Chapter 23: Transition Metals and Coordination Compounds Flashcards
Properties of Transition Metals
- Size
- Ionization energy
- Electronegativity
- Oxidation states
- All have orbitals that can be involved with metallic bonding
- Little variation in size across a row
- 3rd transition row not larger
- Ionization energy: First ionization E of transition elements increases across; move down a group, third transition row has higher ionization energy
- Electronegativity: Increase across a row; increase down from first row (no further increase in 3rd or 4th)
- Exhibit variety of oxidation states
Lanthanide contraction
- Outer electron are held more tightly by nucleus and offset typical increase in size between periods
Transition Metal Electron Configurations
- Ground state e- for first two rows: ns^2(n-d)d^x
- 3/4 rows: ns^2(n-2)f^14(n-1)d^x
Complex ion
- Contains central metal ion bound to one or more ligans
Ligand
Lewis base (e- donor that forms bond with metal)
Coordination compound
Complex ion combines with one or more counter ions
Primary Valence
Oxidation state on central metal atom
Secondary valence
Number of molecules or ions bound to metal ions (this is the coordination number)
Coordinate covalent bond
- Bond formed by donation of pair of e- from ligand to empty orbital in metal
Monodenate
Ligand that only donates one e- pair to central metal
Bidenate
- Ligands that donate two pair of e-
Polydenate
- Ligand that donates more than two pairs of e-
Chelate
- Complex ion with bidenate or polydenate ligand; coordinating ligand is chelating agent
Common Ligand
- Water (H2O)
- Ammonia (NH3)
- Chloride ion
- Carbon monoxide
- Thiocyanite (SCN-)
- Oxalate ion
- Ethylenediamine (en)
- Ethylenediaminetetradacetate (Edia)
Coordination Numbers + Geometrics
- 2: Linear
- 4: Square planar or Tetrahedral
- 6: Octahedral
Structural Isomers
- Atoms connected to each other in different ways
Steroisomers
Atoms connected in same way; ligands have different spatial arrangement around metal atom
Coordination Isomer
- Structural
- Occur when coordinated ligands exchange places with uncoordinated counterion
Linkage isomers
- Structural
- Have ligands that coordinate to the metal in different orientations
- Geometric isomers
- Stereoisomerism
- Ligands bonding to the metal have different spatial arrangements
Cis-Trans Isomers
- Stereo/Geometric
- Compelx ions occur in square plans complexes of general formula MA2B2; or MA4B2
- Cis (same side), trans (opposite sides)
Fac-Mer
- Stereo/Geometric
- Octahedral complexes (MA3B3)
- Fac: Ligands on one side
- Mer: Ligands form an arc
Optical Isomers
- Nonsuperimposable mirror images of one another
- Chiral: Molecules ions that exhibit this quality
Enantiomers: Isomers that exhibit property of optical activity
Identifying and Drawing
1) Decide whether ligands are mono, bi, or polydenate.
2) Determine coordination number and geometry.
3) Draw
4) Rotate one 180˚, if it is non superimposable then it exhibits optical activity
Coordinate valence bond
- Overlap between completely filled atomic orbital and empty atomic orbital
Common Hybridization Schemes
- Linear (sp)
- Tetrahedral (sp3)
- Square planar (dsp2)
- Octahedral (d2sp3)
Crystal Field Theory (general definition)
- Bonding model for transition metal complexes that accounts for color and magnetism
Octahedral Complexes
- Form because attractions between e- on ligands/positive change on metal ion; e- on ligands also repel unhybridized metal d orbital
Strong-field complexes
- Splitting is large
Weak-field complexes
- Splitting is small
Crystal Field Splitting E (∆)
- Difference in E between the split d-orbitals
- day, dyz, and dxz are lower
- dz^2 and dx^2-y^2 are higher
Substance appears to be a color if:
1) Absorbs some of visible light but also transmits wavelengths associated with color
2) Transmits most wavelengths but absorbs complementary color on color wheel
Calculate crystal field splitting energy
Photon = hv = hc/lambda
Spectrochemical series (list?)
- Arranged from ligands that result in largest ∆ to smallest ∆
CN- > NO2 > en > NH3 > H2O > OH- > F- > Cl- > Br- > I- - CN- strongest; cutoff at NH3; remainder are small ∆
Electron filling for crystal field shit
- When energy of a d-orbital is split, lower electron orbit fills first
- Once half-filled, either:
1) Pairs with electrons in lower orbital (or)
2) Goes into empty orbital of higher energy by overcoming ∆
Low-spin complex
- Stronger-field ligands have fewer unpaired electrons (relative to free metal ion)
High-spin complexes
- Complexes with weak field ligands
- Have same number of unpaired e- as free metal ion
“d” possibilities
- d1-d3: Metal ions always have unpaired e-
- d4-d7: Metal ions have low and high spin possibilities
- d8-d10: metal ions always have lower 3 electron orbitals filled (remaining e- fill two higher orbitals)
Tetrahedral and Square Planar Complexes
- Patterns (opposite octahedral formation):
- High E: dxy, dxz, dyz
- Low E: dx^2-y^2, dz^2
