Portal de Periódicos da CAPES

A structural study of the complexation of the sodium ion by the cryptands 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]icosane and 4,7,1 3-trioxa-1,10-diaza bicyclo[8.5.5]icosane

1986; Royal Society of Chemistry; Issue: 6 Linguagem: Inglês

10.1039/dt9860001075

2050-5671

Stephen F. Lincoln, Ernst Horn, Michael R. Snow, Trevor W. Hambley, Ian M. Brereton, T. M. Spotswood,

Analytical Chemistry and Chromatography

The crystal structures of the cryptates formed between sodium ion and 4,7,1 3,18-tetraoxa-1,10-diazabicyclo[8.5.5]icosane, [Na(L1)(NCS)], and 4,7,13-trioxa-1,10-diazabicyclo[8.5.5]icosane, [Na(L3)(NCS)], have been determined by single-crystal X-ray diffraction methods at 295 K and refined by least-squares methods to conventional R values of 0.069 and 0.039 for 1 417 and 2 259 reflections respectively. The respective crystals were of space group Pcab with a= 14.686(3), b= 15.699(4), c= 16.522(5)Å, and Z= 8; and P21/n with a= 9.947(2), b= 15.681(4), c= 12.460(3)Å, β= 95.27(2)°, and Z= 4. Both [Na(L1)(NCS)] and [Na(L3)(NCS)] exist in the 'exclusive' form in which Na+ is located 0.14 and 0.37 A respectively above the planes defined by the three oxygen atoms of the 15-membered cryptand rings. The 13C n.m.r. spectra of these cryptates are consistent with the retention of the exclusive structures in solution whilst the 13C n.m.r. spectra of the analogous Li+ cryptates indicate that they possess 'inclusive' structures in solution. Preliminary 23Na n.m.r. data show the rate of Na+ dissociation from [Na(L1)]+ to be significantly less than that from [Na(L3)]+ as indicated by dissociation rate constants (298.2 K) of 12.1 ± 0.2 and (2.88 ± 0.02)× 104 s–1 respectively determined in N,N-dimethylformamide solvent.