d-block Flashcards
what is the structure of a coordination compound?
central metal ion + shell of ligands
what are the 4 types of ligands?
sigma donor, sigma acceptor, pi donor, pi acceptor
what do sigma and pi donor/acceptor ligands consist of?
sigma: electron density donated/accepted from s or sp hybrid orbitals
pi: electron density donated/accepted from p orbitals only
what is the name for a ligand that can have 2 sites that could possibly bind to the metal ion? give an example and how to determine which part of the molecule binds to the metal ion
ambidentate ligand
- thiocyanate
binding site depends on the identity of the metal ion (soft or hard)
what is hapticity and denticity in coordination chemistry? + draw out the symbols
describes how the ligands bind to the metal center
hapticity (eta): n, number of neighbouring atoms of the same ligand that are simultaneously coordinated to the metal center
denticity (kappa): k, number of non-neighbouring atoms of the same ligand that are coordinated to the metal ion
what is the equation for the formation constant?
k = [concentration for each product] / [concentration for each reactant]
what is the overall formation constant equation?
beta = multiplying all the equilibrium constants for each ligand added
or [MLn] / [M] x [L]^n
or logbetan = logK1 + logK2… + logKn
why would a K value for adding a ligand suddenly increase again?
change in geometry can stabilize the coordination compound making the addition of a ligand more favourable
what does it mean if logK is reaching 0
that means K is reaching 1 which is close to equilibrium
what is the trend with increasing the no. of ligands on metal ion?
decrease in logK (progressively in favour of reactants) because of steric or electronic (repulsion) reasons
what is the relationship between ion size and stability of the complexes it forms? and why? - for s,p,f block
stability decreases as size of ion increases because of less effective nuclear charge and weaker metal ligand bonding
how does the HSAB principle relate to metal complexes? why is the opposite not favoured?
hard ligands form more stable bases with hard cations (same with soft)
hard-soft combinations are not favoured as there is not enough energy to overcome the high solvation energy of a hard species
define hard/soft acids/bases
hard acid: small monocations (highly charged) Ti4+
soft acids: less electropositive metals that are more polarisable (low charge to radius ratio)
hard bases: small, non polarizable donor atoms (NOF)
soft bases: larger relatively polarisable donor atoms (PSI)
why are polydentate ligands in general more stable than monodentate ligands?
- polydentate ligand is less likely to be displaced than monodentate ligands
- chelation + sterics prevents attack from other ligands
- entropy is higher if you replace monodentate with polydentate ligands thus favourable (IMPORTANT POINT) -> entropic drive
-> positive s is favoured = more stable complex
what are the 2 types of coordination in tridentate ligands and how are they coordinated?
meridional (mer-): through the metal ligand
facial (fac-): not through the metal ligand -> looks like a face
what are the coordination modes for tetradentates?
cisalpha, cisbeta, trans
what are the 3 types of tetradentate ligands
open chain (unbranched), tripodal (branched), macrocyclic
what are famous molecules for pentadentate and hexadentate coordination? what are its applications?
EDTA 3-
EDTA 4-
descale boilers (clean corrosion deposits)
treatment of Hg and Pb poisoning + removing excess iron from the body