Hyperfine coupling and local structures of octacyanomolibudenum magnetic complexes and related compounds as studied by solid state 13C and 2H NMR

Article abstract of DOI:10.1016/j.poly.2005.03.151

Three-dimensional polymeric complex of Cu₂[Mo(CN) ₈]·8H₂O (1) is known to undergo a transition from paramagnetic to ferromagnetic state by irradiation with blue light. To elucidate the local structure of this polymeric complex, which is important for switching to ferromagnet, we studied hyperfine coupling of ¹³C-enriched cyanide ions of 1 and of closely related structure known polycyanide complexes of Fe2II[MoIV(13CN)8]·8H2O(2), Mn2II[MoIV(13CN)8]·8H2O(3), [Cu^II(bpy)₂]₂[Mo^IV( ¹³CN)₈]·5H₂O·CH₃OH (4), UV-irradiated K₄[Mo^IV(¹³CN) ₈]·2D₂O (5), Cs₃[Mo^V( ¹³CN)₈]·2H₂O (6), [Cu2II(tren)213CN] (BF4)3(7), and [Ni2II(tetren)213CN](ClO4)3(8) by solid-state ¹³C NMR spectrum. We found two distinct ¹³C NMR signals for the cyanide ions in a paramagnetic phase of 1, i.e. high frequency and low frequency peak. Each of high- and low-frequency peak shows a positive (+19 MHz) and negative (-2 MHz) hyperfine coupling constant (hfcc), respectively. Then we assume that there are two distinct coordination structures for Cu(II) ions of 1. The peak with positive hfcc was also observed for 2 and 3, in which the cyanide ions of [Mo^IV(CN)₈]^4- coordinate to Fe(II) and Mn(II), respectively, in a square planar (SQP) structure. The negative hfcc of -0.79 MHz, which resembles the low frequency peak of 1, was observed for the ¹³C atom of one of the CN ions of 4, which coordinates to the Cu(II) in an equatorial plane of trigonal bipyramidal (TBP) structure. Based on these NMR results, it is suggested that there are two distinct Cu(II) coordination environments in 1, namely SQP and the structure that is largely distorted from SQP. The distortion may be important for ferromagnetic switching by photoinduced electron transfer from Mo(IV) to Cu(II) ion in a collective manner in the solid state.

Full text of DOI:10.1016/j.poly.2005.03.151

Polyhedron 24 (2005) 2599–2606
www.elsevier.com/locate/poly
Hyperfine coupling and local structures of
octacyanomolibudenum magnetic complexes and related
13
2
compounds as studied by solid state C and H NMR
*
Ryo Watanabe, Hiroki Ishiyama, Goro Maruta, Sadamu Takeda
Division of Chemistry, Graduate School of Science, Hokkaido University, Kita 10, Nishi 8, Sapporo 060-0810, Japan
Received 5 October 2004; accepted 25 March 2005
Available online 10 October 2005
Abstract
Three-dimensional polymeric complex of Cu2[Mo(CN)8] Æ 8H2O (1) is known to undergo a transition from paramagnetic to fer-
romagnetic state by irradiation with blue light. To elucidate the local structure of this polymeric complex, which is important for
switching to ferromagnet, we studied hyperfine coupling of 13C-enriched cyanide ions of 1 and of closely related structure known
polycyanide complexes of Fe2 ½Mo ð CNÞ ꢀ ꢁ 8H2O ð2Þ, Mn ½Mo ð CNÞ ꢀ ꢁ 8H2O ð3Þ, [Cu (bpy)2]2[MoIV(13CN)8] Æ 5H2O Æ
IV
IV
II
II
13
II
13
8
2
8
CH3OH (4), UV-irradiated K4[MoIV(13CN)8] Æ 2D2O (5), Cs3[MoV(13CN)8] Æ 2H2O (6), ½Cu2 ðtrenÞ213CNꢀðBF4Þ ð7Þ, and
II
3
½Ni2 ðtetrenÞ213CNꢀðClO4Þ ð8Þ by solid-state 13C NMR spectrum. We found two distinct 13C NMR signals for the cyanide ions
II
3
in a paramagnetic phase of 1, i.e. high frequency and low frequency peak. Each of high- and low-frequency peak shows a positive
(+19 MHz) and negative (ꢂ2 MHz) hyperfine coupling constant (hfcc), respectively. Then we assume that there are two distinct
coordination structures for Cu(II) ions of 1. The peak with positive hfcc was also observed for 2 and 3, in which the cyanide ions
of [MoIV(CN)8]4ꢂ coordinate to Fe(II) and Mn(II), respectively, in a square planar (SQP) structure. The negative hfcc of
ꢂ0.79 MHz, which resembles the low frequency peak of 1, was observed for the 13C atom of one of the CN ions of 4, which coor-
dinates to the Cu(II) in an equatorial plane of trigonal bipyramidal (TBP) structure. Based on these NMR results, it is suggested that
there are two distinct Cu(II) coordination environments in 1, namely SQP and the structure that is largely distorted from SQP. The
distortion may be important for ferromagnetic switching by photoinduced electron transfer from Mo(IV) to Cu(II) ion in a collec-
tive manner in the solid state.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Polycyanide complexes; Octacyanomolibudate; Local magnetic structures; Solid-state 13C NMR; Hyperfine coupling of CN ions
1. Introduction
chemistry of octacyanomolibudate ion has been
studied for many years. The irradiation with light of a
solution containing [MoIV(CN)8]4ꢂ in its charge-transfer
bands results in a photo-oxidation of MoIV(S = 0) to
MoV(S = 1/2) with the ejection of a solvated electron
[4–6]. A similar photo-reaction was observed for a sim-
ple compound of K4[MoIV(CN)8] Æ 2H2O in the solid
state [7], in which a reduction of crystal water molecule
accompanied with photo-oxidation of the MoIV(S = 0)
to MoV(S = 1/2) was assumed. Several irreversible
photo-oxidation reactions in the solid state have been
reported for extended multinuclear complexes [1,7].
Photoinduced ferromagnetic switching is one of the
fascinating subjects in the field of molecular magnetism.
The octacyanometalate ions of a form [MIV(CN)8]4ꢂ
have been employed as building blocks of the photosen-
sitive magnetic materials [1–3].1 The solution photo-
*
Corresponding author. Tel.: +81 11 706 3505; fax: +81 11 706
4841.
E-mail address: stakeda@sci.hokudai.ac.jp (S. Takeda).
M: MO and W.
1
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.03.151

2600
R. Watanabe et al. / Polyhedron 24 (2005) 2599–2606
Ferromagnetic ordering with blue light irradiation at
12.5 ml aqueous solution of the filtered powder was
heated to boil with activated carbon. The solution was
filtered and poured into 85 ml of CH3OH results in
immediate precipitation of yellow powder. The treat-
ment with activated carbon and recrystallization were
repeated three times. The last treatment with D2O in-
low temperature was found for Cu2[Mo(CN)8] Æ 8H2O
[2,3]. The critical temperature was 35 K and this photoin-
duced phase was transformed to the original form with
increasing temperature up to 200 K. Reversible change
of the magnetism with blue and red light irradiation was
found at low temperature [3]. In this change of the magne-
tism, a reduction of Cu(II) to Cu(I) occurs by electron
transfer from Mo(IV) ion with blue light irradiation.
The coordination structure of this reducible Cu(II) ion be-
fore irradiation must be crucial for the photoinduced fer-
romagnetism. However, detailed structure of this
compound is not known. Therefore, we tried to elucidate
the local structure of Cu2[Mo(13CN)8] Æ 8H2O (1) by a
measurement of hyperfine coupling constant (hfcc) of
13C atoms of 13C enriched cyanide ions. The hfcc of a
CN ligand must be sensitive to its coordination bond
and local magnetic structures of a variety of polycyanide
complexes [8,9]. We studied the plus and minus sign and
the magnitude of hfcc of 13C enriched cyanide ions of 1
and of closely related structure-known polycyanide com-
stead of H2O gave
a
deuterated analogue of
K4[MoIV(13CN)8] Æ 2D2O. Anal. Calc. for 5: C, 20.6; H,
0.79; N, 22.2. Found: C, 19.25; H, 0.96; N, 22.95%.
2.1.2. Cu2II [MoIV (13CN)8] ꢁ 8H2O (1)
Slow addition of 0.2 M aqueous solution of CuCl2 to
0.2 M aqueous solution of K4[MoIV(13CN)8] gave red-
purple powder [2]. Filtrated powder was dried in a des-
iccator. Anal. Calc. for 1: C, 16.70; H, 2.80; N, 19.48.
Found: C, 16.95; H, 2.58; N, 19.97%. The same proce-
dure with heavy water solution and deuterated analogue
of 5 gave Cu2[Mo(13CN)8] Æ 8D2O.
2.1.3. Fe2II [MoIV (13CN)8] ꢁ 8H2O (2)
Compound 2 was synthesized after the reference [14]
with 99% 13C enriched 5 instead of normal compound.
Anal. Calc. for 2: C, 17.44; H, 2.77; N, 20.35. Found: C,
15.88; H, 2.86; N, 18.80%. Powder X-ray diffraction pat-
tern agreed well with the structure determined for a single
crystal [15]. The compound 2 may be oxidized in the air. A
fresh yellow powder sample became blue in a few days in
the air. Evacuation of the virgin yellow powder led to col-
or change to green-yellow. Electronic sate may be chan-
ged due to a loss of crystal water. Therefore, for the
NMR measurement, a fresh yellow sample was sealed into
a glass ample with N2 gas for preventing a loss of crystal
water and an effect of oxygen.
IV
IV
II
13
II
plexes of Fe2 ½Mo ð CNÞ8ꢀ ꢁ 8H2O ð2Þ, Mn2 ½Mo
II
IV 13
13
ð CNÞ8ꢀ ꢁ 8H2O ð3Þ, [Cu (bpy)2]2[Mo ( CN)8] Æ 5H2O Æ
CH3OH (4), UV-irradiated K4[MoIV(13CN)8] Æ 2D2O
(5), Cs3[MoV(13CN)8] Æ 2H2O (6), ½Cu2 ðtrenÞ213CNꢀ
II
ðBF4Þ3 ð7Þ, and ½Ni2 ðtetrenÞ213CNꢀðClO4Þ3 ð8Þ by tem-
II
perature dependence of solid-state 13C NMR spectrum.
Broad-line 13C NMR spectrum of higher spin system
has been reported for Mn12-acetate cluster [10–12].
Methyl groups of acetate ions were enriched with 13C
isotope. Although the methyl carbon atoms are apart
from the magnetic Mn ions, the spectrum width is larger
than 4000 ppm for powder sample at 250 K and no ma-
gic angle spinning spectrum was reported. In our case,
the carbon atoms of cyanide ions closely locate to mag-
netic metal ions.
2.1.4. Mn2II [MoIV (13CN)8] ꢁ 8H2O (3)
Compound 3 was synthesized after the reference [15]
with 99% 13C enriched 5 instead of normal compound.
Anal. Calc. for 3: C, 17.22; H, 2.86; N, 20.09. Found:
C, 16.66; H, 2.55; N, 20.05%.
2. Experimental
2.1. Sample preparations
2.1.5. [CuII(bpy)2]2[MoIV(13CN)8] Æ 5H2O Æ CH3OH
(4)
2.1.1. K4[MoIV(13CN)8] Æ 2H2O (5)
Polycrystalline sample of 4 was obtained after the
method of reference [1] with 99% 13C enriched 5 instead
of normal compound. Anal. Calc. for 4: C, 49.98; H,
3.91; N, 19.62. Found: C, 47.31; H, 4.08; N, 18.53%.
Powder X-ray diffraction pattern agreed well with the
structure determined for a single crystal [1].
Warning! Although we have experienced no difficul-
ties, this procedure may produce HCN gas. 99% 13C en-
riched specimen was synthesized by a similar method
reported for normal compound [13]. 1.0 g of MoO3
and 4.6 g of 99% 13C enriched K13CN were milled in a
mortar. 7.5 ml of H2O was slowly added to the milled
mixture in drop-wise at 0 ꢁC and then 1.1 g of 85% aque-
ous (NH2)2 was added. Under ambient temperature,
4.5 ml conc. HCl was added very slowly to the above
solution in 1 h. Resulting solution was heated up to
86 ꢁC for 1 h and was cooled down to room tempera-
ture. Pouring the solution into 85 ml of CH3OH results
in immediate precipitation of brown yellow powder.
2.1.6. Cs3[MoV(13CN)8] Æ 2H2O (6)
Polycrystalline sample of 6 was obtained after the
method of reference [16] with 99% 13C enriched 5 instead
of normal compound. Anal. Calc. for 6: C, 13.00; H,
0.55; N, 15.17. Found: C, 12.96; H, 0.72; N, 15.18%.
Powder X-ray diffraction pattern agreed well with the
structure determined for a single crystal [17].

R. Watanabe et al. / Polyhedron 24 (2005) 2599–2606
2601
2.1.7. [Cu2II (tren)213CN](BF 4)3(7) and
3. Results and discussion
[Ni2II (tetren)213CN](ClO4)3 (8)
Blue crystals of 7 and purple crystals of 8 were ob-
tained after the methods of reference [18] by slow evap-
oration of the solvent. Colorless crystals also appeared
and were taken off. Anal. Calc. for 7: C, 22.12; H,
5.14; N, 17.86. Found: C, 21.85; H, 5.06; N, 17.64%.
Anal. Calc. for 8: C, 24.35; H, 5.73; N, 18.38. Found:
C, 24.65; H, 5.46; N, 18.73%. Powder X-ray diffraction
patterns of 6 and 7 agreed well with the respective struc-
ture reported for each single crystal [18].
3.1. Hyperfine coupling constants of cyanide ions and
local coordination structures of 1
Fig. 1 illustrates a typical 13C NMR spectrum of cya-
nide ions of 1. We found two distinct signals corre-
sponding to two different electronic states of the
cyanide ions. Largely shifted values from the diamag-
netic shift of K13CN (origin of abscissa) indicates an ef-
fect of electronic spins of CuII ions in this compound 1,
in which MoIV ions are diamagnetic. Since each peak
exhibited a small anisotropy and was almost symmetric,
the isotropic shift described in Eqs. (1) and (2) was
determined as the maximum point of the peak. Temper-
ature dependence of the isotropic shift is plotted as a
function of inverse temperature in Fig. 2 for both high
and low frequency peaks. This figure indicates a good
linear relation between the isotropic shift and inverse
temperature as suggested in Eqs. (1) and (2). The hfcc
of each peak was determined from the slope of this fig-
ure to be +19 and ꢂ2.0 MHz for high and low frequency
peak, respectively. The plus and minus sign of the hfcc
indicates that there are two different coordination struc-
tures for the cyanide ions. Nitrogen atoms of the cya-
nide ions are coordinated to CuII ions. Intensity ratio
of the two signals suggests almost 3:1 population of dif-
ferent coordination structures.
To estimate the coordination structures of cyanide
ions around magnetic metal ions, we determined the
hfcc of cyanide ions for two other compounds 2 and 3,
which have a similar unit formula to 1. The crystal struc-
ture of 2 is known, and 2 and 3 are believed to be iso-
morphous [1]. The coordination structure of 2 is
illustrated in Fig. 3, where FeII ion has square-planner
N-coordination of four cyanide ions and axial coordina-
tion of two water molecules. Typical 13C NMR spec-
trum is shown in Fig. 4(a) and (c) for 2 and 3,
respectively. Only a single peak was observed both for
2.2. Solid-state NMR
The 13C NMR spectrum was measured by an echo
pulse sequence for static powder crystalline sample at
an external magnetic field of 7.05 T with a Bruker
DSX300 spectrometer. Various irradiation frequencies
were used to cover the wide spectrum. The envelope of
all the echo signals displays a whole spectral line shape.
When a line shape is almost symmetric, we assume that
the isotropic shift is the center of the spectrum. The shift
was measured from external second reference of the
powder crystalline sample of K13CN (169.6 ppm from
TMS). Assuming a small zero-field splitting, the ob-
served isotropic shift diso consists of the Fermi contact
term, the dipole interaction term (pseudo contact) and
the temperature independent diamagnetic term (chemi-
cal shift) as follows [19,20]:
diso ¼ dFermi þ dPseudo þ ddia
;
ð1Þ
ð2Þ
lB AC
dFermi þ dPseudo
¼
SðS þ 1Þ.
3kBT cC=2p
Electron spin induced on the 13C nucleus by electron
spin of a magnetic metal ion causes a Fermi contact shift
of the NMR resonance line, while anisotropy of the g-
tensor of magnetic metal ions gives a pseudo-contact
shift. The coefficient AC in Eq. (2) is defined as the hfcc
of the 13C nucleus in Hz unit, which includes principal
values of anisotropic g tensor.
Magic angle spinning 13C and 2H NMR (MAS
NMR) spectra were measured by a similar method de-
scribed in reference [21] at a resonance frequency of
75.4 and 46.1 MHz, respectively, and at a magic angle
spinning speed of ca. 9 kHz with a Bruker DSX300 spec-
trometer. The MAS technique gives a high resolution
spectrum with an isotropic shift in some cases. The ther-
mometer of the MAS NMR probe and an effect of spin-
ning speed on temperature increase were carefully
calibrated [21,22]. Uncertainty of the temperature mea-
surement was within 2 K. The 2H NMR shift was mea-
sured from the external second reference of CD3OD
(CD3: 3.35 ppm).
3 : 1
3000
2000
1000
0
-1000
Shift from K13CN / ppm
Fig. 1. Typical 13C NMR spectrum of 99% 13C enriched cyanide ions
IV
II
of Cu2 ½Mo
ð
13CNÞ8ꢀ ꢁ 8H2O ð1Þ at 294 K. The spectrum was mea-
sured with a spin echo technique. The envelope of many echo signals is
illustrated. Magic angle spinning (MAS) at 10 kHz indicated no
resolution enhancement for the higher frequency peak, whereas MAS
technique was effective for the low frequency signal.

2602
R. Watanabe et al. / Polyhedron 24 (2005) 2599–2606
10000
8000
6000
4000
2000
0
Fe(S=2)
Mn(S=5/2)
Cu(S=1/2)
-2000
2
3
4
5
6
7
8
1000/(T/K)
Fig. 2. Temperature dependence of isotropic 13C NMR shift of
IV
II
Cu2 ½Mo
ð
13CNÞ8ꢀ ꢁ 8H2O ð1Þ j, low frequency peak and h, high
IV
IV
II
II
frequency peak; m, Fe2 ½Mo
ð
13CNÞ8ꢀ ꢁ 8H2O ð2Þ; ., Mn2 ½Mo
-
ð
13CNÞ8ꢀ ꢁ 8H2O ð3Þ. The origin of the abscissa is the diamagnetic shift
of polycrystalline sample of K13CN. The hyperfine coupling constants
determined from the slopes of this figure with Eqs. (1) and (2) are
+19 MHz (high frequency peak) and ꢂ2.0 MHz (low frequency peak)
for 1, +4.9 MHz for 2, and +2.3 MHz for 3.
IV
II
Fig. 3. Structure of coordination network of Fe2 ½Mo
ð
13CNÞ8ꢀ ꢁ
2 and 3. A small signal near 0 ppm is impurity due to
slight decomposition.2 The spectrum is almost symmet-
ric and the isotropic shift was determined as the center
of the signal. Temperature dependence of the 13C
NMR shifts is plotted in Fig. 2 for 2 and 3 together with
1. Positive slope for 2 and 3, which have square planar
N-coordination structure around the magnetic metal
center, resembles the slope of high frequency peak of
1. Thus we assigned the high frequency peak of 13C
NMR spectrum of 1 to the cyanide ions that have square
planar like N-coordination to CuII ion in 1. The derived
values of hfcc are summarized in Table 1.
Low frequency peak of 1 indicates that a part of cya-
nide ions of 1 exhibits negative hfcc and their N-coordi-
nation structures are different from the square planar
structure. The negative hfcc was observed for 4, which
has an N-coordination to Cu(II) ion in an equatorial
plane of trigonal bipyramidal structure as shown in
Fig. 5. A typical 13C NMR spectrum of 4 is illustrated
in Fig. 6. Three different isotropic peaks, i.e. a, b, c, were
identified. Two of eight cyanide ions of 4 are directly
coordinated to magnetic Cu(II) ions and their 13C
8H2O ð2Þ after reference [12].
NMR signals should exhibit broader width and largest
magnitude of hfcc, while other six cyanide ions are free
of coordination. The peak c, which shows largest width,
was assigned to the cyanide ions coordinated to Cu(II)
ions. Fig. 7 shows their shifts plotted as a function of in-
verse temperature and the peak c exhibits the largest
magnitude of hfcc. The sign of the hfcc of the peak c
is negative, which is similar to the low frequency peak
of 1. It is considered that the N-coordination geometry
of the cyanide ion with a negative hfcc of 1 is largely de-
formed from the square planar. It is not clear at present
whether two distinct Cu(II) ions exist in 1, one of which
is a square planar type and the other is largely deformed
from the square planar, or all the Cu(II) ions are de-
formed form the square planar, in which three of the
four N-coordination bonds are similar to the square pla-
nar and the rest one is deformed from the square planar
type. Any how, such native deformation of N-coordina-
tion bond from the square planar structure in 1 is prob-
ably relevant to stabilize the reduced Cu(I) ion, which is
produced by blue light irradiation.
2
The compound 2 decomposed in the air. A fresh yellow powder
sample became dark blue in a few days in the air. The blue sample
exhibited a completely different 13C NMR signal from virgin yellow
sample as shown in Fig. 4(b). The signal of blue sample locates near 0
and 3000 ppm, one of which near 0 ppm is the almost the same shift
observed as a small peak in Fig. 4(a). Evacuation of the virgin yellow
powder led to color change to yellow-green. Electronic sate of 2 may be
slightly hanged due to a loss of crystal water. Therefore, for the NMR
measurement of 2, a fresh yellow sample was sealed into a glass ample
with N2 gas for preventing a loss of crystal water and an effect of
oxygen.
We also investigated the motional behavior of crystal
water molecules of deuterated analogue of 1. Solid-state
2H NMR spectrum is narrow, which indicates rapid
and almost isotropic rotation of the crystal water mole-
cule (D2O) at 295 K. A similar behavior was observed
for Prussian-blue analogue [23,24]. Magic angle spinning
2H NMR spectrum showed an intense peak at 6.5 ppm at
295 K. This shift value is almost typical for diamagnetic

R. Watanabe et al. / Polyhedron 24 (2005) 2599–2606
2603
Table 1
a
Hyperfine coupling constant of 13C nucleus of compounds 1, 2, 3, and
4
295K
230K
Compound
1
2
3
4
Spin S of
magnetic
metal ion
Cu(II)
Fe(II)
Mn(II)
Cu(II)
1/2
2
5/2
1/2
Hfcc
+19 MHz
+4.9 MHz +2.3 MHz
(not known) (SQP)
(SQP)
+0.44 MHz
ꢂ0.24 MHz
ꢂ0.79 MHz
(EP-TBP)
IV
ꢂ2 MHz
(not known)
IV
II
II
Compounds are Cu2 ½Mo
ð
13CNÞ8ꢀ ꢁ 8H2O ð1Þ, Fe2 ½Mo
ð
13CNÞ8ꢀꢁ
150K
IV
II
8H2O ð2Þ, Mn2 ½Mo
ð
13CNÞ8ꢀ ꢁ 8H2O ð3Þ, and ½CuIIðbpyÞ2ꢀ2½MoIV
ð
13CNÞ8ꢀ ꢁ 5H2O ꢁ CH3OH ð4Þ. SQ represents the square planer struc-
ture and EP-TBP means equatorial plane of trigonal bipyramidal.
12000
8000
4000
0
-4000
(ppm)
b
295K
(ppm)
8000
4000
0
-4000
c
291K
230K
Fig. 5. Molecular and coordination structure of [CuII(bpy)2]2-
[MoIV 13
CN)8] Æ 5 H2O Æ CH3OH (4) [1].
(
150K
of the peak at 6.5 ppm and the small peak was tentatively
assigned to an impurity.
(ppm) 8000
4000
0
-4000
3.2. Photoreaction of 5 in aqueous solution and in the
crystalline phase, and 13C NMR spectrum of
[MoV(13CN)8]3ꢂ ion
Fig. 4. Typical 13C NMR spectrum of 99% 13C enriched cyanide ions
IV
II
of: (a) Fe2 ½Mo
ð
13CNÞ8ꢀ ꢁ 8H2O ð2Þ, (b) a specimen of 2 stored in the
IV
II
air and (c) Mn2 ½Mo
ð
13CNÞ8ꢀ ꢁ 8H2O ð3Þ. Each spectrum is con-
structed with many echo signals measured with different excitation
frequencies. The origin of the abscissa is the diamagnetic shift of
polycrystalline sample of K13CN.
To obtain an information about hfcc of 13C atom gi-
ven by photoinduced Mo(V) ion (S = 1/2) in the crystal-
line phase of K4[MoIV(13CN)8] Æ 2D2O (5), we measured
13C NMR spectrum for ca. 50 mg of light irradiated
powder specimen of 5. By irradiation with a light (ca.
300–800 nm) of a Xe lamp at room temperature for a
few days, we observed a very broad 13C NMR spectrum
overlapped by a sharp central line of a diamagnetic spe-
cies of 5 as shown in Fig. 8(a). Signal-to-noise ratio is
compounds and suggests no strong interaction between
the crystal water molecules and the magnetic Cu(II) ion
in contrast to the crystal structure of Fe(II) compound
2, in which crystal water molecules directly coordinate
to the Fe(II) ion. A small peak of MAS 2H NMR was also
observed at 28 ppm. However, the intensity was only 3%

2604
R. Watanabe et al. / Polyhedron 24 (2005) 2599–2606
a
293K
Fig. 6. A typical magic angle spinning 13C NMR spectrum of cyanide
ions of 99% 13C enriched sample of [CuII(bpy)2]2[MoIV 13
CN)8] Æ 5-
150K
(
H2O Æ CH3OH (4), which was measured at 300 K with a spinning speed
of 9 kHz. The shift was measured from TMS and a second reference of
K
13CN (169.6 ppm from TMS) was used. a, b and c indicate signals of
isotropic shift. Peaks indicated by asterisks are spinning side bands,
which were clearly distinguished from the isotropic shifts by using
several different spinning speeds.
(ppm)
6000
2000
-2000
-6000
200
180
160
140
120
100
80
b
293K
230K
150K
60
40
2
2.5
3
3.5
1000/(T/K)
4
4.5
5
5.5
Fig. 7. Temperature dependence of the isotropic shift of 13C NMR
lines indicated by a, b and c in Fig. 6. Each temperature slope gave hfcc
of +0.44 (a), ꢂ0.24 (b) and ꢂ0.79 MHz (c), respectively.
(ppm)
6000
2000
-2000
-6000
Fig. 8. 13C NMR spectrum of cyanide ion of [MoV(13CN)8]3ꢂ of (a)
UV-irradiated K4[MoIV 13CN)8] Æ 2D2O (5) and (b) Cs3[MoV(13C-
N)8] Æ 2H2O (6). The origin of the abscissa is the diamagnetic shift of
polycrystalline sample of K13CN. The signal near 0 ppm was assigned
to decomposed fragment, which is diamagnetic.
bad because of conversion from Mo(IV) to Mo(V) is not
enough. The amount of the conversion from Mo(IV) to
(
2
Mo(V) was estimated to be ca. 1.4% from the MAS H
NMR spectrum of ODꢂ ion produced by a reduction of
D2O molecule as shown in Fig. 9.3 Intensity of the sharp
signal of diamagnetic 5 with long relaxation time was
diminished by short repetition time for accumulation
of the signal. The signal of 13C NMR of [MoV(13CN)8]3ꢂ
is very broad and a center of the broad signal is almost
temperature independent in contradiction to a prediction
by Eqs. (1) and (2). To clarify this behavior, we also stud-
ied 13C NMR spectrum of Cs3[MoV(13CN)8] Æ 2H2O (6)
in the crystalline phase. The spectrum is also very broad
and almost temperature independent as illustrated in
3
It is noted that reduction of the crystal water molecule hydrogen-
bonded to the N atom of Mo(IV)–CN by an electron transfer from
Mo(IV) ion with UV-irradiation was concluded in the crystalline
phase. Such a reaction was proposed in solution and in the solid state
[7].

R. Watanabe et al. / Polyhedron 24 (2005) 2599–2606
2605
a
13
4-
IV
[Mo ( CN) ]
8
100000
0
-100000
(Hz)
a
b
D O
2
-
OD
15
10
5
0
-5
(ppm)
b
Fig. 9. Magic angle spinning 2H NMR spectrum of UV-irradiated
K4[MoIV 13
CN)8] Æ 2D2O (5). (a) Full-width spectrum including spin-
(
-20
-30
-40
ning side bands and (b) isotropic shift. The full width spectrum (a)
indicates 180ꢁ flip motion of D2O molecule in the solid state around
the molecular C2 axis. A small signal at 7.9 ppm of (b) was assigned to
(ppm)
ODꢂ ion produced by UV-irradiation, MoIV + D2O ! MoV + ODꢂ
+
Fig. 10. 13C NMR spectrum of cyanide ion of D2O solution of
K4[MoIV 13
CN)8] Æ 2D2O (a) before and (b) after UV-irradiation. The
origin of the abscissa is the diamagnetic shift of polycrystalline sample
of K13CN. Since the reaction product was not identified, signal
assignment was impossible for spectrum (b). Two spectra were
measured with MAS NMR probe for solid.
1/2D2 (›). The intensity of this signal is 1.4% of total intensity of D
signals including all of the spinning side bands. A large signal at
5.4 ppm is crystal water molecule, which is independent of UV-
irradiation. The signal of ODꢂ ion showed no spinning side band,
which indicates rapid isotropic rotation of ODꢂ ion in the crystalline
lattice of 5.
(
3.3. A possible effect of polymeric sequential coordination
structure on the linewidth of 13C NMR spectrum of
cyanide ion
Fig. 8(b). For these compounds, relaxation time of elec-
tron spin may not be matched to the assumed condition
to derive the Eqs. (1) and (2) for 13C NMR in the solid
state.
To investigate further what is the origin of very broad
and almost temperature independent 13C NMR spectrum
observed for UV irradiated 5 and for 6, we tried to mea-
sure the 13C NMR spectrum for Cu(II) and Ni(II) dim-
mer compounds of 7 and 8 in their crystalline phase.
We suspected that isolated electron spin or localized ex-
change interactions closed within a molecule would bring
about a very broad 13C NMR spectrum. Our 13C NMR
measurements for three-dimensional polymeric cyanide
complexes such as Prussian-blue analogues [25] and for
one-dimensional Ni(II) and Cu(II) chain complexes
[26,27], which have extended exchange interactions,
showed narrower and temperature dependent spectrum
and we were able to apply Eqs. (1) and (2). An exception
is hexacyanoferrate ion [FeIII(13CN)6]3ꢂ in the solid state
[23]. This compound showed relatively narrow and tem-
perature dependent 13C NMR spectrum. The compounds
7 and 8 are dinuclear complex of Cu(II) and Ni(II), in
In contrast to the above result for the crystalline
phase, well resolved 13C NMR signals were observed
for light irradiated D2O solution of a deuterated ana-
logue of 5 as illustrated in Fig. 10. Color of the solution
changed immediately from yellow to green by light irra-
diation under a similar condition to the polycrystalline
phase. The observed shifts of 13C NMR signals for the
irradiated solution are not so large, suggesting that the
paramagnetic species of [MoV(13CN)8]3ꢂ was not de-
tected. The hfcc of carbon nucleus of [MoV(13CN)8]3ꢂ
was estimated from quantum mechanical calculation
based on UB3LYP/LanL2DZ for an anti-prism coordi-
nation structure of [MoV(13CN)8]3ꢂ in crystalline phase
of 6. The values are ꢂ26.9 to ꢂ31.7 MHz. All the values
are negative and the magnitude is similar to the value of
|33| MHz determined by ESR for the [MoV(CN)8]3ꢂ ion
in an aqueous solution of K3[MoV(CN)8] [25].

2606
R. Watanabe et al. / Polyhedron 24 (2005) 2599–2606
tion of electron spin to clarify the mechanism of this
a
behavior.
Acknowledgments
294K
This research was supported by grant-in-aid for Sci-
entific Research on Priority Areas ‘‘Application of
Molecular Spins’’ (15087201) and 14740371 from the
Ministry of Education, Culture, Sports, Science and
Technology of Japan and partially by The Mitsubishi
Foundation.
220K
150K
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1000
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Fig. 11. 13C NMR spectrum of cyanide ion of (a)
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II
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