Vanadium(V) Complexes of Polydentate Amino Alcohols:  Fine-Tuning Complex Properties

Abstract

In aqueous solution, the stability, the structure, and the lability of 12 vanadium(V) complexes were determined and related to the amino alcohol ligand properties. The amino alcohols were chosen to maintain a five-coordinate vanadium geometry in the vanadium complex and were based on diethanolamine as the parent ligand. Apparent and composite stability constants were determined for all 12 complexes. Selected complexes were further examined to determine solution structure, lability, and thermodynamic properties. We empirically show that the formation constants for the series of 12 complexes, when plotted as a function of the pK a value for the protonated amino alcohol, generate a curve that initially increases as the pK a value increases and then decreases as the pK a value continues to increase. The observed associations suggest that the electron-donating capacity of the amino alcohol plays a major role in complex stability; however, metal coordination number, sterics in the amino alcohol, and solvation also are found to affect the stability. Determination of the thermodynamic parameters of selected complexes showed that the enthalpic component was the major contributor to the stability of the complex, but that the entropic component opposed this term. A series of studies was conducted to examine whether the lability of these complexes varied from the parent complexes. Unfortunately, the variation in the lability of these complexes was much less than the variation in complex stability. In summary, these studies describe quantitatively the variation in complex stability and lability as the structure of amino alcohol is modified and explain why some complexes show less stability than predicted on the basis of the pK a value. In short, this study provides valuable information for the design of additional vanadium complexes with specific properties.

Carbonate complexes of vanadate

“…It is possible that the enhanced stability of the ML2 complex relative to the carbonato equivalent is again atttributatble to the formation of bridging ligands. The enthalpy of vanadate complexation by alcoholamine ligands has been estimated to be in the range À20 to À30 kJ/mol [13]. The complexation enthalpies determined here, for each additional bicarbonate ligand, at À17 and À25 kJ/mol are therefore within a reasonable range for vanadate complexes.…”

“…A wide range of different types of vanadate complexes have been investigated to date, including those with amino alcohols, alcohols and amino acids, amongst others [10,[13][14][15][16][17][18][19][20]. These studies focused primarily on the determination of equilibrium constants under biologically relevant conditions and the identification of structural features which influence the stability of the complexes.…”

A Wheel‐Shaped Single‐Molecule Magnet of [MnII3MnIII4]: Quantum Tunneling of Magnetization under Static and Pulse Magnetic Fields

“…The ligand H 3 (5-NO 2 -hbide) (N-(2-hydroxy-5-nitrobenzyl)iminodiethanol) was prepared by the literature method. [23] [Mn II 3 Mn III 4 (5-NO 2 -hbide) 6 ]·5 C 2 H 4 Cl 2 (1): MnA C H T U N G T R E N N U N G (OAc) 2 ·4 H 2 O (246 mg, 1 mmol) in methanol (10 mL) was added to the mixture of H 3 (5-NO 2 -hbide) (256 mg, 1 mmol) and triethylamine (303 mg, 3 mmol) in methanol (20 mL), and a brown precipitate formed immediately. The brown precipitate (15 mg) was dissolved in 1,2-dichloroethane (50 mL), and after standing for a week stand dark brown lozenge and hexagon plates crystals of 1 (60 %), which had five and seven solvent molecules, respectively, were obtained.…”

Insulin-enhancing activity of a dinuclear vanadium complex: 5-chloro-salicylaldhyde ethylenediamine oxovanadium(V) and its permeability and cytotoxicity

“…Several vanadium complexes of the Schiff base sal 2 en {N,N′-ethylenediaminebis(salicylideneiminato)} and related ligands have been proposed as insulin-enhancing agents, and for the treatment of obesity and hypertension [11][12][13]. On the other hand, some of oxovanadium (V) complexes with insulin-mimetic activity were reported by D.C. Crans et al [14][15][16].…”