Coordination polymers from mild condition reactions of copper(II) carboxylates with pyrazole (Hpz). Influence of carboxylate basicity on the self-assembly of the [Cu3(μ3-OH)(μ-pz)3]2+secondary building unit

Article abstract of DOI:10.1016/j.ica.2016.05.009

The reaction of some saturated and unsaturated aliphatic copper(II) monocarboxylates, Cu(RCOO)₂[R = C₆H₅CH₂(phenylacetate, Phac), CH₂[dbnd]CHCH₂(vinylacetate, Vnac), C₆H₅

Full text of DOI:10.1016/j.ica.2016.05.009

Accepted Manuscript
Coordination polymers from mild condition reactions of copper(II) carboxylates
with pyrazole (Hpz). Influence of carboxylate basicity on the self-assembly of
the [Cu3(μ 3-OH)(μ-pz)3]2+ secondary building unit
Sara Massignani, Rebecca Scatena, Arianna Lanza, Magda Monari, Francesca
Condello, Fabrizio Nestola, Claudio Pettinari, Federico Zorzi, Luciano Pandolfo
PII:
S0020-1693(16)30238-9
http://dx.doi.org/10.1016/j.ica.2016.05.009
ICA 17045
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
27 February 2016
2 May 2016
3 May 2016
Please cite this article as: S. Massignani, R. Scatena, A. Lanza, M. Monari, F. Condello, F. Nestola, C. Pettinari, F.
Zorzi, L. Pandolfo, Coordination polymers from mild condition reactions of copper(II) carboxylates with pyrazole
(Hpz). Influence of carboxylate basicity on the self-assembly of the [Cu3(μ 3-OH)(μ-pz)3]2+ secondary building unit,
Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.05.009
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Coordination polymers from mild condition reactions of copper(II) carboxylates
with pyrazole (Hpz). Influence of carboxylate basicity on the self-assembly of the
[Cu3(µ3-OH)(µ-pz)3]2+ secondary building unit.
Sara Massignania, Rebecca Scatenaa,b, Arianna Lanzab*, Magda Monaric*, Francesca Condellod,
Fabrizio Nestolae, Claudio Pettinarid, Federico Zorzie, Luciano Pandolfoa*.
Dedicated to the memory of our friend and colleague Professor Rino A. Michelin.
a Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo, 1, I-35131 Padova, Italy.
b
Department für Chemie und Biochemie, Universität Bern, Freiestrasse, 3, CH-3012 Bern,
Switzerland.
c Dipartimento di Chimica “G. Ciamician”, Università di Bologna, Via Selmi, 2, I-40126 Bologna,
Italy.
d Scuola di Farmacia, Università di Camerino, Via S. Agostino, 1, I-62032 Camerino (MC), Italy.
e Dipartimento di Geoscienze, Università di Padova, Via Gradenigo, 6, I-35131 Padova, Italy.
Abstract:
The reaction of some saturated and unsaturated aliphatic copper(II) monocarboxylates, Cu(RCOO)2
[R = C6H5CH2 (phenylacetate, Phac), CH2=CHCH2 (vinylacetate, Vnac), C6H5CH=CH (3-trans-
phenylacrylate, Phacr), C6H5(CH2)2 (3-phenylpropionate, Phpr), c-C6H11 (ciclo-hexylcarboxylate, c-
Hexc), CH3(CH2)10 (laurate, Lau), CH3(CH2)12 (myristate, Myr), (CH3)3C (pivalate, Piv)] with
pyrazole (Hpz) and water in protic solvents, yielded trinuclear triangular derivatives based on the
[Cu(µ3-OH)(µ-pz)3] fragment whose double positive charge is balanced by two coordinated
carboxylate ions, actually [Cu3(µ3-OH)(µ-pz)3(Phac)2], 1, [Cu3(µ3-OH)(µ-pz)3(Vnac)2(Hpz)], 2,
[Cu3(µ3-OH)(µ-pz)3(Phacr)2],
3,
[{Cu3(µ3-OH)(µ-pz)3(Phpr)2(Hpz)}{Cu3(µ3-OH)(µ-
pz)3(Phpr)2(Hpz)(H2O)}]·xH2O·yMeOH, 4, [Cu3(µ3-OH)(µ-pz)3(c-Hexc)2], 5, [Cu3(µ3-OH)(µ-
pz)3(Lau)2], 6, [Cu3(µ3-OH)(µ-pz)3(Myr)2], 7, [Cu3(µ3-OH)(µ-pz)3(Piv)2(HPz)(HPiv)2], 8. This
behavior is consistent with some previously observed features and evidences that the basicity of
carboxylate ions is the key for the deprotonation of Hpz and water, leading to the formation of pz-
and OH- ions, which are determinant for the self-assembly of the trinuclear triangular species.
Single crystal XRD determinations evidenced that in compounds 1, 2 and 5 the trinuclear moieties
further self-assemble generating monodimensional coordination polymers or, in one case
(compound 4), a dodecanuclear discrete assembly.
1

Keywords: Coordination Polymers; Self-assembly; Copper(II); Carboxylates; Pyrazole
1. Introduction
The number of new Coordination Polymers (CPs), obtained according to a broad spectrum of
procedures, is continuously increasing [1-4]. These systems have been demonstrated capability to
act as chemical sensors, light-emitting devices, drug-delivery materials, catalysts, gas storage and
separation species and for this reason they can constitute a technological approach to prevent
pollution, to detect pollutants and to reduce the consumption of not renewable sources. On the other
hand, the use of relatively cheap “bricks” (metals, polytopic ligands) and environmental friendly
procedures (solvents, temperature, pressure) to synthesize CPs is to be pursued. In this context
carboxylates, having numerous possibility to bridge two, three or four metal centers, and azolate
ions [5-14] are among the most promising frameworks for the synthesis of CPs. Moreover, copper
ions, often presenting interesting and useful properties, may be usefully employed as node in CPs
thanks to their coordinative flexibility and trinuclear copper azolate derivatives are assuming an
increasing importance. For example, trinuclear copper(II) azolates containing nine-membered Cu3N6
metallacycles have been demonstrated remarkable activity and selectivity as catalysts, or catalyst
precursors, for the peroxidative oxidation of cyclohexane and cyclopentane to the corresponding
alcohols and ketones [15]. Some luminescent trinuclear thermochromic copper(I) azolate
derivatives can be used as a chemopalette [16], while other trinuclear Cu(I) species present
interesting applications as sensor for volatile organic compounds, due to their luminescence
properties. Thin films of [Cu(4-X-3,5-(CF3)2pz)]3, for example, changes color upon exposure to
benzene vapors [17]. A recently reported hydrophobic CP Cu2L (L = 3,3’,5,5’-tetraethyl-4,4’-
bipyrazolate) has been prepared [18] by the solvothermal reduction of a CP based on a trinuclear
copper(II) azolate [19] and seems to have potentiality for efficient removal of trace organic wastes
(e.g. benzene) from contaminated water. Some species as [Cu3(µ3-O)(L’)3(H2O)3]BF4·H2O (L’ = 4H-
1,2,4-triazol-4-ylacetic acid) showed interesting gas storage and adsorption properties due to the
voluminous void corresponding to a 48% of solvent accessible volume [20].
In this context, in the last years we studied the interaction of numerous copper(II) mono-
carboxylates with pyrazole (Hpz), observing that the reaction conditions and the basicity of the
carboxylates employed play relevant roles in the obtaining of different results. More specifically,
when the reaction of copper(II) acetate, formate or propionate with Hpz was carried out in MeCN a
1D CP based on the [Cu(pz)2] secondary building unit (SBU) [21-23], evidencing the “porosity
without pore” behavior [24], was easily obtained. On the contrary, by reacting a series of copper(II)
carboxylates with Hpz in alcohols or water, different behaviors were observed [9,15,19,25-27]. In
detail, numerous saturated and unsaturated aliphatic copper(II) carboxylates yielded compounds
2

based on the trinuclear triangular moiety [Cu3(µ3-OH)(µ-pz)3]2+, with the double positive charge
balanced by two RCOO- anions, according to the reaction sketched in Scheme 1.
H2O, MeOH or EtOH
3 Cu(RCOO)2 + n Hpz + H2O
[Cu3(µ3-OH)(
µ-pz)3(RCOO)2Lx] + 4 RCOOH
2+
R = H, CH3, CH3CH2, CH2=CH, CH2=C(CH3),
CH3(CH2)2, CH3(CH2)3, CH3(CH2)4, CH3(CH2)5.
L = H2O, MeOH, EtOH, Hpz
N
N
H
x = 0, 1, 2
Cu
Cu
N
O
N
N
Cu
N
Scheme 1
These trinuclear moieties often behave as SBUs generating, through carboxylate bridges, mono- or
bidimensional CPs as well as hexanuclear clusters and/or supramolecular networks. In order to
obtain the [Cu3(µ3-OH)(µ-pz)3] fragment, H2O and Hpz need to be deprotonated to give OH- and pz-
anions and the basicity of the employed carboxylate seems to play a relevant role in this process as
witnessed by the fact that the reactions of CuCl2 or Cu(NO3)2 with Hpz lead to mononuclear
pyrazole complexes, while the same salts yields trinuclear triangular species only if an exogenous
base is added [28]. Moreover, the reaction of copper(II) trifluoroacetate with Hpz (pKa CF3COOH =
0.52), generates exclusively the mononuclear [Cu(CF3COO)2(Hpz)2] species [19], while the reaction
with copper(II) chloroacetate (pKa ClCH2COOH = 2.87) leads to the formation of both mono- and
trinuclear species accompanied by a dinuclear derivative, formed through the dechlorination of a
coordinated chloroacetate ion [29].
Here are reported the results of the reactions, carried out in protic solvents, of selected
copper(II) carboxylates [Phenylacetate (Phac), Vinylacetate (Vnac), 3-trans-Phenylacrylate
(Phacr), 3-Phenylpropionate (Phpr), ciclo-Hexylcarboxylate, (c-Hexc), Laurate (Lau), Myristate
(Myr), and Pivalate (Piv), see Chart 1], with Hpz that, in all cases, exclusively generates the
trinuclear triangular clusters [Cu3(µ3-OH)(µ-pz)3]2+ whose charge is balanced by the
corresponding anions. The structures of some of the above mentioned compounds have been
determined through single crystal (SC) XRD, evidencing that the trinuclear moieties further
self-assemble generating a dodecanuclear discrete assembly or 1D CPs through carboxylates
bridges, while in other cases the presence of the trinuclear triangular CuII moiety has been
inferred by elemental analyses, IR, ESI-MS and magnetic susceptibility measurements.
3

O
O
O
O
O
O
Vinylacetate
Vnac (4.34)
Phenylacetate
Phac (4.31)
trans-Phenylacrylate
Phacr (4.44)
O
O
O
O
(CH2)12
O
O
O
O
O
(CH2)10
O
3-Phenylpropanoate
Phpr (4.66)
cyclo-Hexylcarboxylate
c-Hexc (4.91)
Laurate
Lau (4.95)
Myristate
Myr (4.95)
Pivalate
Piv (5.03)
Chart 1 - List of the carboxylate anions employed with corresponding acids pKa values (in
parentheses) [30].
2. Experimental Section
2.1 Materials and Methods
All the reactions and manipulations were carried out in air by using water or not dried MeOH or
EtOH as solvent(s). Copper(II) pivalate, Cu(Piv)2, was prepared according to the literature methods
[31]. Elemental analyses (C, H, N) were performed with a Fisons Instruments 1108 CHNS-O
elemental analyzer. Infrared spectra from 4000 to 600 cm-1 were recorded with a Perkin Elmer
Spectrum One Model FTIR spectrometer with ATR mode. Positive electrospray mass spectra (ESI-
MS) were obtained with a Series 1100 MSI detector HP spectrometer, using MeOH as mobile
phase. Solutions for ESI-MS were prepared using reagent grade methanol, water and/or acetonitrile,
and obtained data (masses and intensities) were compared with those calculated by using the IsoPro
isotopic abundance simulator [32]. Peaks containing copper(II) ions are identified with the most
intense signal of the isotopic clusters. The magnetic susceptibilities were measured at room
temperature (20-28°C) by the Gouy method with a Sherwood Scientific magnetic balance MSB-
Auto, using HgCo(NCS)4 as calibrant and corrected for diamagnetism with the appropriate Pascal
constants. The magnetic moments (in µB) were calculated from the equation µeff = 2.84(ΧmcorrT)1/2.
2.2 Crystallographic data collection and structure determination
Single crystal X-ray diffraction (SCXRD) experiments were performed at room temperature, with
diffractometers equipped with CCD detectors and using Mo-Kα radiation. The integrated intensity
data were corrected for Lorentz, polarization and absorption effects, and employed for structure
solution and refinement. The experimental procedures (a, b or c), and data treatment (d, e, f, g, h, or
i) are described in detail in the Supplementary Information. XRPD diffraction investigations were
carried out by means of a PANalytical X’Pert Pro diffractometer equipped with an X’Celerator fast
detector and using Cu/Kα radiation. Molecular graphics were generated by using Mercury 3.5.1
4

[33,34] programs. Color codes for all molecular graphics: orange (Cu), blue (N), red (O), grey (C),
white (H). Crystal data and details of data collections for [Cu(Vnac)2(H2O)]2, [Cu(Phpr)2]2 and
compounds 1, 2, 4, 5 and 8 are reported in Table 1.
Table 1 - Crystal data and structural refinement parameters for [Cu(Vnac)2(H2O)]2, [Cu(Phpr)2]2 and
compounds 1, 2, 4, 5 and 8.
Compound
[Cu(Vnac)2(H2O)2]2 [Cu(Phpr)2]2
1
2
Experimental
conditions
Formula
FW, g mol-1
a, d
b, e
c, f
b, g
C16H24Cu2O10
503.43
C18H18CuO4
361.86
C25H23Cu3N6O5
678.11
C20H24Cu3N8O5
647.09
Crystal system monoclinic
triclinic
P-1
monoclinic
C2/c
triclinic
P-1
Space group
a, Å
C2/c
16.875 (2)
21.125 (2)
14.656 (2)
90
5.1987(5)
9.1146(14)
17.6461(19)
88.244(11)
82.600(10)
82.851(18)
822.64(18)
2
23.551(3)
11.4428(15)
9.5994(13)
90
11.3262(5)
11.5228(6)
12.1419(5)
89.818(4)
63.210(4)
67.300(5)
1276.61(12)
2
b, Å
c, Å
α, °
123.984 (17)
90
103.113(2)
90
β, °
γ, °
cell volume,
4332.2 (11)
8
2519.4(6)
4
Å3
Z
Dc, Mg m-3
1.544
1.461
1.788
1.683
2.01
1.344
2.560
2.525
µ(Mo Kα),
F(000)
2064
374
1368
654
crystal size,
0.12×0.10×0.08
2.9 — 25.5
0.17×0.05×0.03 0.30×0.20×0.15 0.18×0.08×0.04
mm3
2.5 — 26.0
12167
2.0 28.1
1.9 — 32.1
34115
θ limits, °
Refl. collected 41790
13284
unique refl. 4033 (0.0429)
1977 (0.1477)
1.036
2987 (0.0340)
1.104
6476 (0.0781)
1.027
2
(
)
1.027
GooF on F
R1[F2 >2•(F2)],
0.0348, 0.0686
0.1036, 0.2950
0.0447, 0.1102
0.061, 0.145
wR2(F2)
largest diff.
peak and hole.
e Å-3
0.335 and -0.298
1.65 and -1.09
1.464 and -1.171 0.78 and -0.58
5

Compound
4
5
8
Experimental
conditions
Formula
FW, g mol-1
a, h
b, i
c, f
C120H132Cu12N32O22·4H2O C23H32Cu3N6O5
C32H52Cu3N8O9
883.43
3209.11
663.16
Crystal system triclinic
triclinic
P-1
triclinic
P-1
Space group
a, Å
P-1
12.251(3)
13.330(2)
22.348(3)
106.265(14)
95.504(16)
93.683(18)
9.6927(7)
11.2730(9)
12.7389(8)
66.651(7)
86.338(6)
87.947(6)
1275.25(17)
2
10.7078(6)
13.0000(7)
17.0288(10)
75.733(1)
88.721(1)
66.500(1)
2099.1(2)
2
b, Å
c, Å
α, °
β, °
γ, °
cell volume, Å3 3471.5(11)
1
Z
Dc, Mg m-3
1.532
1.727
1.398
1.875
2.526
1.562
µ(Mo Kα),
F(000)
1634
678
918
crystal size,
0.15×0.10×0.08
2.8—14.7
0.29×0.08×0.07 0.33×0.27×0.25
mm3
1.7-30.9
1.8—28.7
23123
θ limits, °
Refl. collected 18940
22758
unique refl. 2646 (0.1167)
6567 (0.0605)
0.989
9848 (0.0217)
1.034
2
(
)
1.269
GooF on F
R1[F2 >2•(F2)],
0.103, 0.205
0.046, 0.116
0.040, 0.109
wR2(F2)
largest diff.
peak and hole.
e Å-3
0.369 and -0.297
0.74 and -0.72
0.715 and -0.637
(a-i) – For details of data collection, structure solution and refinement see Supplementary
Information.
2.3 Syntheses
2.3.1. Syntheses of copper(II) carboxylates
2.3.1.1. Synthesis of Cu(Phac)2
To a solution of 19.03 g of phenylacetic acid (139.8 mmol) in 650 mL of water at 50 °C, finely
ground Cu(CO3)Cu(OH)2 (6.83 g, 30.9 mmol) was slowly added. The suspension was stirred
overnight, filtered, and the solid was washed with water and dried under vacuum. The solid was
then continuously extracted with MeOH and the resulting blue-green solution was evaporated in the
air, obtaining green crystals that were filtered, washed with MeOH and dried in the air.
6

Yield: 8.55 g, 42%. Elem. Anal., %. Calcd for Cu(Phac)2: C = 57.57; H = 4.23. Found: C = 57.37; H
= 4.29. IR (ATR, cm-1): 3061, 3035, 2964, 1591, 1581, 1411, 1388. µeff (293 K) = 1.72 BM
(calculated for C16H14CuO4).
2.3.1.2. Synthesis of [Cu(Vnac)2(H2O)]2
A solution obtained by mixing vinylacetic acid (2.05 g, 23.8 mmol) and 1M NaOH solution (24
mL) was added under stirring to a solution of 2.74 g of Cu(NO3)2·2.5H2O (11.8 mmol) in 40 mL of
water. The obtained blue-green solution was allowed to evaporate in the air yielding well-formed
green crystals.
Yield: 0.720 g, 27%. Elem. Anal., %. Calcd for Cu(Vnac)2(H2O): C = 38.17; H = 4.80. Found: C =
38.24; H = 4.77. IR (ATR, cm-1): 3399, 3082, 2983, 1611, 1416, 1385, 1275. µeff (303 K) = 2.29 BM
(calculated for C8H12CuO5).
2.3.1.3. Synthesis of [Cu(Phacr)2]
A 1M NaOH solution (70 mL) was added to a suspension of 9.92 g of 3-trans-phenylacrylic acid
(67 mmol) in 80 mL of water. A solution of 8.02 g of CuSO4·5H2O (32.12 mmol) in 40 mL of water
was then added under stirring, obtaining a light-blue solid which was filtered, washed with water
and dried under vacuum.
Yield: 10.35 g, 90%. Elem. Anal., %. Calcd for Cu(Phpr)2: C = 60.41; H = 3.94. Found: C = 59.15;
H = 3.94. IR (ATR, cm-1): 3083, 3059, 3025, 1639, 1561, 1553, 1404. µeff (293 K) = 1.79 BM
(calculated for C18H14CuO4).
2.3.1.4. Synthesis of [Cu(Phpr)2]2
A suspension of 3-phenylpropanoic acid (5.29 g 35.25 mmol) in 100 mL of water was treated with
35.5 mL of a 1M NaOH solution. A solution of 4.02 g of Cu(NO3)2·2.5H2O (17.28 mmol) in 40 mL
of water was then added under stirring, obtaining blue-green microcrystals which were filtered,
washed with water and dried under vacuum. Recrystallization from EtOH yielded small crystals
which were employed for a SCXRD determination.
Yield: 3.98 g, 64%. Elem. Anal., %. Calcd for Cu(Phpr)2: C = 59.74; H = 5.01. Found: C = 58.58; H
= 4.97. IR (ATR, cm-1): 3028, 2930, 1588, 1496, 1428. µeff (293 K) = 1.86 BM (calculated for
C18H18CuO4).
2.3.1.5. Synthesis of Cu(c-Hexc)2
Cyclohexylcarboxylic acid (10.94 g, 85.4 mmol) suspended in 60 mL of water was treated with 87
mL of 1M NaOH and then CuSO4·5H2O (10 g, 40 mmol), dissolved in 50 mL of water, was added
in small portions under stirring. The obtained suspension was stirred overnight, filtered and the
solid was washed with 200 mL of hot water (60 °C) and dried under vacuum.
7

Yield: 11.63 g, 91%. Elem. Anal., %. Calcd for Cu(c-Hexc)2: C = 52.90; H = 6.98. Found: C =
52.79; H = 6.66. IR (ATR, cm-1): 2931, 2854, 1580, 1506, 1451, 1421, 1286, 762, 730. µeff (293 K)
= 2.03 BM (calculated for C14H22CuO4).
2.3.1.6. Synthesis of Cu(Lau)2
To a solution of 4.95 g of CuSO4·5H2O (19.8 mmol) in 200 mL of water, lauric acid (4.75 g, 23.7
mmol) was added. The suspension was heated at ca. 70°C and 24 mL of 1M NaOH were slowly
added, under vigorous stirring. The resulting green-blue suspension was maintained hot and stirred
for 2 h, the solid was filtered, washed three times with 150 mL of hot (80 °C) water and three times
with 40 mL of MeOH, and then dried under vacuum.
Yield: 5.17 g, 94%. Elem. Anal., %. Calcd for Cu(Lau)2: C = 62.37; H = 10.03. Found: C = 61.98;
H = 9.28. IR (ATR, cm-1): 2916, 2849, 1584, 1510, 1469, 1441, 1422, 1316, 720. µeff (293 K) = 2.13
BM (calculated for C24H46CuO4).
2.3.1.7. Synthesis of Cu(Myr)2
To a solution of 4.89 g of copper(II) acetate monohydrate (24.5 mmol) in 250 mL of EtOH, 11.49 g
of myristic acid (50.3 mmol) dissolved in 175 mL of EtOH was slowly added under vigorous
stirring, obtaining a blue-green suspension which was stirred for an additional hour. The solid was
then filtered, washed four times with 40 mL of EtOH and then dried under vacuum.
Yield: 10.7 g, 84%. Elem. Anal., %. Calcd for Cu(Myr)2: C = 64.89; H = 10.50. Found: C = 64.80;
H = 10.56. IR (ATR, cm-1): 2915, 2849, 15584, 1509, 1468, 1440, 1421, 1318, 721. µeff (293 K) =
2.10 BM (calculated for C28H54CuO4).
2.3.2 Reaction of copper(II) carboxylates with Hpz
2.3.2.1. Reaction of Cu(Phac)2 + Hpz in MeOH. Synthesis of [Cu3(µ3-OH)(µ-pz)3(Phac)2]n (1)
To a suspension of Cu(Phac)2 (1.126 g, 3.37 mmol) in 190 mL of MeOH a solution of 346 mg of
Hpz (5.08 mmol) in 10 mL of MeOH was added under stirring. The obtained dark-blue solution was
slowly evaporated in the air yielding blue crystals of 1.
1. Yield: 541 mg, 71%. Elem. Anal. Calcd for Cu3(OH)(pz)3(Phca)2: C = 44.21; H = 3.56; N =
12.37. Found: C = 44.32; H = 3.53; N = 12.15. IR (ATR, cm-1): 3401, 3111, 3030, 2950, 2892,
1583, 1552, 1598, 1488, 1418, 1394, 1379, 1277, 1178, 1053. µeff (296 K) = 2.14 BM (calculated
for C25H24Cu3N6O5).
2.3.2.2. Reaction of [Cu(Vnac)2(H2O)]2 + Hpz in MeOH. Synthesis of [Cu3(µ3-OH)(µ-
pz)3(Vnac)2(Hpz)]n (2)
To a solution of [Cu(Vnac)2(H2O)]2 (625 mg, 2.65 mmol) in 150 mL of MeOH, a solution of 272
mg of Hpz (3.94 mmol) in 10 mL of MeOH was added under stirring. The resulting deep blue
solution was allowed to evaporate in the air obtaining blue crystals of 2 that were filtered, washed
with cold MeOH and dried under vacuum.
8

2. Yield: 399 mg, 76%. Elem. Anal. Calcd for Cu3(OH)(pz)3(Vnac)2(Hpz): C = 37.12; H = 3.74; N =
17.32. Found: C = 36.60; H = 3.54; N = 16.95. IR (ATR, cm-1): 3218, 3146, 3118, 2979, 2936,
1557, 1489, 1382, 1278, 1179, 1062. µeff (294 K) = 2.69 BM (calculated for C20H24Cu3N8O5).
2.3.2.3. Reaction of Cu(Phacr)2 + Hpz in MeOH. Synthesis of [Cu3(µ3-OH)(µ-pz)3(Phacr)2] (3)
To a suspension of Cu(Phacr)2 (1.001 g, 2.80 mmol) in 200 mL of MeOH a solution of 287 mg of
Hpz (4.21 mmol) in 10 mL of MeOH was added under stirring. The obtained dark-blue solution was
allowed to evaporate in the air yielding blue microcrystals of 3. Further evaporation of mother
liquors lead to a mixture of blue and white crystals and the latter were identified by GC-MS as 3-
trans-fenilacrylic acid.
3. Yield: 231 mg, 35%. Elem. Anal. Calcd for Cu3(OH)(pz)3(Phacr)2: C = 46.12; H = 3.44; N =
11.95. Found: C = 46.16; H = 3.42; N = 11.31. IR (ATR, cm-1): 3429, 2980, 2888, 1638, 1526,
1491, 1450, 1399, 1381, 1280, 1250, 1179, 1058. ESI-MS (+) (MeOH) (higher peaks, relative
abundance %): 198.6 (46) [Cu(Pz)(MeOH)(H2O)2]+, 277.9 (100) [Cu(Phacr)(MeOH)(H2O)2]+, 345.6
(94)
[Cu3(OH)3(pz)(Phacr)(MeOH)]+,
[Cu3(OH)(pz)3(Phacr)(MeOH)(H2O)]+,
[Cu3(pz)3(Phacr)2(MeOH)]+. µeff (296 K) = 2.68 BM (calculated for C27H24Cu3N6O5).
[Cu2(pz)3(H2O)]+,
407.7
(36)
(37)
685.7
[Cu3(OH)3(pz)2(MeOH)]+,
487.6
605.6
717.7
(67)
(16)
(20)
556.7
[Cu3(OH)(pz)3(Phacr)]+,
(32)
[Cu3(pz)3(Phacr)2]+.
2.3.2.4. Reaction of [Cu(Phpr)2]2 + Hpz in MeOH. Synthesis of [{Cu3(µ3-OH)(µ-
pz)3(Phpr)2(Hpz)}{Cu3(µ3-OH)(µ-pz)3(Phpr)2(Hpz)(H2O)}]2·xH2O·yMeOH (4)
To a solution of [Cu(Phpr)2]2 (286 mg, 0.79 mmol) in 80 mL of MeOH a solution of 112 mg of Hpz
(1.65 mmol) in 10 mL of MeOH was added under stirring. The obtained dark-blue solution was let
to evaporate in the air yielding blue crystals of 4.
4.
Yield:
185
mg,
87%.
Elem.
Anal.
Calcd
for
[Cu3(OH)(pz)3(Phpr)2(Hpz)Cu3(OH)(pz)3(Phpr)2(Hpz)(H2O)](H2O)(MeOH): C = 45.26; H = 4.48; N
= 13.85. Found: C = 46.65; H = 4.32; N = 13.59. IR (ATR, cm-1): 3127, 1573, 1400, 1381, 1279,
1177, 1064.
2.3.2.5. Reaction of Cu(c-Hexc)2 + Hpz in MeOH. Synthesis of [Cu3(µ3-OH)(µ-pz)3(c-Hexc)2]n (5)
To a suspension of 1.09 g of Cu(c-Hexc)2 (3.44 mmol) in 100 mL of MeOH, Hpz (384 mg, 5.64
mmol) was added under stirring, obtaining a blue solution and a blue-grey solid, which was filtered,
washed with MeOH and dried under vacuum.
5. Yield 427 mg, 56%. Elem. Anal. Calcd for [Cu3(OH)(pz)3(c-Hexc)2: C = 41.66; H = 4.86; N =
12.67. Found: C = 43.75; H = 4.21; N = 11.81. IR (ATR, cm-1): 3439, 2934, 2854, 1542, 1487,
1414, 1380, 1279, 1227, 1179, 1062, 1054, 884, 780, 766, 732. ESI-MS (+) (MeOH) (higher peaks,
relative abundance %): 198.6 (100) [Cu(Pz)(MeOH)(H2O)2]+, 325.9 (41) [Cu(c-Hexc)(HPz)2]+,
407.7 (35) [Cu3(OH)3(Pz)2(MeOH)]+, 467.6 (58) [Cu3(OH)2(pz)3(MeCN)]+, 475.6 (8)
9

[Cu3(OH)(pz)4]+, (516.8 (37) [Cu3(OH)(pz)4(MeCN)]+, 535.5 (37) [Cu3(OH)(pz)3(c-Hexc)]+, 585.6
(18) [Cu3(OH)(pz)3(c-Hexc)(MeOH)(H2O)]+, 645.7 (24) [Cu3(pz)3(c-Hexc)2]+, 677.7 (14)
[Cu3(pz)3(c-Hexc)2(MeOH)]+, 713.7 (9) [Cu3(pz)3(c-Hexc)2(MeOH)(H2O)2]+. µeff (296 K) = 2.13 BM
(calculated for C23H32Cu3N6O5).
The deep-blue mother liquors were let to evaporate in the air yielding blue tiny bars, suitable for a
SCXRD determination, which were collected, washed with MeOH and dried in the air.
5. Yield 97 mg, 13%. Elem. Anal. Calcd for [Cu3(OH)(pz)3(c-Hexc)2: C = 41.66; H = 4.86; N =
12.67. Found: C = 41.35; H = 4.32; N = 11.95. IR (ATR, cm-1): 3440, 2934, 2854, 1541, 1487,
1413, 1380, 1279, 1227, 1179, 1062, 1054, 884, 782, 765, 733.
2.3.2.6. Reaction of Cu(Lau)2 + Hpz in EtOH. Synthesis of [Cu3(µ3-OH)(µ-pz)3(Lau)2] (6)
To a suspension of 1.00 g of Cu(Lau)2 (2.32 mmol) in 270 mL of EtOH 285 mg of Hpz (4.19 mmol)
dissolved in 10 mL of H2O was added under vigorous stirring. In ca. 10 minutes a deep- blue
solution formed, which was let to evaporate in the air yielding a blue microcrystalline solid, 6,
which was filtered, washed with EtOH and dried in the air. Further evaporation of mother liquors
lead to the formation of few mgs of a floating white solid which was identified by GC-MS as lauric
acid.
6. Yield: 325 mg, 52%. Elem. Anal. Calcd for Cu3(OH)(pz)3(Lau)2: C = 49.09; H = 6.99; N = 10.41.
Found: C = 48.83; H = 7.50; N = 9.90. IR (ATR, cm-1): 2923, 2852, 1571, 1537, 1493, 1441, 1397,
1381, 1303, 1281, 1178, 1059, 886, 770, 754, 722. ESI-MS (+) (MeOH) (higher peaks, relative
abundance %): 198.6 (93) [Cu(pz)(MeOH)(H2O)2]+, 397.9 (100) [Cu(Lau)(Hpz)2]+, 407.6 (18)
[Cu3(OH)3(pz)2(MeOH)]+,
[Cu3(OH)(pz)3(Lau)]+,
539.6
(42)
[Cu3(OH)3(pz)2(MeOH)4(H2O)2]+,
[Cu3(OH)(pz)3(Lau)(MeOH)3(H2O)2]+,
607.7
(22)
739.9
(12)
789.9
(15)
[Cu3(OH)(pz)3(Lau)(MeOH)4(H2O)3]+, 821.9 (25) [Cu3(OH)(pz)3(Lau)(MeOH)5(H2O)3]+. µeff (296 K)
= 1.63 BM (calculated for C33H56Cu3N6O5).
2.3.2.7. Reaction of Cu(Myr)2 + Hpz in EtOH. Synthesis of [Cu3(µ3-OH)(µ-pz)3(Myr)2] (7)
To a vigorously stirred suspension of 1.22 g of Cu(Myr)2 (2.35 mmol) in EtOH (150 mL) 280 mg of
Hpz (4.12 mmol) dissolved in 10 mL of water was added, obtaining a blue solution which was
stirred for 30 min and filtered on paper to eliminate a little solid. The solution was allowed to
evaporate in the air, yielding a blue microcrystalline solid, 7, which was filtered, washed with EtOH
and dried under vacuum. From the evaporation of mother liquors few mgs of a white solid formed,
which was identified by GC-MS as myristic acid.
7. Yield: 425 mg, 63%. Elem. Anal. Calcd for Cu3(OH)(pz)3(Myr)2: C = 51.46; H = 7.47; N = 9.73.
Found: C = 50.86; H = 7.41; N = 9.29. IR (ATR, cm-1): 2923, 2852, 1570, 1536, 1493, 1441, 1397,
1381, 1282, 1178, 1049, 882, 771, 754, 720.
10

ESI-MS (+) (MeOH) (higher peaks, relative abundance %): 198.6 (93) [Cu(pz)(MeOH)(H2O)2]+,
407.6
(30)
[Cu3(OH)3(pz)2(MeOH)]+,
425.9
(80)
[Cu(Myr)(Hpz)2]+,
567
(40)
[Cu3(OH)(pz)3(MeOH)2(H2O)3(MeCN)]+,
635.7
(21)
[Cu3(OH)(pz)3(Myr)]+,
685.8(8)
[Cu3(OH)(pz)3(Myr)(MeOH)(H2O)]+, 727.9 (10) [Cu3(OH)(pz)3(Myr)(MeOH)(H2O)(MeCN)]+, 796.0
(17)
[Cu3(OH)(pz)3(Myr)(MeOH)(H2O)(MeCN)(Hpz)]+,
846.0
(13)
878.0(28)
(5)
[Cu3(OH)(pz)3(Myr)(MeOH)2(H2O)2(MeCN)(Hpz)]+,
[Cu3(OH)(pz)3(Myr)(MeOH)3(H2O)2(MeCN)(Hpz)]+,
946.0
[Cu3(OH)(pz)3(Myr)(MeOH)3(H2O)2(MeCN)(Hpz)2]+. µeff (296 K) = 1.74 BM (calculated for
C37H64Cu3N6O5).
2.3.2.8. Reaction of Cu(Piv)2 + Hpz in MeOH. Synthesis of [Cu3(µ3-OH)(µ-pz)3(Piv)2(HPz)(HPiv)2]
(8)
To a blue-green solution of Cu(Piv)2 (508 mg, 1.91 mmol) in 50 mL of MeOH and 1 mL of water,
Hpz (193 mg, 2.84 mmol) in 10 mL of MeOH was added under stirring. The resulting deep blue
solution was allowed to evaporate in the air, obtaining well-formed blue crystals of 8 that were
filtered, washed with a few drops of cold MeOH and dried in the air.
8. Yield: 399 mg, 71%. Elem. Anal. Calcd for Cu3(OH)(pz)3(Piv)2(Hpz)(HPiv)2: C = 43.51; H =
5.93; N = 12.68. Found: C = 43.79; H = 6.17; N = 12.65.
3. Results and discussion
In the course of our studies on the reaction of Cu(RCOO)2 with Hpz in protic solvents and in
presence of water, we observed that, in most cases, the trinuclear triangular fragment [Cu3(µ3-
OH)(µ-pz)3] spontaneously formed [9,15,19,25-27]. The formation of this species is related to the
presence of OH- and pz- ions in sufficient amounts to assure the self-assembly of three copper ions
around OH and bridged by three pz- to give the trinuclear triangular moiety [Cu3(µ3-OH)(µ-pz)3]2+.
While the formation of the above mentioned anions can be achieved by adding an exogenous strong
base to a mixture of Hpz, water and copper(II) salts [28], in our cases their presence seems to be
related to the basicity of the employed copper carboxylates. Actually, the exclusive formation of the
mononuclear [Cu(CF3COO)2(Hpz)2] species [19] in the reaction of Hpz with copper(II)
trifluoroacetate, as well as the recent isolation of both mono and trinuclear species in the reaction of
copper(II) chloroacetate [29], may be due to the fact that these anions are unable to efficiently
deprotonate Hpz and water being too weak bases (pKb CF3COO- 13.48, pKb ClCH2COO- 11.13). The
here reported reactions of selected copper(II) carboxylates (pKb RCOO- in the range 9.69-8.97)
generate instead only the trinuclear triangular species which are described below.
Incidentally, on preparing copper carboxylates it was possible to isolate crystals of
[Cu2(Vnac)4(H2O)2] and [Cu2(Phpr)4]n which allowed the determination of their molecular structures
11

by SCXRD. The complete structural data and related images (Figures S1-S5) of these compounds
can be found in the Supplementary Information.
3.1. Trinuclear triangular molecular structures
As above said, the reactions of Hpz with all the copper(II) carboxylates employed in this study
exclusively yielded trinuclear triangular CuII derivatives. In some cases it was possible to obtain
their molecular structure through SCXRD determinations, while in other cases the occurrence of the
trinuclear triangular structure was inferred on the bases of other physico-chemical measurements.
From the reaction of Cu(Phac)2 with Hpz the compound [Cu3(µ3-OH)(µ-pz)3(Phac)2]n, 1, was
obtained, in quite good yield, as well-formed blue crystals. In Figure 1, left, the trinuclear triangular
molecular structure of compound 1, where a 2-fold axis passing through C2, O1 and Cu2 is present
[symmetry code i: -x+2,y,-z+1/2], is shown. On the other hand, it is to point out that the apparent
co-planarity of O1 with the Cu3 plane, together with the presence of an elongated thermal ellipsoid
of O1 (see Figure S6) indicates that the latter is disordered over two positions, above and below the
Cu3 plane, with population 0.5/0.5. Incidentally, even though it is evident that the three Cu ions are
capped by a µ3-OH group, the H atom was not detected, likely due to the disordered oxygen. The
two symmetry equivalent Cu1 ions display an almost exact square planar coordination geometry (τ4
= 0.07) [35], while the coordination geometry of Cu2 is approximately TBP (τ5 = 0.71) [36] due to
the fact that Cu2 coordinates, beside O1 and two symmetry equivalent N3 pyrazolate nitrogens, two
O3 carboxylate oxygens pertaining to other two equivalent trinuclear units (symmetry code ii: x,-
y,z-1/2).
Figure 1 – Left: molecular structure of compound 1 with a partial atom numbering scheme. Right:
metallacycles formed through the syn-syn bridging mode of phenylacetate ions in compound 1. H
atoms are omitted for clarity.
Anyhow, all bond distances and angles are in the ranges normally found in this kind of compounds
[15,19,25-29,37-39], and can be retrieved from the corresponding cif file which has been supplied
as Supplementary Information. Each equivalent phenylacetate ion acts as a ditopic syn-syn
bridging linker, joining symmetry equivalent trinuclear units and generating the 12-membered
12

metallacycles shown in Figure 1, right. Moreover, by this way 1D CPs (one of which is shown in
Figure 2), running parallel to the crystallographic c axis, are formed.
Figure 2 – A 1D CP formed by condensed 12-membered metallacycles in compound 1. H-atoms
are omitted for clarity.
No evident supramolecular interactions between the polymeric chains are present, the crystal
packing (see Figure S7) being likely dictated by dispersion forces only.
By reacting copper vinylacetate with pyrazole the compound [Cu3(µ3-OH)(µ-pz)3(Vnac)2(Hpz)]n, 2,
was obtained in fairly good yield. In Figure 3, left, reporting the asymmetric unit of 2, it is evident
the trinuclear triangular copper assembly capped by the µ3-OH fragment. The Cu-O1 bond distances
and the distance of O1 from the plane determined by the three copper ions (ca. 0.472 Å) are in the
ranges normally found for these kinds of compounds [15,19,25-29,37-39].
Figure 3 – Left: asymmetric unit of compound 2 with a partial atom numbering scheme. Right:
different coordination modes of vinylacetate ions in compound 2, indicated by red arrows. H atoms
and coordinated pyrazole skeletons are omitted for clarity.
The two carboxylates display different polytopic behaviors, as sketched in Figure 3, right. In detail,
O4 bridges in a monoatomic asymmetric way Cu2 pertaining to two symmetry related trinuclear
units [Cu2-O4 1.973(3), Cu2i-O4 2.390(4) Å, symmetry code i: –x+1,-y,-z], a feature often found
in the trinuclear triangular copper(II) derivatives bearing carboxylate ions [15,19,26,27]. On the
contrary, O2-C13-O3 carboxylate acts as a tritopic ligand with O2 bridging in a monoatomic way
Cu1 atoms pertaining to two trinuclear units (symmetry code ii: –x+1,-y,-z), while O3 is bonded to

Cu3ii of the second unit. Thus, the three copper ions display all a square pyramidal
pentacoordination geometry (τ5Cu1 = 0.01, τ5Cu2 = 0.1, τ5Cu3 = 0.17). All the other structural parameters
are quite normal for this kind of compounds [15,19,25-29,37-39].
Two kinds of H-bonds are present in the crystal packing of 2 (Figure S8). The stronger ones [40]
involve µ3-OH and O5 not involved in the coordination to copper ions, while coordinated pyrazole
NH groups act as weak H-donors toward O3. Finally, the polytopic behavior of vinylacetate ions
generates 1D CPs running parallel to the crystallographic c axis, shown in Figure S9.
The product of the reaction of Cu(Phpr)2 with Hpz, [{Cu3(µ3-OH)(
µ-pz)3(Phpr)2(Hpz)}{Cu3(µ3-
OH)( -pz)3(Phpr)2(Hpz)(H2O)}]2·xH2O·yMeOH, 4, was obtained as low quality crystals, due to the
µ
high rotational freedom of the carboxylate side chains and the presence of crystallization solvent
molecules (H2O and/or MeOH) in variable amounts. Despite the availability of only low resolution
XRD data, a significant molecular structure could be obtained, from which some information about
the connectivity can be deduced. At a first sight, (see Figure 4) the molecular structure of 4 looks
like that of compound 2, however some relevant differences are present. First of all, in this case the
asymmetric unit consists of a hexanuclear assembly which is formed by two, slightly different,
trinuclear units joined together by two phenylpropionate anions bridging in a monoatomic
asymmetric way Cu1 and Cu4.
Figure 4 – The asymmetric unit of compound 4 with a partial atom numbering scheme.
Analogously to 2, the O7-C40-O8 carboxylate acts instead as a tritopic ligand, where O7 bridges in
a monoatomic way Cu2 ions pertaining to two symmetry equivalent trinuclear units (symmetry
code i: -x+1,-y+1,-z+2), while O8 is bonded to Cu3i (Figure 5). Finally, Cu-µ3-OH bond distances
as well as the distances of µ3-O from the planes defined by Cu3 ions (ca. 0.477 and 0.533 Å for O1
and O2, respectively) are in the ranges normally found for this kind of compounds [15,19,25-29,37-
39].

Figure 5 – Dodecanuclear assembly of compound 4. H atoms are omitted for clarity.
The similarity of 4 to 2 ends here, because in this case the dodecanuclear assemblies are no more
connected each-other, (a feature which would lead to the formation of a CP) each Cu6 ion being
capped by a molecule of water. Excluding Cu5, having a square planar coordination (τ4 = 0.06)
[41], all the other copper ions display a square pyramidal geometry (τ5Cu1 = 0.097, τ5Cu2 = 0.16, τ5Cu3
=
0.23, τ5Cu4 = 0.089, τ5Cu6 = 0.15). Two quite strong H-bonds [40] connect the two capping OH
fragments and carboxylate oxygens not involved in copper coordination (O4 and O6), while another
strong H-bond likely involves [42] O10 and coordinated water molecule. Moreover, other H-bonds
likely involve coordinated and crystallization water molecules as H-donors [42]. Anyway, these
interactions generate 1D supramolecular networks running parallel to the bisector of the angle
formed by the crystallographic a and c axes, as shown in Figures S10.
The reaction of copper cyclo-hexylcarboxylate with Hpz yielded a blue-grey microcrystalline
powder (yield 56%) and a blue solution from which some well-formed crystals (yield 13%) of
[Cu3(µ3-OH)(µ-pz)3(c-Hexc)2]n, 5, suitable for a SCXRD determination, were obtained. IR spectra
and elemental analyses of the two fractions are almost identical and ESI-MS of the microcrystalline
compound indicates the presence of trinuclear fragments (see Experimental Section). Moreover,
cell parameters and XRPD diffractogram (Table S1 and Figure S11) of the microcrystalline
compound fit quite well with those calculated from the SCXRD determination.

Figure 6 – Molecular structure of compound 5 with a partial atom numbering scheme.
In compound 5 (Figure 6) the usual trinuclear triangular structure is present, where Cu-µ3-OH
distances as well as the distance of O1 from the plane defined by the copper ions (ca. 0.437 Å) are
quite normal for this kind of compounds [15,19,25-29,37-39]. Both carboxylate anions display a
ditopic behavior with O4C17O5 that bridges Cu3 and Cu2i of a symmetry related trinuclear unit
(symmetry code i: –x+1,-y,-z+1) in a syn-anti mode, while O2C10O3 joins Cu1 and Cu3ii
[symmetry code ii: –x,-y,-z+1] in a syn-syn fashion. Thus, Cu1 and Cu2 display both a square
planar geometry (τ4Cu1 = 0.1, τ4Cu2 = 0.04) [43] while Cu3 has a square pyramidal coordination (τ5 =
0.25). Due to the ditopic behavior of the carboxylates, two slightly different 12-membered
metallacycles, whose mean planes are almost perpendicular, formed. Moreover, these cycles
generate 1D CPs running parallel to the crystallographic a axis (Figure 7). Interestingly, this
behavior, including the syn-syn and syn-anti bridging modes of the two carboxylates, is quite
identical to that found in the previously reported parent compound [Cu3(µ3-OH)(µ-
pz)3{CH2=C(CH3)COO}2]n [27].
Figure 7 – A 1D CP formed by condensed 12-membered metallacycles in compound 5. H-atoms
are omitted for clarity.

From the reaction of copper pivalate with pyrazole we isolated in quite good yield the trinuclear
triangular compound, [Cu3(µ3-OH)(µ-pz)3(Piv)2(HPz)(HPiv)2], 8. This compound was previously
obtained with a completely different synthetic procedure and was already characterized by SCXRD
[44]. Nevertheless, we found some minor structural differences compared to the reported structure,
thus the most relevant structural features of compound 8 are shown and discussed in the
Supplementary Information.
The reactions of copper(II) phenylacrylate, laurate and myristate with Hpz, generated
microcrystalline derivatives 3, 6 and 7, respectively, for which we were unable to achieve SCXRD
determinations. On the other hand, on the bases of other chemical-physical determinations, we
suggest, also in these cases, the existence of structures based on the [Cu3(µ3-OH)(µ-pz)3] core. First
of all, the finding of corresponding carboxylic acids in the mother liquors of the syntheses of
compounds 3, 6, and 7 is in agreement with the reaction sketched in Scheme 1. Moreover, all
elemental analyses data of compounds 3, 6, and 7 fit quite well with the trinuclear formulations
indicated in the Experimental Section, while reasonable mononuclear species, based on the
[Cu(RCOO)2(Hpz)n] (n = 2 or 4) formulation, have quite different calculated elemental analyses, as
shown in Table 2.
Table 2 – Comparison among calculated elemental analyses of Cu3(OH)(pz)3(RCO2)2,
Cu(RCO2)2(Hpz)2 and Cu(RCO2)2(Hpz)4 species and experimental data (in bold)
3
6
7
C
H,
N
C
H
N
C
H,
N
Found
46.16 3.42
46.12 3.44
58.35 4.49
57.18 4.80
11.31 48.83 7.50
11.95 49.09 6.99
11.34 60.22 9.10
17.78 58.87 8.51
9.90
50.86 7.41
9.29
9.73
8.56
14.17
Cu3(OH)(pz)3(RCO2)2
Cu(RCO2)2(Hpz)2
Cu(RCO2)2(Hpz)4
10.41 51.46 7.47
9.36 62.40 9.55
15.26 60.77 8.92
The room temperature magnetic susceptibilities values evidence, for all compounds, some kind of
antiferromagnetic interaction among the three CuII ions, a feature typically found in previously
reported trinuclear triangular copper(II) derivatives [15,19,25-29,37-39]. Also ESI-MS spectra of 3,
6 and 7 support the presence of trinuclear structures, several signals being typical of Cu3 fragments.
It is well known that aggregation phenomena, leading to oligomeric specie, may occur in ESI-MS
conditions, thus the sole ESI-MS data do not furnish an exhaustive proof of the existence of
trinuclear assemblies even in the solid-state [45-49], nevertheless these data suggest this possibility
and can be used, together with the above indicated determinations, to reasonably propose for
compounds 3, 6 and 7 trinuclear triangular structures, based on the Cu3(µ3-OH)(µ-pz)3 moiety,
analogously to what previously reported [26].
4. Conclusions
17

The reaction in protic solvents of copper(II) carboxylates with Hpz and water yielded eight new
derivatives in which the trinuclear triangular [Cu3(µ3-OH)(µ-pz)3] motif was exclusively found. In
compounds 1, 2, and 5 the trinuclear fragments further act as SBUs and self-assemble, through
carboxylates bridges, generating different 1D CPs, while, in the case of 4, the self-assembly is
limited to four trinuclear units, yielding a dodecanuclear moiety capped by coordinated water
molecules. In this latter compound, as well as in compound 2, the tritopic behavior of one
carboxylate is in some way reminiscent of the polymeric structure of numerous copper(II)
carboxylates, based on the repetition of the [Cu2(RCOO)4] moiety. In compound 8, which was
obtained according to a completely different procedure with respect to that already published [44],
pivalate ions display only a monotopic behavior, possibly due to the steric hindrance of the (CH3)3C
groups, thus neither CPs nor hexanuclear assemblies are present, resulting in an isolated trinuclear
triangular structure (see Supplementary Information). Noteworthy, in this case the coordination
schemes of Cu2 and Cu3 ions are instead completed through the coordination of two pivalic acid
molecules which formed, as byproduct, in the formation of pz- and OH- anions, that generate the
trinuclear triangular assembly. Concerning compounds 3, 6 and 7, we were unable to obtain good-
quality single-crystals to be employed for SCXRD determinations, but the presence of the trinuclear
triangular CuII moiety has been inferred on the bases of the presence of carboxylic acids in the
reaction mother liquors, of the elemental analyses, IR, ESI-MS and magnetic susceptibility
measurements, evidencing analogies with the previously reported trinuclear triangular copper(II)
systems [15,19,25-29,37-39].
In any case, as suitable concentrations of OH- and pz- anions are needed for the self-assembly of the
trinuclear triangular [Cu3(µ3-OH)(µ-pz)3] motif, these results clearly indicate that involved
carboxylates are basic enough to ensure a sufficient concentration of OH- and pz- anions, to drive
the reaction toward the formation of trinuclear compounds. In any case, in this process, no
exogenous strong bases are needed and, in most cases, carboxylate ions also behave as useful
polytopic linkers, yielding CPs. A further step in our work will provide to employ, in the reaction
with Hpz, copper(II) bicarboxylates, with the aim to connect trinuclear units to easily obtain 2D or
3D CPs through a very simple and cheap synthetic procedure, which can be carried out in eco-
friendly solvents as water or alcohols.
Acknowledgments
This work was financially supported by the Research Project DESCARTES of the Italian Ministry
of the University and Research (PRIN-2010-BNZ3F2) and by the University of Padova PRAT
CPDA134272/13. M.M. wishes to thank the University of Bologna for financial support.
Appendix A. Supplementary material
18

Supplementary data associated with this article can be found, in the online version, at: ……
moreover, crystallographic data of [Cu(Vnac)2(H2O)]2, [Cu(Phpr)2]2 and compounds 1, 2, 4, 5, 8
have been deposited at the Cambridge Crystallographic Data Center, CCDC 1454761-1454767.
These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
Special Issues of Chem. Soc. Rev. 38 (2009) 1201-1508.
Thematic Issue on Metal-Organic Frameworks of Chem. Rev. 112 (2012) 673-1231.
Y.R. Cook, Y-R. Zheng, P.J. Stang, Chem. Rev. 113 (2013) 734.
Special Issue of Chem. Soc. Rev. 43 (2014) 5403-6176.
N. Masciocchi, S. Galli, A. Sironi, Comments Inorg. Chem, 26 (2005) 1.
J.P. Zhang, X.M. Chen, Chem. Commun. (2006) 1689.
J. Klingele, S. Dechert, F. Meyer, Coord. Chem. Rev. 253 (2009) 2698.
A. Phan, C.J. Doonan, F.J. Uribe-Romo, C. B. Knobler, M. O'Keeffe, O. M. Yaghi, Acc.
Chem. Res. 43 (2010) 58-67.
[9]
C. Pettinari, N. Masciocchi, L. Pandolfo, D. Pucci, Chem.-Europ. J. 16 (2010) 1106.
[10] A.A. Mohamed, Coord. Chem. Rev. 254 (2010) 1918.
[11] J. Olguin, S. Brooker, Coord. Chem. Rev. 255 (2011) 203.
[12] W. Ouellette, S. Jones, J. Zubieta, CrystEngComm 13 (2011) 4457.
[13] G. Aromi, L.A. Barrios, O. Roubeau, P. Gamez, Coord. Chem. Rev. 255 (2011) 485.
[14] J.P. Zhang, Y.B. Zhang, J.B. Lin, X.M. Chen, Chem. Rev. 112 (2012) 1001.
[15] C. Di Nicola, Y.Yu. Karabach, A. M. Kirillov, M. Monari, L. Pandolfo, C. Pettinari, A.J.L.
Pombeiro, Inorg. Chem. 46 (2007) 221.
[16] S.-Z. Zhan, M. Li, S.W. Ng, D. Li, Chem.-Eur. J. 19 (2013) 10217.
[17] C. V. Hettiarachchi, M. A. Rawashdeh-Omary, D. Korir, J. Kohistani, M. Yousufuddin,
H.V. Rasika Dias, Inorg. Chem. 52 (2013) 13576.
[18] J.-H. Wang, M. Li, D. Li, Chem.-Eur. J. 20 (2014) 12004.
[19] M. Casarin, C. Corvaja, C. Di Nicola, D. Falcomer, L. Franco, M. Monari, L. Pandolfo, C.
Pettinari, F. Piccinelli, P. Tagliatesta, Inorg. Chem. 43 (2004) 5865.
[20] A. D. Naik, M. M. Dirtu, A. Léonard, B. Tinant, J. Marchand-Brynaert, B.-L. Su, Y. Garcia,
Cryst. Growth Des. 10 (2010) 1798.
[21] A. Cingolani, S. Galli, N. Masciocchi, L. Pandolfo, C. Pettinari, A. Sironi, J. Am. Chem.
Soc. 127 (2005) 6144.
[22] A. Bencini, M. Casarin, D. Forrer, L. Franco, F. Garau, N. Masciocchi, L. Pandolfo, C.
Pettinari, M. Ruzzi, A. Vittadini, Inorg. Chem. 48 (2009) 4044.
19

[23] M. Casarin, D. Forrer, L. Pandolfo, C. Pettinari, A. Vittadini, CrystEngComm 17 (2015)
407.
[24] J.L. Barbour, Chem. Commun. (2006) 1163.
[25] M. Casarin, C. Corvaja, C. Di Nicola, D. Falcomer, L. Franco, M. Monari, L. Pandolfo, C.
Pettinari, F. Piccinelli, Inorg. Chem. 44 (2005) 6265.
[26] C. Di Nicola, F. Garau, Y.Yu. Karabach, L.M.D.R.S. Martins, M. Monari, L. Pandolfo, C.
Pettinari, A.J.L. Pombeiro, Eur. J. Inorg. Chem. (2009), 666.
[27] S. Contaldi, C. Di Nicola, F. Garau, Y.Yu. Karabach, L.M.D.R.S. Martins, M. Monari, L.
Pandolfo, C. Pettinari, A.J.L. Pombeiro, Dalton Trans. (2009) 4928.
[28] For a comprehensive review on Cu(II) trinuclear triangular complexes see: E. Zangrando,
M. Casanova, E. Alessio, Chem. Rev. 108 (2008) 4979.
[29] S. Carlotto, M. Casarin, A. Lanza, F. Nestola, L. Pandolfo, C. Pettinari, R. Scatena, Cryst.
Growth Des. 15 (2015) 5910.
[30] CRC Handbook of Chemistry and Physics 84th Ed. (2003-2004). pKa values for lauric and
myristic acid were calculated at http://www.chemicalize.org/ (accessed 23/02/2016).
[31] Y. Muto, N. Hirascima, T. Tokii, M. Kato, I. Suzuki, Bull. Chem. Soc. Jpn. 59 (1986) 3672.
[32] M.W. Senko, IsoPro Isotopic Abundance Simulator, v. 2.1: National High Magnetic Field
Laboratory, Los Alamos National Laboratory: Los Alamos, NM, (1994).
[33] C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, M. Towler, J.
van de Streek, J. Appl. Crystallogr. 39 (2006) 453.
[34] C.F. Macrae, I.J.Bruno, J. A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L.
Rodriguez-Monge, R. Taylor, J. van de Streek, P.A. Wood, J. Appl. Crystallogr. 41 (2008)
466.
[35] L. Yang, D.R. Powell, R. P. Houser, Dalton Trans. (2004) 955.
[36] A. W. Addison, N. T. Rao, J. Reedijk, J. van Rijn, G. C. Verschoor, J. Chem. Soc. Dalton
Trans. (1984) 1349.
[37] P.A. Angaridis, P. Baran, R. Bo a, F. Cervantes-Lee, W. Haase, G. Mezei, R. G. Raptis, R.
Werner, Inorg.Chem. 41 (2002) 2219.
[38] M. Casarin, A. Cingolani, C. Di Nicola, D. Falcomer, M. Monari, L. Pandolfo, C. Pettinari,
Cryst. Growth Des. 7 (2007) 676.
[39] R. Bo a, L. Dlhá , G. Mezei, T. Ortiz-Pérez, R. G. Raptis, J. Telser, Inorg. Chem. 42 (2003)
5801.
[40] T. Steiner, Angew. Chem. Int. Ed. 41 (2002) 48.
[41] A weak chelating interaction [Cu5-O10 2.79(2) Å] is also present.
[42] H atoms of water molecules were not located.
20

[43] In the case of Cu2 a weak chelating interaction [Cu2-O4i 2.622(3) Å] is also present.
[44] J-H. Zhou, Z. Liu, Y-Z. Li, Y. You Song, X-T. Chen, X-Z. You, J. Coord. Chem. 59 (2006)
147.
[45] M. Fujita, F. Ibukuro, H. Hagihara, K. Ogura, Nature 367 (1994) 720.
[46] R. Colton, A. D'Agostino, J. C. Traeger, Mass Spectrom. Rev. 14 (1995) 79.
[47] S. Favaro, L. Pandolfo, P. Traldi, Rapid Commun. Mass Spectrom. 11 (1997) 1859.
[48] L.S. Bonnington, R.K. Coll, E.J. Gray, J. I. Flett, W. Henderson, Inorg. Chim. Acta 290
(1999) 213.
[49] A. Cingolani, Effendy, M. Pellei, C. Pettinari, C. Santini, B.W. Skelton, A.H. White, Inorg.
Chem. 41 (2002) 6633.
21

Graphical Abstract for
Coordination polymers from mild condition reactions of copper(II) carboxylates with
pyrazole (Hpz). Influence of carboxylate basicity on the self-assembly of the [Cu3(µ3-OH)(µ-
pz)3]2+ secondary building unit.
by
Sara Massignani, Rebecca Scatena, Arianna Lanza, Magda Monari, Francesca Condello, Fabrizio
Nestola, Claudio Pettinari, Federico Zorzi, Luciano Pandolfo.
22

Highlights for:
Coordination polymers from mild condition reactions of copper(II) carboxylates with
pyrazole (Hpz). Influence of carboxylate basicity on the self-assembly of the [Cu3(µ3-OH)(µ-
pz)3]2+ secondary building unit.
by
Sara Massignani, Rebecca Scatena, Arianna Lanza, Magda Monari, Francesca Condello, Fabrizio
Nestola, Claudio Pettinari, Federico Zorzi, Luciano Pandolfo.
Cu carboxylates and pyrazole in alcohols yield trinuclear triangular CuII assemblies
Trinuclear triangular CuII moieties self-assemble to give coordination polymers
Basicity of carboxylates is the determining key for the trinuclear assembly
Coordination polymers are obtained through cheap and simple procedures
23