Isolation and complexation of the cis isomer of the pendant arm macrocycle 6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine

Abstract

The cis isomer of the pendant arm macrocyclic hexaamine 6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L²) has been isolated for the first time. The ligand has been complexed with cadmium(II) and characterised structurally. The complex [CdL²][ClO₄]₂ crystallises in the monoclinic space group P2₁/n, a= 10.238(1), b= 16.445(2), c= 13.106(2)Å, β= 103.33(1)°, and Z= 4. The Cd–N bond lengths are not unusual by comparison with those exhibited by typical CdN₆²⁺ complexes, compared with the generally short M–N bond lengths that have been observed in sexidentate co-ordinated complexes of the trans isomer L¹. Reaction of L¹ with cadmium(II) does not yield a hexaamine complex, instead the pendant primary amines are not co-ordinated and the four secondary amines encircle the metal centre.