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
what is the effect of Hg and Pb poisoning on the body?
displace sulfur in amino acids and also displace Zn which is important for muscle contraction
what are some of the functions of macrocyclic ligands? + how are they named?
no. of total atoms in cycle-crown - no. of hetero atom
uses: haemoglobin (2 anionic and 2 neutral nitrogens in the porphyrin compound coordinating with the iron), vitamin B12 (cobalt) -> formation of RBC and function of brain and CNS
what is the trend d orbital stability down a group?
increasing stability (due to less experienced nuclear charge) therefore preference towards filling d orbitals
what is the equation for d occupancy?
group number - oxidation state
what is the trend in oxidation stats down the group?
higher oxidation states become more common due to lower effective nuclear change meaning that ionization energies are much lower as the atom size gets bigger
what is the kepert model for coordination geometry?
lone pairs are ignored and only considers repulsion between groups/ligands
no. of d electrons does not effect the shape of the metal complex
what are association and dissociation reactions? what is its reversibility?
association is irreversible: adding ligands to product a new geometry (eg. square planar to octahedral)
dissociation is reversible: taking away ligands but depends on the strength the ligands bind to the metal ion
why do metals such as copper, silver and gold have lower coordination numbers to ligands?
they already have a lot of electrons so do not need to bind to ligands for electron donation
what are the 2 coordination geometries for 5 ligands and what are the energy differences between them?
trigonalbipyramidal and square based pyramid which have a very small energy difference thus can interconvert
why is the only 1 signal for trigonal bipyramidal?
fluxionality of axial and equatorial ligands makes them indistinguishable (rapid interchange same NMR spec)
what are the 2 geometries for 6 coordination metal complexes?
octahedral and trigonal prismatic
what are the 2 reasons for distortion of the perfect octahedral shape complex
different ligands, jahn-teller effect (electronic related)
what are inner and outer sphere complexes?
inner: anion as a ligand directly bound to the metal centre (primary coordination sphere)
outer: counterion esque, bound to the positive metal complex electrostatically
what is nuclearity?
how many metal complexes is the ligand bound to (eg. ligand bridging)
or metal-metal bond
mononuclear, dinculear, trinuclear -> polynuclear
what are polynuclear complexes?
multiple metal centers within a complex
what is the sequence of naming a metal complex
[ metal ion, ligands in alphabetical order]oxidation state of metal complex counter ion
- if there is a hydride it comes first
- if there are things within the square brackets that need brackets {} are used instead
-for neutral atoms the donor atom would be the closest to the metal ligand (eg. OH2 rather than H2O)
what is the naming system for no. of ligands in a complex
within a ligand: di, tri, tetra..
no. of that ligand in a metal complex (if the ligand itself contains a di,tri,tetra): bis, tris, tetrakis, pentakis
if there is a numerical value associated with the ligand (eg. methyl), then the other form is included
what is the suffix for anionic complexes?
ligand metal name -ate
what are the 2 numbers that you can write after naming the metal complex?
- oxidation state of the metal ion
- overall charge of the metal complex (metal oxidation state - total charge from ligands)
what are the 2 types of isomers in coordination chemistry?
constitutional isomers: same empirical formula but different atom connectivity
stereoisomers: same connectivity but individual atoms are arranged differently in space
what are linkage isomers and how can you interchange between them?
the metal complexes that form when the same ligand uses a different atom to coordinate with the metal complex
change them photochemically or with heat (has colour changes)
what are inner sphere outer sphere isomers called?
ionisation isomerism (switch between the counterion and a ligand)
or hydrate isomerism (which includes water)
what is coordination isomerism?
ligands that have the same empirical formula but the metal centers are switched (or switching of ligands between metal ions)
-> can also have some ligands switch between ions to change its oxidation state
check L10 S64 for examples
what is an example of geometric isomerism?
- cis and trans organisation of ligands in a sqaure planar metal complex
- if the ligands are being detattched from equatorial to axial etc.
arises from detaching ligands and reattaching them in a different way
the angle between a certain set of ligands changes due to detachment
what is ligand isomerism?
ligands in different isomeric forms (different connectivity within the ligand itself but should not effect bonding to metal ion)
what is conformational isomerism and what is an example?
more than one known stereochemistry for a coordination number (eg. trigonal bipyramidal and square planar for 5 coordinate OR square planar and tetrahedral for 4 coordinate)
what are the requirements for optical isomerism
chirality but doesn’t have to be all different substituents
mirrored non-superimposable images
what is polymerisation isomerism?
same molecular formula but they 2 metal ligands can join together to create a different molecular weight metal complex
