Solution and solid-state properties of luminescent M-M bond-containing coordination/organometallic polymers using the RNC-M2(dppm)2-CNR building blocks (M = Pd, Pt; R = Aryl, Alkyl)

Two families of organometallic polymers built upon the bimetallic M2(dppm)2L(2)2+ fragments (M = Pd, Pt; dppm = bis(diphenylphosphino)methane, L = 1,4-diisocyano-2,3,5,6-tetramethylbenzene (diiso), 1,8-diisocyano-p-menthane (dmb), 1-isocyano-2,6-dimethylbenzene, 1-isocyano-4-isopropylbenzene, and tert-butylisocyanide) were synthesized and fully characterized (1H and 31P NMR, X-ray crystallography (model compounds), IR, Raman, chem. anal., TGA, DSC, powder XRD, 31P NMR T1 and NOE, light scattering, and conductivity measurements). Evidence for polymers in the solid state is provided from the swelling of the polymers upon dissolution and the formation of stand-alone films. However, these species become small oligomers when dissolved. The materials are luminescent in the solid state at 298 and 77 K and in PrCN solution at 77 K. These emissions result from triplet 3(d sigma d sigma*) states despite the presence of low-lying pi-pi* MO levels according to DFT calculations for the aryl isocyanide model compounds. The emission band maxima are located between 640 and 750 nm and exhibit lifetimes of 3-6 ns for the Pd species and 3-4 micros for the Pt analogues in PrCN solution at 77 K. No evidence of intramolecular excitonic photoprocesses was found in any of the polymers.