Frański Rafał, Onyszkiewicz Magdalena, Gierczyk Błażej
Faculty of Chemistry, Adam Mickiewicz University, Poznań, Poland.
Rapid Commun Mass Spectrom. 2017 Aug 15;31(15):1279-1289. doi: 10.1002/rcm.7908.
Coordination of a metal cation by a nitro group is rare and the interaction between them is usually weak. Examples of complexes in which such an interaction takes place are metal complexes of cyclams containing nitrophenyl or nitrobenzyl substituents. It seemed to be interesting to check if in the complexes of the respective crown ether conjugates the interaction can also take place.
We synthesized the respective conjugates of aza-18-crown-6, namely fluoro-substituted N-nitrophenylaza-18C6 conjugates. Their complexes with alkali and alkali earth metal cations were generated in the gas phase by electrospray ionization mass spectrometry (ESI-MS). Both collision-induced dissociation 'in-source' and collision-induced dissociation tandem mass spectrometry (ESI-CID-'in-source' and ESI-CID-MS/MS) were used to study the gas-phase stabilities of the generated complexes.
The gas-phase decomposition of the studied complexes indicated that the complexes formed by the conjugates containing a nitro group at the ortho position are more stable than those formed by the conjugates with a nitro group at the para position.
This indicates that a metal cation complexed by crown ether ring is additionally coordinated by a nitro group in the scorpionate mode. To the best of our knowledge, our finding provide the first example of a complex in which a metal cation complexed by a crown ether ring is additionally coordinated by a nitro group.
硝基与金属阳离子的配位很少见，且它们之间的相互作用通常较弱。发生这种相互作用的配合物的例子是含有硝基苯基或硝基苄基取代基的环胺金属配合物。检验在相应的冠醚共轭物配合物中是否也能发生这种相互作用似乎很有趣。
我们合成了氮杂-18-冠-6的相应共轭物，即氟取代的N-硝基苯基氮杂-18C6共轭物。通过电喷雾电离质谱（ESI-MS）在气相中生成它们与碱金属和碱土金属阳离子的配合物。采用源内碰撞诱导解离和碰撞诱导解离串联质谱（ESI-CID-源内和ESI-CID-MS/MS）来研究生成的配合物的气相稳定性。
所研究配合物的气相分解表明，在邻位含有硝基的共轭物形成的配合物比在对位含有硝基的共轭物形成的配合物更稳定。
这表明由冠醚环络合的金属阳离子以螯合模式被硝基额外配位。据我们所知，我们的发现提供了第一个由冠醚环络合的金属阳离子被硝基额外配位的配合物的例子。
