Structural investigation of [H2cyclam] [O3SCF3]2 (cyclam=1,4,8,11-tetraazacyclotetradecane)

The 14-membered macrocyle 1,4,8,1 1-tetraazacyclotetradecane (cyclam), a weIl-known N4-donor cyclic system, exhibits great flexibility in accommodating a range of host metal ions and five different arrangements of the chiral nitrogen donor centers are possible in the resulting complexes (Lindoy, 1989). For instance, in cis-[CrCl2(cyclam)]+ (House and McKee, 1984) the absolute configuration is of the type (RRRR), in trans-[ReO2(cyclam)]+ (Luna et al., 1992) it is (RSSR), while in cis-[MoCl2(cyclam)]+ (Hyldtoft et al., 1989) it is (RSRR). In order to gain a deeper understanding of the flexibility of cyclam and of its doubly protonated form, H2cyclam2+, we evaluated the energy content of all conformations. In addition, we present the crystal structure of [H2cyclam] [O3SCF3]2 and a comparison with the data found in [H2cyclam] [ClO4]2 (Nave and Truter, 1974) is reported.