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Outline of Topics on Coordination Chemistry 1. Structures of the Basic

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Outline of Topics on Coordination Chemistry 1. Structures of the Basic Outline of Topics on Coordination Chemistry You must be familiar with common ligands, their charge, and dn for each T-metal Ti V Cr Mn Fe Co Ni Cu Zn +2 ion 2 3 4 5 6 7 8 9 10 1. Structures of the basic Coordination Geometries 2 thru 8 2. Stereoisomers in Octahedral and Square Planar Complexes 3. VBT, CFT, and MO Theory in brief /applications 4. Applications of LFSE , magnetism, and spectra 5. Mechanisms of Octahedral Substitution in Co(III) and Cr(III) 6. Mechanism of Square Planar Substitution in Pt(II) the trans effect 7. Electron Transfer Reactions - Marcus theory. Nobel Prizes related to Inorganic Chemistry 1901 van’t Hoff LeBel Tetrahedral carbon/ stereochemistry (1867) 1913 Alfred Werner Coordination chemistry (1893) 1912 Victor Grignard RMgX reagent 1954 L. Pauling nature of chemical bond 1962 Max Perutz Hemoglobin structures 1963 Ziegler & Natta Titanium catalysts for stereoreg polymerization 1964 Dorothy Crowfoot Hodgkin Vitamin B12 structure (Co) 1973 G. Wilkinson and E. O. Fischer ferrocene and sandwiches 1979 H. C. Brown, G. Wittig hydroboration, P ylids 1983 Henry Taube electron transfer reactions of metal complexes 1985 H. Hauptman and J. Karle Direct methods to solve phase problem 1987 Lehn, Pedersen, Cram supramolecular chem/crown ether/host guest 1992 Rudy Marcus adiabatic theory of electron transfer 1996 Kroto, Curl, Smalley C60 2001 Nyori, Knowles, Sharpless chiral metal catalysts Rh, Ti 2005 Grubbs, Chauvin, Schrock metathesis / carbenes Ru, Mo 2010 Heck, Suzuki, Negishi organometallic catalysis PdP4 Kolbe on van’t Hoff http://ursula.chem.yale.edu/~chem125/125/history/Kolbe.html I have recently published an article in Journal für praktische Chemie (14 , 288 ff.) giving as one of the reasons for the contemporary decline of chemical research in Germany the lack of well-rounded as well as thorough chemical education. Many of our chemistry professors labor with this problem to the great disadvantage of our science. As a consequence of this, there is an overgrowth of the weed of the seemingly learned and ingenious but in reality trivial and stupefying natural philosophy. This natural philosophy, which had been put aside by exact science, is at present being dragged out by pseudoscientists from the junk-room which harbors such failings of the human mind, and is dressed up in modern fashion and rouged freshly like a whore whom one tries to smuggle into good society where she does not belong. A J. H. van't Hoff who is employed at the Veterinary School in Utrecht appears to find exact chemical research not to his taste. He deems it more convenient to mount Pegasus (evidently loaned from the Veterinary School) and to proclaim in his "La chimie dans l'espace" how, to him on the chemical Parnassus which he ascended in his daring flight, the atoms appeared to be arranged in the Universe. Werner Theory of Coord. Complexes 1893 at age 26 # AgCl ppt # ions from Conductivity Werner CoCl 3 - 6 NH 3 3 4 luteo [Co(NH 3)6]Cl 3 - 5 NH 3 2 3 purpeo [Co(NH 3)5 Cl]Cl 2 1 - 4 NH 3 1 2 violo/praeseo [Co(NH 3)4Cl 2]Cl * IrCl 3 - 3 NH 3 0 0 Ir(NH 3)3Cl 3 PtCl 4 -6 NH 3 4 5 [Pt(NH3)6]Cl 4 - 5 NH 3 3 4 [Pt(NH 3)5Cl]Cl 3 - 4 NH 3 2 3 [Pt(NH 3)4Cl 2]Cl 2 * -3 NH 3 1 2 [Pt(NH 3)3Cl 3]Cl * -2 NH 3 0 0 Pt(NH 3)2Cl 4 * -KCl - NH 3 0 2 K[Pt(NH 3)Cl 5] 2 - 2 KCl 0 3 K 2[PtCl 6] 1 cis or trans-dichlorotetraamminecobalt (III) chloride 2. potassium hexachloroplatinate(IV) CHEM 3030 LAB EXPTS 1. Synthesis of [Co(NH 3)4(CO 3)]NO 3 , [Co(NH 3)5Cl]Cl 2 IR, Conductivity 2. [Cr(NH 3)6](NO 3)3 liq NH 3, UV-Vis 3. Magnetic Susceptibility Gouy and Evans Methods 2+ 4. Linkage Isomers of Co(NH 3)5(NO 2) UV-Vis, IR 5. X-ray Structure of an Iron Macrocyle in P2 12121 SHELX software 6. Coordination Chemistry of Nickel UV-Vis , IR, or magnetism Common Ligands HS 184 , 204 3rd - monodentates: aqua, halides, NH 3, CN , PR 3, thf, py, dmso, NCS - bidentates: en, acac -, oxalate 2-, bipy, phen, diphos, glycinate - - - 2- , dmgh mono or bi : RCOO CO 3 polydentates : dien, trien, porphyrin 2-, Pc 2-, edta 4-, 18crown, cyclam Paramagnetism HS 579 673 3rd µ in Bohr magnetons = sqr(n(n+2) where n = # unpaired e’s 1. 1.73 2. 2.84 3. 3.87 4. 4.89 5. 5.9 BM spin only values Bonding Approaches to Coordination Complexes 1. Lewis. Electron pair bond concept. Ligands are e-pair donors, metals e- pair acceptors. dative bond -both electrons in bond come from ligand. 2. VBT (Pauling) Vacant hybrid orbitals on metal are generated from LCAO suited to each geometry ( tetrahedral sp 3 etc) Bonds are formed by e-pair donation from ligand orbital into vacant hybrid orbitals on metal. 3. CFT. Bethe 1930. The degeneracy of d orbitals is lifted by the electrostatic field of ligands (taken as point charges) in various symmetries. In octahedral symmetry t 2g (-4Dq) and eg (+6Dq) separated by ∆o = 10 Dq. Bonding is presumed to be purely ionic. 4. MOT LCAO-MO’s are generated by combining symmetry adapted LGO’s with metal orbitals. Bonding and antibonding combos. Electrons then fill levels from bottom up according to Hund’s rules. Valence Bond Theory Pauling 1930’s hs-555/ 639 AO’s lack the directional character necessary for bond formation in many geometries. Hybrid orbitals are linear combinations of AO’s with suitable directionality . - 10 4 linear sp Ag(CN) 2 d (sp) 0 BM 2 5 2 6 trigonal sp Fe(N(SiMe 3)2)3 d (sp ) 5.9 BM 3 2- 8 3 8 tetrahedral sp NiCl 4 d (sp ) 2.8 BM 2 2- 8 2 8 square planar dsp PtCl 4 d (dsp ) 0 BM 3 0 3 10 5 coordinate dsp PF 5 d (dsp ) 0 BM 2 3 3+ 6 12 octahedral d sp (inner) Co(NH 3)6 d (hyb) 0 BM 3 2 2+ 8 12 sp d (outer) Ni(NH 3)6 d (hyb) 2.84 BM 3 3 4- 2 14 7 coordinate d sp V(CN) 7 d (hyb) 2.84 BM 4 3 4- 2 16 8 coordinate d sp W(CN) 8 d (hyb) 0 BM 5 3 2- 0 18 9 coordinate d sp ReH 9 d (hyb) 0 BM In CFT the energies of the d orbitals are obtained from perturbation theory using the electrostatic potential V and the d orbital wavefunctions. Edz2 = ∫ ψdz2 Voct ψdz2 = +6Dq and Exy = -4Dq etc. Dq = 1/6 ze 2 r4/a 5 where r 4 is the mean radius 4 of the electron and a is the metal ligand bond length. CFSE ( in units of Dq) see p-563 of HS z2 x2-y2 xy xz yz One on z 5.14 -3.14 -3.14 0.57 0.57 Linear 10.28 -6.28 -6.28 1.14 1.14 trigonal -3.21 5.46 5.46 -3.85 -3.85 trigonal bipy 7.07 -0.82 -0.82 -2.71 -2.71 square -4.28 12.28 2.28 -5.14 -5.14 tetrahedral -2.67 -2.67 1.78 1.78 1.78 square pyram 0.86 9.14 -0.86 -4.57 -4.57 octahedral +6.00 +6.00 -4.00 -4.00 -4.00 Spectrochemical series - orders ligand in terms of increasing Dq I- < F - < OH - < ox 2- ~ H2O < NH3 < en < bipy < phen < CN - < R - < CO Dq values in cm -1 and pairing energies (avg PE/electron) hs 559/642 +2 ions Ti V Cr Mn Fe Co Ni 6F - 730 6 H 2O 1240 1400 780 940 930 850 6 NH 3 1020 1080 3 en 910 1100 1150 PE 23,500 25,500 17,600 22,500 +3 ions Ti V Cr Mn Fe Co Rh 6F - 1700 1500 1400 1310 2264 6 H 2O 2030 1785 1740 2100 1370 1820 2720 3 ox 2- 1800 1700 1400 1800 2600 6 NH 3 2160 2290 3410 3 en 2190 2400 3460 6 CN - 2660 3500 3220 4490 PE 28000 30,000 21,000 ∆ Predicting Hi or Low spin from PE and 0. Pairing energy for Co +3 PE = 21,000 cm -1 per electron 3- ∆ CoF 6 0 = 10Dq = 13,000 ∆ cfse for low spin = 24Dq - 4 Dq = 20 Dq =26,000 cm -1 cost of pairing 2 electrons = 42,000 cm -1 cost exceeds benefit . 3+ ∆ -1 Co(NH 3)6 0 = 10Dq = 23,000 cm ∆cfse = 20Dq = 46,000 cm -1 benefit exceeds cost *This calculation assumes that PE is independent of ligand. A better criterion is to compare ∆/B for the complex with the crossover point in the Tanabe Sugano diagram at ∆/B = 20 3- ∆ 5 CoF 6 0/B = 13,000/763 = 17 high spin T2g 3+ ∆ 1 Co(NH 3)6 0/B = 23,000/530 = 43 low spin A1g Examples of CFSE effects. ∆ 1. Stability constants, lattice energies, Hhyd, etc (Fig 20.26-28 of HS) show a big M or W pattern across the transition series. (V for strong field) weak field cfse = 4,8,12,6,0,4,8,12,6,0 Dq for d 1 thru d 10 max at d 3 and d 8 strong field cfse = 4,8,12,16,20,24,18,12,6,0 Dq for d 1 thru d 10 max at d 6 2.
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