Influence of the Pt→Ag Donor−Acceptor Bond and Polymorphism on the Spectroscopic and Optical Properties of Heteropolynuclear Benzoquinolateplatinum(II) Complexes

Abstract

A new cyclometalated derivative, (NBu4)[Pt(bzq)(C6Cl5)2] (2) (bzq = 7,8-benzoquinolate), and three novel polymetallic species containing donor−acceptor Pt→Ag bonds, (NBu4)[{Pt(bzq)(C6F5)2}2Ag] (3) and [{Pt(bzq)(C6X5)2}Ag(PPh3)] (X = F (4), Cl (5)), have been synthesized and characterized by X-ray diffraction methods. 3 is prepared by reaction of (NBu4)[Pt(bzq)(C6F5)2] (1) with AgClO4 in 1:1 or 1:0.5 molar ratio, while 4 and 5 are the results of the reaction of the corresponding (NBu4)[Pt(bzq)(C6X5)2] (X = F (1), Cl (2)) precursors with [Ag(OClO3)(PPh3)] in 1:1 molar ratio. 3 has been found to crystallize in two forms: monoclinic (3a) and triclinic (3b), which differ not only in the conformation of the basic Pt2Ag anion (anti and planar 3a, staggered and nonplanar 3b), but also in the crystal packing (π···π extended structure 3a, and a stacked dimer 3b) and luminescence at 298 K (orange 3a, green 3b). At 77 K, the orange band (568 nm) of 3a, attributed to a ππ* excimeric emission, is not detected, and both polymorphs exhibit identical green emission (3LC/3MLCT). Spectroscopic study of 4 and 5 (UV−vis and luminescence) was also performed to examine the role of the Pt→Ag donor−acceptor bond. The most significant feature is the blue shift observed in the low-energy UV absorption and the appearance of two, close, distinct, structured emissions with short (487 4; 490 nm 5) and long (502 nm 4, 5) lifetime, but only in the solid state at 77 K.