Ni3versus Ni30: A Truncated Octahedron Metal–Organic Cage Constructed with [Ni5(CN)4]6+Squares and Tripodal Tris-tacn Ligands That are Large and Flexible

Article abstract of DOI:10.1002/chem.201604598

Reactions of trinickel complex of tripodal tris-tacn ligand N(CH₂-m-C₆H₄-CH₂tacn)₃(L, tacn=1,4,7-triazacyclononane) in acetonitrile–methanol solution with and without phosphate led to two complexes of distinct nuclearities, [(Ni^IICl)₃(CH₃OH)₃(HPO₄)L](PF₆) (Ni₃, 1) and [(Ni^II₅(CN)₄(H₂O)₈Cl)₆L₈]Cl₃₀(Ni₃₀, 2). Ligand L takes upward and downward conformation in the structure of 1 and 2, respectively. It is proposed that phosphate directs the upward conformation of Ni₃L to form 1. In the absence of phosphate, Ni₃L assembles with cyanide ions, which are formed by Ni-catalyzed C?CN bond cleavage of acetonitrile, to give a nano-sized Ni₃₀cage. Complex 2 represents a discrete truncated octahedron cage assembled with [Ni₅(CN)₄]⁶⁺squares and large and flexible triangular ligands, which is scarcely observed for self-assembled metal-organic cages. The magnetic properties of 1 and 2 were examined, showing intriguing magnetic properties.

Full text of DOI:10.1002/chem.201604598

A Journal of
Accepted Article
Title: Ni3 vs Ni30. A Truncated Octahedron Metal-Organic Cage
Constructed with [Ni5(CN)4]6+ Squares and Tripodal Tris-tacn
Ligands that are Large and Flexible
Authors: Zongyao Zhang, Kunyi Zheng, Tianlong Xia, Lijin Xu, and Rui
Cao
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Ni3 vs Ni30. A Truncated Octahedron Metal-Organic Cage
Constructed with [Ni5(CN)4]6+ Squares and Tripodal Tris-tacn
Ligands that are Large and Flexible**
Zongyao Zhang, Kunyi Zheng, Tianlong Xia, Lijin Xu, and Rui Cao*
Abstract: Reactions of trinickel complex of tripodal tris-tacn ligand
N(CH2-m-C6H4-CH2tacn)3 (L, tacn = 1,4,7-triazacyclononane) in
acetonitrile-methanol solution with and without phosphate led to two
complexes of distinct nuclearities, [(NiIICl)3(CH3OH)3(HPO4)L](PF6)
Recently, Cao and Lippard designed a series of multidentate
tripodal ligands using the tribenzylamine scaffold functionalizing
either its ortho or meta position with different ligand
appendages.[26-29] The resulted trinuclear metal complexes have
been shown to be able to capture biologically relevant μ3-
oxoanions, such as phosphate and carbonate, and effectively
catalyze the hydrolysis of phosphate esters. In the course of
exploring this ligand system, we found that such tris(xylyl) linker
arms are highly flexible, and ligands functionalizing at the meta
positions have various conformations. For example, Scheme 1
displays the two conformers of tripodal tris-tacn ligand N(CH2-m-
C6H4-CH2tacn)3 (L, tacn = 1,4,7-triazacyclononane) with three
arms pointing to either upward or downward direction. The
upward conformer was observed in μ3-oxoanion-directed
assembly of M3L (M = Mn, Cu, or Zn),[26] but attempts to
structurally determine the downward conformer of L and its
metal complexes were unsuccessful largely due to the high
flexibility of the ligand.
(Ni3, 1) and [(NiII (CN)4(H2O)8Cl)6L8]Cl30 (Ni30, 2). Ligand L takes
5
upward and downward conformation in the structure of 1 and 2,
respectively. It is proposed that phosphate directs the upward
conformation of Ni3L to form 1. In the absence of phosphate, Ni3L
assembles with cyanide ions, which are formed via Ni-catalyzed
C−CN bond cleavage of acetonitrile, to give nano-sized Ni30 cage.
Complex
2 represents a discrete truncated octahedron cage
assembled with [Ni5(CN)4]6+ squares and large and flexible triangular
ligands, which is scarcely observed for self-assembled metal-organic
cages. Magnetic properties of 1 and 2 were examined, showing
intriguing magnetic properties.
Self-assembled metal-organic coordination cages have attracted
extensive research interests because of their intrinsic structural
features and their potential applications in host-guest chemistry
and material science.[1-12] The construction of metal-organic
cages is realized by the self-assembly of metal ions or metal
clusters typically occupying the vertexes of
a
discrete
polyhedron and organic ligands linking them as either the edges
or the faces of the polyhedron. Recent efforts have resulted in a
variety of coordination cages with single metal ions,[13-18] M2,[19-21]
Scheme 1. Schematic representation showing the upward and downward
conformations of ligand L. The downward conformer is thermodynamically
more favored due to the less steric hindrance between three bulky ligand arms.
[22-25]
and M4
metal clusters acting as vertexes, but cages with
vertexes of higher nuclearity metal clusters are very rare. On the
other hand, rigid linear/bent or facial ligands with preorganized
binding angles are usually required for the assembly of cages
because ligands of flexible conformation and binding ability
generally result in mixed coordination species.[8] Therefore,
molecular metal-organic cages using building blocks of high-
nuclearity metal clusters as vertexes and flexible ligands as
linkages are scarcely reported in the literature.
Herein we reported the synthesis and X-ray structures of two
nickel complexes of L with distinct nuclearities. Reactions of L
and NiCl2 in acetonitrile-methanol solutions with and without
phosphate led to Ni3 complex 1 and Ni30 complex 2, respectively
(Scheme 2). Similar to our previous results, phosphate directs
the upward conformation of Ni3L to give 1. Unexpectedly, in the
absence of phosphate, a nano-sized Ni30 cage 2 was formed
through the assembly of downward Ni3L with in situ generated
cyanide ions. The truncated octahedron cage of 2 is unique as it
is constructed with pentanuclear [Ni5(CN)4]6+ squares and large
and flexible ligand L triangles. Magnetic properties of 1 and 2
were also examined, showing intriguing magnetic properties.
Reaction of three equivalents of NiCl2 with one equiv. of L in
an acetonitrile-methanol mixture gave a clear light green solution
at room temperature. After addition of one equiv. of Na2HPO4
and stirring the mixture at 60 °C for 6 h, an excess amount of
solid NH4PF6 was added. Slow evaporation of the resulted
solution led to the isolation of green crystals of 1 in 66% yield.
Crystallographic studies revealed that 1 was analogue to the
trimetallic complexes we reported previously (Scheme 2 and
[*]
Z. Y. Zhang, K. Y. Zheng, Prof. Dr. L. J. Xu, Prof. Dr. R. Cao
Department of Chemistry
Renmin University of China, Beijing 100872 (China)
E-mail: ruicao@ruc.edu.cn
Prof. Dr. R. Cao
School of Chemistry and Chemical Engineering
Shaanxi Normal University, Xi’an 710119 (China)
Prof. Dr. T. L. Xia
Department of Physics
Renmin University of China, Beijing 100872 (China)
We are grateful for support from the “Thousand Talents Program” of
China, the National Natural Science Foundation of China (No.
21101170 and 21573139), the Fundamental Research Funds for the
Central Universities, and the Research Funds of Renmin University
of China.
[**]
Figure 1A).[26] It crystallizes in the trigonal space group R
a = 15.5930(9) Å, c = 78.327(9) Å, V = 16493(2) Å3, and Z =
3
c with
Supporting information for this article is available on the WWW
under
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10.1002/chem.201604598
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12.[30] The trinickel unit of 1 is located at the special position with
a crystallographically required C3 axis passing through the
central N atom (N1) and μ3-phosphate group (P1, O2). The three
symmetric tacn-based ligand arms each bind one NiII atom
through three N atoms. The three Ni atoms are bridged together
by a phosphate group with each Ni binding to one of the three
facial O atoms, resulting in a Ni···Ni separation of 5.499 Å. The
distorted octahedral coordination sphere of each Ni is filled by a
terminal chloride and a methanol group (Figure 1B).
thermodynamically more stable due the less steric hindrance
between the three bulky ligand arms.[26] This result is therefore
another example illustrating the templating effect of phosphate in
the tris(xylyl) trimetallic system.
Significantly, reaction of NiCl2 and L in acetonitrile-methanol
solution without the addition of Na2HPO4 gave Ni30 complex 2,
whose structure was unexpected (Scheme 2). After heating and
stirring the reaction mixture at 60 °C for 6 h, the clear light green
solution gradually turned to purple. During slow evaporation, this
solution became more intensely purple colored, and finally led to
the isolation of violet crystalline prisms of 2 in 3 weeks with a
moderate yield (see Supporting Information for details).
Crystallographic studies revealed that complex 2 crystallized
in the tetragonal space group I4 with a = 32.4457(15) Å, c =
29.6336(13) Å, V = 31196(2) Å3, and Z = 2.[30] The discrete
coordination cage of 2 consists of 30 Ni atoms, 24 cyanide ions,
8 tris-tacn ligand L, 6 chloride ions, and 48 aqua groups, which
together afford a nano-sized molecular cage of 30 Å in diameter
(Figure 2A). This Ni30 cage is located at a special position with
the crystallographically required C4 axis passing through the Cl1-
Ni6-Ni9-Cl1 axis, and it can be in principle viewed as a truncated
octahedron[31,32] with six [Ni5(CN)4]6+ squares occupying the
vertexes and eight tripodal L ligands linking them as the faces of
the octahedron (Figure 2B and 2D). For each [Ni5(CN)4]6+ square,
four Ni atoms reside at the four corners of a square planar, and
they are bridged together through a μ4-Ni(CN)4 unit (Figure 2C).
For μ2-η1,η1-groups linking the central and corner Ni atoms, we
assigned them as cyanide ions based on (1) they are two-atom
units with a linear bridging mode and (2) the bond lengths of
1.154(13) Å (by average) between the two atoms are very short.
All these results are consistent with triply-bonded groups. As it is
not likely to form C≡C groups under the synthetic conditions, we
assigned them as cyanide ions, which could be generated in situ
via Ni-catalyzed C−CN bond cleavage of acetonitrile. Such bond
activations have been investigated in detail by Jones and co-
workers experimentally and theoretically, who demonstrated that
Ni complexes were able to catalyze the C−CN bond cleavage of
various organic nitrile complexes.[33-35]
Scheme 2. Synthesis of Ni3 complex 1 and Ni30 complex 2 from the reaction of
Ni3L with and without phosphate ions in acetonitrile-methanol solutions.
The central Ni atom is coordinated by four cyanide ions via
the C atoms and is bound to an additional axial chloride ligand,
giving a square pyramid geometry. The average Ni−C distance
is 1.858(12) Å, and the average Ni−Cl distance is 2.856(15) Å.
Based on comparison of this Ni−C distance to many others
reported in [Ni(CN)4]2− units,[36] this Ni atom has a d8 NiII
electronic structure. The average C−Ni−C bond angle of 89.78°
shows that the Ni atom is located almost perfectly at the center
of the square planar. For the four corner Ni atoms, each is
coordinated by a tacn moiety of the ligand arm through three N
atoms, and is bound to the N atom of the bridging cyanide group.
The octahedral coordination geometry of these corner Ni atoms
is filled by two additional aqua ligands. BVS calculation of 2.29
suggests d8 NiII electronic structures for these corner Ni atoms.
Two points are worth noting. First, the average Ni−O bond
length of 2.102(11) Å (with the range of 2.038(11) to 2.128(8) Å)
is consistent with terminal aqua ligands instead of terminal
hydroxyl ligands, as Ni−OH bond lengths are typically smaller
than 1.90 Å.[37] The Ni−O bond is calculated to contribute BVS of
only 0.28-0.35 to these O atoms. Second, the shorter Ni−CN
distance of 1.858(12) Å and the longer Ni−NC distance of
Figure 1. (A) Thermal ellipsoid plot (50% probability) of the X-ray structure of
1. All hydrogen atoms are omitted for clarity. (B) Ball-and-stick representation
of the [Ni3(PO4)] coordination environment. Color code: green, nickel; light
green, chlorine; grey, carbon; blue, nitrogen; red, oxygen; pink, phosphorus.
In the structure of 1, the triply bridging phosphate group is
disordered over two opposite orientations with 80% pointing into
the inner cavity of the molecular backbone and the rest 20%
pointing out of the inner cavity as determined by free structural
refinement. The fourth, uncoordinated O atom (O2) of phosphate
is protonated, which is suggested by long P1−O2 bond distance
of 1.599(6) Å as compared to short P1−O1 bond distance of
1.479(3) Å. Bond valence sum (BVS) calculation also suggested
that the P1−O2 bond only contributed BVS of 1.01 to this O2
atom. In addition, in the X-ray structure of 1, one PF6− counterion
per trinickel unit was found, further confirming the
monoprotonation of O2 atom. The three ligand arms of L adopt a
upward orientation to capture the [Ni3(HPO4)]4+ unit. As we
demonstrated previously, the downward conformer is
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2.048(13) Å further confirm the X-ray structure assignment that
the bridging cyanide ions bind to the central and corner Ni atoms
via C and N atoms, respectively.[36]
that NiII ions have strong binding affinity with cyanide ions. As a
result, Ni-cyanide species with extended structures are easily
formed, which are highly challenging to be isolated and
crystallized. The use of multidentate capping ligands, such as
tacn, is considered to prevent the growth of extended structures
and thus is beneficial for the isolation of complex 2 in our
experiments. On the other hand, we also tried to synthesize
complex 2 starting from NiCl2, ligand L and K2[Ni(CN)4].
However, precipitates immediately appeared upon mixing with
K2[Ni(CN)4], which is consistent with the formation of insoluble
Ni-cyanide
species
with
extended
structures
(i.e.
−Ni−C≡N−Ni−N≡C−Ni−). We rationalized that during the
synthesis of 2 under our experimental conditions, cyanide ions
were gradually generated in situ through Ni-catalyzed C−CN
bond cleavage of acetonitrile.[33-35] The generation of cyanide
ions and their assembly with NiII ions and L ligands to form 2 are
concomitant, which prevents the accumulation of cyanide ions in
the reaction mixture. It is therefore considered to be another
reason for the successful isolation of 2. Third, [Ni5(CN)4]6+ unit
has a 4-fold rotational symmetry, while tripodal ligand L has a 3-
fold rotational symmetry. The combination of these two
symmetry elements is essential for the formation of truncated
octahedron cages (Figure 2D). It is necessary to note that ligand
L is large and flexible, and is in principle not favored to be used
for the self-assembly of coordination metal-organic cages.
Figure 2. (A) Thermal ellipsoid plot (50% probability) of the X-ray structure of
2. All hydrogen atoms and chloride ions are omitted for clarity. (B) Schematic
representation of the molecular structure of 2 with an octahedron geometry.
(C) Ball-and-stick illustration of the [Ni5(CN)4]6+ coordination environment. (D)
The assembly of truncated octahedron by [Ni5(CN)4]6+ squares and L ligands.
Color code: green, nickel; light green, chlorine; grey, carbon; blue, nitrogen;
red, oxygen.
Therefore, symmetry-directed assembly is also a possible
reason for the formation of 2. Although complex 2 was obtained
unexpectedly, it is unique to represent a discrete truncated
octahedron cage having [Ni5(CN)4]6+ squares as vertexes and
large and flexible tripodal L ligands linking them as the faces of
the polyhedron.
It is interesting to compare the synthesis and structure of 1
and 2. The only difference in the synthesis of 1 and 2 is the
presence or absence of phosphate ions. As we demonstrated
previously, ligand L has various conformations with upward and
downward conformers depicted in Scheme 1.[26] The templating
effect of phosphate directed the formation of 1, which resembles
several trimetallic complexes of L we reported before. The large
In [Ni5(CN)4]6+ squares, the average Ni(corner)···Ni(central)
separation is 5.046 Å, and the average Ni(corner)···Ni(corner)
separation is 7.066 Å. In the X-ray structure of 2, 36 chloride
ions were found. Six of them bind to the six central Ni atoms,
and the rest are found as counter ions in the crystal lattice.
Based on crystallographic studies, molecular formula of 2 can be
2−
binding constant of HPO4 with Ni3L, which was determined to
unambiguously determined to be [(NiII (CN)4(H2O)8Cl)6L8]Cl30. In
be 3.15×105 M−1 (Figure S3), was the possible driving force for L
to adopt thermodynamically less favorable upward conformation.
In the absence of phosphate, L takes downward conformation,
and Ni3L assembles with in situ generated cyanide ions to give 2.
In our work, the mild reaction conditions, compared with high-
pressure, high-temperature solvothermal conditions, has also
brought new examples for building up large metal-organic cages.
Transition metal-cyanide clusters have recently attracted
particular research interests due to their magnetic properties.[38-
41] We therefore investigated the magnetism of complexes 1 and
2. The temperature dependence of magnetic susceptibility of 1
and 2 were measured in 2.5-300 K with an applied field of 100
Oe. The MT value of 1 at 300 K is about 3.6 cm3 mol−1 K, which
is larger than the spin only value of three isolated NiII ions with S
= 1 (3.0 cm3 mol−1 K). As shown in Figure 3A, the susceptibility
exhibits a monotonic rise in MT with decreasing temperature,
suggesting the ferromagnetic coupling between NiII ions. At low
temperature, MT value approaches 4.1 cm3 mol−1 K, which is
slightly higher than the theoretical value of 3.9 cm3 mol−1 K for
an S = 3 ground state of NiII (3F4, g = 5/4). The MT value of 2 at
5
addition, a number of co-crystallized solvent water molecules
were also found in the X-ray structure. Interestingly, molecules
of 2 form one-dimensional chains in X-ray crystal structure along
the c axis through intermolecular Ni6−Cl1−Ni9 interactions with
Ni6−Cl1 bond distance of 2.903(6) Å and Ni9−Cl1 bond distance
of 2.928(6) Å (Figure S4). In addition, unlike 1, the tris-tacn
ligand L in 2 adopts the downward conformation. This relatively
more spread geometry makes the three Ni atoms bound to the
same ligand L to have Ni···Ni separation about 15 Å, which is
much larger than the Ni···Ni separation of 5.499 Å as observed
in the structure of 1. It is necessary to note that no chloride ions
and/or solvent water molecules are found in the inner cavity of 2,
although it is positively charged and its outside diameter is about
30 Å. We rationalize that the inner cavity of 2 has only a small
size of 5.4×5.4×5.4 Å3, which is likely due to the bulky ligand L.
Although [Ni5(CN)4]6+ units have been reported in
literature,[36] to the best of our knowledge, complex 2 represents
the first example bearing such [Ni5(CN)4]6+ squares as vertexes
of cage-like coordination polyhedrons. Possible explanation is
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300 K is about 20.0 cm3 mol−1 K (Figure 3B), which is much
smaller than the spin only values of 30 isolated NiII ions with S =
1 (30.0 cm3 mol−1 K). As we know, the degeneracy of Landau
levels of the central NiII ions will be lifted within square planar
crystal field, which results in the central NiII ions with effective S
= 0. As a result, the number of NiII ions contributing magnetic
moment is 24, instead of 30 as intuitively thought. The curve
between 50 and 300 K is well described by Curie-Weiss law with
Curie constant C = 19.7 cm3 mol−1 K, which is obtained by linear
fit of temperature dependent M−1. The value of the Weiss
temperature near zero and the curvature of MT clearly indicate
the paramagnetism of 2. When temperature decreases, MT
approaches 13.5 cm3 mol−1 K, which may be attributed to the
zero field splitting.
[6]
[7]
[8]
S. Horiuchi, T. Murase, M. Fujita, J. Am. Chem. Soc. 2011, 133, 12445-
12447.
N. Rodríguez-Vázquez, M. Amorín, I. Alfonso, J. R. Granja, Angew.
Chem. Int. Ed. 2016, 55, 4504-4508.
C. Gütz, R. Hovorka, C. Klein, Q. Q. Jiang, C. Bannwarth, M. Engeser,
C. Schmuck, W. Assenmacher, W. Mader, F. Topić, K. Rissanen, S.
Grimme, A. Lützen, Angew. Chem. Int. Ed. 2014, 53, 1693-1698.
R. M. Zhu, J. Lübben, B. Dittrich, G. H. Clever, Angew. Chem. Int. Ed.
2015, 54, 2796-2800.
[9]
[10] M. Kieffer, B. S. Pilgrim, T. K. Ronson, D. A. Roberts, M. Aleksanyan, J.
R. Nitschke, J. Am. Chem. Soc. 2016, 138, 6813-6821.
[11] J. Park, L. B. Sun, Y. P. Chen, Z. Perry, H. C. Zhou, Angew. Chem. Int.
Ed. 2014, 53, 5842-5846.
[12] P. D. Frischmann, V. Kunz, F. Würthner, Angew. Chem. Int. Ed. 2015,
54, 7285-7289.
[13] X. P. Zhou, J. Liu, S. Z. Zhan, J. R. Yang, D. Li, K. M. Ng, R. W. Y. Sun,
C. M. Che, J. Am. Chem. Soc. 2012, 134, 8042-8045.
[14] Y. R. Zheng, W. J. Lan, M. Wang, T. R. Cook, P. J. Stang, J. Am.
Chem. Soc. 2011, 133, 17045-17055.
[15] D. Fujita, H. Yokoyama, Y. Ueda, S. Sato, M. Fujita, Angew. Chem. Int.
Ed. 2015, 54, 155-158.
[16] N. Kishi, M. Akita, M. Yoshizawa, Angew. Chem. Int. Ed. 2014, 53,
3604-3607.
[17] D. M. Wood, W. J. Meng, T. K. Ronson, A. R. Stefankiewicz, J. K. M.
Sanders, J. R. Nitschke, Angew. Chem. Int. Ed. 2015, 54, 3988-3992.
[18] W. J. Ramsay, F. T. Szczypiński, H. Weissman, T. K. Ronson, M. M. J.
Smulders, B. Rybtchinski, J. R. Nitschke, Angew. Chem. Int. Ed. 2015,
54, 5636-5640.
−1
Figure 3. Plots of temperature dependence of χMT and χM for complexes 1
(A) and 2 (B).
[19] D. Tian, Q. Chen, Y. Li, Y. H. Zhang, Z. Chang, X. H. Bu, Angew. Chem.
Int. Ed. 2014, 53, 837-841.
In conclusion, we reported two nickel complexes of distinct
nuclearities with the use of tripodal tris-tacn ligand L. The Ni3
complex 1 resembles the trimetallic complexes we reported
recently, in which a biologically relevant [M3(PO4)] core is kept
within the backbone of L. The Ni30 complex 2 can be viewed as
a nano-sized cage of truncated octahedron with six [Ni5(CN)4]6+
squares occupying the vertexes and eight L ligands linking them
as the faces of the octahedron. Various conformations of L and
the templating effect of phosphate are the origins to form these
different products under similar synthetic conditions. Although
complex 2 is obtained unexpectedly, it is noteworthy in several
aspects, including (1) cyanide ions are generated in situ under
mild reaction conditions, and the direct use of [Ni(CN)4]2− for the
assembly of 2 is unsuccessful; (2) complex 2 represents the first
example to have pentanuclear M5 building blocks as vertexes
and lagre and flexible ligands as linkages of polyhedrons; (3)
symmetry-directed assembly of C4-symmetry [Ni5(CN)4]6+
squares and C3-symmetry L ligands is a possible reason for the
formation of 2. Magnetic studies revealed the ferromagnetism of
1 and the paramagnetism of 2.
[20] M. J. Prakash, M. Oh, X. F. Liu, K. N. Han, G. H. Seong, M. S. Lah,
Chem. Commun. 2010, 46, 2049-2051.
[21] X. S. Wang, M. Chrzanowski, W. Y. Gao, L. Wojtas, Y. S. Chen, M. J.
Zaworotko, S. Q. Ma, Chem. Sci. 2012, 3, 2823-2827.
[22] K. C. Xiong, F. L. Jiang, Y. L. Gai, D. Q. Yuan, D. Han, J. Ma, S. Q.
Zhang, M. C. Hong, Chem. Eur. J. 2012, 18, 5536-5540.
[23] K. C. Xiong, F. L. Jiang, Y. L. Gai, D. Q. Yuan, L. Chen, M. Y. Wu, K. Z.
Su, M. C. Hong, Chem. Sci. 2012, 3, 2321-2325.
[24] M. Liu, W. P. Liao, C. H. Hu, S. C. Du, H. J. Zhang, Angew. Chem. Int.
Ed. 2012, 51, 1585-1588.
[25] X. X. Hang, B. Liu, X. F. Zhu, S. T. Wang, H. T. Han, W. P. Liao, Y. L.
Liu, C. H. Hu, J. Am. Chem. Soc. 2016, 138, 2969-2972.
[26] R. Cao, P. Müller, S. J. Lippard, J. Am. Chem. Soc. 2010, 132, 17366-
17369.
[27] R. Cao, B. D. McCarthy, S. J. Lippard, Inorg. Chem. 2011, 50, 9499-
9507.
[28] X. Liu, P. W. Du, R. Cao, Nat. Commun. 2013, 4, 2375.
[29] Y. Y. Ning, M. Gao, K. Y. Zheng, Z. Y. Zhang, J. Zhou, X. Hao, R. Cao,
J. Mol. Catal. A: Chem. 2015, 403, 43-51.
II
3
[30] Crystal data for 1: [(Ni Cl)3(CH3OH)3(HPO4)L](PF6), trigonal, R c, a =
15.5930(9) Å, c = 78.327(9) Å, V = 16493(2) Å3, Z = 12, T = 153(2) K,
38917 reflections collected, 3788 unique (Rint = 0.0332), final R1
=
0.0606, wR2 = 0.1703 for 3207 observed reflections [I > 2σ(I)]. Crystal
data for 2, [(NiII5(CN)4(H2O)8Cl)6L8]Cl30, tetragonal, I4, a = 32.4457(15)
Å, c = 29.6336(13) Å, V = 31196(2) Å3, Z = 2, T = 150(2) K, 299083
reflections collected, 32064 unique (Rint = 0.0810), final R1 = 0.1069,
wR2 = 0.2756 for 22399 observed reflections [I > 2σ(I)]. CCDC 1492717
(1) and 1492718 (2) contain the supplementary X-ray data for this
paper. These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[31] M. C. Hong, Y. J. Zhao, W. P. Su, R. Cao, M. Fujita, Z. Y. Zhou, A. S. C.
Chan, J. Am. Chem. Soc. 2000, 122, 4819-4820.
Keywords: self-assembly • tripodal ligand • nickel • coordination
cage • flexible
[1]
[2]
A. J. McConnell, C. S. Wood, P. P. Neelakandan, J. R. Nitschke, Chem.
Rev. 2015, 115, 7729-7793.
L. Chen, Q. H. Chen, M. Y. Wu, F. L. Jiang, M. C. Hong, Acc. Chem.
Res. 2015, 48, 201-210.
[3]
[4]
[5]
A. Galan, P. Ballester, Chem. Soc. Rev. 2016, 45, 1720-1737.
M. D. Ward, Chem. Commun. 2009, 4487-4499.
Y. Fang, T. Murase, S. Sato, M. Fujita, J. Am. Chem. Soc. 2013, 135,
613-615.
[32] N. Li, F. L. Jiang, L. Chen, X. J. Li, Q. H. Chen, M. C. Hong, Chem.
Commun. 2011, 47, 2327-2329.
[33] N. M. Brunkan, D. M. Brestensky, W. D. Jones, J. Am. Chem. Soc.
2004, 126, 3627-3641.
This article is protected by copyright. All rights reserved.

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[34] T. A. Ateşin, T. Li, S. Lachaize, W. W. Brennessel, J. J. García, W. D.
Jones, J. Am. Chem. Soc. 2007, 129, 7562-7569.
[35] B. D. Swartz, N. M. Reinartz, W. W. Brennessel, J. J. García, W. D.
Jones, J. Am. Chem. Soc. 2008, 130, 8548-8554.
[36] F. Meyer, R. F. Winter, E. Kaifer, Inorg. Chem. 2001, 40, 4597-4603.
[37] D. G. Huang, O. V. Makhlynets, L. L. Tan, S. C. Lee, E. V. Rybak-
Akimova, R. H. Holm, Proc. Natl. Acad. Sci. USA 2011, 108, 1222-1227.
[38] M. P. Shores, J. J. Sokol, J. R. Long, J. Am. Chem. Soc. 2002, 124,
2279-2292.
[39] D. E. Freedman, D. M. Jenkins, A. T. Iavarone, J. R. Long, J. Am.
Chem. Soc. 2008, 130, 2884-2885.
[40] D. Pinkowicz, H. Southerland, X. Y. Wang, K. R. Dunbar, J. Am. Chem.
Soc. 2014, 136, 9922-9924.
[41] S. Chorazy, R. Podgajny, K. Nakabayashi, J. Stanek, M. Rams, B.
Sieklucka, S. Ohkoshi, Angew. Chem. Int. Ed. 2015, 54, 5093-5097.
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Entry for the Table of Contents
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Zongyao Zhang, Kunyi Zheng, Tianlong
Xia, Lijin Xu, and Rui Cao*
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Page No. – Page No.
Ni3 vs Ni30. A Truncated Octahedron
Metal-Organic Cage Constructed with
[Ni5(CN)4]6+ Squares and Tripodal
Tris-tacn Ligands that are Large and
Flexible
Unique coordination cage: Trinickel complex of tripodal tris-tacn ligand assembles
with cyanide ions, which are formed in situ via Ni-catalyzed C−CN bond cleavage of
acetonitrile, to give a nano-sized Ni30 cage under mild conditions. This molecular
cage is unique because it represents a discrete truncated octahedron assembled
with pentanuclear [Ni5(CN)4]6+ squares and large and flexible triangular tris-tacn
ligands, which has been scarcely observed for self-assembled metal-organic cages.
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