Guest complexes sulfur-containing

X, and the p-xylene complex at 100-120°C. Charge transfer is a factor in the host-guest complex of 4-methyl-3,5-dinitrobenzoic acid with 2,6-dimethylnaphthalene.74 Charge transfer with tetranitrofluorenone has also been used to remove 60% of the dialkyldibenzothiophenes from petroleum that contains 1920 ppm sulfur, although no inclusion compound is involved.75 As polynitro compounds are often explosive, a better charge acceptor is needed. 

The same fluorinated mercuracycle links thiocyanate anions (in acetone solution) and the tetra-n-butylammonium salt of [(n-C6F4Hg)3SCN] has been isolated and structurally characterized [6]. The crystal structure contains a helical chain of alternating (o-C6F4FIg)3 molecules and SCN ions. The stacks are held by sulfur atoms at Hg- -S distances in the range 3.06-3.36 A, with one longer at 3.87 A. Thus, both host-guest complexation and supramolecular self-assembly if observed with these compounds. 

The sulfur-containing receptors form host-guest complexes with soft metal cations such as Cu+, Ag+, Hg " ", and Pd " " their stability depends on the size of macrocycle and in some cases spectral data suggest an interaction between the iron atom and the metal coordinated by the macrocycle, as shown in 60. 

The sulfur-containing receptors have little affinity for hard cations but can form extractable host-guest complexes with soft cations such as Ag+, Hg +, T1+, Pd +, and Pt +. Silver is found to interact strongly with sulfur [138, 139]. It was even possible to isolate 1 1 host-guest silver and mercury complexes in a large sulfur-containing macrocycle a linear HgC molecule is hosted in the cavity, but in the 1 2 complex a second mercury atom is externally attached to the ruthenium atom [140-142]. Palladium and platinum are also selectively complexed by polythia-coronands [143-148]. Some X-ray diffraction studies on palladium [147, 148] and platinum [143, 145] complexes established that the coordination of the metal occurs by interaction with the sulfur sites. 

Besides the ferrocene crown ether ligands described earlier, a variety of related macrocyclic ferrocenophanes containing various sulfur, oxygen, and nitrogen heteroatoms have been reported by a number of groups (110-115) (Scheme 21). These ligands complex transition metal guest cations such as Ag(I), Cu(I), and Pd(II) (116,117). Of particular... 

The host guest chemistry of crown ethers continues to be exploited for the development of new ionophores for the selective recovery of Hg(II). A novel crown ring system containing a redox switchable trithiadiazapentalene/trithiotriuret unit (17/18) allows control of Hg(II) in solvent extraction experiments between chloroform and water. The thiocar-bonyl sulfur donor sites outside the macrocycUc cavity of (18) are responsible for strong complexation and extractabiUty into chloroform. 

---