ISSN:
1572-901X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Summary The pentadentate macrocycle 1,4,7,10,13-penta-azacyclo-hexadecane [16]aneN5=(3)=L} has been prepared and a variety of copper(II), nickel(II) and cobalt(III) complexes of the ligand characterised. The copper complex [CuL](ClO4)2, on the basis of its d-d spectrum, appears to be square pyramidal, while [NiL(H2O)](ClO4)2 is octahedral. The copper(II) and nickel(II) complexes dissociate readily in acidic solution and these reactions have been studied kinetically. For the copper(II) complex, rate=kH[complex][H+]2 with kH =4.8 dm6 mol−2s−1 at 25 °C and I=1.0 mol dm−3 (NaClO4) with ΔH≠=43 kJ mol−1 and ΔS 298 ≠ =−89 JK−1 mol−1. Dissociation rates of the copper(II) complexes increase with ring size in the order: [15]aneN5 〈 [16]aneN5 〈 [17]aneN5. For the dissociation of the nickel(II) complex, rate=kH[Complex][H+] with kH=9.4×10−3 dm3mol−1 s−1 at 25 °C and I =1.0 mol dm−3 (NaClO4) with ΔH≠=71 kJ mol−1 and ΔS 298 ≠ =−47 JK−1mol−1. The cobalt(III) complexes, [CoLCl](ClO4)2, [CoL(H2O)]-(ClO4)3, [CoL(NO2)](ClO4)2, [CoL(DMF)](ClO4)3 (DMF=dimethylformamide) and [CoL(O2CH)](ClO4)2 have been characterised. The chloropentamine [CoCl([16]aneN5)]2+ undergoes rapid base hydrolysis with kOH=1.1× 105dm3 mol−1s−1 at 25°C and I=0.1 mol dm−3 (ΔH≠=73 kJ mol−1 and ΔS 298 ≠ =98 JK−1 mol−1). Rapid base hydrolysis of [CoL(NO2)]2+ is also observed and the origins of these effects are considered in detail.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01225989
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