Modulation of Metallophilic and π–π Interactions in Platinum Cyclometalated Luminophores with Halogen Bonding

Abstract

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 IC6F5 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⋅⋅⋅IC6F5 has little effect on the charge distribution, but strongly affects 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 yield dynamic XB‐supported systems, exemplified by thermally regulated transition 3↔3⋅⋅⋅IC6F5.

Photophysics and Excited State Dynamics of Cyclometalated [M(Phbpy)(CN)] (M = Ni, Pd, Pt) Complexes: A Theoretical and Experimental Study

“…The crystal structures of [Pd­(Phbpy)­(CN)] and [Ni­(Phbpy)­(CN)] were both solved in the triclinic space group P 1̅. They are isostructural to the recently reported complex [Pt­(Phbpy)­(CN)], and all crystal structures show very similar features (for details, see SI) including pronounced stacking ( vide infra ). In the crystal, the Ni and Pd compounds form dimeric structures with head-to-tail stacking as recently reported in the solid state for the Pt derivative [Pt­(Phbpy)­(CN)] and other [M­(Phbpy)­X] complexes. − A closer look reveals short metal···metal contacts of 3.1965(4)/​3.3278(4) Å (Ni), 3.2152(10)/​3.2917(9) Å (Pd), and 3.2865(4)/3.2232(4) Å (Pt) for the three complexes [M­(Phbpy)­(CN)] (two values correspond to two independent molecules found in the unit cell); these dimeric units are separated by interdimer M···M distances of 5.261/​4.933 Å (Ni), 5.205/​5.084 Å (Pd), and 5.229/​5.030 Å (Pt), respectively (Figure and Figure S1, SI).…”

“…Furthermore, in recent years, quantum chemical modeling of excited states and their dynamics using density functional theory (DFT) have been the key for robust structure–property relationships for such triplet or TADF emitters. ,− …”

Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me2dpb)Cl] Obtained from C‒H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me2dpbH)

“…The d 8 electron configured metals adopt square-planar geometries with open coordination vacancies in the axial positions. These axial flanks can lead to metal–metal (M···M) and/or π···π stacking interactions in aggregates with red-shifted emissions from MMLCT states (metal–metal-to-ligand charge transfer character, eventually with excimeric M···M shortening), along with metal-perturbed ligand-centred (π‒π*) excited configurations of the monomeric species [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ].…”

Long-range supramolecular synthon polymorphism: a case study of two new polymorphic cocrystals of Ph2Te2–1,4-C6F4I2

“…In recent decades, the growing attention to non-covalent interactions has significantly expanded the crystal engineering toolkit 1–9 ‡‡See also CrystEngComm Themed Collections: “Halogen Bonding in Crystal Engineering Editor's collection, 2020”, “Halogen bonding: from self-assembly to materials and biomolecules, 2013”. and has sparked increased interest in cocrystals. 10–15 Directional, specific and tunable non-covalent interactions (especially σ- and π-hole 16,17 ones) make it possible to directly influence the packing of molecular cocrystals, expanding the structural landscape 17–22 of their components and allowing a deeper understanding of the fundamental molecular mechanisms of crystal formation.…”