Synthesis of two configurational isomers of a 14-membered tetraaza macrocycle bearing N-CH2CH2CONH2 pendent arms and their copper(II) complexes: Crystal structures of the complexes

Two isomers of 1,8-bis(N-carbamoylethyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L2) bearing two N-CH2CH2CONH2 groups, C-meso-L2 and C-racemic-L2, have been prepared and characterized. Each isomer reacts with Cu(II) ion to form a five-coordinate complex, [Cu(C-meso-L2)](ClO4)2 (1) or [Cu(C-racemic-L2)](ClO4)2 (2), in which only one pendent amide group is coordinated to the metal ion. The crystal structure of 1 · CH3CN shows that the complex possesses trans-III-type N-configuration and has a slightly distorted square-pyramidal coordination geometry with a relatively long axial Cu–O (N-CH2CH2CONH2) bond (2.207(3) Å). On the other hand, 2 exhibits trans-V configuration and has a slightly distorted trigonal bipyramidal coordination geometry with a very short equatorial Cu–O (N-CH2CH2CONH2) bond (2.007(3) Å); the Cu–O distance is distinctly shorter than the Cu–N distances (2.062(4)–2.090(4) Å). The complex 1 exhibits a d–d transition band at approximately 565 nm, whereas the band for 2 is observed at approximately 770 nm.