Abstract
Herein we report the results of preparing metal compounds (where the metal ions are Co2+, Ni2+, Cu2+, Zn2+) 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 Cl2·nH2O salts (except for anhydrous CoCl2), 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(H2O)2]2+ species. Finally, in the case of HCl added to the reaction medium, the cyclam can be di-protonated and appears as [(cyclam)H2]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 {(H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+)}∞.
Funding source: National Science Foundation
Award Identifier / Grant number: 0443538 - Bruker X-ray Diffractometer & 2018753 - Rigaku Synergy-S X-ray Diffractometer
Acknowledgments
We acknowledge the National Science Foundation for NSF-CRIF Grant No. 0443538 for part of the purchase of the Bruker X-ray diffractometer and NSF-CRIF Grant No. 2018753 for part of the purchase of the Rigaku X-ray diffractometer. We thank Dr. Catherine Housecroft and Dr. E. C. Constable for their helpful discussions on the chemistry of these cyclam ligands and their metal complexes.
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Author contributions: Mah Noor is the undergraduate student who prepared most of the complexes under direct supervision of RAL. Hamza Chah and David Tresp are the undergraduate and graduate students, respectively, who prepared the Co(II)cyclam complex under anhydrous conditions using Schlenk-line techniques. IB and RAL wrote the manuscript.
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Conflict of interest statement: The authors have declared that no competing interests exist.
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Research funding: This work was supported by the National Science Foundation, Bruker X-ray Diffractometer (0443538) and Rigaku Synergy-S X-ray Diffractometer (2018753).
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Supplementary Material
This article contains supplementary material (https://doi.org/10.1515/zkri-2023-0026).
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