A Cis-Folded Macrocyclic Nickel(Ii) Complex - Molecular-Structure And Thermal-Reaction Of Cis-Diaqua (1,4,7,11-Tetraazacyclotetradecane) Nickel(Ii) Chloride

The single-crystal X-ray structure and thermal behavior of cis-[Ni(isocyclam)(H2O)2]Cl2.2H2O(isocyclam= 1,4,7,11-tetraazacyclotetradecane) are reported. The complex crystallizes in the monoclinic space group P2(1)/c. The unit cell parameters of the complex, NiCl2C10N4O4H32 (fw = 402.01), are a = 12.55 (1) angstrom, b = 8.11 (1) angstrom, c = 18.22 (1) angstrom, beta = 98.48 (6)-degrees, and Z = 4. The complex has a distorted octahedral geometry with two coordinated water molecules in cis positions and the isocyclam ligand coordinated in a folded fashion. The elongation in the bond distances and the deviation from a regular octahedron in the bond angles around the Ni(II) center are more pronounced than those in the corresponding cis-[Ni(cyclam)(H2O)2]Cl2.2H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane). The isocyclam complex undergoes thermal deaquation-anation in the solid state to produce cis-[NiCl2(isocyclam)]. The cis-dichloro complex, when further heated, undergoes isomerization to the trans form with a change in configuration from folded to coplanar chelation of the isocyclam. The isomerization is exothermic and irreversible. In contrast, cis-[NiCl2(cyclam)] obtained by heating the corresponding diaqua complex, cis-[Ni(cyclam)(H2O)2]Cl2.2H2O, exhibits no thermal isomerization in the solid state.