Recent from talks
Oxohalide
Knowledge base stats:
Talk channels stats:
Members stats:
Oxohalide
In chemistry, oxohalides or oxyhalides are a group of chemical compounds with the chemical formula AmOnXp, where X is a halogen, and A is an element different than O and X. Oxohalides are numerous. Molecular oxohalides are molecules, whereas nonmolecular oxohalides are polymeric. Some oxohalides of particular practical significance are phosgene (COCl2), thionyl chloride (SOCl2), and sulfuryl fluoride (SO2F2).
Oxohalides can be seen as compounds intermediate between oxides and halides. There are three general methods of synthesis:
In addition, various oxohalides can be made by halogen exchange reactions and this reaction can also lead to the formation of mixed oxohalides such as POFCl2 and CrO2FCl.
In relation to the oxide or halide, for a given oxidation state of an element A, if two halogen atoms replace one oxygen atom, or vice versa, the overall charge on the molecule is unchanged and the coordination number of the central atom decreases by one. For example, both phosphorus oxychloride (POCl3) and phosphorus pentachloride, (PCl5) are neutral covalent compounds of phosphorus in the +5 oxidation state.
Oxohalides of elements in high oxidation states can be strong oxidizing agents, with oxidizing power similar to the corresponding oxide or halide. Most oxohalides are easily hydrolyzed. For example, chromyl chloride is hydrolyzed to chromate in the reverse of the synthetic reaction, above. The driving force for this reaction is the formation of A-O bonds which are stronger than A-Cl bonds. This gives a favourable enthalpy contribution to the Gibbs free energy change for the reaction
Many oxohalides can act as Lewis acids. This is particularly so with oxohalides of coordination number 3 or 4 which, in accepting one or more electron pairs from a Lewis base, become 5- or 6-coordinate. Oxohalide anions such as [VOCl4]2− can be seen as acid-base complexes of the oxohalide (VOCl2) with more halide ions acting as Lewis bases. Another example is VOCl2 which forms the trigonal bipyramidal complex VOCl2(N(CH3)3)2 with the base trimethylamine.
The vibrational spectra of many oxohalides have been assigned in detail. They give useful information on relative bond strengths. For example, in CrO2F2, the Cr–O stretching vibrations are at 1006 cm−1 and 1016 cm−1 and the Cr–F stretching vibrations are at 727 cm−1 and 789 cm−1. The difference is much too large to be due to the different masses of O and F atoms. Rather, it shows that the Cr–O bond is much stronger than the Cr–F bond. M–O bonds are generally considered to be double bonds and this is backed up by measurements of M–O bond lengths. It implies that the elements A and O are chemically bound together by a σ bond and a π bond.
Oxohalides of elements in high oxidation states are intensely coloured owing to ligand to metal charge transfer (LMCT) transitions.
Hub AI
Oxohalide AI simulator
(@Oxohalide_simulator)
Oxohalide
In chemistry, oxohalides or oxyhalides are a group of chemical compounds with the chemical formula AmOnXp, where X is a halogen, and A is an element different than O and X. Oxohalides are numerous. Molecular oxohalides are molecules, whereas nonmolecular oxohalides are polymeric. Some oxohalides of particular practical significance are phosgene (COCl2), thionyl chloride (SOCl2), and sulfuryl fluoride (SO2F2).
Oxohalides can be seen as compounds intermediate between oxides and halides. There are three general methods of synthesis:
In addition, various oxohalides can be made by halogen exchange reactions and this reaction can also lead to the formation of mixed oxohalides such as POFCl2 and CrO2FCl.
In relation to the oxide or halide, for a given oxidation state of an element A, if two halogen atoms replace one oxygen atom, or vice versa, the overall charge on the molecule is unchanged and the coordination number of the central atom decreases by one. For example, both phosphorus oxychloride (POCl3) and phosphorus pentachloride, (PCl5) are neutral covalent compounds of phosphorus in the +5 oxidation state.
Oxohalides of elements in high oxidation states can be strong oxidizing agents, with oxidizing power similar to the corresponding oxide or halide. Most oxohalides are easily hydrolyzed. For example, chromyl chloride is hydrolyzed to chromate in the reverse of the synthetic reaction, above. The driving force for this reaction is the formation of A-O bonds which are stronger than A-Cl bonds. This gives a favourable enthalpy contribution to the Gibbs free energy change for the reaction
Many oxohalides can act as Lewis acids. This is particularly so with oxohalides of coordination number 3 or 4 which, in accepting one or more electron pairs from a Lewis base, become 5- or 6-coordinate. Oxohalide anions such as [VOCl4]2− can be seen as acid-base complexes of the oxohalide (VOCl2) with more halide ions acting as Lewis bases. Another example is VOCl2 which forms the trigonal bipyramidal complex VOCl2(N(CH3)3)2 with the base trimethylamine.
The vibrational spectra of many oxohalides have been assigned in detail. They give useful information on relative bond strengths. For example, in CrO2F2, the Cr–O stretching vibrations are at 1006 cm−1 and 1016 cm−1 and the Cr–F stretching vibrations are at 727 cm−1 and 789 cm−1. The difference is much too large to be due to the different masses of O and F atoms. Rather, it shows that the Cr–O bond is much stronger than the Cr–F bond. M–O bonds are generally considered to be double bonds and this is backed up by measurements of M–O bond lengths. It implies that the elements A and O are chemically bound together by a σ bond and a π bond.
Oxohalides of elements in high oxidation states are intensely coloured owing to ligand to metal charge transfer (LMCT) transitions.