Boroxole ring structure

Table III. Infrared Vibrations of Boroxole Ring Structure Goubeau h- ...

Figure 5.4 Boroxol ring structures in vitreous boric oxide and alkali borate glasses...

Tossell, J. A., and P. Lazzeretti (1990). Calculation of the structure, vibrational spectra, and polarizability of boroxine, H3B3O3, a model for boroxol rings in vitreous BjO,. J. Phys. Chem. 94, 1723-24. 

The structure of the alkoxyboron difluorides has recently aroused some interest, and the historical consideration of the structure of these compounds has been outlined. Although the chemical shifts of these compounds are comparatively high (+01 to -f0 8) this does not imply quadricovalency (see above discussion) > however, the formation of the pyridine co-ordination complexes of the alkoxyboron difluorides (11) did not give appreciably higher B chemical shifts, and it was concluded that the boron atom in alkoxyboron difluorides was already tetracovalent. Molecular-weight determination confirmed the trimeric structure similar to the boroxole ring system. 

Fig. 14.1 Left The BO3 triangle (indicated here BO3/2). Right The B3O6 boroxol ring (indicated here B3O9/2). Both units are self-similar the replacement of all triangles by boroxol units in a given 2D- or 3D-structure, increases the number of atoms by a factor of 3, the surface by 2 and the volume by 2 the density is thus lowered from the initial one by a factor in 2D or in 3D...

To gain deeper insights, a structural analysis was carried out according to the different atomic sites. There are two possible sites for boron atoms inside or outside a boroxol ring. For oxygens, up to 4 different sites, labelled A, B, C, D in [42] and in Fig. 14.10 can be defined. The results, which are similar in both BP and BR... 

Boroxol Rings in Crystalline Structures Predictions of New B2O3 Polymorphs from First-Principles... 

Given the trend observed in Fig. 14.20, it seems natural to ask the following questions (i) what would be the energy of a structure entirely made of boroxol rings (/ = 100 %) Could it compete with that of the known crystal, B2O3 -I (ii) what is the driving force... 

Fig. 14.25 Views of the TIO polymorph. In this structure, half of the boron atoms are in boroxol rings. Channels-Uke arrangements, made by larger rings, are clearly visible...

Fig. 14.28 Schematic temperature-density phase diagram of B2O3. As the liquid is cooled and approaches the glass transition, path (A), it undergoes a structural transition from a BO3- to a boroxol-dominated network. A similar structural transition ctm be induced by stretching the liquid, path (1). Along both paths, boroxols rings form to compensate the interned negative pressure...

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