A new dimeric Ni(II)complex,[Ni_(2)L^(1)_(2)(CH_(3)CN)_(4)](ClO_(4))_(2)·2CH_(3)CN(1),was synthesized using an N_(2)O donor reduced Schiff base[(HL1)=2-[(3-methylamino-propylamino)-methyl]-4-phenol].Surprisingly,...A new dimeric Ni(II)complex,[Ni_(2)L^(1)_(2)(CH_(3)CN)_(4)](ClO_(4))_(2)·2CH_(3)CN(1),was synthesized using an N_(2)O donor reduced Schiff base[(HL1)=2-[(3-methylamino-propylamino)-methyl]-4-phenol].Surprisingly,during an attempt to replace its ClO_(4)-ion with SCN-,the N_(2)O donor ligand in situ converted to a tetradentate N_(2)O_(2)donor ligand and formed a metal complex,[Ni(HL^(2))(NCS)(CH_(3)CN)](2).A probable mechanism via deaminative coupling for this conversion is proposed.Using 2 as a metalloligand under basic conditions,a trinuclear metal complex,[Ni3(L^(2))2(NCS)2(H_(2)O)4]·H_(2)O(3),was prepared.Single crystal structural characterization revealed that in all three metal complexes,the Ni(II)atoms were in an octahedral environment with coordinated solvent molecules(CH_(3)CN in 1 and 2 and H_(2)O in 3).Among the three metal complexes,1 and 3 showed catecholase-like biomimicking activity.The calculation of the turnover numbers(K_(cat)=7.9 for 1,14.5 for 3)reveals that 3 is a better catalyst than 1.Mechanistic cycles are proposed for this biomimicking activity on the basis of ESI-MS spectrometry and iodometric measurements.Temperaturedependent magnetic susceptibility measurements suggest that the Ni(II)ions in metal complexes 1 and 3 are antiferromagnetically coupled(J=-32.22 cm^(-1) for 1,J=-10.4 cm^(-1) for 3),consistent with their geometries and bridging angles.Theoretically calculated J values(J=-40.15 cm^(-1) for 1,J=-14.53 cm^(-1) for 3)by the DFT method corroborate well with the experimental values.展开更多
基金the University Grants Commission(UGC),New Delhi,for the Senior Research Fellowship[Sr.No.2061510240,Ref No.–21/06/2015(i)EU-V].
文摘A new dimeric Ni(II)complex,[Ni_(2)L^(1)_(2)(CH_(3)CN)_(4)](ClO_(4))_(2)·2CH_(3)CN(1),was synthesized using an N_(2)O donor reduced Schiff base[(HL1)=2-[(3-methylamino-propylamino)-methyl]-4-phenol].Surprisingly,during an attempt to replace its ClO_(4)-ion with SCN-,the N_(2)O donor ligand in situ converted to a tetradentate N_(2)O_(2)donor ligand and formed a metal complex,[Ni(HL^(2))(NCS)(CH_(3)CN)](2).A probable mechanism via deaminative coupling for this conversion is proposed.Using 2 as a metalloligand under basic conditions,a trinuclear metal complex,[Ni3(L^(2))2(NCS)2(H_(2)O)4]·H_(2)O(3),was prepared.Single crystal structural characterization revealed that in all three metal complexes,the Ni(II)atoms were in an octahedral environment with coordinated solvent molecules(CH_(3)CN in 1 and 2 and H_(2)O in 3).Among the three metal complexes,1 and 3 showed catecholase-like biomimicking activity.The calculation of the turnover numbers(K_(cat)=7.9 for 1,14.5 for 3)reveals that 3 is a better catalyst than 1.Mechanistic cycles are proposed for this biomimicking activity on the basis of ESI-MS spectrometry and iodometric measurements.Temperaturedependent magnetic susceptibility measurements suggest that the Ni(II)ions in metal complexes 1 and 3 are antiferromagnetically coupled(J=-32.22 cm^(-1) for 1,J=-10.4 cm^(-1) for 3),consistent with their geometries and bridging angles.Theoretically calculated J values(J=-40.15 cm^(-1) for 1,J=-14.53 cm^(-1) for 3)by the DFT method corroborate well with the experimental values.
