Tetrahedra linkage

In contrast to the other types of tetrahedron linkage already described, the three-dimensional frameworks commonly exist in a number of entirely different forms which give rise to several quite distinct families of petrologically important minerals. A few silicates have structures based on the frameworks found in the various forms of silica. Thus the structures of kalsilite, K(AlSi)04, and nepheline, Na3K(Al4Si4)016, can be regarded as derived from that of tridymite by the replacement of one-half of the silicon ions by aluminium and the introduction of the appropriate number of alkali ions to restore neutrality. The structures of carnegeite, Na(AlSi)04, and eukryptite, Li(AlSi)04, are similarly related to those of cristobalite and quartz, respectively. It will be noted that in all these minerals aluminium is, of course, always present and that the 0 (Si, Al) ratio is always 2 1. 

The tetrahedron linkage described by (I) can be calculated from the composition of the compound, to be exact, from the anion to central atom ratio (n/m ). The linkage type (II), (III) and the formation of a psi-tetrahedron (IV) can be derived from a modified generalized 8 - N rule, I. e. one needs to calculate the VEC value of the compound. The anion sharing according to (I) is independent of the VEC value and can occur in addition to case (II), (III) and/or (IV). 

Karhunen, P Rummakko, P. Sipila, J. Brunow, G. Kilpelainen, I. Dibenzo- dioxocins a novel type of linkage in softwood lignins. Tetrahedron Lett. 1995, 36, 169-170. 

Bauer U, Ho W-B, Koskinen AMP. A novel linkage for the solid-phase synthesis of hydroxamic acids. Tetrahedron Lett 1997 38 7233-7236. 

Fonseca ASC, Gonfalves MST, Costa SPG (2007) Photocleavage studies of fluorescent amino acid conjugates bearing different types of linkages. Tetrahedron 63 1353-1359... 

Kers, A. and Stawinski, J., A new type of nucleotide analogue with 4-py-ridylphosphonate internucleotide linkage, Tetrahedron Lett., 40, 4263, 1999. 

Bernatowicz MS, Daniels SB, Koster H (1989) A comparison of acid-labile linkage agents for the synthesis of peptide C-terminal amides. Tetrahedron Lett 30 4645-4648... 

G. H. Veeneman and J. H. van Boom, An efficient thioglycoside-mediated formation of glycosidic linkages promoted by iodonium dicollidine perchloride, Tetrahedron Lett. 37 275... 

N. K. Kochetkov, N. N. Malysheva, E. M. Klimov, and A. V. Demchenko, Synthesis of polysaccharides with 1,2-c -glycosidic linkages by tritylthiocyanate polycondensation. Stereoregular a-(l-6)-D-glucan, Tetrahedron Lett., 33 (1992) 381-384. 

Patek M, Lebl M, Safety-catch anchoring linkage for synthesis of peptide amides by Boc/Fmoc strategy, Tetrahedron Lett., 32 3891-3894, 1991. 

The extent of breakdown of the network structures present in a pure liquid solvent can be viewed in the following way. The Si04 tetrahedron is accepted as the basic structural unit in a mixture of metallic oxide and fused silica. However, are the tetrahedra linked together at all and, if so, how are they linked together What is the number of links per silicon Water molecules are the basic structural unit in an aqueous solution, but extensive linkage and intermolecular bonding occurs in pure water. How is this linkage in molten SiOj affected by the presence of new ions dissolved in it (Section 5.1) ... 

Alsina, J., Giralt, E., and Albericio, F. (1996) Use of A-tritylamino acids and PyAOP for the suppression of diketopiperazine formation in Fmoc/ Bu solid-phase peptide synthesis using alkoxybenzyl ester anchoring linkages. Tetrahedron Lett. 37, 4195-4198. 

Solid-phase synthesis of a naturally occurring f -(1 5)-linked d-galactofuranosyl heptamer containing the artificial linkage arm L-homoserine. Tetrahedron Lett. 1987 28 6695-6698. 89. 

The broken lines represent the edges of the tetrahedron formed by the four copper atoms, the apex formed by the central copper atom being tilted to show all the bonds joined to this atom. The iodine atoms are depicted on the faces of the tetrahedron in order to show their linkage to the neighboring copper atoms. Actually, they lie well above the plane of the tetrahedral faces. The iodine atom on the rear face of the tetrahedron is not shown. The unbroken lines without barbs represent covalent links those with barbs represent coordinate links. These are formal linkages, but all the Cu-I links are of course identical 36). 

---