In solution, Vaska's complex is known to bind $$O_2$$ reversibly. In the product, oxidation state of the metal ion center coordination geometry and mode of binding of $$O_2$$, respectively are

Correct option is A

​Vaska's complex is the trivial name for the chemical compound trans-carbonylchlorobis(triphenylphosphine)iridium(I), which has the formula IrCl(CO)[P(C₆H₅)₃]₂. This square planar diamagnetic organometallic complex consists of a central iridium atom bound to two mutually trans triphenylphosphine ligands, carbon monoxide and a chloride ion.

Vaska's complex can undergo oxidative addition and is notable for its ability to bind to O₂ reversibly. It is a bright yellow crystalline solid.

​Studies on Vaska's complex helped provide the conceptual framework for homogeneous catalysis. Vaska's complex, with 16 valence electrons, is considered "coordinatively unsaturated" and can thus bind to one two-electron or two one-electron ligands to become electronically saturated with 18 valence electrons. The addition of two one-electron ligands is called oxidative addition. Upon oxidative addition, the oxidation state of the iridium increases from Ir(I) to Ir(III). The four-coordinated square planar arrangement in the starting complex converts to an octahedral, six-coordinate product. Vaska's complex undergoes oxidative addition with conventional oxidants such as halogens, strong acids such as HCl, and other molecules known to react as electrophiles, such as iodomethane (CH₃I).

Vaska's complex binds O₂ reversibly:

$$\text{IrCl(CO)[P(C}_6\text{H}_5)_3]_2 + \text{O}_2 \rightleftharpoons \text{IrCl(CO)[P(C}_6\text{H}_5)_3]_2\text{O}_2$$

​The dioxygen ligand is bonded to Ir by both oxygen atoms, called side-on bonding. The resulting dioxygen adduct reverts to the parent complex upon heating or purging the solution with an inert gas, signaled by a colour change from orange back to yellow.

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