Modulation of metallophilic and π-π interactions in platinum cyclometalated luminophores with halogen bonding.

Luminescent cyclometalated complexes [M(C^N^N)CN] (M = Pt, Pd; HC^N^N = pyridinyl- (M = Pt 1 , Pd 5 ), benzyltriazolyl- (M = Pt 2 ), indazolyl- (M = Pt 3 , Pd 6 ), pyrazolyl-phenylpyridine (M = Pt 4 )) decorated with cyanide ligand, have been explored as nucleophilic building blocks for the construction of halogen-bonded (XB) adducts using IC 6 F 5 as an XB donor. The negative electrostatic potential of the CN group afforded CN … I noncovalent interactions for platinum complexes 1 - 3 ; the energies of XB contacts are comparable to those of metallophilic bonding according to QTAIM analysis. Embedding the chromophore units into XB adducts 1 - 3 … IC 6 F 5 has a little effect on the charge distribution, but strongly effects Pt … Pt bonding and π-stacking, which lead to excited states of MMLCT (metal-metal-to-ligand charge transfer) origin. The energies of these states and the photoemissive properties of the crystalline materials are primarily determined by the degree of aggregation of the luminophores via metal-metal interactions. The adduct formation depends on the nature of the metal and the structure of the metalated ligand, the variation of which can afford dynamic XB-supported systems, exemplified by thermally regulated transition 3 ↔ 3 … IC 6 F 5 .