149274-87-3Relevant academic research and scientific papers
Nickel(II) complexes of azacyclams: Oxidation and reduction behavior and catalytic effects in the electroreduction of carbon dioxide
Abbà, Fabio,De Santis, Giancarlo,Fabbrizzi, Luigi,Licchelli, Maurizio,Lanfredi, Anna Maria Manotti,Pallavicini, Piersandro,Poggi, Antonio,Ugozzoli, Franco
, p. 1366 - 1375 (2008/10/08)
A wide range of functionalized azacyclam complexes of NiII have been prepared through a template reaction which involves the open-chain tetramine complex [NiII(2·3·2-tet)]2+, formaldehyde, and a locking fragment which is a primary carboxamide or sulfonamide, either aliphatic or aromatic (RNH2). The crystal and molecular structure has been determined for the low-spin [3-(4-tolylsulfonyl)-1,3,5,8,12-pentaazacyclotetradecane]nickel(II) complex. The crystal structure consists of three crystallographycally indipendent cationic complexes. Single-crystal X-ray diffraction data were collected with the use of Ni-filtered Cu Kα radiation: space group Pbca with a = 23.128(3) A?, b = 22.891(3) A?, c = 27.595(4) A?, α = 90°, β = 90°, γ = 90°; V = 14609(3) A?3, and Z = 24 (R = 0.051, Rw = 0.059). All the investigated azacyclam derivatives display the typical solution behavior of the NiII macrocyclic complexes: inertness toward demetalation by strong acids and the blue-to-yellow interconversion in coordinating media. Electrochemical investigations in acetonitrile have shown that E1/2 values associated with NiIII/NiII and NiII/NiI couples are influenced by the nature of the substituent appended to the azacyclam ring: such an effect is interpreted on the basis of a π interaction between the metal center and the fifth nitrogen atom inserted in the azacyclam ring. Water soluble NiII-azacyclam complexes catalyze the electroreduction of CO2, as indicated by cyclic voltammetry investigations and controlled-potential coulometry studies, with an efficiency comparable to that of [NiII(cyclam)]2+. Such a high efficiency is strictly related to the structural features of the cyclam and azacyclam framework: a 14-membered cycle forming a 5,6,5,6 sequence of chelate rings. Even small deviations from such a geometrical arrangement cause the electrocatalytic effect to be drastically reduced or completely lost.
