Anion Template Effect on the Self-Assembly and Interconversion of Metallacyclophanes

• Published in: Journal of the American Chemical Society Vol. 127; no. 37; pp. 12909 - 12923
• Main Authors: Campos-Fernández, Cristian Saul, Schottel, Brandi L, Chifotides, Helen T, Bera, Jitendra K, Bacsa, John, Koomen, John M, Russell, David H, Dunbar, Kim R
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 21-09-2005
• Subjects: Anions - chemistry; Cations - chemistry; Chemistry; Condensed matter: structure, mechanical and thermal properties; Coordination compounds; Crystallography, X-Ray; Exact sciences and technology; Heterocyclic Compounds, 1-Ring - chemistry; Inorganic chemistry and origins of life; Inorganic compounds; Magnetic Resonance Spectroscopy; Metal complexes; Metals, Heavy - chemistry; Models, Molecular; Molecular Structure; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Physics; Preparations and properties; Pyridines - chemistry; Spectrometry, Mass, Electrospray Ionization; Spectrophotometry, Infrared; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Encapsulation; Nickel Complexes; Molecular structure; Nitrogen heterocycle; Manganese Complexes; Chemical stability; Organic ligand; Tetranuclear complex; NMR spectrometry; Inorganic synthesis; Transition metal Complexes; Copper Complexes; X ray diffraction; Geometrical structure; Inorganic anion; Molecular assembly; Complexes Mixed; Six membered ring; Acetonitrile; Chemical reactivity; Mass spectrometry; Crystalline structure
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja052108q

Reactions of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) with solvated first-row transition metals M(II) (M(II) = Ni, Zn, Mn, Fe, Cu) have been explored with emphasis on the factors that influence the identity of the resulting cyclic products for Ni(II) and Zn(II). The relatively small anions, namely [ClO4]- and [BF4]-, lead to the formation of molecular squares [{M4(bptz)4(CH3CN)8}⊂X][X]7, (M = Zn(II), Ni(II); X = [BF4]-, [ClO4]-), whereas the larger anion [SbF6]- favors the molecular pentagon [{Ni5(bptz)5-(CH3CN)10}⊂SbF6][SbF6]9. The molecular pentagon easily converts to the square in the presence of excess [BF4]-, [ClO4]-, and [I]- anions, whereas the Ni(II) square can be partially converted to the less stable pentagon under more forcing conditions in the presence of excess [SbF6]- ions. No evidence for the molecular square being in equilibrium with the pentagon was observed in the ESI-MS spectra of the individual square and pentagon samples. Anion-exchange reactions of the encapsulated ion in [{Ni4(bptz)4(CH3CN)8}⊂ClO4][ClO4]7 reveal that a larger anion such as [IO4]- cannot replace [ClO4]- inside the cavity, but that the linear [Br3]- anion is capable of doing so. ESI-MS studies of the reaction between [Ni(CH3CN)6][NO3]2 and bptz indicate that the product is trinuclear. Mass spectral studies of the bptz reactions with Mn(II), Fe(II), and Cu(II), in the presence of [ClO4]- anions, support the presence of molecular squares. The formation of the various metallacyclophanes is discussed in light of the factors that influence these self-assembly reactions, such as choice of metal ion, anion, and solvent.