Facile Synthesis of 3-(Azol-1-yl)-1-adamantanecarboxylic Acids—New Bifunctional Angle-Shaped Building Blocks for Coordination Polymers

Article abstract of DOI:10.3390/molecules24152717

For the first time, orthogonally substituted azole-carboxylate adamantane ligands were synthesized and used for preparation of coordination polymers. The angle-shaped ligands were prepared by the reaction of 1-adamantanecarboxylic acid and azoles (1H-1,2,

Full text of DOI:10.3390/molecules24152717

molecules
Article
Facile Synthesis of
3-(Azol-1-yl)-1-adamantanecarboxylic Acids—New
Bifunctional Angle-Shaped Building Blocks for
Coordination Polymers
Dmitry Pavlov 1 , Taisiya Sukhikh 2,3 , Evgeny Filatov 2,3 and Andrei Potapov 1,2,4,
*
1
Kizhner Research Center, National Research Tomsk Polytechnic University, 30 Lenin Ave.,
634050 Tomsk, Russia
2
Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3 Lavrentiev
Ave., 630090 Novosibirsk, Russia
Department of Natural Sciences, Novosibirsk State University, 2 Pirogov Str., 630090 Novosibirsk, Russia
Department of Chemical Technology, Polzunov Altai State Technical University, 46 Lenin Ave.,
656038 Barnaul, Russia
3
4
*
Correspondence: potapov@niic.nsc.ru; Tel.:+79234034103; Fax: +73833309489
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 4 July 2019; Accepted: 26 July 2019; Published: 26 July 2019
Abstract: For the first time, orthogonally substituted azole-carboxylate adamantane ligands were
synthesized and used for preparation of coordination polymers. The angle-shaped ligands
were prepared by the reaction of 1-adamantanecarboxylic acid and azoles (1H-1,2,4-triazole,
3-methyl-1H-1,2,4-triazole, 3,5-dimethyl-1H-1,2,4-triazole, 1H-tetrazole, 5-methyl-1H-tetrazole)
in concentrated sulfuric acid.
Variation of the solvent and substituents in azole
rings allowed to prepare both 1D and 2D copper(II) and nickel(II) coordination
polymers, [Cu2(trzadc)4(H2O)0.7
]·
DMF
·
0.3H2O, [Cu(trzadc)2(MeOH)] MeOH, [Ni(trzadc)2(MeOH)2]
·
and [Cu2(mtrzadc)3(MeOH)]+NO3 (trzadc-3-(1,2,4-triazol-1-yl)-adamantane-1-carboxylic acid;
mtrzadc-3-(3-methyl-1,2,4-triazol-1-yl)-adamantane-1-carboxylic acid) which were structurally
–
characterized by single crystal X-ray diffraction. Complex [Cu(trzadc)2(MeOH)] MeOH was shown
·
to act as a catalyst in the Chan-Evans-Lam arylation reaction.
Keywords:
adamantane; carboxylate ligands; chain structures; heterocyclic ligands;
metal-organic frameworks
1. Introduction
Adamantane has been recognized for
a
long time as an important molecule
for crystal design.
moiety is 1,3,5,7-tetrakis(1,2,4-triazol-4-yl)adamantane
1,3,5,7-adamantanetetracarboxylic acid can produce spectacular frameworks [
of different adamantane derivatives have been designed and their coordination ability explored [
An example of exploiting the potential of the adamantane
], but even more simple
]. A number
14].
[1
2
3
–
Metal-organic frameworks (MOFs) that feature metal ions with a ‘mixed’ coordination environment
are often of great interest [15], and in case of adamantane usually achieved through a ‘mixed-ligand’
approach [16], which turns a two-component reaction into a much more complicated system, reducing
reproducibility and ease of handling. One way to avoid this problem is to combine various functions
in a single molecule, but no examples of coordination compounds built using two or more different
donor groups linked by an adamantane backbone have been reported so far. This fact is probably due
to synthetic difficulties in such functionalization [
3,
17]. Functional moieties with different coordination
Molecules 2019, 24, 2717; doi:10.3390/molecules24152717
www.mdpi.com/journal/molecules

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modes linked by a rigid platform like adamantane may be expected to form structures with complex
geometry of great interest; producing a ‘mixed’ coordination environment for metal ion, so looking for
ways to synthesize such species is always an actual challenge.
Following our interest in adamantane-based ligands [18], in this paper, we would like
to communicate a method for the synthesis of the new adamantane-based ligands—3-(1,2,4-
triazol-1-yl)-1-adamantanecarboxylic acid, 3-(tetrazol-1-yl)-1-adamantanecarboxylic acid and their
methyl derivatives. Along with synthesis of new ligands themselves, several coordination polymers
were synthesized and structurally characterized.
2. Results and Discussion
2.1. Symthetic Approach
For the synthesis of ligands, we employed the very well-known property of adamantane to form
a carbocation with the charge localized at bridgehead carbon under highly acidic conditions [19
(Scheme 1).
–21]
Scheme 1. Reaction scheme between azoles (AzH) and 1-adamantanecarboxylic acid.
This reaction went smoothly for both unsubstituted and 3,5-substituted 1,2,4-triazoles, as well
as tetrazoles—much to our surprise, because usually, adamantylation of azoles can be achieved by
substitution reaction of bromo- or hydroxy- groups [22–26]. Despite the fact that the carboxylic
moiety destabilizes adamantyl cations to a significant extent, the reaction between azoles and
1-adamantanecarboxylic acid proceeded smoothly and gave new bifunctional adamantane derivatives
in good yields. Hence, this reaction is an example of useful C-H functionalization.
To further explore interactions of 1-adamantylcarboxylic acid with different azoles, we attempted
the same procedure for diazoles, but reactions with both pyrazole and imidazole were unsuccessful,
and gave 3-hydroxyadamantane 1-carboxylic acid as products with 65% yield.
These observations correspond well with previous studies on the reactivity of azoles and adamantyl
cations in acidic media [22–26], where it was determined that adamantylation with 1-adamantanol is
possible with fairly acidic pyrazoles, the approximate limit to the pKBH+ being 0.8 [26]. Acidities of
both unsubstituted pyrazole and imidazole are much lower (0.47 and 0.39) than that value [27].
2.2. Synthesis and IR Spectra of Coordination Polymers
Reaction of trzadcH with copper(II) and nickel(II) nitrates in methanol at 4:1 ratio afforded
pale-blue and pale-green crystalline 1D coordination polymers 2 and 3. Reaction with copper nitrate in

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DMF at the same ratio afforded bright-blue crystals
1
with different composition. At the same time,
some amorphous green product precipitated. The reaction in dry DMF afforded only amorphous
green solid, which turned blue on prolonged exposure to air. All attempts to obtain a crystalline
form of this product have failed and no other attempts at characterization of the compound were
made. Pure compound
1 could be prepared by addition of an equimolar amount of water. Reaction of
mtrzadcH with copper(II) nitrate in methanol yielded bright-green crystals of 2D coordination polymer
4, its higher dimensionality is probably due to the additional steric hindrance introduced by methyl
group (see discussion below).
All of the IR spectra demonstrate coordination-induced shifts of bands corresponding to vibrations
of azole rings and carboxylic groups (Figure S7).
The broad band at 3456 cm−1 in the spectrum of compound
1
can be attributed to lattice water.
Bands of asymmetric and symmetric carboxylic C-O stretching vibrations appear at 1578 cm−1 and
1350 cm−1 228 cm−1) compared to 1682 cm−1 and 1229 cm−1 453 cm−1) in the uncoordinated
ligand. For compounds and separation between carboxylic stretching vibration bands ( ) is 265
and 185 cm−1, respectively. In case of compound value is 314 cm−1. These observations are
consistent with non-equivalence of metal-oxygen bonds in compounds 1–4 evident from structural
data [28 29]. Stretching OH vibration bands of uncoordinated methanol can be seen in the spectrum
of compound
(
∆
(∆
2
3
∆
4, ∆
,
2
at 3381 cm−1 but in the spectra of compounds
3 and 4 with coordinated methanol
molecules these bands were not detected. Extremely intense band at 1415 cm−1 in the spectrum of
compound 4 indicates the presence of uncoordinated NO3− ion.
2.3. Crystal Structure of 3-(1,2,4-Triazol-1-yl)-1-adamantanecarboxylic Acid
Compound trzadcH crystallizes in a monoclinic crystal system, P21/n space group, the unit cell
contains four formula units of the compound (Figure 1). The molecules of trzadcH are involved in
O–H···N intermolecular hydrogen bonding via carboxylic groups and nitrogen atoms in position 4 of
1,2,4-triazole cycles (O···N distance of 2.677 Å, O–H···N angle of 165.48◦). Hydrogen bonds link the
molecules into 1D chains, oriented at an angle of 39.2 degrees to the c axis (Figure S5).
Figure 1. The structure of the compound trzadcH showing adamantane centroid (ctr) and φCctrN
angle. H atoms are omitted.
In order to describe and compare the geometries of different angle-shaped N,O-ligands, we
defined the angle φCctrN comprising the carbon atom of the carboxylic group, the centroid of the linker
(adamantine in our case) and nitrogen donor atom (N atom at position 4 of triazole ring for compound
trzadcH). The value of this angle for trzadcH (110.6◦) is noticeably different from φCctrN values
calculated for most of other angle-shaped ligands commonly used for the synthesis of coordination
polymers (Table 1), indicating the perspectivity of the synthesized family of ligands for the construction
of coordination polymers with new topologies.

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Table 1. Angle-shaped ligands commonly used for the synthesis of coordination polymers.
◦
Ligand
φCctrN
,
CSD Code, Reference
110.6
this work
112.6
119.4
127.0
NUYXAH [30]
YEWFUE [31]
O
N
N
N
O
CIJVUP [32]
136.3
66.1
BOZTAM [33]
138.3
66.8
LAGNOZ [34]
ATAMEP [35]
139.4
66.3
143.6
143.7
RIQSOC [36]
JAZHOK [37]
YEDBOB [38]
144.8
65.5
2.4. Crystal Structures of Coordination Polymers
The non-isostructural complexes 1–3 are 1D coordination polymers revealing the bridging nature
of the trzadc– ligand (Figures 2 and 3). It coordinates to the metals via one N of triazole and one
O atom of carboxyl moiety to form 1D chains. Two trzadc– are arranged between adjacent central
atoms; thus, the ligands occupy four coordination sites of the metal forming a square environment.
Other sites are occupied by water or methanol: two molecules in the complex
coordination environment of Ni, and one molecule in with a square pyramidal arrangement of Cu.
Compound contains the first Cu atom in a square planar environment (without solvent molecules),
2, revealing octahedral
3
1
while the second Cu atom features partially occupied (of 70%) water molecules in a coordination
shell according to analysis of residual electron density map (Figure S14). Thus, this Cu atom has a
mixed square pyramidal/square planar environment. The reason for partial occupancy of water can be
corresponding with the bond distance Cu–O of 2.40 Å, being longer than typical Cu–OH2 bonds (of
1.95–2.20 Å) found in CSDB (v. 5.40, February 2019). As a result, the weak Cu–O interaction leads
to defects in the crystal packing. Note that structure
1 contains partially occupied (of 30%) solvate
water molecule close to coordinated one. However, they do not compete for the formation of hydrogen
bonds (Figure S1a), and there is enough space in the structure for their joint presence.

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(a)
Figure 2. The structure of 1D chain of the complexes
(b)
1 (a) and 2 (b). Adamantane units are coloured
blue, coordination polyhedra of the central atoms are coloured orange. Hydrogen atoms and solvate
molecules are omitted; dashed red lines indicate intramolecular hydrogen bonds.
(a)
(b)
Figure 3. The structure of 1D chain of the complex 3 (a) and structure of the complex 4 (b). Adamantane
units are coloured blue, coordination polyhedra of the central atoms are coloured orange. Hydrogen
atoms and nitrates are omitted; dashed red lines indicate intramolecular hydrogen bonds.
Overall geometry and crystal packing of 1D chains of complexes
However, in , adamantane units are arranged on one side from the CuNO plane (Figure S3), while in
and , adamantane units lie on both sides of the corresponding plane. Furthermore, complex
1–3 are somewhat close (Figure S2).
3
1
2
3
reveals
tight packing of the chains (with intramolecular hydrogen bonds between the methanol and carboxyl
moiety), while and have solvate DMF, water or methanol molecules filling the space between the
1
2
chains. The solvate molecules connect the chains via hydrogen bonds forming 2D-layered structures
(Figure S1).
The structure of complex
methyl substituent in the triazole moiety. This group prevents arrangement of the ligands to form a
square coordination environment of Cu, which is observed for . Instead, pentagonal pyramidal
environment is implemented in with two N atoms in apical and basal positions for the first Cu atom
and one N atom in the apical position for the second one (Figure 3). The latter further coordinates the
methanol molecule. In contrast to , the carboxylate moiety serves as a bridging group connecting
4 significantly differs from that of 1–3 because of the presence of a
1–3
4
1–3
two adjacent central atoms. Thus, a 2D-layered structure of 4 is observed.
In principle, trzadc– and mtrzadc– ligands have two degrees of freedom, viz. rotation of triazole
around C–N bond and rotation of carboxyl moiety around C–O bond (Figure S4). According to analysis
of the corresponding torsion angles (Table S2), conformation of the ligand can vary within certain
limits, adjusting to the central atom environment.
2.5. Powder X-Ray Diffraction and Thermal Studies
Powder X-Ray diffraction was used to confirm phase purity of the bulk product. As experimental
PXRD patterns match simulated ones sufficiently (Figure S5), we conclude that synthesis provides
product of high purity with good crystallinity.
All of the coordination polymers demonstrate similar thermal stability. (Figure S8) In case of
1,
only DMF molecules are lost during the initial step (219–281 ◦C)—calc. mass loss 5.98%, observed

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6.13%. Water loss along with the gradual organic ligand degradation started at 315 ◦C and completed
at 430 ◦C. Compound
loses one uncoordinated methanol molecule during the first thermolysis step
(90–200 ◦C), followed by deep degradation of the ligand and coordinated methanol loss in the range of
270–580 ◦C. As for , coordinated methanol molecules remain bond up to the temperature of 190 ◦C,
then a mass loss of 10.2% occurs, corresponding to two methanol molecules (calc. 10.4%). Coordination
of polymer
demonstrated an extremely exothermic decomposition process in the range of 220–260 ◦C
2
3
4
with a rapid mass loss, consistent with the presence of nitrate ions.
2.6. Catalytic Activity Studies
Considering a vacant coordination site of a copper atom in compound
2 and coordinated solvent
molecules in compounds
1 and 3, as well as numerous applications of chain coordination polymers
as catalysts [39 40], we decided to test their catalytic activity for the Chan-Evans-Lam N-arylation
,
reaction (CEL arylation), which is known to be efficiently catalysed by various metal complexes [41
]
and copper salts [42].
We found that compound
2 serves as an efficient catalyst for the CEL arylation reaction,
with imidazole and phenylboronic acid as model substrates (Scheme 2). The reaction was performed at
40◦ using methanol as a solvent on air with 1:1.5 molar ratio of reagents adding 5 mol% of the catalyst.
With these conditions, we achieved 99% conversion (GC) of the starting imidazole after 24 h.
Scheme 2. Model reaction for the investigation of catalytic properties of polymer 2.
Interestingly enough, compound
(Table 2, entries 8–9), which allows us to conclude that not only copper itself is crucial, but also
its coordination environment, being square planar in and mixed square pyramidal/square planar in 1.
1 demonstrated no catalytic activity in this reaction, as well as 3
and
4
2
Also, it might be due to stronger bonding of water compared to the methanol molecules.
Table 2. Influence of the reaction conditions and catalyst choice on the result of the reaction.
Entry
Solvent
Result
1
2
3
4
5
6
7
8
9
Methanol
Methanol a
Methanol b
DMSO
99% conversion
60% conversion
92% conversion
-
-
Water
Dichloromethane 13% conversion
Ethanol
15% conversion
Methanol c
Methanol d
-
No reaction
Reaction conditions: 0.1 mmole imidazole (6.3 mg), 0.15 mmoles (18,3 mg) phenylboronic acid, 6 mg compound 2,
1 mL methanol, 40 ◦C, 24 h on air.—Degradation of the polymer. a—reaction at room temperature. b—0.12 mmoles
(14,6 mg) of phenylboronic acid were used. c—4 was used as a catalyst, d—1 or 3 were used as catalysts.
Furthermore, we found that methanol is an essential condition for the success of the reaction.
We have tested a number of different solvents, some of them gave low conversions and in some cases,
the polymer had dissolved completely (DMSO and water), in case of ethanol, partial dissolution was
also noted; all results are summarized in Table 3.

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Table 3. Crystallographic data of the ligand trzadcH and the complexes 1–4.
Compound
trzadcH
1
2
3
4
Empirical formula
Formula weight
Space group
C13H17N3O2
247.29
C55H73Cu2N13O10
1203.34
C55H76Cu2N12O11
1208.35
C28H40N6NiO6
615.37
C43H58Cu2N10O10
1002.07
P21/c
P21/n
P–1
P–1
P–1
11.1449(11)
6.7467(5)
15.3121(17)
90
100.142(10)
90
1133.35(19)
4
1.449
0.100
528.0
0.17 × 0.15 × 0.08
6.52 to 62.93
12.0509(5)
13.5356(5)
17.4158(8)
97.022(2)
108.9450(10)
95.3130(10)
2640.15(19)
2
1.514
0.880
1264.0
0.27 × 0.13 × 0.08
6.6424(2)
12.0031(4)
17.8350(6)
70.4510(10)
81.2370(10)
81.8090(10)
1317.96(7)
1
6.6392(5)
9.7528(7)
11.6021(8)
66.060(2)
81.403(2)
74.214(2)
660.07(8)
1
10.1256(3)
14.5363(4)
30.4164(8)
90
95.9110(10)
90
4453.1(2)
4
1.495
1.025
2096.0
0.35 × 0.3 × 0.22
3.108 to 57.488
a/Å
b/Å
c/Å
α/◦
β/◦
γ/◦
Volume/Å3
Z
ρcalcg/cm3
µ/mm−1
F(000)
1.522
0.883
636.0
1.548
0.792
326.0
Crystal size/mm3
2Θ range for data
collection/◦
0.3 × 0.15 × 0.12
3.66 to 57.612
0.31 × 0.18 × 0.17
3.844 to 57.49
3.61 to 52.746
−14 ≤ h ≤ 12,
−8 ≤ k ≤ 8,
−19 ≤ l ≤ 19
9394
−15 ≤ h ≤ 15,
−16 ≤ k ≤ 14,
−21 ≤ l ≤ 21
30381
−8 ≤ h ≤ 8,
−16 ≤ k ≤ 16,
−24 ≤ l ≤ 24
20394
−8 ≤ h ≤ 8,
−13 ≤ k ≤ 13,
−15 ≤ l ≤ 15
12721
−13 ≤ h ≤ 13,
−15 ≤ k ≤ 19,
−38 ≤ l ≤ 41
62483
Index ranges
Reflections collected
2601 [Rint = 0.0460,
Rsigma = 0.0505]
164
10753 [Rint = 0.0320,
Rsigma = 0.0425]
737
6840 [Rint = 0.0238, 3415 [Rint = 0.0241,
11544 [Rint = 0.0270,
Rsigma = 0.0182]
591
Independent reflections
Rsigma = 0.0246]
Rsigma = 0.0194]
parameters
364
189
Goodness-of-fit on F2
1.027
1.023
1.053
1.055
1.045
R1 = 0.0463,
wR2 = 0.0923
R1 = 0.0733,
wR2 = 0.1026
0.34/−0.24
R1 = 0.0405,
wR2 = 0.0971
R1 = 0.0558,
wR2 = 0.1044
1.03/–0.53
R1 = 0.0385,
wR2 = 0.1029
R1 = 0.0427,
wR2 = 0.1059
1.51/–0.70
R1 = 0.0269,
wR2 = 0.0732
R1 = 0.0280,
wR2 = 0.0739
0.68/–0.46
R1 = 0.0272,
wR2 = 0.0704
R1 = 0.0312,
wR2 = 0.0723
0.48/–0.34
Final R indexes [I >= 2σ (I)]
Final R indexes [all data]
Largest diff. peak/hole/e Å−3
Additionally, we investigated the influence of reactant ratios and temperature. The reaction does
occur at the room temperature, but it is inefficiently slow (Table 2, entry 2), giving only 60% conversion
in 24 h. A decrease of the amount of boronic acid leads to the decrease of conversion (92%, Table 2,
entry 3).
To elucidate the possibility of the homogenous catalysis happening and to prove our claim for the
recyclability of the catalyst, we recovered the compound after running a reaction in a single cycle and
run PXRD on the recovered sample (Figure 4). The sample was washed with methanol and dried on
air prior to analysis.
Figure 4. PXRD of the compound 2 before and after running the reaction.
As evident from the diffractogram, compound
2 remains crystalline and no new phases are
observed, which proves that the process happening is heterogenous and our catalyst could be reused
several times without losing its crystalline state.

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3. Materials and Methods
3.1. Materials
All reagents were of reagent grade and used as received without further purification.
3(5)-Methyl-1,2,4-triazole [43] and 3,5-dimethyl-1,2,4-triazole [44,45] were synthesized according
to the literature.
3.2. Methods
Thermogravimetric analysis (TGA) coupled to differential scanning calorimetry (DSC) was carried
out with a NETZSCH 449F3 instrument (Erich NETZSCH GmbH & Co. Holding KG, Selb, Germany))
at a heating rate of 10 K/min in a stream of argon, scanning range—30–800 ◦C. Samples were air-dried
for several days prior to analysis. GC-MS analyses were performed on an Agilent 7890A GC combined
with an Agilent 5975C mass detector (Agilent Technologies, Santa Clara, CA, USA); carrier gas was
helium. IR spectra were recorded on Agilent Cary 630 FTIR spectrometer equipped with a diamond
ATR (attenuated total reflectance) tool. NMR spectra were recorded on a Bruker AVANCE III HD
instrument (Bruker, Billerica, MA, USA) and are referenced to the solvent residual signal. Elemental
analyses were carried out on Carlo Erba CHNS analyser (Val de Reuil, France).
3.2.1. X-ray Structure Determination
Single-crystal X-ray diffraction data were collected at 150 K on a Bruker-DUO APEX CCD
diffractometer (graphite monochromatized Mo Kα radiation, λ = 0.71073 Å, ϕ and ω scans of narrow
frames, Bruker Corporation, Billerica, MA, USA) equipped with a 4K CCD area detector (Table 3).
Absorption corrections were applied using the SADABS program [46]. The crystal structures were
solved by direct methods and refined by full-matrix least-squares techniques with the use of the
SHELXTL package [47] and Olex2 GUI [48]. Atomic thermal displacement parameters for non-hydrogen
atoms were refined anisotropically. The positions of H atoms were calculated corresponding to their
geometrical conditions and refined using the riding model. In the complex 1, both coordinated and
solvate water molecules show non-integer occupancies (of ca. 70/30% correspondingly) as clearly
indicated by residual electron density map (Figure S14). Thus, the occupancies were refined with their
sum constrained to unity to have reasonable atomic displacement parameters of O atoms.
3.2.2. Ligand Synthesis
General method for preparation of all presented compounds is described below. Completion of
the reactions was determined by TLC with bromocresol green solution as a stain.
10 mmol of the appropriate azole (1H-1,2,4-triazole, 3-methyl-1H-1,2,4-triazole,
3,5-dimethyl-1H-1,2,4-triazole, 1H-tetrazole or 5-methyl-1H-tetrazole) and 10 mmol of 1-adamantane
carboxylic acid were placed in 20 mL screwcap vial and dissolved in 10 mL of 98% concentrated
◦
sulfuric acid. The mixture was cooled to 0 C using an ice bath. After cooling, 10 mmol (1010
mg) of potassium nitrate were added in small portions over the period of 30 min. Once all of the
nitrate has been added, the ice bath was removed, and the mixture was stirred for another 4 h at
room temperature. After 4 h of stirring, reaction mixture was poured on 100 g of crushed ice with
shaking and allowed to stand until it reached room temperature. Quenched mixture was filtered and
neutralized with saturated NaHCO3 solution. Precipitate was filtered, washed with copious amounts
of distilled water and dried in vacuum desiccator. Products are sufficiently pure for the synthesis of
coordination compounds, but for the analysis the small portions of each compound were recrystallized
from the mixture of water/MeOH (9:1).
3-(1,2,4-Triazol-1-yl)-adamantane-1-carboxylic acid (trzadcH) Yield 88%, colorless crystals.
C13H17N3O2 (247.30): calcd. C 63.14, H 6.93, N 16.99; found C 63.38, H 7.09, N 17.13. Mp = 201–202 ◦C,
1H NMR (400 MHz, CDCl3):
δ
= 1.67 (s, 2 H, CH2), 1.82 (t, 2 H, CH), 2.08 (t, 4 H, CH2), 2.17 (s, 2 H,
CH), 2.26 (s, 2 H, CH2), 7.97 (s, 1 H, trz), 8.59 (s, 1 H, trz), 12.53 (s, 1 H, COOH), ppm. 13C (100 MHz,

Molecules 2019, 24, 2717
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CDCl3):
δ
= 29.0, 34.9, 37.7, 41.4, 42.2, 43.6, 58.5, 141.1, 151.3, 177.6, ppm. FT-IR (cm−1):
ν
= 2921 (s),
2849 (s), 1682 (s), 1506 (m), 1455 (w), 1363 (w), 1318 (w), 1285 (s), 1229 (s), 1132 (s), 1084 (s), 973 (m), 883
(w), 837 (s), 704 (s). m/z (methyl ester): 261 (100%), 202 (44%), 133 (91%), 100 (58%).
Crystals suitable for single crystal X-Ray diffraction were obtainted by heating the compound in
water to 150 ◦C in a sealed ampoule and slow cooling to room temperature.
3-(3-Methyl-1,2,4-triazol-1-yl)-adamantane-1-carboxylic acid (mtrzadcH) Yield 65%, colorless crystals.
C14H19N3O2 (261.32): calcd. C 64.35, H 7.33, N 16.08; found C 64.62, H 7.07, N 16.41. Mp = 179–180 ◦C,
1H NMR (400 MHz, CDCl3):
δ
= 1.66 (s, 2 H, CH2), 1.80 (t, 2 H, CH), 2.04 (t, 4 H, CH2), 2.13 (s, 2 H,
CH2), 2.23 (s, 5 H), 8.40 (s, 1 H, trz), 12.34 (s, 1 H, COOH), ppm. 13C (100 MHz, CDCl3):
= 14.28, 29.0,
34.9, 37.7, 41.4, 42.2, 43.6, 58.10, 141.5, 159.6, 177.6, ppm. FT-IR (cm−1):
= 3131 (w), 2922 (s), 2960 (s),
δ
ν
1685 (s), 1527 (m), 1458 (m), 1320 (m), 1244 (s), 1086 (m), 1023 (m), 867 (s), 717 (s). m/z (methyl ester):
275 (89%), 216 (28%), 193 (63%), 133 (100%), 91 (47%).
3-(3,5-Dimethyl-1,2,4-triazol-1-yl)-adamantane-1-carboxylic acid (dmtrzadcH) Yield 47%, colourless
needles. C15H21N3O2 (275.35): calcd. C 65.43, H 7.69, N 15.26; found C 65.71, H 7.48, N 15.49.
Mp = 244–245 ◦C, 1H NMR (400 MHz, (CD3)2SO):
δ
= 1.49–1.79 (m, 7 H), 2.13 (m, 7 H), 2.23 (s, 4 H),
2.49 (s, 4 H), 12.25 (s, 1H, COOH), ppm. 13C (100 MHz, (CD3)2SO):
= 14.0, 15.9, 29.3, 34.8, 37.6, 40.8,
42.3, 43.0, 60.1, 151.1, 156.6, 177.8, ppm. FT-IR (cm−1):
= 3437 (w), 2915 (s), 2860 (s), 1691 (s), 1533 (m),
δ
ν
1408 (s), 1347 (m), 1257 (s), 1224 (s), 1078 (s), 989 (m), 891 (m), 851 (m), 739 (m), 693 (s). m/z (methyl
ester): 289 (61%), 230 (25%), 193 (93%), 161 (48%), 133 (100%), 91 (40%).
3-(Tetrazol-1-yl)-adamantane-1-carboxylic acid (ttzadcH) Yield 81%, white powder. C12H16N4O2
(248.28): calcd. C 58.05, H 6.50, N 22.57; found C 58.36, H 6.61, N 22.68. Mp = 195–197 ◦C, 1H NMR
(400 MHz, (CD3)2SO):
1H, COOH), ppm. 13C (100 MHz, (CD3)2SO):
177.33, ppm. FT-IR (cm−1):
= 3145 (w), 2911 (s), 2862 (s), 1708 (s), 1458 (m), 1291 (m), 1260 (w), 1221
δ
= 1.71 (s, 2 H), 1.85 (s, 4 H), 2.22 (s, 4 H), 2.32 (m, 4 H), 8.94 (s, 1 H, ttz), 12.34 (s,
δ
= 29.06, 34.58, 37.49, 41.24, 42.25, 43.07, 64.09, 153.22,
ν
(s), 1165 (m), 1093 (m), 1092 (m), 1040 (s), 901 (m), 697 (s).
1-(5-Methyl-tetrazol-1-yl)-adamantane 3-carboxylic acid (mttzadcH) Yield 76%, white powder.
C13H18N4O2 (262.31): calcd. C 59.53, H 6.92, N 21.36; found C 59.79, H 6.68, N 21.66. Mp = 179–180
◦C, 1H NMR (400 MHz, (CD[
3
])2SO):
H), 2.60 (s, 2 H), 11.14 (s, 1 H, COOH), ppm. 13C (100 MHz, (CD3)2SO):
41.19, 42.59, 42.77, 63.46, 162.25, 181.68, ppm. FT-IR (cm−1):
= 2932 (s), 2863 (s), 1708 (s), 1501 (m),
δ
= 1.88 (s, 2 H), 2.08 (m, 4 H), 2.41 (s, 4 H), 2.51 (s, 3 H), 2.57 (s, 2
δ
= 10.82, 28.99, 34.71, 37.30,
ν
1458 (m), 1363 (w), 1336 (m), 1208 (s), 1142 (s), 1101 (m), 980 (w), 902 (m), 849 (m), 716 (s), 667 (s).
3.2.3. Preparation of Coordination Compounds
All the complexes were prepared under solvothermal conditions as follows. 2 mL of 0.1 M ligand
solution (0.2 mmol) in methanol (compounds 2–4) or DMF (compound 1) was mixed with 1 mL 0.1 M
solution (0.1 mmol) of appropriate metal nitrate hydrate in a 4 mL screwcap vial. Vial was placed in
oven at 80 ◦C for methanol and 120 ◦C for DMF for 24 h. Upon cooling to room temperature, crystals
suitable for single crystal X-Ray analysis were formed, washed with 4 mL of fresh solvent and stored
under pure solvent.
[Cu2(trzadc)4(H2O)0.7
]
·
DMF 0.3H2O (1) Bright blue crystals. Yield 23%. C55H75Cu2N13O11
·
(1221.35): calcd. C 54.07, H 6.19, N 14.91; found C 54.40, H 6.01, N 15.19. IR, cm−1: 3466 (v, O-H),
2907 (v, C-H), 1663 (va, C-O), 1368 (vs, C-O).
[Cu(trzadc)2(MeOH)] MeOH (2) Pale blue crystals. Yield 40%. C28H40CuN6O6 (620.20): calcd. C
·
54.51, H 6.50, N 13.55; found C 54.24, H 6.37, N 13.80. IR, cm−1: 3338 (v, O-H), 2910 (v, C-H), 1611 (va,
C-O), 1346 (vs, C-O).
[Ni(trzadc)2(MeOH)2] (3) Pale green plates. Yield 32%. C14H20N3NiO3 (337.02): calcd. C 49.87, H
5.98, N 12.47; found C 49.63, H 6.21, N 12.42. IR, cm−1: 2895 (v, C-H), 1560 (va, C-O), 1375 (vs, C-O).
–
[Cu2(mtrzadc)3(MeOH)]+NO3 (4) Bright green crystals. Yield 36%. C43H58CuN10O10 (938.53):
calcd. C 55.01, H 6.23, N 14.93; found C 54.78, H 6.10, N 14.70. IR, cm−1: 2913 (v, C-H), 1606 (va, C-O),
1415 (v, N-O), 1292 (vs, C-O).

Molecules 2019, 24, 2717
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3.2.4. Catalytic Activity Tests
In a typical procedure, 10 mL vial was loaded with 0.1 mmol (6.8 mg) of imidazole, 0.15 mmol
(18.3 mg) of phenylboronic acid 1 mL of methanol and 6 mg of compound 2. This mixture was left
stirring on an oil bath at 40 ◦C for 24 h. Next, the mixture was centrifuged to recover the catalyst and
supernatant analyzed by GC to calculate the conversion.
4. Conclusions
In summary, we have developed a pathway for the production of a new kind of adamantane-based
ligands and successfully employed them for the preparation of several coordination polymers.
The proposed method is robust, provides moderate to high yields and is easy to perform. It also allows
a facile synthesis of the coordination polymers with mixed coordination environment, which may be
very useful as demonstrated by catalytic activity of one of the complexes.
Supplementary Materials: The following are available online at http://www.mdpi.com/1420-3049/24/15/2717/s1,
Figure S1: Representation of a layer built from 1D chains of the complexes an solvate molecules for
1
and
2,
Figure S2: Representation of 1D chains of
1
(a),
2
(b) and
3
2
(c) showing their similarity, Figure S3: Structure view
along 1D chain showing difference between
3
(a) and
1–
(b, on the example of
1
), Figure S4: Representation of
torsion angles of trzadc– and mtrzadc– ligands on the example of trzadc–, Figure S5: Intermolecular hydrogen
bonds between molecules of trzadcH, Table S1: Torsion angles (deg.) for trzadc– and mtrzadc– ligands in the
complexes
dmtradc (a); IR spectra of ttzadc
and compound (d), Figure S8: TGA/DSC curves for compounds 1–4
1–
4
., Figure S6: The PXRD patterns for compounds
mttzadc (b); IR spectra of trzadc and compounds 1–3 (c); IR spectra of mtrzadc
, Figure S9: NMR spectra of the trzadc,
1–4, Figure S7: IR Spectra of trzadc, mtrzadc,
,
4
Figure S10: NMR spectra of the mtrzadc, Figure S11: NMR spectra of the dmtrzadc, Figure S12: NMR spectra
of the ttzadc, Figure S13: NMR spectra of the mtrzadc, Figure S14: Residual electron density map (0.55 eÅ–3
level) for the complex
1 with full occupancy of coordinated and solvate water molecules. CCDC 1922178 (1),
1922180 ( ), 1922179 (3), 1922177 (4), and 1922176 (trzadcH) contain the supplementary crystallographic data
2
for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Author Contributions: Conceptualization, D.P. and A.P.; Data curation, D.P. and T.S.; Funding acquisition, A.P.;
Investigation, D.P. and E.F.; Methodology, D.P. and A.P.; Software, T.S.; Supervision, A.P.; Visualization, T.S.;
Writing – original draft, D.P. and T.S.; Writing – review & editing, A.P.
Funding: The reported study was supported by the Russian Science Foundation, grant No. 19-73-20087.
Conflicts of Interest: The authors declare no conflict of interest.
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2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
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