Rationale Flashcards
Aqueous solutions of [M(H2O)6]2+ are extremely pale pink whereas those of
[Ni(H2O)6]2+ are a bright green.
Mn2+
- high spin, d5, Oh
- no spin-or Laporte-allowed absorption
- therefore, weak forbidden transitions and a pale colour
Ni2+,
- d8, Oh
- no laporte-allowed but three spin-allowed transitions
- therefore, stronger bands, more colour
The major band in the electronic spectrum of the pink [Co(H2O)6]2+ ion has a
maximum at 513 nm (ε = 0.5 L mol-1 cm-1). On the addition of concentrated
hydrochloric acid the solution turns blue and is more intensely coloured with
absorption maxima at 625, 670, and 700 nm (ε = 35-60 L mol-1 cm-1).
For octahedral [MoCl6]3- with pi-donor Cl- ligands, the pertinent portion of its MO diagram is: see image
For the Mo2+ complex, both Cl- => Mo sigma and pi-bonding is relatively diminished. Hence, its eg* and t2g* levels are lower in energy, evidently by approximately the same amount since the splitting energy is about the same for both complexes
Somewhat surprisingly, the Δo values for both [MoCl6]3- and [MoCl6]4- are
approximately 19,000 cm-1.
The microstate table for p4 leads to the same free-ion terms as for p2 (done in class), namely
1D, 3P and 1S
The ground state term is 3P
The infrared spectrum of [(η5-C5H5)Mo(CO)3]2 in CCl4 exhibits three strong bands at
1961, 1917, and 1909 cm-1.
Spectrum reflects the complex having the molecular structure (see image) with all terminal carbonyl ligands
Ligand substitution reactions at four-coordinate palladium(II) centres generally have
ΔS‡ and ΔV‡ less than zero, whereas for four-coordinate palladium(0) complexes,
ΔS‡ and ΔV‡ are generally greater than zero.
Four-coordinate Pd(II) d8 complexes are square-planar and react associatively whereas four-coordinate Pd(0) d10 complexes are tetrahedral and react dissociatively
The rate of oxidation of [Cr(OH2)6]2+ by [CoCl(NH3)5]2+ is high (kobs = 6.0 x 105 M-1
s-1) compared to that of its oxidation by [Co(NH3)6]3+ (kobs = 1.0 x 10-3 M-1 s-1).
There is, however, little difference in analogous reactivity between [V(OH2)6]2+ and
[RuCl(NH3)5]2+ or [Ru(NH3)6]3+ as oxidants
Reaction between [Cr(OH2)6]2+ (high-spin d4) and [Co(NH3)5]2+ occurs via an inner-sphere mechanism, but wiht [Co(NH3)6]3+ via an outer-sphere mechanism.
The analogous V(II) complex (d3) is substituationally inert, and so its reactions with the Ru(III) complexes both occur via an outer-sphere mechanism
Cobaltocene, a very air-sensitive, black solid, generally behaves as a reducing agent.
Cp2Co is a 19 C complex that readily loses the extra electron to form 18 electrons [Cp2Co]+ which is isoelectronic with ferrocene
Square-planar substitution reactions frequently show two-term rate laws of the form:
Rate = k1[Complex] + k2[Complex][Y]
where Y is the incoming ligand.
Both pathways (both terms in the rate law) are considered to be associative in spite of the difference in order.
The k2 term easily fits an associative mechanism. The accepted explanation for the k1 term is a solvent-assisted reaction, with solvent replacing the leaving ligand in the first step.
In general, ethyl complexes of transition metals are less thermally stable than the analogous methyl
complexes.
Ethyl complexes can readily undergo beta-H elimination reactions. Methyl complexes cannot.
The compound trans-Fe(o-phen)2(NCS)2 has a magnetic moment of 0.65 Bohr magnetons at 80 K,
increasing with temperature to 5.2 Bohr magnetons at 300 K.
The compound trans-Fe(o-phen)2(NCS)2 contains Fe2+ (d6). At 80 K it has 0 unpaired electrons (assumimng a spin-only magnetic moment), and at 300 K it has 4 unpaired electrons.
The increase in magnetic moment wih temperature can be explained by the spin crossover.
t2g6 (80K) => t2g4eg2 (300K)
Which should be a stronger-field ligand in a transition-metal amide complex (e.g.
MNMe2), an amide ligand with an M-N-C angle of 120°, or an amide ligand with an MN-
C angle of 109°? Why?
An Amide ligand with an M-N-C angle of 120 degree is both a sigma and a pi donor
An amide ligand with an M-N-C angle of 109 degree is only a sigma donor-hance the stronger field ligand
The substitutionally inert complex, Re(S2CNR2)3, cannot be resolved into
enantiomers
Either the complex is octahedral and racemizes rapidly or it is trigonal prismatic and not optically active.
The Δo values for both [WCl6]3- and [WCl6]4- are approximately 20,000 cm-1.
For the W2+ complex, both Cl- => W sigma and pi bonding is realtively diminished. Hence, its Eg* and T2g* levels are lower in energy, evidently by approximately the same amount since Δo is the same for both tungsten complexes.
[FeF6]3- is colourless whereas [CoF6]3- is coloured.
Transitions in [FeF6]3- are both Laporte- and spin forbidden, whereas those in [CoF6]3- are only Laporte forbidden.
The IR spectrum of Pt(NH3)2Cl2 as a Nujol mull exhibits νPt-Cl at 330 and 323 cm-1.
The complex must have a cis-square-planar geometry.
The Nujol-mull IR spectrum of orange Fe2(CO)9 exhibits strong absorptions at 2082, 2019 and 1829
cm-1. However, its 13C NMR spectrum in C6D6 at room temperature is reported to consist of a
single sharp resonance at δ 212.9
Fe2(CO)9 has the molecular structure (see image) which is stereochemically non-rigid in solutions
