et al.

ferent structures rather than the expansion of ring
sizes in the channels. In this study, we used the
zinc-gallium bimetallic system and found that
increasing the template from 4C-containing (4C´)
butylamine to 6C´ hexylamine was sufficient to
enlarge the channel sizes from 24R to 28R, creating
28R-NTHU-13 with a channel diameter exceeding
1 nm (Table 1). In subsequent reactions
[table S2 (26)], the use of longer amine (8C´
octylamine, 10C´ decylamine, or 12C´ dodecylamine)
created the larger ring products 40R- and
48R-NTHU-13, respectively. The use of 14C´
tetradecylamine, 16C´ hexadecylamine, and 18C´
octadecylamine led to the synthesis of 56R-
NTHU-13, 64R-NTHU-13, and 72R-NTHU-13
in which pore sizes were as large as 3.5 nm
(Table 1).
We used single-crystal x-ray diffraction to
characterize all six structures in the NTHU-13
family (figs. S1 to S10 and table S3). Four channels
were determined in the unit cells for 40R-,
48R-, 56R-, 64R-, and 72R-NTHU-13 (Fig. 1A),
and eight channels were found in the orthorhombic
cell for 28R-NTHU-13 (fig. S3). Except for
the latter, the channel walls were constructed exclusively
from the following three building blocks:
anionic chains of ∞[GaF(HPO 3) 2] 2– (block A),
neutral chains of ∞[Zn(HPO3)] (block B), and an
anionic trimeric cluster of [Zn(HPO 3) 2(H 2O) 4] 2–
(block C) (Fig. 2). Block A was located at the
four corners of the square-shaped channels (Fig.
2A); both A and C were linked only to B and
were never adjacent. A generalized formula of
[A(BC)nBA] describes the stoichiometry and connectivity
of the four faces or edges of the inorganic
walls: n = 1 for each face or edge of the
40R channel, n = 2 for the 56R channel, and n =3
for the 72R channel. When n = 0, the corresponding
channel face is ABA and is observed to
form 24R channels. Hence, the 40R, 56R, and
72R square-windowed channels can be viewed
as the systematic expansion of the 24R channel
by inserting one or more BC pairs as the proliferation
unit (Fig. 2B). The rectangular-windowed
48R and 64R channels contain two mixed n values
(n and n + 1) to describe the shorter and
longer window edges (Table 1 and table S4). An
increase of one BC pair would add four polyhedra
to each channel edge, leading to an expansion
by 16 rings for square-windowed channels (24R
to 40R; 40R to 56R; 56R to 72R) and 8 rings for
rectangular-windowed channels (40R to 48R; 48R
to 56R; 56R to 64R; 64R to 72R).
For each 8-ring expansion, there was an approximate
0.8-nm increase in the channel diameter
and an ~18 Å increase in the unit cell length
(Table 1) in addition to a periodic change in the
wall structure symmetry. As illustrated in Fig. 3,
the wall structure shows 2/m symmetry along a
(or b)whenn = 1 (or for odd numbers); however,
2/c symmetry is observed when n = 2 (or for even
numbers). These results explain why both 40Rand
72R-NTHU-13 are in the I41/amd space group,
56R-NTHU-13 belongs in space group I4 1/acd,
and the orthorhombic 48R- and 64R-NTHU-13
possess both the m and c glide planes in their
space group symmetry. Notably, each BC pair
incorporates additional zinc ions and phosphite
groups into the framework at a fixed 5:6 ratio,
which causes the Ga concentration to decrease as
the channels are expanded. The heterometal centers
of Ga 3+ provide the NTHU-13 family with a
key structural component: block A. When n = ∞,
the NTHU-13 system would reach a maximum
M/P value of 5/6 (where M is the total number of
Zn and Ga centers, and P is the number of phosphite
groups) and would form lamellar structures.
The 56R and 72R channels (with free diameters
of 2.52 nm and 3.5 nm, respectively) are
in the mesopore regime, which is a mesoporous
framework with tetragonal symmetry showing
regularly spaced inorganic channels with ordered
wall structures at the atomic level (27). Among
all reported crystalline inorganic frameworks to
date, 72R-NTHU-13 possesses the lowest framework
density (5.28) and the highest nonframework
volume (75.7%) (table S1). The channel
space was partially occupied by organized assemblies
of monoprotonated amine molecules
(~50%) with a density near that of the pure
molecular liquid or solid state (Table 1). The templates
were distributed quite near the inorganic
wall with their ammonium heads pointing primarily
toward the negatively charged blocks A
and C (and are also likely to contain hydrogen
bonds, because the closest N … O distances were
observed to fall in the range of 2.83 to 2.90 Å).
Their long carbon chain skeletons were disordered
and pointed toward the hydrophobic region of the
channel centers (fig. S9). Within each of the 56R,
64R, or 72R channels per unit cell, there exist 16,
18, or 20 monoprotonated template-amine molecules.
Elemental analysis data (table S5) and
solid-state nuclear magnetic resonance studies
using 1 H, 13 C, and 19 F confirmed the content of
the organic templates and the presence of fluoride
(figs. S11 to S13).
Thermogravimetric analysis (fig. S14) combined
with variable-temperature powder x-ray
diffraction measurements (fig. S15) were used to
determine the thermal stability of 40R-, 48R-,
and 56R-NTHU-13, which were thermally stable
up to 175°C. When transparent colorless crystals
of 40R-NTHU-13 were treated with 0.05 M
parafuchsin hydrochloride (in ethanol), the
crystals changed to a pink color (fig. S16), which
indicates that the dye molecules were adsorbed.
Cs + ion exchange was performed by treating powder
samples of 40R- and 48R-NTHU-13 with a
0.01 M CsCl ethanol solution, and positive results
were confirmed by x-ray fluorescence data
in combination with powder x-ray diffraction
measurements (table S6 and fig. S17). The empty
space inside the channels was detected even in
the presence of the residual templates, as indicated
by preliminary results from gas adsorption
measurements performed on 56R-NTHU-13 samples
(fig. S18).
Relative to the aluminosilicates, the crystals
of NTHU-13 are less robust in nature, and so far
have not yet shown impressive conventional porerelated
properties such as gas sorption (the maximum
CO2 uptake of 56R-NTHU-13 at 1 atm is
0.32 mmol/g; see figs. S18 and S19). However,
very large inorganic channels may display unexpected
properties such as pore-related photoluminescence,
as we previously reported (5–7). When the
40R channel framework was successfully doped
with Mn 2+ ions, an unusual broad band of nearly
white light emission under ultraviolet excitation was
displayed by the resultant Mn@40R-NTHU-13
(fig. S20). Thus, the host lattice of 40R-NTHU-13
revealed the ability to create a white-light phosphor
from single-activator doping.
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Acknowledgments: Supported by National Science
Council of Taiwan grants NSC100-2113-M-007-016-MY3,
NSC101-2113-M-033-007-MY3, and NSC101-2113-M-008-006-MY3.
X.B. was supported by NSF grant DMR-0846958. Crystallographic
data for the reported crystal structures have been deposited
at the Cambridge Crystallographic Data Centre with
codes 892384–892387 and 915187–915191.
Supplementary Materials
www.sciencemag.org/cgi/content/full/339/6121/811/DC1
Materials and Methods
Figs. S1 to S20
Tables S1 to S6
References (29–36)
29 October 2012; accepted 14 December 2012
10.1126/science.1232097
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