The first observed complex of 11-crown-3 ether. X-ray crystal structure and NMR study of (benzo-11-crown-3)[sub 2] �LiNCS

Buchanan, G W; Azad, M; Yap, G PA
February 2002
Canadian Journal of Chemistry;Feb2002, Vol. 80 Issue 2, p148
Academic Journal
The title complex crystallizes in the monoclinic P2[sub 1] /c space group, with a = 7.7397(8), b = 18.287(2), c = 17.4726(19) �, � = 94.008(2)�, and Z = 4. The coordination geometry around the lithium cation is pseudooctahedral. The effects of lithium complexation on the [sup 1] H and [sup 13] C solution NMR spectra are discussed. In the solid-state [sup 13] C NMR spectrum at 300 K, very long aliphatic proton spin lattice relaxation times are observed along with broadening of the aliphatic carbon resonances. These results are attributed to the dipolar washout phenomenon, where the presence of a low amplitude motion of the same frequency as the [sup 1] H decoupler, leads to less effective removal of the [sup 1] H�[sup 13] C dipolar coupling. At 330 K, there is some sharpening of the aliphatic resonances since there is less interference between the motion and the decoupling frequency.Key words: crown ether analog, lithium complex.Le complexe mentionn� dans le titre cristallise dans le groupe d'espace P2[sub 1] /c avec a = 7,7397(8), b = 18,287(2) et c = 17,4726(19) �, � = 94,008(2)� et Z = 4. La g�om�trie de coordination autour du cation lithium est pseudoocta�drique. On discute des effets de la complexation avec le lithium sur les spectres RMN du [sup 1] H et du [sup 13] C. En RMN du [sup 13] C � l'�tat solide � 300 K, on observe que les temps de relaxation spin r�seau des protons aliphatiques sont tr�s longs et que les r�sonances des carbones aliphatiques sont �largies. Ces r�sultats sont attribu�s au ph�nom�ne d'�puration dipolaire dans lequel la pr�sence d'un mouvement de faible amplitude de fr�quence �gale � celle du d�coupleur [sup 1] H conduit � une �limination moins efficace du couplage dipolaire [sup 1] H�[sup 13] C. � 330 K, les r�sonances aliphatiques deviennent plus pr�cises parce qu'il y a moins d'interf�rence entre le mouvement et la fr�quence de d�couplage.Mots cl�s : analogue d'�ther couronne, complexe de lithium.[Traduit par la R�daction]


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