66
4 Halogenation of Metal Clusters
by experimental and theoretical have been done on the structures and properties of
coinage metal clusters; [64, 68–71] in particular, their mass abundance spectra have
been studied and explained by the one-electron shell model [72, 73].
The Cu n Cl n+1
− species closely resemble the alkali halide cluster cations where
the intensities of the M n X n−1
+ species (such as Na n Cl n−1
+ and Cs n I n−1
+ ) were found
to be greater than other products with different stoichiometries [59, 60, 62, 74–78].
There is one more metal atom than the halogen in the alkali halide cluster cations,
whereas the number of chlorine atoms is one more than the copper atoms in the
Cu n Cl n+1
− species. Actually previous investigations using electrospray ionization
mass spectrometry (ESI–MS) [43] on alkali halide clusters have observed both the
M n X n−1
+ and M n X n+1
− showing unusually high intensities [60, 61]. The existence
of Cu n Cl n+1
− species, similar to M
+ (MX) n , reveals the ‘F-center’ localization in bulk
alkali halide crystals [79–81], but there is reasonable difference because the interaction of excess electrons plays an important role in the outcome of the observed
halide clusters [81–85]. There is no observation of large values of n (>6) in the
Cu n Cl n+1
− species due to vigorous reactions and multiple collisions in the fast-flow
reaction apparatus [86] The optimized chemical structures of the Cu n Cl n+1
− species
(Fig. 4.8) demonstrate reasonable stability with a cubic structure arrangement, especially Cu 4 Cl 5
− , which mimics previously reported result on structures and stabilities
of Na n Cl n−1
+ and Cs n I n−1
+ [59]. Abundant studies of mass spectrometric results
and ultraviolet absorption analysis on charged alkali halide clusters have shown that
the alkali metal halide clusters have a strong tendency to assume cubic nanocrystal
arrangements that resemble portions of bulk simple cubic, rock salt lattices [59,
87–92]. Nevertheless, it is worth mentioning that an alkali halide cluster does not
necessarily have the NaCl crystal structure during the initial stages of growth, for
instance, it can be ring growth [93].
4.5 Silver Clusters Reacting with Halogen
The reactivity of silver cluster anions with chlorine has also been clearly demonstrated, where three classes of reaction products are observed, including [Ag n Cl n+1 ]
– ,
[Ag n Cl 2 ]
– and [Ag n Cl]
– . Among them, [Ag n Cl n+1 ]
– species were observed only in
the small mass range (n ≤ 4), likely due to reactions in analogy with aforementioned
[Cu n Cl n+1 ]
– series. When a [Ag n ]
– cluster reacts with a Cl 2 molecule, the first-step
could follow one of the following channels:
[Ag n ]
−
+ Cl 2 → Ag n−1 + [AgCl 2 ]
−
→
(4.13)
[Ag n ]
−
+ Cl 2 → [Ag n Cl 2 ]
−
→
(4.14)
[Ag n ]
−
+ Cl 2 → AgCl + [Ag n−1 Cl]
−
→
(4.15)
4 Halogenation of Metal Clusters
by experimental and theoretical have been done on the structures and properties of
coinage metal clusters; [64, 68–71] in particular, their mass abundance spectra have
been studied and explained by the one-electron shell model [72, 73].
The Cu n Cl n+1
− species closely resemble the alkali halide cluster cations where
the intensities of the M n X n−1
+ species (such as Na n Cl n−1
+ and Cs n I n−1
+ ) were found
to be greater than other products with different stoichiometries [59, 60, 62, 74–78].
There is one more metal atom than the halogen in the alkali halide cluster cations,
whereas the number of chlorine atoms is one more than the copper atoms in the
Cu n Cl n+1
− species. Actually previous investigations using electrospray ionization
mass spectrometry (ESI–MS) [43] on alkali halide clusters have observed both the
M n X n−1
+ and M n X n+1
− showing unusually high intensities [60, 61]. The existence
of Cu n Cl n+1
− species, similar to M
+ (MX) n , reveals the ‘F-center’ localization in bulk
alkali halide crystals [79–81], but there is reasonable difference because the interaction of excess electrons plays an important role in the outcome of the observed
halide clusters [81–85]. There is no observation of large values of n (>6) in the
Cu n Cl n+1
− species due to vigorous reactions and multiple collisions in the fast-flow
reaction apparatus [86] The optimized chemical structures of the Cu n Cl n+1
− species
(Fig. 4.8) demonstrate reasonable stability with a cubic structure arrangement, especially Cu 4 Cl 5
− , which mimics previously reported result on structures and stabilities
of Na n Cl n−1
+ and Cs n I n−1
+ [59]. Abundant studies of mass spectrometric results
and ultraviolet absorption analysis on charged alkali halide clusters have shown that
the alkali metal halide clusters have a strong tendency to assume cubic nanocrystal
arrangements that resemble portions of bulk simple cubic, rock salt lattices [59,
87–92]. Nevertheless, it is worth mentioning that an alkali halide cluster does not
necessarily have the NaCl crystal structure during the initial stages of growth, for
instance, it can be ring growth [93].
4.5 Silver Clusters Reacting with Halogen
The reactivity of silver cluster anions with chlorine has also been clearly demonstrated, where three classes of reaction products are observed, including [Ag n Cl n+1 ]
– ,
[Ag n Cl 2 ]
– and [Ag n Cl]
– . Among them, [Ag n Cl n+1 ]
– species were observed only in
the small mass range (n ≤ 4), likely due to reactions in analogy with aforementioned
[Cu n Cl n+1 ]
– series. When a [Ag n ]
– cluster reacts with a Cl 2 molecule, the first-step
could follow one of the following channels:
[Ag n ]
−
+ Cl 2 → Ag n−1 + [AgCl 2 ]
−
→
(4.13)
[Ag n ]
−
+ Cl 2 → [Ag n Cl 2 ]
−
→
(4.14)
[Ag n ]
−
+ Cl 2 → AgCl + [Ag n−1 Cl]
−
→
(4.15)