title: Anion template effect on the self-assembly and interconversion of metallacyclophanes.
abstract: 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} subsetX][X]7, (M = Zn(II), Ni(II); X = [BF4]-, [ClO4]-), whereas the larger anion [SbF6]- favors the molecular pentagon [{Ni5(bptz)5-(CH3CN)10} subsetSbF6][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} subsetClO4][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.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA.
authors.forename: Cristian Saul
authors.initials: CS
authors.lastname: Campos-Fernández
authors.forename: Brandi L
authors.initials: BL
authors.lastname: Schottel
authors.forename: Helen T
authors.initials: HT
authors.lastname: Chifotides
authors.forename: Jitendra K
authors.initials: JK
authors.lastname: Bera
authors.forename: John
authors.initials: J
authors.lastname: Bacsa
authors.forename: John M
authors.initials: JM
authors.lastname: Koomen
authors.forename: David H
authors.initials: DH
authors.lastname: Russell
authors.forename: Kim R
authors.initials: KR
authors.lastname: Dunbar
mesh_terms: D000838:Anions / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D018360:Crystallography, X-Ray; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D019216:Metals, Heavy / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013055:Spectrophotometry, Infrared
chemical_list: C505506:3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; D000838:Anions; D002412:Cations; D006573:Heterocyclic Compounds, 1-Ring; D019216:Metals, Heavy; D009942:Organometallic Compounds; D011725:Pyridines