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Download 1 Transition metals and coordination chemistry ※ Transition metals
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21 Transition metals and coordination chemistry ※ Transition metals in general Importance Cr stainless steel Mn steelmaking Pt, Pd catalysts Fe transport of oxygen nitrogen fixation (Mo also) Zn catalyst in biological system Co vitamin B12 Similarity within a period adding inner d, f electrons: less effect on chemistry lanthanides and actinides Metallic Ag Cu best heat conductor of heat and e the second Ionic compounds often contain more than one oxidation state Forms complex ions usually colored: electron transition between d orbitals often paramagnetic: contain unpaired electrons 1 Electron configurations and oxidation states The first row Sc Ti 4s23d1 V Cr Mn Fe Co 4s23d2 Ni Cu 4s23d8 4s13d5 Zn 4s23d10 4s13d10 Oxid state 3+ 2+ Contain higher oxid states Ex. 2+ Higher nuclear charge: less higher oxid states Mn: 2+, 3+, 4+, 7+ 2+ is very common due to loss of two 4s electrons Oxidation potential large small stronger reducing ability atomic radii Size La large Y Electron-electron repulsion Sc 3d small small atomic number big change 4d large 5d Similar: lanthanide contraction Filling inner 4f orbitals small effect on size Increasing nuclear charge offsets the increase of n 2 ※ Coordination compounds L L Metaln+ L Yn L Counter ion Mn+ + mL (MLm)n+ Kcomplex Ligand using lone electron pair to form a bond to a metal ion Donor atom atom of the ligand bound to the metal ion Coordination number the number of donor atoms Ex. [Co(NH3)5Cl]Cl2: Co3+ has a coordination # of 6 ◎ Ligands Monodentate ligand (單牙配基): forms one bond Bidentate ligand: forms two bonds chelates (螯合物) Polydentate ligand Ex. H2C CH2 H2N NH2 ethylenediamine (en) O O C CH2 H2C N CH2CH2 N O C CH2 H2C O O C O C O O ethylenediaminetetraacetate (EDTA) Chelating agents form more stable complexes 3 ◎ Nomenclature Ex. [Co(NH3)5Cl]Cl2 pentaamminechlorocobalt(III) chloride Rules • Cation before anion • Ligands before metal (in formula: metal first) arrange in alphabetical order (prefix does not count) • Anionic ligands end in O Neutral N3 Br OH 2 CO3 2 C2O4 CN azido bromo hydroxo carbonato oxalato cyano NH3 H2O CO NO ammine aqua carbonyl nitrosyl N pyridine • Oxidation number in ( ) • Prefix mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 • With complicated ligand name bis( ) 2 tris( ) 3 tetrakis( ) 4 : Ex. [Co(en)3]Cl3 tris(ethylenediamine)cobalt(III) chloride • Complex is anion: end in -ate Ex. K4[Fe(CN)6] potassium hexacyanoferrate(II) 4 ※ Isomerism Structural isomerism: different bonding Stereoisomerism: different space arrangement ◎ Structural isomerism Coordination isomerism [Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4 Linkage isomerism Cl H3N H3N O N O Co NH3 Cl NH3 nitro yellow Cl H3N H3N O Co NH3 N NH3 O nitrito Cl red tetramminechloronitrocobalt(III) chloride tetramminechloronitritocobalt(III) chloride ◎ Stereoisomerism Geometrical isomers Cl Pt NH3 H3N NH3 Cl Cl Pt Cl NH3 cis trans yellow (cisplatin: a cancer drug) pale yellow Cl H3N H3N Co Cl trans green Cl NH3 H3N NH3 H3N Co NH3 Cl NH3 cis violet 5 Optical isomers Enantiomers (對掌體;鏡像異構) Mirror images but not superimposable (Compounds with this property are chiral (掌性的)) mirror H HN N Co N H HN H N N H NH HN NH HN NH H N Co N NH H NH H N Co N NH H mirror achiral Cl H2N Co H2N Cl NH2 H2N Co Cl Cl NH2 NH2 NH2 NH2 same (contain a plane of symmetry: must be achiral) Properties of enantiomers most physical and chemical properties are the same but rotate plane polarized light in different direction 平面偏極光 6 ※ Bonding in complex ion ◎ The localized electron model based on the valence bond theory M–L Considered as covalent bond Can be viewed as M L M L Lewis acid Lewis base Number of hybridized metal orbitals = Number of ligands Ex. 3+ Co(NH3)6 coordination # = 6 d2sp3 octahedral ◎ The crystal field model focuses on the energies of d orbitals Color and magnetic properties of transition metals: related to d orbitals Interaction between ions and ligands: Electronic attraction and repulsion Only ionic bonding is considered Five d orbitals same E when not used in bonding When ligands approach repulsions occur between ligand electrons and d orbital electrons 7 Octahedral complexes Lz z L Lx Lz z L L L L y y x y x dxz L L y L Lx x L dxy Lz dyz L y L L dx2y2 dz2 L The repulsive interactions in dz2 and dx2-y2 are the highest E dz2 , dx2-y2 eg 6Dq if field from ligands were spherical 4Dq t2g dxy , dxz , dzx : crystal field splitting energy (a measurement of crystal field strength of the ligand) d orbitals in free metal ion Ex. Co3+ Strong field (large ) Weak field (small ) Low spin High spin E Spectrochemical series CN > NO2 > en > NH3 > H2O > OH > F > Cl > Br > I Strong field ligands Weak field ligands 3+ Co(NH3)6 : diamagnetic 3 CoF6 : paramagnetic 8 Ex. Cr3+ E h [Cr(H2O)6]Cl3 violet weaker L smaller absorbs longer wavelength yellow [Cr(NH3)6]Cl3 stronger L larger absorbs shorter wavelength Note: For a given ligand As charge on the metal ion increases weak-field ligand may become strong field (M-L distance smaller) Tetrahedral crystal field z L y dxy , dxz , dzx dz2 , dx2-y2 longer L None of the 3d orbitals points to the ligands E shorter L x is smaller than octahedral field Always high spin 9 Square planar field L L L remove ligands L L L L on z axis L L L octahedral field square planar field E dx2y2 octahedral dz2 dx2y2 dxy dz2 if field from ligands were spherical dxy dyz dxz dyz dxz Linear field L L L remove ligands L L on xy plane L L octahedral field L linear field E dz2 oactahedral dz2 dx2y2 dyz dxz if field from ligands were spherical dxy dyz dxz dxy dx2y2 10 ※ Biological importance Transition metals easily undergo oxid. and red. electron transfer transport and storage of O2 as catalysts and drugs S Cys Iron in cytochrome c (細胞色素) Cys S N N Fe N CO2 N CO2 11
