Preparation, properties and crystal structure of two isomers of <f>R,R,S,S</f>- and <f>R,S,R,S</f>-[chloro(1,3,10,12,16,19-hexaazatetracyclo[17,3,1,112,16,04,9]tetracosane)copper(II)]+

Two isomers (<f>R,S,R,S</f>- and <f>R,R,S,S</f>-) of five coordinate complex [Cu(L)Cl]+ have been separated and characterised. These two isomers have significantly different spectrochemical and electrochemical properties. Absorption maximum of <f>R,S,R,S</f>-[Cu(L)Cl]+ shifts to longer wavelength and its reduction potential shifts to more positive direction comparing those of <f>R,R,S,S</f>-[Cu(L)Cl]+. <f>R,S,R,S</f>-[Cu(L)Cl]+ is significantly distorted to trigonal-bipyramidal structure, whereas <f>R,R,S,S</f>-[Cu(L)Cl]+ retains almost square-planar geometry. The average bond distance of Cu–N in basal plane of <f>R,S,R,S</f>-[Cu(L)Cl]+ is longer by 0.024 A˚ than that of <f>R,R,S,S</f>-[Cu(L)Cl]+, whereas the bond distance of Cu–Cl in former is shorter by 0.200 A˚ than that in latter. The isolated square-planar complexes of <f>R,R,S,S</f>- and <f>R,S,R,S</f>-[Cu(L)](ClO4)2 are converted to the <f>R,R,S,S</f>- and <f>R,S,R,S</f>-[Cu(L)Cl]+ by the addition of Cl− in nitromethane solution with the rate constants, <f>k=1.70</f> (±0.02) and 8.31 (±0.07) M−1 s−1, respectively. [Copyright &y& Elsevier]