Taking the Third Route for Construction of POMOFs: The First Use of Carboxylate-Functionalized MnIIIAnderson-Evans POM-Hybrid Linkers and Lanthanide Nodes

Article abstract of DOI:10.1021/acs.cgd.0c01138

The purpose of the present contribution is to illustrate how to design and grow crystals of POMOFs based on POM-hybrid linkers with lanthanide ions as nodes. Thus, the MnIII-centered Anderson-Evans polyoxometalate (Mn-A-E-POM) was functionalized with 4-(((1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)amino)methyl)benzoic acid (H4L) to afford the hybrid inorganic-organic POM [N(n-C4H9)4]4[(MnMo6O18)(HL)(L)] (1), which in turn reacts with lanthanide salts and yields two three-dimensional frameworks with the general formulas Ln(DMF)6Ln(DMF)5Ln3(DMF)10[(MnMo6O18)(L)2]3·xDMF (2; Ln = La-Nd) and [Ln(DMF)4(H2O)]2[Ln3(DMF)6][(MnMo6O18)(L)2]3·xDMF (3; Ln = Y, Sm-Lu). The differentiation in these two families results from the lanthanide contraction. The crystallization process is crucial for obtaining these two families in a bulk pure phase. Family 2 can be obtained by stirring, while for family 3 the less energy demanding layering method proved to be the most efficient pathway. Notably, the change in the ionic radii causes a change in space group (from P21 (family 2) to P21/c (family 3); however, the topology of the frameworks is unaffected.

Full text of DOI:10.1021/acs.cgd.0c01138

pubs.acs.org/crystal
Article
Taking the Third Route for Construction of POMOFs: The First Use of
Carboxylate-Functionalized MnIII Anderson−Evans POM-Hybrid
Linkers and Lanthanide Nodes
Marcel P. Merkel,* Christopher E. Anson, George E. Kostakis, and Annie K. Powell*
Cite This: Cryst. Growth Des. 2021, 21, 3179−3190
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: The purpose of the present contribution is to
illustrate how to design and grow crystals of POMOFs based on
POM-hybrid linkers with lanthanide ions as nodes. Thus, the
MnIII-centered Anderson−Evans polyoxometalate (Mn-A-E-POM)
was functionalized with 4-(((1,3-dihydroxy-2-(hydroxymethyl)-
propan-2-yl)amino)methyl)benzoic acid (H4L) to afford the
hybrid inorganic−organic POM [N(n-C4H9)4]4[(MnMo6O18)-
(HL)(L)] (1), which in turn reacts with lanthanide salts and
yields two three-dimensional frameworks with the general formulas Ln(DMF)6Ln(DMF)5Ln3(DMF)10[(MnMo6O18)(L)2]3·xDMF
(2; Ln = La−Nd) and [Ln(DMF)4(H2O)]2[Ln3(DMF)6][(MnMo6O18)(L)2]3·xDMF (3; Ln = Y, Sm−Lu). The differentiation in
these two families results from the lanthanide contraction. The crystallization process is crucial for obtaining these two families in a
bulk pure phase. Family 2 can be obtained by stirring, while for family 3 the less energy demanding layering method proved to be the
most efficient pathway. Notably, the change in the ionic radii causes a change in space group (from P21 (family 2) to P21/c (family
3); however, the topology of the frameworks is unaffected.
So far there do not seem to be any type 3 POMOFs where
carboxylate-functionalized Anderson−Evans POMs provide
hybrid linkers and lanthanide ions act as nodes. This requires
the initial synthesis of a suitable organic linker, which in the
following step is attached to a polyoxometalate.30 We chose to
use the combination of a flexible organic ligand with an
Anderson−Evans (A-E) POM, as a central part of a linear
linker in order to construct a robust framework with
lanthanides as nodes. The A-E POM has a planar metal
{M′M6} core within the moiety {M′(OH)6M6O24}. The
simple replacement of M′ is hard to achieve; however, starting
from the α-octamolybdate POM [α-Mo8O26]4− provides a
relatively easy means to target the desired {M′M6} through
formal replacement of the two tetrahedrally coordinated
{MO4} units above and below the plane with M′ in the
center of this plane.31 In contrast to the postfunctionalization
of the hexavanadate hybrid used by Wei et al.,32 we chose 4-
(((1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)amino)-
methyl)benzoic acid (H4L) as a suitable ligand, with two types
of functional groups: the tris(alkoxo) (tris) and the benzoic
acid groups. H4L was grafted onto the MnIII-centered
INTRODUCTION
■
Coordination polymers (CPs), also called metal− organic
frameworks (MOFs), are built up using organic building blocks
(so-called linkers) and inorganic building blocks (so-called
secondary building units (SBUs)), forming 3D porous
frameworks.1 Here, the linkers contain functional groups,
such as carboxylate,2,3 amine,4 pyridyl,2 nitrile,5 sulfonate,5 and
phosphonate,6 coordinating to the SBUs, which may be based
on Zn,3,4 Ni,6 Cu,2,7 Na,5 Ag,5 Mg,4 Fe,8 Cr,9 or other metal
ions and thus build up a network. Another class of materials
are the polyoxometalates (POMs), which are anionic metal
oxide clusters composed of transition metals (so-called metal
addenda atoms; M = W, Mo, Nb, V, Ta) in high oxidation
states.10,11 A combination of POMs and MOFs results in
polyoxometalate-based metal−organic frameworks, the so-
called POMOFs.12 These compounds may combine and/or
improve the properties of POMs and MOFs.13−15 This field of
research is still in its infancy but is currently receiving an
increasing amount of attention due to emergent applications in
many fields such as catalysis,16−18 proton conduction,19,20
sorption,21 and electrode materials.11 So far three subgroups of
POMOFs have been described in the literature: (1) POMs
occupying the cavities of a MOF structure (POM@MOF;
Figure 1a),17,21−23 (2) POMs used as SBUs in the MOF
network (Figure 1b),11,24−27 and (3) POMs as part of the
linker of the framework (Figure 1c).18,28,29 Among all these
approaches, the last (route 3) has barely been explored.
Received: August 14, 2020
Revised: April 23, 2021
Published: May 6, 2021
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190
© 2021 American Chemical Society
3179

Crystal Growth & Design
pubs.acs.org/crystal
Article
Figure 1. The three subgroups of POMOFs: POMs occupying the cavities of a MOF structure (POM@MOF) (a), POMs used as SBUs in the
MOF network (b), and POMs as part of the linker of the framework (c).
H2O. The reaction mixture was stirred for 20 h at room temperature,
whereas the solid 4-(chloromethyl)benzoic acid was completely
dissolved after 30 min and a white precipitate occurred after 7 h of
addition. The white precipitate was filtered off and washed with H2O
Anderson−Evans POM (A-E POM) via the hydroxyl groups of
the tris group to give [N(n-C4H9)4]4[(MnMo6O18)(HL)(L)]
(1). In a next step, the free carboxylate groups and terminal
oxygen (Ot) atoms of this hybrid were used in order to
coordinate to a series of lanthanides, resulting in two families
(2 × 20 mL) and acetone (2 × 15 mL), followed by drying under
vacuum to yield 10.2 g (68%). The product was characterized using
of frameworks with the general formulas Ln(DMF)6Ln-
(DMF)5Ln3(DMF)10[(MnMo6O18)(L)2]3·xDMF (2; Ln =
La−Nd) and [Ln(DMF)4 (H2 O)]2 [Ln3 (DMF)6 ]-
[(MnMo6O18)(L)2]3·xDMF (3; Ln = Y, Sm−Lu). In order
to simplify complex structures, especially 3D frameworks, a
topological analysis can be used to identify and reduce the
individual moieties to nodes and connectors in a simplified
network. This makes it easier to describe the architecture of
the scaffold.33−35
1H NMR (DMSO-d6): δ 3.21 (s, 6H), 3.82 (s, 2H), 7,43 (d, 2H),
7.81 (d, 2H).
Preparation of [N(n-C4H9)4]4[(MnMo6O18)(HL)(L)]·3DMF (1).
[N(n-C4H9)4]4[Mo8O26] was synthesized according to the literature
method.36 A mixture of [N(n-C4H9)4]4[Mo8O26] (1.100 g, 0.50
mmol), Mn(OAc)3·2H2O (0.201 g, 0.75 mmol), 4-HOOC(C6H4)-
CH2NHC(CH2OH)3 (H4L; 0.438 g, 1.71 mmol), tetrabutylammo-
nium bromide (0.215 g, 0.67 mmol), and 20 mL of DMF was stirred
for 22 h at 85 °C. The resulting suspension was centrifuged and the
orange supernatant was placed in a diethyl ether atmosphere; after 2
days orange crystals had formed. For a higher yield, the diethyl ether
diffusion was continued for another 13 days and the crystals were air-
dried to yield 1.012 g (57% based on Mn; 64% based on Mo). Anal.
Calcd for MnMo6O28C88N6H171 (2391.901 g/mol) ([N(n-C4H9)4]4-
[(MnMo6O18)((OCH2)3CNHCH2(C6H4)COOH)((OCH2)3-
CNHCH2(C6H4)COO)]): C, 44.19; N, 3.51; H, 7.21. Found: C,
44.26; N, 3.58; H, 7.28. FT-IR (KBr, cm−1): 3470 (br, m), 2964 (s),
2932 (sh), 2875 (s), 1713 (sh), 1675 (s), 1611 (sh, w), 1479 (s),
1390 (m), 1258 (w), 1156 (w), 1087 (m), 1043 (m), 942 (sh),
922(s), 904 (sh), 771 (sh), 670 (s), 569 (w), 505 (w), 455 (w).
Preparation of Ln(DMF)6Ln(DMF)5Ln3(DMF)10[(MnMo6O18)-
L]3·xDMF (2; Ln = La−Nd). A boundary layer of a DMF/MeOH
mixture (1/1 v/v, 2 mL) was rapidly pipetted over a solution of [N(n-
C4H9)4]4[(MnMo6O18)((OCH2)3CNHCH2(C6H4)COOH)-
((OCH2)3CNHCH2(C6H4)COO)]·3DMF (1; 10 mg, 0.0042 mmol)
dissolved in 1 mL of DMF. A solution of Ln(NO3)3·5/6H2O (Ln =
La−Nd; 10 mg, 0.0231 mmol) dissolved in 1 mL of MeOH was
rapidly pipetted on top to give a three-layered system. Yellow crystals
of 2 were obtained from the lower layer after 5 days and were dried
under vacuum.
EXPERIMENTAL SECTION
■
General Considerations. All reagents and solvents were used as
received from commercial suppliers without further purification. To
determine the carbon, hydrogen, nitrogen, and sulfur fractions of the
samples, elemental analysis was carried out using a “Vario Micro
Cube” device from PerkinElmer. Infrared spectra were recorded on a
PerkinElmer Spectrum GX FT-IR spectrometer as KBr pellets in the
range 4000−400 cm−1 with a resolution of 8 cm−1. The following
abbreviations are used to describe the peak characteristics: br = broad,
sh = shoulder, s = strong, m = medium, and w = weak. NMR spectra
of the compounds were measured using Bruker Ultrashield plus 500
(500 MHz) and Varian 500 MHz spectrometers. 1H and 13C
measurements were recorded using deuterated solvents and
referenced to tetramethylsilane (TMS) as an internal standard (δ =
0 ppm). The structures were measured using single-crystal X-ray
diffraction (SCXRD) on area detector diffractometers: IPDS II (Mo
Kα, λ = 0.71073 Å, detector image plate) and STADIVARI (Ga Kα, λ
= 1.34143 Å, detector Dectris Eiger2 R 4 M (detector type HPC))
(STOE). The measurements were taken at temperatures of 150 and
180 K. The crystals were attached to the goniometer head with
perfluoroether oil. Powder X-ray diffraction (PXRD) measurements
were performed on an STOE STADI-P diffractometer with Cu Kα
radiation.
The following compounds were synthesized according to the
aforementioned layering method.
Compound 2-La Layering. Yield: 4.5 mg (47% based on 1). Anal.
Calcd for C147H253La5Mn3Mo18N31O109 (6784.987 g/mol) (La-
(DMF)6La(DMF)5La3(DMF)10[(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·4DMF): C, 26.02; N, 6.40; H, 3.76. Found: C,
26.15; N, 6.52; H, 3.91. FT-IR (KBr, cm−1): 4312 (br, sh), 3315 (br,
w), 2930 (m), 2855 (sh), 2817 (sh), 1650 (s), 1612 (sh), 1552 (w),
1499 (w), 1424 (m, sh), 1386 (m), 1303 (w), 1251 (m), 1175 (w),
1115 (m), 1070 (m), 1040 (m), 949 (s), 912 (s), 776 (w), 663 (br,
s), 565 (sh), 460 (w), 414 (w).
Preparation of 4-HOOC(C6H4)CH2NHC(CH2OH)3 (H4L). Syn-
thesis of the ligand H4L was performed by an SN2 reaction between
tris(hydroxymethyl)aminomethane and 4-(bromomethyl)benzoic
acid. 4-HOOC(C6H4)CH2NHC(CH2OH)3 (H4L) was synthesized
according to the literature method.29 4-(Chloromethyl)benzoic acid
(10.0 g, 58.6 mmol) was added over a period of 2 min to a solution of
tris(hydroxymethyl)aminomethane (35.6 g, 294 mmol) in 300 mL of
3180
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
Compound 2-Ce Layering. Yield: 3.9 mg (42% based on 1). Anal.
Calcd for C144H246N30O108Mn3Mo18Ce5 (6717.945 g/mol) (Ce-
(DMF)6Ce(DMF)5Ce3 (DMF)10[(MnMo6O1 8)((OCH2)3-
CNHCH2(C6H4)COO)2]3·3DMF): C, 25.75; N, 6.25; H, 3.69.
Found: C, 25.64; N, 6.35; H, 3.44. FT-IR (KBr, cm−1): 4315 (br, sh),
3317 (br, w), 2932 (m), 2857 (sh), 2820 (sh), 1655 (s), 1613 (sh),
1549 (w), 1501 (w), 1427 (m, sh), 1387 (m), 1300 (w), 1253 (m),
1178 (w), 1118 (m), 1073 (m), 1043 (m), 951 (s), 915 (s), 777 (w),
665 (br, s), 566 (sh), 461 (w), 415 (w).
Compound 2-Pr Layering. Yield: 3.2 mg (35% based on 1). Anal.
Calcd for C135H225N27O105Mn3Mo18Pr5 (6502.622 g/mol) (Pr-
(DMF)6Pr(DMF)5Pr3(DMF)10[(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3): C, 24.94; N, 5.82; H, 3.47. Found: C, 25.18; N,
5.44; H, 3.47. FT-IR (KBr, cm−1): 4315 (br, sh), 3316 (br, w), 2933
(m), 2858 (sh), 2821 (sh), 1653 (s), 1612 (sh), 1550 (w), 1500 (w),
1428 (m, sh), 1389 (m), 1300 (w), 1251 (m), 1176 (w), 1114 (m),
1071 (m), 1042 (m), 950 (s), 913 (s), 775 (w), 664 (br, s), 563 (sh),
460 (w), 413 (w).
Compound 2-Nd Layering. Yield: 3.7 mg (41% based on 1). Anal.
Calcd for C135H225N27O105Mn3Mo18Nd5 (6519.294 g/mol) (Nd-
(DMF)6 Nd(DMF)5Nd3(DMF)10[(MnMo6O18)((OCH2)3-
CNHCH2(C6H4)COO)2]3): C, 24.87; N, 5.80; H, 3.48. Found: C,
24.52; N, 5.73; H, 3.46. FT-IR (KBr, cm−1): 4310 (br, sh), 3313 (br,
w), 2932 (m), 2857 (sh), 2818 (sh), 1651 (s), 1613 (sh), 1553 (w),
1498 (w), 1425 (m, sh), 1387 (m), 1305 (w), 1252 (m), 1176 (w),
1117 (m), 1071 (m), 1041 (m), 948 (s), 913 (s), 777 (w), 664 (br,
s), 567 (sh), 461 (w), 415 (w).
In order to obtain larger amounts in a microcrystalline powder
form of 2, [N(n-C4H9)4]4[(MnMo6O18)((OCH2)3CNHCH2(C6H4)-
COOH)((OCH2)3CNHCH2(C6H4)COO)]·3DMF (1; 200 mg,
0.084 mmol) was dissolved in 20 mL of DMF and a solution of
Ln(NO3)3·5/6H2O (Ln = La−Nd; 200 mg, 0.462 mmol) dissolved in
20 mL of MeOH was added with stirring over a period of 1 min at
room temperature. The solution turned turbid within 30 s and was
stirred for a further 1.5 h. The resulting powder was dried under
vacuum.
5.63; H, 3.56. FT-IR (KBr, cm−1): 4312 (br, sh), 3315 (br, w), 2932
(m), 2855 (sh), 2819 (sh), 1650 (s), 1613 (sh), 1552 (w), 1497 (w),
1424 (m, sh), 1386 (m), 1306 (w), 1251 (m), 1175 (w), 1116 (m),
1070 (m), 1042 (m), 949 (s), 914 (s), 776 (w), 663 (br, s), 566 (sh),
460 (w), 414 (w).
Preparation of [Ln(DMF)4 (H2O)]2 [Ln3(DMF)6][(MnMo6O18)-
((OCH2)3 CNHCH2 (C6H4)COO)2]3·xDMF (3; Ln = Y, Sm−Lu). A
boundary layer of a DMF/MeOH mixture (1/1 v/v, 2 mL) was
rapidly pipetted over a solution of [N(n-C4H9)4]4[(MnMo6O18)-
((OCH2)3CNHCH2(C6H4)COOH)((OCH2)3CNHCH2(C6H4)-
COO)]·3DMF (1; 10 mg, 0.0042 mmol) dissolved in 1 mL of DMF.
A solution of Ln(NO3)3·5/6H2O (Ln = Y, Sm−Lu; 10 mg, 0.0231
mmol) dissolved in 1 mL of MeOH was rapidly pipetted on top to
give a three-layered system. Yellow crystals of 3 were obtained from
the lower layer after 5 days and were dried under vacuum.
The following compounds were synthesized according to the
aforementioned layering method.
Compound 3-Y Layering. Yield: 3.2 mg (35% based on 1). Anal.
Calcd for C138H236N28O108Mn3Y5Mo18 (6351.738 g/mol) ([Y-
(DMF)4(H2O)]2[Y3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·8DMF): C, 26.09; N, 6.18; H, 3.75. Found: C,
25.76; N, 6.44; H, 4.11. FT-IR (KBr, cm−1): 4314 (br, sh), 3315 (br,
w), 2930 (m), 28556(sh), 2817 (sh), 1650 (s), 1613 (sh), 1552 (w),
1450 (w), 1424 (m, sh), 1386 (m), 1304 (w), 1251 (m), 1175 (w),
1165 (m), 1070 (m), 1040 (m), 952 (s), 912 (s), 776 (w), 665 (br,
s), 565 (sh), 460 (w), 412 (w).
Compound 3-Sm Layering. Yield: 4.5 mg (52% based on 1). Anal.
Calcd for C120H194N22O102Mn3Mo18Sm5 (6220.446 g/mol) ([Sm-
(DMF)4(H2O)]2[Sm3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·2DMF): C, 23.17; N, 4.95; H, 3.14. Found: C,
23.01; N, 5.20; H, 3.45. FT-IR (KBr, cm−1): 4313 (br, sh), 3313 (br,
w), 2930 (m), 2855 (sh), 2819 (sh), 1650 (s), 1613 (sh), 1554 (w),
1499 (w), 1425 (m, sh), 1386 (m), 1305 (w), 1251 (m), 1177 (w),
1117 (m), 1071 (m), 1041 (m), 949 (s), 912 (s), 776 (w), 665 (br,
s), 565 (sh), 462 (w), 414 (w).
Compound 3-Eu Layering. Yield: 5.6 mg (62% based on 1). Anal.
Calcd for C129H215N25O105Mn3Mo18Eu5 (6447.747 g/mol) ([Eu-
(DMF)4(H2O)]2[Eu3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·5DMF): C, 24.03; N, 5.43; H, 3.36. Found: C,
23.95; N, 5.71; H, 3.60. FT-IR (KBr, cm−1): 4313 (br, sh), 3315 (br,
w), 2930 (m), 2856 (sh), 2817 (sh), 1650 (s), 1612 (sh), 1553 (w),
1499 (w), 1424 (m, sh), 1386 (m), 1305 (w), 1251 (m), 1175 (w),
1114 (m), 1070 (m), 1042 (m), 949 (s), 912 (s), 778 (w), 665 (br,
s), 565 (sh), 460 (w), 414 (w).
Compound 3-Gd Layering. Yield: 3.6 mg (42% based on 1). Anal.
Calcd for C117H187N21O101Mn3Mo18Gd5 (6181.802 g/mol) ([Gd-
(DMF)4(H2O)]2[Gd3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·DMF): C, 22.73; N, 4.76; H, 3.05. Found: C, 22.37;
N, 4.95; H, 3.35. FT-IR (KBr, cm−1): 4312 (br, sh), 3317 (br, w),
2930 (m), 2855 (sh), 2819 (sh), 1650 (s), 1613 (sh), 1552 (w), 1499
(w), 1424 (m, sh), 1388 (m), 1303 (w), 1251 (m), 1175 (w), 1118
(m), 1070 (m), 1040 (m), 949 (s), 913 (s), 776 (w), 663 (br, s), 565
(sh), 462 (w), 414 (w).
Compound 3-Tb Layering. Yield: 4.1 mg (45% based on 1). Anal.
Calcd for C129H215N25O105Mn3Mo18Tb5 (6482.554 g/mol) ([Tb-
(DMF)4(H2O)]2[Tb3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·5DMF): C, 23.90; N, 5.40; H, 3.42. Found: C,
23.75; N, 5.56; H, 3.58. FT-IR (KBr, cm−1): 4312 (br, sh), 3315 (br,
w), 2930 (m), 2855 (sh), 2818 (sh), 1650 (s), 1612 (sh), 1556 (w),
1498 (w), 1424 (m, sh), 1387 (m), 1303 (w), 1251 (m), 1176 (w),
1115 (m), 1071 (m), 1040 (m), 948 (s), 912 (s), 776 (w), 663 (br,
s), 566 (sh), 460 (w), 415 (w).
Compound 3-Dy Layering. Yield: 4.2 mg (48% based on 1). Anal.
Calcd for C117H187Dy5Mn3Mo18N21O101 (6208.411 g/mol) ([Dy-
(DMF)4(H2O)]2[Dy3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·DMF): C, 22.63; N, 4.74; H, 3.04. Found: C, 22.51;
N, 5.06; H, 3.38. FT-IR (KBr, cm−1): 4312 (br, sh), 3315 (br, w),
2931 (m), 2855 (sh), 2817 (sh), 1651 (s), 1612 (sh), 1552 (w), 1499
(w), 1425 (m, sh), 1386 (m), 1304 (w), 1251 (m), 1175 (w), 1115
The La−Nd-containing compounds 2 could best be obtained using
a stirring method.
Compound 2-La Stirring. Yield: 76 mg (41% based on 1). Anal.
Calcd for C141H239N29O107Mn3Mo18La5 (6638.799 g/mol) (La-
( D M F ) 6 L a ( D M F ) 5
La3(DMF)10[(MnMo6O18)((OCH2)3CNHCH2(C6H4)COO)2]3·
2DMF): C, 25.51; N, 6.12; H, 3.63. Found: C, 25.33; N, 6.37; H,
3.97. FT-IR (KBr, cm−1): 4311 (br, sh), 3317 (br, w), 2931 (m),
2856 (sh), 2815 (sh), 1651 (s), 1613 (sh), 1553 (w), 1498 (w), 1425
(m, sh), 1388 (m), 1304 (w), 1252 (m), 1176 (w), 1116 (m), 1073
(m), 1041 (m), 951 (s), 913 (s), 778 (w), 660 (br, s), 567 (sh), 461
(w), 415 (w).
Compound 2-Ce Stirring. Yield: 77 mg (40% based on 1). Anal.
Calcd for C150H260N32O110Mn3Mo18Ce5 (6864.133 g/mol) (Ce-
(DMF)6Ce(DMF)5Ce3(DMF)10[(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·5DMF): C, 26.25; N, 6.53; H, 3.82. Found: C,
26.02; N, 6.74; H, 3.93. FT-IR (KBr, cm−1): 4310 (br, sh), 3317 (br,
w), 2931 (m), 2856 (sh), 2818 (sh), 1651 (s), 1613 (sh), 1555 (w),
1497 (w), 1423 (m, sh), 1384 (m), 1301 (w), 1254 (m), 1178 (w),
1119 (m), 1073 (m), 1042 (m), 952 (s), 913 (s), 778 (w), 662 (br,
s), 567 (sh), 461 (w), 415 (w).
Compound 2-Pr Stirring. Yield: 82 mg (45% based on 1). Anal.
Calcd for C135H225N27O105Mn3Mo18Pr5 (6502.622 g/mol) (Pr-
(DMF)6Pr(DMF)5Pr3(DMF)10[(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3): C, 24.94; N, 5.82; H, 3.47. Found: C, 25.13; N,
5.47; H, 3.48. FT-IR (KBr, cm−1): 4312 (br, sh), 3315 (br, w), 2931
(m), 2852 (sh), 2817 (sh), 1653 (s), 1612 (sh), 1552 (w), 1489 (w),
1424 (m, sh), 1387 (m), 1305 (w), 1253 (m), 1178 (w), 1117 (m),
1072 (m), 1042 (m), 950 (s), 913 (s), 777 (w), 662 (br, s), 566 (sh),
460 (w), 415 (w).
Compound 2-Nd Stirring. Yield: 79 mg (43% based on 1). Anal.
Calcd for C135H225N27O105Mn3Mo18Nd5 (6519.294 g/mol) (Nd-
(DMF)6Nd(DMF)5Nd3(DMF)10[(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3): C, 24.87; N, 5.80; H, 3.48. Found: C, 24.62; N,
3181
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
Scheme 1. Synthetic Path of This Work: Starting from the Synthesis of the Organic Ligand LH4, Followed by Its Use to Form 1
(L−POM−L), Which Was Then Further Reacted with Ln(NO3)3 in Order to Form Families 2 and 3
(m), 1071 (m), 1040 (m), 949 (s), 912 (s), 775 (w), 663 (br, s), 565
(sh), 461 (w), 414 (w).
w), 2931 (m), 2855 (sh), 2817 (sh), 1651 (s), 1612 (sh), 1552 (w),
1499 (w), 1422 (m, sh), 1386 (m), 1303 (w), 1252 (m), 1175 (w),
1115 (m), 1071 (m), 1040 (m), 949 (s), 912 (s), 778 (w), 663 (br,
s), 565 (sh), 461 (w), 414 (w).
Compound 3-Yb Layering. Yield: 3.8 mg (44% based on 1). Anal.
Calcd for C129H215N25O105Mn3Mo18Yb5 (6553.127 g/mol) (([Yb-
(DMF)4(H2O)]2[Yb3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·5DMF): C, 23.64; N, 5.34; H, 3.31. Found: C,
23.93; N, 5.71; H, 3.38. FT-IR (KBr, cm−1): 4312 (br, sh), 3315 (br,
w), 2932 (m), 2855 (sh), 2817 (sh), 1652 (s), 1612 (sh), 1552 (w),
1499 (w), 1426 (m, sh), 1386 (m), 1303 (w), 1253 (m), 1175 (w),
1117 (m), 1070 (m), 1041 (m), 949 (s), 912 (s), 775 (w), 663 (br,
s), 566 (sh), 460 (w), 415 (w).
Compound 3-Lu Layering. Yield: 3.1 mg (34% based on 1). Anal.
Calcd for C129H215N25O105Mn3Mo18Lu5 (6562.762 g/mol) ([Lu-
( D M F ) 4 ( H 2 O ) ] 2
[Lu3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2(C6H4)COO)2]3·
5DMF): C, 23.61; N, 5.34; H, 3.30. Found: C, 23.24; N, 5.66; H,
3.65. FT-IR (KBr, cm−1): 4313 (br, sh), 3315 (br, w), 2932 (m),
2855 (sh), 2817 (sh), 1651 (s), 1612 (sh), 1553 (w), 1499 (w), 1425
(m, sh), 1386 (m), 1305 (w), 1251 (m), 1175 (w), 1116 (m), 1070
(m), 1040 (m), 949 (s), 913 (s), 776 (w), 663 (br, s), 565 (sh), 461
(w), 414 (w).
Compound 3-Ho Layering. Yield: 4.0 mg (43% based on 1). Anal.
Calcd for C126H208N24O104Mn3Mo18Ho5 (6439.485 g/mol) ([Ho-
(DMF)4(H2O)]2[Ho3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·4DMF): C, 23.50; N, 5.22; H, 3.26. Found: C,
23.26; N, 5.44; H, 3.58. FT-IR (KBr, cm−1): 4312 (br, sh), 3316 (br,
w), 2930 (m), 2855 (sh), 2817 (sh), 1651 (s), 1612 (sh), 1552 (w),
1499 (w), 1426 (m, sh), 1386 (m), 1305 (w), 1251 (m), 1175 (w),
1116 (m), 1070 (m), 1041 (m), 949 (s), 912 (s), 776 (w), 665 (br,
s), 565 (sh), 461 (w), 414 (w).
Compound 3-Er Layering. Yield: 3.8 mg (39% based on 1). Anal.
Calcd for C147H257N31O111Mn3Mo18Er5 (6962.785 g/mol) ([Er-
(DMF)4(H2O)]2[Er3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·11DMF): C, 25.36; N, 6.24; H, 3.72. Found: C,
24.98; N, 6.45; H, 3.93. FT-IR (KBr, cm−1): 4312 (br, sh), 3316 (br,
w), 2930 (m), 2856 (sh), 2817 (sh), 1650 (s), 1613 (sh), 1552 (w),
1499 (w), 14254 (m, sh), 1386 (m), 1305 (w), 1251 (m), 1175 (w),
1115 (m), 1071 (m), 1040 (m), 949 (s), 913 (s), 776 (w), 663 (br,
s), 566 (sh), 460 (w), 414 (w).
Compound 3-Tm Layering. Yield: 3.4 mg (35% based on 1). Anal.
Calcd for C147H257N31O111Mn3Mo18Tm5 (6971.161 g/mol) ([Tm-
(DMF)4(H2O)]2[Tm3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2]3·11DMF): C, 25.33; N, 6.23; H, 3.72. Found: C,
25.22; N, 6.46; H, 3.89. FT-IR (KBr, cm−1): 4313 (br, sh), 3315 (br,
In order to obtain larger amounts of a microcrystalline powder
form of Dy containing 3, [N(n-C4H9)4]4[(MnMo6O18)((OCH2)3-
3182
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
CNHCH2(C6H4)COOH)((OCH2)3CNH(C6H4)COO)]·3DMF (1;
200 mg, 0.084 mmol) was dissolved in 20 mL of DMF and a solution
of Dy(NO3)3·6H2O (200 mg, 0.462 mmol) dissolved in 20 mL of
MeOH was added with stirring over a period of 1 min at room
temperature. The solution turned turbid within 30 s and was stirred
for a further 1.5 h. The resulting powder was dried under vacuum to
yield 78 mg (40% based on 1). Anal. Calcd for
C150H264Dy5Mn3Mo18N32O112 (7012.443 g/mol) ([Dy(DMF)4-
(H2O)]2[Dy3(DMF)6][(MnMo6O18)((OCH2)3CNHCH2(C6H4)-
COO)2]3·12DMF): C, 25.69; N, 6.39; H, 3.79. Found: C, 25.42; N,
6.12; H, 3.96. FT-IR (KBr, cm−1): 4313 (br, sh), 3315 (br, w), 2931
(m), 2855 (sh), 2817 (sh), 1651 (s), 1613 (sh), 1552 (w), 1499 (w),
1425 (m, sh), 1386 (m), 1305 (w), 1251 (m), 1176 (w), 1115 (m),
1071 (m), 1040 (m), 949 (s), 913 (s), 776 (w), 663 (br, s), 566 (sh),
460 (w), 415 (w).
six oxo ligands, which are further shared with the organic
ligand and MoVI centers of the surrounding octahedra. The
length of the L−POM−L hybrid linker is either 22.3 or 22.9 Å.
In addition, there are three DMF molecules per asymmetric
unit in the lattice; one of these was identified via the
SQUEEZE function within PLATON.38
In the crystal structure of 1 the individual [(MnMo6O18)-
(HL)(L)]4− hybrids form zigzag chains via hydrogen bonds
between two carboxylate groups of the organic ligands of two
different hybrid units with an O···O distance of 2.420(5) Å and
an O−H···O angle of 163.6° (Figure 2b).
Figure 3 shows an extract of the chains formed by the POM
hybrids in views along the a, b, and c axes. In the structure, two
types of L−POM−L units form the chains resulting in two
types of chains with an A−B alternation.
For a better understanding, these two types of links within
the chains are colored in red and green. The view along the b
axis (Figure 3b) reveals that each chain is formed by an A−B
alternation of green and red hybrids. It also shows that, in the
a−c plane, the chains lie parallel to each other. The shortest
distance between two terminal oxygen atoms of two
neighboring polyanions is 8.7 Å. In the b−c plane (Figure
3a) and the a−b plane (Figure 3c) the chains have tilt angles of
107.5 and 96.3°, respectively.
RESULTS AND DISCUSSION
■
Scheme 1 shows the synthetic path of this work. The ligand
H4L was synthesized using the SN2 reaction between 4-
(chloromethyl)benzoic acid and tris(hydroxymethyl)-
aminomethane at room temperature in water.37 This organic
ligand H4L was then reacted with [N(n-C4H9)4]4[α-
Mo8O26],36 MnIII(OAc)3·2H2O, and tetrabutylammonium
bromide (TBA-Br) in DMF at 85 °C, forming compound 1
(L−POM−L). The two tetrahedrally coordinated MoVI ions
above and below the planar ring structure of the [α-Mo8O26]4−
moiety are now absent and the MnIII ion originating from
Mn(OAc)3 is inserted in the center of the ring. Additionally,
two triply deprotonated organic ligands HL3− are grafted onto
the resulting A-E POM. This POM hybrid was then combined
with lanthanide ions from Ln(NO3)3 to form type 3 POMOFs,
where the POM is present as part of the linker and the nodes
are the lanthanide ions.
Figure 4 shows the simulated (simu) and experimental (exp)
PXRD patterns of 1. The 2θ values of the reflections of 1-exp
shows a good agreement with those of 1-simu.
The reaction of the hybrid compound 1 with lanthanide
metals (Ln = Y, La−Lu) results in two families of frameworks
with the formulas Ln(DMF)6Ln(DMF)5Ln3(DMF)10-
[(MnMo6O18)((OCH2)3CNHCH2(C6H4)COO)2]3·xDMF
(2; Ln = La−Nd) and [Ln(DMF)4(H2O)]2[Ln3(DMF)6]-
[(MnMo6O18)((OCH2)3CNHCH2(C6H4)COO)2]3·xDMF
(3; Ln = Y, Sm−Lu). The differentiation in these two families
results from the lanthanide contraction, where the later
lanthanide ions have significantly smaller ionic radii in
comparison to the earlier ions. This also explains the decrease
in coordination sites at the lanthanide centers with increasing
atomic number within the lanthanide series. Two approaches
to obtaining single crystals were explored: namely, a layering
and a stirring method. In the case of the layering method, a
boundary layer of a mixture of DMF/MeOH (1/1 v/v) was
rapidly pipetted over a solution of 1 dissolved in DMF in order
to avoid mixing of the solvents. Then a solution of Ln(NO3)3·
5/6H2O (Ln = Y, La−Lu) dissolved in MeOH was rapidly
pipetted on top to give a three-layered system. Yellow crystals
of the families of 2 and 3, respectively, were obtained from the
lower layer after 5 days and were dried under vacuum (yield:
34−62%). In the case of the stirring method, 1 was dissolved in
DMF and a solution of Ln(NO3)3·5/6H2O (Ln = Y, La−Lu)
dissolved in MeOH was added with stirring over a period of 1
min at room temperature. The solution turned turbid within
30 s and was stirred for a further 1.5 h. The resulting powder
was dried under vacuum (yield: 40−45% based on 1
depending on Ln = Y, La−Lu). For the description of the
family 2, the Ce3+ compound is chosen as representative for
the other structures. The crystallographic data of this
compound are given in Table S2. As shown in Figure 5, the
structure of 2 consists of three {(MnMo6O18)((OCH2)3-
CNHCH2(C6H4)COO)2}5− units plus one {Ce(DMF)6}3+,
one {Ce(DMF)5}3+, and one {Ce3(DMF)10}9+ unit.
The structure of 1 is shown in Figure 2a, and the
crystallographic data are given in Table S1. The core of this
Figure 2. L−POM−L hybrid in 1: single hybrid (a) and 1D “zigzag”
chains (b). Color code: A-E POM, green ring with red polyhedral
models; O, red; C, gray; N, blue; H, black. TBA counterions and
DMF molecules are omitted for clarity. For (b), the C and N atoms
are shown with a wire/stick design and only H atoms of carboxylate
groups are shown.
compound is the Mn A-E POM {MnIIIMoVI6O18} with the
ligand L3− attached to it via the deprotonated hydroxyl groups,
above and below the plane. Additionally, one of the
carboxylate groups of each hybrid is deprotonated, resulting
in a total charge of 4−, which is balanced by four TBA
counterions. The six MoVI metal addenda atoms and the
central heteroatom MnIII have an octahedral coordination
geometry, and the coordination sites of MnIII are completed by
To simplify the description of the structure, A-E POMs with
different connection modes are marked in different colors in
3183
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
Figure 3. Views along the a axis (a), b axis, (b) and c axis (c) of the crystal structure of 1. Color code: A-E POMs, green and red polyhedral
models; O, red, H (only of carboxylate groups), black; C, gray wire/stick; N, blue wire stick. TBA counterions and DMF molecules are omitted for
clarity.
Figure 6. Figure 6a reveals that the A-E POM hybrid shown in
green links to the {Ce(DMF)5}3+ unit with Ce2 (unit 2) as the
central atom via one terminal oxygen (Ot) atom. Another A-E
POM hybrid colored in red also binds to this Ce2 (unit 2)
atom via two Ot atoms opposite to the green A-E POM. This
red A-E POM hybrid is then attached to one {Ce(DMF)6}3+
moiety with Ce1 (unit 1) as its center through two Ot atoms,
which lie opposite to the two Ot atoms coordinating to the first
{Ce(DMF)5}3+ unit. A third A-E POM hybrid shown in blue
binds to the {Ce(DMF)6}3+ unit via one Ot atom opposite to
those of the red A-E POM. This blue A-E POM hybrid also
links via a carboxylate group, which is part of the organic
linker, to a {Ce3(DMF)10}9+ unit containing Ce3, Ce4, and
Ce5 (unit 3). As shown in Figure 6b) five additional A-E
POMs coordinate to this {Ce3(DMF)10}9+ unit via carboxylate
groups coming from two green, two blue, and two red A-E
POM hybrids. The {Ce3(DMF)10}9+ moiety is hexagonally
coordinated by the six A-E POMs.
The distance between the Ce3+ centers in the {Ce-
Figure 4. Simulated (simu) and experimental (exp) PXRD patterns of
1.
(DMF)5}3+ (unit 2) and the {Ce(DMF)6}3+ (unit 1) units is
12.4 Å, whereas the distances between two Mn atoms of the
POM moieties are about 12.2 Å. The Mn−Ce distances
3184
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
Figure 5. Structure of 2-Ce. Color code: A-E POMs, green ring with red polyhedral models; Ce, orange; O, red; C, gray wire/stick; N, blue wire/
stick. Lattice DMF molecules and H atoms are omitted for clarity. DMF molecules coordinating to Ce atoms are represented by their O atoms.
Figure 6. (a) Structure of 2-Ce. DMF molecules and H atoms are omitted for clarity. (b) Six A-E POMs coordinating to {Ce3(DMF)10}9+ unit via
carboxylate groups. Color code: A-E-POMs, green, red, blue polyhedral models; Ce, orange; O, red; C, gray wire/stick; N, blue wire/stick. Lattice
DMF molecules and H atoms are omitted for clarity. DMF molecules coordinating to Ce atoms are represented by their O atoms.
between a core of a hybrid and a Ce ion of the {Ce(DMF)5}3+
(unit 2) and the {Ce(DMF)6}3+ (unit 1) parts, respectively,
are 6.1 and 6.9 Å. The Ce−Ce distances within the
{Ce3(DMF)10}9+ (unit 3) unit are 4.2 Å, whereas the Ce−
Mn distance between the Ce3 unit and a hybrid ranges from
12.1 to 14.0 Å. The largest OCOO−OCOO distances within one
POM hybrid range from 22.4 to 23.2 Å. In comparison to the
hybrid linker compound 1, the hybrids in 2-Ce are on average
compressed by 0.3 Å. In 2-Ce several DMF molecules, which
coordinate to the Ce centers, are disordered. For this reason,
only the O atoms of two DMF molecules of the {Ce-
(DMF)6}3+ (unit 2) unit, one DMF molecule of the
{CeDMF)5}3+ (unit 1) moiety, and six DMF molecules of
the {Ce3(DMF)10}9+ (unit 3) part could be refined.
Furthermore, only 2 DMF molecules in the lattice could be
crystallographically identified, whereas 15 additional DMF
molecules are suggested via the SQUEEZE function within
PLATON.38 The green A-E POM is disordered. During the
refinement process, it was not possible to model this disorder
with partial occupancy atoms, only as single components with
highly anisotropic thermal ellipsoids with significant residual
electron density surrounding this polyanion. When the A-E-
POM is considered to be wheel, the organic parts
{(OCH2)3CNHCH2(C6H4)COO} correspond to its axle.
The POM can rotate around this axis and is bonded to just
one Ce2 atom, so that the POM can undergo a high amplitude
of vibration. The amplitude of the vibration of the atoms
within the POM increases as we move farther from the central
Mn atom. Due to the fact that the organic ligands are not
linear, with the C−N bond forming a kink, this organic part is
also 2-fold disordered about the direction of rotation. For
some of these ligands this disorder could be modeled, but for
others it was necessary to use one set of highly anisotropic
atoms.
The SHAPE39 analysis shows that the Ce3+ ions are square-
antiprismatic (SAPR) (eight coordinated Ce2 and Ce3) and
capped-square-antiprismatic (CSAPR) (nine-coordinated Ce1,
Ce4, Ce5) coordinated (Table S4 and Figure S23).
Figure 7 shows the PXRD patterns of the family 2-Ln with
Ln = La−Nd. The simulated pattern (2-Ce simu) serves as a
reference. From all of the PXRD patterns of 2-Ln, it is clearly
seen that the samples contain the desired products. However,
the patterns with the labeling “L” (synthesized via a layering
method) show some extra reflections at e.g. 2θ values of 6.2,
8.8, 10.8, and 24.1°, respectively. This reveals that during the
crystallization process at least one other unknown compound
crystallizes. It was found that the formation of this byproduct
could be avoided by using a stirring method (labeled in Figure
7 with “S”).
For q description of the structure of the 3 series, Dy was
chosen as a representative for Ln. The crystallographic data of
this compound are given in Table S3. The unit cell is very
similar to that of compound 2-Ce and is closely isostructural,
but the smaller ionic radius of Dy3+ results in a change of the
3185
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
distance of one OCOO functional group to the other within one
hybrid ranges from 22.7 to 22.9 Å, which in comparison to the
free hybrid 1 is compressed on average by 0.3 Å.
As a result of the presence of an inversion center and a c
glide in the space group P21/c only one mono Dy unit is
represented rather than the two Ce units (unit 1 and unit 2)
for the compound 2-Ce.
The SHAPE39 analysis shows that the Dy1 ion is square-
antiprismatic (SAPR) 8-fold coordinated (Table S5 and Figure
S24).
In addition, the carboxylate groups of the hybrids coordinate
to the {Dy3(DMF)6}9+ moiety, where the ratio of red to green
polyanions coordinating to this core is 2:4 (Figure 10b). In
comparison to the environment of the 2 family (Figure 10a),
two blue POMs become equivalent to the green POMs. The
inversion center of the centrosymmetric space group P21/c in
the crystal structure of 3-Dy is between Dy3 and its inversion
equivalent Dy3A within the {Dy3(DMF)6}9+ moiety. Due to
this inversion center the middle Dy atom of the
{Dy3(DMF)6}9+ unit is disordered. Furthermore, the coordi-
nating carboxylate groups and the phenyl groups bound to
these carboxylate groups are also disordered (kink at N
disorder). Nevertheless, the 2-fold disorder could be modeled
for all of the organic ligands.
Figure 7. PXRD-patterns of the 2-Ln family (with Ln = La−Nd).
Abbreviations: simu, simulation; S, stirring method; L, layering
method. The 2θ values of reflections of the byproducts are highlighted
in orange boxes.
Due to the high degree of disorder, it was not possible to
determine the geometries of the Dy atoms within the
{Dy3(DMF)6}9+ unit. When a dummy atom was placed
between the 2-fold disordered Dy3 atom (Dy3A and Dy3B)
(Figure S25) approximate distances of 12.6−13.5 Å between
the Dy atoms of the {Dy3(DMF)6}9+ moiety to the Mn atoms
of the L−POM−L units could be estimated.
monoclinic space group from P21 to the centrosymmetric
space group P21/c. The framework structure of compound 3-
Dy is shown in Figure 8 and consists of three {(MnMo6O18)-
((OCH2)3CNHCH2(C6H4)COO)2}5− moieties, two {Dy-
(DMF)4(H2O)}3+ moieties, and one {Dy3(DMF)6}9+ moiety.
Furthermore, five DMF molecules can be identified in the
lattice by using the OLEX2 solvent mask.40
Figure 11 shows the PXRD patterns of the series 3-Ln with
Ln = Y, Sm−Lu. The simulated pattern (3-Dy simu) serves as
a reference. It is clearly seen that all of the measured samples,
including those with L (synthesized via layering method) and S
(synthesized under stirring conditions), correlate with 3-Dy
simu. However, the synthesis under stirring conditions was
only successful in the case of Dy; in all other cases the PXRD
patterns did not agree with the simulated pattern. For this
reason, these patterns are not shown in Figure 11.
For a simple description of the structure, A-E POMs with
different coordination modes are marked in different colors. As
shown in Figure 8b, the red A-E POM coordinates to two
{Dy(DMF)4(H2O)}3+ units (Dy1) via two terminal oxygen
atoms. Additionally, these Dy3+ ions are further linked to the
green hybrids by one terminal oxygen atom, resulting in a
coordination number of 8. Within this part of the structure
(Figure 9) the Dy−Mn distances are 6.1 and 6.8 Å and the
Mn−Mn distance between one green and one red hybrid is
12.1 Å. The Mn−Mn distance between two green POMs
amounts to 23.6 Å. The Dy−Dy distance is 12.1 Å. The
Topological Analyses. Families 2 and 3 both form
complex 3D structures, and therefore their topological analyses
Figure 8. Structure of compound 3-Dy. Color code: A-E POMs, green ring with red polyhedral models (a); A-E POMs, green and red polyhedral
models (b); Dy, orange; O, red; C, gray wire/stick; N, blue wire/stick. Lattice DMF molecules and H atoms are omitted for clarity. DMF and H2O
molecules of the {Dy(DMF)4(H2O)}3+ units are represented by their O atoms. DMF molecules of the {Dy3(DMF)6}9+ moiety are omitted for
clarity.
3186
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
Figure 9. Extracts of the structure of 3-Dy. Color code: A-E POMs, green and red polyhedral models; Dy, orange; O, red; C, gray wire/stick; N,
blue wire/stick. DMF, water molecules, and H atoms are omitted for clarity.
Figure 10. Comparison of the Ln3 environment of the 2 (a) and 3 (b) families. Color code: A-E POMs: green, red, and blue polyhedral models;
Ln, orange; O, red; C: gray wire/stick; N, blue wire/stick. DMF, water molecules, and H atoms are omitted for clarity.
{(MnMo6O18)((OCH2)3CNHCH2(C6H4)COO)2} units
(green and blue spheres), providing triply coordinating linker
hybrids (Figure 12i,ii). Furthermore, there is one MnCe2 unit,
which is based on one {(MnMo6O18)((OCH2)3CNHCH2-
(C6H4)COO)2}, one {Ce3+(DMF)6} (Ce1), and one
{Ce3+(DMF)5} (Ce2) unit (red spheres, Figure 12iii). The
hybrid coordinates to the Ce cations via two terminal atoms of
two diametrically opposed POM moieties. Thus, this crystallo-
graphically potentially 6-fold linker now extends to the Ce
cations and becomes a 4-fold linker from a topological point of
view. Topologically (Figure 12a) blue and green spheres are
linked to the red spheres, which corresponds to the
coordination of the blue and green labeled A-E POM moieties
of the hybrids to the Ce1 and Ce2 ions, respectively, via the
terminal oxygen atoms of the POMs shown in Figure 6. The
fourth component of the topology is provided by the Ce3
centers originating from one {Ce39+(DMF)10} unit (purple
sphere, Figure 12iv). As shown in Figure 12, it is clearly seen
that each purple sphere is hexagonally connected to two green,
Figure 11. PXRD patterns of the 3-Ln series (with Ln = Y, Sm−Lu).
two blue, and two red spheres. This corresponds to the
Abbreviations: simu, simulation; S, stirring method; L, layering
coordination of the POM hybrids to the {Ce39+(DMF)10}
method.
moiety via the carboxylate groups. The topology of this
structure can be discussed in two ways. (i) The A-E POM
hybrids are 3- and 6-fold linkers, respectively, connected to
each other via the coordination of terminal oxygen atoms to
Ce ions (Ce1 and Ce2), and the {Ce39+(DMF)10} units
represent the nodes, which are hexagonally coordinated by the
are helpful. As shown on the left side of Figure 12, a
topological analysis reveals that the structure of compound 2-
Ce includes four topologically different units. The structure
contains two MnIII cores resulting from two independent
3187
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
Given that both families of structures exhibit the same
topology, it is pertinent to check that the acentric space group
for the 2 family is correct and that an inversion symmetry has
not been missed. The crystal structure of 2-Ce refines in the
space group P21 with a Flack χ parameter of 0.125(4) for a
Friedel coverage of 82.4%. This indicates that the crystal used
for the measurement was partially twinned by inversion, such
that 87.5% of the crystal was made up of domains in which the
structure has the same handedness as the refined structure,
with 12.5% consisting of domains of the opposite enantiomer.
The magnitude of the standard uncertainty in the refined Flack
parameter (0.004) is in good agreement with the expected
value estimated from the amount of resonant scattering in the
structure (0.003). In contrast, for a genuinely centrosymmetric
structure refined (incorrectly) in P21, one would expect χ to
take a value close to 0.5, with a standard uncertainty much
higher than that found here.42 Conversely, attempts to refine
the structure of 3-Dy in P21 rather than P21/c led to severe
correlation between parameters that are related by the P21/c
inversion symmetry, and the disorder of the Dy3 moiety still
could not be resolved.
It is clear that in the 3 family, in which the heavier but
smaller lanthanide cations have a lower coordination number
and fewer DMF ligands on the trinuclear Ln3 moiety, any
ordering of the orientation of that moiety must be at best short
range in nature. For the 2 family, on the other hand, the larger
ionic radii of Ln3+ has resulted in a Ln3 unit with 10 rather than
6 DMF ligands, and this unit now shows long-range ordering,
with the resulting ordered domains being large enough to
diffract in their own right, even if this ordering did not extend
through the complete crystal.
We note that, within a batch of a compound from the 2
family, one enantiomer of the structure will dominate in some
crystals and the opposite enantiomer in others. Furthermore,
the numbers of such crystals will be equal, such that a
polycrystalline batch forms a racemic conglomerate.43 As Flack
points out, a consequence of this is that a technique such as
CD spectroscopy will not be able to detect the chirality of the
structure from a polycrystalline sample.
CONCLUSIONS
■
Figure 12. Comparison of the topology of the 2 family (left side) to
the 3 family (right side): topological nets along the a axis (a), b axis
(b) and c axis (c) created from the L−POM−L 3-connecting unit,
shown in green and blue, the 4-connecting unit shown in red, and 6-
connecting unit, which is the Ln3 unit.
We have developed an elegant triad approach involving flexible
building units of a POM, an organic ligand, and lanthanides to
develop a third route for constructing POMOFs. We not only
have used a new approach to combining POMs using MOF
design principles but have also performed topological analyses
and identified an interesting switch from an achiral to a chiral
space group without changing the underlying topology. These
findings are of interest in terms of the potential of chiral
switching in framework materials. The properties of these
newly explored POMOFs are under investigation.
carboxylate groups of the POM linkers. (ii) Every colored
sphere in the topological representation of this structure is a
node, which means that all of the POM moieties of the POM
hybrids become a junction. As a result, if the structure is
viewed in this way, the organic residues and the Ce1 and Ce2
ions now become the connecting units.
The topology can be identified as a 3,4,6-coordinated 3-
nodal net with ToposPro point symbol {610.83.102}{63}2-
{65.10} and labeled as 3,4,6T281.41
A topological analysis of 3-Dy reveals that the structure has
the same topology as that of the closely isostructural
compound 2-Ce. In Figure 12 the topology of the 2 family
(left side) is compared to the 3 family (right side). Due to the
change in space group from acentric P21 (2 family) to the
centrosymmetric space group P21/c (3 family), the blue
spheres in the topology of the 2 family become equivalent to
the green spheres in the topology of the 3 family.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.cgd.0c01138.
■
sı
Crystallographic and structural details, 1H and 13C NMR
spectra, FTIR spectra, and SHAPE analyses (PDF)
Accession Codes
CCDC 2008219−2008221 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
3188
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
(6) Bendi, R.; Kumar, V.; Bhavanasi, V.; Parida, K.; Lee, P. S. Metal
Organic Framework-Derived Metal Phosphates as Electrode Materials
for Supercapacitors. Adv. Energy Mater. 2016, 6, 1501833.
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.
(7) Liu, J.; Lukose, B.; Shekhah, O.; Arslan, H. K.; Weidler, P.;
Gliemann, H.; Bräse, S.; Grosjean, S.; Godt, A.; Feng, X.; Mullen, K.;
̈
AUTHOR INFORMATION
■
Magdau, I. B.; Heine, T.; Wöll, C. A novel series of isoreticular metal
organic frameworks: realizing metastable structures by liquid phase
epitaxy. Sci. Rep. 2012, 2, 1−5.
Corresponding Authors
Marcel P. Merkel − Institute of Nanotechnology, Karlsruhe
Institute of Technology Campus North, 76344 Eggenstein-
Leopoldshafen Karlsruhe, Germany; Institute of Inorganic
Chemistry, Karlsruhe Institute of Technology, 76131
Karlsruhe, Germany; orcid.org/0000-0001-5243-9881;
Email: marcel.merkel@kit.edu
Annie K. Powell − Institute of Nanotechnology, Karlsruhe
Institute of Technology Campus North, 76344 Eggenstein-
Leopoldshafen Karlsruhe, Germany; Institute of Inorganic
Chemistry, Karlsruhe Institute of Technology, 76131
Karlsruhe, Germany; orcid.org/0000-0003-3944-7427;
Email: annie.powell@kit.edu
(8) Song, G.; Wang, Z.; Wang, L.; Li, G.; Huang, M.; Yin, F.
Preparation of MOF(Fe) and its catalytic activity for oxygen
reduction reaction in an alkaline electrolyte. Chin. J. Catal. 2014,
35, 185−195.
̈
(9) Bauer, S.; Stock, N. Funktionale porose Materialien: MOFs -
Metallorganische Gerstustrukturen. Chem. Unserer Zeit 2008, 42, 12−
19.
(10) Huheey, J.; Keiter, E.; Keiter, R. Anorganische Chemie-Prinzipien
̈
̈
von Struktur und Reaktivitat, 5th ed.; De Gruyter: Berlin, 2014.
(11) Nohra, B.; El Moll, H.; Rodriguez Albelo, L. M.; Mialane, P.;
Marrot, J.; Mellot-Draznieks, C.; O’Keeffe, M.; Ngo Biboum, R.;
Lemaire, J.; Keita, B.; Nadjo, L.; Dolbecq, A. Polyoxometalate-Based
Metal Organic Frameworks (POMOFs): Structural Trends, Ener-
getics, and High Electrocatalytic Efficiency for Hydrogen Evolution
Reaction. J. Am. Chem. Soc. 2011, 133, 13363−13374.
Authors
Christopher E. Anson − Institute of Inorganic Chemistry,
Karlsruhe Institute of Technology, 76131 Karlsruhe,
Germany; orcid.org/0000-0001-7992-7797
George E. Kostakis − University of Sussex, Brighton BN1
9RH, United Kingdom; orcid.org/0000-0002-4316-4369
(12) Hagrman, D.; Zubieta, C.; Rose, D. J.; Zubieta, J.; Haushalter,
R. Komposite aus eindimensionalen Koordinationspolymeren Ma-
trices und Molybdanoxid- Untereinheiten: Polyoxomolybdatcluster in
[{Cu(4,4′-bpy)}4Mo8O26] und [{Ni(H2O)2(4,4′-bpy)2}2Mo8O26]
und eindimensionale Oxidketten in [{Cu(4,4′-bpy)}4Mo15O47]·
8H2O. Angew. Chem. 1997, 109, 904−907.
(13) Rafiee, E.; Nobakht, N. Keggin type heteropoly acid,
encapsulated in metal-organic framework: A heterogeneous and
recyclable nanocatalyst for selective oxidation of sulfides and deep
desulfurization of model fuels. J. Mol. Catal. A: Chem. 2015, 398, 17−
25.
(14) Zhang, Z. M.; Zhang, T.; Wang, C.; Lin, Z.; Long, L. S.; Lin, W.
Photosensitizing Metal−Organic Framework Enabling Visible-Light-
Driven Proton Reduction by a Wells−Dawson-Type Polyoxometalate.
J. Am. Chem. Soc. 2015, 137 (9), 3197−3200.
(15) Du, D. Y.; Qin, J. S.; Li, S. L.; Su, Z. M.; Lan, Y. Q. Recent
advances in porous polyoxometalate-based metal−organic framework
materials. Chem. Soc. Rev. 2014, 43, 4615−4632.
(16) Wang, X.; Chang, Z.; Lin, H.; Tian, A.; Liu, G.; Zhang, J.
Assembly and photocatalysis of two novel 3D Anderson-type
polyoxometalate-based metal−organic frameworks constructed from
isomeric bis(pyridylformyl)piperazine ligands. Dalton Trans. 2014, 43,
12272−12278.
(17) Song, J.; Luo, Z.; Britt, D. K.; Furukawa, H.; Yaghi, O. M.;
Hardcastle, K. I.; Hill, C. L. A Multiunit Catalyst with Synergistic
Stability and Reactivity: A Polyoxometalate-Metal Organic Frame-
work for Aerobic Decontamination. J. Am. Chem. Soc. 2011, 133,
16839−16846.
(18) Li, X.-X.; Wang, Y.-X.; Wang, R.-H.; Cui, C.-Y.; Tian, C.-B.;
Yang, G.-Y. Designed Assembly of Heterometallic Cluster Organic
Frameworks Based on Anderson-Type Polyoxometalate Clusters.
Angew. Chem., Int. Ed. 2016, 55, 6462−6466.
(19) Wei, M.; Wang, X.; Duan, X. Crystal Structures and Proton
Conductivities of a MOF and Two POM−MOF Composites Based
on CuII Ions and 2,2′-Bipyridyl-3,3′-dicarboxylic Acid. Chem. - Eur. J.
2013, 19, 1607−1616.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.cgd.0c01138
Funding
We thank the Helmholtz POF STN, Helmholtz Association
and Karlsruhe House of Young Scientists (KHYS) for funding
the short-term stay of M.P.M. at the University of Sussex
(United Kingdom).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Prof. Dr. Dieter Fenske and Dr. Olaf Fuhr for
collecting the crystallographic data.
REFERENCES
■
(1) According to IUPAC this is the relationship between CPs and
MOFs: a metal−organic framework, abbreviated MOF, is a
coordination polymer (or alternatively coordination network) with
an open framework containing potential voids: Batten, S. R.;
Champness, N. R.; Chen, X. M.; Garcia-Martinez, J.; Kitagawa, S.;
Ohrström, L.; O’Keeffe, M.; Suh, M. P.; Reedijk, J. Coordination
polymers, metal-organic frameworks and the need for terminology
̈
guidelines. CrystEngComm 2012, 14, 3001−3004.
(2) Brown, K.; Zolezzi, S.; Aguirre, P.; Venegas-Yazigi, D.; Paredes-
Garcia, V.; Baggio, R.; Novak, M. A.; Spodine, E. [Cu(H2btec)-
(bipy)]∞: a novel metal organic framework (MOF) as heterogeneous
catalyst for the oxidation of olefins. Dalton Trans. 2009, 1422−1427.
(3) Rowsell, J. L. C.; Eckert, J.; Yaghi, O. M. Characterization of H2
Binding Sites in Prototypical Metal-Organic Frameworks by Inelastic
Neutron Scattering. J. Am. Chem. Soc. 2005, 127, 14904−14910.
(4) Siegelman, R. L.; McDonald, T. M.; Gonzalez, M. I.; Martell, J.
D.; Milner, P. J.; Mason, J. A.; Berger, A. H.; Bhown, A. S.; Long, J. R.
Controlling Cooperative CO2 Adsorption in Diamine-Appended
Mg2(dobpdc) Metal−Organic Frameworks. J. Am. Chem. Soc. 2017,
139, 10526−10538.
(20) Wei, M.; Wang, X.; Sun, J.; Duan, X. A 3D POM−MOF
composite based on Ni(II) ion and 2,2′-bipyridyl-3,3′-dicarboxylic
acid: Crystal structure and proton conductivity. J. Solid State Chem.
2013, 202, 200−206.
(21) Yang, H.; Li, J.; Zhang, H.; Lv, Y.; Gao, S. Facile synthesis of
POM@MOF embedded in SBA-15 as a steady catalyst for the
hydroxylation of benzene. Microporous Mesoporous Mater. 2014, 195,
87−91.
(22) Sha, J.; Huang, L.; Peng, J.; Pang, H.; Tian, A.; Zhang, P.; Chen,
Y.; Zhu, M. Assembly of two novel Lindqvist polyoxoanion-templated
(5) Lennartson, A.; McKenzie, C. J. Bridging nitrile groups in a
metal-organic framework. J. Coord. Chem. 2012, 65, 4194−4202.
3189
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190

Crystal Growth & Design
pubs.acs.org/crystal
Article
coordination polymers with standard honeycomb cavities. Solid State
Sci. 2009, 11, 417−421.
(23) Shi-Zhou; Kong, Z. G.; Wang, Q. W.; Li, C. B. A novel
polyoxometalate-templated chiral three-fold interpenetrated metal-
organic framework: Synthesis, structure and properties. Inorg. Chem.
Commun. 2012, 20, 131−134.
(24) Marleny Rodriguez-Albelo, L.; Ruiz-Salvador, A. R.; Sampieri,
A.; Lewis, D. W.; Gomez, A.; Nohra, B.; Mialane, P.; Marrot, J.;
Secheresse, F.; Mellot-Draznieks, C.; Ngo Biboum, R.; Keita, B.;
Nadjo, L.; Dolbecq, A. Zeolitic Polyoxometalate-Based Metal-Organic
Frameworks (Z-POMOFs): Computational Evaluation of Hypo-
thetical Polymorphs and the Successful Targeted Synthesis of the
Redox-Active Z-POMOF1. J. Am. Chem. Soc. 2009, 131, 16078−
16087.
(41) Blatov, V. A.; Shevchenko, A. P.; Proserpio, D. M. Applied
Topological Analysis of Crystal Structures with the Program Package
ToposPro. Cryst. Growth Des. 2014, 14, 3576−3586.
(42) Flack, H. D.; Bernardinelli, G.; Clemente, D. A.; Linden, A.;
Spek, A. L. Centrosymmetric and Pseudo-Symmetric Structures
Refined as Non-Centrosymmetric. Acta Crystallogr., Sect. B: Struct. Sci.
2006, B62, 695−701.
(43) Flack, H. D. Chiral and Achiral Crystal Structures. Helv. Chim.
Acta 2003, 86, 905−921.
(25) Qin, J. S.; Du, D. Y.; Guan, W.; Bo, X. J.; Li, Y. F.; Guo, L. P.;
Su, Z. M.; Wang, Y. Y.; Lan, Y. Q.; Zhou, H. C. Ultrastable
Polymolybdate-Based Metal−Organic Frameworks as Highly Active
Electrocatalysts for Hydrogen Generation from Water. J. Am. Chem.
Soc. 2015, 137, 7169−7177.
(26) Li, S.; Ma, H.; Pang, H.; Zhang, L.; Zhang, Z.; Lin, H. The first
3D POMOF based on α-metatungstate and mixed-ligand. Inorg.
Chem. Commun. 2014, 44, 15−19.
(27) Zhu, P.-P.; Sun, L.-J.; Sheng, N.; Sha, J.-Q.; Liu, G.-D.; Yu, L.;
Qiu, H.-B.; Li, S.-X. Tuning the Helical Structures of Wells−Dawson
Polyoxometalate Based Hybrid Compounds by Using Isomeric
Ligands. Cryst. Growth Des. 2016, 16, 3215−3223.
(28) Yazigi, F.-J.; Wilson, C.; Long, D.-L.; Forgan, R. S. Synthetic
Considerations in the Self-Assembly of Coordination Polymers of
Pyridine-Functionalized Hybrid Mn-Anderson Polyoxometalates.
Cryst. Growth Des. 2017, 17, 4739−4748.
(29) Han, J. W.; Hill, C. L. A Coordination Network That Catalyzes
O2-Based Oxidations. J. Am. Chem. Soc. 2007, 129, 15094−15095.
(30) Blazevic, A.; Rompel, A. The Anderson−Evans polyoxometa-
late: From inorganic building blocks via hybrid organic−inorganic
structures to tomorrows “Bio-POM. Coord. Chem. Rev. 2016, 307,
42−64.
(31) Pope, M. T. Heteropoly and Isopoly Oxometalates. In Inorganic
Chemistry Concepts; Springer-Verlag: Berlin, 1983; Vol. 8.
(32) Yin, P.; Bayaguud, A.; Cheng, P.; Haso, F.; Hu, L.; Wang, J.;
Vezenov, D.; Winans, R. E.; Hao, J.; Li, T.; Wei, Y.; Liu, T.
Spontaneous Stepwise Self-Assembly of a Polyoxometalate−Organic
Hybrid into Catalytically Active One-Dimensional Anisotropic
Structures. Chem. - Eur. J. 2014, 20, 9589−9595.
(33) Zhao, C.; Ma, H.; Pang, H.; Li, S.; Zhang, Z.; Yu, Y. A new
POMOF consisting of [VW12]4− clusters and metal-organic nano-
tubes: Synthesis, structure, electrocatalytic and luminescent proper-
ties. Inorg. Chem. Commun. 2016, 69, 57−61.
(34) Chai, D. F.; Wang, M.; Zhang, C.; Ning, F.; Xu, W.; Pang, H.;
Ma, H. A novel 3D POMOF based on dinuclear copper (II)-oxalate
complexes and Keggin polyoxoanions with excellent photocatalytic
activity. Inorg. Chem. Commun. 2017, 83, 16−19.
(35) Li, L.; Sun, J. W.; Sha, J. Q.; Li, G. M.; Yan, P. F.; Wang, C.
Construction of POMOFs with different degrees of interpenetration
and the same topology. CrystEngComm 2015, 17, 633−641.
(36) Ginsberg, A. P. Inorganic Syntheses; Wiley: 1990; p 27.
(37) Hill, C. L.; Anderson, T. M.; Han, J. W.; Hillesheim, D. A.;
Geletii, Y. V.; Okun, N. M.; Cao, R.; Botar, B.; Musaev, D. G.;
Morokuma, K. New complexes and materials for O2-based oxidations.
J. Mol. Catal. A: Chem. 2006, 251, 234−238.
(38) Spek, A. L. PLATON SQUEEZE: a tool for the calculation of
the disordered solvent contribution to the calculated structure factors.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 9−18.
(39) Llunell, M.; Casanova, D.; Cirera, J.; Alvarez, S.; Alemany, P.
SHAPE: Program for the Stereochemical Analysis of Molecular Fragments
by Means of Continuous Shape Measures and Associated Tools, ver. 2.1;
Universitat de Barcelona: Barcelona, 2013.
(40) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A.
K.; Puschmann, H. OLEX2: a complete structure solution, refinement
and analysis program. J. Appl. Crystallogr. 2009, 42, 339−341.
3190
https://doi.org/10.1021/acs.cgd.0c01138
Cryst. Growth Des. 2021, 21, 3179−3190