Carbonyls/Carbonyl Clathrates of Iridium

[budullewraagh]

i was looking through a book on the elements today when i came across iridium. interestingly enough, it mentioned the Ir- oxidation state, as well as the Ir+, which, apparently, are very rare. In addition, it mentioned a clathrate where iridium is at a neutral state.

 

Ir-1: [ir(CO)3(PPh3)]-

Ir(O): [ir4(CO)12]

Ir+1: [ir(CO)Cl(PPh3)2]

 

has anyone ever tried making any these? is anyone familiar with any of these?

 

the concept of reducing elemental iridium to an anion is most intriguing.

[akcapr]

oh those, i make those everyday.....not

[Skye]

Ir-1: [ir(CO)3(PPh3)]

It should have an oxidation state of 0, as there are no charged ligands.

 

The other two are right though.

[budullewraagh]

that was a typographical error; forgot to add in the fact that it is an anionic complex. changed to:

"Ir-1: [ir(CO)3(PPh3)]-"

 

btw, the complex with Ir in the +1 state is called Vaska's Complex, formed from an iridium salt (usually IrCl3 hydrates or H2IrCl6) and triphenylphosphine, dimethylforamide and aniline under nitrogen.

 

a quote from wikipedia:

 

"Vaska's complex, with 16 valence electrons, is therefore unsaturated and can bind to one two-electron or two-electron ligand before it becomes electronically saturated. Vaska's complex is most famous because it undergoes oxidative addition. The iridium in Vaska's complex has an assigned oxidation state of Ir(I). During oxidative addition the Ir(I) center inserts into the σ-bond of the reactant. In this process, the oxidation state of the iridium increases 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 CH3I.

 

An interesting characteristic of Vaska's complex is that it binds O2 reversibly.

 

IrCl(CO)[P(C6H5)3]2 + O2 <—> IrCl(CO)[P(C6H5)3]2O2.

 

This reaction is simply carried out by bubbling O2 through a solution of Vaska's complex in toluene."

[akcapr]

is oxidation state in alot of cases just the ionic charge?

[BenSon]

Yeah thats right its just good to remeber some standard oxidation rules for common elements like oxygen and hydrogen, their oxidation numbers will change depending on what they have bonded to.

 

~Scott

[akcapr]

if someone told me that seriously it would have explained like 80% of wat i wanted to know about oxidation. thx

[BenSon]

Yeah you can mostly use the ionic charge and that will get you through alright. But there are exceptions such as superoxides, here is a quote from wiki these are the rules you should know when using oxidation numbers

 

There are a number of rules that can be used in determining the oxidation number of a molecule or ion:

 

The oxidation number of (neutral) atoms equal zero.

In neutral molecules, the sum of the oxidation numbers adds up to zero.

Fluorine always has a −1 oxidation number within compounds.

Oxygen has an oxidation number of −2 in compounds, except (i) in the presence of fluorine, in which fluorine's oxidation number takes precedence; (ii) in oxygen-oxygen bonds, where one oxygen must neutralize the other's charge; (iii) in peroxide compounds, in which it takes an oxidation number of −1; (iv) in superoxides, where oxygen has an oxidation number of −½.

Group I ions have an oxidation number equal to +1 within compounds.

Group II ions have an oxidation number of +2 within compounds.

Halogens, besides fluorine, generally have −1 oxidation numbers in compounds. This rule can be broken in the presence of oxygen or other halogens, where the oxidation numbers can be positive.

Hydrogen always has an oxidation number of +1 oxidation number in compounds, except in metal hydrides where instead it is −1.

 

Enjoy, I always foreget "Oxygen has an oxidation number of −2 in compounds, except (i) in the presence of fluorine, in which fluorine's oxidation number takes precedence;" that one

 

~Scott

[Skye]

that was a typographical error; forgot to add in the fact that it is an anionic complex. changed to:

"Ir-1: [ir(CO)3(PPh3)]-"

 

btw' date=' the complex with Ir in the +1 state is called Vaska's Complex, formed from an iridium salt (usually IrCl3 hydrates or H2IrCl6) and triphenylphosphine, dimethylforamide and aniline under nitrogen[/quote']

I hadn't heard of that -1 iridium. As far as the +1 state goes, I believe cobalt and rhodium both form similar complexes which undergo oxidative addition.

[budullewraagh]

i searched online and found almost nothing of the iridium anion. it seems to be incredibly rare and generally unheard of. the concept of reducing iridium in such a way is too intriguing to just overlook, but i'm coming up with nothing. i'll check out harvard libraries in two weeks and i'll ask my associates.

[woelen]

is oxidation state in alot of cases just the ionic charge?

For simple ions: yes. Examples: oxide, chloride, bromide, sulfide, etc.

 

For more complex ions: no. For these situations you have to use some 'rules' for determining the oxidation state of all elements in such ions. Another poster has given some of these 'rules', together with exceptions. Oxidation state is a nice concept, but it must be used with care and you always have to be aware for pitfalls, when using this concept.

 

For budullewraagh: Metals can sometimes be in really weird oxidation states. The nitroso-complex of iron (produced in the brown ring test for nitrate, but also made by adding a nitrite to an acidic solution of a ferrous salt) has iron in its +1 oxidation state. The ion is [Fe(NO)](2+). The nitroso-ligand has formal charge +1, so the oxidation state of the iron must be +1.

 

What to think of rhenium, which can be brought in the -1 oxidation state, by adding zinc to an aqueous solution of a rhenium salt?