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Coordination Compounds Peculiar compounds of transition metals Coordination Compounds • Transition metals have s, d and p orbitals all available for bonding • Don’t obey the octet rule • They are most stable with filled d, s and p orbitals – s2d10p6 (18 e-) • Transition metals act like a Lewis acid (electron pair acceptor) so as to fill valence orbitals • Transition metals will bond with Lewis bases (e- pair donors) – species with lone pairs, these are called ligands Transition Metal Complexes Most often these complexes are octahedral or tetrahedral in shape with the metal at the center Here we see • Cl• F• H2O • NH3 are behaving as ligands • Lewis bases that bind with transition metals are also called ligands • Some ligands bind once to the metal (monodentate) – NH3, H2O, CO, Cl-, Br-, I-, CN-, SCN- • Some bind twice (bidentate) – oxalate, ethylenediamine, salicylate • Some three times (tridentate) – diethylenetriamine • Some are even hexadentate – Ethylenediaminetetraacetic acid Ligands Coordination Number of TM ions Transition Metals will have a coordination number (CN) that helps get them as close to 18 valence electrons as possible (can go higher up to 20 or lower) • • • • • • • • Cu2+ [Ar] 3d9 Cr3+ [Ar] 3d3 Fe3+ [Ar] 3d5 Fe2+ [Ar] 3d6 Ni2+ [Ar] 4s23d8 Co2+ [Ar] 3d7 Mn2+ [Ar] 3d5 Zn2+ [Ar] 3d10 CN = 4 (total 17 e-) CN = 6 (total 15 e-) CN = 6 (total 17 e-) CN = 6 (total 18 e-) CN = 4 (total 18 e-) CN = 6 (total 15 e-) CN = 6 (total 17 e-) CN = 4 (total 18 e-) MO Diagram Octahedral Complex (CN = 6) d-orbitals split, and the gap is responsible for the color of many TM complexes Jahn-Teller Distortion in Cu2+ • In some cases like [Cu(NH3).2H2O]2+ an distorted octahedron is more stable than CN=4 more stable Color of TM Complexes • In transition metal complexes the d-orbitals (essentially nonbonding) split in energy • Electrons in the lower d-orbitals can absorb visible light and go into an unoccupied d-orbital Cu2+ D oct = free ion octahedron • Lowest energy transition is determined by Δoct distorted octahedron hc l Color of TM Complexes • In transition metal complexes the d-orbitals (essentially nonbonding) split in energy • Electrons in the lower d-orbitals can absorb visible light and go into an unoccupied d-orbital Weak and Strong Ligands • The size of the splitting Δoct depends on the type of ligand • The stronger the ligand metal bond the larger Δoct is Small Δoct large Δoct Part A: Synthesis [Cu(NH3)4]SO4.H2O(s) • 3g Copper (II) sulfate pentahydrate • Add 15 mL H2O (dissolve solid) • Add 2.5x calculated volume of conc. NH3 (fume hood) • Add 25 mL ethanol to reduce solubility • Place in ice water for 10 mins • Filter out solid using a Buchner funnel • Wash in ammonia/ethanol • Allow to dry till next lab Test Tube Copper(II)Sulfate 0.1661M Ligand 0.1661M 1 5 drops 5 mL diethylenetriamine Part B: 2 A: To make 5 drops • Part [Cu(NH3)4]SO4.H5 2mL O(s) ethylenediamine 3 5 drops 5 mL NH3* 4 5 drops 5 mL EDTA 5 5 drops 5 mL sodium salicylate 6 5 drops 1 mL 6M NH3 4 mL DI H2O • Measure the spectra, and extract Δ for each ligand • Determine the spectro-chemical series for these 6 ligands L Part B Sample mass of 0.1661M Copper Sulfate mass of 0.1661M Ligand 1 0.10 0.90 2 0.15 0.85 7 0.45 0.55 The Experiment • Part C: Determine y in CuLy where L0.80 = 3 0.20 ethylenediamine, diethylenetriamine, 4 0.30 0.70 salicylate, and Ethylenediaminetetraacetic 5 0.35 0.65 acid 6 0.40 0.60 • 2 ligands to0.50 9examine, ethylene 0.55 diamine, and one 0.45 assigned by me0.60 10 0.40 • Record the absorbance at the value of λmax you determine in Part B 8your group will 0.50 be given Part C: Determining y in CuLy • One of the objectives of this experiment is to determine y for different ligands L that complex with Cu2+ Complex Ligand [Cu(dien)y]2+ dien=ethylenediamine [Cu(trien)y]2+ trien = diethylenetriamine [Cu(EDTA)y]2- EDTA = Ethylenediaminetetraacetic acid [Cu(sali)y]2-y sali = salicylate 4y • We will do this using Job’s method • First find a strong absorption wavelength λmax for the CuLy • The mole fraction x=[L]/[Cu2+] is varied from small to large while the intensity of the color of the solution is measured at that wavelength λmax • when y = x the color will have the largest absorbance