Arsenic pentachloride

Antimony pentachloride Arsenic trichloride Arsenic pentoxide Arsenic pentachloride is a chemical compound of arsenic and chlorine with the formula . This compound was first prepared in 1976 through the UV irradiation of arsenic trichloride, AsCl3, in liquid chlorine at −105 °C.{{cite journal | doi-access =free AsCl5 is similar to phosphorus pentachloride, PCl5 in having a trigonal bipyramidal structure where the equatorial bonds are shorter than the axial bonds (As-Cleq = 210.6 pm, 211.9 pm; As-Clax= 220.7 pm).

The pentachlorides of the elements above and below arsenic in group 15, phosphorus pentachloride and antimony pentachloride are much more stable and the instability of AsCl5 appears anomalous. The cause is believed to be due to incomplete shielding of the nucleus in the 4p elements following the first transition series (i.e. gallium, germanium, arsenic, selenium, bromine, and krypton) which leads to stabilisation of their 4s electrons making them less available for bonding. This effect has been termed the d-block contraction and is similar to the f-block contraction normally termed the lanthanide contraction.

Although AsCl5 is quite unstable, adducts with phosphorus pentachloride and trimethylphosphine oxide are stable under standard conditions.