Some cyclic tetra-amines and their metal-ion complexes. Part VI. The crystal structure of acetato-C-rac-(5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)nickel(II) perchlorate

Abstract

The structure of acetato-C-rac- (5.7,7.12,14.14-hexamethyl-I ,4,8,11 -tetra-azacyclotetradecane) nickel (11) perchlorate has been investigated by single-crystal three-dimensional X-ray methods. The blue prismatic crystals are monoclinic, space group P2,/c, with a = 9.39. b = 30.67. c = 9.57 8, p = 11 9.3". Z = 4. The structure was solved by Patterson and Fourier syntheses, and refined by least-squares methods to a final R of 0.1 20 for the 2753 visually estimated independent reflexions.The cyclic tetra-amine is folded, with the four secondary amine groups co-ordinated to adjacent octahedral sites of the nickel (11) ion. The acetate ion functions as a symmetric chelate, occupying the two remaining sites. The cyclic tetra-amine is the C-rac-modification, and both pairs of asymmetric nitrogens also have the racemic arrangement, but the pairs are of opposite helicity.The relative energies of the 36 configurations of the co-ordinated 5,7,7,12,14,14-hexamethyl-l,4,8,11 -tetra-azacyclotetradecane macrocycles, arising from the pair of asymmetric carbon centres and two pairs of asymmetric nitrogen centres, are discussed in terms of the conformational energies of the chelate ring systems and methyl substituent interaction energies.The space-group determination of cis-oxalato-C-rac-(5,7.7.12.14.14-hexamethyl-l,4,8,11 -tetra-azacyclotetradecane)cobalt(lll) perchlorate is also reported : Pccn. with a = 16.03, b = 9.61, c = 15.1 2 A, 2 = 4.

Crystal and molecular structure of bis(perchlorato)(γ-C-meso-5,5,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)copper(II)

“…Bond lengths and angles in the macrocyclic ligand itself are in good agreement with those in related metal complexes (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and those in (H2cyclam)-(C104)2 (33).…”

Crystal and molecular structure of di(perchlorato)(1,4,8,11-tetraazacyclotetradecane)copper (II). Cu(cyclam) (ClO4)2

“…Such a folded arrangement of the ligand appears to be particularly favorable for the c~-form of the ligand tetb in which the NH groups are found on alternate sides of the molecular plane on passing round the macrocycle (see Fig. 6) (Curtis et al, 1973b;Whimp et al, 1970).…”

“…6. Nitrogen atom configurations of coordinated 1,4,8,11-tetraazacyclotetradecane (cyctam) in the c~, ~ and 11 modes (Whimp et al, 1970). A plus sign at an asymmetric nitrogen center indicates that the hydrogen atom at that center is above the plane of the flattened macrocycle; a minus sign, that it is below.…”

“…Relative energies of the possible configurations of the chelate rings in cyclam have been assessed (Whimp et al, 1970) and it was concluded that the ct-and t3-forms will be less stable than the "y-form. The o~-configuration is present in cis[Co(cyclam)C12 ] C1 (see ref.…”

Configurations of metallocyclams and relevance to anti-HIV activity

“…The configurations that are symmetrical about the diagonal can fold to form cis isomers, e.g., the trans-V isomer can fold to give the cis-V structure. Semi-quantitative analysis of the relative strain energies of the five isomers indicates that the trans-III form is the most stable [8,9]. However, it has been noted that trans-I is more favoured for squareplanar complexes, while octahedral complexes prefer trans-III [10].…”