Group 15 elements trihalides

A coordination compound, or complex, is formed when a Lewis base (ligand) is attached to a Lewis acid (acceptor) by means of a lone-pair of electrons. Where the ligand is composed of a number of atoms, the one which is directly attached to the acceptor is called the donor atom . This type of bonding has already been discussed (p. 198) and is exemplified by the addition compounds formed by the trihalides of the elements of Group 13 (p. 237) it is also the basis of much of the chemistry of the... 

Electric discharge in a mixture of PC13 and H2 produces P2C14, and white phosphorus dissolved in carbon disulfide reacts with I2 to produce P2I4. All of the trihalides of the group VA elements are known, and they can be prepared by reaction of the elements, although there are other preparative methods. The fluorides are prepared as follows ... 

Table 14.6 shows some of the properties of the trihalides of the group VA elements. 

Because of the reactive covalent bonds to halogen atoms, all of the trihalides of the group VA elements hydrolyze in water. It is found that the rates decrease in the order P > As > Sb > Bi, which agrees with the decrease in covalent bond character that results from the increase in metallic character of the central atoms. Not all of the trihalides react in the same way. The phosphorus trihalides react according to the equation... 

Table 14.6 Physical Properties of the Trihalides of Group VA Elements. ...

When looking for other molecules with lone electron-pairs that perhaps will combine these electrons with d electrons of platinum metals, there are, first of all, the trihalides of the nitrogen-phosphor group of elements. Complexes formed from chlorides of the platinum... 

Their hydrides MH3, and trihalides are pyramidal but pentahalides are trigonal bipyramidal Group-16 Elements Chalcogens Increasing Decreasing Exceptions Trends Trends... 

All of the trihalides of the Group VA elements are known. In principle, the direct action of the appropriate halogen on the elements leads to the formation of the trihalides. However, such reactions may not always be the best preparative methods. The fluorides are prepared by the following reactions ... 

Table 13.2 shows some of the properties of the trihalides of the Group VA elements. Several trends in the data shown in Table 13.2 are of interest. For example, the trihalides of phosphorus and arsenic can be considered as covalent molecules. As a result, the intermolecular forces are dipole-dipole and London forces that are weak. Therefore, the melting and boiling points increase with molecular weight as expected. The trifluorides of antimony and bismuth are essentially ionic compounds and the melting points are much higher than those of the halogen derivatives that are more covalent. 

Trihalides of the Group VA elements are pyramidal (C3v) with an unshared pair of electrons on the central atom. Typically, the molecules are Lewis bases, and they form acid-base adducts and metal complexes. In accord with the hard-soft interaction principle, these species are better electron pair donors toward soft electron pair acceptors. Therefore, most of the complexes of these EX3 molecules contain second and third row transition metals or first row metals in low oxidation states. 

Redistribution of substituents tends to be especially facile for halides, hydrides, and alkyls of Groups I—III nontransition elements because these compounds are electron-deficient. Bridging groups are present in many of these compounds. Even in the boron trihalides that are not bridged, a bridged transition state making use of the empty valence shell orbitals is possible, so that redistribution can occur with a relatively low activation energy (113) ... 

The trihalides (except the fluorides), and other R3M compounds such as the trialkyls, triaryls, mixed R2MX compounds, and A1H3, all function as Lewis acids, forming 1 1 adducts with a great variety of Lewis bases. This is one of the most important aspects of the chemistry of the Group 13 elements. The Lewis acidity of the A1X3 groups (where X = Cl, CH3, etc.) has been extensively studied thermodynamically, and basicity sequences for a variety of donors have been established. 

Finally trifluorides are found among the group 11 elements. AgFs contains highly elongated AgFe octahedra which are connected to a 3D framework. It is one of the few metallic fluorides known so far. An forms a stable molecular trihalides with each of the halides, AU2X6, with square-planar coordinated An atoms. ... 

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