Reaksi Senyawa AnorganikSenyawa Anorganik

Prinsip-prinsip dasar / hukum dasar reaksi

Reaksi

Perubahan atau transformasiDiamati dengan

Spektroskopi

Struktur Energi

Spektroskopi

Energi I Energi II Struktur I Struktur II

Reaksicepat

lambat Dapat ditentukan mekanismenya

Ada 2 aspek reaksi :Ada 2 aspek reaksi :1. Aspek Termodinamika : Energi ikat, ∆H, ∆G, ∆S, potensial redoks, K stabilitas2. Aspek kinetika : laju reaksi, mekanisme reaksi, besaran-besaran TD

yang menyangkut keadaan intermediet (madya)yang menyangkut keadaan intermediet (madya), kompleks teraktivasi.

Reaksi terjadi apabila struktur yang baru > kestabilannya

Bandingkan : KNO3 padat dicampur NaCl padat dalam air dengan

AgNO3 pdt dicampur NaCl padat dalam air

Introduction to Inorganic Reaction MechanismsScope of the course

•Limited to solution reactions•"classical inorganic" reactions which occur at metal centres in

coordination complexes(mechanisms of organometallic reactions given on the other subject)

Elementary Reaction Kinetics and MechanismElementary Reaction Kinetics and MechanismTransition State Theory

Note: only applies when transition state in equilibrium with the reactantsdoes not apply in reactions which are at diffusion controlled limitdoes not apply in reactions which are at diffusion controlled limitTherefore: fast reactions are favoured by

Note: since the rate is exponentially dependent on both ∆S‡ and ∆ Eact, small rate changes are "not significant" for the interpretation of mechanism with these very crude theories.p y

Effects of Pressure on the Rate of Reactions

Measurements of Rates of Reactions

i t" i i t > 1 i•"inert" species i.e. t1/2 > 1 min

We can use classical static techniques, e.g. light absorption, pH measurements

•"labile" species: i.e. t1/2 ca. 1 min-1msp 1/2

Use stop flow measurements, rapid mixing, fast spectroscopy

•"rapid"reactions: -relaxation techniques + fast spectrophotometry

General Comments:We cannot conclude a mechanism from a rate law !e ge.g.

(i) involvement of solvent (pseudo-first order behaviour)(ii) complex reactions with only one rate limiting step.Fi ll b l di h iFinally remember you can only disprove a mechanism you can never prove a mechanism.A rate law can at best only be consistent with a mechanistic scheme, it

itcan never prove it.

Definitions:(1) "Lability" and "Inert" arekinetic terms !!(1) Lability and Inert arekinetic terms !!(2) "Stable" and "Unstable" are thermodynamic statements(3) "Intimate" Mechanism refers to the details of the mechanism on the molecular scale.on the molecular scale.

Substitution at Square Planar Metal Complexes

For further information concerning the elements, why not try the On-line Periodic Table from the University of Sheffield - Web-Elements

Examples of Square Planar Transition Metal Complexes:

Ni(II) (mainly d8) Rh(I) Pd(II) Ir(I) Pt(II) Au(III)

General Rate Law:

Factors Which Affect The Rate Of Substitution

1. Role of the Entering Group

2. The Role of The Leaving Group

3 The Nature of the Other Ligands in the Complex3. The Nature of the Other Ligands in the Complex

4. Effect of the Metal Centre

An illustration of the importance of solvent on the substitution pathways for square planar reaction centres p y q p

3. The Nature of other Ligands in the Complex

The Trans LigandsThe Trans Ligands

Definition;

The trans effect is best defined as the effect of a coordinated ligand

upon the rate of substitution of ligands opposite to it.

For example, in the substitution reactions of Pt(II) square planar

complexes, labilizing effect is in the order;

H2O ~ OH- ~ NH3 ~ amines ~ Cl- < SCN- ~ I- < CH3- < Phosphines ~

H- < Olefins < CO ~ CN-H- < Olefins < CO CN-

Note that the "labilizing effect" is used to emphasise the fact that this

is a kinetic phenomenon.

Note that the "labilizing effect" is used to emphasise the fact that this is a g pkinetic phenomenon.

This labilization may arise because of destabilisation (a thermodynamic term) of the ground state and/or a stabilisation of the transition state.

The trans influence is purely a thermodynamic phenomenon. That is,

ligands can influence the ground state properties of groups to which

they are trans. Such properties include;

(i) Metal-Ligand bond lengths

(ii) Vibration frequency or force constants(ii) Vibration frequency or force constants

(iii) NMR coupling constants

The trans influence series based on structural data, has been given as;

R- ~ H- >= PR > CO ~ C=C ~ Cl- ~ NH3R ~ H >= PR3 > CO ~ C C ~ Cl ~ NH3

* The cis ligands The cis ligandsIn cases where a relatively poor nucleophile act as the entering group

N t C ith th t i b l it t i thNote: Compare with the trans series below, it acts in the same way.

The Intimate Mechanism for Substitution at Square Planar Complexes

The assiciative pathways utilized in the substitution of one ligand forThe assiciative pathways utilized in the substitution of one ligand for another at a square planar reaction centre

TYPICAL REACTION COORDINATES

The 1st order dependence of the rate of the reaction on:the concentration of the substrate the concentration entering reagent Indicates that these complexes undergo substitution of ligands by a bimolecular mechanism.bimolecular mechanism.Some important points concerning the "intimate" mechanismProfile A applies when the energies of the reactants and products are almost equal and in which the energies of the transition states are almostalmost equal, and in which the energies of the transition states are almost equal.Profile B is appropriate to a reaction for which the bond breaking is rate determining (d mechanism from the intermediate)determining (d mechanism from the intermediate)Profile C depicts the situation when bond forming is rate determining, a situation in which the entering group (Y) lies higher in the trans effect series than the leaving group.In a few cases the intermediate is reasonable stable and so lies at lower energy than the products.For example;

For example; p ;

A reaction profile for a reaction where a quasi-stable intermediate is formed before

the transition state: bond breaking in the five-coordinate intermediate is morethe transition state: bond breaking in the five coordinate intermediate is more

important than bond making to form the intermediate

General Substitution Reactions of Octahedral ComplexesStudies on octahedral complexes have largely been limited to two types ofStudies on octahedral complexes have largely been limited to two types of reaction:•Replacement of coordinated solvent ( eg water). Perhaps the most thoroughly studies replacement reactions of this type is the formation of a

l i f h d t d t l i i l ticomplex ion from a hydrated metal ion in solution.

•Anation: When the entering group is an ion the reaction is called anation.

•Solvolysis Since the majority of such reactions have been carried out in•Solvolysis. Since the majority of such reactions have been carried out in aqueous solution, hydrolysis is a more appropriate term. Hydrolysis reactions have been done under acidic or basic conditions.

Electron Transfer ReactionsOuter Sphere Electron TransferElectron transfer reactions may occur by either of both of two mechanisms: outer or inner sphere mechanisms. In principle all outer sphere mechanism involves electron transfer from reductant to oxidant with the coordination shells or spheres of each staying intact. That is one reactant becomes involved in the outer or second coordination sphere of the other reactant and an electron flows from the reductant to oxidant Such a mechanism isand an electron flows from the reductant to oxidant. Such a mechanism is established when rapid electron transfer occurs between two substitution-inert complexes.

Inner Sphere Electron Transfer

A i h h i i i hi h th t t d id t hAn inner sphere mechanism is one in which the reactant and oxidant share a

ligand in their inner or primary coordination spheres the electron being

transferred across a bridging group.g g g p

Inner Sphere Electron TransferInner Sphere Electron TransferThe reduction of hexaamminecobalt(3+) by hexaaquochromium(2+) occurs slowly (k = 10-3 M-1sec-1) by an outer sphere mechanism.

However, if one ammonia ligand on Co(III) is substituted by Cl-, reaction nowHowever, if one ammonia ligand on Co(III) is substituted by Cl , reaction now occurs with a substantially greater rate (k = 6 x 105 M-1 sec-1).

4 categories based on rate of exchange coordinated water :

1. Extreemly fast (1st order rate constant 108 s-1) alkali metas and alkali earth metal

2. Exchange water is fast (1st order rate constant 105 - 108 s-1) dipositive transition metal, Mg2+, tripositive lanthanides

3. Relative slow. (1st order rate constant 1 - 104 s-1) tripositive transition metal, Be2+, Al3+

4 Slow for only inert complexes (1st order rate constant 10-1 – 10-9 s-1) Cr3+4. Slow , for only inert complexes (1 order rate constant 10 – 10 s ) Cr , Ru3+, Pt2+, Co3+

Senyawa kompleks :

Senyawa yang dalam larutannya terionisasi mempunyai ion kompleksSenyawa yang dalam larutannya terionisasi mempunyai ion kompleks

Ion kompleks :

• Ion yang terdiri dari atom pusat dan dikelilingi ligand

• Ikatannya kovelen koordinasi

• Logamnya mempunyai valensi sekunder

Valensi sekunder (= bil koordinasi) menentukan bentuk molekul dari ( )komplekstidak terionisasi

Velensi primer menentukan muatan ion kompleksterionisasiterionisasi

STEREOKIMIA DAN ISOMER

Stereokimia : Bidang ilmu kimia yang mempelajari tentang struktur ruang senyawa kimia

Isomer : Rumus molekul sama struktur berbeda ( isomer geometri dan isomer ruang)

Bilangan koordinasi 4 :Bilangan koordinasi 4 :Tetrahedral : tidak mempunyai isomerPlanar MA2B2 (cis dan trans)

Isomer geometri : struktur geometrinya sama tetapi tatanan ligand dalam struktur berbeda

MABCD : isomer geometrinya ada 3MABCD : isomer geometrinya ada 3kemungkinan struktur yang lain square piramidal

Cara membedakan isomer cis dan trans

1. Fisika : lihat momen dipolnya

Pt(NH3)2Cl2

BA AB

A B A B

M M

Cis momen dipolnya ≠ 0

trans momen dipolnya = 0

2. Spektroskopi : IR spektra2. Spektroskopi : IR spektra

Dari stretching (mulur pendek spt per pegas)

Jenis stretching :M-AM-BM-A (B)

M-AM-BM-A (A)

M-B (A)peak lebih rumit peak sederhana

M-B (B)

3. Kimia : dengan mereaksikan dengan senyawa kimiaNH NH

K2[PtCl4] [α-Pt(NH3)2Cl2] [Pt(NH3)4Cl2]NH3 NH3

AgNO3

+ H2C2O4

+ HClH2C2O4

[β-Pt(NH3)2Cl2] trans

AgNO3+[Pt(NH3)2C2O4]Non elektrolit

H2C2O4+

[Pt(NH3)2(OOCCOOH)2]

ONH3

Pt C ODibasic acid

O

Pt

NH3C O

ONH3C

CO

O

O

NH3

Pt C

OC

O

CO

OH

OH

Isomer-isomer yang lain :1 I li d t k l k d li i1. Isomer ligand : suatu seny kompleks dgn ligan yang mempunyai rumus

kimia sama tetapi berbeda strukturnya.Misalnya : 1,2 diaminopropana dan 1,3 diamino propana

o,m, p-toluidine2. Isomer ionisasi :

Stuktur kompleks sama hasil ionisasi berbeda

Misalnya : [Co(NH3)5SO4]Br ⇋ [Co(NH3)5SO4]+ + Br-

[Co(NH ) Br] SO [Co(NH ) Br]2+ + SO 2-[Co(NH3)5Br] SO4 [Co(NH3)5Br]2+ + SO42

Sebab berbeda ligan dalam inner sphere3. Isomer pelarut : solvatasi

Senyawa kompleks bila dilarutkan oleh air (isomer hidrat)

[Cr(H2O)6]Cl3 ⇋ [Cr(H2O)6] 3+ + 3 Cl- ungu[Cr(H2O)5Cl]Cl2 [Cr(H2O)5Cl] 2+ + 2 Cl- hijau muda[ ( 2 )5 ] 2 [ ( 2 )5 ] j

4. Isomer koordinatGaram yang terbentuk dari kation dan anion kompleks yang menunjukkanGaram yang terbentuk dari kation dan anion kompleks yang menunjukkan sifat isomerisasi dengan melalui penggantian satu ligan atau lebih dari kation ke anion.

Mi lMisalnya :[Co(NH3)6]3+[Cr(CN)6]3- dan [Co(CN)6]3-[Cr(NH3)6]3+

Tata susunan ligan yang terikat oleh atom pusat adalah berbedaAtom pusatnya berbeda

Reaksi pada square planar :

S b tit i kl filikSubstitusi nukleofilik

Substitusi elektrofilik

Addisi oksidatif

Dikenal di dalam kimia organik

Eliminasi reduktif

PtMeCl(PMe2Ph)2 PtMe(N3)(PMe2Ph)2 + Cl-N3

-

( 2 )2 ( 3)( 2 )2

Nu Subst

PtCl2(PMe2Ph)2 + MeHgClCl2

El Subst

PtMeCl3(PMe2Ph)2 PtCl2(PMe2Ph)2 + MeCl3( 2 )2

Add Ox El red