The first anion template cubic cyanometallate cage and its 3,5-dimethyltris(pyrazolyl)methane iron(II, III) tricyanide building blocks

Article abstract of DOI:10.1016/j.inoche.2008.07.022

Several 3,5-dimethyltris(pyrazolyl)methane iron(II, III) tricyanide building units have been prepared and characterized. Treatment of K[(HC(3,5-Me₂Pz)₃)Fe^II(CN)₂] (K⁺1^-) with Fe^II(H²O)⁶(BF⁴)² affords a new anion template cubic cyanometallate cage [(BF₄) ? {Fe^II(H₂O)}₄{(HC(3,5-Me₂Pz) ₃)Fe^II (CN)₃}₄](BF₄)³ 3.

Full text of DOI:10.1016/j.inoche.2008.07.022

Inorganic Chemistry Communications 11 (2008) 1264–1266
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Inorganic Chemistry Communications
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The first anion template cubic cyanometallate cage and its
3,5-dimethyltris(pyrazolyl)methane iron(II,III) tricyanide building blocks
b
b
c
Chu-Chen Shi a, Chi-Shian Chen a,b, Sodio C.N. Hsu a, , Wen-Yann Yeh , Michael Y. Chiang , Ting-Shen Kuo
*
a Faculty of Medicinal and Applied Chemistry, and Center of Excellence for Environmental Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan
b Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
c Department of Chemistry, National Taiwan Normal University, Taipei 116, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Several 3,5-dimethyltris(pyrazolyl)methane iron(II, III) tricyanide building units have been prepared and
characterized. Treatment of K[(HC(3,5-Me2Pz)3)FeII(CN)2](K+1-) with FeII(H2O)6(BF4)2 affords a new anion
template cubic cyanometallate cage [(BF4) ꢀ {FeII(H2O)}4{(HC(3,5-Me2Pz)3)FeII (CN)3}4](BF4)3 3.
Ó 2008 Elsevier B.V. All rights reserved.
Received 1 July 2008
Accepted 22 July 2008
Available online 6 August 2008
Keywords:
Iron complex
Cyanide
3,5-dimethyltris(pyrazolyl)methane
Crystal structure
The Prussian blue (PB) and its analogues which are insoluble
polymerics by virtue of the sixfold bridging of the octahedral
[M(CN)6]nꢁ subunits have garnered interest recently because of
their electrocatalytic, electrochromic, ion-exchange, ion-sensing,
and photomagnetic properties [1,2]. Facially coordinated tripodal
ligands were introduced to replace three of these CN groups which
block one face of the octahedron [3,4]. Polymerization could be
thus inhibited, and a family of cages with a box-like architecture
results. Some early examplesmþshowed that the reaction of
cyanometallate boxes, ½M8ðCNÞ12ꢂ4ðnꢁmþÞ, from the displacement of
the labile MeCN or H2O ligand [5–21]. As part of our interest in this
area, we are focusing on the coordination complexes of iron, which
have the same components as classic Prussian blue materials and
will offer the potential for comparison with classic Prussian blue
materials. Surprisingly, despite the prevalence of facile type scorpi-
onate ligands such as tris(pyrazolyl)borates and tris(pyrazol-
yl)methane in inorganic chemistry, only tris(pyrazolyl)borate
iron(II,III) tricyanide and some derived clusters and networks have
been described [22–32]. The related tris(pyrazolyl)methane has a
framework identical to that of the borate ligands, contains a carbon
atom in place of the boron atom, and hence, acts as neutral ligands.
In an effort to extend the chemistry of Prussian blue type’s com-
plexes, we have chosen 3,5-dimethyltris(pyrazolyl)methane
(HC(3,5-Me2Pz)3) as a capping ligand to synthesize its cyanometal-
late complexes and to investigate their reactivity toward cyano-
metallate cage formation. Herein, we report the preparation and
characterization of a new cubic cyanometallate cage containing
an anion template and its 3,5-dimethyltris(pyrazolyl)methane iro-
n(II,III) tricyanide building blocks.
The tricyano complex K[(HC(3,5-Me2Pz)3)FeII(CN)3](K+1ꢁ) was
readily prepared by treatment of a methanol solution of FeCl2 with
HC(3,5-Me2Pz)3 followed by the addition of a slight excess of KCN
[33]. The addition of PPh4Cl to the reaction mixture produced or-
ange microcrystals of PPhþ4 1ꢁ in an excellent yield [34]. Chemical
oxidation of 1ꢁ with iodine or ferrocenium hexaflouorophosphate
in acetonitrile produces a yellowish brown precipitate (HC(3,5-
Me2Pz)3)FeIII(CN)3 2 [35]. Infrared spectroscopy performed on an
acetonitrile solution of 1ꢁ confirmed the presence of C3v symmetry
coordinated with cyanide ligands with strong stretches appearing
at 2070 cmꢁ1(s) and 2057 cmꢁ1(vs), which are shifted by 20 and
7 cmꢁ1, respectively, from that of tetraethylammonium cyanide
(2050 cmꢁ1). Same tendency also can be observed in 2 which is ir-
on(III) derivatives of 1ꢁ. The infrared spectrum of the microcrystal-
line sample of 2 contains only one peak at 2124 cmꢁ1(s). They are
shifted to higher energies relative to 1ꢁ, suggesting the presence of
oxidation of the iron center that decreases the charge delocaliza-
nꢁ
mþ
fac ꢁ LMðCNÞ3 with LMðH2OÞ3 or LMðMeCNÞ3
resulted in
tionþ via
p back-bonding. The mCN stretching absorptions of
PPh4 1ꢁ and 2 are also found at relatively high energies and are
comparable to their borate analogues [(HB(3,5-Me2Pz)3)-
FeII(CN)3]2ꢁ (2041 cmꢁ1(s), 2017 cmꢁ1(vs)) and [(HB(3,5-Me2Pz)3)-
FeIII(CN)3]ꢁ (2115 cmꢁ1(s)) [25].
X-ray crystallographic analysis of PPhþ4 1ꢁ, K+1ꢁ, and 2 revealed
that the FeII or FeIII ions are in an octahedral N3C3 coordination
sphere with slight deviations of the coordination angels from the
* Corresponding author. Tel.: +886 73121101; fax: +886 73125339.
E-mail address: sodiohsu@kmu.edu.tw (S.C.N. Hsu).
1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2008.07.022

C.-C. Shi et al. / Inorganic Chemistry Communications 11 (2008) 1264–1266
1265
tively longer values are exhibited by PPhþ4 1ꢁ salt, which may be
due to the potassium cyanide interaction. The longer Fe–C bond
distances range from 1.916(11) to 1.929(10) Å for 2 suggest that
FeIII derivatives exhibit less
p back-bonding relative to divalent
analogues, which also consist of infrared data. Related to known
borate analogues [(HB(3,5-Me2Pz)3)Fe(CN)3]ꢁ/2ꢁ, [25] [(HC(3,5-
Me2Pz)3)Fe(CN)3]0/ꢁ (1ꢁ and 2) probably exhibit longer Fe–C bonds
and shorter Fe–N bonds, due to a significant difference between
the electron charge properties of borate and methane complexes.
The reaction of 1ꢁ with FeII(H2O)6(BF4)2 leads to the formation
of a new anion template cubic cyanometallate cage [(BF4) ꢀ {FeII(-
H2O)}4{(HC(3,5-Me2Pz)3)FeII(CN)3}4](BF4)3 3 [36]. Cage 3 is an air
sensitive yellow compound that becomes insoluble green product
after exposure to air. Infrared spectroscopy studies on the samples
of cage 3 in the solid state revealed only a single mCN band at
2090 cmꢁ1, which are shifted by +20 cmꢁ1 compared to the start-
ing material 1ꢁ, consistent with bridging cyanide interaction
[32,37]. Using NaPF6 to exchange the anion gives an intractable
mixture. The reaction of 1ꢁ with FeII(H2O)6(PF6)2 (or FeII(H2O)6(-
ClO4)2) also give similar intractable mixtures. Recently, a neutral
all iron cubic cyanometallate cage was synthesized, which did
not contain any ion inside the cage [31]. The cage 3 reported here
is the first cyanometallate cage containing an anion template in-
side the cage.
Fig. 1. Thermal ellipsoid plot of the anionic unit in PPhþ4 1ꢁ with important atom
labeled. Hydrogen atoms were omitted for the sake of clarity. Selected bond
distances (Å) and bond angles (deg): Fe(1)–N(2) 2.038(5), Fe(1)–N(4) 2.018(5),
Fe(1)–N(6) 2.037(5), Fe(1)–C(17) 1.925(7), Fe(1)–C(18) 1.902(7), Fe(1)–C(19)
1.912(7), C(17)–N(7) 1.151(8), C(18)–N(8) 1.166(8), C(19)–N(9) 1.148(7), N(6)–
Fe(1)–C(19) 176.1(2), N(4)–Fe(1)–C(18) 177.2(2), N(2)–Fe(1)–C(17) 178.7(2), Fe(1)–
C(17)–N(7) 178.5(6), Fe(1)–C(18)–N(8) 178.2(6), Fe(1)–C(19)–N(9) 177.7(6), C(17)–
Fe(1)–C(18) 89.5(3), C(17)–Fe(1)–C(19) 89.5(3), C(18)–Fe(1)–C(19) 91.5(3), N(2)–
Fe(1)–N(4)86.6(2), N(2)–Fe(1)–N(6) 87.1(2), N(4)–Fe(1)–N(6) 85.9(2).
Single-crystal X-ray studies revealed that 3 was a distorted cu-
bic box composed of both six and four coordinate eight iron verti-
ces and crystallized in the cubic space group P23. P23 symmetry
was imposed on the box framework (Fig. 2). The HC(3,5-Me2Pz)3
ligand was disordered at the threefold symmetry axes. Reflecting
the high crystallographic symmetry of the salt, the guest anion
BFꢁ4 is disordered at the three equivalent positions. The refine-
ments indicate that the F atoms are oriented near the four coordi-
nation Fe sites about 2.785 Å. The local geometry of four
coordination Fe sites is a distorted tetrahedron with CN–Fe–NC an-
gles of about 109.3 ° which were composed of three nitrogen-
bound bridging cyanide ligands and one terminal water molecule.
Significant distortions of the cage 3 allow for formation of the
pseudocubic structure from octahedral and tetrahedral corners;
these occur at the 12 unique Fe–N„C angles around four coordina-
tion Fe sites. This distortion is present at each of the four coordina-
tion Fe sites to 166.3(9)°. An examination of the cube body
diagonals reveals a slight compression along one of the C3 axes,
which lowers the overall symmetry of the cage. Another six coor-
dination Fe sites have NC–Fe–CN angles around 87.7°, and the
Fe–C„N angle is nearly linear (176.8(9)°), which, coming from
1ꢁ, still keeps the slightly distorted octahedral N3C3 geometry.
The coordination bond lengths of cyanide have a pronounced dif-
ference when the Fe–CCN (1.873(10) Å) is compared with the Fe–
NCN (2.016(8)Å).
ideal values (Fig 1 for the anion of PPhþ4 1ꢁ; K+1ꢁ, and 2 see Supple-
mentary material).þThe Fe–C bond distances range from 1.902(7) to
1.925(7) Å for PPh4 1ꢁ and 1.817(17) to 1.868(19) Å for K+1ꢁ. The
smallest Fe–C bond distances are found in K+1ꢁ, while compara-
The preparation of 3,5-dimethyltris(pyrazolyl)methane iron tri-
cyanides and their use as building blocks to prepare a new cubic all
iron cyanometallate cage have been described. The anion template
in the iron cubic cyanometallate cage only works for the BFꢁ4 anion.
Efforts are underway to use 3,5-dimethyltris(pyrazolyl)methane
iron tricyanide 1ꢁ and 2 as building blocks to be incorporated with
other transition metal ions in the presence of different anion tem-
plates and to investigate the ion-exchange, ion-sensing, and mag-
netic properties of those cyanometallate cage compounds.
Acknowledgements
Fig. 2. Thermal ellipsoid plot of the cationic unit in 3 with important atom labeled.
Hydrogen atoms and coordinated water molecule (on Fe(2)) were omitted for the
sake of clarity. Selected bond distances (Å) and bond angles (deg): Fe(1)–C(1)
1.873(10), Fe(1)–N(2) 2.023(7), Fe(2)–N(1) 2.016(8), Fe(2)–O(1) 2.300(8), C(1)–N(1)
1.175(14), B(1)–F(1) 1.32(2), N(2)–Fe(1)–C(1) 177.8(4), Fe(1)–C(1)–N(1) 176.8(9),
C(1)–N(1)–Fe(2) 166.3(9), N(1)–Fe(2)–O(1) 109.6(3).
We gratefully acknowledge the financial support of the National
Science Council (Taiwan). We thank Mr. Min-Yuan Hung (Center
for Resources, Research and Development, Kaohsiung Medical Uni-
versity) for his assistance with the compound characterization.

1266
C.-C. Shi et al. / Inorganic Chemistry Communications 11 (2008) 1264–1266
[29] Z.-G. Gu, W. Liu, Q.-F. Yang, X.-H. Zhou, J.-L. Zuo, X.-Z. You, Inorg. Chem. 46
Appendix. Supplementary. material
(2007) 3236.
[30] C.-F. Wang, W. Liu, Y. Song, X.-H. Zhou, J.-L. Zuo, X.-Z. You, Eur. J. Inorg. Chem.
(2008) 717.
CCDC Nos. 693371, 625279, 625280 and 693372 contains the
supplementary crystallographic data for K+1ꢁ, PPh4þ1ꢁ, 2 and 3.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
[31] M. Nihei, M. Ui, N. Hoshino, H. Oshio, Inorg. Chem. 47 (2008) 6106.
[32] D. Li, R. Clerac, O. Roubeau, E. Harte, C. Mathoniere, R. Le Bris, S.M. Holmes, J.
Am. Chem. Soc. 130 (2008) 252.
[33] Synthesis of [K][(HC(3,5-Me2Pz)3)FeII(CN)3] K+1ꢁ:
A solution of HC(3,5-
Me2Pz)3 (1.00 g, 3.36 mmol) in 10 mL of MeCN was added to a solution of
FeCl2 (0.426 g, 3.36 mmol) in 20 mL of MeCN. This mixture was stirred at room
temperature for 2 h and a solution of KCN (0.76 g, 11.76 mmol) in 50 mL of
MeOH was added to stir at room temperature for another 2 hrs. The solvent
removed by rotary evaporation to give an yellow solid. This yellow solid was
extracted by MeCN (0.5 L ꢃ 8) to give an yellow solution. The yellow solution
was concentrated by slow rotary evaporation (20 mL) to give yellow
microcrystals (0.67 g (85%)). Yellow crystals suitable for X-ray analysis and
elementally analysis of complex K+1ꢁ were grown by allowing an aqueous
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CN 2056 cmꢁ1. IR
(KBr):
m
CN 2050, 2072 cmꢁ1. ESI–MS(ꢁ): m/z 432 [(HC(3,5-Me2Pz)3)Fe(CN)3].
Anal. Calc. for C19H22FeKN9.5 H2O (found): C, 40.64 (40.75); H, 5.74 (5.76); N,
22.45 (22.59).
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(0.63 g, 1.68 mmol) in 10 mL of MeCN was added to a solution of [K][(HC(3,5-
Me2Pz)3)FeII(CN)3] K+1ꢁ (0.79 g, 1.68 mmol) in 20 mL of MeOH. This mixture
was stirred at room temperature for 2 hours and the solvent removed by
rotary evaporation. The solid was dissolved in CH2Cl2 and the solution was
then filtered. After reducing the volume of the filtrate to 5 mL, then 50 mL of
Et2O was added to precipitate an orange solid, and dried under vacuum to
yield 1.03 g (80%). Single crystals suitable for X-ray analysis and elementally
analysis of complex PPhþ4 1ꢁ were obtained by diffusion of Et2O into MeCN
solution. 1H NMR(CD3CN, d): 2.526(s, 9H, CH3), 2.688(s, 9H, CH3), 5.932(s, 3H,
Pz), 7.663(s, 1H, CH). 13C NMR(CD3CN, d): 11.028, 15.788, 68.023, 108.554,
142.149, 159.569, 174.723. IR (MeCN): vCN 2058, 2070 cmꢁ1. IR (KBr): vCN
2057, 2071 cmꢁ1
.
ESI–MS(ꢁ): m/z 432 [(HC(3,5-Me2Pz)3)Fe(CN)3]ꢁ. ESI–
MS(+): m/z 339 PPhþ4 . Anal. Calc. for C43H42FeN9P (found): C, 66.93 (66.98);
H, 5.49 (5.61); N, 16.34 (16.25).
[35] Synthesis of (HC(3,5-Me2Pz)3)FeIII(CN)3 2:
A solution of ferrocenium
hexaflouorophosphate (0.10 g, 0.367 mmol) in 10 mL of MeCN was added to
a solution of [PPh4
][(HC(3,5-Me2Pz)3)FeII(CN)3] PPhþ4 1ꢁ (0.283 g, 0.367 mmol)
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A
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