2Transition metal complexes Objectives:Describe common shapes of transition metal complexesExplain why transition metal complexes are colouredOutcomes:Revise understanding of the terms complex and ligandDescribe the shape of some specific transition metal complexesExplain why solutions appear colouredUse a visible spectrum to deduce the colour of a complex ion in solution
3CO-ORDINATION NUMBER & SHAPE the shape of a complex is governed by the number of ligands around the central ionthe co-ordination number gives the number of ligands around the central iona change of ligand can affect the co-ordination numberCo-ordination No. Shape Example(s)6 Octahedral [Cu(H2O)6]2+4 Tetrahedral [CuCl4]2-Square planar Pt(NH3)2Cl22 Linear [Ag(NH3)2]+
4Predict the shape of the following complexes [Co(NH3)5Cl]2+[Cr(H2O)4Cl2]+[FeCl4]-
5Check your understanding For each of the following complexes, give the charge on the central metal ion and its coordination number and its name[Co(NH3)6]3+[Cu(NH3)4(H2O)2]2+CuCl42-[Fe(CN)6]4-K4[Fe(CN)6]Na2CoCl4[Co(NH3)6]Cl3[Cu(CN)2]-What shape is each of the complex ions likely to be?Define each of the following terms, using the complex [Ni(CN)4]2- to illustrate your answer:LigandCoordination numberShape
6Complexes and colourComplex formation is often accompanied by a change in colour.Example: Adding ammonia to aqueous copper (II) sulphate: Light blue to deep blue colour changeQ: How does colour arise?
7ColourA solution appears coloured because certain wavelengths of visible light are absorbed by the solutionblue and green not absorbedwhite lighta solution of copper(II)sulphate is blue becausered and yellow wavelengths are absorbedAbsorbed colourλ (nm)Observed colourRed650Green500Orange600Blue450Yellow550Dark blue430Violet400Green-yellow560
8COLOURED IONS a solution of copper(II)sulphate is blue because red and yellow wavelengths are absorbed
9COLOURED IONS a solution of copper(II)sulphate is blue because red and yellow wavelengths are absorbed
10COLOURED IONS a solution of nickel(II)sulphate is green because violet, blue and red wavelengths are absorbed
11Visible spectroscopy (Absorption spectroscopy) A spectrophotometer measures the absorption of light at different wavelengthsBlankAnalyserMSamplePMRecorderQuartz mirror splits light beam in twoLight sourceM = monochromator: selects wavelengthPM = photomultiplier: converts light into electric currentAnalyser: Compares two electric currents. Any difference is dependent on the absorption of light by the sampleRecorder: pen traces absorption spectrum
12What happens when light is absorbed? Electrons are excited to a higher energy level
13INCREASING ENERGY / DISTANCE FROM NUCLEUS What happens when light is absorbed?44p4d4fIRONINCREASING ENERGY / DISTANCE FROM NUCLEUS3d4s33p1s2 2s2 2p6 3s2 3p6 4s2 3d6In an isolated atom or ion, the isolated d orbitals have the same energy
14There are 5 different orbitals of the d variety What happens when light is absorbed?xyxzyzThere are 5 different orbitals of the d varietyx2-y2z23d ORBITALS
15SPLITTING OF 3d ORBITALS Placing ligands around a central ion causes the energies of the d orbitals to changeSome of the d orbitals gain energy and some lose energyIn an octahedral complex, two (z2 and x2-y2) go higher and three go lowerIn a tetrahedral complex, three (xy, xz and yz) go higher and two go lowerDegree of splitting depends on the CENTRAL ION and the LIGANDThe energy difference between the d orbitals corresponds to the frequency of visible light.The energy difference between the levels affects how much energy is absorbed when an electron is promoted. The amount of energy governs the colour of light absorbed.OCTAHEDRALTETRAHEDRAL3d3d
16What happens when light is absorbed? Theoryions with a d10 (full) or d0 (empty) configuration are colourless(there needs to be at least 1 electron which can be excited AND there needs to be an empty d orbital which can be occupied when the electron is excited)ions with partially filled d-orbitals tend to be colouredit is caused by the ease of transition of electrons between energy levelsenergy is absorbed when an electron is promoted to a higher levelthe frequency of light is proportional to the energy differenceions with d10 (full) Cu+,Ag+ Zn2+or d0 (empty) Sc3+ configuration are colourlesse.g. titanium(IV) oxide TiO2 is whitecolour depends on ... transition elementoxidation stateligandcoordination number
17Plenary Describe two common shapes of transition metal complexes Explain why solutions are coloured in terms electronsWhat does the colour of a transition metal complex depend upon?