756
Chemistry Letters Vol.36, No.6 (2007)
.
Formation of Single Crystal of Hofmann Clathrate, Ni(NH3)2Ni(CN)4 0.5H2O,
at Higher Temperature by Means of Spray Pyrolysis of Sucrose and Nickel Nitrate
Takeshi Kashiwagi, Hiroe Suzuki, Masashi Nina, Hiroyasu Nishiguchi,
Katsutoshi Nagaoka, and Yusaku Takita
Department of Applied Chemistry, Faculty of Engineering, Oita University, Oita 870-1192
(Received February 19, 2007; CL-070188; E-mail: takita@cc.oita-u.ac.jp)
.
Single crystal of Ni(NH3)2Ni(CN)4 0.5H2O was formed by
the pyrolysis of mist of aqueous sucrose and nickel nitrate solu-
tion at higher temperatures as 873–1073 K in an inert gas without
using harmful organic and inorganic compounds such as NH3
and HCN.
The inclusion compounds in general, particularly clathrates,
have been a subject of many theoretical and experimental studies
as a result of their fundamental significance in understanding the
nature of interactions between the molecular and ionic species,
and also their practical importance.1,2 Detailed spectroscopic
.
studies of Hoffman clathrates with Ni(NH3)2Ni(CN)4 mG
(G = benzene, benzene derivatives, H2O, and so on) and the
characterization of various metals and guest molecules have
been carried out so far.3–7
Generally, clathrates were prepared in an aqueous phase,
.
for example the compounds M(daon)Ni(CN)4 G (M = Co, Ni,
or Cd; G = 1,2-dichlorobenzene or 1,4-dichlorobenzene) were
1µm
.
Figure 1. SEM image of the Ni(NH3)2Ni(CN)4 0.5H2O
prepared by adding 1,8-diaminooctane to
a solution of
formed at 873 K before separation by a magnet.
K2Ni(CN)4, MCl2, water, and ethanol saturated with the guest
molecules.4
Most of metal complexes are prepared at relatively low
temperatures near ambient temperature, because they are usually
prepared in aqueous or organic medium. However, authors
found the slightly selective formation of single crystal of Hof-
1173 K, no carbon materials were obtained. This may be due
to small space velocity and low reaction temperature for carbon
formation. On the contrary, in the experiment using Ni(NO3)2
without sucrose, greyish black materials were recovered in a
water trap. The SEM images revealed that the products were
distorted spheres with 2–16 mm in diameter. Most of spheres
appear to have an egg shell shape and have a hole in the wall.
From TEM images of the sample showed that the particle
appears to have an egg shell structure and that the wall seems to
be composed of small particles with 0.15–0.37-nm diameter.
It was shown by XRD that this products was composed of
only NiO.
Experiments were carried out using a solution of 0.05 M
Ni(NO3)2 and 0.05 M sucrose at various reaction temperatures.
As expected, the products were obtained at 873–1173 K. At
873 K, distorted spheres with 2–20 mm in diameter and thin
sheets larger than those of spheres in size were obtained. Spheres
were similar to those from sucrose-free Ni(NO3)2 in shape and,
each sphere had a hole in the wall. Presence of the hole suggest-
ed that inside materials come out through the hole at high tem-
peratures and generate a sphere with an egg shell structure. From
TEM image, Ni metal particles with 3–17 nm in diameter were
dispersed in the products. The product at 973 K was composed
of distorted spheres similar to those synthesized at 873 K in
shape but the size was larger. Relatively small aggregate of
platelets of about 2.2 mm and rectangular solids were formed
(Figure 1). At 1073 K, size of spheres increased and the forma-
tion of aggregates of platelets and sheets were increased. Ni par-
.
mann complex, Ni(CN)2(NH3) 0.25H2O, during the pyrolysis
of a mist of solution containing sucrose and nickel nitrate in
an inert gas as Ar without using harmful and ligand compounds
such as NH3 and HCN at 873–1073 K, which are much higher
temperatures than those in ordinal metal complex synthesis.
Sucrose (Wako pure chem. Co., reagent grade) as a carbon
source and nickel nitrate (Wako Pure Chem. Co., Pure grade)
were used. An aqueous solution containing sucrose and
.
Ni(NO3)2 6H2O was fed into a reactor made of stainless steel
with 10 cm in diameter by a spray. Feed rates of the liquid and
Ar as a carrier gas are shown in Figures. A schematic diagram
of the reaction system is shown in Figure 1. The reactor is heated
by a 40-cm electric heater. The gas stream after the reaction was
introduced into a water trap and the products were collected into
water. The recovered water containing products was separated
by a magnet to two portions. Both portions were filtrated off,
washed with pure water, and dried at 343 K overnight. The sam-
ples obtained were analyzed by XRD, TG-DTA, MAS-NMR,
SEM, and TEM-ED.
First of all, we tried to check the products from component
materials using this method and apparatus. The experiments
using a sucrose solution without Ni salts and a sucrose free Ni
salt solution were carried out. When a sucrose solution without
Ni salt was sprayed into the reactor at 873, 973, 1073, and
Copyright ꢀ 2007 The Chemical Society of Japan
Kashiwagi, Takeshi
