Transition metal-Group 13 element complexes ionic compounds

Attempts to classify carbides according to structure or bond type meet the same difficulties as were encountered with hydrides (p. 64) and borides (p. 145) and for the same reasons. The general trends in properties of the three groups of compounds are, however, broadly similar, being most polar (ionic) for the electropositive metals, most covalent (molecular) for the electronegative non-metals and somewhat complex (interstitial) for the elements in the centre of the d block. There are also several elements with poorly characterized, unstable, or non-existent carbides, namely the later transition elements (Groups 11 and 12), the platinum metals, and the post transition-metal elements in Group 13. 

Reactions between anionic species containing one or more group-IIIB elements (particularly boron) and complexes of transition-metal halides are used to produce an immense number of ionic boron-containing compounds. For this reason a strong selection factor must be made. 

The first part of this section deals with complex compounds with arsenic, antimony or bismuth acting as central atoms. They have been ordered according to the coordination number of the element and, within these sections, according to the donor properties of the ligands and to an ionic or covalent type of the complex. In the second part we report on organoelement compounds coordinated to transition metals or main group elements. 

Non-classically bonded compounds. There are many compounds in which metal-to-carbon bonding cannot be explained as either ionic or covalent in the simple sense of a 2c-2e M—C bond or bonds. The largest and most important class of these non-classical molecules comprises those formed primarily by the transition elements in which unsaturated groups are attached to metal atoms by interaction of the n electrons with metal orbitals. These include simple metal—alkene complexes of the types (10-XX) and (10-XXI) as well as those in which cyclopentadienyl and benzene rings are... 

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