Luminescent polymorphism of mononuclear Cu(I) complexes with pyrazolo[1,5-a][1,10]phenanthrolines

Abstract

Six copper(I) complex compounds with new bidentate phenanthroline-like ligands, pyrazolo[1,5-a][1,10]phenanthroline-3-carbonitrile (L1) and 1-(pyrazolo[1,5-a][1,10]phenanthrolin-3-yl)ethan-1-one (L2), have been synthesized. A reaction of copper(I) iodide with L1 or L2 leads to the formation of binuclear complexes [Cu2(Ln)2I2]·Solv, which have rhomboid binuclear fragment {Cu2I2} according to the single crystal X-ray diffraction. These complexes are gradually oxidized on air and do not show any photoluminescence. At the same time, reaction between the ligand (L1 or L2), triphenylphosphine and copper(I) iodide produces mononuclear coordination compounds [CuLn(PPh3)I]. It has been discovered that the [CuL1(PPh3)I] complex can be isolated as two polymorph modifications. The mononuclear complexes demonstrate microsecond red luminescence: λmax = 700 nm for [CuL2(PPh3)I], λmax = 640 nm for the first polymorph of [CuL1(PPh3)I] (2a) and λmax = 700 nm for the second polymorph (2b). Also for [CuL1(PPh3)I] polymorphs excitation-dependent emission has been detected at 77 K.