Question

PI5 is suggested to be uncertain and might be a combination of PI3 and I2. There are hypotheses involving the donation of electrons: phosphorus donating its 3s electron pair to the molecular orbital of I2, or I2 donating an electron to the 3d orbital of phosphorus. Are the suggestions of phosphorus donating its 3s electron pair to the molecular orbital of I2 or I2 donating its electron to the 3d orbital of phosphorus correct? Do these hypotheses align with current molecular orbital theory? Assuming the existence of the isomer IX3P−I−IIX3P−I−II, which is not mentioned in Wikipedia and lacks sourcing, does the currently accepted molecular orbital theory support a three-center four-electron bond model? The proposed model involves a three-center four-electron bond, where the bridging iodine acts as a Lewis acid bonded to two Lewis bases (IX− and PIX3). Is this model in line with the modern understanding of molecular orbital theory?

Answer 1

The suggestions of phosphorus donating its 3s electron pair to the molecular orbital of I2 or I2 donating its electron to the 3d orbital of phosphorus are not correct. The proposed three-center four-electron bond model involving a bridging iodine is not supported by the modern understanding of molecular orbital theory.

Step-by-step explanation:

The suggestions of phosphorus donating its 3s electron pair to the molecular orbital of I2 or I2 donating its electron to the 3d orbital of phosphorus are not correct hypotheses according to current molecular orbital theory.

In a molecule of phosphorus pentachloride (PCl5), the phosphorus atom exhibits sp³d hybridization, where the five valence electrons are directed towards the corners of a trigonal bipyramid. Other examples of atoms with sp³d hybridization include the sulfur atom in SF4 and the chlorine atoms in ClF3 and CIF4+.

The proposed model of a three-center four-electron bond involving a Lewis acid (bridging iodine) bonded to two Lewis bases (IX- and PIX3) is not in line with the modern understanding of molecular orbital theory. Currently, there is no support for a three-center four-electron bond model in the accepted molecular orbital theory.