3d Flashcards
what analytical technique is good at characterising M-CO compounds
IR is good at characterising CO compounds
what analystical technique isnt good at characterising CO compounds and why
NMR isnt,, esp 13C NMR
bc theres no CH bonds,, meanign the intensity will be even smaller
the CO are also fluxional on the compound which means they move around
why do bridging carbonyls look like and whats cool about them
bridging carbonyls are when the carbonyl is used as a bridge between other stuff.
so u3(CO) means the CO is bridging 3 diff things together while u2(CO) means ur bridging 2 diff things together using a CO.
bridging CO have an even small // slower stretching frequency bc theres more backbonding into its pi* orbital.
this is bc its bonded to more metals than if it was just a single bond.
how can we reduce the steric crowding in complexes with CO + how does this affect certain interactions
we turn terminal CO’s into bridging ones.
this weakens the sigma interaction but strengthens the pi interaction
whats an example of bridging CO complexes
(CO)4 - Co – Co ( CO)4
whats special about the terminal and bridging CO’s
theyre fluxional meaning they keep on changing places
what must a stretching CO mode be in order to be IR active
the CO stretching mode must have a change in dipole moment for it to be IR active!!!
what are 2 ways we can see if a CO stretching mode is IR active or not
drawing the moelcule out and putting arrows on the CO to represent their stretches and see if any of the arrows strengthen eachothers directionality, if they do,, its IR active bc that represents a change in dipole.
we can use point group character tables,, we find the reducible and irreducible operations and then see how many of these correspond to the moelcule,, then look at the end of the table and see if theyre IR or raman active. Ir is the LHs, while Raman is the RHS one.
if all stretches u find for ur complex using point group theory are IR active,, what does this mean
it means we should expect to see 4 Ir absorption bands.
what does raman require
a change in polarisability
to look on the graph to see if our stretches are IR active,, what do we need to look for
we need to look for x, y , z on the LHS of the graph
how many IR bands we have corresponds to what
how many of our stretches are IR active!!!
remember that stoichiometry affects this!!!
so if u have 2A1 + B1 + B2 and all are IR active,, u get 4 abs bands
