Self-Alignment of Low-Valent Octanuclear Palladium Atoms

A linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm) was used to synthesize linear octapalladium-extended metal atom chains as discrete molecules of [Pd-8(mu-dpmppm)(4)](BF4)(4) (1) and [Pd-8(mu-dpmppm)(4)L-2](BF4)(4) (L = 2,6-xylyl isocyanide (XylNC; 2), acetonitrile (3), and N, N-dimethylformamide (dmf; 4)), which are stable in the solution states and show interesting temperature-dependent photochemical properties in the near IR region. Variable temperature NMR studies demonstrated that at higher temperature T approximate to 140 degrees C the Pd-8 chains were dissociated into Pd-4 fragments, which were thermodynamically self-aligned to restore the Pd-8 chains at lower temperature T < 60 degrees C. The coldspray ionization mass spectra suggested a possibility for further aggregation of the linear tetrapalladium units.