Transition Metals and Coordination Chemistry
Transition Metals Similarities within a given period and within a given group. Last electrons added are inner electrons (d s, f s).
20_431 Ce Th Pr Pa d U Pm Sm Pu Eu Am Gd Cm Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb o Lu Lr Sc Y La Ac Ti Zr Hf Unq V b Ta Unp Cr Mo W Unh Mn Tc Re Uns Fe Ru Os Co Rh Ir i Pd Pt Cu Ag Au Zn Cd Hg Uno Une Uun Uuu p
20_432 d-block transition elements Sc Ti V Cr Mn Fe Co i Cu Zn Y Zr b Mo Tc Ru Rh Pd Ag Cd La* Hf Ta W Re Os Ir Pt Au Hg Ac Unq Unp Unh Uns Uno Une Uun Uuu f-block transition elemen ts *Lanthanides Ce Pr d Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Actinides Th Pa U p Pu Am Cm Bk Cf Es Fm Md o Lr
Atomic radii (nm) 20_435 0.2 Y La 1st series (3d) 2nd series (4d) 0.15 Sc Ti Hf Zr Ta b V W Mo Cr Re Tc Mn Os Ru Fe 3rd series (5d) Au Ag Ir Pt Rh Pd Co i Cu 0.1 Atomic number
Multiple Oxidation States
Metallic Behavior/Reducing Strength Lower oxidation state = more metallic
Color and Magnetism e - in partially filled d sublevel absorbs visible light moves to slightly higher energy d orbital Magnetic properties due to unpaired electrons
Electronegativity increases down column
Chromium Chemical properties reflect oxidation state
Valence-State Electronegativity Electronegativity, E: electron pulling power Valence-state E: metal in higher oxidation state is more positive has stronger pull on electrons is more electronegative Effective E
Manganese
Silver
Weak Reducing Agent, H 2 Q
Mercury
Coordination Compound Consist of a complex ion and necessary counter ions [Co(H 3 ) 5 Cl]Cl 2 Complex ion: [Co(H 3 ) 5 Cl] 2+ Co 3+ + 5 H 3 + Cl - = 1(3+) + 5 (0) + 1(1-) = 2+ Counter ions: 2 Cl -
[Co(H 3 ) 6 ]Cl 3 [Pt(H 3 ) 4 ]Br 2 Complex ion remains intact upon dissolution in water
Complex Ion Species where transition metal ion is surrounded by a certain number of ligands. Transition metal ion: Ligands: Lewis acid Lewis bases Co(H 3 ) 6 3+ Pt(H 3 ) 3 Br +
Ligands Molecule or ion having a lone electron pair that can be used to form a bond to a metal ion (Lewis base). coordinate covalent bond: metal-ligand bond monodentate: one bond to metal ion bidentate: two bond to metal ion polydentate: more than two bonds to a metal ion possible
Formulas of Coordination Compounds 1. Cation then anion 2. Total charges must balance to zero 3. Complex ion in brackets K 2 [Co(H 3 ) 2 Cl 4 ] [Co(H 3 ) 4 Cl 2 ]Cl
ames of Coordination Compounds 1. Cation then anion 2. Ligands in alphabetical order before metal ion neutral: molecule name* anionic: -ide -o prefix indicates number of each 3. Oxidation state of metal ion in () only if more than one possible 4. If complex ion = anion, metal ending -ate
Examples K 2 [Co(H 3 ) 2 Cl 4 ] potassium diamminetetrachlorocobaltate(ii) [Co(H 3 ) 4 Cl 2 ]Cl tetraamminedichlorocobalt(iii) chloride
20_441 Isomers (same formula but different properties) Structural isomers (different bonds) Stereoisomers (same bonds, different spatial arrangements) Coordination isomerism Linkage isomerism Geometric (cis-trans) isomerism Optical isomerism
Structural Isomerism 1 Coordination isomerism: Composition of the complex ion varies. [Cr(H 3 ) 5 SO 4 ]Br and [Cr(H 3 ) 5 Br]SO 4
Structural Isomerism 2 Ligand isomerism: Same complex ion structure but point of attachment of at least one of the ligands differs. [Co(H 3 ) 4 (O 2 )Cl]Cl and [Co(H 3 ) 4 (OO)Cl]Cl
Linkage Isomers [Co(H 3 ) 5 (O 2 )]Cl 2 Pentaamminenitrocobalt(III) chloride [Co(H 3 ) 5 (OO)]Cl 2 Pentaamminenitritocobalt(III) chloride
Stereoisomerism 1 Geometric isomerism (cis-trans): Atoms or groups arranged differently spatially relative to metal ion Pt(H 3 ) 2 Cl 2
20_444 H 3 Cl Co H 3 H 3 Cl Co H 3 H 3 H 3 H 3 Cl Cl H 3 Cl Cl Co Co Cl Cl (a) (b)
Stereoisomerism 2 Optical isomerism: 20_446 Have opposite effects on plane-polarized light (no superimposable mirror images) Polarizing filter Unpolarized light Tube containing sample Polarized light Rotated polarized light
20_448 Left hand Right hand Mirror image of right hand
20_449 Co Mirror image of Isomer I Co Co Isomer I Isomer II
20_450 Cl Co The trans isomer and its mirror image are identical. They are not isomers of each other. Cl Co Cl Isomer II cannot be superimposed exactly on isomer I. They are not identical structures. Cl Cl Cl Cl trans Co cis Co Cl Co Cl Cl Isomer I Isomer II (a) (b) Isomer II has the same structure as the mirror image of isomer I.
Crystal Field Theory Focus: energies of the d orbitals Assumptions 1. Ligands: negative point charges 2. Metal-ligand bonding: entirely ionic strong-field (low-spin): large splitting of d orbitals weak-field (high-spin): small splitting of d orbitals
20_454 e g (d z 2, dx 2 y 2 ) t 2g (d xz, d yz, d xy ) E = crystal field splitting Free metal ion 3d orbital energies
High spin Low spin
[V(H 2 O) 6 ] 2+ [V(H 2 O) 6 ] 3+ [Cr(H 3 ) 6 ] 3+ [Cr(H 3 ) 5 Cl] 2+s
20_459 Tetrahedral Complexes d z 2 d x 2 y 2 (a) (b) d xy d xz d yz
20_461 Square Planar & Linear Complexes d x 2 - y 2 d z 2 E Free metal ion d xz d xy d z 2 d yz Complex E Free metal ion d xz d yz d xy d x 2 - y 2 Complex x (a) M y (b) M z Approach along x-and y-axes Approach along z-axis
Hemoglobin & Oxyhemoglobin