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The chromium(III)-quinolinato complexes, [Cr(quinH) 3 ] 0 , [Cr(quinH) 2 (H 2 O) 2 ] + and [Cr(quinH)(H 2 O) 4 ] 2+ (where quinH = N,O-bonded quinolinic acid anion), were obtained and characterized in solution. The tris-quinolinato complex undergoes acid-catalyzed aquation to give the diaqua-product, whereas subsequent ligand liberation processes are exceptionally slow. Kinetics of the aquation were studied spectrophotometrically over the 0.1-1.0 M HClO 4 range, at I = 1.0 M. The first aquation stage, the chelate-ring opening at the Cr-N bond, is much faster than the second one. The following rate laws were established: k obs = k 1 + k )1 /Q 1 [H + ] and k obs = k 2 Q 2 [H + ]/(1 + Q 2 [H + ]), where k 1 and k 2 are the rate constants for the chelate-ring opening and the ligand liberation, respectively, k )1 is the rate constant of the chelate-ring closure, Q 1 and Q 2 are the protonation constants of the pyridine nitrogen and 3-carboxylate group in the one-end bonded intermediate, respectively. Kinetic parameters have been determined and the mechanism has been discussed.

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The chromium(III) complexes with a new potential chromium transporting ligand-2,5-pyridinedicarboxylic acid (isocinchomeronic acid, icaH 2 ):[Cr(icaH) 3 ] 0 , [Cr(icaH) 2 (H 2 O) 2 ] + and [Cr(icaH)(H 2 O) 4 ] 2+ (where icaH = N,O-bonded isocinchomeronic acid anion), have been obtained and characterized in solution. The [Cr(icaH) 3 ] 0 complex undergoes aquation in acidic media to the diaquaproduct. Kinetics of this process was studied spectrophotometrically in the 0.1-1.0 M HClO 4 range, at I = 1.0 M. The first aquation stage, the chelate-ring opening at the Cr-N bond, is a much faster than the second one. The rate laws are of the form: k obs = k 1 + k -1 /Q 1 [H + ] and k obs = k 2 Q 2 [H + ]/ (1 + Q 2 [H + ]), where k 1 and k 2 are the rate constants for the chelate-ring opening and the ligand liberation, respectively, k -1 is the rate constant of the chelate-ring closure, Q 1 and Q 2 are the protonation constants of the pyridine nitrogen and 5-carboxylate group in the one-end bonded intermediate, respectively. The results are discussed in terms of potential pharmaceutical application of the complex.

Two complexes, 3 ] 0 and [Cr(2-hnic) 3 ] 0 (where 3-hpic = hydroxypicolinic acid and 2-hnic = 2-hydroxynicotinic acid anions), were prepared and characterized in solution. The 3-hpic ligand forms a 5-membered chelate ring via pyridine nitrogen and carboxlate oxygen atoms, whereas the 2-hnic ligand forms a 6-membered chelate ring via carboxylate and phenolate oxygen atoms. The kinetics of the acid-catalyzed aquation were studied spectrophotometrically in the 0.1-1.0 M HClO 4 range, at I ¼ 1:0 M . The rate equations for the first aquation step -the chelate-ring opening -was determined and a mechanism was proposed. In the case of [Cr(3-hpic) 3 ] 0 , the reversible chelate-ring opening at the CrAN bond precedes much slower than the second aquation step -a one-end bonded ligand liberation. The equation rate is of the form: k obs ¼ k 1 þ k À1 =Q 1 [H þ ], where k 1 and k À1 are the rate constants for the forward and the reverse processes in the unprotonated substrate and Q 1 is the protonation constant of the non-bonded pyridine nitrogen atom. In the case of [Cr(2-hnic) 3 ] 0 , the chelate-ring opening at the CrAO (phenolate) bond is the rate-determining step. The observed pseudo-first order rate constant increases as [H þ ] increases:where k 0 and k H are the rate constants of the spontaneous and acid catalyzed processes and Q H is the protonation constant of the coordinated phenolate oxygen atom. The results lead to the conclusion that an aquation mechanism depends on the coordination mode of the ligand.