title: Coordination chemistry of a new rigid, hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand.
abstract: The hexadentate bispidine-based ligand 2,4-bis(2-pyridyl)-3,7-bis(2-methylenepyridine)-3,7-diazabicyclo[3.3.1]nonane-9-on-1,5-bis(carbonic acid methyl ester), L(6m), with four pyridine and two tertiary amine donors, based on a very rigid diazaadamantane-derived backbone, is coordinated to a range of metal ions. On the basis of experimental and computed structural data, the ligand is predicted to form very stable complexes. Force field calculations indicate that short metal-donor distances lead to a buildup of strain in the ligand; that is, the coordination of large metal ions is preferred. This is confirmed by experimentally determined stability constants, which indicate that, in general, stabilities comparable to those with macrocyclic ligands are obtained with the relative order Cu(2+) > Zn(2+) >> Ni(2+) < Co(2+), which is not the typical Irving-Williams behavior. The preference for large M-N distances also emerges from relatively high redox potentials (the higher oxidation states, that is, the smaller metal ions, are destabilized) and from relatively weak ligand fields (dd-transition, high-spin electronic ground states). The potentiometric titrations confirm the efficient encapsulation of the metal ions since only 1:1 complexes are observed, and, over a large pH range, ML is generally the only species present in solution.
authors.affiliation: Universität Heidelberg, Anorganisch-Chemisches Institut, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Bleiholder
authors.forename: Heidi
authors.initials: H
authors.lastname: Börzel
authors.forename: Peter
authors.initials: P
authors.lastname: Comba
authors.forename: Rosana
authors.initials: R
authors.lastname: Ferrari
authors.forename: Matthias
authors.initials: M
authors.lastname: Heydt
authors.forename: Marion
authors.initials: M
authors.lastname: Kerscher
authors.forename: Shigemasa
authors.initials: S
authors.lastname: Kuwata
authors.forename: Gabor
authors.initials: G
authors.lastname: Laurenczy
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Lawrance
authors.forename: Achim
authors.initials: A
authors.lastname: Lienke
authors.forename: Bodo
authors.initials: B
authors.lastname: Martin
authors.forename: Michael
authors.initials: M
authors.lastname: Merz
authors.forename: Bernd
authors.initials: B
authors.lastname: Nuber
authors.forename: Hans
authors.initials: H
authors.lastname: Pritzkow