The aqueous solution and solid state
pro
perties of (4-hydroxy
pyridine-2,6-dicarboxylato)dioxovanadate(V) (alsoreferred to as (4-hydroxydi
picolinato)dioxovanadate(V) or (chelidamato)dioxovanadate(V) and abbreviated [VO
2(di
pic-OH)]
-) were investigated. By using
1H,
13C,
17O, and
51V NMR 1D and 2D s
pectrosco
py, the s
pecies
presentin solution, together with
pKa values, equilibrium constants, and labilities, were characterized. The com
plex is moststable at acidic
pH down to
pH 1 where it is
protonated. The stability of this com
plex is higher than that of the
parent di
picolinatodioxovanadate(V) com
plex. The di
pic-OH ligand is coordinated in a tridentate manner throughoutthe
pH range studied, and the vanadium(V) atom is five-coordinate. Solid state structures of (NMe
4)[VO
2(di
pic-OH)]·H
2O (monoclinic,
P2
1/
n) and Na[VO
2(di
pic-OH)]·2H
2O (triclinic,
P) were determined. The discrete com
plexanions in (NMe
4)[VO
2(di
pic-OH)]·H
2O are connected by hydrogen bonding between the hydroxyl grou
p, a watermolecule, and a carboxylate oxygen atom. Changing the counterion from NMe
4+ to sodium ion in Na[VO
2(di
pic-OH)]·2H
2O leads to the formation of a
polymeric structure. Dynamic
processes in solution were ex
plored by using
1H and
13C EXSY NMR s
pectrosco
py; exchange between com
plex and free ligand below
pH 4 was observed. Thedifferences between the di
picolinatodioxovanadate(V)
parent com
plex and the [VO
2(di
pic-OH)]
- com
plex in thesolid state and in solution demonstrate the subtle consequences of the one substitutional difference between thetwo ligands. The insulin-mimetic
pro
perties of this com
pound are likely to be of mechanistic interest in develo
pingan understanding of the mode of action of the few known insulin-mimetic vanadium(V) com
plexes.