Bis(nitrate)diaquauranyl(vi) synthon to generate [1 × 2 + 1 × 1] and [1 × 1 + 1 × 1] co-crystalized 3d⋯5f self-assemblies

Abstract

The syntheses, characterization and crystal structures of four copper(II)/nickel(II)⋯uranyl(VI) self-assemblies of composition [{Ni^IIL¹}₂·{(U^VIO₂)(NO₃)₂(H₂O)₂}] (1), [{Cu^IIL²}₂·{(U^VIO₂)(NO₃)₂(H₂O)₂}]·0.68H₂O (2), [{Ni^IIL²}₂·{(U^VIO₂)(NO₃)₂(H₂O)₂}] (3) and [{Cu^IIL³}·{(U^VIO₂)(NO₃)₂(H₂O)₂}]_n (4) are described in this investigation (H₂L¹, H₂L² and H₂L³ are the Schiff base ligands obtained on condensing 3-ethoxysalicylaldehyde with ethylenediamine, o-phenylenediamine and trans-1,2-diaminocyclohexane, respectively). Compounds 1 and 4 crystallized in the monoclinic P2₁/n and C2/c space groups, respectively, while compounds 2 and 3 crystallized in the triclinic space group P. Two water molecules of the [(U^VIO₂)(NO₃)₂(H₂O)₂] moiety in 1–4, have a linear H₂O–U–OH₂ arrangement. Each of these two water molecules in 1–3 interacts with the O(phenoxo)₂O(ethoxy)₂ compartment of a mononuclear copper(II) or nickel(II) moiety due to the formation of bifurcated hydrogen bonds between each of the two water hydrogen atoms and a pair of one phenoxo and one ethoxy oxygen atoms resulting in the interlinking of the two mononuclear 3d units by the [(U^VIO₂)(NO₃)₂(H₂O)₂] synthon and therefore these three compounds may be considered as supramolecular dimers. Compounds 1–3 are also two component [1 × 2 + 1 × 1] co-crystals consisting of two mononuclear copper(II) or nickel(II) units and one [(U^VIO₂)(NO₃)₂(H₂O)₂] moiety. On the other hand, in 4, two water molecules, from two different [(U^VIO₂)(NO₃)₂(H₂O)₂] moieties, interact with one O(phenoxo)₂O(ethoxy)₂ compartment resulting in the formation of a self-assembled one-dimensional topology. Again, since one mononuclear copper(II) unit and one [(U^VIO₂)(NO₃)₂(H₂O)₂] moiety exist in a single crystal in 4, this compound is a two component [1 × 1 + 1 × 1] co-crystal. The outcomes of the present study utilize [(U^VIO₂)(NO₃)₂(H₂O)₂] synthon to derive 3d⋯5f co-crystals, provide the first observation of the interaction of two water molecules with one O(phenoxo)₂O(ethoxy)₂ compartment, demonstrate the formation of supramolecular dimers and show the first example of a one-dimensional self-assembly resulting from water⋯O₄ compartment hydrogen bonds, and the first example of [1 × 2 + 1 × 1] co-crystals in 3-ethoxysalicylaldehyde-diamine ligand system.