First examples of 3d-uranium compounds derived from single-compartment Schiff base ligands: Syntheses, crystal structures and d–d band correlation

This paper deals with the syntheses, characterization, crystal structures and UV–Vis spectroscopy of three diphenoxo-bridged dinuclear CuII(UVIO2) compounds [CuII(MeCN)L1(UVIO2)(NO3)2] (1), [CuII(MeCN)L2(UVIO2)(NO3)2] (2) and [CuII(MeCN)L3(UVIO2)(NO3)2] (3) derived from the single-compartment Schiff base ligands H2L1 (2:1 condensation product of salicylaldehyde and 1,3-diaminopropane), H2L2 (2:1 condensation product of salicylaldehyde and 1-ethyl-1,3-diaminopropane) and H2L3 (2:1 condensation product of 2-hydroxyacetophenone and 1,3-diaminopropane). While copper(II) occupies the N2O2 compartment, uranium(VI) center is linked with Schiff base ligand through the two bridging phenoxo oxygen atoms. Copper(II) is pentacoordinated and distorted square pyramidal, while the uranium(VI) center is octacoordinated and distorted hexagonal bipyramidal in which the two uranyl oxygen atoms occupy the apical positions. Electronic spectra of 1–3 and the corresponding mononuclear CuII compounds have been recorded and a previously reported but practically unexplored correlation regarding d–d band position has been highlighted. Although the correlation is not valid for only mononuclear or only dinuclear compounds derived from different ligands, a nice correlation is found out on comparing the spectra of dinuclear compounds with the corresponding mononuclear compounds.