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ICO Part B (ORI) study materials
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ICO Part B (ORI) practice questions

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Question 1Laboratory safety and experimental technique

Before starting an experiment in the laboratory, which document should be consulted to understand the hazards, required PPE, and emergency procedures for the chemicals involved?

  1. The material safety data sheet (SDS) for each chemical Correct answer.
  2. The previous student's laboratory notebook
  3. The laboratory's equipment maintenance log
  4. The purchase order for the reagents

Explanation

The SDS provides standardized hazard, handling, PPE, and first-aid information for each chemical. Reviewing it before work begins is a basic requirement of chemical safety practice. Other documents do not describe chemical hazards.

Question 2Laboratory safety and experimental technique

A student must transfer a small volume of concentrated hydrochloric acid. Which combination of personal protective equipment is appropriate for this task?

  1. Latex examination gloves and a face shield
  2. Safety glasses only, since the volume is small
  3. Safety goggles, nitrile gloves, and a laboratory coat Correct answer.
  4. A laboratory coat and cotton gloves

Explanation

Corrosive acids require eye protection, chemically resistant gloves, and a lab coat to protect skin and clothing. Even small volumes can splash. Safety glasses alone leave the eyes inadequately protected against splashes.

Question 3Laboratory safety and experimental technique

What is the primary purpose of a chemical fume hood during laboratory work?

  1. To filter solid waste from aqueous solutions
  2. To sterilize glassware before use
  3. To maintain a constant temperature for reactions
  4. To protect the worker from inhalation of vapors and aerosols Correct answer.

Explanation

A fume hood draws air away from the worker and exhausts it, reducing inhalation exposure to hazardous vapors and aerosols. It is an engineering control, not a sterilization or temperature device. Solid waste separation is unrelated to hood function.

Question 4Laboratory safety and experimental technique

Which container is appropriate for storing a waste organic solvent in the laboratory?

  1. A labeled, compatible, capped container designated for that waste stream Correct answer.
  2. An open beaker placed in the fume hood
  3. A glass bottle sealed with a cork stopper
  4. A plastic water bottle with the original label removed

Explanation

Waste solvents must be kept in closed, compatible containers that are clearly labeled with their contents. Open or mislabeled containers allow evaporation and create confusion during disposal. Compatibility prevents container failure.

Question 5Laboratory safety and experimental technique

In the event that a chemical splashes into a person's eyes, what is the correct immediate action?

  1. Flush the eyes with water at an eyewash station for at least 15 minutes and seek medical help Correct answer.
  2. Rinse briefly with water and return to work
  3. Wait to see whether irritation develops before acting
  4. Apply a neutralizing solution to the eye

Explanation

Immediate and prolonged flushing with water at an eyewash station is the standard first response to eye exposure. Medical evaluation follows. Neutralizing agents are not used in the eye because they can cause additional injury.

Question 6Laboratory safety and experimental technique

Which practice best reduces the risk of a fire when using a flammable solvent such as diethyl ether?

  1. Heat the solvent over an open flame to evaporate it quickly
  2. Work with the solvent in an unventilated corner of the lab
  3. Store the solvent near a Bunsen burner for convenience
  4. Keep ignition sources away and use the solvent in a fume hood Correct answer.

Explanation

Flammable solvents have low flash points, so removing ignition sources and ventilating the workspace are essential precautions. Open flames and unventilated areas increase fire and explosion risk. Convenience storage near burners is unsafe.

Question 7Laboratory safety and experimental technique

A student needs to prepare a dilute acid solution from a concentrated stock. Which procedure is correct?

  1. Mix the acid and water simultaneously in equal portions
  2. Add water slowly to the concentrated acid
  3. Add the acid to water only after heating the water to boiling
  4. Add the acid slowly to water while stirring Correct answer.

Explanation

Dilution of concentrated acid is strongly exothermic, so acid must be added slowly to water with stirring to dissipate heat. Adding water to concentrated acid can cause violent boiling and splattering. Heating the water increases the hazard.

Question 8Laboratory safety and experimental technique

Why should a centrifuge be loaded with tubes of equal mass placed symmetrically opposite one another?

  1. To ensure all samples reach the same temperature
  2. To prevent vibration and rotor imbalance that can damage the instrument or release samples Correct answer.
  3. To reduce the total run time of the centrifuge
  4. To keep the tubes from evaporating during spinning

Explanation

Balanced loading prevents the rotor from vibrating or failing at high speed. Imbalance can damage the centrifuge and cause tube breakage with aerosol release. Temperature, run time, and evaporation are not the reason for balancing.

Question 9Laboratory safety and experimental technique

Which action is appropriate when a mercury thermometer breaks on the laboratory bench?

  1. Rinse the mercury down the sink with plenty of water
  2. Wipe the mercury up with a paper towel and discard it in regular trash
  3. Sweep the mercury into a dustbin with a broom
  4. Evacuate the immediate area, ventilate, and use a mercury spill kit to collect the droplets Correct answer.

Explanation

Mercury is toxic and volatilizes at room temperature, so the area should be ventilated and the spill collected with a dedicated spill kit. Sweeping or washing it down the drain spreads contamination. Mercury must never be discarded in regular trash.

Question 10Laboratory safety and experimental technique

What is the correct way to heat a volatile flammable liquid in the laboratory?

  1. Use a heating mantle or water bath with no open flame Correct answer.
  2. Use a Bunsen burner with a visible flame
  3. Use a hot plate that is not rated for flammable environments
  4. Heat it in a sealed container over an open flame

Explanation

Volatile flammable liquids should be heated with devices that have no open flame, such as a heating mantle or water bath. This prevents ignition of vapors. Sealed containers and open flames create explosion and fire hazards.

Question 11Laboratory safety and experimental technique

Which statement correctly describes the use of a biological safety cabinet (BSC) versus a chemical fume hood?

  1. A BSC protects the sample and worker from biological aerosols, while a fume hood protects the worker from chemical vapors Correct answer.
  2. A BSC is intended for storing flammable solvents
  3. A fume hood is designed to sterilize biological samples
  4. A BSC and a fume hood are interchangeable for all hazardous work

Explanation

A BSC uses HEPA filtration to contain biological aerosols and protect the product, whereas a fume hood ventilates chemical vapors to the outside. They serve different hazard classes and are not interchangeable. Neither device sterilizes samples or stores solvents.

Question 12Laboratory safety and experimental technique

When weighing a hygroscopic solid on an analytical balance, which technique improves accuracy?

  1. Weigh the solid on an open watch glass for a long period
  2. Use a closed weighing vessel and minimize exposure to air Correct answer.
  3. Weigh the solid while it is still warm from drying
  4. Add the solid directly to the balance pan without a container

Explanation

Hygroscopic solids absorb moisture from air, so a closed vessel and minimal exposure reduce mass drift. Weighing on an open surface or directly on the pan allows moisture uptake and contamination. Warm samples can cause convection currents that destabilize the reading.

Question 13Laboratory safety and experimental technique

A reaction produces a noxious gas. Which setup is most appropriate for conducting it safely?

  1. Perform the reaction in a fume hood with the sash lowered as far as practical Correct answer.
  2. Perform the reaction in a sealed glovebox without ventilation
  3. Perform the reaction on an open bench with a fan blowing toward the user
  4. Perform the reaction near an open window with the door closed

Explanation

A fume hood captures and exhausts noxious gases, and keeping the sash low improves containment. A fan directed at the user disperses gas into the breathing zone. A sealed box without ventilation can accumulate dangerous pressure or concentration.

Question 14Laboratory safety and experimental technique

What is the purpose of adding a boiling chip (anti-bumping granule) before heating a liquid?

  1. To provide nucleation sites that promote smooth boiling and prevent superheating Correct answer.
  2. To neutralize acidic vapors produced during heating
  3. To indicate the temperature of the liquid
  4. To raise the boiling point of the liquid

Explanation

Boiling chips contain pores that release trapped air and provide nucleation sites, preventing sudden superheating and bumping. They do not change the boiling point, neutralize vapors, or measure temperature. Chips must be added before heating, not to an already hot liquid.

Question 15Laboratory safety and experimental technique

Which practice is required when working alone in a laboratory with hazardous materials?

  1. Store all chemicals on the bench for quick access
  2. Ensure someone knows you are present and that emergency contacts are available Correct answer.
  3. Disable the fire alarm to avoid false triggers
  4. Lock the laboratory door so no one can enter

Explanation

Working alone with hazardous materials requires that another person be aware of your presence and that emergency help can be reached. Isolation, disabling alarms, or cluttering benches increases risk. Many institutions restrict or prohibit lone work with high-hazard materials.

Question 16Laboratory safety and experimental technique

A student notices that a reagent bottle's label is faded and unreadable. What is the most appropriate action?

  1. Relabel the bottle with the name of the most likely chemical
  2. Treat the contents as unknown and follow the institution's unknown-chemical procedure Correct answer.
  3. Smell the contents to identify the chemical
  4. Use the reagent anyway if the bottle is in the expected location

Explanation

Unlabeled or illegible containers must be treated as unknown and handled through the institution's unknown-chemical procedure, which may include analysis or professional disposal. Smelling chemicals is dangerous and unreliable. Guessing the identity or using it based on location risks a hazardous reaction.

Question 17Laboratory safety and experimental technique

A reaction must be carried out under an inert atmosphere. Which combination of techniques is consistent with good laboratory practice for this purpose?

  1. Use oxygen instead of nitrogen to maintain inert conditions
  2. Flame-dry or oven-dry glassware, assemble under inert gas flow, and use a bubbler to monitor pressure Correct answer.
  3. Assemble the apparatus in air, then purge once briefly with inert gas
  4. Seal the flask completely without any pressure relief

Explanation

Air- and moisture-sensitive reactions require dry glassware, an inert atmosphere maintained during assembly, and a bubbler or similar device to monitor pressure and exclude air. A sealed flask without relief can rupture, and oxygen is not inert.

Question 18Laboratory safety and experimental technique

A researcher plans to use a rotary evaporator to remove a flammable solvent. Which precaution is most important?

  1. Operate the evaporator without the condenser attached
  2. Cap the receiving flask tightly to prevent solvent loss
  3. Use a water bath above the solvent's boiling point to speed evaporation
  4. Ensure the condenser coolant and vacuum are working and that no ignition sources are nearby Correct answer.

Explanation

Rotary evaporation of flammable solvents requires a functioning condenser and vacuum plus exclusion of ignition sources to prevent vapor release and fire. Operating without a condenser releases solvent vapor into the room. Overheating the bath can cause bumping and loss of control.

Question 19Laboratory safety and experimental technique

When setting up a vacuum filtration, why should the filter flask be clamped and the apparatus checked for cracks before use?

  1. Because clamping improves the filtration rate
  2. Because an evacuated flask under mechanical stress can implode and scatter glass and liquid Correct answer.
  3. Because cracks allow the filtrate to be sterilized
  4. Because clamping prevents the filter paper from tearing

Explanation

A filter flask under vacuum is subjected to external pressure, so cracks or stress can cause implosion and injury. Clamping secures the apparatus and reduces the chance of tipping. Filtration rate, sterilization, and paper tearing are not the reasons for these precautions.

Question 20Laboratory safety and experimental technique

A sealed ampoule of a volatile, toxic liquid must be opened. Which sequence best minimizes exposure?

  1. Cool the ampoule, open it behind a shield in a fume hood, and transfer the contents with appropriate PPE Correct answer.
  2. Open the ampoule while holding it close to the face to observe the contents
  3. Warm the ampoule to increase volatility, then open it on the bench
  4. Open the ampoule in a closed room without ventilation

Explanation

Cooling reduces the vapor pressure of a volatile liquid, and opening it in a fume hood behind a shield contains any release. Appropriate PPE protects against splashes. Warming the ampoule or working without ventilation increases exposure.

Question 21Synthesis and characterization of inorganic and coordination compounds

In a typical UV-Vis absorption spectrum of [Ti(H2O)6]3+, what does the single broad band near 500 nm arise from?

  1. A π→π* transition within the aquo ligands
  2. A d-d transition of the Ti(III) centre, split by the octahedral ligand field Correct answer.
  3. A spin-forbidden f-f transition of titanium
  4. A ligand-to-metal charge transfer from water to titanium

Explanation

Ti(III) is a d1 ion, so in an octahedral field the single electron is promoted from the t2g to the eg set, giving one Laporte-forbidden d-d band. Water has no low-lying π orbitals and titanium has no f electrons, so the other assignments are inconsistent with the electronic structure.

Question 22Synthesis and characterization of inorganic and coordination compounds

Which technique directly measures the number of unpaired electrons in a coordination compound in the solid state?

  1. Thermogravimetric analysis
  2. Variable-temperature magnetic susceptibility Correct answer.
  3. Single-crystal X-ray diffraction
  4. Infrared spectroscopy

Explanation

Magnetic susceptibility, measured as a function of temperature, yields the effective magnetic moment, from which the number of unpaired electrons is derived. The other methods probe vibrational modes, atomic positions, or mass loss and do not give spin state directly.

Question 23Synthesis and characterization of inorganic and coordination compounds

What information does the infrared stretching frequency of a coordinated CO ligand provide about a metal carbonyl complex?

  1. The oxidation state of the carbonyl carbon atom
  2. The number of unpaired electrons on the metal
  3. The extent of metal-to-ligand π back-donation, since stronger back-donation lowers ν(CO) Correct answer.
  4. The coordination number of the complex

Explanation

Back-donation populates the CO π* orbital, weakening the C-O bond and shifting ν(CO) to lower wavenumber. The position of the carbonyl stretch therefore reports on electron density at the metal and the donor strength of co-ligands.

Question 24Synthesis and characterization of inorganic and coordination compounds

In 1H NMR of a diamagnetic coordination complex, what does the integration of a signal represent?

  1. The coupling constant between neighbouring protons
  2. The chemical shift of the protons in ppm
  3. The relaxation time of the protons
  4. The relative number of equivalent protons giving rise to that resonance Correct answer.

Explanation

Peak areas in an NMR spectrum are proportional to the number of equivalent nuclei resonating at that frequency, so integration gives relative proton counts. Chemical shift, coupling, and relaxation are separate parameters reported by different features of the spectrum.

Question 25Synthesis and characterization of inorganic and coordination compounds

Which analytical method is most suitable for determining the metal-to-ligand ratio in a coloured coordination complex by titrating until the absorbance changes?

  1. Spectrophotometric titration Correct answer.
  2. Flame atomic emission spectroscopy
  3. Powder X-ray diffraction
  4. Differential scanning calorimetry

Explanation

Spectrophotometric titration monitors absorbance as titrant is added, and the break point in the absorbance curve gives the stoichiometric metal-to-ligand ratio. The other techniques measure elemental emission, phase identity, or thermal events and do not report a solution binding ratio directly.

Question 26Synthesis and characterization of inorganic and coordination compounds

What does the term 'effective magnetic moment' (μeff) of a coordination compound typically allow you to estimate?

  1. The oxidation state of the ligand donor atoms
  2. The molar extinction coefficient of the d-d band
  3. The number of unpaired electrons per metal centre Correct answer.
  4. The metal-ligand bond length

Explanation

The spin-only formula μeff = √(n(n+2)) μB links the measured moment to n, the number of unpaired electrons. Bond lengths, extinction coefficients, and ligand oxidation states are obtained from diffraction or spectroscopy, not magnetic data.

Question 27Synthesis and characterization of inorganic and coordination compounds

Which of these techniques is a bulk elemental method that can confirm the metal content of a coordination compound?

  1. Cyclic voltammetry
  2. Raman spectroscopy
  3. Inductively coupled plasma optical emission spectrometry Correct answer.
  4. 1H NMR spectroscopy

Explanation

ICP-OES atomises and excites the sample, and the emission intensity gives the metal concentration, confirming elemental composition. NMR, Raman, and voltammetry probe nuclear environments, vibrational modes, and redox behaviour respectively, not bulk metal content.

Question 28Synthesis and characterization of inorganic and coordination compounds

What does a single-crystal X-ray diffraction experiment yield directly for a coordination compound?

  1. The molar mass of the complex in solution
  2. A three-dimensional model of atom positions, from which bond lengths and angles are derived Correct answer.
  3. The rate constant for ligand substitution
  4. The spin state of the metal centre

Explanation

Single-crystal XRD measures diffraction intensities that are Fourier-transformed into an electron density map, giving atomic coordinates and hence bond metrics. Spin state, solution molar mass, and kinetic rate constants require other methods.

Question 29Synthesis and characterization of inorganic and coordination compounds

A complex shows a magnetic moment of about 5.9 μB at room temperature. Which spin state is most consistent with this value for an octahedral first-row transition metal ion?

  1. High-spin, with three unpaired electrons
  2. High-spin, with five unpaired electrons Correct answer.
  3. Diamagnetic, with zero unpaired electrons
  4. Low-spin, with one unpaired electron

Explanation

The spin-only value for n = 5 is √35 ≈ 5.9 μB, matching a high-spin d5 configuration such as Mn(II) or Fe(III). One unpaired electron gives about 1.7 μB and three give about 3.9 μB, while a diamagnetic sample would show essentially zero moment.

Question 30Synthesis and characterization of inorganic and coordination compounds

In the 1H NMR spectrum of [PtCl2(NH3)2] (cis isomer) in D2O, how many distinct ammonia proton environments are observed?

  1. Three, because of coupling to 195Pt
  2. One, because all six protons are equivalent by symmetry
  3. Zero, because the protons exchange too rapidly
  4. Two, because the two ammonia ligands are inequivalent in the cis geometry Correct answer.

Explanation

In the cis isomer the two NH3 ligands occupy different coordination sites, so their protons are not related by symmetry and give two resonances. The trans isomer has higher symmetry and would give a single environment.

Question 31Synthesis and characterization of inorganic and coordination compounds

A coordination compound analysed by CHN combustion gives a carbon content slightly lower than calculated. Which is the most reasonable interpretation?

  1. The sample may contain residual solvent or be partially hydrated, lowering the mass fraction of carbon Correct answer.
  2. The complex has adopted a different coordination geometry
  3. The ligand has undergone a spin-crossover transition
  4. The metal centre has changed oxidation state during the analysis

Explanation

Combustion analysis reports mass fractions, so extra non-carbon mass such as solvent or water lowers the observed carbon percentage relative to the anhydrous formula. Oxidation state, spin state, and geometry do not change the elemental mass fractions of a fixed formula.

Question 32Synthesis and characterization of inorganic and coordination compounds

In the infrared spectrum of a metal complex with two bridging carbonyl ligands, what is expected relative to terminal CO stretches?

  1. Bridging ν(CO) bands appear at higher wavenumber than terminal ν(CO) bands
  2. Bridging CO ligands give no infrared absorption
  3. Bridging ν(CO) bands appear at lower wavenumber than terminal ν(CO) bands Correct answer.
  4. Bridging and terminal CO stretches are always degenerate

Explanation

A bridging carbonyl accepts back-donation from two metal centres, so its C-O bond is weakened more than a terminal carbonyl and its stretch shifts to lower wavenumber. The number of bridging versus terminal bands also reflects molecular symmetry.

Question 33Synthesis and characterization of inorganic and coordination compounds

Which observation would most strongly support a low-spin d6 octahedral configuration for a complex such as [Fe(CN)6]4-?

  1. A diamagnetic moment near zero and a single intense MLCT band Correct answer.
  2. A magnetic moment near 4.9 μB and a weak d-d band
  3. A paramagnetic moment near 1.7 μB and no charge-transfer bands
  4. A magnetic moment near 5.9 μB and a strong d-d band

Explanation

A low-spin d6 ion has a filled t2g set with no unpaired electrons, so it is diamagnetic. Cyanide is a strong-field ligand that also produces intense metal-to-ligand charge-transfer bands, consistent with the observed data.

Question 34Synthesis and characterization of inorganic and coordination compounds

What does the term 'Laporte-forbidden' mean for a d-d transition in an octahedral complex?

  1. The transition is forbidden because the ligand is a weak-field ligand
  2. The transition is forbidden because it violates spin conservation
  3. The transition is symmetry-forbidden because it does not change parity, so it is weak but gains intensity by vibronic coupling Correct answer.
  4. The transition is forbidden because the metal is in a low oxidation state

Explanation

In a centrosymmetric octahedral complex, d orbitals have the same parity, so d-d transitions are electric-dipole forbidden. They become weakly allowed through vibronic coupling that transiently breaks the centre of symmetry, giving the low extinction coefficients typical of d-d bands.

Question 35Synthesis and characterization of inorganic and coordination compounds

A cyclic voltammogram of a coordination complex shows a reversible one-electron wave with a peak separation of about 60 mV. What does this indicate?

  1. An irreversible process with a slow electron transfer
  2. A chemically reversible, diffusion-controlled one-electron redox process Correct answer.
  3. A two-electron process with coupled chemical reaction
  4. A purely capacitive current with no Faradaic process

Explanation

A peak separation near 59 mV and equal anodic and cathodic peak currents are the signature of a reversible, diffusion-controlled one-electron transfer. Larger separations suggest slow kinetics, and unequal currents suggest coupled chemistry.

Question 36Synthesis and characterization of inorganic and coordination compounds

In the mass spectrum of a coordination compound containing a single chlorine atom, what pattern is expected for the molecular ion?

  1. A single peak with no isotope splitting
  2. Two peaks in roughly 3:1 intensity separated by 2 m/z units Correct answer.
  3. Three peaks in 1:2:1 intensity separated by 1 m/z unit
  4. Two peaks of equal intensity separated by 1 m/z unit

Explanation

Chlorine consists of 35Cl and 37Cl in about 3:1 abundance, so a single chlorine gives a two-peak isotope pattern separated by 2 mass units. The equal-intensity 1:1 pattern is characteristic of a single bromine atom.

Question 37Synthesis and characterization of inorganic and coordination compounds

Which of the following best describes how 31P NMR can be used to characterise a phosphine-ligated coordination compound?

  1. The 31P chemical shift equals the metal-ligand bond length
  2. The 31P spectrum measures the number of unpaired electrons
  3. The number and chemical shifts of 31P signals report on the number of inequivalent phosphorus environments and their electronic environment Correct answer.
  4. The 31P signal area gives the metal oxidation state directly

Explanation

Each inequivalent phosphorus nucleus gives a separate resonance, and chemical shift is sensitive to coordination and electron density at the metal. Integration gives relative numbers of nuclei, not oxidation states or bond lengths.

Question 38Synthesis and characterization of inorganic and coordination compounds

A thermogravimetric analysis of a hydrated coordination compound shows mass loss between 80 and 120 °C followed by a stable plateau. What is the most likely interpretation?

  1. A spin-crossover transition without mass change
  2. Oxidation of the metal centre by atmospheric oxygen
  3. Loss of lattice or coordinated water, leaving an anhydrous complex that is stable over the plateau range Correct answer.
  4. Decomposition of the metal-ligand framework to a metal oxide

Explanation

Mass loss at low temperature followed by a plateau is characteristic of stepwise dehydration, because water is weakly bound relative to the coordination framework. Framework decomposition and oxide formation typically occur at much higher temperatures and give larger, often multi-step, mass losses.

Question 39Synthesis and characterization of inorganic and coordination compounds

Why is the 1H NMR spectrum of a paramagnetic high-spin Fe(III) complex often spread over a wide chemical shift range?

  1. The protons undergo rapid chemical exchange with solvent
  2. The protons couple strongly to 13C nuclei
  3. The complex is polymeric in solution
  4. Unpaired electrons create large local magnetic fields at the protons, causing large contact and pseudocontact shifts Correct answer.

Explanation

Unpaired electron density interacts with nearby nuclei through contact and pseudocontact mechanisms, producing shifts far larger than in diamagnetic compounds and often severe line broadening. Exchange, aggregation, and carbon coupling do not produce this characteristic wide dispersion.

Question 40Synthesis and characterization of inorganic and coordination compounds

In the electronic spectrum of an octahedral d3 complex such as [Cr(NH3)6]3+, how many spin-allowed d-d bands are expected?

  1. Two, because the 4T1g(P) state is inaccessible
  2. One, because all d-d transitions are degenerate
  3. Four, because each d orbital splits into two levels
  4. Three, corresponding to transitions from the 4A2g ground state to the 4T2g, 4T1g(F), and 4T1g(P) excited states Correct answer.

Explanation

For a d3 ion in an octahedral field, the 4A2g ground state gives three spin-allowed transitions to the 4T2g, 4T1g(F), and 4T1g(P) terms. The transitions are all spin-allowed because the quartet spin multiplicity is conserved.

Question 41Synthesis and characterization of inorganic and coordination compounds

A complex of formula [M(L)2Cl2] shows a single ν(CO) band in its infrared spectrum. What does this suggest about the arrangement of the two carbonyl-containing ligands?

  1. A polymeric structure with bridging CO ligands
  2. A cis arrangement in which the two CO groups are inequivalent
  3. A mixture of cis and trans isomers in equal amounts
  4. A trans arrangement in which the two CO groups are related by symmetry Correct answer.

Explanation

In a trans arrangement the two CO groups are related by a centre of symmetry and give a single infrared-active ν(CO) band. A cis arrangement would give two bands because the two CO groups are inequivalent.

Question 42Synthesis and characterization of inorganic and coordination compounds

Which combination of techniques would best establish both the solid-state structure and the spin state of a new iron coordination polymer?

  1. Elemental analysis for connectivity and UV-Vis for spin state
  2. Single-crystal XRD for connectivity and magnetic susceptibility for spin state Correct answer.
  3. Mass spectrometry for connectivity and NMR for spin state
  4. IR spectroscopy for connectivity and TGA for spin state

Explanation

Single-crystal diffraction gives the atomic connectivity and bond metrics, while variable-temperature magnetic susceptibility gives the number of unpaired electrons. The other combinations provide compositional or spectroscopic data but not both structure and spin state unambiguously.

Question 43Synthesis and characterization of inorganic and coordination compounds

A coordination compound shows a magnetic moment of about 1.7 μB at room temperature that drops sharply on cooling. What is the most likely explanation?

  1. A high-spin d5 system with five unpaired electrons
  2. A d10 system with a full d shell
  3. A low-spin d5 or d7 system with one unpaired electron undergoing antiferromagnetic coupling or spin crossover Correct answer.
  4. A diamagnetic d6 system with no unpaired electrons

Explanation

A room-temperature moment near 1.7 μB corresponds to one unpaired electron, and the decrease on cooling indicates antiferromagnetic coupling or a spin-state change. High-spin d5 would give about 5.9 μB and d10 or low-spin d6 would be essentially diamagnetic.

Question 44Synthesis and characterization of inorganic and coordination compounds

In the 195Pt NMR spectrum of a square-planar platinum(II) complex with two inequivalent phosphine ligands, what would you expect?

  1. A 195Pt signal whose chemical shift equals the Pt-P bond length
  2. Two 31P resonances coupled to a single 195Pt resonance, giving satellites that confirm the Pt-P connectivity Correct answer.
  3. A single 31P resonance with no coupling to platinum
  4. No observable 195Pt signal because Pt(II) is paramagnetic

Explanation

Inequivalent phosphines give two 31P environments, each showing coupling to the NMR-active 195Pt nucleus as satellites. The 195Pt resonance itself is observed because Pt(II) is diamagnetic in a square-planar d8 configuration.

Question 45Synthesis and characterization of inorganic and coordination compounds

A new coordination compound is characterised by UV-Vis, IR, and magnetic susceptibility. The UV-Vis shows two d-d bands, the IR shows a single ν(CO) band, and the moment is about 1.9 μB. Which structural assignment is most consistent?

  1. A low-spin d5 or d7 complex with a trans arrangement of two CO ligands and one unpaired electron Correct answer.
  2. A high-spin d5 complex with a cis arrangement of two CO ligands and five unpaired electrons
  3. A d10 complex with terminal CO ligands and no d-d bands
  4. A diamagnetic d6 complex with a cis arrangement of two CO ligands

Explanation

A moment near 1.9 μB indicates one unpaired electron, consistent with a low-spin d5 or d7 configuration, and a single ν(CO) band indicates a trans arrangement with equivalent CO groups. High-spin d5 would give about 5.9 μB, and diamagnetic or d10 complexes would not show this combination.

Question 46Synthesis and characterization of inorganic and coordination compounds

In the infrared spectrum of a coordination complex, a sharp band near 2100 cm⁻¹ that is absent in the free ligand is most diagnostic of which feature?

  1. A chelating nitrate group
  2. A terminally bound carbonyl ligand Correct answer.
  3. An outer-sphere perchlorate counter-ion
  4. A bridging aqua ligand

Explanation

Terminal metal-bound CO absorbs in the 2000–2150 cm⁻¹ region, shifted from free CO at about 2143 cm⁻¹, and the band is sharp because it is a strong, localized stretching mode. Bridging carbonyls appear at distinctly lower wavenumbers, and nitrate or perchlorate give bands in other regions.

Question 47Synthesis and characterization of inorganic and coordination compounds

A complex of the type [Co(NH3)4Cl2]⁺ is isolated and its electronic spectrum shows two spin-allowed d-d bands in the visible region. This observation is most consistent with which geometry?

  1. Square planar
  2. Octahedral with trans chlorides Correct answer.
  3. Linear two-coordinate
  4. Tetrahedral

Explanation

An octahedral d6 cobalt(III) centre gives two spin-allowed d-d transitions (¹A₁g→¹T₁g and ¹A₁g→¹T₂g), matching the two observed visible bands. The Co(NH3)4Cl2⁺ formulation with two trans chlorides is a classic octahedral arrangement that fits this pattern.

Question 48Synthesis and characterization of inorganic and coordination compounds

A compound analyses as [Ni(en)3]SO4 by elemental and conductivity data. Which set of observations would best confirm that all three ethylenediamine ligands are chelating rather than monodentate?

  1. A single ν(SO) band in the IR and a melting point above 200 °C
  2. Three distinct ¹³C environments and conductivity consistent with a 1:3 electrolyte
  3. A magnetic moment near 2.8 μB and a broad N–H stretch in the IR
  4. A single ¹³C NMR environment for the en carbons and a molar conductivity consistent with a 1:1 electrolyte Correct answer.

Explanation

Chelating en ligands give a symmetric tris-chelate cation in which the two carbon atoms of each ring are equivalent, so one ¹³C environment is seen. The sulfate is the only counter-ion, so the complex behaves as a 1:1 electrolyte in solution.

Question 49Synthesis and characterization of inorganic and coordination compounds

A new copper(II) complex is characterised by UV-Vis, IR, and magnetic susceptibility. The UV-Vis shows one broad d-d envelope, the IR confirms coordinated carboxylate, and the magnetic moment is about 1.9 μB at room temperature. Which conclusion is best supported?

  1. A mononuclear copper(II) centre with a d9 configuration Correct answer.
  2. An antiferromagnetically coupled dinuclear copper(II) complex
  3. A diamagnetic copper(I) species
  4. A high-spin octahedral copper(III) centre

Explanation

A room-temperature moment near 1.9 μB is close to the spin-only value for one unpaired electron, consistent with a mononuclear d9 copper(II) ion. The single broad d-d envelope and carboxylate IR bands support a simple Cu(II) carboxylate complex rather than strong magnetic coupling.

Question 50Synthesis and characterization of inorganic and coordination compounds

A complex [M(L)2X2] shows a single sharp ν(CO) band in the IR, one ³¹P environment in the ³¹P NMR, and a single ¹H environment for the two L methyl groups. Which structural assignment is most consistent with all three observations?

  1. A five-coordinate species with one L ligand uncoordinated
  2. Cis, with the two L ligands adjacent and the two X ligands adjacent
  3. Trans, with the two L ligands mutually trans and the two X ligands mutually trans Correct answer.
  4. A mixture of cis and trans isomers in equal proportions

Explanation

A trans arrangement of identical L ligands and identical X ligands gives a centrosymmetric molecule with equivalent L groups and equivalent CO oscillators, so one ν(CO) band and one ³¹P environment are expected. The equivalence of the two methyl environments follows from the same symmetry.