Synthesis, characterisation, and solution behaviour of two dioxomolybdenum(VI) complexes of a bis(catecholamide) siderophore analogue

Abstract

The bis(catecholamide) α,αЈ-bis(2,3-dihydroxybenzoylamino)-m-xylene (H 4 L 3 ) has been synthesized and characterised. It is an analogue of the naturally occurring siderophore azotochelin and structurally related to an approved enterobactin model. Two dioxomolybdenum() complexes of it have been synthesized, namely a di-and a mono-nuclear one. Variable-temperature proton NMR studies of the initially obtained dinuclear compound revealed that three kinetic processes are operative in Me 2 SO solution: geometrical isomerisation at lower temperatures, and inversion of configuration concomitant with dissociation into the monomer at higher temperatures. In contrast, the mononuclear complex obtained in this way isomerises and inverts almost simultaneously at 343-353 K. The crystal structure of Na 2 [MoO 2 L 3 ] confirmed the mononuclear nature of the complex and revealed that the cis, cis, cis geometrical isomer is adopted in the solid state.

Synthesis and Structure of the Molecular Rectangle [{MoO2(C17H14N2O6)}2]4-

“…The geometry around the octahedral MoO 6 centres is distorted in a way typical for MoO 2 2+ core structures [2,8]. Due to their strong structural trans-influence, the two double bonded oxygen atoms are oriented cis to each other, and the Mo±O single bonds trans to the oxo ligands experiencing this influence are significantly longer [2.117(3) As evident from Figure 2, the planes of the amide groups are held nearly coplanar with the associated aromatic rings by intramolecular hydrogen bonding between the amide protons and the corresponding ortho-hydroxylates: d(N´´´O) = 2.70 and 2.71 A Ê .…”

“…The assembly of a molecular rectangle or box-like structure in combination with molybdenum as angular building block requires a ligand with planar bi-dentate subunits. On reaction of catecholamides with molybdate, two oxo-ligands remain coordinated to the molybdenum atom, thereby sealing up two adjacent coordination sites of the octahedral metal centre [2,8]. The four vacant coordination sites allow the binding of two catecholamides in a perpendicular orientation of the planar subunits, which is essential for the formation of molecular rectangles.…”

An [{Fe(mecam)}2]6− Bridge in the Crystal Structure of a Ferric Enterobactin Binding Protein

“…Which structure predominates depends on the type of spacer used 21. If the geometrical constraints of the spacer are not unequivocal, mixtures of species are obtained and additional stabilizing effects, such as interactions with cationic guests,23 π stacking,2 solvent, and temperature,24 determine the nuclearity.…”

An [{Fe(mecam)}2]6− Bridge in the Crystal Structure of a Ferric Enterobactin Binding Protein

“…Which structure predominates depends on the type of spacer used. [21] If the geometrical constraints of the spacer are not unequivocal, mixtures of species are obtained and additional stabilizing effects, such as interactions with cationic guests, [23] p stacking, [2] solvent, and temperature, [24] determine the nuclearity. Interestingly, in contrast to enterobactin, mecam delivers very little Fe to the cytoplasm.…”