Cages and clusters: metal cluster chemistry including metal carbonyls and halide type clusters - Question Bank

1. In metal carbonyl clusters, the metal-metal bond order is generally considered to be:
A) Always a single bond
B) Variable and can be fractional
C) Always a double bond
D) Non-existent
2. The term 'cage compounds' in metal cluster chemistry refers to:
A) Structures with only metal-metal bonds
B) Structures where metal atoms form a discrete, enclosed framework
C) Linear polymers of metal atoms
D) Simple mononuclear complexes
3. Which of the following is a characteristic structural motif in certain metal halide clusters?
A) Isolated metal atoms
B) Linear chains of metal atoms
C) Planar square metal arrangements
D) Metal octahedra sharing edges or vertices
4. The catalytic activity of metal clusters is often attributed to:
A) Their ability to activate small molecules
B) The presence of low-valent metal centers
C) The unique electronic and structural properties allowing for multi-site reactions
D) All of the above
5. What is the typical coordination number of a metal atom in the core of a metal halide cluster like [Nb6Cl12]2+?
A) 2
B) 4
C) 6
D) 12
6. The 'delta-bond' in metal clusters arises from the overlap of:
A) s-orbitals
B) p-orbitals
C) d-orbitals
D) f-orbitals
7. In the context of metal clusters, 'ligand stripping' refers to:
A) Adding more ligands to the cluster
B) Removing ligands from the cluster
C) Replacing one type of ligand with another
D) Breaking metal-metal bonds
8. The reactivity of metal clusters is often influenced by:
A) The strength of the metal-metal bonds
B) The nature of the ligands
C) The overall electronic structure and steric accessibility
D) All of the above
9. Which of the following is a common bridging halide in metal halide clusters?
A) F-
B) Cl-
C) Br-
D) I-
10. The cluster formula [Os10(CO)32]^2- has a skeletal electron count that suggests a structure related to:
A) A single metal atom
B) A diatomic metal unit
C) A closed polyhedral cage
D) A linear chain
11. The synthesis of heteronuclear metal clusters involves:
A) A single type of metal atom
B) At least two different types of metal atoms
C) Only non-metal atoms
D) Only alkali metal atoms
12. Which of the following is a key characteristic of metal clusters that distinguishes them from simple coordination compounds?
A) Presence of only sigma bonds between metal and ligands
B) Absence of metal-metal bonding
C) Direct metal-metal bonding and delocalized electron systems
D) High solubility in water
13. The term 'polyhedral skeletal electron count' (PSE) is synonymous with:
A) The total number of valence electrons
B) The number of metal-metal bonds
C) The skeletal electron count (SEC)
D) The number of bridging ligands
14. The 'jelly roll' structure is observed in which type of metal cluster?
A) Metal carbonyl clusters
B) Metal halide clusters
C) Metal boride clusters
D) Metal phosphide clusters
15. Metal halide clusters of the type [M6X12]n+ often feature:
A) Terminal halide ligands
B) Edge-sharing octahedral metal cores
C) Face-sharing octahedral metal cores
D) Linear metal chains
16. The bridging mode of a CO ligand in a metal cluster is often denoted by:
A) COt
B) COb
C) CO+
D) CO-
17. Which of the following metal carbonyls is a simple mononuclear complex and NOT a cluster?
A) Fe2(CO)9
B) Co2(CO)8
C) Ni(CO)4
D) Ru3(CO)12
18. The '18-electron rule' for mononuclear complexes is adapted for clusters by considering:
A) The total number of valence electrons from all metal atoms and ligands
B) Only the valence electrons of the central metal atom
C) The number of ligand donor atoms
D) The number of metal-metal bonds only
19. What is the typical charge of the metal atoms in common metal carbonyl clusters?
A) Highly positive
B) Neutral or slightly negative
C) Highly negative
D) Always positive
20. The compound Re3Cl11^2- is an example of a metal halide cluster with:
A) Discrete trinuclear units
B) Infinite chains of metal atoms
C) A single metal atom
D) A tetrahedral metal core
21. Which of the following metals is LEAST likely to form stable, isolable carbonyl clusters?
A) Iron
B) Cobalt
C) Nickel
D) Copper
22. A cluster with a 'closo' structure according to Wade's Rules would have how many vertices in its polyhedral cage?
A) n+1
B) n+2
C) n
D) n-1
23. What is the significance of the 'Wade's Rules' in predicting cluster geometry?
A) They predict the oxidation state of the metals
B) They relate the number of skeletal electrons to the polyhedral shape
C) They determine the bond order between metal atoms
D) They indicate the stability of the cluster
24. The synthesis of metal halide clusters often involves:
A) High-pressure carbonylation
B) Reductive condensation of metal halides
C) Ligand exchange reactions in solution
D) Direct reaction with CO gas
25. Which metal cluster is famously known for its 'snowman' structure?
A) Fe3(CO)12
B) Co4(CO)12
C) Os3(CO)12
D) Rh6(CO)16
26. In the context of metal clusters, 'interstitial atoms' refer to:
A) Atoms that form the outer shell of the cluster
B) Atoms located within the voids of the metal framework
C) Ligands attached to the metal atoms
D) Metal atoms forming the cluster core
27. What is the typical geometry of a 'butterfly' metal cluster?
A) Tetrahedral
B) Square planar
C) Planar with four metal atoms forming a rhombus
D) Linear
28. The 'delta bond' is a type of metal-metal bond that can be found in clusters, particularly those involving:
A) First-row transition metals
B) Second and third-row transition metals
C) Lanthanides
D) Alkali metals
29. Which of the following is NOT a typical characteristic of metal carbonyl clusters?
A) High reactivity
B) Often colored compounds
C) Tendency to form extended ionic lattices
D) Catalytic activity
30. The term 'carbonyl' in metal carbonyl clusters refers to the presence of:
A) Carbon atoms directly bonded to the metal
B) Carbon monoxide (CO) ligands
C) Carbide ligands (C2-)
D) Organic carbon chains
31. What is the primary driving force for the formation of metal-metal bonds in clusters?
A) Electrostatic attraction between metal ions
B) Formation of delocalized bonding orbitals
C) Ligand field stabilization
D) Hydrogen bonding between metal atoms
32. The structure of the [Nb6Cl12]2+ cluster can be described as:
A) A linear chain of metal atoms
B) A discrete metal dimer
C) An octahedral arrangement of metal atoms surrounded by edge-bridging chlorides
D) A tetrahedral cluster
33. Which of the following is a characteristic feature of metal halide clusters?
A) Presence of CO ligands
B) Formation of discrete molecular units
C) Often form extended solid-state structures
D) Typically soluble in nonpolar solvents
34. In halide clusters like [Nb6Cl12]2+, the metal atoms are typically in what coordination environment concerning the halides?
A) Terminal halides
B) Face-bridging halides
C) Edge-bridging halides
D) Corner-sharing halides
35. The famous 'infinite chains' of metal halide clusters often exhibit:
A) High electrical conductivity
B) Low magnetic susceptibility
C) Inertness to chemical reactions
D) Gas phase stability
36. Which type of metal halide cluster is characterized by a linear arrangement of metal atoms, each bonded to six halide ligands?
A) Triple-bridged linear chains
B) Quadruple-bonded dimers
C) Metal octahedra sharing vertices
D) Linear chains of M2X9 units
37. Metal halide clusters typically involve metal atoms bonded to:
A) Oxygen atoms
B) Carbon atoms
C) Halogen atoms
D) Nitrogen atoms
38. The synthesis of metal clusters often involves reactions under:
A) Atmospheric pressure and low temperature
B) High pressure of CO and elevated temperature
C) A vacuum at room temperature
D) Aqueous solutions with mild heating
39. Which element is known for forming a wide variety of stable metal carbonyl clusters?
A) Gold
B) Platinum
C) Iron
D) Sodium
40. What is the general formula for a simple metal carbonyl M(CO)n where M is a transition metal?
A) M(CO)n
B) M(CO)n-x
C) M(CO)n+x
D) M(CO)2n
41. The metal-metal bonds in clusters are typically:
A) Purely ionic
B) Strongly polar covalent
C) Covalent, often delocalized
D) Weak van der Waals forces
42. Which of the following is a common bridging ligand in metal carbonyl clusters?
A) CO (terminal)
B) H2
C) CO (bridging)
D) Cl-
43. Metal carbonyl clusters are often formed from transition metals in which oxidation state?
A) High positive oxidation states
B) Low or zero oxidation states
C) Intermediate positive oxidation states
D) Only negative oxidation states
44. What does the 'nido' designation in Wade's Rules indicate about a cluster's structure?
A) A complete, closed polyhedral cage
B) A polyhedral cage with one vertex missing
C) A polyhedral cage with two vertices missing
D) A linear chain structure
45. Which rule is often used to predict the structure of metal carbonyl clusters?
A) Hund's Rule
B) Aufbau Principle
C) 18-Electron Rule (or Wade's Rules for clusters)
D) Pauli Exclusion Principle
46. The 'skeletal electron count' (SEC) in metal clusters is crucial for determining:
A) The exact bond length between metal atoms
B) The number of bridging ligands
C) The geometric structure (polyhedral shape)
D) The solubility of the cluster
47. In metal cluster chemistry, the term 'ligand' most commonly refers to:
A) Metal atoms within the cluster core
B) Non-metal atoms in the cluster core
C) Atoms or molecules bonded to the metal atoms
D) The overall charge of the cluster
48. Which of the following is a common example of a metal carbonyl cluster?
A) Fe(CO)5
B) Ni(CO)4
C) Co2(CO)8
D) Cr(CO)6
49. What is the defining characteristic of a metal cluster compound?
A) A single metal atom bonded to ligands
B) Multiple metal atoms bonded directly to each other
C) Metal atoms arranged in a linear chain
D) Metal ions forming an ionic lattice
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