A “Flexible” Rigid Rod, trans-Pt(PMe₃)₂(C≡CC₆H₄CN)₂ (L1), to Form 2D [{Cu₂(μ₂-X)₂}₂(μ₄-L1)]_n Polymers (X = Br, I) Exhibiting the Largest Bathochromic Emissions

Abstract

The trans-Pt(PMe)(C≡CCHCN) organometallic ligand L1, which is prepared from 4-ethynylbenzonitrile and cis-Pt(PMe)Cl, binds CuX salts to form two strongly luminescent two-dimensional coordination polymers (CPs) [{Cu(μ-X)}(μ-L1)] (X = I, CP1; X = Br, CP2). The emission quantum yields, Φ ≈ 30% at 298 K, are the largest ones for all CPs built upon the trans-Pt(PMe)(C≡CCHX) motifs (X = SMe, CN). X-ray crystallography reveals that, to accommodate these layered CPs, L1 must undergo major distortions of the C≡C-C angles (∼159°) and significant rotations about the Pt-CC bonds, so that the dihedral angles made by the two aromatic planes is 90° in a quasi-identical manner for both CPs. Together, these two features represent the largest distortion for trans-Pt(PMe)(C≡CCHX) complexes among all of the CPs built upon this type of ligand (2 of 16 entries). Concurrently, CP1 and CP2 also exhibit the most red-shifted emissions (λ = 650 and 640 nm, respectively) known for this type of chromophore at room temperature. The {Cu(μ-X)} rhomboids adopt the trans- (X = I, common) and cis-geometries (X = Br, extremely rare) making them "isomers" if excluding the fact that the halides are different. Density functional theory (DFT) and time-dependent DFT suggest that the triplet emissive excited state is metal/halide-to-ligand charge transfer in both cases despite this difference in rhomboid geometry.

A Platinum(II) Organometallic Building Block for the Design of Emissive Copper(I) and Silver(I) Coordination Polymers

“…One interesting class of organometallic ligands includes the platinum­(II)-containing complexes, which are sometime reported to be highly emissive , and electrochromic . An interesting class of materials is the trans -bis­(phenylacetynyl)­bis­(phosphine)­platinum­(II) species ( L2a – c ; Chart ), which is prone to form coordination polymers through η 2 -CC coordination with copper and silver. , Upon introduction of supplementary coordination sites, 1D and porous 2D coordination polymers are formed with copper­(I) halide salts and have the particularity of being strongly luminescent, , with emission exhibiting quantum yields reaching 30% and extending well into the near-IR region . Concurrently, structurally related polynuclear complexes containing a trans -dicyanobis­(phosphine)­platinum­(II) unit are also known, − which can also exhibit emission on occasions, , but to the best of our knowledge, no coordination polymer incorporating this synthon within its chain has been prepared.…”

“…Moreover, when the MeS center is solicited, 2D grids are generated; otherwise the resulting CP is 1D. This observation is also consistent with previous studies on the organometallic ligands L2b and L2c (Chart ), which demonstrates that when the SMe or CN groups are involved in the coordination network, then 2D CPs are systematically produced. − A key difference between L1 and L2b is that the solvent molecules are found between layers in CP4–CP7 , whereas in CPs of the type [Cu 4 I 4 ( L2b )·solvent] n (solvent = MeCN, PrCN), the crystallization guests are found inside the cavity. This difference stems from the difference in ligand dimensions between the shorter L1 and longer L2b .…”

“…30,31 Upon introduction of supplementary coordination sites, 1D and porous 2D coordination polymers are formed with copper(I) halide salts and have the particularity of being strongly luminescent, 32,33 with emission exhibiting quantum yields reaching 30% and extending well into the near-IR region. 34 Concurrently, structurally related polynuclear complexes containing a trans-dicyanobis-(phosphine)platinum(II) unit are also known, 35−37 which can also exhibit emission on occasions, 38,39 but to the best of our knowledge, no coordination polymer incorporating this synthon within its chain has been prepared. We now report the synthesis and characterization of a new and versatile organometallic ligand, trans-cyano(p-ethynyl(methyl thioether)benzene)bis(trimethylphosphine)platinum(II) (L1; Chart 1), which can act as a tridentate ligand (η 2 -CC;…”