Mixed-Ligand Organometallic Polymers Containing the “Pd₂(dmb)₂²⁺” Fragment: Properties of the {Pd₂(dmb)₂(diphos)²⁺}<i>_n</i> Polymers/Oligomers in Solution and in the Solid State

The 1:1 reaction between the d9−d9 Pd2(dmb)2Cl2 complex (dmb = 1,8-diisocyano-p-menthane) and the diphosphine ligands (diphos) bis(diphenylphosphino)butane (5, dppb), bis(diphenylphosphino)pentane (6, dpppen), bis(diphenylphosphino)hexane (7, dpph), and bis(diphenylphosphino)acetylene (8, dpa) in the presence of LiClO4 leads to the {[Pd2(dmb)2(diphos)](ClO4)2}n polymers. These new materials are characterized by NMR (1H, 13C, 31P), IR, Raman, and UV−vis spectroscopies (466 < λmax(dσ−dσ*) < 480 nm), by ATG, XRD, and DSC methods, and by the capacity to make stand-alone films. From the measurements of the intrinsic viscosity in acetonitrile, the Mn ranges from 16000 to 18400 (12 to 16 units). The dinuclear model complex [Pd2(dmb)2(PPh3)2](ClO4)2 (4) is prepared and investigated as well. The molecular dynamic of the title polymers in acetonitrile solution is investigated by means of 13C spin−lattice relaxation time (T1) and nuclear Overhauser enhancement methods (NOE). The number of units determined by T1/NOE methods is 3 to 4 times less than that found from the measurements of intrinsic viscosity, and is due to flexibility in the polymer backbone, even for bridging ligands containing only one (dmb) or two C−C single bonds (dpa). During the course of this study, the starting material Pd2(dmb)2Cl2 was reinvestigated after evidence for oligomers in the MALDI-TOF spectrum was noticed. In solution, this d9−d9 species is a binuclear complex (T1/NOE). This result suggests that the structure of the title polymers in solution and in the solid state may not be the same either. Finally, these polymers are strongly luminescent in PrCN glasses at 77 K, and the photophysical data (emission lifetimes, 1.50 < τe < 2.75 ns; quantum yields, 0.026 < Φe < 0.17) are presented. X-ray data for [Pd2(dppe)2(dmb)2](PF6)4: monoclinic, space group C2/c, a = 24.3735 Å, b = 21.8576(13) Å, c = 18.0034(9) Å, b = 119.775(1)°, V = 8325.0(8) Å3, Z = 4.