Complex Formation of 2, 6‐Bis‐(2′‐hydroxyphenyl)pyridine with Al^III, Fe^III and Cu^II

Abstract

Complex formation of 2, 6‐bis(2′‐hydroxyphenyl)pyridine (H2Li) with Fe3+ and Cu2+ was investigated in a H2O/DMSO medium (mole fraction xDMSO = 0.2) by potentiometric and spectrophotometric methods. The pKa values of [H3Li]+ are 2.25, 10.51 and 14.0 (25 °C, 0.1 M KCl). The formation constants of [FeIII(Li)]+ and [CuII(Li)] (25 °C, 0.1 M KCl) are log β1 = 21.5 for Fe3+ and log β1 = 18.5 for Cu2+. The crystal structures of [Al(Li)2Na(EtOH)3], [Fe(Li)2Na(EtOH)3], and [Cu(Li)(py)]2 were investigated by single‐crystal X‐ray diffraction analyses. The FeIII and the AlIII compound are isotypic and crystallize in the monoclinic space group P21/n. Al‐compound (215 K): a = 12.599(3) Å, b = 16.653(3) Å, c = 17.525(4) Å, β = 100.27(3)°, Z = 4 for C40H40AlN2NaO7; Fe‐compound (293 K): a = 12.753(3) Å, b = 16.715(3) Å, c = 17.493(3) Å, β = 99.68(3)°, Z = 4 for C40H40FeN2NaO7. Both compounds contain a homoleptic, anionic bis‐complex [M(Li)2]‐ of approximate D2 symmetry. The Cu compound crystallized as an uncharged, dinuclear and centrosymmetric [Cu(Li)(py)]2 complex in the monoclinic space group P21/n with (293 K) a = 13.386(3) Å, b = 9.368(2) Å, c = 14.656(3) Å, β = 100.65(3)°, Z = 2 for C44H32Cu2N4O4. The structural properties and in particular the possible influence of the ligand geometry on the stability of the metal complexes is discussed.

A boronate prochelator built on a triazole framework for peroxide-triggered tridentate metal binding

“…In contrast, one equivalent of NTA does not change the spectrum of a solution of Cu–deferasirox at all, indicating that deferasirox is significantly stronger than NTA for Cu 2+ binding (Fig. 6), which is consistent with the known stability constants of deferasirox for Cu 2+ of 18.8 and 23.9 for log β 1 and log β 2 , respectively [30]. Additionally, we tested the strength of binding of deferasirox to copper using EDTA, which has a higher affinity for Cu 2+ than NTA, with a log β 1 value of 18.78 [31].…”

“…The change in spectrum of TIP upon the addition of Cu 2+ suggests that even in its prochelator form, TIP retains binding capacity for cupric ions. Notable also is a weak band centered ~650 nm that can be observed at higher concentrations of TIP plus Cu 2+ (not shown), which is very similar to the d-d band observed for Cu 2+ complexed to deferasirox [30]. …”

Synthesis and Study of Multifunctional Cyclodextrin–Deferasirox Hybrids

“…As described above, 1 , 2 , and 3 form a 2:1 chelator/iron complex at physiological pH with high stability constant . Compound 3 also has a moderate affinity for Cu 2+ as demonstrated by the value of 18.8 for log β (CuL), and 23.9 for log β 2 (CuL 2 ) reported elsewhere . As observed for iron, we anticipate the conjugation with CyD does not significantly modify the copper‐binding ability of the chelators .…”

“…[27,28] Compound 3 also has amoderate affinity for Cu 2 + as demonstrated by the value of 18.8 for log b (CuL), and 23.9 forl og b 2 (CuL 2 ) reported elsewhere. [38] As observed for iron, we anticipatet he conjugation with CyD does not significantly modify the copper-binding ability of the chelators. [12,31] Moreover,w ec onfirmed through UV/Vis and CD spectroscopy that both derivatives maintain the ability of 3 to complex copper ions.…”

Tridentate facial coordination mode of an unsymmetrical tetradentate diazine ligand in an iron(III) complex

“…Coordination of two metal ions by salpahn À will form a five-membered chelate ring on one metal centre and a six-membered chelate ring on the other metal centre. It is known that the ligands which form five-membered chelate rings prefer large metal ions and the ligands which form six-membered chelate rings prefer small metal ions [40]. For this reason, possibly salpahn À behaves as tridentate and binds a single trivalent iron centre with the formation of two six-membered chelate Symmetry transformations used to generate the equivalent atoms: (a) Àx + 3/2, Ày + 3/2, Àz, (b) Àx + 3/2, Ày + 1/2, Àz, (c) Àx + 3/2, y À 1/2, Àz À 1/2.…”