Fluorous Metal–Organic Frameworks and Nonporous Coordination Polymers as Low-κ Dielectrics

Article abstract of DOI:10.1002/adfm.201904707

A fluorous metal–organic framework [Cu(FBTB)(DMF)] (FMOF-3) [H₂FBTB = 1,4-bis(1-H-tetrazol-5-yl)tetrafluorobenzene] and fluorous nonporous coordination polymer [Ag₂(FBTB)] (FN-PCP-1) are synthesized and characterized as for their structural, thermal, and textural properties. Together with the corresponding nonfluorinated analogues lc-[Cu(BTB)(DMF)] and [Ag₂(BTB)], and two known (super)hydrophobic MOFs, FMOF-1 and ZIF-8, they have been investigated as low-dielectric constant (low-κ) materials under dry and humid conditions. The results show that substitution of hydrogen with fluorine or fluoroalkyl groups on the organic linker imparts higher hydrophobicity and lower polarizability to the overall material. Pellets of FMOF-1, FMOF-3, and FN-PCP-1 exhibit κ values of 1.63(1), 2.44(3), and 2.57(3) at 2 × 10⁶ Hz, respectively, under ambient conditions, versus 2.94(8) and 3.79(1) for lc-[Cu(BTB)(DMF)] and [Ag₂(BTB)], respectively. Such low-κ values persist even upon exposure to almost saturated humidity levels. Correcting for the experimental pellet density, the intrinsic κ for FMOF-1 reaches the remarkably low value of 1.28, the lowest value known to date for a hydrophobic material.

Full text of DOI:10.1002/adfm.201904707

FULL PAPER
Nonporous Coordination Polymers
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Fluorous Metal–Organic Frameworks and Nonporous
Coordination Polymers as Low-κ Dielectrics
Simona Galli,* Alessandro Cimino, Joshua F. Ivy, Carlotta Giacobbe, Ravi K. Arvapally,
Rebecca Vismara, Stefano Checchia, Mustafa A. Rawshdeh, Christian T. Cardenas,
Waleed K. Yaseen, Angelo Maspero, and Mohammad A. Omary*
1. Introduction
A fluorous metal–organic framework [Cu(FBTB)(DMF)] (FMOF-3)
[H2FBTB = 1,4-bis(1-H-tetrazol-5-yl)tetrafluorobenzene] and fluorous
Due to the increased demand for tran-
sistors with decreased size and higher
nonporous coordination polymer [Ag2(FBTB)] (FN-PCP-1) are synthesized
speed, integrated circuits (ICs) have been
and characterized as for their structural, thermal, and textural properties.
Together with the corresponding nonfluorinated analogues lc-[Cu(BTB)
(DMF)] and [Ag2(BTB)], and two known (super)hydrophobic MOFs,
FMOF-1 and ZIF-8, they have been investigated as low-dielectric constant
(low-κ) materials under dry and humid conditions. The results show that
substitution of hydrogen with fluorine or fluoroalkyl groups on the organic
linker imparts higher hydrophobicity and lower polarizability to the overall
material. Pellets of FMOF-1, FMOF-3, and FN-PCP-1 exhibit κ values of
1.63(1), 2.44(3), and 2.57(3) at 2 × 106 Hz, respectively, under ambient con-
ditions, versus 2.94(8) and 3.79(1) for lc-[Cu(BTB)(DMF)] and [Ag2(BTB)],
respectively. Such low-κ values persist even upon exposure to almost satu-
rated humidity levels. Correcting for the experimental pellet density, the
intrinsic κ for FMOF-1 reaches the remarkably low value of 1.28, the lowest
value known to date for a hydrophobic material.
progressively improved.[1–5] Typical IC
mean size is on the 10 nm order of mag-
nitude, which has allowed an increase
in microprocessor working frequency to
THz levels. Accompanying this increase
in speed are limiting factors at the con-
ductor–insulator interconnects, such as
signal propagation delay, power dissipa-
tion, and cross-talk noise, which limit
ultralarge-scale integration of ICs.
A
turning point to overcome these draw-
backs was the switch from aluminum to
copper, first realized in a product by IBM
in 1997.[6] The next major step forward
was the replacement of silica [dielectric
constant (κ) ≈ 3.9–4.5[3] depending on the
deposition and processing methods] with
materials showing lower κ. The Interna-
tional Technology Roadmap for Semicon-
ductors (ITRS)[7] set the κ value of low-κ[8] materials for future
chip generations beyond 2016 in the range 2.1−2.5.
In recent years, the quest for low-κ materials as insulators
in ICs has focused on inorganic compounds having bonds of
lower polarizability than Si O bonds and/or lower density
than silica (2.2–2.4 g cm ). Replacement of Si O bonds with
Prof. S. Galli, Dr. A. Cimino, R. Vismara, Prof. A. Maspero
Dipartimento di Scienza e Alta Tecnologia
Università dell’Insubria
Via Valleggio 11, 22100 Como, Italy
E-mail: simona.galli@uninsubria.it

Prof. S. Galli
−3

Consorzio Interuniversitario Nazionale per la Scienza
e Tecnologia dei Materiali
Via Giusti 9, 50121 Firenze, Italy

Si F bonds, as in fluorinated silica glasses, led in 2000 to the
introduction of the first low-κ material into an IC. Overall,
fluorinated silica glasses have shown κ values around 3.6.[1]
Dr. A. Cimino, Dr. J. F. Ivy, Dr. R. K. Arvapally, M. A. Rawshdeh,
C. T. Cardenas, Dr. W. K. Yaseen, Prof. M. A. Omary
Department of Chemistry


Substitution of silica Si O bonds with Si C bonds, yielding
silicon oxycarbides (SiOC:H), has resulted in a significant
lowering of κ (e.g., down to 2.8 at 106 Hz for PECVD-depos-
ited SiOC:H thin films[9,10]). Fluorinated organic materials
University of North Texas
Denton, TX 76203, USA
E-mail: Mohammad.Omary@unt.edu

have been tested as well: C F bonds have lower polarizability
Dr. C. Giacobbe, Dr. S. Checchia
European Synchrotron Radiation Facility
71 avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France
3
−1

(0.56 Å ) and higher energy (485 kJ mol ) than C H bonds
(0.65 Å3 and 414 kJ mol−1, respectively).[2] Thus, Teflon-like
materials can, in principle, exhibit lower dielectric constant
and somewhat higher (albeit still inadequate) thermal sta-
bility; for example, polytetrafluoroethylene shows κ values as
low as 1.9.[11]
Prof. M. A. Omary
Department of Chemistry
Yarmouk University
Irbid 21163, Jordan
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adfm.201904707.
Advantages are conveyed to an insulator also by porosity. The
main components of air, N2, and O2, are nonpolar, hence the
dielectric constant of air is, to a first approximation, equal to
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that of a vacuum (=1). Notable results in this context have been
obtained with xerogels and aerogels, showing κ values lower
than 2.[12,13]
afford remarkable thermal stability to MOFs and N-PCPs, often
exceeding 400 °C in air.
Despite these appealing premises, only few papers regarding
None of the classes of insulators quoted above is immune to
drawbacks. To be processed, an IC must show adequate thermal
stability and mechanical properties. At the end of Cu-based or
Al-based IC processing, devices undergo annealing at tempera-
tures of ≈350 °C or 400–450 °C, respectively, under forming gas
(N2:H2 = 1:9 v/v). While inorganic compounds generally meet
these stability requirements (e.g., PECVD-deposited κ-SiOC-0
is stable up to ≈550 °C[14]), organic compounds do not (m.p. of
polytetrafluoroethylene = 260 °C). The mechanical properties of
amorphous porous dielectrics such as aerogels or xerogels are
severely compromised by an increase in porosity,[12,13] raising
integration issues with other IC components. Manufacturable
solutions are still a challenge.
MOFs and N-PCPs as low-κ dielectrics have appeared.[15–30]
A
first point of reference was set by Zagorodniy et al.[15] These
authors estimated static dielectric constants as low as 2.0 for
a handful of Zn(II)-carboxylate IRMOFs by applying the sem-
iempirical Clausius–Mossotti approach, which neglected the
orientation and distortion contributions to the molecular polar-
izability,[1] influencing the value of κ at the frequencies at which
microelectronic chips operate (105–109 Hz). By first-principle
DFT calculations, Warmbier et al.[16] subsequently showed
that the κ values reported in[15] were underestimated by less
than 10%. As far as it is known,[45–49] promising experimental
evidence of κ lower than 2.5 is still infrequent, manifested only
by: a) the 2.33( 0.05) value of κ reported[50] for ZIF-8 thin films
at 105 Hz stored under ambient conditions with estimated
≈60% relative humidity; b) the 2.4 value shown[51] at 105 Hz by
pellets of [Sr(1,3-BDC)] (1,3-H2bdc = benzene-1,3-dicarboxylic
acid); and c) the 1.2 and 2.1 values reported for films of MOF-3
and MOF-5 at 2 × 106 Hz, respectively.[18] These authors claim
that films of MOF-5 are stable if exposed to water vapors, but
they do not report κ measurements performed after exposure
to humidity. Previous experimental[52,53] and computational[54]
pieces of evidence exist for the fact that MOF-5 undergoes a
phase change if exposed to moisture.
Recent theoretical and experimental investigations have
drawn the attention to nonfluorous[15–29] and fluorous[30]
metal–organic frameworks as low-κ materials. Fluorous
metal–organic frameworks (FMOFs) and fluorous nonporous
coordination polymers (FN-PCPs) are potentially prom-
ising alternatives to current low-κ dielectrics, as they possess
a
number of desirable traits in one material, namely:
i) Controlled and reproducible chemical composition;
ii) reproducible crystal structure, which allows controlled and
reproducible physicochemical properties, which is not always
the case with amorphous materials; iii) low adsorptivity of
high-κ species. High-κ substances, such as water (κ ≈ 80)
and other polar compounds, are produced or present in the
environment during IC processing and/or post fabrication.
Adsorption of polar compounds dramatically increases κ as
observed, e.g., with κ-SiOC-0/1/2.[10] Absence of porosity, as
in FN-PCPs, inhibits the adsorption of high-κ compounds. In
both FMOFs and FN-PCPs, fluorination promotes an intrinsic
increase in hydrophobicity. Despite its permanent porosity,
FMOF-1 (Ag2[Ag4Tz6]; HTz = 3,5-bis(trifluoromethyl)-1,2,4-
triazole, Scheme 1), the first fluorous MOF to appear in the
literature,[31] is superhydrophobic, as demonstrated by experi-
mental contact angles of 158°.[32]
Within this landscape, FMOF-1 appeared to us an ideal
case-study to test the feasibility of FMOFs as low-κ dielectrics.
To widen the scope of this investigation, we also focused the
attention on a novel FMOF and a novel FN-PCP. We have
synthesized for the first time the fluorinated ligand 1,4-bis(1-
H-tetrazol-5-yl)tetrafluorobenzene (H2FBTB, Scheme 1) and
employed it to build up the Cu(II)-based (FMOF-3) and Ag(I)-
based (FN-PCP-1) derivatives isostructural to the already known
MOF [Cu(BTB)(DMF)][55] and N-PCP [Ag2(BTB)][56] (H2BTB =
1,4-bis(1-H-tetrazol-5-yl)benzene[57]), respectively. FMOF-3 rep-
resents a more economical choice of the metal center (copper
vs silver), as already done by Miljanic´ and co-workers with
extensively fluorinated MOFs (MOFFs),[33,58] whereas FN-PCP-1
provides a platform for comparison upon varying the metal
center with the same ligand.
In this work, after briefly summarizing the main structural
features, we report on the thermal stability, hydrophobicity,
and dielectric properties of FMOF-1, FMOF-3, and FN-PCP-1
in comparison to their nonfluorinated counterparts. The
results of high-resolution in situ and operando powder X-ray
diffraction studies on FMOF-3 and FN-PCP-1 are also provided
to enlighten the structural response of these materials under
an AC current of increasing frequency. Overall, these case-
studies demonstrate that FMOFs and FN-PCPs show a signifi-
cant potential as promising novel classes of low-κ dielectrics.
Recently, three perfluorinated copper(II)-based MOFs have
been reported to exhibit hydrophobic behavior with contact
angles in the range 108–151°.[33] In principle, superhydro-
phobic FMOFs allow a platform for further reduction of κ,
potentially impeding water to access the pores, hence impeding
an increase of the effective κ value.
As demonstrated by previous work of some of us, the exploi-
tation of azolate-[31–39] and poly(azolate)-based[40–44] spacers can
2. Results and Discussion
2.1. Synthesis
Scheme 1. The molecular structure of a) 3,5-bis(trifluoromethyl)-1,2,4-
triazole (HTz), and b) 1,4-bis(1-H-tetrazol-5-yl)tetrafluorobenzene
(H2FBTB).
FMOF-1 was synthesized by following the previously reported[34]
procedure. The fluorinated ligand H2FBTB (Scheme 1) was
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prepared for the first time by applying the so-called Demko–
Sharpless protocol.[59] The reader is referred to Sections S5 and S6
of the Supporting Information for a detailed description of
the synthesis and crystal structure of the ligand. Contrary to
[Cu(BTB)(DMF)], the isolation of which requires a strict con-
trol of acidity and temperature,[55] FMOF-3·DMF was prepared
in a straightforward manner (4 h, 90% yield) in DMF by using
copper(II) acetate as the source of metal ions. The choice of
the metal(II) salt is crucial for the development of the reaction.
The acidity of H2FBTB is due to the presence of the N-H func-
tionality[60] and is modulated by the electron withdrawing effect
of the fluorine atoms on the phenyl ring. The acetate anion is
sufficiently basic to deprotonate both tetrazole rings, gener-
ating FBTB2− in situ without the need for an extra base. Finally,
FN-PCP-1 was isolated by reacting H2FBTB with silver(I) nitrate
in water at reflux. As H2FBTB is soluble in aqueous solutions,
its reaction with AgNO3 proceeds easily in 4 h with a yield
amounting to 90%.
2.2. Crystal Structure Analysis
For the sake of comprehension of the subsequent sections,
the reader is provided with a brief description of the main
structural features of FMOF-1, FMOF-3, and FN-PCP-1. The
tetragonal crystal structure of FMOF-1 comprises AgN3 and
Ag4N12 nodes (Figure 1a) and µ3-Tz− linkers within a 3D
porous network possessing 1D hexagonal channels running
along the a- and b-axes (Figure 1b) and having an aperture
of ≈0.5 nm.[61] The walls of the channels are decorated by
CF3 groups, which impart hydrophobic character to the pores
and, consequently, to the overall material (see below). Toroid-
shaped cavities are present within the walls surrounding the
channels. At 100 K, even though the void volume amounts to
43%[62] of the unit cell volume, the calculated density (dc) is
rather high (1.76 kg L−1).[39]
FN-PCP-1, isostructural to [Ag2(BTB)],[56] is built up of tetra-
hedral AgN4 nodes (Figure 2a) and µ8-FBTB2− spacers. Overall,
Figure 1. Representation of the crystal structure of FMOF-1. a) The AgN3 and Ag4N12 nodes (the CF3 groups have been omitted for clarity). b) Portion
of the crystal packing viewed along the [100] direction. The 1D hexagonal channels running parallel to the [100] direction and the toroid-shaped cages
can be easily visualized. Horizontal axis, c; vertical axis, b. Carbon, gray; fluorine, light green; nitrogen, blue; silver, fuchsia.
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on the ambient-temperature structural model
of FMOF-3 yielded an SSA of ≈780 m2 g−1.
This temperature-dependent dynamic pore
opening/closure certainly deserves further
investigations that, nonetheless, are out of
the scope of this work.
2.3. Thermal Stability
The thermal behavior of FMOF-1, FN-PCP-1,
and FMOF-3 was investigated by cou-
pling thermal analysis, performed under a
flow of N2, to in situ variable-temperature
PXRD (VT-PXRD), carried out in air. The
main results are depicted in Figure 4 and
Figures S3 and S4 of the Supporting Infor-
mation, whereas numeric parameters are
collectively provided in Table 1. Thin-film
assessment under forming gas conditions
has not yet been pursued at this fundamental
stage of our investigation (see, in this respect,
the Conclusion section).
Figure 2. Representation of the crystal structure of FN-PCP-1. a) The tetrahedral AgN4 node.
b) Portion of the crystal packing viewed, in perspective, along the [011] direction. Horizontal
axis, a. Carbon, gray; fluorine, light green; nitrogen, blue; silver, fuchsia. For a representation
along the [010] direction, the reader is addressed to Figure S1 (Supporting Information).
As previously assessed by thermogravi-
metric analysis (TGA),[38] FMOF-1 is stable
under N2 up to 400 °C. Besides confirming
it is a (4,8)-connected nonporous and dense (dc = 2.94 kg L−1)
network, with a rather complex 3D architecture (Figure 2b;
Figure S1, Supporting Information). Absence of porosity was
confirmed by N2 adsorption measurements at 77 K and up to
1 bar (Figure S2a, Supporting Information), which revealed a
Brunauer, Emmet, and Teller (BET) specific
this evidence, VT-PXRD (Figure 4a) shows that neither loss
of crystallinity nor phase transitions occur before decomposi-
tion. A parametric Le Bail refinement of the VT-PXRD data in
the temperature range 30–390 °C (Figure 4b) reveal anisotropic
thermal expansion: While the a-axis increases by 1.8% with a
surface area of only 6.4 m2 g−1.
FMOF-3, exhibiting the same structural
motif of [Cu(BTB)(DMF)][55] and [Cu(4-
2H+)(H2O)] [4
= 1,1’-bis(tetrazol-5-yl)tetra-
fluorobiphenyl],[33] shows an orthorhombic
(4,4)-connected 3D network in which 1D
chains of trans-CuN4O2 octahedral nodes
(Figure 3a) and µ4-FBTB2− spacers define
the vertices and walls, respectively, of 1D
rhombic channels (Figure 3b; dc = 1.77 kg L−1).
As in the case of [Cu(BTB)(DMF)], also
in FMOF-3,DMF is bound to the metal
centers and is not completely removed by
thermal activation under vacuum (PXRD
evidence). Incidentally, the rather small
value (≈62 m2 g−1) of the BET specific sur-
face area (SSA) retrieved by N2 adsorption
measurements at 77 K (Figure S2a, Sup-
porting Information) suggests the presence
of a closed-pore form under these condi-
tions, an occurrence already observed with
[Cu(BTB)(DMF)][55] as well as with other
MOFs.[63–67] The BET specific surface area
could be estimated from the CO2 adsorption
isotherm measured at 273 K as 183 m2 g−1
(Figure S2b, Supporting Information).
Figure 3. Representation of the crystal structure of FMOF-3. a) Portion of the 1D chain of trans-
CuN4O2 nodes running along the [100] direction. b) Portion of the crystal packing viewed, in
perspective, along the [100] direction. An ordered model for the ligand has been used and the
DMF molecules [but the oxygen atoms in (a)] have been removed for clarity. Horizontal axis,
b; vertical axis, c. Carbon, gray; copper, fuchsia; fluorine, light green; nitrogen, blue; oxygen,
Finally, calculations with Materials Studio[68] red; sliver, fuchsia.
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FN-PCP-1 is stable under N2 up to 360 °C (Figure S3a, Sup-
porting Information). A parametric Le Bail treatment of the
VT-PXRD data acquired in the range 30–350 °C (Figure S3b,c,
Supporting Information) highlights that, while the a- and b-
axes vary negligibly (less than 0.2%; ∂a/∂T = 8.0 × 10−5 Å°C−1,
∂b/∂T = 6.0 × 10−5 Å°C−1), the c-axis increases by about 1.6%
(∂c/∂T = 4.5 × 10−4 Å°C−1), implying an overall volumetric
thermal expansion of 1.6% (CTE = 4.7 × 10−5 °C−1). FMOF-3 is
stable up to only 270 °C, both under N2 and in air (Figure S4a,b,
Supporting Information). The ≈4 wt% loss observed (Figure S4a,
Supporting Information) in the temperature range 50–140 °C
can be ascribed to the loss of clathrated DMF molecules
(0.25 mol of DMF per formula unit; theoretical loss 4.2 wt%).
Notably, the nonfluorinated analogue [Cu(BTB)(DMF)] is less
stable, as it undergoes a phase transition to a low-crystallinity
phase already at 100 °C.[55] A parametric Le Bail refinement of
the VT-PXRD data acquired in the temperature range 30–250 °C
disclosed a 0.8% expansion of the unit cell volume (Figure S4c,
Supporting Information),[70] with a CTE of 3.7 × 10−5 °C−1. The a-
axis is almost unaffected by temperature increase (∂a/∂T = −2.0 ×
10−5 Å°C−1) while the b- and c-axis, the diagonals of the rhombic
channels, vary by −0.3% and 1.2% (∂b/∂T = −3.2 × 10−4 Å°C−1,
∂c/∂T = 4.9 × 10−4 Å°C−1), respectively. This implies a slight
modification[71] of the aperture of the channels.
2.4. Hydrophobicity
FMOF-1 is superhydrophobic,[32] showing experimental con-
tact angles near 160°. Contrary to the prototypical adsorbents
BPL carbon and zeolite-5A, it does not adsorb water up to 95%
relative humidity.[38] Finally, it is stable if exposed to water
vapor at room temperature for at least 70 d (Figure 5). Since
pressing this MOF into pellets to measure the dielectric con-
stant brings about amorphization, we also monitored a pellet
of FMOF-1 exposed to water vapor at room temperature: The
pellet is stable for at least 70 d (Figure S5, Supporting Informa-
tion). These observations prove that, despite having hexagonal
channels wider than the kinetic diameter of water (2.6 Å[72]),
FMOF-1 displays extraordinary hydrophobicity.
To gain preliminary insights on the hydrophobicity of
FN-PCP-1, we measured its contact angle and monitored its sta-
bility versus water vapor, as detailed in the Experimental Section.
This material shows an experimental contact angle of ≈75°, to be
compared to the value of ≈55° of the nonfluorinated counterpart
(Figure 6). Moreover, it is stable at least up to 48 d if exposed
to water vapor at ambient temperature (Figure S6a, Supporting
Information), whereas FMOF-3 is not as stable under the same
conditions (Figure S6b, Supporting Information), though its con-
tact angle is ≈86° (Figure S7, Supporting Information).[73]
Figure 4. Thermal behavior of FMOF-1. a) Plot of the powder X-ray
diffraction patterns measured in situ versus temperature while heating in
air in 20 °C steps within the temperature range 30–490 °C. b) Percentage
variation of the unit cell parameters (pT) versus temperature. At each
temperature, the values (pT) have been normalized versus those at 30 °C
(p30). a, green circles; c, red diamonds; V, blue triangles.
rate (∂a/∂T) of 7.0 × 10−4 Å°C−1, the c-axis decreases by 0.9%
with a rate (∂c/∂T) of 9.7 × 10−4 Å°C−1, which implies a slight
modification of the aperture of the 1D channels running parallel
to the [100] direction. Overall, the unit cell volume increases by
2.7%, which corresponds to a coefficient of thermal expansion
(CTE) of 7.4 × 10−5 °C−1 in this temperature range (lower than
the 100 ppm°C−1 limit for IC integration).[69]
Table 1. Decomposition temperatures, variation rates of the unit cell
axes versus temperature and volumetric coefficients of thermal expan-
sion (CTEs) for FMOF-1, FN-PCP-1, and FMOF-3·DMF.
Tdec [°C]
(∂a/∂T)
[Å°C−1
(∂b/∂T)
[Å°C−1
(∂V/∂T)
[Å3°C−1
CTE [°C−1
]
The hydrophobic behavior of the materials herein is attrib-
uted to the fluorination of the ligands bonded to the Cu(II) or
Ag(I) centers. Whilst we are cognizant about copper and silver
being problematic for silicon-based IC devices, we have not
experienced any metallization of the copper(II) or silver(I) ions
of the title compounds on extended storage under ambient con-
ditions, at elevated temperatures, or even under extended UV
irradiation–perhaps due to a “Teflon coating” influence of the
fluorinated ligands on the metal centers.
]
]
]
FMOF-1a)
400
400
260
7.0 × 10−4
8.0 × 10−5
7.0 × 10−4
6.0 × 10−5
9.7 × 10−4
4.5 × 10−4
7.4 × 10−5
4.7 × 10−5
3.7 × 10−5
FN-PCP-1b)
−2.0 × 10−5 −3.2 × 10−4 4.9 × 10−4
FMOF-
3·DMFc)
Variation rates and CTEs estimated in the range: a)30–390 °C; b)30–350 °C;
c)30–240 °C.
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FMOF-1 shows average κ values of 1.89(1)
(best value 1.89) and 1.63(1) (best value 1.63)
when pressed at 0.5 and 0.7 kbar, respec-
tively. This remarkable result demonstrates
that FMOFs can in principle be used as
low-κ materials for technology nodes below
7 nm.[1] Moreover, this result confirms the
higher effectiveness of CF3 groups in confer-
ring hydrophobicity versus direct fluorina-
tion on the skeleton of the ligand, as already
observed with the Ni8(OH)4(H2O)2(L)6
[L = bis(pyrazolate) ligand] MOFs.[74]
To consider the air gaps reasonably present
in the pellets, we measured the pellet density
by pycnometry (Table 3) and corrected the
observed values of κ by applying the par-
allel medium approximation to calculate the
κ values corresponding to the bulk (Table 3,
Figure 5. PXRD monitoring of a powdered sample of FMOF-1 exposed to water vapor at ambient
temperature (a magnified version can be seen in Figure S8 of the Supporting Information).
κcorr). As for FMOF-1 pressed at 0.7 kbar, the
intrinsic κ reaches the remarkably low value
2.5. Measurement of the Dielectric Constant
of 1.28, which as far as it is known, is the lowest κ values ever
reported for a hydrophobic material, witnessing that FMOFs
can be platforms for ultralow-κ properties.[76]
The value of the dielectric constant for H2FBTB, FMOF-1,
FN-PCP-1, and FMOF-3 pressed into pellets was assessed at
room temperature by metal–insulator–metal parallel plate
capacitance measurements at 2 V and in the frequency range
2 Hz –2 × 106 Hz. The results described below are collected
in Table 2 while the curves depicting the behavior of κ versus
frequency are reported in Figure 7 and Figure S9 (Supporting
Information). The positive effect of fluorination is evident
already in the case of the ligands: At 2 × 106 Hz, H2FBTB and
H2BTB show average κ values of 2.55(2) and 4.17(1), respec-
tively (Figure S9, Supporting Information). This trend is main-
tained also in the case of the fluorinated and nonfluorinated
coordination frameworks: FN-PCP-1 shows an average value of
κ of 2.57(3) versus the average value of 3.79(1) for [Ag2(BTB)]
(best values 2.53 and 3.78, respectively). FMOF-3 shows average
and best values of κ of 2.44(3) and 2.36, respectively, in compar-
ison with the values of 2.94(8) and 2.85 of lc-[Cu(BTB)(DMF)].
Both FN-PCP-1 and FMOF-3 could, therefore, be used for
10 nm technology nodes.[1]
To test the performance of FN-PCP-1, FMOF-3, and FMOF-1
against water vapor when pressed into pellets, we also esti-
mated the dielectric constant after placing the pellets of the
three compounds for 24 h in an air-tight cell at nearly saturated
humidity levels. The materials show only a slight increase of κ,
reaching average values of 2.64(4), 2.51(3), and 2.11(1), respec-
tively, at 2 × 106 Hz. Toward practical use, however, we caution
that thin films, where the surface to volume ratio is much
higher, may afford lower resistance to humidity.
To put these measurements into perspective with a standard
hydrophobic MOF, we measured the dielectric constant of a
pellet of ZIF-8,[77] which has a contact angle of ≈56°,[78] under
conditions similar to those adopted for the other materials
herein. The average and best values obtained at room tem-
perature and 2 × 106 Hz previous to exposure to water vapors
[1.95(3) and 1.91, respectively] can be only indirectly compared
versus those of Eslava and co-workers,[50] who performed their
measurements on an in situ grown thin film at 60% RH to
attain κ = 2.33 at 100 kHz. Additionally, pressing ZIF-8 into
pellets brings about partial amorphization (PXRD evidence;
see Figure S10, Supporting Information). The measurements
on amorphous ZIF-8, nevertheless, remain useful to calibrate
the dielectric properties for different hydrophobic chemical
compositions. After exposing a pellet of
According to recent ITRS Roadmap reports, manufacturable
solutions exist and are being optimized for materials with κ in
the range 2.6–3.0, and are known for materials with κ in the
range 2.4–2.8.[1]
ZIF-8 to water vapor for 24 h, at 2 × 106 Hz
the κ magnitude started at 5.90, then pro-
gressively decreased to 2.00 along consecu-
tive measurements (Figure S11, Supporting
Information). This behavior likely suggests
that the water adsorbed onto the surface of
the pellet is progressively released, whereas
the initial drastic elevation upon nearly satu-
rated RH is consistent with the type-3 H2O
adsorption isotherm at RH > 80% reported
in ref. [50] In the case of FN-PCP-1, FMOF-3,
and FMOF-1, the five consecutive repetitions
Figure 6. Estimation of the contact angle for a) [Ag2(BTB)] and b) FN-PCP-1.
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Table 2. Values of κ at 2 V and 2 × 106 Hz for FMOF-1 (pressed at
0.5 and 0.7 kbar), FN-PCP-1, [Ag2(BTB)], FMOF-3, lc-[Cu(BTB)(DMF)],
and ZIF-8 under ambient and near saturated humidity levels.
Table 3. Bulk and pellet densities and observed and corrected values
of κ at 2 V and 2 × 106 Hz for FMOF-1 (pressed at 0.5 and 0.7 kbar),
FN-PCP-1, and FMOF-3.
b)
b)
κ at 2 × 106 Hz
(ambient RH)
κ at 2 × 106 Hz
(≈saturated RH)
Compound
FMOF-1a)
FN-PCP-1
FMOF-3
Compound
κobs
dpellet [kg L−1
1.59 [2.46]
1.88
]
dbulk [kg L−1
]
κcorr
1.89(1) [1.63(1)]
2.57(3)
1.76
2.24 [1.28]
4.97
FMOF-1, batch 1a)
FMOF-1, batch 2
FN-PCP-1
1.89(1) [1.63(1)]
2.00(1)
n.a.
2.11(1)
2.64(4)
n.a.
2.94
2.44(3)
1.57
1.77
3.20
2.57(3)
a)Values for a pellet pressed at 0.7 kbar are in square brackets; b)at 2 × 106 Hz and
[Ag2(BTB)]
3.79(1)
ambient RH.
FMOF-3
2.44(3)
2.51(3)
n.a.
lc-[Cu(BTB)(DMF)]
ZIF-8
2.94(8)
pending both the optimization of deposition of contiguous films
of the former, and the phase identification in both cases.
1.95(3)
5.90
a)Values for a pellet pressed at 0.7 kbar are in square brackets.[75]
2.6. High-Resolution PXRD
yielded almost superimposable values (Figure S11, Supporting
Information).
Visual inspection of the HR-PXRD data acquired on pellets of
FN-PCP-1 and FMOF-3 (Figure S13, Supporting Information)
clearly suggested that the structural features of the two com-
pounds are not affected by the passage of an AC current with
increasing frequency in the range 0–5 × 105 Hz. To support this
qualitative observation, Rietveld refinements were carried out
on selected HR-PXRD data. Figure S14 of the Supporting Infor-
mation provides representative examples of the final stage of
the Rietveld refinements, whereas Table S1 of the Supporting
Information collects the main crystallographic details retrieved
from all the data. As is evident from Table S1 of the Sup-
porting Information, the unit cell parameters of FN-PCP-1 and
FMOF-3 undergo negligible variations (less than 0.1%), well
within experimental error, as a function of frequency.
We have performed preliminary film-casting studies for
FMOF-1 as we have discovered that, counterintuitively versus the
normal behavior of MOFs and CPs, it can dissolve and recrys-
tallize upon casting on a solid support from solutions of certain
organic solvents. However, such thin films did not contain the
desired FMOF-1 phase (see Figure S12, Supporting Information).
Additionally, from visual inspection, they seemed not to be con-
tiguous. Thicker films (≈40 µm) with better uniformity were suc-
cessfully cast on silicon upon tuning deposition conditions (e.g.,
varying the concentration, temperature, and/or solvent compo-
sition). However, these films did not contain the same phase as
that of FMOF-1, either (Figure S12, Supporting Information). We
have not pursued κ measurements for these thin and thick films,
3. Conclusion
Herein, we have demonstrated that fluorinated metal–organic
frameworks and fluorinated nonporous coordination polymers
show a promising potential as low-κ materials upon further
development following this fundamental investigation of their
basic electrical, structural, and thermal properties in crystalline
forms. Pellets of FMOF-3 and FN-PCP-1, which is stable under
water vapor at least for 48 d, show average κ values of 2.44(3) and
2.57(3), respectively, at 2 × 106 Hz under ambient conditions,
which increase only modestly–to 2.51(3) and 2.64(4), respectively–
after exposure to water vapor at RH conditions near saturation.
Even more promising, after being pressed at 0.7 kbar,
FMOF-1, stable under water vapor for at least 70 d, shows pellet
κ values of 1.63(1) at 2 × 106 Hz and intrinsic κ values as low
as 1.28 at 2 × 106 Hz under ambient conditions, one of the
lowest κ values ever reported for a MOF and the lowest for a
hydrophobic material. Hence, FMOF-1 shows potential even as
an ultralow-κ material. Distinct from FN-PCPs, FMOFs offer a
platform for further development of ultralow-κ materials, given
the modest surface area of ≈800 m2 g−1 of FMOF-1; hence,
additional development of FMOFs with higher surface area
while maintaining water stability and superhydrophobicity due
to perfluorination should, in principle, offer an opportunity for
further reduction in κ values even below 1.28.
Figure 7. Variation of κ as a function of frequency at 2 V for FMOF-1
(pressed at 0.5 and 0.7 kbar), FN-PCP-1, [Ag2(BTB)], FMOF-3, and
lc-[Cu(BTB)(DMF)].
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Synthesis of lc-[Cu(BTB)(DMF)]·CH3OH: Attempts to obtain [Cu(BTB)
(DMF)] in the form of microcrystalline powders by following the
procedure adopted by Dincaˇ and co-workers[55] to grow single crystals
invariably failed, yielding cyan powders of a low-crystallinity phase
(lc-[Cu(BTB)(DMF)]·CH3OH). The latter could be isolated also by
following a slightly different path, namely: In a Schlenk tube, H2BTB
(0.100 g, 0.47 mmol) was dissolved in DMF (5 mL). After raising the
temperature up to 60 °C, Cu(OAc)2 (0.093 g, 0.47 mmol) was added
under vigorous stirring. The reaction mixture was kept at 135 °C for 4 h
under vigorous stirring. A bluish precipitate was formed. The mixture
was allowed to cool down to room temperature and the solid was
collected under vacuum filtration, washed with methanol (10 mL) and
dried under vacuum (100 °C, 10−4 bar, 4 h) to afford a cyan powder.
Yield: 69%. IR (cm−1): 3453 (b), 2933 (w), 2870 (w), 1652 (vs), 1494 (w),
1436 (w), 1403 (w), 1388 (m), 1252 (w), 1096 (m), 1062 (w), 1031 (w),
1007 (w), 853 (w), 739 (w), 663 (w). Elem. Anal. calc. for lc-[Cu(BTB)
(DMF)]·CH3OH (FW = 394.9 g mol−1): C, 39.54; H, 4.34; N, 31.92%;
found: C, 38.95; H, 4.78; N, 31.45%. For the measurement of κ,
lc-[Cu(BTB)(DMF)]·CH3OH was activated at 120 °C and 10−4 bar for 12 h
to remove clathrated CH3OH.
Synthesis of [Cu(FBTB)(DMF)]·0.25DMF (FMOF-3·DMF): In a Schlenk
tube, H2FBTB (0.100 g, 0.35 mmol) was dissolved in DMF (5 mL). After
raising the temperature up to 60 °C, Cu(OAc)2 (0.069 g, 0.35 mmol) was
added under vigorous stirring. The reaction mixture was kept at 135 °C
for 4 h under vigorous stirring. A cyan precipitate was formed. The
mixture was allowed to cool down to room temperature and the solid
was collected by vacuum filtration, washed with methanol (10 mL), and
dried under vacuum (100 °C, 10−4 bar, 4 h) to afford the title compound
as cyan microcrystalline powders. Yield: 90%. IR (cm−1): 1499 (s),
1486 (s), 1417 (w), 1403 (w), 1384 (w), 1356 (vw), 1274 (vw), 1220 (vw),
1105 (w), 1070 (vw), 984 (s), 802 (s), 736 (m), 669 (m). Elem. Anal.
calc. for [Cu(FBTB)(DMF)]·0.25DMF (FW = 439.4 g mol−1): C, 32.14; H,
2.01; N, 29.51%; found: C, 31.82; H, 1.89; N, 30.32%. For the structural
characterization, assessment of hydrophobicity, measurement of κ,
and high-resolution powder diffraction, FMOF-3·DMF was activated at
120 °C and 10−4 bar for 12 h to remove clathrated DMF.
Additional investigations of the material compositions
herein, as is or upon slight alterations, are warranted to assess
the hydrothermal stability under forming gas as well as the
mechanical properties in functional forms (i.e., thin films on Ta
or W, their nitrides, or Cu).
4. Experimental Section
Materials and Methods: All the solvents and reagents were obtained
from commercial suppliers and used without further purification. IR
spectra were acquired in attenuated total reflectance on a diamond
crystal by means of
a Nicolet iS10 instrument over the range
4000–500 cm−1; in the following, band maximum positions were
reported in cm−1, while band shapes and intensities are denoted as:
b = broad, versus = very strong, s = strong, m = medium, w = weak,
1
and vw = very weak. H, 13C(APT) and 19F NMR spectra were recorded
at 400, 100, and 376 MHz, respectively, on
a Bruker Avance
400 spectrometer in DMSO-d6. 1H, 13C, and 19F NMR data were
reported as follows: Chemical shifts (in ppm, referenced to internal
TMS for 1H and 13C and TFA for 19F) and multiplicity (s = singlet,
m = multiplet, dm = doublet of multiplets). TGA was performed with
a Netzsch STA 409 instrument under a flow of N2, in the temperature
range 30–900 °C and at a heating rate of 10 °C min−1. Elemental
analyses were obtained with a Perkin Elmer CHN Analyser 2400 Series II.
Powder X-ray diffraction patterns for qualitative analysis prior to
functional characterization were acquired in the 3−35° 2θ range, with
steps of 0.02° and time/step of 1 s, on a Bruker AXS D8 Advance
diffractometer equipped with a Cu-Kα tube (λ = 1.5418 Å), a Bruker
Lynxeye linear position-sensitive detector, a filter of nickel in the
diffracted beam, and the following optics: Primary beam Soller slits
(2.3°), fixed divergence slit (0.5°), receiving slit (8 mm). The generator
was set at 40 kV and 40 mA.
Synthesis of the H2FBTB Ligand: The reader is referred to Section S5
of the Supporting Information for details on the synthesis of H2FBTB
and Section S6 (Figure S15 and S16, Supporting Information) for the
description of the crystal and molecular structure (CCDC number:
1 824 197).
Synthesis of the NH4Tz Ligand: NH4Tz was prepared according to
procedures previously reported by Tipping and co-workers for four
synthetic steps, with steps 1–2 according to Bell et al.[79] while steps 3–4
according to Abdul-Ghani et al.[80]
Synthesis of [Zn(MeIm)] (ZIF-8): ZIF-8 was isolated in the form of
white microcrystalline powders by following a previously reported
synthesis.[78] Zinc nitrate hexahydrate (98%) and 2-methylimidazole
(HMeIm) (99%) were purchased from Sigma-Aldrich and used without
further purification.
Powder X-ray Diffraction Structural Analysis: Microcrystalline samples
of FMOF-3 and FN-PCP-1 were lightly ground with agate mortar
and pestle. Then, they were deposited in the hollow of a silicon zero-
background plate 0.1 mm deep. After fast preliminary acquisitions in
the 2θ range 3–35° for qualitative analysis, diffraction data for structure
refinements were collected at room temperature, in the 2θ range 5–105°,
with steps of 0.02° and a total scan time of ≈12 h, on the Bruker AXS D8
Advance diffractometer described above. Comparison between the PXRD
patterns of FMOF-3 versus [Cu(BTB)(DMF)][55] and FN-PCP-1 versus
[Ag2(BTB)][56] suggested that the two fluorinated compounds are
isostructural to the nonfluorinated counterparts. Hence, refinement
of the crystal structures of FMOF-3 and FN-PCP-1 were carried out,
by applying the Rietveld method[81] as implemented in TOPAS-R,[82]
starting from the structural models of [Cu(BTB)(DMF)] and [Ag2(BTB)],
respectively. The independent portion of the FBTB2− ligand and the DMF
molecule in FMOF-3 were described through rigid bodies, imposing
idealized bond distances and angles.[83] The presence of orientation
disorder, with respect to the main axis of the ligand, affecting the phenyl
ring in FMOF-3 was verified during the final stages of the refinement
and was found beneficial (as proved by the lowering of the figures of
merit Rp and Rwp). For both compounds, the background was modeled
by a polynomial function. A refined, isotropic thermal parameter was
assigned to the metal atoms; lighter atoms were assigned an isotropic
thermal parameter 2.0 Å2 higher. The peak shapes were described
with the fundamental parameters approach.[84] For FN-PCP-1, peak
shape anisotropy was described according to the model proposed
by Stephens[85] for orthorhombic space groups using Lorentzian and
Synthesis of the H2BTB Ligand: H2BTB was prepared according to a
previously published protocol.[56]
Synthesis of Ag2[Ag4Tz6] (FMOF-1): FMOF-1 was isolated in the form
of white microcrystalline powders by following a previously reported
procedure.[31] Batches of FMOF-1 were verified by comparison of their
N2 adsorption isotherms and PXRD patterns to published ones.
Synthesis of [Ag2(BTB)]: [Ag2(BTB)] was obtained in the form of
brownish microcrystalline powders by following a previously reported
procedure.[56] IR (cm−1): 1377 (m), 1278 (m), 1219 (vw), 1157 (m),
1109 (w), 1083 (w), 1039 (w), 1005 (w), 845 (s), 741 (s). Elem. Anal.
calc. for [Ag2(BTB)] (FW = 427.7 g mol−1): C, 22.44; H, 0.94; N, 26.18%;
found: C, 23.36; H, 1.16; N, 25.68%.
Synthesis of [Ag2(FBTB)] (FN-PCP-1): In a Schlenk tube, AgNO3
(0.100 g, 0.35 mmol) was suspended in distilled water (6 mL). After
raising the temperature up to 60 °C, H2FBTB (0.118 g, 0.69 mmol)
was added under vigorous stirring. The reaction mixture was refluxed
for 4 h under vigorous stirring. A light brown solid was formed. The
mixture was allowed to cool down to room temperature and the solid
was collected by vacuum filtration, washed with distilled water (10 mL)
and methanol (10 mL), and dried under vacuum (100 °C, 10−4 bar,
4 h) to afford the title compound as a light brown microcrystalline
powder. Yield: 92%. IR (cm−1): 1492 (s), 1481 (s), 1399 (m), 1356 (w),
1258 (w), 1152 (w), 981 (s), 793 (s). Elem. Anal. calc. for [Ag2(FBTB)]
(FW = 499.9 g mol−1): C, 19.22; H, 0.00; N, 22.42%; found: C, 19.63;
H, 0.15; N, 22.45%.
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that of air, the latter measured after setting the same distance, among
the capacitors, at which the capacitance of the pellet was measured. The
instrument was calibrated each time it was switched on by measuring
the dielectric constant of a 12 mm wide, 1 mm thick pellet of Teflon.
As a representative example of the calibration procedure, we obtained
κ = 1.903(5) (Figure S18, Supporting Information) versus κ = 1.9–2.1
reported in the literature.[11] Each measurement, on both Teflon and the
title materials, was repeated five times on the same pellet, alternating
one acquisition on the pellet to one on air. The pellets (12 mm wide,
1 mm thick) were prepared by pressing a sample of each material at
0.5 kbar for 5 min and were kept in a desiccator prior to measurement.
The structural integrity of the pressed samples was verified by means of
PXRD. In the case of FMOF-1, pelletization brings about amorphization
(Figure S19, Supporting Information). To verify the dependence of κ
on the degree of amorphization, pellets of FMOF-1 were prepared by
pressing the material at different pressures (0.5 and 0.7 kbar) for 5 min.
As for the measurements of the dielectric constant after pellet exposure
to water vapor, prior to the measurements, the pellet was left 24 h in an
air-tight cell at nearly saturated humidity levels.
High-Resolution Powder X-Ray Diffraction: High-resolution PXRD in
situ and operando measurements were performed at the ID22 beamline
of the European Synchrotron Radiation Facility (Grenoble, France).
Samples of FMOF-3 and FN-PCP-1 were pressed into (1 mm thick,
0.6 mm wide) pellets at 0.5 kbar for 5 min. The pellets were sandwiched
between two coverslips coated with indium-tin oxide (sheet resistance
5 Ω sq−1) using conductive silver paint contacts. The sides of the cell
were attached to a function generator (Fluke PM-5136); the applied
voltage between the coverslips was measured via an oscilloscope.
HR-PXRD data were acquired on the pellets in the absence of electric
current and while applying an AC current of constant voltage (2 V) and
different frequencies (in the 1–5 × 105 Hz range). Data were acquired
at 31 keV (λ = 0.399 Å, calibrated with the Si NIST standard SRM 640c
at room temperature), with a beam size of 1.0 × 1.0 mm2 (FMOF-3)
or 1.2 mm (horizontal) by 1.5 mm (vertical) (FN-PCP-1) defined by
water-cooled slits and monochromated by a cryogenically cooled Si
111 channel-cut crystal. A bank of nine detectors, each preceded by a
Si 111 analyzer crystal, was scanned vertically to measure the diffracted
intensity. Rietveld refinements of the crystal structures were carried out
with TOPAS-R using, as starting point, the crystal structure obtained at
ambient conditions. For FN-PCP-1, peak shape anisotropy was described
according to the model proposed by Stephens[86] for orthorhombic space
groups using the Lorentzian contribution alone. Preferred orientation
along the [101][89] crystallographic direction was corrected with the
March-Dollase[90] model. For FMOF-3, the peak shape was described
with a tan(θ)-dependent Lorentzian contribution diversified for the [00l]
classes of reflections and the other ones. Preferred orientation along
the [111] direction was corrected with the March-Dollase model. In
both cases, the Bragg reflections belonging to Ag (from the silver paint)
were modeled with the crystal structure of silver retrieved from the
Inorganic Crystal Structure Database (ICSD code 604 631). Figure S12 of
the Supporting Information collects the HR data measured for the two
compounds at all the frequencies essayed, Figure S13 of the Supporting
Information provides representative examples of Rietveld refinements,
while Tables S1.1 and S1.2 compile the main crystallographic data and
Rietveld refinement results.
Gaussian contributions, while in the case of FMOF-3 1/cos(θ)-dependent
spherical harmonics were necessary. The final Rietveld refinement plots
are supplied in Figure S17 (Supporting Information). Fractional atomic
coordinates are provided in the Supporting Information as CIF files.
Main crystallographic details for FN-PCP-1: orthorhombic, Fddd, a =
17.2720(4) Å, b = 13.5506(3) Å, c = 9.6507(3) Å, V = 2258.7(1) Å3, Z =
32, Z’ = 8, dc = 2.94 kg/L, F(000) = 1872, RBragg = 3.70%, Rp = 4.12%,
and Rwp = 5.50%, for 4751 data and 37 parameters in the 10–105° (2θ)
range. CCDC number: 1 824 198.
Main crystallographic details for FMOF-3: orthorhombic, Imma, a =
7.0087(4) Å, b = 24.307(1) Å, c = 9.2770(7) Å, V = 1580.4(2) Å3, Z = 16,
Z’ = 4, dc = 1.77 kg/L, F(000) = 836, RBragg = 1.20%, Rp = 2.42% and
Rwp = 3.23%, for 4951 data and 46 parameters in the 6–105° (2θ) range.
CCDC number: 1 824 199.
Variable-Temperature Powder X-Ray Diffraction: In situ variable-
temperature powder X-ray diffraction (VT-PXRD) experiments were
performed on FMOF-1, FMOF-3, and FN-PCP-1. 30 mg samples of
the three compounds were ground with agate mortar and pestle and
deposited in the hollow of an aluminum sample holder. By means of
a custom-made sample heater (Officina Elettrotecnica di Tenno, Ponte
Arche, Italy), mounted on the Bruker AXS D8 Advance diffractometer
described above, the samples were heated in air from 30 °C up to
decomposition, with steps of 20 °C; a PXRD pattern was acquired in
isothermal conditions at each step, covering a suitable low-to-medium-
angle 2θ range. Treating the data acquired before loss of crystallinity by
means of a Le Bail parametric refinement[86] enabled us to investigate the
behaviour of the unit cell parameters as a function of the temperature.
Note: when comparing the results of TGA and VT-PXRD, the reader
must be aware that the thermocouple of the latter set-up is not in direct
contact with the sample, this determining a slight difference in the
temperature at which the same event is detected by the two techniques.
The temperatures deriving from TGA are more reliable.
N2 Adsorption Measurements: N2 adsorption isotherms were measured
on FN-PCP-1 and FMOF-3 with a standard static volumetric technique
at 77 K and up to 1 bar, using a Micromeritics ASAP 2020 accelerated
surface area and porosimetry analyzer. FMOF-3·DMF was preliminarily
activated under vacuum (120 °C, 10−4 bar, 12 h) and stored at ambient
conditions. Prior to measurement, the samples were activated in situ
by heating at 100 °C under vacuum for 2 h. Specific surface areas were
calculated using the BET model.[87]
CO2 Adsorption Measurement: Adsorption and desorption isotherms
were obtained via a TA Instruments Q5000 SA and VTI-SA high
sensitivity thermogravimetric dynamic sorption analyzer which enabled
sorption analysis of a dry powder sample of FMOF-3 at 273 K by
monitoring the weight change of the sample as a function of relative
pressure of CO2. The balance has a signal resolution of 0.01 µg, and a
sensitivity of 0.1 µg.
Chemical Stability Tests: To monitor the stability of FMOF-1, FN-PCP-1,
and FMOF-3 versus water vapor, 15 mg samples were deposited in
the hollow of aluminum sample-holders. Preliminary PXRD data were
acquired in a suitable low-to-medium angle 2θ range. Then, the sample
holders were introduced into an air-tight water-vapor saturated cells. At
different time points, each sample was checked by PXRD, adopting the
same conditions employed for the preliminary acquisitions.
Measurement of the Contact Angle: 1-mm thick pellets of [Ag2(BTB)],
FN-PCP-1, and FMOF-3 were prepared by pressing batches of the three
materials at 0.5 kbar for 5 min. A drop of distilled water was then laid
down the surface. A series of pictures was taken with a common camera
and processed by the software ImageJ[88] to estimate the contact angle.
Measurement of the Dielectric Constant: The value of the real
component of the dielectric constant of samples of FMOF-1, FMOF-3,
and FN-PCP-1 pressed into pellets was assessed at room temperature
by metal-insulator–metal parallel plate capacitance measurements at
2 V and in the frequency range 2–2 × 106 Hz with an Agilent E4980A
Precision LCR Meter with an Agilent 16048A Test Leads connection
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
to
a custom-made sample-holder and measuring head (Officina
Elettrotecnica di Tenno, Ponte Arche, Italy). The real component of κ
was estimated as the ratio between the capacitance of the pellet and
S.G., A.C., and J.F.I. contributed equally to this work. Under the
supervision of A.M., A.C. carried out the synthesis and preliminary
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characterization (elemental analysis, infrared spectroscopy, thermo-
gravimetric analysis) of H2BTB, H2FBTB, FN-PCP-1, FMOF-3,
lc-[Cu(BTB)(DMF)], and [Ag2(BTB)]. Under the supervision of M.A.O.: a)
J.F.I. and A.C. carried out the synthesis and characterization of FMOF-1
and measured the N2 adsorption isotherms for FN-PCP-1 and FMOF-3.
b) J.F.I. carried out the synthesis and preliminary characterization of
ZIF-8 and the calculation of the specific surface area of FMOF-3 with
Materials Studio. c) M.R. measured the experimental contact angle
on FN-PCP-1 and [Ag2(BTB)] and performed the thin film casting
studies of FMOF-1 on low-carbon steel. d) R.A. measured the CO2
adsorption isotherm on FMOF-3. e) C.C. performed the synthesis of
the triazolate ligand. f) W.Y. performed the thin film casting studies of
FMOF-1 on Si. Under the supervision of S.G.: a) C.G. unraveled the
crystal structure of FN-PCP-1 and FMOF-3, carried out the VT-PXRD
experiments on FN-PCP-1 and FMOF-3, and measured the dielectric
constants of H2BTB, H2FBTB, FN-PCP-1, and FMOF-3. b) R.V. carried
out the VT-PXRD experiment on FMOF-1, measured the dielectric
constant of FMOF-1 and ZIF-8 and the experimental contact angle of
FMOF-3, monitored the chemical stability of FMOF-1, FN-PCP-1, and
FMOF-3. c) R.V., C.G., and S.C. carried out the experiment at ESRF and
the successive data treatment. Finally, S.G. and M.A.O. contributed to
the manuscript writing and editing, and corresponded with each other
on data interpretation and manuscript decisions. The authors thank
Prof. Bruce E. Gnade, Thomas R. Cundari, and Giovanni Palmisano for
helpful discussions. The Galli group acknowledges the University of
Insubria for partial funding. M.A.O. greatly acknowledges support of his
group’s contributions from the Welch Foundation (B-1542) and the U.S.
National Science Foundation (CHE-1413641 for research support and
CHE-1726652 for equipment support). The authors are also grateful to
the European Synchrotron Radiation Facility (experiment CH-4795).
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©
Adv. Funct. Mater. 2019, 1904707
1904707 (11 of 11)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim