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–CC–R–CC–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 CCH⋯πCC hydrogen bonds dominating structure 1 are gradually replaced by CC–H⋯F ones with the increase of fluorination (3 → 5), or completely replaced by CCH⋯N and NH⋯πCC bonds in 2, and CCH⋯O in 6 and 7. The related platinum-based polymers, trans-[–Pt(PnBu3)2–CC–R–CC–]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.