Coordination Chemistry of a New Rigid, Hexadentate Bispidine-Based Bis(amine)tetrakis(pyridine) Ligand
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- 作者：Christian Bleiholder ; Heidi Bö ; rzel ; Peter Comba ; Rosana Ferrari ; Matthias Heydt ; Marion Kerscher ; Shigemasa Kuwata ; Gabor Laurenczy ; Geoffrey A. Lawrance ; Achim Lienke ; Bodo Martin ; Michael Merz
- 刊名：Inorganic Chemistry
- 出版年：2005
- 出版时间：October 31, 2005
- 年：2005
- 卷：44
- 期：22
- 页码：8145 - 8155
- 全文大小：303K
- 年卷期：v.44,no.22(October 31, 2005)
- ISSN：1520-510X
文摘
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), L6m, with four pyridine and two tertiary amine donors, based on a veryrigid diazaadamantane-derived backbone, is coordinated to a range of metal ions. On the basis of experimentaland computed structural data, the ligand is predicted to form very stable complexes. Force field calculations indicatethat short metal-donor distances lead to a buildup of strain in the ligand; that is, the coordination of large metalions 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 Cu2+ > Zn2+ 
Ni2+ <Co2+, which is not the typical Irving-Williams behavior. The preference for large M-N distances also emerges fromrelatively high redox potentials (the higher oxidation states, that is, the smaller metal ions, are destabilized) andfrom relatively weak ligand fields (dd-transition, high-spin electronic ground states). The potentiometric titrationsconfirm the efficient encapsulation of the metal ions since only 1:1 complexes are observed, and, over a large pHrange, ML is generally the only species present in solution.
Ni2+ <Co2+, which is not the typical Irving-Williams behavior. The preference for large M-N distances also emerges fromrelatively high redox potentials (the higher oxidation states, that is, the smaller metal ions, are destabilized) andfrom relatively weak ligand fields (dd-transition, high-spin electronic ground states). The potentiometric titrationsconfirm the efficient encapsulation of the metal ions since only 1:1 complexes are observed, and, over a large pHrange, ML is generally the only species present in solution.