The versatility of 1,4,8,11-tetraazacyclotetradecane (cyclam) in the formation of compounds of Co2+, Ni2+, Cu2+, and Zn2+ with metal ions in and out of the cyclic ligand ring

Abstract Herein we report the results of preparing metal compounds (where the metal ions are Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ ) with the cyclic ligand 1,4,8,11-tetraazacyclotetradecane [cyclam] under a variety of conditions of metal-ligand ratios and solvent media. In all cases, we used metal Cl 2 ·nH 2 O salts (except for anhydrous CoCl 2 ), as specified. Outcome: we isolated species with a four-coordinate metal in the N4 cavity of the ligand alone, and also with either one or two additional axial ligands. Those axial ligands can be (a) a single chloride, leading to penta-coordinated moncationic products; (b) two chlorides, leading to octahedral-neutral compounds; (c) two waters, giving rise to hexa-coordinated [(cyclam)metal(H 2 O) 2 ] 2+ species. Finally, in the case of HCl added to the reaction medium, the cyclam can be di-protonated and appears as [(cyclam)H 2 ] 2+ in the crystals. With such a variety of products, it is not surprising that since the metal coordination numbers vary, the cyclam ligand stereochemistries are thereby affected. Interestingly, the [(cyclam)metal] species are invariably hydrogen-bonded to one another in infinite strings of two kinds: (1) those for which the crystal’s Z′ = 1 have single strings; (2) when Z′ = 2, there is a pair of homogeneous strings attached to one another by a variety of hydrogen-bonding linkages. Finally, we observed an interesting pair of hydroxonium cations: the first is hydoxonium cations in a pleated 2-D sheet consisting of fused pentagons located between sheets of [(cyclam)metal] moieties; the second one is an infinite string of composition {(H 3 O + )-(H 2 O)-(H 3 O + )-(H 2 O)-(H 3 O + )-(H 2 O)-(H 3 O + )} ∞ .