy metal-to-ligand charge-transfer (MLCT) transitions, probably mixed with some halide-to-ligand charge-transfer (XLCT) character for 1 and 2. Complexes 1–3 show the solid-state emissions at ambient temperature, varying with the second auxiliary ligand coordinated to the {Cu(cbpy)(PPh3)} motif, which most likely originate from the MLCT excited states, perhaps involving some XLCT character for 1 and 2.