Coordination Sphere & Oxidation State
Determine the oxidation state and d-electron configuration of cobalt in [Co(NH3)5Cl]2+.
Co is +3; Co3+ is 3d6.
Arrange F-, H2O, NH3 and CN- in increasing order of crystal-field strength.
F- < H2O < NH3 < CN-.
Name the isomerism shown by [Co(NH3)5SO4]Br and [Co(NH3)5Br]SO4.
Ionisation isomerism.
For a d6 octahedral complex, state the number of unpaired electrons in its high-spin and low-spin forms.
High spin: 4 unpaired electrons. Low spin: 0.
Write the octahedral crystal-field configuration of a high-spin d5 ion.
t2g3 eg2.
Find the coordination number and oxidation state of chromium in [Cr(en)2Cl2]+.
Oxidation state = +3; coordination number = 6.
Give the IUPAC name of K3[Cr(C2O4)3].
Potassium tris(oxalato)chromate(III).
Write the linkage isomer of [Co(NH3)5(NO2)]Cl2 using an unambiguous ligand formula.
[Co(NH3)5(ONO)]Cl2, containing O-bonded nitrito-O.
Predict the hybridisation, geometry and magnetic nature of [Ni(CO)4].
sp3 hybridisation; tetrahedral; diamagnetic.
Calculate the CFSE of an octahedral d3 complex in terms of delta-o.
t2g3 eg0; CFSE = -1.2 delta-o (stabilisation magnitude 1.2 delta-o).
One mole of CoCl3·5NH3 gives two moles of AgCl with excess AgNO3. Write its coordination formula.
[Co(NH3)5Cl]Cl2.
Write the formula of tetraamminedichloridocobalt(III) hexacyanidoferrate(III).
[Co(NH3)4Cl2]3[Fe(CN)6].
How many geometrical isomers are possible for square-planar [MA2B2]? Describe them.
Two: cis (identical ligands adjacent) and trans (identical ligands opposite).
Explain why [NiCl4]2- is paramagnetic but [Ni(CN)4]2- is diamagnetic. Include geometry and hybridisation.
[NiCl4]2-: weak-field, sp3 tetrahedral, 2 unpaired electrons. [Ni(CN)4]2-: strong-field, dsp2 square planar, 0 unpaired electrons.
Calculate the CFSE of a low-spin octahedral d6 complex, ignoring pairing energy.
t2g6 eg0; CFSE = -2.4 delta-o (stabilisation magnitude 2.4 delta-o).
CrCl3·6H2O gives two moles of AgCl per mole with excess AgNO3. Write its structural formula and chromium coordination number.
[Cr(H2O)5Cl]Cl2·H2O; coordination number = 6.
Give the IUPAC name of [Co(NH3)4Cl(ONO)]Cl, including the O-bonded ligand.
Tetraamminechloridonitrito-O-cobalt(III) chloride.
How many geometrical isomers are possible for octahedral [MA3B3]? Identify them.
Two: facial (fac) and meridional (mer).
Using VBT, determine the hybridisation, orbital type and number of unpaired electrons in [FeF6]3-.
Fe3+ is d5; outer-orbital sp3d2; 5 unpaired electrons.
An octahedral complex absorbs 500 nm light. Calculate delta-o per photon using h = 6.626×10^-34 J s and c = 3.0×10^8 m s^-1.
delta-o = hc/lambda = 3.98×10^-19 J per photon.
A Pt4+ complex contains four NH3 and two coordinated Cl-. Write its chloride salt and the number of ions produced per formula unit in water.
[Pt(NH3)4Cl2]Cl2; it produces 3 ions.
Write the formula and charge of the coordination entity in potassium bis(oxalato)diaquachromate(III).
K[Cr(C2O4)2(H2O)2]; the coordination entity has charge -1.
For [Co(en)2Cl2]+, identify the optically active geometrical form and state the total number of stereoisomers.
The cis form is optically active and has delta and lambda enantiomers; trans is inactive. Total stereoisomers = 3.
A Co2+ octahedral complex has magnetic moment 3.87 BM. Find its unpaired electrons and predict high or low spin.
Using mu = sqrt[n(n+2)], n = 3; it is high-spin d7.
Compare [CoF6]3- and [Co(CN)6]3- by d-orbital configuration, CFSE, unpaired electrons and magnetism. Ignore pairing energy.
[CoF6]3-: high-spin d6, t2g4 eg2, CFSE -0.4 delta-o, 4 unpaired, paramagnetic. [Co(CN)6]3-: low-spin d6, t2g6 eg0, CFSE -2.4 delta-o, 0 unpaired, diamagnetic.