Synthesis and optical characterisation of platinum(II) poly-yne polymers incorporating substituted 1,4-diethynylbenzene derivatives and an investigation of the intermolecular interactions in the diethynylbenzene molecular precursors

A series of 1,4-diethynylbenzene (1) derivatives, H-C≡C-R-C≡C-H with R = C₆H₃NH₂ (2), C₆H₃F (3), C₆H₂F₂-2,5 (4), C₆F₄ (5), C₆H₂(OCH₃)₂-2,5 (6) and C₆H₂(OⁿC₈H₁₇) ₂-2,5 (7) has been synthesised and their crystal structures determined by single crystal (2-5) or powder (6, 7) X-ray diffraction. The C≡CH⋯π_C≡=C hydrogen bonds dominating structure 1 are gradually replaced by C≡C-H⋯F ones with the increase of fluorination (3 → 5), or completely replaced by C≡CH⋯N and NH⋯π_C≡C bonds in 2, and C≡CH⋯O in 6 and 7. The related platinum-based polymers, trans-[-Pt(PⁿBu₃)₂-C≡C-R-C≡C-]) _n (R = as above and C₆H₄,) have been prepared and characterised by spectroscopic methods and thermogravimetry, which show that the amino- and methoxy-derivatives have lowest thermal stability while the fluorinated ones exhibit increasing thermal stability with increasing fluorination. Optical spectroscopic measurements reveal that substituents on the aromatic spacer group do not create strong donor-acceptor interactions along the rigid backbone of the organometallic polymers.