A 4-tert-butylcalix[4]arene tetrahydroxamate podand based on the 1-oxypiperidine-2-one (1,2-PIPO⁻) chelate. Self-assembly into a supramolecular ionophore driven by coordination of tetravalent zirconium or hafnium(iv)

Abstract

K+ is encapsulated by 2 : 2 complexes of tetravalent zirconium or hafnium with the calix[4]arene podand 1H4 carrying four cyclic hydroxamate binding units.

Synthesis and Structural Study of Tetravalent (Zr4+, Hf4+, Ce4+, Th4+, U4+) Metal Complexes with Cyclic Hydroxamic Acids

“…This result is quite significant with regard to the lack of information on this subject, and highly useful with respect to the design of specific chelators for tetravalent metals, with applications in medical imaging ( 89 Zr 4+ ) and sequestration of highly toxic actinides such as Pu 4+ . Considering our previous work on a C 4 ‐symmetric podand (L) that bears four terminal 1,2‐PIPO – chelating units appended to a calix[4]arene scaffold,13a the facial instead of lateral binding mode observed herein for the nearly square‐antiprismatic [Zr( 1 ) 4 ] and [Zr( 6 ) 4 ] complexes provides a straightforward explanation for the formation of a [M 2 (L) 2 ]‐type supramolecular assembly rather than the desired [M(L)] stoichiometry. It now becomes clear that a tetrapodal ligand design does not appear to be well suited for creating useful 89 Zr 4+ sequestering agents.…”

“…In that respect, we envisioned that it would be interesting to explore the potential of chelators based on 1 H or 2 H, which have been ignored so far, for the coordination of tetravalent metals, including actinides. As a first step towards that goal, an octadentate tetrahydroxamic calix[4]arene podand that bears four terminal binding motifs derived from 3 H has been prepared and structurally characterized 13a. This receptor, which can be considered to be the first ever abiotic ligand that possesses only cyclic six‐membered hydroxamate groups, was shown to self‐assemble into a dimeric species of 2:2 stoichiometry upon coordinating to Zr 4+ or Hf 4+ rather than to form a mononuclear 1:1 complex.…”

Complexes of Fe(III) and Ga(III) Derived from the Cyclic 6‐ and 7‐Membered Hydroxamic Acids Found in Mixed Siderophores

“…[1a] We reported a structural study of the complexes of deprotonated 1-hydroxy-2piperidinone (PIPO À ) with tetravalent metal cations, including Zr 4 + , Hf 4 + , Ce 4 + , Th 4 + , and U 4 + . [15] We subsequently developed Zr(IV) chelators obtained either by attaching four optically active amino-functionalized PIPOH derivatives to a calix [4]arene platform [16] or by coupling a carboxylic acid-functionalized PIPOH derivative to the primary amine terminal residue of desferriferrioxamine B. [17] We now wish to disclose the results of the structural coordination chemistry studies that we carried out with the trivalent metal cations Fe 3 + , and Ga 3 + , a diamagnetic analog of Fe 3 + , with the cyclic hydroxamic acids PIPOH and AZEPOH.…”

Effects of preorganization in the chelation of UO22+by hydroxamate ligands: cyclic PIPO−vs.linear NMA−

“…27 Shortly before, we also described the very first receptor incorporating PIPO-based binding units. 29 This tetrapodal calix [4]arene derivative was shown to strongly bind zirconium(IV) and hafnium(IV) together with an additional alkaline cation (Alk = Na + or K + ) to form an inclusion complex of [Alk  M2L2] formula.…”