Multistep Oligometal Complexation of the Macrocyclic Tris(N₂O₂) Hexaoxime Ligand

Abstract

A macrocyclic oxime ligand H(6)L, which has an O(6) cavity surrounded by three N(2)O(2) chelate sites, was synthesized and the multistep oligometal complexation behavior was investigated. Upon complexation with zinc(II), the H(6)L ligand afforded two kinds of hexanuclear complexes, L(2)Zn(6) then LZn(6). Each of the complexation steps proceeded highly efficiently. In the latter complex, a Zn(3)(μ(3)-OH) unit was incorporated into the trimetalated ligand, LZn(3). The integrated N(2)O(2) chelate coordination sites provide a unique environment for a homometallic complex. The different nature of the peripheral N(2)O(2) sites and the central O(6) site is particularly suitable for the selective formation of heterometallic complexes. Complexation with the zinc(II) ion in the presence of alkaline earth (Ca and Ba) or rare earth (La, Eu, Lu) metal ions afforded the heterotetranuclear complexes LZn(3)M (M=Ca, Ba, La, Eu, Lu), in which zinc(II) and ion M occupied the N(2)O(2) and O(6) sites, respectively. Titration experiments showed that the heterometallic complexes LZn(3) Ca and LZn(3) Ba were converted into the homometallic complex LZn(6) whereas LZn(3)La was not. As a result, the binding affinity in the central O(6) site of the LZn(3) unit is apparently in the order of Ca(2+), Ba(2+) <Zn(3)(μ(3)-OH)<La(3+). This difference in the affinities of metal ions as well as the ionic sizes makes the novel conversion efficient, particularly in the case of the three-step conversion from H(6)L to H(2)LZn(2)Ba, LZn(3)Ba, then LZn(6).

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

“…We have already demonstrated that a binding selectivity trend of alkali metal << Zn 2+ < alkaline earth < rare earth metal ions was observed in the shorter L 1 Zn2M system [57] and related complexes [79][80][81][82][83] without chiral auxiliary. If the longer L 4 Zn3M system having a chiral auxiliary also shows a similar selectivity trend, Ba 2+ in the L 4 Zn3Ba can be efficiently replaced by La 3+ .…”

Unprecedented Dinuclear CuII N,O-Donor Complex: Synthesis, Structural Characterization, Fluorescence Property, and Hirshfeld Analysis

“…In the crystal structure of the Cu II complex, there were three intermolecular (C8−H8A···O1, C24−H24A···Cl5, and C25−H25A···O8) and one intramolecular (C24−H24A···O3) hydrogen bondings (see Table 4), which played a role in stabilizing the crystal structure of the Cu II complex [72,73]. As a result, the Cu II complex formed a self-assembled infinite two-dimensional supramolecular structure via intermolecular hydrogen bondings, as shown in Figure 3.…”

“…In the Hirshfeld surface, the existence of strong interactions showed up as red spots [74], while the blue regions were related to weak contacts. The Hirshfeld surface analysis of the Cu II complex is as depicted in Figure 4a (see Table 4), which played a role in stabilizing the crystal structure of the Cu II complex [72,73]. As a result, the Cu II complex formed a self-assembled infinite two-dimensional supramolecular structure via intermolecular hydrogen bondings, as shown in Figure 3.…”

Lanthanide induced variability in localised CoII geometries of four triangular L3Co3IILnIII complexes

“…31 This metal cation templated route provided a vast improvement in yield over their previous metal-free attempts to perform 3 + 3 Schiff base condensations of 1,4diformylbenzene-2,3-diol with various diamine linkers. 32 This same method involving templated macrocyclisation was later extended to include various combinations of trivalent lanthanide ions with Zn II , [33][34][35][36][37][38][39][40] Cu II , [41][42][43][44][45][46] Ni II , 47 or Co II centres. 48 Families of triangular macrocyclic complexes containing Zn II , Cu II , and Ni II with a variety of Ln III have been investigated by Brooker et al for their magnetic properties.…”