Transition Metals Occupy the d-block of periodic table Have d-electrons in valence shell Some characteristics of Transition Metals and their compounds 1.Exhibit more than one oxidation state 2.Many of their compounds are colored 3.They exhibit interesting magnetic properties. 4.They form an extensive series of compounds known as metal complexes or coordination compounds.

e.g., Reduction of V 5+ by metallic Zn VO 2 (H 2 O) 4 + yellow-orange VO(H 2 O) 5 2+ blue V(H 2 O) 6 3+ green V(H 2 O) 6 2+ violet Exhibit more than one oxidation state Many of their compounds are colored Transition Metals

ELECTRON CONFIGURATIONS 3d elements: Sc  Zn Ar 3s 2 3p 6 Sc [Ar]3d 1 4s 2 K [Ar]4s 1 Ti [Ar]3d 2 4s 2 Ca [Ar]4s Zn [Ar]3d 10 4s 2 Note: 4s is filled before 3d, but when oxidized, 4s electrons are lost before 3d. Ti[Ar]3d 2 4s 2 Ti 2+ [Ar]3d 2 4s 0 Ti 3+ [Ar]3d 1 4s 0 Ti 4+ [Ar]3d 0 4s 0 Ti 5+ does not exist!

TRANSITION METALS: Sc  Mn Oxidation States: Highest oxidation states of Sc, Ti, V, Cr, Mn = number of valence (4s + 3d) electrons. Sc [Ar]3d 1 4s 2 Sc 3+ [Ar]maximum Mn [Ar]3d 5 4s 2 Mn 7+ [Ar]maximum Trend from Sc  Mn: The max. oxidation state becomes increasingly unstable. Sc 3+, Ti 4+ are stable (maximum oxidation states). Sc 2 O 3 Stable oxide. Mn 7+ Exists but is easily reduced. MnO 4 - Strong oxidizing agent. Transition Metals

Magnetic Properties Diamagnetic: unaffected by a magnetic field no unpaired electrons Paramagnetic: influenced by a magnetic field unpaired electrons Transition metals and their compounds are often paramagnetic  Have unpaired d-electrons Eg. Ti 2+ Mn 2+

TRANSITION METAL IONS Transition metal ions are Lewis acids  they accept electron pairs. Ligands are Lewis bases  molecules or ions which donate electron pairs. Ligands bonded to metal ions  metal complexes or coordination compounds. Coordination number: number of electron donor atoms attached to the metal. Chelates are ligands possessing two or more donor atoms.

COORDINATION COMPOUNDS Metals-Lewis acids Ligands -Lewis bases. Ligand molecules have lone pair electrons. –Anions - F , Cl , Br , CN , SCN , NO 2 , etc. –Neutral ligands: NH 3, H 2 O, CO mono-dentate -(single claw to hold onto metal d orbital) Ex. :NH 3, H-:O:-H, CH 3 -:O:-H Bi-dentate -(has 2 claws to hold onto metal d orbitals). Has 2 or more functional groups on ligands that have lone pairs Example :NH 2 -CH 2 -CH 2 -H 2 N: (= en or ethylenediammine)

Coordination # = 4 Tetrahedral, e.g. [Zn(NH 3 ) 4 ] 2+ Square Planar, e.g. [Ni(CN) 4 ] 2  Square Planar, e.g. [PtCl 3 (C 2 H 4 )]  COORDINATION COMPOUNDS

Coordination # = 6 Octahedral, e.g. [CoF 6 ] 3- Octahedral, e.g. [Co(en) 3 ] 3+ COORDINATION COMPOUNDS

IMPORTANT CHELATING LIGANDS Porphine EDTA

CHELATE EFFECT Chelating ligands form more stable compounds. [Ni(H 2 O) 6 ] NH 3  [Ni(NH 3 ) 6 ] H 2 O K f = 4x10 8 [Ni(H 2 O) 6 ] en  [Ni(en) 3 ] H 2 O K f = 2x10 18 CHELATE EFFECT IS AN ENTROPY EFFECT Cd CH 3 NH 2  [Cd(CH 3 NH 2 ) 4 ] 2+  G° =  37.2kJ  H° =  57.3kJ  S° =  67.3J/K Cd en  [Cd(en) 2 ] 2+  G° =  60.7kJ  H° =  56.5kJ  S° = +14.1J/K

PROPERTIES OF TRANSITION METALS Transition Metal Complexes have different properties – color (all except Zn or Sc 3+ white compounds) solubility-depends on complex reduction potential – lower than free ions Ag + (aq) + e   Ag(s)E° 1/2 = +0.80V [Ag(CN) 2 ]  (aq) + e   Ag(s)+ 2CN  (aq) E° 1/2 =  0.31V

Co 3+ F-F- F-F- F-F- F-F- F-F- F-F- (3d 6 )

CRYSTAL FIELD SPLITTING dx 2 -y 2 dz 2 d xy d yz d xz   = crystal field splitting energy Spectrochemical series: CN  > NO 2  > en > NH 3 > H 2 O > OH - > F  > Cl  decreasing  d-electron energy

SPECTROCHEMICAL SERIES CN - CO NO 2 - en NH 3 H 2 O Oxalate OH - F - SCN - Cl - Br - I - Color seen is complementary to absorbed color Absorbed light Strong field ligands Weak field ligands UV IR

COLOR WHEEL RED GREEN VIOLET ORANGE YELLOWBLUE

CRYSTAL FIELD SPLITTING ENERGY  depends on 1. Metal 2. Oxidation state 3. Ligands P = spin pairing energy P does not depend on the ligands P <   Low Spin Complex P >   High Spin Complex

SPIN PAIRING OCTAHEDRAL COMPLEXES E CoF 6 3- Co(CN) 6 3- High spin Paramagnetic Low spin (spin paired) diamagnetic

USES OF TRANSITION METALS Ti Lighter and stronger than steel. Ti and its alloys are used in jet engines, planes, and in special high temp applications, e.g. in the reentry shield on the Apollo capsules. TiO 2 is a white pigment in all white paints. V Vanadium steel (Fe/V alloy) is the toughest steel known. It is used in car springs. V 2 O 5 is a catalyst used in sulfuric acid production. Cr Stainless Steel = 73% Fe,18% Cr, 8% Ni, 1% C Chromium is electroplated to make shiny metal parts. Mn Mn steel (Fe/Mn alloy) is very tough and can withstand shock and abrasion – used in bulldozer blades and armor plates on warships.

CHROMIUM OXIDES Cr(III) Oxide, Cr 2 O 3 Abrasive, Refractory Semiconductor, Green pigment Amphoteric Cr(IV) Oxide, CrO 2 Recording tape (magnetic material) Cr(VI) Oxide, CrO 3 Red Chrome plating, corrosion inhibitor Na 2 Cr 2 O 7 Tanning, metal corrosion inhibitor