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

Abstract

Six‐ and seven‐membered cyclic hydroxamic acids are found as terminal binding units in different families of siderophores, including exochelins and mycobactins. The simplest models of these preorganized chelating ligands were known, but their coordination chemistry with Fe3+, the target metal ion of siderophores, had never been reported. Four complexes were synthesized and studied: two Fe3+ complexes, one with the six‐membered ring hydroxamate PIPO− and one with the seven‐membered ring hydroxamate AZEPO−, and the two corresponding Ga3+ complexes. X‐ray diffraction studies showed that the interligand repulsion energies were better minimized in the case of the AZEPO− complexes whatever the metal cation considered, and that the Fe−O bond distances were shorter in [Fe(AZEPO)3] by comparison with [Fe(PIPO)3].

Structural Diversity in Ga/In-Hydroxamate Metal–Organic Materials

“…They are all constructed from the same basic node of In 3+ chelated by three hydroxamate groups from three TDHA ligands, but variations in coordination modes and (θ) angles led to very different outcomes. The robust formation of identical Ga/In­(hydroxamate) 3 nodes in these MOMs suggested that these moieties were stable and favored, concurring with previously reported hydroxamate-chelated Group 13 metal complexes. , Moreover, similar phenomena were recorded in the MOF literature where identical PBUs/SBUs could be interconnected by ligands of the same basic geometry to form diverse topologies. − …”

“…The robust formation of identical Ga/In-(hydroxamate) 3 nodes in these MOMs suggested that these moieties were stable and favored, concurring with previously reported hydroxamate-chelated Group 13 metal complexes. 37,38 Moreover, similar phenomena were recorded in the MOF literature where identical PBUs/SBUs could be interconnected by ligands of the same basic geometry to form diverse topologies. 39−42 For SUM-82, NH 3 •H 2 O was a key factor in the reaction between In(NO 3 ) 3 •4.5H 2 O and H 2 -TDHA when used as a modulator (Figure 3a).…”