Mechanistic and Descriptive Chemistry Flashcards
(89 cards)
1
Q
CoCl2 structure and properties
A
- Blue solid
- Ionic lattice, Co2+ surrounded by 6 Cl- ions (each shared by 3 Co)
- MP = 726, BP = 1049
- Dissolves in water and alcohols
2
Q
OsO4 properties and structure
A
- Nearly colourless solid
- Not very ionic, Os8+ surrounded by O2-
- MP = 39.5, BP = 130
- Dissolves in CCl4 (non-polar solvent)
3
Q
Oxidation states of titanium
A
- Highest = Ti(IV) (d0), most common
- Ti(III) (d1) can be made but is mildly reducing (i.e. easily oxidised)
- Ti(II) (d2) is strongly reducing, few complexes known
4
Q
Oxidation states of vanadium, examples in compounds and examples of reactions
A
- Highest = V(V) (d0), also common (most common and most stable = V(IV) (d1)(e.g. [V(O)(acac)2])
- E.g. V2O5, VF5 (NOT VCl5, only VCl4), [V(O)2(ox)2]3-, [VF6]-
- In aq. solution, V(V) is mildly oxidising
- E.g. V2O5 + aq. HCl –> Cl2 + V(IV) species
- E.g. V2O5 + aq. SO3^2- –> [V(O)(H2O)4]2+
5
Q
Oxidation states of chromium, examples of compounds and example of a reaction
A
- Highest = Cr(VI), strongly oxidising (gets reduced itself)
- Very few compounds known
- E.g. CrO3, [CrO4]2-, [Cr2O7]2-, CrF6, CrO2Cl2
- E.g. CrO3 + secondary alcohol (+ pyridine) –> ketone
- Most common = Cr(III) (d3), strongly favours octahedral geometry due to high CFSE
6
Q
Oxidation states of manganese, examples of compounds and example of a reaction
A
- Highest = Mn(VII), very oxidising (gets strongly reduced)
- E.g. [MnO4]-; [Mn2O7] and [MnO3F] are explosive (unstable)
- E.g. [MnO4]- + Bn(CH3)2 –> Bn(COOH)2
- Ox. states between (VI) and (II) uncommon
7
Q
Oxidation states of iron and example of complex and how it is made
A
- Highest = Fe(VI) (d2)
- E.g. [FeO4]2- (tetrahedral), only complex
- Made by IO4^- oxidation of Fe(III) in pH 14 solution
- Most complexes are Fe(III) or Fe(II) (d5 or d6)
8
Q
Highest oxidation state of cobalt and examples of complexes
A
- Highest (with normal ligands) = Co(IV) (d5)
- E.g. [CoF6]2-, Ba2CoO4
- Rare since Co(III) is low-spin (d6) so hard to disrupt
9
Q
Highest oxidation state of nickel
A
- Highest = Ni(IV) (d6)
- More common than Co(IV), gains stability from low spin d6 configuration
10
Q
Oxidation states of copper and features
A
- Highest = Cu(III) (d8)
- Most are diamagnetic, square planar
- ‘Normal’ oxidation state = Cu(II)
- Also many complexes of Cu(I)
11
Q
Describe the trend in energy required for oxidation of a metal across the 3d metal period from Sc –> Zn
A
- Energy required increases from Sc (d1) to Zn (d10)
- 2389 kJ/mol –> 3833 kJ/mol
12
Q
Contrast the 3d metals with 4d/5d metals and give examples
A
- For 4d/5d metals, high oxidation states are mosre common and more stable than for 3d metals
- For 4d/5d metals, there are similarities between elements in the same group but the 3d element in that group is different
- E.g. Cr(VI) is strongly oxidising whereas Mo(VI) and W(VI) are barely oxidising at all
- E.g. [ReO4]- is quite inert: if Re is burned in air it gives Re(VII) whereas burning Mn in air gives Mn(II) and Mn(III)
- E.g. Highest ox. state for Fe = Fe(VI) whereas for Ru and Os it is M(VIII). Similar for Co and Rh/Ir.
- E.g. similar to Ni, Pd highest ox. state M(IV) but Pt can be M(VI) or M(V).
13
Q
Compare and contrast the ionic radii for 3d-5d ions
A
- 4d/5d cations similar in size but bigger than 3d cations
- 4/5d orbitals are more spread out (less concentrated) than 3d orbitals
- Lanthanide contraction causes atomic radii of 5d metals to be very similar to their 4d metal counterparts, leads to them having similar chemical properties
14
Q
Which few metals are found in their ‘native’ states and what did they used to be called?
A
- Gold
- Silver
- Gold/silver alloys
- Sometimes platinum
Used to be called ‘noble’ metals.
15
Q
Give examples of (most) metals that are found as minerals and their compounds (5 examples)
A
- Copper e.g. CuFeS2
- Iron e.g. Fe2O3, Fe3O4
- Titanium e.g. TiO2
- Chromium e.g. FeCrO2
- Molybdenum e.g. MoS2
16
Q
What happens to sulfides when exposed to air and why is this a problem?
A
- Sulfides are usually ‘roasted’ - oxidised in air to give oxides and SO2
- This is a problem because oxides then need to be reduced to give metals
17
Q
Give an example of a reducing agent and an equation for the reaction between it and a metal oxide. How does this affect Gibbs free energy?
A
- Cheapest reducing agent = carbon (from coal, oil or charcoal)
- MOx + x/2 C –> M + x/2 CO2
- More electropositive the metal, more endothermic the reaction
- Because 2 solids react to make a liquid and x/2 moles of gas, change in entropy is positive so change in Gibbs free energy will eventually become negative
18
Q
Abundancy/ores of titanium and how to isolate it (in principle). What are the problems with isolating it like this?
A
- Abundant but widely distributed
- Most abundant transition metal after Fe
- 0.6% Earth’s crust by weight
- Ores: TiO2 (rutile), FeTiO3 (ilmenite) - found on beaches in Australia
Isolation:
- In principal, TiO2 (s) + 2C (s) –> Ti (s) + 2CO (g)
- However, Ti = very electropositive
- At large enough T to give negative delta G for feasible reaction, Ti + C –> TiC
- TiC has rock salt structure and is hard and inert
19
Q
How to actually isolate titanium
A
- Kroll process: First convert TiO2 –> TiCl4
- TiO2 + 2C + 2Cl2 –> TiCl4 + 2CO
- TiCl4 can be distilled under vacuum
- Next, reduce with an even more electropositive metal: TiCl4 + 4Na –> Ti + 4NaCl or TiCl4 + 2Mg –> Ti + 2MgCl2 (requires 800 degrees Celsius, batch reactor, argon atmosphere)
- Wash out/evaporate metal halide (recycle)
- Gives Ti as a ‘sponge’, has to be melted into an ingot
20
Q
What are the uses and properties of titanium?
A
- Alloys used widely in aerospace, hi-tech sports equipment, etc.
- Very corrosion-resistant (doesn’t rust)
- About 60% the density of steel
- Very high heat resistance (alloys don’t ‘creep’ (deform) on heating)
- About twice the elongation of steel with similar tensile strength (resistance to breaking when pulled or stretched)
21
Q
What are the properties/chemistry of Ti(IV)? Give 2 compounds and reactions, how compounds are made, uses
A
TiCl4:
- mp = -23 C, bp = 136 C
- Rapidly hydrolysed by water (violent reaction): TiCl4 + H2O –> TiO2 + 4HCl
- Strongly acid aqueous solution contains some [Ti=O(H2O)5]2+ with other Ti(mu-OH)2 Ti species
TiO2:
- Made by Ti(SO4)2 hydrolysis
- Widely used as a white pigment
A few complexes containing Ti=O units can be made e.g. TiCl4 (hydrolyse in ‘wet’, DMSO) –> [Ti=O(OSMe2)5]2+ +2Cl- + 2HCl
22
Q
Compare and contrast Ti(IV) and V(IV)
oxo complexes, specifically the reactions and their products. Give equations. Reference infrared spec.
A
V2O5 + aq. SO2/Na2CO3 –> [V(O)(H2O)5]2+
[V(O)(H2O)5]2+ + 2Hacac –> [V(O)(acac)2]
Ti(IV) + Hacac/Na2CO3 –> [Ti(O)(acac)2]
The V complex is a monomer (In IR, V=O stretch at 1005 cm-1), whereas the Ti complex is a dimer [(acac)2Ti(mu-O)2 Ti(acac)2] (In IR, Ti-O stretches around 880 cm-1)
23
Q
Discuss Ti in halide complexes (reactions in different conditions, products, ligands used, complexes formed)
A
- Dissolving TiF4 in aq. HF gives mainly [TiF6]2-
- TiCl4 + neutral monodentate ligands in non-polar solvents:
- 1 equiv. L (L = pyridine, NMe3, THF, Me2O, etc) gives [TiCl4(L)]2
- 2 equiv. L gives octahedral [TiCl4(L)2), cis and trans
- Ti(IV) is d0, so has no stereochemical preferences
24
Q
What is the ligand ‘das’ and how does it react with TiCl4?
A
- ‘das’ is a very good chelate ligand as 1,2-benzene ring has very rigid backbone
- 1,2-bis(dimethylarsino)-benzene
- TiCl4 + 1das (in toluene) –> [TiCl4(das)] (octahedral)
- TiCl4 + 2das (in toluene) –> [TiCl4(das)2] (8-coordinate)
25
Discuss Ti(III) chemistry (2 main forms, reactions, colours, structures, uses)
- TiCl3 is an important starting material and has 2 main forms: alpha and beta
- 2TiCl4 + H2 (at 800 C) --> alpha-TiCl3 + HCl (Violet solid)
- TiCl4 + AlR3 (hexane, room temp.) --> beta-TiCl3 (brown solid)
- Beta form converted to alpha at equal to or greater than 300 C
- Alpha form consists of sheets of TiCl6 octahedra
- Beta form consists of single chains of TiCl6 octahedra, sharing edges
- Beta form is a catalyst (with AlClR2) for alkene polymerisation (give mainly isotactic - all methyl groups oriented same way)
26
Discuss alpha-TiCl3 (complexes formed, ligands used, geometry, conditions, d-electrons)
- Forms complexes [TiCl3(L)3] with many donor ligands e.g. L = pyridine (mer), THF, CH3CN
- Have to be made in strict absence of oxygen to prevent oxidation to Ti(IV)
- Complexes all coloured since Ti(III) = d1, has single d-d transition in visible region
- In water, [Ti(H2O)6]3+ can be made e.g. by dissolving Ti in dil. HCl
- In more conc. HCl, complexes[TiCl(H2O)5]2+ and [TiCl2(H2O)4]+ also form
- If solution left to crystallise, [TiCl2(H2O)4]Cl.2H2O is the product
- In chloride-containing molten salts, alpha-TiCl3 forms [TiCl6]3-
27
Discuss Ti(II) chemistry (reactions, colours, crystal structures, properties)
- TiCl4 + Ti --> 2TiCl2 (black solid). Ionic; consists of layers of edge-sharing octahedra
- TiO2 + Ti --> 2TiO (probably defective i.e. not strictly Ti1O1). Has NaCl structure.
- Ti(II) complexes are rare as it is very strongly reducing
- TiCl2 + 2 Me2PCH2CH2PMe2 --> trans-[TiCl2(dmpe)2]
- TiCl4 + 2 Na (THF) --> 'TiCl2(THF)n' (reacts with pyridine to give trans-[TiCl2(py)4]
28
Why is there an interest in Ti(II)? Give 2 reasons.
Organic chemistry:
- TiCl3 + Mg (or Zn/Cu or LiAlH4) --> either Ti(II) species or Ti nanoparticles
- These are active in the McMurray coupling reaction: R2C=O + O=CR2 --> R2C=CR2 (+ TiO2)
Dinitrogen chemistry:
- trans-[TiCl2(py)4] + LiN(SiMe3)2 + N2 (pyridine) --> (N(SiMe3)2)(py)2(Cl)-Ti=N-N=Ti(Cl)(py)2(N(SiMe3)2)
- Ti(II) reduces triple bond of NN and gets itself oxidised to Ti(IV) (since Ti=NR is isoelectronic with Ti=O)
29
Zirconium and hafnium occurrence, trend and origin
Zirconium:
- Crystal abundance 0.02%
Hafnium:
- Crystal abundance 0.0004%
Decline in abundance 3d->4d->5d is general
Elements made by nuclear fusion in supernovae
Heavier the nucleus, less likely it is to form
30
Compare zirconium (Zr) and hafnium (Hf) chemistry (atomic radii, how they are isolated/separated, ores)
- Both have similar atomic radii (1.45 Zr, 1.44 Hf A) and ionic radii (M(IV) 0.74, 0.75 A) due to lanthanide contraction
- Makes their chemistry very similar and they occur together in nature
- Widely distributed so worthwhile ores are rare. Main ores are ZrO2 (baddeleyite) and ZrSiO4 (zircon)
- Separated by solvent extraction or chromatography. Difficult because of similar chemical properties
- Elements obtained via Kroll process, like Ti
31
Uses of Zr and Hf (inc. organometallic complexes) and company that makes compounds containing these metals
- Zr used as fuel cladding for nuclear fuels (has low neutron capture cross-section)
- Hf does capture neutrons so Zr has to be separated from Hf before use
- Zr and Hf organometallic complexes re now widely used as catalysts to polymerise alkenes (partly replaced beta-TiCl3 for this)
- Hf used to be fairly useless but hafnium dioxide now being used as a high dielectric constant insulator layer for the 'gates' of small (sub-45nm) transistors
- Mel Chemicals (Manchester) - local firm making Zr and Hf compounds
32
Use of hafnium dioxide and how it works (include equations). Why is this reactant used and give two examples of different reactants that could be used.
- Used as 'Gate dielectric' in silicon chip transistors (amplifier/switch in electronic circuits)
- To put down thin films of HfO2 needed, electronics industry uses chemical vapour deposition (CVD) and related technologies
- In CVD, precursor compound evaporated and passed over heated surface, where it decomposes to desired solid-state material
- So we need volatile Hf complexes e.g. HfCl4 + HOtBu --> [Hf(OtBu)4] + 4HCl
- Need steric bulk of tBu to stop formation of polynuclear, alkoxy-bridged species that wouldn't be volatile
- Another method is to use bidentate ligands like HOCH2CH2NMe2: HfCl4 + HOCH2CH2NMe2 --> [Hf(OCH2CH2NMe2)4] + 4HCl
- This is 8-coordinate, with tertiary amine groups coordinated too
33
Compare and contrast Ti(IV) with Zr(IV) and Hf(IV) chemistry (size, coordination, structures formed, d electrons, properties of structures, occurrence, reactions, etc)
- Unlike most 3d/4d/5d groups, Ti(IV) chemistry is quite similar to Zr(IV) and Hf(IV)
- However, Zr and Hf are bigger than Ti, they prefer higher coordination numbers
- e.g. with F-, Ti (IV) forms octahedral [TIF6]2-
with Zr(IV), both [ZrF6]2- and pentagonal bipyramidal [ZrF7]3- are known (8 coordinate Cu(II)2[ZrF8].12H2O can also be isolated)
- All these d0 ions have no CFSE so no preference for octahedral geometry
- e.g. (2) TiCl4/TiBr4 tetrahedral, monomeric whereas ZrCl4/ZrBr4 (and Hf compounds) are polymeric, octahedral
- ZrCl4 is white solid (solid-->gas at 330 C)
- Zr/Hf have much less tendency to form M(III) compounds/complexes, don't form M(II) compounds at all (no equiv. of [Ti(H2O)6]3+ known)
- No mononuclear Zr(III)/Hf(III) complexes known
- Heating colourless ZrX4/HfX4 (X=Cl, Br) with powdered aluminium gives corresponding dark blue/green MX3 e.g. 3ZrCl4 + Al --> 3ZrCl3 + AlCl3
- Only a few complexes of [Zr2Cl6(L)4 have been made (L = phosphine/pyridine)
- Structure has Zr-Zr bond, complexes are diamagnetic since both d-electrons are in bonding orbital
34
What is the history/properties of chromium? (Origin, compounds, colours, properties, electron config., abundance)
- First isolated 1798 by Louis Vauquelin (France) from crocoite (PbCrO4)
- Bright colours of compounds noted (e.g. PbCrO4 = red, Cr2O3 = pale green, [CrO4]2- in solution = lemon-yellow)
- Hard (but brittle), bright silver coloured metal, m.p. = 1903 C
- Electron config. = 4s1 3d5 - emphasises small 4s/3d energy separation
- Abundance in Earth's crust = 0.01 % by mass (ca. 100 ppm)
35
What are the occurrence, extraction and uses of chromium? (Inc. isolation of Cr from alloy, main ox. states, main source, structure, abundance in alloys, how they're made)
- Occurs as Cr(III) or Cr(VI), main source = chromite (FeCr2O4) - often contains some Mg2+ in place of Fe2+, can also contain Al3+ in place of Cr3+
- Chromite has spinel structure, Cr(III) on octahedral sites, Fe(II) on tetrahedral sites
- Most smelted with charcoal and coke in electric arc furnace at high T to give ferrochrome (FeCr alloy used as additive in specialist steels)
- 'Stainless steel' ~ 18% Cr
- 'Chrome moly' ~ 5% Cr and 5% Mo
- Isolation: FeCr2O4 + Ca(OH)2/NaOH, (O2, 1000 C) --> [CrO4]2-
- Extracted with water; filter off Fe(OH)3
- Cr(VI) reduced with C/S to give Cr2O3
- Cr2O3 reduced to Cr with Al/Si
36
What are the compounds of Cr(II) and Cr(III)? (halides and oxides) How are they made, conditions, colours, properties, what they dissolve in
- Dominant oxidation states, more common and more stable
Halides:
- Anhydrous CrX2 (X = F, Cl, Br): from HX gas + finely-divided Cr, 600-700 C. e.g. CrI2 made from Cr + I2
- Anhydrous CrX3 (X = Cl, Br): from finely-divided Cr + X2 gas (in a tube furnace)
Oxides:
- Sulfur reaction of Na2[Cr2O7] used to make Cr2O3 (pale green solid)
- Amphoteric; dissolves in acid [Cr(H2O)6]3+ and base [Cr(OH)6]3-
37
What are the high-spin complexes of Cr(II) like? Give reaction producing complex and colour of complex. Give reduction of complex and colour of product. Why isn't Cr(II) complex useful in water? What is done to change this? What is produced?
- d4, 6-coordinate, Jahn-Teller distorted
- Na2[Cr2O7] + Zn/HCl --> [Cr(H2O)6]2+ (bright blue solution)
- E0 = 0.41 V
- Slowly reduces H2O to give H2 + [Cr(H2O)6]3+ (violet)
- So [Cr(H2O)6]2+ in water isn't useful as starting material for Cr(II) complexes
- e.g. [Cr(H2O)6]2+ + XS H2NCH2CH2NH2 --> [Cr(en)3]3+ + 1/2H2
- So made in non-aq. solvents:
- e.g. CrX2 + 2H2NCH2CH2NH2 (EtOH, N2 atmosphere) --> trans-[CrX2(en)2] (X = Cl, Br)
38
What are the low spin complexes of Cr(II) and what are they formed from? Give equations.
- Only very strong field ligands are capable of giving low spin Cr(II)
- e.g. CrX2 + 2 diars (n-BUOH, N2) --> trans-[CrX2(diars)2] (X = Cl, Br)
- e.g. CrX2 + excess CN- (water, N2) --> [Cr(CN)6]4-
39
What is a compound of Cr(II)-acetate? How is it formed (give equation and colour, starts with diff. Cr(II) complex))? Mention d-electrons and orbitals and how they overlap to give bonds.
- Blue [Cr(H2O)6]2+ solution + NaOAc --> brick-red solid 'Cr(OAc)2.H2O'
- This is still Cr(II) but it has no unpaired electrons
- d-orbitals overlap to make Cr-Cr bonds
- 2 dz^2 orbitals overlap to give sigma bond
- 2 dxz and dyz orbitals overla to give 2 degenerate pi bonds
- 2 dxy orbitals overlap to give 4th bond (delta bond)
- All d-electrons on 2 Cr(II) are now paired: complex is diamagnetic; Cr-Cr distance is 236 pm; clearly a short, strong bond
40
What are the properties of Cr(III) (mention CFSE) and what are ligand exchange reactions like? (Give an example). Is this reaction favourable and why (not)? Give an example.
- Most stable & common ox. state for Cr
- d3, so strong driving force for octahedral geometry in complexes to max. CFSE
- Ligand exchange reactions = slow (like Co(III), low spin d6)
- e.g. CrCl3 + excess H2O --> [Cr(H2O)6]3+ (aq) + 3Cl- (aq)
- Above reaction should be favourable, but CrCl3 only dissolves in water extremely slowly
- Due to very slow rate of ligand substitution at Cr(III)
41
How do we persuade CrCl3 to dissolve? (What reagents are used, what mechanism occurs, what are the 2 main species in solution?)
- Add catalytic amount of reducing agent e.g. Sn(II) to generate some Cr(II)
- This causes CrCl3 to dissolve by mechanism:
- Cr(III)3Cl8 (in solid lattice) + Cr(II)O6 --> Cr(III)3Cl8Cr(II)O5 + O (e- transfer from Cr(II) to Cr(III) --> same molecular formula but a Cr(III) and Cr(II) have swapped (ligand, sub. by water) --> Cr(III)2Cl6 + Cr(II)O6 + Cr(III)O5Cl ([CrCl(H2O)5]2+ in solution)
- Main species in solution = [CrCl(H2O)5]Cl2 and [CrCl2(H2O)4]Cl
42
What is a good route to many Cr(III) complexes? Give examples of reactions, colours of complexes, properties of Cr(III) (Lewis terms), which type of ligands it does and doesn't bind to.
- Good route = starting with Cr(II)
- e.g. [Cr(H2O)6]2+ (blue) + air --> [Cr(H2O)6]3+ (violet)
- e.g. [Cr(H2O)6]2+ + excess aq. H2NCH2CH2NH2 --> [Cr(en)3]3+ + 1/2 H2
- Above reaction also works for other bidentate/multidentate amine ligands
- Or, CrCl3 + L-L (refluxing THF/MeOH, catalytic Zn dust) --> [Cr(L-L)3]3+ (L-L = bipy, phen, H2NCH2CH2NH2 etc.)
- Cr(III) = hard Lewis acid; likes hard ligands e.g. [CrF6]3-, [Cr(acac)3] etc
- Soft ligands like diars and phosphines do not form complexes with common Cr(III) starting materials
43
What is the gemstone ruby made of? What structure does it have?
- Ruby = crystalline form of Al2O3 with some Cr(III) impurity (0.05-0.1%)
- Cr(III) replaces some Al(III) in an octahedral hole
- Cr2O3 is also in an octahedral oxide ion environment
44
Why is ruby red but Cr2O3 is green?
- Cr(III) larger than Al(III): 'too big' for Al(III) site in ruby
- Since Cr-O distances are short, crystal field strength = abnormally high
- So d-d bands for Cr(III) in ruby are at higher than usual energy
45
What are emeralds made of and what structure do they have? Why are they green?
- Green form of colourless mineral 'beryl' Be3Al2(SiO3)6
- Cr(III) replaces some of Al3+ in octahedral holes
- Cr(III)-O distances close to those seen in Cr2O3 so emeralds are green (like Cr2O3)
46
How are compounds of Cr(IV) made? Give examples of compound and conditions needed to make it. What structure does it have and what properties does it have (compared to another)? What is it used for?
- CrO2 made by partial decomposition of CrO3 at 800 C under pressure
- Has rutile (TiO2) structure
- TiO2 is white, diamagnetic, d0
- CrO2 is dark brown, ferromagnetic, metallic, d2
- used extensively in magnetic data recording i.e. cassette tapes
47
What are Cr(VI) compounds (previously) used for in chemistry (a --> b, conditions)? Why are they no longer used? Give equation, product and properties.
- 'Jones reagent' - CrO3 in pyridine oxidises secondary alcohols to ketones
- Not used so much nowadays as Cr(VI) = known carcinogen
- CrO3 + HCl (g) --> CrO2Cl2 'chromyl chloride' - dense, orange liquid
48
What are some properties of Cr(VI) imides? How is the formation of imide reaction driven? How is the product stabilised?
- M=NR unit isoelectronic with M=O (same number of electorns/same electronic structure)
- =NR better s-donor than =O. Probably also better p-donor
- Reaction driven by elimination of 2HCl and formation of -OSiR3 from -NSiR3
- Product kinetically stabilised by steric protection: bulky t-Bu and Me3Si groups
49
Occurrence (compounds), extraction (via reduction) and uses of molybdenum and tungsten
Molybdenum:
- Main mineral = MoS2 (often occurs together with Pb/Cu)
- Oxidation: 2MoS2 + 7O2 --> 2MoO3 + 4SO2
- Reduced with H2 to Mo
- Important component of hydrodesulfurisation catalysts. used to remove S from crude oil
Tungsten:
- Various salts of [WO4]2- :
- e.g. CaWO4 (scheelite), FeWO4/MnWO4 (wolframite), PbWO4 (stolzite)
- Generally converted to H2WO4 then to WO3 then to W with H2
- Used to make tungsten carbide (WC), almost as hard as diamond, used in cutting tools
Both:
- ca. 10^-4 % crystal abundance (quite rare elements)
- Used in steelmaking for producing hard/strong steel alloys
50
Contrast Cr(VI) with Mo(VI) and W(VI) properties and reactions i.e. oxidation.
- Cr(VI) highly oxidising whereas Mo(VI) and W(VI) oxides quite stable towards reduction
- Burning Cr in air generates Cr2O3, burning Mo/W generates MO3
51
What is the structure of WO3? Give an example of a reduction reaction and the colour change. How does the structure change after this reaction? What causes the colour change?
- WO3 consists of corner-sharing WO6 octahedra (called the ReO3 structure)
- W(VI) reduced to W(V): 2WO3 (pale yellow) + 2BuLi --> 2LiWO3 (deep blue) + Bu-Bu
- Results in Li+ being inserted into WO3 lattice and creation of some W(V) sites
- Colour arises from intervalence charge transfer transition; promotion of an e- from W(V) across a W-O-W bridge onto a neighbouring W(VI)
52
What compounds are polyoxometallates formed from (give reaction example)? What are some examples of molybdenum and tungsten POM anions? What is the current interest in these in research?
- Formed from MoO3 and WO3 (and some other 4d/5d metals)
- MoO3 + strong aq. base --> monomeric, tetrahedral anions MO4^2-
- On careful acidification, these condese together to make discrete POM anions e.g. [Mo7O24]6- and [W6O19]2-
- Many POM anions precipitated using various cations
- Great current research interest 'metal oxide nanoclusters'
53
What are some reactions to make Mo(VI) and W(VI) halide compounds and what are some of these compounds? What colour are they? How many d electrons do they have? What do the halides react with to make? What is the order of stability?
- M + 3F2 (room temp.) --> MF6 (both stable and colourless)
- WCl6 and WBr6 can be made from W and Cl2/Br2
- WCl6 very dark blue, WBr6 very dark green
- This is because since W(VI) = d0, there must be charge transfer (high W ox. state, ligand-to-metal charge transfer)
- MoCl6 first made in 2013: MoF6 + 2BCl3 (-78 C) --> MoCl6 + 2BF3
- MoBr6 = unknown
- Stability of M(VI): W > Mo >>> Cr or 5d > 4d >>> 3d
- All these halides react vigorously with water to make [X4M=O] or [M(=O)2X2] + HX
54
How are M(V) halides made?
- Using Cl2/Br2: M + Cl2/Br2 --> MX5 (M = Mo, W; X = Cl,Br)
55
How do Mo(V) and W(V) compounds (i.e. metal halides) react in aq. conditions? What complexes do they form? Mention d electrons, metal bonds and property. What type of ligands do they react with? Give examples.
- MoCl5 + aq. acid --> [Mo2O4(H2O)6]2+
- This is Mo(V), d1 but diamagnetic
- Has Mo-Mo bond
- WCl5 + conc. aq. HCl --> Cl3W=O
- W=OCl3 + 2L (L = neutral ligand) --> [WOCl3(L)2]
- L = THF, pyridine, PMe3; L2 = bipy
56
How are Mo(IV) and W(IV) sulfides made (equations and conditions)? What is their structure?
- MoCl5 + 2.5Na2S (heat, sealed tube) --> MoS2 + 5NaCl (+ 1/2 S)
- WO3 + H2S --> WS2
- Compounds have layered structure (like graphite) with triply-bridging S and trigonal prismatic M
57
How are Mo(IV) and W(IV) halides made (equations, conditions, ligands)?
- Either by reduction of M(VI)/M(V) halides
- e.g. 2WCl6 + [W(CO)6] --> 3WCl4 + 6CO (in refluxing chlorobenzene
- OR from MO2 and CX4
- e.g. MoO2 + CCl4 --> MoCl4 + CO2 (520K, sealed tube)
- Halides react with neutral ligands to give octahedral complexes
- e.g. MoCl4 + 2,2'-bipyridine --> [MoCl4(bipy)]
- Cr(IV) complexes of this kind are unknown; very rare and oxidising ox. state
58
What are the cyanide complexes of Mo(IV) and W(IV)? What coordination/shape are they and what complex can they be oxidised to?
- K4[Mo(CN)8].2H2O is the first known 8-coordinate complex (1939)
- Corresponding W complex has also since been made
- [Mo(CN)8]4- usually square antiprismatic
- Can be oxidised to Mo(V): [Mo(CN)8]3-
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Occurrence of the ox. states M(II) and M(III) for Mo and W (reduction of M(V) to M(III) equation, how WCl3 is made, halides structure/conformation)
- M(III) quite rare, generally easily oxidised to M(IV) or M(V)
- M(II) and M(III) ox. states closed inter-related for Mo and W so are considered together
- MoCl5 + SnCl2 --> MoCl3 (+SnCl4)
- WCl3 made from oxidation of 'WCl2' with Cl2
- 6WCl6 + 8Bi --> W6Cl12 + 8BiCl3
- Halides are molecular clusters with strong M-M interaction
- e.g. MoCl3/WCl3 structure: Discrete molecular clusters with strong internal M-M interavtions. Typical of early-mid 4d/5d metal halides in low ox. states
- d-d bonding much more common with more diffuse 4/5d orbitals
- MoCl2: MoCl6 octahedra again with 8Cl- ions occupying triangular faces of octahedra and 2 axial Mo atoms each having terminal Cl-, giving MoCl10^2+ units; these have 4 more Cl- ions bridging to neighbouring units to give overall 2D layer structure
- Treatment with 'extra' Cl- gives salts containing [Mo6Cl14]2- ions
60
Abundance of nickel in earth's crust
0.016%
many meteorites contain Ni with Fe
61
Main ores of nickel
kupfernickel (NiAs)
Millerite (NiS)
Other sources are complex silicate minerals
62
Acidity/basicity of nickel in Lewis terms
'intermediate' Lewis acid
found with both hard and soft bases
63
How are nickel ores converted to nickel?
NiAs/NiS --> Ni2S3 then 'roasted' in air to give NiO (+SO2)
NiO reduced with C but impure Ni cannot be purified with treatment with O2 (has to be refined electrolytically or via Mond process)
64
What is Mond process?
Ni + 4CO --> [Ni(CO)4]
volatile, colourless, covalent, very toxic liquid
Can be distilled under vacuum
heating to > 180 C regerates Ni (+4CO recycled)
99.9-99.99% pure Ni made this way
65
Uses of nickel
- Cheap jewellery
- 25% Coins (US nickel) 75% Cu
- Problems with dermatitis
- Raney nickel (Ni:Al alloy) = hydrogenation cat. (grind to fine powder, add to strong aq. base)
- 2Al + 6H2O + 6OH- --> 2[Al(OH)6]3- + 3H2
- Leaves Ni with high SA and loaded with H2
- Monel metal - resistive to F2 and other aggressive fluorides e.g. UF6
66
Ni(II) common starting material and what is added to give coloured products?
NiCl2.6H2O
[NiCl2(H2O)4].2H2O in solid state and [Ni(H2O)6]2+ in water
Adding NH3 gives blue [Ni(NH3)6]2+
Adding en gives purple [Ni(en)3]2+
Adding bipy gives pink [Ni(bipy)3]2+
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What shape are Ni(II) complexes?
Octahedral; 2 unpaired electrons
68
Which geometry do 4-coordinate Ni(II) complexes have? (2 types)
Tetrahedral:
Green/blue
3 d-d bands
Red region of spectrum (small delta)
2 unpaired electrons
Planar:
- red/yellow
- d-d bands overlap
- UV blue region (large delta)
- Diamagnetic
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Examples of 5-coordinate nickel complexes?
Trigonal bipyramidal (diamagnetic) e.g. [NiI2(PMe3)3]
trigonal bipyramidal (2 unpaired electrons) e.g. [Ni(O=PMe3)5]2+
Square-based pyramidal (diamagnetic) e.g. [Ni(CN)5]3-
70
What are complexes of Ni(III) like in terms of coordination and spin? How are they made?
6 coordinate, low spin
Made by oxidation of Ni(II)
71
Properties of nickel fluorides and examples of compound and what it is made from
NiF3 unstable, oxidising, black solid, salt
Made from [NiF6]2- decomposing in anhydrous HF solution
72
Properties of nickel oxides, example of complex
NiO.OH (anode material in Ni-Cd batteries and Li ion batteries)
Likes N donors (esp. anionic)
73
Ni(IV) properties, what they are made from, example of product and its colour
d6, low spin
fluorination of NiF2/KF mixture under pressure gives purple-red K2[NiF6]
Complex oxide = BaNiO3
trans-[NiX2(das)2]2+ and [NiX2(dp)2]2+ made by HNO3/HCl/HClO4 oxidation of Ni(III)
74
Platinum abundance in Earth's crust, types of ores, acidity wrt Lewis
very rare, 10^-6%
sulfides and arsenides
soft Lewis acid
75
Ore smelted to give Cu and Ni rich crude metal
Refined electrolytically
Insoluble anode sludge collects under anode, contains impurities such as Pt metals, Au, Ag
Dissolve in aqua regia (3:1 conc. HCl/conc. HNO3). Dissolves any Pd/Pt and [MCl6]2- complexes
Separate by fractional crystallisation (separated by their solubilities)
Pt recovered by heating to decompose (NH4)2[PtCl6]
Pd obtained by reducing (NH4)2[PdCl6] with formic acid (HCOOH)
76
Uses of palladium
- Catalyst for synthetic chem. (C-C bond-forming reactions)
- Automotive cat. converter alongside Pt
- Jewellery and dentistry
77
Uses of platinum
- Jewellery and dentistry
- Automotive cat. converters (with Rh)
- Catalyses N2 oxidation to NO2
- Fuel cell catalyst (fuel oxidation and O2 reduction to H2O)
78
complexes of Pd(II) and Pt(II)
d8, always square planar, diamagnetic even with weak field ligands
Exception: PdF2 (purple) 2 unpaired electrons per Pd octahedral (dissolves in water to give square planar [Pd(H2O)4]2+
Pt inert to ligand sub. (rates of ligand sub. slow)
79
complexes of Pd(III) amd Pt(III)
very rare
[Pt(EtNH2)4]2+ (pale yellow) treated in water with Cl2
Product = deep red, PtCl3.4EtNH2
alternating square planar [Pt(II)L4]2+ and octahedral trans-[Pt(IV)Cl2(L)4]2+
80
Pd(IV) and Pt(IV)
Common oxidation state for Pt but not at all for Pd, needs anionic ligands or very strong donors like Me-
PtX4 with all halides but only PdF4
[PtX6]2- for all halides but [PdI6]2- never been isolated
81
How are thermodynamics and kinetics used to explain why a complex cannot react to give a certain complex?
1. Reaction unfavourable (thermodynamics)
2. Reaction too slow to give observable rate at room temp. (kinetics)
82
How stable/unstable and labile/inert is [Ni(H2O)6]2+ to treatment with 14CN- and in water?
Radiolabel taken up instantaneously so it is labile wrt ligand exchange
Very stable in water
83
What are the types of mechanism for ligand substitution at metal ions?
- Dissociative (D): similar to Sn1 in C chemistry
- E.g. LnM-X (octahedral) + Y --> [LnM + X + Y] (5 coord intermediate) --> LnM-Y + X where Ln = other ligands
- Associative (A): not similar to anything in C chemistry
- E.g. LnM-X (octahedral) + Y --> [LnM(X)(Y)] (7 coord intermediate) --> LnM-Y + X
- Interchange (I): similar to Sn2 in C chemistry
- E.g. LnM-X (octahedral) + Y --> [X...LnM...Y] (trans. state, can't exist on its own) --> LnM-Y + X
84
What is the stoichiometric mechanism (D, A or I?)
Interchange: M-X breaks as M-Y forms so there's no definite intermediate
85
What is the intimate mechanism if I is the stoichiometric mechanism?
- Very unusual for M...X bond to be broken at the exact same time M...Y is formed
- So interchange mechanisms are subdivided according to intimate mechanism:
- If M...X bond breaking = more advanced at trans. state than M...Y formation, intimate mech. = dissociative interchange (Id) [X...MLn + Y]
- If M...Y bond formation = more advanced at trans. state than M...X bond breaking, intimate mech. = associative interchange (Ia) [Y...MLn-X]
86
Which complexes (i.e. organometallic, square planar) react with which mechanisms (D or A)?
- Octahedral trans. metal complexes = I (Ia/Id)
- Organometallic (18VE) complexes = D
- Square planar complexes = A
87
What can be measured to determine the mechanism?
1. Rate law: measure how rate depends on [Y], [LnM-X], etc. Easier for inert complexes (slow reactions)
2. Vary identities of X,Y and Ln
- I.e. for D/Id: rate depends on identity of X because bond breaking = key process
for A/Ia: rate depends on Y because bond formation = key
- Increase steric bulk of Ln as it will speed up rate of D/Id reactions (easier for X to leave) but slows down A/Ia reactions (harder for Y to enter)
3. Effect of T on rate (delta H, delta S)
4. Effect of pressure on rate (delta V)
88
What is the trans effect?
Ability of ligands to labilise ligands trans to themselves vua ground state or transition state stabilisation
89
What is the order of trans effect strength of ligands?
CN- > I- > PR3 > NH3
