Inorganic Chemistry
ARTICLE
II
ꢀ1
important to emphasize that the unique photomagnetic response
arises from the ability to form heterostructures of the two
components because physical mixtures of the two components
and mixed-metal solid solutions of the two phases do not show
Fe ) cm . EDS: 13.7:49.2:36.9 (Rb/Co/Fe). Anal. Calcd for
1.52Rb0.28Co1.00Fe0.75: C, 20.14; H, 1.11; N, 23.50.
C
H N O
4.51 3.02 4.51
Found: C, 19.85; H, 0.93; N, 23.17.
Core/Shell Particles. The previously prepared core particle solu-
tion was diluted with water to 400 mL. An aqueous solution (200 mL) of
MCl
5 mM), when applicable, and an aqueous solution (200 mL) of K
CN)
10 mL/h, peristaltic pump) under stirring at room temperature. Once
the addition was complete, the particles were filtered using a 0.45 μm
filter and rinsed with ultrapure water before being redispersed in 400 mL
of water for use in the next step. To isolate the particles, instead of water,
the particles were redispersed in acetone and dried under reduced
pressure.
2
4
the same behavior.
The unique behavior of the heterostructured film led us to
investigate whether similar effects could be seen in other
nanometer-scale heterostructures, such as core/shell particles.
Synthetic routes to core/shell particles of Prussian blue analo-
2
6H
O (M = Ni or Co, 0.76 mmol, 3.8 mM) and RbCl (1.5 mmol,
2
3
0
3
M -
0
(
6
(M = Fe or Cr, 0.84 mmol, 4.2 mM) were added dropwise
(
25
gues have already been described. In 2006, Brinzei et al.
reported a way to stabilize cyanometallate particles by electro-
statics, without the use of surfactants. This method allows the
surface of the particle to remain reactive, permitting the sub-
sequent epitaxial growth of successive layers of different PBAs to
generate elegant core/shell and core/shell/shell particles with
KNiCr/RbCoFe Particles (AB). Purple powder (94% yield). IR (KBr):
II
III
2
6
2160 (w, νCN, Co ꢀNCꢀFe (high-spin, HS)), 2120 (w, νCN
,
dimensions of less than ∼50 nm.
II
III
II
II
ꢀ1
Co ꢀNCꢀFe (LS)), 2096 (w, ν , Co ꢀNCꢀFe ) cm . EDS:
CN
The present report describes heterostructured particles
4
.0:3.5 (Ni/Cr), 1.2:4.0:3.1 (Rb/Co/Fe).
of Rb Co [Fe(CN) ] mH O (B) with K Ni [Cr(CN) ]
a
b
6 c
3
2
j
k
6 l
3
RbCoFe/KNiCr Particles (BA). Purple powder (98% yield). IR (KBr):
nH O (A). In a previous study of B particles, we observed
II
III
II
III
2
2
2
172 (w, νCN, Ni ꢀNCꢀCr ), 2159 (w, νCN, Co ꢀNCꢀFe (HS)),
that magnetic order and persistent photoinduced magnetism
II III II
CN
111 (w, ν , Co ꢀNCꢀFe (LS)), 2093 (w, ν , Co ꢀNCꢀ
2
7
CN
is lost if particles are smaller than ∼10 nm. Also, the thin-
film heterostructures that showed the cooperative effects
between the two components had dimensions of approxi-
mately 200 nm/layer. Therefore, we targeted heterostruc-
tured particles of a somewhat larger scale than had previously
II
ꢀ1
Fe ) cm . EDS: 4.0:3.2 (Ni/Cr), 1.0:4.0:3.4 (Rb/Co/Fe).
Core/Shell/Shell Particles. To 400 mL of the previously synthe-
sized core/shell particles was added an aqueous solution (300 mL) of
MCl2 6H O (M = Ni or Co, 1.0 mmol, 3 mM) and RbCl (1.5 mmol,
mM), when applicable, and a solution (300 mL) of K
Fe or Cr, 1.2 mmol, 4 mM). The rate of addition was kept very low
10 mL/h, peristaltic pump) under stirring at room temperature. The
particles were subsequently isolated by filtration using a 0.45 μm filter
and washed with nanopure water. The particles were redispersed and
washed with acetone and dried under reduced pressure.
3
2
0 0
3 6
M (CN) (M =
5
2
6
been reported. Building on the methods of Catala et al.,
routes to building successive layers of around 50ꢀ100 nm of
cyanometallate on preformed particles have been developed.
The resulting particle heterostructures also exhibit the co-
operative photomagnetic behavior reported previously in
heterostructured thin films.
(
KNiCr/RbCoFe/KNiCr Particles (ABA). Purple powder (97% yield). IR
II
III
II
III
(
(
KBr): 2173 (w, νCN, Ni ꢀNCꢀCr ), 2160 (w, ν , Co ꢀNCꢀFe
CN
II III
HS)), 2120 (w, νCN, Co ꢀNCꢀFe (LS)), 2096 (w, νCN
,
’
EXPERIMENTAL SECTION
II
II
ꢀ1
Co ꢀNCꢀFe ) cm . EDS: 4.0:2.8 (Ni/Cr), 1.2:4.0:3.2 (Rb/Co/Fe).
Materials. K
tions of potassium cyanide with CrCl
3
Cr(CN)
6
was synthesized by treating aqueous solu-
6H O and used after recrys-
RbCoFe/KNiCr/RbCoFe Particles (BAB). Purple powder (97% yield).
II
III
IR (KBr): 2167 (w,
ν
CN
,
Ni ꢀNCꢀCr ), 2158 (w,
CN
ν ,
3
2
3
2
8
II
III
II
III
tallization from methanol. Deionized water used in synthetic
procedures was obtained from Barnstead NANOpure. All of the
other reagents were purchased from Sigma-Aldrich or Fisher-Acros
and used without further purification. The filters used during the
synthesis are Fast PES Bottle Top Filters with 0.2 or 0.45 μm pore
size (Nalgene).
Co ꢀNCꢀFe (HS)), 2113 (w, νCN, Co ꢀNCꢀFe (LS)), 2093
II II ꢀ1
(w, νCN, Co ꢀNCꢀFe ) cm . EDS: 4.0:3.3 (Ni/Cr), 1.1:4.0:3.1
(/Rb/Co/Fe).
Instrumentation. IR spectra were recorded on a Nicolet 6700
Thermo Scientific spectrophotometer. Typically, 64 scans are taken
ꢀ1
ꢀ1
between 2200 and 1900 cm with a precision of 0.482 cm . Powder
samples were mixed with KBr and pressed into a pellet using 3000 psi
(20 MPa). A scan of pure KBr is taken as a background reference.
Inductively coupled plasma mass spectrometry (ICP-MS) for elemental
analysis on nickel, cobalt, chromium, and iron was performed by
Complete Analysis Laboratories, Inc., Parsippany, NJ. Combustion
analysis to determine carbon, hydrogen, and nitrogen (CHN) percen-
tages was performed by the University of Florida Spectroscopic Services
Laboratory. Transmission electron microscopy (TEM) was performed
on a JEOL-2010F high-resolution transmission electron microscope at
200 kV. The TEM grids (carbon film on a holey carbon support film, 400
mesh, copper from Ted-Pella, Inc.) were prepared by dropping, onto the
grid, 20 μL of a solution containing 5 mg of sample dispersed by
sonication in 2 mL of EtOH for 30 min. Energy-dispersive X-ray
spectroscopy (EDS/EDX) was performed with an Oxford Instruments
EDS X-ray Microanalysis System coupled to the high-resolution TEM
(HRTEM) microscope. A total of four scans were performed on
different parts of the sample and then averaged to give relative atomic
percentages for chromium and iron. Chemical formulas are based on the
metal composition from EDS and ICP-MS, adding water and potassium
as determined by the number of trivalent metal vacancies to ensure
electroneutrality. Powder X-ray diffraction (XRD) diffractograms were
Core Particles. The synthesis was carried out at room temperature.
An aqueous solution (100 mL) of MCl
2
6H
2
O (M = Ni or Co, 0.40
3
mmol, 4 mM) and an equal volume of an aqueous solution containing
0 0
3 6
K M (CN) (M = Fe or Cr, 0.45 mmol, 4.5 mM) were simultaneously
added dropwise to 200 mL of nanopure water. In the preparation of
RbCoFe particles, RbCl (0.8 mmol, 8 mM) was included in the NiCl2
solution. The solution was kept under vigorous stirring for 1 h after
complete addition. The particles were subsequently filtered under
vacuum using a 0.45 μm filter for the RbCoFe particles and a 0.2 μm
filter for the KNiCr particles before being washed with ultrapure water
and before being redispersed in 100 mL of water for use in the next step.
To isolate the particles, instead of water, the particles were redispersed in
acetone and dried under reduced pressure.
KNiCr Particle (A). K2.68Ni [Cr(CN) ] . Light-green powder
4
6 3.92
II
III
(
76% yield). IR (KBr): 2174 (s, νCN, Ni ꢀNCꢀCr ), 2124 (b, νCN
,
III
ꢀ1
terminal NCꢀCr ) cm . EDS (Ni/Cr): 6.54:5.84. Anal. Calcd for
C
H N O K
.35 1.28 5.35 0.64 0.67
Ni1.00Cr0.89: C, 22.91; H, 0.45; N, 26.73.
5
Found: C, 23.54 ; H, 0.63; N, 27.95.
4 6
RbCoFe Particle (B). Rb1.68Co [Fe(CN) ]3.00. Purple powder
II
III
(
(
93% yield). IR (KBr): 2159 (w, νCN, Co ꢀNCꢀFe (HS)), 2111
II III II
CN
w, νCN, Co ꢀNCꢀFe (low-spin, LS)), 2093 (w, ν , Co ꢀNCꢀ
4
296
dx.doi.org/10.1021/ic1022054 |Inorg. Chem. 2011, 50, 4295–4300