Self-Assembly of Lanthanide-Covalent Organic Polyhedra: Chameleonic Luminescence and Efficient Catalysis

Chameleonic Luminescence and E ﬃ cient Catalysis

Article

Self-Assembly of Lanthanide-Covalent Organic Polyhedra:

∥

Shi-Long Han, Jian Yang, Debakanta Tripathy, Xiao-Qing Guo, Shao-Jun Hu, Xiao-Zhen Li,

Li-Xuan Cai, Li-Peng Zhou, and Qing-Fu Sun*

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c01780

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sı Supporting Information

ABSTRACT: A series of multinuclear lanthanide-covalent organic polyhedra (LnCOPs), including pillar-typed triangular prisms 1-

III

Ln and tetrahedra 2-Ln (Ln = La , Sm , Eu ), have been constructed for the ﬁrst time, through either one-pot subcomponent

self-assembly or postassembly metalation. In contrast to the known tetrahedral cages based on transition metals, the pillar-typed

polyhedra were favored from the same organic components in the presence of lanthanides. Besides this, facile transmetalations

between the 1-Ln polyhedra endow cascade chameleonic luminescence. Meanwhile, the open metal sites and pendent amine groups

on 1-Ln enable these polyhedra to catalyze the Henry reaction eﬃciently.

INTRODUCTION

(LnCOPs), which will combine both a supramolecular cavity

and unsaturated coordinated metal sites on one single

polyhedron.

Herein, we report for the ﬁrst time the syntheses of a series

of such multinuclear LnCOPs. In contrast to the known

tetrahedral polyhedra formed with transition-metals, the

■

Molecular polyhedra are attractive compounds because of their

appealing structures and potential applications in separation,

catalysis, recognition, etc. Discrete metallosupramolecular

polyhedra formed through the coordination-directed assembly

approach have witnessed fast development in the past decades

because of the well-established synthetic strategy as well as

their fascinating functions. Meanwhile, porous covalent

polyhedra constructed through dynamic covalent chemistry

have gained increasing attention recently, due to their high

stability, good solubility, and facile functionalization. Up to

now, the function of covalent organic polyhedra has depended

combination of L, TREN, and trivalent lanthanide ions

III

(

Ln ) favors the formation of 1-Ln pillared polyhedra, either

through one-pot subcomponent self-assembly or postassembly

metalation (Scheme 1). Transmetalation transformations were

III

realized from 1-La to other isostructural 1-Ln (Ln= Sm ,

III

Eu ) polyhedra, resulting in chameleonic changes in emission

color. Taking advantage of the available open metal sites and

pendent amine groups on the LnCOPs, we also demonstrated

that they are able to catalyze the Henry reaction in high yield.

largely on the organic ligands and their deﬁned cavity. It is

natural to expect that metal decoration onto the covalent

organic polyhedra will bring diversiﬁed properties and

functions.

RESULTS AND DISCUSSION

■

With regard to their intrinsic optical, electromagnetic, and

Our ﬁrst idea was to start with the preparation of an empty [4

4] organic polyhedron 2 from L and TREN and then do

catalytic properties, we envisage that introduction of the

lanthanides with supramolecular architectures will create a new

class of functional compounds. Previously, subcomponent

postassembly metalation to obtain the 2-Ln₄complexes.

self-assembly of ligand L possessing three pyridyl aldehyde

groups, tris(2-aminoethyl)amine (TREN), and transition

metals (M = Zn, Fe, Cd) was reported to give tetrahedral

Received: June 16, 2020

polyhedra. With seven coordination sites available at each

vertex (four N atoms from TREN and three N atoms from

pyridyls) on this polyhedron, this skeleton is ideal for

construction of lanthanide-covalent organic polyhedra

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

D and S7 −S11 ), while inverse addition (L added into TREN)

Article

Scheme 1. Two Synthetic Routes toward the Self-Assembly of 1-Ln and 2-Ln₄

However, it turned out to be not straightforward; direct

reaction of equimolar L with TREN in one portion at 2.5 mM

concentration gave a mixture of 1 and 2 (Figures S29 and

S30 ). Interestingly, dropwise addition of TREN into a highly

dilute solution of L in chloroform (0.25 mM) at reﬂuxed

temperature led to pure polyhedron 2 quantitatively (Figures

1E). Diﬀusion-ordered NMR spectroscopy (DOSY) shows

that all signals have the same diﬀusion coeﬃciency, conﬁrming

the formation of a single species (Figure 1F). Electrospray

ionization time-of-ﬂight mass spectroscopy (ESI-TOF-MS)

indicated the formation of a complex with a formula of 1-La₃·

(OTf) instead of a tetrahedral 2-La ·(OTf) (Figure 1G). It

was speculated that the Lewis acidity of lanthanides acted as

catalysts to accelerate the conversion of 2 to 1 during this

process, and the coordination requirements of lanthanides

could drive this process as well.

One-pot subcomponent self-assembly gave similar results.

Reaction of equimolar L, TREN, and La(OTf) in CD CN at

50 °C for 5 h led to a homogeneous yellow solution whose

spectroscopic data were consistent with those for 1-Ln₃

observed above. Transmetalation from the known 2-Zn ₄

tetrahedral polyhedron to 2-La was not successful (Figure

S37 ), possibly due to the weaker coordination nature of

lanthanides compared to transition metals. Other isostructural

-Ln type (Ln = Sm, Eu) LnCOPs could also be synthesized

in a similar manner by replacing La(OTf)₃with the

corresponding metal sources, whose formation were also

con ﬁ rmed by H, COSY, and DOSY NMR and ESI-TOF-MS

(

Figures S17 −S23 ).

Suitable crystals of 1-Eu were obtained by slow vapor

diﬀusion of diethyl ether into an acetonitrile solution of the

complex. X-ray diﬀraction analysis shows that this trinucleate

complex crystallized in the P6(3)/m space group. As shown in

Figure 1. Partial H NMR spectra (A−D, 400 MHz, CDCl , 298 K)

III

Figure 2A and 2C, each Eu center is nine-coordinated with

of (A) L, (B) TREN, (C) 1, (D) 2, and (E) 1-La (600 MHz,

CD CN, 298 K); (F) H DOSY spectra of 1-La ; and (G) ESI-TOF-

MS spectrum of 1-La ·(OTf) . Signals in the dashed square are from

two pyridyl N atoms, four N atoms of the TREN unit, and

−

III

three O atoms of three OTf ; the Eu centers are separated by

TREN.

1.7 Å. Unexpectedly, one of the −NH amino group on the

TREN was unreacted, probably due to larger ionic radii and

irregular coordination geometries for lanthanides compared to

transition metals.

at room temperature gave an exclusive formation of [2 + 3]

polyhedron 1 (Figures 1C and S2 −S6), indicating that the

addition order determined the formation of either 1 or 2. To

be mentioned, 1 and 2 were observed to interconvert to each

other gradually in solution because of the nature of dynamic

covalent imine bond (Figures S31 and S32 ).

We envisaged that, upon metalation, the tetrahedral

conformation of polyhedron 2 could be ﬁxed. Unexpectedly,

addition of Ln(OTf) to the solution of freshly prepared

polyhedron 2 led to the formation of 1-Ln , exclusively. The

downﬁeld shifting of protons was observed for the H NMR

Counterions are known to inﬂuence the assembly process

and have crucial impact on the structural formation.

Subcomponent self-assembly of equimolar L, TREN, and

III

Ln(NO ) ·6H O (Ln = La , Sm , Eu ) instead of using

3 3

Ln(OTf)

in CD CN resulted in insoluble suspension. Because

of bad solubility, NMR spectra could not give any useful

information. However, ESI-TOF-MS for the ﬁltrate suggested

the formation of a mixture of 1-Ln and 2-Ln (Figures S24 −

3 4

S26 ), neither of which could be isolated. This is clearly

III

spectrum, indicating the complexation with La ions (Figure

diﬀerent from the exclusive formation of 1-Ln₃when

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

region. The excitation and luminescence spectra of 1-Ln (Ln

III

Sm , Eu ) polyhedra are displayed in Figure 3. Upon

Figure 3. Excitation (black-dashed lines) and emission (solid color

lines, for the visible region only) spectra of 1-Eu and 1-Sm in

Figure 2. X-ray crystal structures of (A) 1-Eu ·(OTf) and (B) 2-Eu ·

CH CN.

(

NO ) . Eu−Eu distances are indicated by dashed lines. (C) The

coordination geometries on the Eu centers of 1-Eu ·(OTf) . (D) The

coordination geometries on the Eu centers of 2-Eu ·(NO ) .

excitation at 324 nm in the ligand level, 1-Eu₃displays

Hydrogen and the counterion are omitted for clarity. Color code:

red, Eu; gray, C; reddish, O; blue, N; yellow, S; cyan, F.

characteristic line-like emission peaks at 580, 595, 615, 650,

and 680 nm, corresponding to D → F (J = 0−4) transitions

III

of Eu (Figure 3). The photoluminescent quantum yield

Ln(OTf) salts were used. The formation of the 2-Eu was also

(PLQY) of 1-Eu is 5.07% in acetonitrile solution (Figure

III

unambiguously established from an exiguous crystal obtained

by slow evaporation of the acetonitrile mixture. X-ray

diﬀraction analysis shows that this tetranucleate complex

crystallized in the Pca2(1) space group. As anticipated, the 2-

S56 ). Characteristic Sm emissions at 560, 595, 640, and 700

nm (corresponding to G → H , J = 5/2−11/2) were also

obtained for 1-Sm , but the sensitization e ﬃ ciency was too low

to be determined (Figure 3 and Figure S53). Besides this,

metal-ion triggered chameleonic color changes were revealed

by taking advantage of the fast and eﬃcient transmetalation

process. As shown in Figure 4A, with the addition of

Sm(OTf) to 1-La solution, the typical blue ﬂuorescence at

Eu polyhedron displays a distorted tetrahedral conformation

III

where four Eu ions sit on the vertices and four ligands span

the faces (Figure 2B). Due to the large ionic radius and higher

III

coordination numbers of the Eu ions, each metal center is

nine-coordinated with three pyridyl N atoms, four N atoms of

450 nm arising from the ligand gradually weakened,

accompanied by the evolving of the characteristic Sm

−

III

TREN, and two O atoms of one NO₃anion (Figure 2D). The

coordination of NO₃⁻ions on the vertices reduces the T

emission.

III

symmetry of the polyhedron into a C symmetry, which is

When the quantity of Sm ions approaches 1 equiv, the

intensity of Sm emission gets saturated, indicating complete

III

quite diﬀerent from that of the previously reported 2-Zn₄

polyhedron. As a result, the six edges (deﬁned by the Eu−Eu

distances) of the tetrahedron are unequal, with four edges

measured to be 12.2−12.7 Å and the remaining two

orthogonally arranged edges being 10.9 Å.

conversion from 1-La to 1-Sm . Further addition of Eu(OTf)

into the system led to a yellow-to-red color switching. The

III

Eu emission kept getting stronger until 10 equiv of Eu(OTf)

was added to the solution (Figure 4B). This is consistent with

Based on our previous ﬁnding on that the formation

constants for diﬀerent lanthanide-organic tetrahedra of the

same ligand show exponential growth across the light-to-heavy

the H NMR titration experiment (Figure S34). Proof-of-

concept anticounterfeiting application was then demonstrated

with the chameleonic property of these complexes. When 1 or

lanthanide series, a transmetalation transformation starting

1-La was used as the ﬂuorescent ink, the blue printing pattern

from polyhedron 1-La to other polyhedra 1-Ln (Ln = Sm,

of 1 can be visualized under UV lamp (254 nm). When the

Eu) was then tested. Indeed, when Sm(OTf) (1 equiv) was

pattern was smeared with the solution of Eu(OTf) , the color

added to 1-La (1 equiv), compared to metal ions prepared

from one-pot synthesis, H NMR indicated the instant metal-

ion metathesis with the quantitative formation of the 1-Sm₃

changed into red immediately (Figure S49 ). As a control, no

such blue-to-red color change could be observed when the

ligand L was used (Figure S49), suggesting that construction of

the organic polyhedron 1 is necessary for fast and stable

chelation of the lanthanide ions.

Figure S33 ). Similar transformation for 1-La → 1-Eu was

3 3

also achieved (Figure S35 ). However, transmetalation

between the neighboring lanthanides, i.e., 1-Sm → 1-Eu ,

Henry/Nitroaldol reaction is an important C−C bond

III

requires the addition of a large excess amount of Eu salts

Figure S34 ). It is worth noting that a cascade transformation

of 1-La → 1-Sm → 1-Eu was also successful (Figure S36).

formation reaction of nitroalkane with carbonyl compounds.

Shibaski et al. developed a series of rare-earth−binol complexes

containing alkoxides as the base and rare-earth elements as

Such metal-ion triggered transformations between diﬀerent

LnCOPs have also been conﬁrmed by the luminescence

titration experiments (see discussion below).

Lewis acids for the eﬃcient catalysis of Henry reactions. 1-

Ln polyhedra with open metal sites and pendent amine

groups provide ideal Lewis acid/base pairs for catalysis. We

Photophysical studies conﬁrmed that the organic polyhe-

dron can sensitize the lanthanide luminescence in the visible

choose C H CHO, p-OHC H CHO, p-NO C H CHO, and

nitromethane/nitroethane as typical substrates. When poly-

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

saturated coordination on the metal centers (Table 1, entry 5).

Besides, unsubstituted benzaldehyde and substrate with an

electron-donating hydroxyl group failed to be activated under

standard conditions (Table 1, entries 6 and 7). Less reactive

nitroethane also gave a satisfactory result (Table 1, entry 8).

Furthermore, both 1-Sm and 1-Eu showed low activity with

much lower yields possibly due to its smaller ion radius

III

compared with La , indicating that the nature of the

lanthanide ions also plays an important role (Table 1, entries

, 9, and 10, respectively). In order to verify the necessity of

the framework of catalyst 1-La , we mixed a 3:1:1 ratio of 2-

picolinaldehyde, TREN, and La(OTf) to produce a noncage

catalyst system PAT-La, which gave a similar yield (92%)

compared to 1-La under the same conditions (Table 1, entries

and 11). It seemed that the cage framework of the catalyst 1-

La does not have an obvious impact on the catalytic activity,

possibly due to its barely available cavity (Figure 2A). Further

exploration on the catalytic properties by virtue of the central

cavity on such Ln-COPs complex is still underway.

Luminescent titrations were conducted to shed light on the

reaction mechanism. With the addition of CH NO to the

III

solution of 1-Eu in acetonitrile, the Eu emission was slightly

enhanced, suggesting that nitromethane can compete with the

coordinating solvent molecules that usually deactivate the

III

luminescence of Eu . Moreover, addition of p-NO C H CHO

into 1-Eu led to a signiﬁcant decrease of the 1-Eu emission,

Figure 4. (A) Emission spectra of 1-La (2.5 × 10⁻M in CH CN)

−1

with a quenching constant K of 1.026 × 10 M calculated

with the addition of 0−1.6 equiv of Sm(OTf) . (B) Emission spectra

of 1-Sm (2.5 × 10 M in CH CN) with the addition of 0−10 equiv

−

from the Stern−Volmer equation, indicating a strong

interaction between substrate and catalyst (Figures S60 and

S61).

of Eu(OTf)₃.

hedron 1-La ·(OTf) (3 mol %) was used as the catalyst, a

CONCLUSIONS

yield of 96% was reached after 24 h for p-NO C H CHO

■

(Table 1, entry 1). As a control, no product was obtained in

In summary, we have shown that lanthanide functionalization

on covalent organic polyhedra is feasible by both one-pot

subcomponent self-assembly or postassembly metalation. The

LnCOPs obtained in this study show interesting chameleonic

emission properties and excellent catalytic performance. This

work oﬀers a new platform for the design of functional metal-

containing covalent organic materials.

Table 1. Henry Reaction Catalyzed by LnCOPs

entry

catalyst

R₁

R₂

yield (%)

EXPERIMENTAL SECTION

1-La ·(OTf)

La(OTf)₃

p-NO C H

CH₃

■

p-NO C H

General Information. All chemicals were purchased from

commercial sources and used without further puriﬁcation unless

otherwise noted. Nuclear magnetic resonance (NMR) spectra were

recorded using Bruker AVANCE III 400 or 600 MHz spectrometers.

Chemical shifts are reported in ppm relative to the residual internal

nondeuterated solvent signals. Electrospray ionization time-of-ﬂight

mass spectroscopy (ESI-TOF-MS) spectra were recorded on an

Impact II UHR-TOF mass spectrometer from Bruker. Data analysis

was conducted with the Bruker Data Analysis software (ver. 4.3), and

simulations were performed with the Bruker Isotope Pattern software.

UV−vis spectra are recorded on a UV-2700 UV−visible spectropho-

tometer from Shimadzu. Excitation and emission spectra were

recorded on a FS5 spectrophotometer from Edinburg Photonics.

Synthesis of L (1,3,5-Tris(4′,4″,4′′′-formylpyridine)-

benzene). Ligand L was synthesized following a reported

p-NO C H

TREN

p-NO C H

2-Zn ·(OTf)

p-NO C H

1-La ·(OTf)

C H

1-La ·(OTf)

p-OHC H

1-La ·(OTf)

p-NO C H

1-Sm ·(OTf)

p-NO C H

2 6

1-Eu ·(OTf)

p-NO C H

PAT-La

p-NO C H

Reaction conditions: 5 mg of aldehyde, 0.5 mL of nitroalkane, 3 mol

catalyst at 50 °C for 24 h. NMR yield based on aldehydes. Alkene

side product was observed.

procedure. Under a nitrogen atmosphere, to a solution of 1,3,5-

tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene (680 mg, 1.5

mmol) in dry DMF (120 mL) was added 5-bromo-2-pyridinecarbox-

aldehyde (1.25 g, 6.7 mmol), K CO (3 g, 22 mmol), and Pd(PPh )

3 4

the presence of La(OTf) (Table 1, entry 2). Though empty

organic polyhedron 1 or TREN could also catalyze the

reaction, only 14% and 34% yields were obtained, respectively,

due to the formation of the eliminated alkene product (Table

, entries 3 and 4), suggesting that the 1-La was more eﬃcient

and selective. It is worth pointing out that the known 2-Zn₄

(

516.9 mg, 0.44 mmol). The reaction mixture was stirred at 90 °C for

4 h. The solvent was removed under reduced pressure and the solid

residue was triturated with water, collected by ﬁltration, and washed

with water (3 × 100 mL), hot diethyl ether (2 × 50 mL), and hot

hexane (2 × 50 mL). The dried solid was triturated with CH Cl and

polyhedron could not catalyze this reaction, possibly due to its

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

collected again. The resulting solid was redissolved in hot CHCl , and

Synthesis of 1-Sm -(OTf) . To a suspension of L (5 mg, 12.7

3 9

then the insoluble materials were ﬁltered oﬀ and Et O was added to

μmol) and TREN (2.0 μL,12.7 μmol) in 600 μL of CD CN was

the ﬁltrate to precipitate out pure product L as a pale solid (130 mg,

added Sm(OTf) (7.6 mg, 12.7 μmol), and then the mixture was

stirred at 50 °C for 5 h. The turbid suspension gradually turned into a

homogeneous pale brown solution. The solvent was removed under

4%). H NMR (400 MHz, CDCl , 298 K): δ 10.18 (s, 3H), 9.12 (s,

H), 8.19 (d, J = 10.1 Hz, 3H), 8.13 (d, J = 8.1 Hz, 3H), 7.95 (s, 3H).

These data are consistent with those described in the literature.

reduced pressure, and then the solid was washed with CHCl (2 × 5

Synthesis of 1. To a solution of TREN (4.0 μL, 25 μmol, 1.5

equiv) in chloroform (20 mL) was added drop-wisely a solution of L

mL); pure product was obtained as a pale brown solid (yield 7 mg,

40%). H NMR (600 MHz, CD CN, 298 K): δ 8.87 (s, 1H), 7.98 (d,

(6 mg, 16 μmol, 1.0 equiv) in chloroform (5 mL). The reaction

J = 7.6 Hz, 1H), 7.88 (d, J = 7.6 Hz, 1H), 7.36 (s, 1H), 7.00 (s, 1H),

mixture was stirred at room temperature for half an hour. The

6.01 (s, 1H), 5.40 (s, 1H), 3.92 (d, J = 16.1 Hz, 1H), 2.17 (s, 1H),

reaction progress was monitored by H NMR spectroscopy. After the

1.85 (s, 1H), 1.50 (s, 2H). C NMR (151 MHz, CD CN, 298 K): δ

reaction was completed, the reaction solution was washed with

saturated aqueous K CO three times. The organic phase was

171.53, 152.66, 146.87, 137.84, 136.46, 136.40, 127.53, 125.51, 58.15,

39.53, 37.17, 14.67. ESI-TOF-MS for 1-Sm -(OTf) : calcd [1-Sm -

collected and dried over anhydrous Na SO . Solvent was removed

(OTf)₆] 821.0287, found 821.0293; calcd [1-Sm -(OTf) ]

3 7

under reduced pressure to give 1 as a light yellow solid (6 mg, 67%).

1306.0193, found 1306.0216.

Synthesis of 1-Eu -(OTf) . To a suspension of L (5 mg, 12.7

H NMR (400 MHz, CDCl , 298 K): δ 8.65 (s, 1H), 8.29 (s, 1H),

.74 (d, J = 8.2 Hz, 1H), 7.69 (m, 1H), 7.58 (s, 1H), 3.84−3.75 (m,

μmol) and TREN (2.0 μL,12.7 μmol) in 600 μL of CD CN was

H), 2.97−2.85 (m, 3H), 2.81−2.70 (m, 1H), 2.68−2.61 (m, 1H).

added Eu(OTf) (7.7 mg, 12.7 μmol), and then the mixture was

C NMR (151 MHz, CDCl , 298 K): δ 162.87, 153.63, 147.09,

stirred at 50 °C for 5 h. The turbid suspension gradually turned into a

homogeneous pale brown solution. The solvent was removed under

38.63, 134.99, 134.10, 124.43, 120.67, 107.75, 90.16, 58.35, 52.76.

ESI-TOF-MS for 1: calcd [C H N + H]⁺1117.6260, found

reduced pressure, and then the solid was washed with CHCl (2 × 5

72 18

1117.6267; calcd [C H N + 2H] 559.3166, found 559.3163.

mL); pure product was obtained as a pale brown solid (yield 7 mg,

72 18

Synthesis of 2. To a solution of L (10 mg, 25 μmol, 1.0 equiv) in

58%). Although the H NMR spectrum was diﬃcult to assign due to

III

chloroform (100 mL) was added drop-wisely a solution of tris(2-

aminoethyl)amine (TREN) (4.0 μL, 25 μmol, 1.0 equiv) in

chloroform (5 mL). The reaction mixture was stirred and reﬂuxed

for 4 h. The reaction progress was monitored by H NMR

spectroscopy. After the reaction was completed, the reaction solution

was washed with saturated aqueous K CO three times. The organic

phase was collected and dried over anhydrous Na SO . Solvent was

removed under reduced pressure to give 2 as a light yellow solid (8

mg, 66%). H NMR (400 MHz, CDCl , 298 K): δ 8.44 (s, 1H), 8.14

the paramagnetic nature of Eu . Mass spectrum and X-ray crystal

structure analyses conﬁrm the formation of 1-Eu -(OTf) without

doubt. ESI-TOF-MS for 1-Eu -(OTf) : calcd [1-Eu -(OTf) ]

1308.0221, found 1308.0234.

General Procedure for One-Pot Subcomponent Self-

Assembly of 1-Ln -(NO and 2-Ln -(NO 12. To a suspension

of L (5 mg, 12.7 μmol, 1 equiv) and TREN (2.0 μL, 12.7 μmol, 1

equiv) in 600 μL of CD CN was added Ln(NO O (12.7 μmol,

)

) ·6H

3 3 2

1 equiv), and then the mixture was stirred at 50 °C for 5 h. The

(

s, 1H), 7.78 (dd, J = 8.3, 2.1 Hz, 1H), 7.73 (d, J = 8.2 Hz, 1H), 7.64

s, 1H), 3.86 (d, J = 9.8 Hz, 1H), 3.65 (t, 1H), 3.20 (t, 1H), 2.59 (d, J

resulted mixture was ﬁltered, and the ﬁltrate was used for H NMR

directly; however, no detectable signals were observed, probably

because of the bad solubility of these nitrate-coordinated lanthanide

complexes in acetonitrile. Other solvents like DMSO, DMF, and

MeOH turned out to be not successful for dissolving these complexes

either, even though these lanthanide assemblies were detected by ESI-

TOF-MS to conﬁrm the formation of 1-Ln -(NO ) and 2-Ln₄-

12.9 Hz, 1H). ¹³C NMR (151 MHz, CDCl , 298 K): δ 162.14,

53.79, 147.11, 140.45, 136.34, 135.36, 126.13, 121.81, 59.20, 54.85.

ESI-TOF-MS for 2: calcd [C₁₂₀H₁₀₈N₂₈+ Na] 1964.9233, found

964.9284.

General Procedure for Postassembly Metalation of 2 with

3 9

Ln(OTf) and Ln(NO ) ·6H O. To a suspension of 2 (5 mg, 1 equiv)

(NO₃)₁₂as a mixture in each reaction. ESI-TOF-MS for 1-La -

3 3

in 600 μL of CD CN was added Ln(OTf) or Ln(NO ) ·6H O (4

(NO ) : calcd [1-La -(NO ) ] 635.0877, found 635.0877. ESI-

3 9 3 3 5

TOF-MS for 2-La -(NO ) : calcd [2-La -(NO ) ] 748.3649,

equiv), and then the mixture was stirred at 50 °C for 1 h. The resulted

4 3 12 4 3 8

mixture was ﬁltered, and the ﬁltrate was used for H NMR and ESI-

found 748.3641. ESI-TOF-MS for 2-Sm -(NO ) : calcd [2-Sm -

4 3 12 4

MS directly; the results showed no signiﬁcant diﬀerence between one-

pot subcomponent self-assembly (see below) and postassembly

metalation in terms of the composition of the products. As

demonstrated in the article text, this is probably because of the

nature of a dynamic covalent imine bond and because Lewis acidity of

lanthanides might accelerate the interconversion between 1 and 2,

and coordination modes of lanthanides prefer to form 1-Ln -type

structure due to eﬃcient π−π stacking between two pillared ligand L

in 1. Consequently, 1-Ln were obtained even though 2 was used. As

a result, a one-pot subcomponent self-assembly strategy was used for

constructing 1-Ln -(NO ) , 1-Ln -(OTf) , and 2-Ln -(NO ) , as

described below for convenience.

Synthesis of 1-La -(OTf) . To a suspension of L (5 mg, 12.7

μmol) and TREN (2.0 μL, 12.7 μmol) in 600 μL of CD CN was

added La(OTf) (7.4 mg, 12.7 μmol), and then the mixture was

stirred at 50 °C for 5 h. The turbid suspension gradually turned into a

homogeneous pale brown solution. The solvent was removed under

(NO ) −L] 920.8059 (note: under these MS conditions, one of the

ligands was lost), found 920.8055. ESI-TOF-MS for 1-Sm -(NO ) :

3 12

calcd [1-Sm -(NO ) ] 1001.6451, found 1001.6133. ESI-TOF-MS

3 7

for 2-Eu -(NO ) : calcd [2-Eu -(NO ) −L] 923.1420 (note:

under these MS conditions, one of the ligands was lost), found

23.1411. ESI-TOF-MS for 1-Eu -(NO ) : calcd [1-Eu -(NO ) ]

3 9

3 3 9 3 3 6

648.4358, found 648.4356.

Synthesis of 2-Zn -(OTf) . 2-Zn -(OTf) was synthesized

according to the reported literature. ESI-TOF-MS for 2-Zn₄-

(

OTf) : calcd [2-Zn -(OTf) (H O)] 533.9015, found 533.9022;

8 4 3 2

calcd [2-Zn -(OTf) (H O)] 989.1375, found 989.1375; calcd [2-

Zn -(OTf) (H O)] 1558.1826, found 1558.1853. See H NMR

4 5 2

spectrum in the Supporting Information.

H NMR Titration for Transmetalation Transformations

III

between 1-Ln -(OTf) (Ln = La , Sm , Eu ) or between 2-

3 9

Zn -(OTf) and 2-La -(OTf) . To a solution of 1-La -(OTf) (1.0

4 8 4 12 3 9

mM in CD CN, 500 μL), an aliquot of a concentrated solution of

reduced pressure, and then the solid was washed with CHCl (2 × 5

Sm(OTf)₃(10 mM, CD CN) was titrated in NMR tube until

transmetalation transformation completed as monitored by chemical

mL); pure product was obtained as a pale brown solid (yield 12 mg,

5%). H NMR (400 MHz, CD CN, 298 K): δ 9.09 (s, 1H), 8.54 (s,

shift. Transmetalation transformations between other 1-Ln -(OTf)

H), 8.26 (d, J = 9.4 Hz, 1H), 7.88 (s, 1H), 7.85 (d, J = 8.0 Hz, 1H),

.49 (t, J = 15.3 Hz, 1H), 4.01−3.92 (m, 1H), 3.74−3.62 (m, 1H),

were performed in the same way by replacement with corresponding

lanthanide salts. Titration results showed that it was not successful for

transmetalation transformation from 2-Zn -(OTf) to 2-La -(OTf) .

.23 (s, 1H), 3.06−2.98 (m, 2H), 2.80−2.74 (m, 1H). C NMR (151

MHz, CD CN, 298 K): δ 167.07, 151.16, 147.80, 138.09, 137.78,

General Procedure for Catalytic Transformation of the

Henry Reaction. To a reaction vial equipped with a stirring bar was

added 5 mg of aldehyde, 0.5 mL of CH NO or CH CH NO , and

37.33, 127.61, 126.41, 58.19, 56.69, 49.21, 38.87, 36.76. ESI-TOF-

MS for 1-La -(OTf) : calcd [1-La -(OTf) ] 809.0161, found

809.0147.

catalyst (3% mol), and the reaction mixture stirred at 50 °C for 24 h.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Complete contact information is available at:

Article

The solvent was evaporated under reduced pressure. The residue was

Academy of Sciences, Fuzhou 350002, People’s Republic of

China

Debakanta Tripathy − State Key Laboratory of Structural

Chemistry, Fujian Institute of Research on the Structure of

Matter, Chinese Academy of Sciences, Fuzhou 350002, People’s

Republic of China

dissolved in CDCl (700 μL), and the yield was determined with

,3,5-trimethoxybenzene (1 mg, 0.00595 mmol) as an internal

standard.

Single-Crystal X-ray Diﬀraction Studies. Suitable single

crystals for complexes 1-Eu -(OTf)₉and 2-Eu -(NO ) were

3 12

obtained by slowly evaporating their acetonitrile solution. The X-ray

Xiao-Qing Guo − State Key Laboratory of Structural Chemistry,

Fujian Institute of Research on the Structure of Matter, Chinese

Academy of Sciences, Fuzhou 350002, People’s Republic of

China; Fujian College, University of Chinese Academy of

Sciences, Beijing 100049, People’s Republic of China

Shao-Jun Hu − State Key Laboratory of Structural Chemistry,

Fujian Institute of Research on the Structure of Matter, Chinese

Academy of Sciences, Fuzhou 350002, People’s Republic of

China; Fujian College, University of Chinese Academy of

Sciences, Beijing 100049, People’s Republic of China

Xiao-Zhen Li − State Key Laboratory of Structural Chemistry,

Fujian Institute of Research on the Structure of Matter, Chinese

Academy of Sciences, Fuzhou 350002, People’s Republic of

China

Li-Xuan Cai − State Key Laboratory of Structural Chemistry,

Fujian Institute of Research on the Structure of Matter, Chinese

Academy of Sciences, Fuzhou 350002, People’s Republic of

China

Li-Peng Zhou − State Key Laboratory of Structural Chemistry,

Fujian Institute of Research on the Structure of Matter, Chinese

Academy of Sciences, Fuzhou 350002, People’s Republic of

China; orcid.org/0000-0003-3820-2591

diﬀraction studies for 1-Eu -(OTf) (CCDC code: 2002431 ) were

carried out on a microfocus metaljet diﬀractometer using Ga Kα

radiation (λ = 1.3405 Å), and those for 2-Eu -(NO ) (CCDC code:

3 12

002432 ) were carried out on a Bruker D8 VENTURE photon II

diﬀractometer with an Iμs 3.0 microfocus X-ray source using the

APEX III program. The structures were solved by direct methods and

reﬁned by full-matrix least-squares on F with anisotropic displace-

ment using the SHELX software package. The electron residuals in

such cases were removed by the SQUEEZE routine.

Crystal Data for 1-Eu -(OTf) . Space group P63/m; a = b =

7.3224(10) Å, c = 17.4451(6) Å; α = β = 90°, γ = 120°; V =

1278.2(9) Å ; Z = 2; T = 299.09(11) K. Anisotropic least-squares

reﬁnement for the framework atoms and isotropic reﬁnement for the

other atoms on 4221 independent merged reﬂections [R(int) =

.1133] converged at residual wR = 0.2848 for all data; residual R =

.0785, wR = 0.2411 [I > 2σ(I)], and goodness of ﬁt (GOF) = 0.905.

Crystal Data for 2-Eu -(NO ) . Space group Pca21; a =

3 12

4.605(5) Å, b = 18.508(4) Å, c = 31.822(6) Å; α = β = γ = 90°;

V = 14492(5) Å ; Z = 4; T = 100 K. Anisotropic least-squares

reﬁnement for the framework atoms and isotropic reﬁnement for the

other atoms on 28413 independent merged reﬂections [R(int) =

.0867] converged at residual wR = 0.2318 for all data; residual R =

.0801, wR = 0.2022 [I > 2σ(I)], and goodness of ﬁt (GOF) = 1.032.

ASSOCIATED CONTENT

sı Supporting Information

■

https://pubs.acs.org/10.1021/acs.inorgchem.0c01780

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c01780.

Author Contributions

These authors contributed equally.

∥

Additional experimental details including ﬁgures and

tables (PDF)

Notes

The authors declare no competing ﬁnancial interest.

Accession Codes

ACKNOWLEDGMENTS

CCDC 2002431 −2002432 contain the supplementary crys-

tallographic data for this paper. These data can be obtained

free of charge via www.ccdc.cam.ac.uk/data_request/cif , or by

emailing data_request@ccdc.cam.ac.uk , or by contacting The

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

This work was supported by the National Natural Science

Foundation of China (21825107, 21901245) and the Strategic

Priority Research Program of the Chinese Academy of

Sciences (XDB20000000).

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