Summary Inorganic Chemistry _ v0.05

8/11/2019 Summary Inorganic Chemistry _ v0.05

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Summary inorganic chemistry part 1

Paragraph 6.11: Coordination complexes. In a Coordination complex a central atom or

ion is coordinated by one or more molecules or ions (ligands) which act as

Lewis bases (donates electrons), forming coordinate bonds with the centralatom or ion which acts as a Lewis acid (accepts electrons). toms in the

ligands that are directly bonded are called donor atoms. line is used to

denote the interaction between an anionic (negati!e ion) ligand and the

acceptor, an arrow is used to show the donation of an electron pair from a

neutral ligand to an acceptor. "he resulting species from a coordinate bond is

called an adduct. Can be indicated by a dot, e.g.# $%&'"$.

eutral complexes are usually sparingly soluble in water, but readily soluble in

organic sol!ents. "he p$ also has an e*ect, $+can compete for the ligand, and $ -can act

as ligand.

Paragraph 6.12: Stability constants. etal ions are often

hydrated, /($0)123+ is often written as 3+. 45uilibrium

constants (normally written without /$02 because that6s the

unity) for each displacement step (e.g. 78depicted on the right

here) can be ta9en together by multiplying them (also see

right), resulting in the o!erall stability constant n. :sually

stability constant 7ndecreases with increasing n (more ligands).

$ighly charged ions more negati!e ;hydcantly

negati!e) ? ;@=substantially negati!e.

umber of donor atoms through which ligand

coordinates is called denticity of ligand (mono-, didentate etc).

Aolydentates ? chelate ring (chelate from crab6s claw) with bite

angle B--. 1 membered ring is stabili3ed D-bonding.


2/18

Paragraph 19.2: Ground state e- congurations. etals are elements that readily lose

electrons to form cations. F-bloc9 metals shown in image below. transition element (G d-

bloc9 metal) is an atom that has incomplete d-subshell or forms cations with incomplete

subshells. 4ach group of d-bloc9 metals consists of three members and is called a triad, >rst

and second row metals denoted by hea!ier. irst, second and third row correspond

respecti!ely >lling %d, Hd, and Ed orbitals, from which there are howe!er minor de!iations.

0+and %+ions of >rst row metals all ha!e /r2%dn.

Paragraph 19.!: Physical properties. etallic radii show little !ariation across a gi!en

row of d-bloc9, the >rst row metal is has smallest radii, the second and third are similar. "his

last fact is due to the lanthanoid (La (E) J Lu (8))contraction# the steady decrease in si3e

along the lanthanoid elements. etals of d-bloc9 hard, ductile, malleable, less !olatile then s-

bloc9. ll %d metals ha!e !alues of I48and I40larger than those of calcium and all (except

3inc) ha!e ha!e higher !alues of Ka$=, which ma9e them less reacti!e than calcium.


3/18

(..) (paramagnetism). Intercon!ersion between oxidation states characteristic of d-

bloc9 metals. pparent oxidation state from molecular or empirical formula may be

misleading, e.g. La%+(I-)0(e-), sometimes metal-metal bonds or ambiguous oxidation states,

e.g. /"i(bpy)%2n-(n =, 8, 0).

Paragraph 19.6: &lectroneutrality. Aauling6s electroneutrality principle estimates charge

distribution by assuming charge on single atom only -8 to +8. O

Co

NH3+

NH3+

NH3+

NH3+

+H3N

+H3N

3-

Co

H3N

NH3

NH3

NH3

H3N

H3N

3+

Co

NH3+

NH3+

NH3+

NH3+

NH3+

NH3+

3+

Co

NH31/2+

NH31/2+

NH31/2+

NH31/2+

H3N

H3N

1/2+

1/2+

conventional 100% covalent 100% ionic inbetween

Paragraph 19.': Coordination numbers.Coordination numbers and geometries are often

distorted from regular geometries, because e.g. steric e*ects. If there6s a small energy

di*erence between geometries, Puxional beha!iour in solution may be obser!ed.

In the 7epert model the metal lies at the centre of a sphere o!er which the ligands are

free to mo!e. "he ligands are considered to repel each other li9e Qguration. Common arrangement in the table on the right, not all are predicted by 7epert

because electronic factors or the inherent constraints of ligands. "ripodal ligands are ligands

containing three arms, each with a donor atom, originating from central atom or group which

also may be donor.

Coordination number 2. :ncommon, restricted only a few metal-ions (d8=). Coorindation

number 3. lso uncommon, also in!ol!ing d8=.


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is called the Uahn-"eller e*ect. lso a small group of d=and d8trigonal prismatic or distorted

trigonal prismatic en!ironment. Coordination number 7.4arly second V third row (and also

lanthanoids and actinoids), rcationmust be relati!ely large. In reality much distortion from

these structures. Coordination numbers 8, 9 and 10. (..)

Paragraph 19.(: )somerism. (..) (Read blue boxes).

Ligand

s

Geometr !bridi"atio

n0 linear sp

% trigonal planar sp0

H tetrahedralW sp%

H s5uare planar sp0d

E trigonal bipyramidal sp%d

E s5uare based pyramidal sp%d

1 octahedral sp%d0

pentagonal bipyramidal sp%d%

S dodecahedral sp%dH

S s5uare antiprismatic sp%dH

S hexagonal bipyrimidal X

T tricapped trigonal

prismatic

sp%dE


5/18

Paragraph 2*.2: $alence bond

theory. Qalence bond theory

(hybridi3ation and o!erlap)#

hybridi3ation schemes can be used to

describe bonding d-bloc9 metals. &ut

!alence bond theory is !ery unrealistic

when trying to describe metal

complexes. guration, where electrons are put unpaired in %d shell to achie!e diamagnetism (or high

spin) and Hd shell thus has to be used for hybridi3ation.

Paragraph 2*.!: crystal eld theory.

Ligands are considered points charges and

there are no co!alent metal-ligand interactions.

4lectrostatic >eld crystal >eld. g. 0=.0,

if spherical approach ligands, all %d orbitals

would be raised. &ut octahedral approach# d30

and dx0-y0raised more than dy3, dyxand d3x(the

closer the ligand, the greater the raise in

energy, - Y - repulsion). "he separation

energy is Koct, because the total energy remains the same, and two and three orbitals are at

the same energy le!el, energy is splitted =.1 and =.H Koct. agnitude of Koctis determined by

the strength of the crystal field# Koct(strong field) Z Koct(wea9 >eld). Nith absporption

spectrum ion, e-promotion from t0g to eg(the resulting orbitals from splitting the d-orbital)

can be seen and Koctcan thus be estimated. Koctdetermined by identity and oxidation metal

and nature of ligands. Koctdepends on ligands as follows#

"

L

L

L

L

L

L

n+#

$

%


6/18

/wea9 field# Koct[2 I\] &r\] lled completely >rst, and in high spin the aufbau principle goes for

all orbitals. "he electrons will >ll the orbitals creating the lowest C


7/18

complex will thus be low spin. "he other way around# if Koct] A (wea9 crystal >eld), it is more

energy ecient to put the electrons in the higher orbital (eg) >rst, if these are empty.

-a$n/e**er distortions.Uahn-"eller distortions originate

if electron density is not e5ually distributed. "he

metal-ligand bond lengths are stretched if nearby

orbitals are >lled and !ice !ersa (see image), leading

to a distortion. "his is often the case in octahedral dH

and dTcomplexes.

/$e -a$n/e**er t$eorem states t$at an non*inear mo*eu*ar sstem in a degenerate

e*etroni state #i** be unstab*e and #i** undergo distortion to 'orm a sstem o' *o#er

smmetr and *o#er energ, t$ereb remoing t$e degenera.

/etra$edra* rsta* +e*d. dxy, dy3, dx3orbitals nearer to ligands than

d30 and dx0-y0. Ktet HT'Koct, because Ktet is smaller, tetrahedral

complexes are high spin. lso di*erent colours. In eHH- Uahn-

"eller distortions lead to di*erent bond angles.

uare *anar rsta* +e*d.Can be deri!ed by remo!ing two trans ligands from an

octahedral con>guration. 4.g. from 3-axis, d30greatly stabili3ed, dy3and dx3(also

point partially in 3-direction) also stabili3ed, dx0-y0 is massi!ely destabili3ed, whereas dxy is

moderately destabili3ed. /iClH20- is tetrahedral, while /Ad(II)BH23- and /At(II)BH23- are both

s5uare planar, because Ad and At (0ndand %rdrow) cause larger crystal >elds.

t$er rsta* +e*ds.


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+ctahedral Pentagonal bipyramidal S,uare antiprismatic

S,uare planar S,uare pyramidal etrahedral

rigonal bipyramidal

Paragraph 2*.": olecular orbital theory. olecular orbital theory o*ers alternati!e for

the crystal >eld theory. irst ta9e a loo9 at %.0 and pp 8=T.

Paragraph !.2: Symmetry operations / elements. symmetry operation is an

operation which lea!es it in a con>guration that is indistinguishable from its original

con>guration. "he operation is carried out with respect to symmetry elements, i.e. points,

lines or planes. "he symmetry operation around an n-fold axis is noted by Cn, n-fold meaning

that a (%1=n) rotation leads to the same con>guration. If a molecule possesses more than

one axis, the axis with the highest n-!alue is called the principal axis.


9/18

!(!ertical). !refers to the plane bisecting the ($--$) bond and !6 refers to the plane in

which the molecule lies. d(dihedral) label is gi!en if the plane bisects an angle between

two Cnaxes.

"he center of in!ersion is the point from which you can draw an in>nite number of

straight lines such that each line passes through (a) pair(s) of similar points, one on each

side of the centre of symmetry and at e5ual distance from it.

rotation followed by a rePection through a plane perpendicular to that axes, which

is called the improper rotation axis, resulting in the same con>guration, is designated with


10/18

mb

o*

eration *ement am*e

Cn Rotation n-fold axis

(%1=n)

RePection Alane

i Centre


11/18

Paragraph 2*.": olecular orbital theory continued3. theory does consider

co!alent interactions in complexes.

t$eor (based on $ater 4 120: ;6)

theory compares symmetries to establish a molecular orbital diagram. or example, a

>rst row metal has %d, Hs and Hp !alence shells. "hose can be di!ided in di*erent

symmetries.

Hs a8gsymmetryHp t8usymmetry%dx0-y0, %d3 egsymmetry%dxy, %dy3, %dx3 t0gsymmetry

It is 9nown that only p orbitals of the ligands interact with the metal.

ore precise, only the p3orbitals (if each ligand is gi!en its own axis

set). urthermore, from an examination of how many of these p orbitals

are the same after hsymmetry operations it can be concluded that

the L@ is a sum of 8g, "8uand 4gsymmetries. 1 new wa!efunctions

can thus be deri!ed by mixing the p orbitals.

"o construct the diagram, orbitals of same symmetry are

mixed. rbitals with another symmetry become non-bondingorbitals. Fisplayed to the left an image of bonding in


12/18

"here is greater o!erlap between the metal s and p orbitals and the ligand p orbitals than

between the metal %d and the ligand p, which leads to more stabili3ation. If there is no Dbonding, the energy le!els between t0gand eg` correspond with Koct. b!iously, if the eg, t8u

and a8g orbitals are >lled (which can be done by the electrons supplied by the ligands), the

remaining electrons (from the metal) are di!ided depending on wea9 or strong >eld, ust as

in the crystal >eld theory.

Com*ees #it$ < bonding a*so.


13/18

ll the orbitals below the green orbitals (see picture).

or better, but still 5ualitati!e pictures, see p. E1S boo9. $owe!er, conclusions can be

drawn#

- Koctdecreases in going from -only complex to - and D-complex (compare abo!e

donor picture to picture on pre!ious pageW and bare in mind that eg` stays e5ual).

o or a complex with D-donor ligands, increased D-donation (X) stabili3es t0gle!el

and destabili3es t0g`, thus decreasing Koct.

- Koct!alues are relati!ely large for D-acceptor ligands, and those complexes are thus

li9ely to be low spin.

o or a complex with D-acceptor ligands, increased D-acceptance stabili3es t0g,

increasing Koct.

urthermore, since >lling antibonding orbitals is detrimental for complex-formation,

octahedral complexes with D-accepting ligands will not be fa!oured by dnZ1. n obser!ation


14/18

can be made that d-bloc9 metals tend to obey the e*ecti!e atomic number rule or the 8S-

electron rule. lling the !alance shell. "he 8S-eletron rule is useless for higher

oxidation state metals, can be rationali3ed by smaller energy seperations. ther complexes

than octahedral fall out of the scope of this discussion (see p. E=).

(..W some exceptions for ).

Paragraph 2*.%: 4igand eld theory. Non6t go in to mathematics of ligand >eld theory,

howe!er, ligand >eld theory is an extension to crystal >eld theory which is freely

parameteri3ed (as opposed to locali3ed >eld from point charge). It is also con>ned to d

orbitals. part from Koctit also uses Racah parameters which are obtained from electronic

spectroscopic data.

Paragraph 2*.6: &lectronic spectra.bsorptions arise from transition between electronic

energy le!els#

- "ransitions between metal-centred orbitals possessing d-character (jd-d6 transitions).

o Nea9er.

o Can be mas9ed due C" transition.

- "ransitions between metal- and ligand-centred s which transfer charge from metal

to ligand or !ice !ersa.

o ore intense.

o LC"# metal-to-ligand charge transfer

o LC"# ligand-to-metal charge transfer

k is wa!elength, is propagation speed en c is the speed of light, is the

wa!enumber.

bsorptions are relati!ely fast in comparison to molecular !ibrations and rotations (with

which the energy le!els change), hence, the obser!ed absorption fre5uencies !ary. "here isan absorption maximum kmax (nm), with corresponding max (absorbance), kmax is used to

describe the particular band. "he molar extinction coefficient (a9a molar absorpti!ity) max#

Nhere maxis the molar extinction coecient, maxthe maximum absorption (

kmax), c the concentration, and l the pathlength (in cm) of the spectrometer

cell.

c

==

1

=c

A!a%!a%


15/18

ote (without explanation) that#

- d8,H,1,Tcomplexes consist of one absorption.

- d0,%,,Scopmlexes consist of three absorptions.

- dEcomplexes consist of a series of wea9 but sharp absorptions.

e*etion ru*es.


16/18

4.g. a @ouy balance# sample is hung in balance and magnetic >eld

applied to it, sample mo!es and di*erence in weight can be read

out, from which magnetic susceptibility, m, can be determined.

;erromagnetism, anti'erromagnetism and 'errimagnetism. If metal

centres are separated by diamagnetic species, they are said to be magnetically dilute.

Nhen paramagnetic species are close together (bul9 metal), or separated by species able to

transmit magnetic interactions (as many d-bloc9 oxides, Puorides and chlorides are), the

metal centres can couple (interact). "his may gi!e rise to ferromagnetism or

antiferromagnetism.

In a ferromagnetic material, large domains of dipoles

are aligned in the same direction. In anantiferromagnetic material, neighbouring magnetic

dipoles are aligned oppositely. bo!e the Curie

temperature ("c) the thermal energy is sucient to

o!ercome the alignment. ntiferromagnetism occurs

be*o# the qel temperature ("). errimagnetism

occurs when relati!e !alues of momenta are di*erent.

Nhen a bridging ligand facilitates coupling of

electron spins on adacent metal centres, this

happens by super-exchange. "he two metal centres

(in image on the left and right) interact with two

spin-paired electrons in the same orbital of a ligand. guration in the also has to be spin-paired, the result is an anti-parallel coupling of

the two metal centres.

Paragraph 2*.9: ligand eld stabili5ation energies 4S&3. Lgurations, it shows

remar9able similarities with other thermodynamic energy trends, such as lattice energies

and hydration enthalpies of metals. Fe!iation from the dotted line may thus be ta9en as

measures of thermochemical L


17/18

s can be seen the >gure abo!e, d=,E,8=complexes should

not fa!our octahedral or tetrahedral con>gurations.

$owe!er, other factors should be ta9en into account. 4.g.

the smaller si3e of tetrahedral complexes results in

higher lattice and sal!ation energies, hence, for example

i0+(dS) does not form tetrahedral complexes in a5ueous

solutions, only in melts or non-a5ueous media.

(..W !erhaal o!er spinels).

Paragraph 2*.1*: he )r$ing-7illiams series. In a5ueous solutions, water is replaced by

other ligands, and the position of this e5uilibrium will be related to the di*erence between

the two L


18/18

"his trend can also be explained by dependency on dncon>gurations (and not only on the e*

increment leading to a decrease in radius). $owe!er, this trend also doesn6t explain the

stability of copper. Copper is !ery stabile because a dTcomplex has a Uahn-"eller distortion.

"his also renders the image of a >xed ionic radius useless. ppearantly in this distortions H

stronger bonds compensate for the 0 wea9er (longer) bonds in such a way to ma9e it more

stabile than i(II).

Paragraph 2*.11: oxidation states in a,ueous solutions. 4=!alues (..W nog le3en- na

deel 0).

+o8 nog doen:

- Chelaat e*ect meer uitleg 3ie %S

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Summary Inorganic Chemistry _ v0.05