THE ELEMENTS OF SUBGROUPS IIB, IIIB, AND IVB

All the crystalline monohalides of In exist except InF, which is known only as a 

For compounds apparently containing divalent Ga, In, or Tl, there are two simple possibilities equal numbers of M and M (or and M in a covalent compound) or ions (M-M) analogous to The former alternative has been 

InS may be described as built of puckered 3-connected layers similar to those in GeS and SnS), but the layers are translated relative to their positions in GeS so that there are close In-In contacts between the layers (2-80 A). The structures are compared in Fig. 26.2. As a result In has a distorted tetrahedral arrangement of 4 nearest neighbours (3 S, 2-57 A, 1 In, 2-80 A). A S atom has 3 In neighbours and also 1 S at the surprisingly short distance of 3-09 A (in addition to 4 S at 3-71 A and 2 S at 3-94 A) confirmation of this distance would seem desirable. 

Projections of the structures of (a) InS, (b) GeS (layers perpendicular to plane of paper), showing one In-In bond in (a) as a broken line. 

Compounds of divalent Ge are well known. There is no evidence that GeO is a stable phase at temperatures below 1000°K (compare SiO), but compounds stable at ordinary temperatures include GeS, all four dihalides, and complex halides such as MGeCla. The Ge ion is not stable in water, and its crystal structure shows that GeF2 is not a simple ionic crystal (p. 929). There seem to be no simple ionic crystalline stannous compounds. In solution Sn presumably exists as complexes its easy conversion into Sn gives stannous compounds their reducing properties. Lead presents a quite different picture. The stable ion is Pb . This has no reducing properties, and there is no evidence that Pb can exist in aqueous solution, but it certainly exists in crystalline compounds such as Pb02 (rutile structure). 

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