New chromium(III)–picolinamide complexes. Kinetics and mechanism of picolinamide liberation in HClO4 solutions |
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| Authors: | Ma?gorzata Pazderska-Szab?owicz Adam Karpiński Ewa Kita |
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| Institution: | (1) Department of Chemistry, N. Copernicus University, 87-100 Torun, Poland |
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| Abstract: | Two new chromium(III) complexes with picolinamide (pica) and oxalates, Cr(C2O4)2(N,N′-pica)]2− and Cr(C2O4)2(N,O-pica)]−, were obtained and the kinetics of their aquation in HClO4 solutions were studied. The aquation leads to pica liberation and proceeds in two stages: (i) the chelate-ring opening at
the Cr–amide bond and (ii) the Cr–N-pyridine bond breaking, which gives free pica and cis-Cr(C2O4)2(H2O2)2]−. In the case of N,N′-bonded pica the kinetics of both stages was determined and in the case of the N,O-bonded pica only the second stage was
investigated. The following rate laws were established: (k
obs)1 = k
0 + k
1
Q
1H+] and (k
obs)2 = k
2
Q
2H+], where k
0 and k
1 are the rate constants of the chelate-ring opening in the unprotonated and protonated starting complex, and k
2 is the rate constant of the pica liberation from the protonated intermediate. Kinetic parameters are calculated and the aquation
mechanism is discussed. |
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| Keywords: | |
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