 Welcome to MSB lecture series on advanced transformation chemistry. In my previous lecture, I had initiated discussion on physical and chemical properties of transfer elements. Let me continue from where I had stopped. If you consider metals such as titanium, zirconium, iron, nickel, copper, silver, gold and platinum, they are used in many ways in everyday life. However, molecular complexes, organometallic compounds, transient metal chalcogenides, I mean solid state compounds and halides are extensively used in inorganic and bioinorganic areas of research, besides their utility in homogeneous as well as heterogeneous catalysis for a variety of organic transformations. Before we little deep into coordination compounds, let us try to understand acid-base concept and hard acids and hard bases have high charge. That means acids have positive and bases have negative charges to size ratio. That means they have high charge to size ratio and also metals are always in their higher oxygen states and hard acids are not very polarizable and have high charge densities. Metal ions with high positive charges and smaller ionic sizes tend to be hard acids. That is the reason early metals, when you strip off all valence electrons, they always try to be hard acids and hence they are oxophilic and halophilic. Early transmittal ions of 3D series tend to be always hard Lewis acids. Small anions and neutral molecules tend to be hard bases. If you want to consider examples for hard acids, H plus, F e 3 plus and aluminum 3 plus are examples of hard acids as far as main group acid and bases are concerned and in case of hard bases F minus, O 2 minus, OH minus hydroxide. Let us try to understand what are soft acids and soft bases. Soft acids or soft bases have a low charge to radius ratio with metals in their low oxygen state. This is exactly opposite to hard acids and hard bases. They are normally larger ions and are polarizable. For example, I minus iodide and S 2 minus sulfide are soft bases and low valent transition metals are metal ions such as silver plus or copper plus or soft acids. Also 4D and 5D metals in their plus 1 and plus 2 ox states as well as later transition metals with filled or almost completely filled with the orbitals or soft acids. Acids such as trimethyl boron, F e 2 plus, P b 2 plus are intermediate acids whereas pyridine and aniline are intermediate bases. An element can also change its hard and soft character depending on its oxygen state. For example, let us consider hydrogen. H plus is a hard acid whereas H minus is a soft base. Similarly, nickel 3 plus is a hard acid whereas nickel 0 in nickel tetracharbonyl for example, is a soft acid. So the figures that I am going to show hard soft trends for acids and bases in the periodic table. For bases the major hard soft discontinuity is between second row that is for nitrogen, oxygen, fluorine and the rows below. You can see here hard and soft acid and bases have given here and if you see the left side of the periodic table and covering almost alkali metals and alkaline earth metals and partly 3D and 4D and 5D metals they are all hard acids and they have less number of electrons in their valence shell and they exist in their highest possible acid states and are hard acids. And if you just look into elements put in blue color they are all soft acids you can consider here and whereas in case of donor atoms in blue in color are soft bases that means soft Lewis acids I would say carbon, phosphorus, arsenic, antimony, selenium, tellurium, bromine and iodine whereas nitrogen, sulfur have partial or intermediate character. Chlorine is also intermediate in nature whereas oxygen and fluorine are hard bases. And here aluminum, silicon, gallium, germanium and tin are when it comes to metallic properties they are soft hard acids. Hard acids interact more strongly with hard bases than they do with soft bases that is the reason the combination of hard acid and hard base is more stable and similarly a combination of soft acid and soft base is very stable. But other way round is considering hard acid and soft base are soft acid and hard base they are relatively less stable. So soft acids interact more strongly with the soft bases than hard bases. Hard hard and soft soft interactions results in the formation of most stable complexes and hard acid bind halides in this order you can see the order shown whereas soft acids follow the opposite trend. For example if you consider early metal fluorides are more stable whereas late metal iodides are more stable. The softest metal ion in the period table is gold plus in aqueous solution it forms stable complexes with soft bases such as phosphines and cyanide but not with hard bases such as oxide and fluoride. And here I have shown some examples of for gold plus one complexes here it is linear and of course we have extensively studied gold chemistry in our laboratory and we have examples for different geometries of gold. For example in these examples it is linear in this one it is trigonal planar whereas in this case gold plus one state being tetrahedral and again it is trigonal planar. The affinity of oxygen plus for soft cyanide minus is very high and hence AUCN twice 2 minus is very stable that means the gold can be oxidized by oxygen in the air in the presence of cyanide. The affinity of gold plus for soft cyanide is very high and hence AUCN twice anion is very stable that gold can be oxidized by oxygen in the air in the presence of cyanide. So this property is exploited in separating gold from sand and other oxides for example you can see when gold is reacted with cyanide that means basically we are taking sodium or potassium cyanide with water dissolved oxygen is good enough it forms this disino orate anion. This reaction is used in gold mining to separate small flakes of gold from large volumes of sand and other oxides. Silver is similarly dissolved by air oxidation in cyanide solutions and this is called cyanide process. The precious metals are separated from the solution using chemical reducing agents or by electroplating. AU3 plus anion gold 3 plus anion due to its higher charge is harder than gold plus and can form complexes with harder bases such as water and amines and auric iodide or rs iodide that is AUi a combination of soft and soft is stable but AUi3 it is a combination of hard and soft is unknown that means one hard acid and other one soft base extreme ones is unknown similar to PBI4. Similarly AUF has never been isolated but AUF3 is stable AUF3 is stable because AU3 plus is hard acid. The use of cyanide ion on a large scale in mining however creates a potentially serious environmental hazard. Cyanide spill at Bea Mary in Romania in 2000 resulted in the worst environmental disaster in Europe. Highly toxic cyanide is gradually oxidized by air to the less toxic cyanide ion. In laboratories cyanide plating solutions are typically disposed of by using bleach to oxidize cyanide to cyanide and the metal is recovered as an insoluble or soluble chloride salt. For example sodium cyanide on treatment with sodium hydroxide in presence of chlorine gives NaCNO plus 2 NaCl plus H2O. So this reaction takes place in the pH range of 10 to 11.5 and sodium cyanide on further reaction with sodium hydroxide or bleach say sodium hydroxide plus 3Cl2 gives 6 NaCl plus 2 CO2 plus N2 plus 2 H2O. So this takes place in the pH range of 8.5 to 9 and similarly cyanide can also be neutralized by using thiosulfate and this process is used in cyanide poisoning in the living beings. And using base should not be considered and if very small quantity of cyanide poisoning is there sodium thiosulfate is can be used. So on January 30th, 2000 the dam containing toxic waste material from the Bea Mary Oral gold mine in northwestern Romania burst and released 100,000 cubic meters of wastewater that was heavily contaminated with cyanide into the lapis and some tributaries of the river Tisa one of the biggest river in Hungary and because of this disaster wildlife was severely impacted by the Bea Mary cyanide leak and all living things along the that river bank were killed and in Serbia 200 tons of fish in the rivers were killed and 80 percent of all aquatic life was totally destroyed the cyanide leak affected at least 32 fish species in that river. So you can imagine the kind of disaster we had because of cyanide process and letting cyanide to contaminate river. Let us come back to transition element series if we look into the first transition series scandium through copper 3D subcell is filling starting from 3D1 to 3D9 and you can see irregularities when you go to chromium. So chromium is supposed to have 3D4 4S2 and similarly copper should have 3D9 4S2 because the electronic configuration listed is slightly different. The reason is we know the fact that half filled and completely filled electronic configuration gives a stability as a result what happens one electron from 4S2 is added to have 3D5 and 4S1 electronic configuration for chromium and similarly copper assume an electronic configuration of 3D10 and 4S1. So this is because of extra stability and of course this anomaly we also see with nickel group where we have D8 and S2 electronic configuration. If you look into nickel it is perfect no issues it shows D8 and S2 electronic configuration but if you go to 4D palladium just below nickel it has 4 instead of 4D8 5S2 electronic configuration it has 4D10 and 5S0 electronic configuration and again there is a difference in the electronic configuration of platinum as well platinum instead of having D8 S2 electronic configuration it has D9 S1 electronic configuration that means the electronic configuration of platinum is 5D9 and 6S1. When we look into second transition series we go through yttrium to silver and again 4D sub shell is filling irregularities are observed for neobium which skips from 4D3 5S2 4D4 5S1 and palladium which goes from 4D8 5S2 to 4D10 5S0 that is what I did mention and irregularities are observed for 4D3 5S2 if you just look into it that also but in this case there is as such no benefit for the stability but the reason is not clear why neobium instead of having 4D3 5S2 electronic configuration it has 4D4 5S1 probably to facilitate more metal-metal bonding and also when you go for higher orbital the energy difference will be smaller and the size is bigger as a result these orbits can diffuse into each other and hence probably this kind of promotion of electron either way it should take much energy and that is the reason probably electrons can be moving or dissociating or associating easily between the neighboring orbitals. When you look into third transition series lanthanum to hoffmium through gold 5D sub shell is filling again irregularities are observed only in case of platinum that I already mentioned the fourth transition series which is incomplete ok actinium to element 104 through element 111 and here 6D sub shell is filling and of course now we have completed the series this slide shows the electronic configuration of 3D series starting from scandium to zinc we have D1 system here and we have D10 system since all the valence orbitals are completely filled here and zinc do not really follow the trends that are observed among trans-new elements and in contrast the chemical and physical properties of zinc cadmium mercury are much more related to main group elements. So metal complexes of 3D series show up to 6 coordination and rarely show 7 coordination 3D series metals or elements are relatively smaller in size and as a result they cannot go beyond 6 coordination whereas 4D and 5D series can show up to 9 coordination for example there is a tungsten 2 complex shown here this can have either capital octahedral geometry or pentagonal biferminal geometry and here coordination number is 7 and in case of this hydride homolyptic hydride rhenium H9 2 minus rhenium is in plus 9 state having tricaptagonal prismatic geometry and higher actin states are more stable in the case of 4D and 5D metal series compared to 3D series. So 3D series prefer to have lower actin states whereas metals in 4D and 5D tend to stabilize with higher actin states and of course here the reason is very simple the size is little larger compared to 3D as a result valence electrons are little away from the nucleus and as a result it is very easy to ionize electrons in 4D and 5D series. For example hexachlorotungsten, osmium tetroxide and PTF6 and here tungsten exists in plus 6 actin state whereas in this one osmium exists in plus 8 actin state and whereas in this case platinum is in plus 6 state. So 3D metals generally show plus 2 and plus 3 actin states. For example very few molybdenum tungsten compounds exist in plus 3 states whereas chromium compounds are many with chromium in plus 3 actin state and 4D and 5D metals generally possess higher enthalpies of atomization compared to 3D metals this is due to the relatively greater metal metal bonding. So while explaining the radius and also melting point I did discuss about these aspects. Let us look into the standard reduction potential for some metals in the first period. So values I have given here and here if you just see I have included calcium also and starts with calcium and end with zinc here as you see the values of alkaline earth metal is negative that means it can be readily oxidized and as the value decreases they tend to be more and more reducible in character that means copper 2 plus can be readily reduced to copper compared to calcium 2 plus getting reduced to calcium in its zero valence state and this redox potential is very very important when we want to use these metal complexes in various applications. Let us look into this question here in what way does the value of E naught for the Fe 2 plus to Fe couple depend on the first two ionization energies of Fe gaseous that means here one should look into the enthalpy or heat of formation of Fe 2 plus is it comparable with the two ionization energies required to remove two electrons from the gaseous iron atom to form Fe 2 plus. So first consider Fe 2 plus takes two electrons in irreversible fashion to form Fe S Fe. So E naught for the Fe 2 plus to Fe couple refers to the reduction process this is the redox potential I am referring to E naught is redox potential relative to the reduction 2 H plus it takes two electrons in irreversible fashion to form hydrogen molecule that means the sum of the first and second ionization energies that is IE 1 and IE 2 refers to the process Fe g giving Fe 2 plus that means you have to take one electron for using first ionization energy and apply another second ionization energy and take strip another electron to form di cation. Now to understand this one this thermo chemical cycle I have shown here first you consider Fe 2 plus aqueous and when you add two electrons it forms a Fe and then a Fe on atomization it forms a Fe gaseous and then when you apply first ionization energy and second ionization energy so you can remove one electron at a time to eventually form Fe 2 plus and then Fe 2 plus hydration and hydration it forms aqueous that means hexa aqua iron 2 plus. So here delta hydration G naught is the Gibbs energy change for the hydration of the ashes Fe 2 plus ion this cycle illustrates the contribution that the ionization energies of Fe makes to delta G naught 1 here the Gibbs free energy change also with the reduction of Fe 2 plus to Ag that is the one. So this is in turn related to redox potential of this couple that means you can relate free energy Gibbs free energy to this equation delta G naught equals minus Z Fe naught where F is 96485 coulombs per mole and in this case is a two electron process Z equals 2. So using this one for any reaction one can find out delta G or any missing component can be found out. Let me discuss little bit about the reactivity series before I conclude this lecture the reactivity series is a series of metals in order of reactivity from highest to lowest it is used to determine the products of single displacement reactions whereby metal A will replace another metal B in a solution if A is higher in the series this information also comes from the redox potential table. So activity series of some of the more common metals is listed here in the descending order of reactivity you can see here and also of course this is the oxidation half reaction I have given and for comparison I have also included alkaline metals and alkaline earth metals and also main group elements along with some chosen transient elements and one should give more importance to these signs this is very important this will tell you about how easily one can be oxidized or a metal or a element can be reduced or oxidized and this chart shows the reactivity for example whether they react with water if not they react with acid or they are not at all reactive. So let me stop here and continue further discussion on transmetallic chemistry in my next lecture until then have a wonderful time reading chemistry. Thank you.