Synthesis, structure, and chromogenic properties of polymethylene-vaulted trans-bis(salicylaldiminato)palladium(II) complexes

The synthesis, structure, and chromogenic properties of polymethylene-vaulted trans-bis(salicylaldiminato)palladium(II) complexes are described. A series of the Pd complexes incorporating nona-, deca-, undeca- and dodecamethylene bridges (1a: n = 9; 1b: n = 10; 1c: n = 11; 1d: n = 12) was prepared by the treatment of Pd(OAc)2 with the corresponding N,N′-bis(salicylidene)-1,ω-alkanediamines. The trans-coordination, vaulted structures, and crystal packing of 1a–d have been unequivocally established from X-ray diffraction studies. Complexes 1a–d exhibit linker-dependent chromatic properties in 2-methyl-2,3,4,5-tetrahydrofuran, where the absorption wavelengths at around 400 nm are shifted hypsochromically with a decrease in the linker length, which is in contrast to the structure-independence of the absorption properties for the corresponding polymethylene-vaulted Pt analogues 2a–d observed under the same conditions. Density functional theory and time-dependent DFT calculations revealed that the present specific linker dependence in the chromism of 1 is ascribed to specific alteration of the d–π conjugation on the flexible trans-bis(salicylaldiminato)palladium coordination platforms by variation of the coordination planarity.

Graphical abstractPolymethylene-vaulted trans-bis(salicylaldiminato)palladium(II) complexes exhibit highly regular variations in absorption intensities and wavelengths with changes in the linkage length.Figure optionsDownload full-size imageDownload as PowerPoint slide