Iron(II)–alkoxide and –aryloxide complexes of a tris(thioether)borate ligand: synthesis, molecular structures, and implications on the origin of instability of their iron(II)–catecholate counterpart

The phenyltris[(tert-butylthio)methyl]borate ligand, [PhTt tBu], has been studied extensively as a platform for coordination, organometallic, and bioinorganic chemistry, especially with 3d metals. While [PhTt tBu]Co(3,5-DBCatH) (3,5-DBCatH is 3,5-di-tert-butylcatecholate), a CoII–monoanionic catecholate complex, was successfully isolated to model the active site of cobalt(II)-substituted homoprotocatechuate 2,3-dioxygenase (Co-HPCD) [Wang et al. (2019). Inorg. Chim. Acta, 488, 49–55], its iron(II) counterpart, [PhTt tBu]Fe(3,5-DBCatH), was not accessible via similar synthetic routes. Switching the nucleophile from catecholate to alkoxide or aryloxide, however, led to the successful isolation of three highly air-sensitive FeII–alkoxide and –aryloxide complexes, namely, (triphenylmethoxo){tris[(tert-butylsulfanyl)methyl]phenylborato-κ3 S,S′,S′′}iron(II), [Fe(C21H38BS3)(C19H15O)], (2), (2,6-dimethylphenolato){tris[(tert-butylsulfanyl)methyl]phenylborato-κ3 S,S′,S′′}iron(II), [Fe(C21H38BS3)(C8H9O)], (3), and bis{μ-tris[(tert-butylsulfanyl)methyl]phenylborato-κ3 S,S′:S′′}bis[(phenolato-κO)iron(II)] toluene disolvate, [Fe2(C21H38BS3)2(C6H5O)2]·2C7H8, (4). In the solid state, compounds (2) and (3) are monomeric, with [PhTt tBu] acting as a tridentate ligand. In contrast, compound (4) crystallizes as a dimeric complex, wherein each [PhTt tBu] ligand binds to an iron centre with two thioethers and binds to the other iron centre with the third thioether. The molecular structures of (2)–(4) demonstrate a diversity in the binding modes of [PhTt tBu] and highlight its potential use for assembling multinuclear complexes. In addition, the successful isolation of (2)–(4), as well as the structural information of a [PhTt tBu] modification product, namely, bis{μ-tris[(tert-butylsulfanyl)methyl](2-oxidophenolato)borato-κO,O′,S,S′:O′}dicobalt(II), [Co2(C21H37BO2S3)2], (5), obtained from the reaction of [PhTt tBu]CoCl with potassium monoanionic catecholate, shed light on the origin of the instability of [PhTt tBu]Fe(3,5-DBCatH).

Smart dual T1 MRI-optical imaging agent based on a rhodamine appended Fe(iii)-catecholate complex

The high spin Fe(iii) complex Fe(RhoCat)3 is reported as a smart dual-modal T1 MRI-optical imaging probe to visualize the NO molecule and an acidic pH environment.

Carrier-microencapsulation using Al-catecholate complex to suppress arsenopyrite oxidation: Evaluation of the coating stability under simulated weathering conditions

Arsenopyrite (FeAsS) is the most common primary arsenic-sulfide mineral in nature, and its oxidation causes the release of toxic arsenic (As). To mitigate these problems, carrier-microencapsulation (CME), a technique that passivates sulfide minerals by covering their surfaces with a protective coating, has been developed. In the previous study of authors on CME, Al-catecholate complex significantly suppressed arsenopyrite oxidation via electron donating effects of the complex and the formation of an Al-oxyhydroxide coating. For the application of this technique to real tailings, however, further study should be carried out to elucidate long-term effectiveness of the coating to suppress arsenopyrite oxidation. This study investigates the stability of the coating formed on arsenopyrite by Al-based CME using weathering tests. The Al-oxyhydroxide coating suppressed arsenopyrite oxidation until about 50 days of the experiment, but after this, the amounts of oxidation products like dissolved S and As increased due to the gradual dissolution of the coating with time as a result of the low pH of leachate. This suggests that co-disposal of Al-based CME-treated arsenopyrite with minerals that have appropriate neutralization potentials, so that the pH is maintained at around 5 to 8 where Al-oxyhydroxide is stable.

Characterization of Chromium-tris(catecholate) Complex: A Theoretical Study

Phenolic compounds generally have special smell and are easily soluble in water, organic solvents (alcohols, esters, chloroform, ethyl acetate) and in alkali. Phenols produce coloured complexes with heavy metal ions, such as with chromium ion. The molecular details underlying the cross-linking mediated by transition metal ions are largely unknown. Using HF/DFT hybrid approach B3LYP, this study examines the structure, binding energy, spectroscopic and electronic properties of complex formed by the attachment of Cr3+ with a catechol ligand. Our study shows that the binding of Cr3+ with the catechol ligand is not as strong as the binding of other metal ions with catechol.The calculated FTIR spectra show strong IR intensities due to large charge polarization. The UV-Vis absorption spectrum of the tris-catecholato-Cr3+complex shows a clear ligand-to-metal charge transfer. The calculated electronic band gap is 4.06 eV which is in the range of transition metal ion tris-catechol complexes. Thermodynamic properties studied in this work show that the metal ion-ligand binding energy (532.99 kcal/mol) is close to those of the hexa-aqua complexes (ranging from 540 to 553 kcal/mol). Dhaka Univ. J. Sci. 65(2): 113-117, 2017 (July)

Fluorescence behaviour of an anthracene–BODIPY system affected by spin states of a dioxolene–cobalt centre

Fluorescence of an anthracene–BODIPY unit incorporated in a dioxolene ligand was effectively quenched in the low-spin cobalt(iii) catecholate complex compared with that in the high-spin cobalt(ii) semiquinonate complex.