Diaquadinitratouranyl(VI) enforces the O(phenoxo)2O(methoxy)2 compartment of 3-methoxysalicylaldehyde-diamine ligands to interact with water molecules

This report presents the syntheses, characterization and crystal structures of [{CuIIL1}2·{(UVIO2)(NO3)2(H2O)2}] (1), [{CuIIL2}2·{(UVIO2)(NO3)2(H2O)2}]·2H2O (2) and [{CuIIL3}2·{(UVIO2)(NO3)2(H2O)2}]·2H2O (3) derived from three 3-methoxysalicylaldehyde-diamine Schiff base compartmental ligands H2L1, H2L2 and H2L3, in which the diimine moieties come from ethylenediamine, trans-1,2-diaminocyclohexane and ortho-phenylenediamine, respectively. Compounds 2 and 3 crystallize in triclinic crystal system having P 1 ¯ space group, while compound 1 crystallizes in monoclinic symmetry with space group P21/c. The three structures are similar. The two coordinated water molecules in diaquadinitratouranyl(VI) occupy the two trans positions in the hexagonal basal plane of the hexagonal bipyramidal coordination environment. Each of these two water molecules interact, by forming bifurcated hydrogen bonds, with each of the two O(phenoxo)2O(methoxy)2 compartments resulting in the stabilization of the [1 × 2 + 1 × 1] trimetallic self-assemblies. The d–d spectra of 1–3 and the corresponding mononuclear copper(II) complexes [CuIIL1(H2O)]/[CuIIL2(H2O)]/[CuIIL3(H2O)] have been recorded. The previously proposed but little addressed correlation of d–d band position with the displacement of the copper(II) center from the least-squares basal plane has been highlighted, revealing the utilization of this correlation accompanied with the FT-IR data to judge the nature of water molecule in the mononuclear complexes. The unique features in the composition of 1–3 have been discussed.