Structural and Luminescence Studies on π···π and Pt···Pt Interactions in Mixed Chloro-Isocyanide Cyclometalated Platinum(II) Complexes^†

Abstract

[Pt(bzq)Cl(CNR)] [bzq = benzoquinolinate; R = tert-butyl ((t)Bu 1), 2-6-dimethylphenyl (Xyl 2), 2-naphthyl (2-Np 3)] complexes have been synthesized and structurally and photophysically characterized. 1 was found to co-crystallize in two distinct pseudopolymorphs: a red form, which exhibits an infinite 1D-chain ([1](infinity)) and a yellow form, which contains discrete dimers ([1](2)), both stabilized by interplanar pi...pi (bzq) and short Pt...Pt bonding interactions. Complex 3, generated through the unexpected garnet-red double salt isomer [Pt(bzq)(CN-2-Np)(2)][Pt(bzq)Cl(2)] 4, crystallizes as yellow Pt...Pt dimers ([3](2)), while 2 only forms pi...pi (bzq) contacting dimers. Their electronic absorption and luminescence behaviors have been investigated. According to Time-Dependent Density Functional Theory (TD-DFT) calculations, the lowest-lying absorption (CH(2)Cl(2)) has been attributed to combined (1)ILCT and (1)MLCT/(1)ML'CT (L = bzq, L' = CNR) transitions, the latter increasing from 1 to 3. In solid state, while the yellow form [1](2) exhibits a green (3)MLCT unstructured emission only at 77 K, the 1-D form [1](infinity) displays a characteristic low-energy red emission (672 nm, 298 K; 744 nm, 77 K) attributed to a mixed (3)MMCT [d(sigma*)-->p(sigma)]/(3)MMLCT [dsigma*(M(2))-->sigma(pi*)(bzq)] excited state. However, upon exposure to standard atmospheric conditions, [1](infinity) shows an irreversible change to an orange-ochre solid, whose emissive properties are similar to those of the crude 1. Complexes 2 and 3 (77 K) exhibit a structured emission from discrete fragments ((3)LC/(3)MLCT), whereas the luminescence of the garnet-red salt 4 is dominated by a low energy emission (680 nm, 298 K; 730 nm, 77 K) arising from a (3)MMLCT excited state. Solvent (CH(2)Cl(2), toluene, 2-MeTHF and CH(3)CN) and concentration-dependent emission studies at 298 K and at 77 K are also reported for 1-3. In CH(2)Cl(2) solution, the low phosphorescent emission band is ascribed to bzq intraligand charge transfer (3)ILCT mixed with metal-to-ligand (L = bzq, L' = CNR) charge transfer (3)MLCT/(3)ML'CT character with the Pt to CNR contribution increasing from 1 to 3, according to computational studies.

Cytotoxic performances of new anionic cyclometalated Pt(II) complexes bearing chelated O^O ligands

“…The UV–visible absorption spectra in dimethylsulfoxide (DMSO) solution of the Aliz series 4 – 7 are shown in Figure . All the cyclometalated complexes 4 – 6 displayed intense bands in the UV region between 280 and 330 nm assigned to the allowed 1 LC(π–π*) transitions localized on the PhPy, ThPy and Bzq ligands . The low‐energy absorption bands between 330 and 650 nm of 4 – 7 were instead attributed to a mixed (metal–ligand charge transfer (MLCT)–ligand‐centred (LC)) character, which predominantly involved the chelating ligand, in agreement with the experimental and theoretical electronic spectra of the Aliz molecule …”

Pt(II) Complexes with Azolate-containing Bidentate Chelate: Design, Photophysics, and Application

“…This feature is akin to that of Pt(II) complexes with severe aggregation in the solid state, particularly to those with a 1D infinite‐chain‐like stacking arrangement . Thus, we can confidently assign this lowest energy emission to MMLCT, for which the packing arrangement is probably switching from the single Pt(II) complex and/or Pt 3 trimer to the infinite metal chain‐like structure which is stabilized by the formation of chain‐like Pt⋯Pt interaction after rinsing with acetone. Moreover, the formation of a red‐emitting solid can be also achieved using solvents such as THF, CHCl 3 , DMF, and methanol, confirming its link to the solvent polarity in altering the stacking interaction in the solid state.…”

Pt2Tl Building Blocks for Two-Dimensional Extended Solids: Synthesis, Crystal Structures, and Luminescence

“…The trinuclear “Pt 2 Tl” units rearrange in the crystal generating two-dimensional (2D) networks through additional stabilizing contacts. On one hand, the “Pt 2 Tl” units stack through intermolecular Pt···Pt (3.340 Å, 3.310 Å 2A ; 3.401 Å, 3.240 Å 2B ) interactions − and weak π–π contacts between the NHC and the acac ligands (the shortest atomic separation between two neighboring units is 3.467 Å 2A ; 3.429 Å 2B , see Figures b and b), giving rise to almost linear PtB–Tl–PtA··PtA–Tl–PtB···PtB wires in 2A [angles: PtB–Tl–PtA: 169.813°, Tl–PtA··PtA: 158.77°, Tl–PtB···PtB: 165.32°] and zigzag chains in 2B [angles: PtB–Tl–PtA: 145.512°, Tl–PtA··PtA: 177.80°, Tl–PtB···PtB: 160.07°]. These chains appear linked together through two additional Tl–E (E′) (E, E′ = N 2A , O 2B ) bonds with the R substituents of the R–C^C* groups (R= CN 2A , CO 2 Et 2B ) belonging to the two adjacent chains (see Figures c and c).…”