The 3rd supplement continues the updating of the original 20 volumes on boron compounds published between 1974 and 1979. The first supplement consisting of 3 volumes covered all the literature uniformly up to the end of 1977, whereas the two volumes of the 2nd supplement have extended the literature coverage of boron compounds to 1980 and the four volumes of the 3rd supplement to 1984. The present volume continues the description of boron compounds with halogens, presenting those with chlorine, bromine and iodine. The compounds with chalcogens are completed here along with those of boron with S, Se, Te and Po. The final chapter on carboranes contains the carboranes themselves, together with metallacarboranes, and in the last section a description of carborane-containing polymers, mostly derived from the three isomeric dicarbadodecarboranes. Volume 4 of the 3rd supplement brings this supplement series to an end. It will be supplemented by a separately appearing index volume, which contains all the boron compounds dealt with in volumes 1 - 4 of this supplement series.

The present issue, Volume 2 of "Boron Compounds" 4th Supplement of the Gmelin Hand book, updates the previous issues by reporting the literature on boron-oxygen systems published up to 1988. For some important recent developments literature is covered through mid-1992; this concerns, for example, the compounds ~-Ba3[B306h and U[B305J which became of interest as materials with nonlinear optical properties. The volume directly com plements the earlier "Boron Compounds" 3rd Supplement Volume 2. In the original literature, alternative formulations are frequently used for the same com pound. This is especially true for many borates. Often, these species are neither completely heteropolar nor covalent, and an experimentally based decision has not been made. Hence, the use of brackets does not necessarily reflect a truly salt-like character. Volume 1 (systems with hydrogen and noble gases) of this particular supplement will be published subsequently, whereas Volume 3a (boron and nitrogen), Volume 3b (boron and nitrogen, boron and fluorine), and Volume 4 (boron compounds containing Cl, Br, I, S, Se, and Te, as well as a section containing carboranes) have already been published. All volumes of the 4th supplement will be augmented by a formula index. The IUPAC nomenclature is generally adhered to; thf means tetrahydrofuran; and occa sionally additional abbreviations for compounds are explained in the text. Positive signs for chemical shifts of the NMR signals indicates downfield shifts from the references, usually internal (CH3)4Si for olH and 013C with others being specified.