The Synthesis and Crystallographic Characterization of Emissive Pt(II) and Au(I) Compounds Exploiting the 2-Ethynylpyrimidine Ligand

The luminescent properties of Au(I) and Pt(II) compounds are commonly tuned by exploiting the alkynyl ligand with varying electron density. Herein, we describe the synthesis of three new emissive transition metal compounds, ^tbpyPt(C₂pym)₂, Ph₃PAuC₂pym, and Cy₃PAuC₂pym (where HC₂pym = 2-ethynylpyrimidine), verified by ¹H-NMR, EA, and a single-crystal X-ray diffraction analysis. The ^tbpyPt(C₂pym)₂ complex crystallized as an Et₂O solvate in the orthorhombic space group Pbca with Z = 24 with three unique Pt(II) species within the unit cell. The Cy₃PAuC₂pym species crystallizes in a monoclinic space group with one unique complex in the asymmetric unit. Changing the identity of the phosphine from Cy₃P to Ph₃P influences interactions within the unit cell. Ph₃PAuC₂pym, which also crystalizes in a monoclinic space group, has an aurophilic bonding interaction Au–Au distance of 3.0722(2) Å, which is not present in crystalline Cy₃PAuC₂pym. Regarding optical properties, the use of an electron-deficient heterocycle provides an alternate approach to blue-shifting the emission of Pt(II) transition metals’ compounds, where the aryl moiety is made more electron-deficient by exploiting nitrogen within this moiety instead of the typical strategy of decorating the aryl ring with electron withdrawing substituents (e.g., fluorines). This is indicated by the blue-shift in emission that occurs in ^tbpyPt(C₂pym)₂ (λ_max, emission = 512 nm) compared to the previously reported ^tbpyPt(C₂2-py)₂ (where HC₂2-py = 2-ethynylpyridine) complex (λ_max, emission = 520 nm).