Planar compounds trichloride

The diphenyliodine(III) halides have dimeric structures in the solid state,63 directly comparable with that of IC13.29 Thus, these compounds have a planar coordination of the iodine atom by two carbon and two bridging halogen atoms. This corresponds to the 12-electron, octahedral arrangement. The I—Cl bonds in the chloride, of 3.085 A, are longer than those of 2.70 A in the trichloride and presumably reflect the significance63 of the ionic form [Ph2I]+[Cl] 2. 

Iodine monobromide, a solid resulting from direct combination of the elements, is endothermic and extensively dissociated in the vapor. It is used instead of Br2 in some industrial processes. Despite the general instability of the BrX compounds, the fluorosulfate (BrOS02F) obtained by treating Br2 with S206F2, is stable to 150°C. Iodine trichloride (IC13) is also formed (like IC1) by treatment of liquid chlorine with the stoichiometric quantity of iodine, or with a deficiency of iodine followed by evaporation of the excess of chlorine. It is a fluffy orange powder, unstable much above room temperature, with a planar dimeric structure (13-VIII). 

Boron is a Group HTA element that forms many covalent compounds by bonding to three other atoms. Typical examples include boron trifluoride, BF3 (mp — 127°C) boron trichloride, BCI3 (mp — 107°C) boron tribromide, BBr3 (mp -46°C) and boron triiodide, BI3 (mp 50°C). All are trigonal planar nonpolar molecules. 

The bicyclic compound (14) formed by the reaction of phosphorus trichloride with an amino-diketone <84JA1164> has been shown to be planar, which has been interpreted as evidence for the delocalized dipolar canonical structure (15) rather than the neutral form (14). It forms a silver complex with trigonal bipyramidal stereochemistry at phosphorus <91JA1071>. 

The general tendencies of changes in molecular constants along a series of lanthanide compounds are also well known. Because of the lanthanide contraction in going from lanthanum to lutetium, various constants decrease or increase monotonically. The question of the shape of lanthanide trichlorides therefore becomes very important. Indeed, these molecules can be pyramidal, or planar, or pyramidal for lanthanum but gradually flattening to planar as we go to lutetium. 

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