Potentiometric pH-titration
and electron spin resonance studies have shown the existence of mono-meric, dimeric and dinuclear vanadyl chelates of certain
polyaminocarboxylic acids. The ligands studied include
ethylenediaminetetraacetic (edta), ethyleneglycolbis(β- aminoethyl ether)-N,N?-tetra-acetic
(egta), diethylenetriaminepentaacetic
(dtpa) and triethylenetetraaminehexaace-
tic (ttha) acids. All the ligands form 1 : 1
chelates. The addition of ethylene glycol to the aqueous solution in each case
provides circumstances for the study of the monomeric chelates, though it is
not equally effective in all cases. The 1 : 1 vanadyl egta
chelate above pH 5.5 gave rise to ΔMS = � 2 and ΔMS
= � 1 transitions from which structural and magnetic parameters have been determined
and interpreted in terms of the formation of a dimeric form of a hydrolytic
product of the 1 : 1 chelate. Firm evidence for the formation of dinuclear
chelates occurs only in the vanadyl ttha system. Here
the room tem- perature e.s.r. spectrum shows the
presence of weak exchange coupling between the vanadyl ions in the dinuclear
chelate.
Crystal structure, electron spin resonance, and magnetic exchange coupling in bis(.mu.-chloro)bis[cyclopentadienyl(triethylphosphane)vanadium(II)]
