Mixed-ligand hydroxocopper(II)/pyridazine clusters embedded into 3D framework lattices

Article abstract of DOI:10.1039/c4dt00174e

Rational combination of pyridazine, hydroxo and carboxylate bridging ligands led to the assembly of three types of mixed-ligand polynuclear Cu(ii) clusters (A: [Cu₂(μ-OH)(μ-pdz)(μ-COO)]; B: [Cu ₄(μ₃-OH)₂(μ-pdz)₂]; C: [Cu₅(μ-OH)₂(μ-pdz)₄(μ-COO) ₂(μ-H₂O)₂]) and their integration into 3D framework structures. Mixed-ligand complexes [Cu₂(μ-OH){TMA}(L) (H₂O)] (1), [Cu₄(μ₃-OH)₂{ATC} ₂(L)₂(H₂O)₂]·H₂O (2) [Cu₄(μ₃-OH)₂{TDC}₃(L) ₂(H₂O)₂]·7H₂O (3) (L = 1,3-bis(pyridazin-4-yl)adamantane; TMA^3- = benzene-1,3,5- tricarboxylate, ATC^3- = adamantane-1,3,5-tricarboxylate, TDC ^2- = 2,5-thiophenedicarboxylate) and [Cu₅(μ-OH) ₂{X}₄(L)₂(H₂O)₂] ·nH₂O (X = benzene-1,3-dicarboxylate, BDC^2-, n = 5 (4) and 5-hydroxybenzene-1,3-dicarboxylate, HO-BDC^2-, n = 6 (5)) are prepared under hydrothermal conditions. Trigonal bridges TMA^3- and ATC^3- generate planar Cu(ii)/carboxylate subtopologies further pillared into 3D frameworks (1: binodal 3,5-coordinated, doubly interpenetrated tcj-3,5-Ccc2; 2: binodal 3,8-coordinated tfz-d) by bitopic pyridazine ligands. Unprecedented triple bridges in 1 (cluster of type A) support short Cu...Cu separations of 3.0746(6) A. The framework in 3 is a primitive cubic net (pcu) with multiple bis-pyridazine and TDC^2- links between the tetranuclear nodes of type B. Compounds 4 and 5 adopt uninodal ten-coordinated framework topologies (bct) embedding unprecedented centrosymmetric open-chain pentanuclear clusters of type C with two kinds of multiple bridges, Cu(μ-OH)(μ-pdz)₂Cu and Cu(μ-COO)(μ-H₂O)Cu (Cu...Cu distances are 3.175 and 3.324 A, respectively). Magnetic coupling phenomena were detected for every type of cluster by susceptibility measurements of 1, 3 and 4. For binuclear clusters A in 1, the intracluster antiferromagnetic exchange interactions lead to a diamagnetic ground state (J = -17.5 cm^-1; g = 2.1). Strong antiferromagnetic coupling is relevant also for type B, which consequently results in a diamagnetic ground state (J₁ = -110 cm^-1; J₂ = -228 cm^-1, g = 2.07). For pentanuclear clusters of type C in 4, the exchange model is based on a strongly antiferromagnetically coupled central linear trinuclear Cu ₃ group (J₁ = -125 cm^-1) and two outer Cu centers weakly antiferromagnetically coupled to the terminal Cu ions of the triad (J₂ = -12.5 cm^-1). the Partner Organisations 2014.

Full text of DOI:10.1039/c4dt00174e

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Mixed-ligand hydroxocopper(II)/pyridazine clusters
embedded into 3D framework lattices†
Anna S. Degtyarenko,a Marcel Handke,b Karl W. Krämer,c Shi-Xia Liu,*c
Silvio Decurtins,c Eduard B. Rusanov,d Laurence K. Thompson,e Harald Krautscheidb
and Konstantin V. Domasevitch*a
Cite this: Dalton Trans., 2014, 43,
8530
Rational combination of pyridazine, hydroxo and carboxylate bridging ligands led to the assembly of
three types of mixed-ligand polynuclear Cu(II) clusters (A: [Cu2(μ-OH)(μ-pdz)(μ-COO)]; B: [Cu4(μ3-
OH)2(μ-pdz)2]; C: [Cu5(μ-OH)2(μ-pdz)4(μ-COO)2(μ-H2O)2]) and their integration into 3D framework struc-
tures. Mixed-ligand complexes [Cu2(μ-OH){TMA}(L)(H2O)] (1), [Cu4(μ3-OH)2{ATC}2(L)2(H2O)2]·H2O (2)
[Cu4(μ3-OH)2{TDC}3(L)2(H2O)2]·7H2O (3) (L = 1,3-bis(pyridazin-4-yl)adamantane; TMA3− = benzene-
1,3,5-tricarboxylate, ATC3− = adamantane-1,3,5-tricarboxylate, TDC2− = 2,5-thiophenedicarboxylate) and
[Cu5(μ-OH)2{X}4(L)2(H2O)2]·nH2O (X = benzene-1,3-dicarboxylate, BDC2−, n = 5 (4) and 5-hydroxy-
benzene-1,3-dicarboxylate, HO-BDC2−, n = 6 (5)) are prepared under hydrothermal conditions. Trigonal
bridges TMA3− and ATC3− generate planar Cu(II)/carboxylate subtopologies further pillared into 3D frame-
works (1: binodal 3,5-coordinated, doubly interpenetrated tcj-3,5-Ccc2; 2: binodal 3,8-coordinated
tfz-d) by bitopic pyridazine ligands. Unprecedented triple bridges in 1 (cluster of type A) support short
Cu⋯Cu separations of 3.0746(6) Å. The framework in 3 is a primitive cubic net (pcu) with multiple bis-
pyridazine and TDC2− links between the tetranuclear nodes of type B. Compounds 4 and 5 adopt unino-
dal ten-coordinated framework topologies (bct) embedding unprecedented centrosymmetric open-
chain pentanuclear clusters of type C with two kinds of multiple bridges, Cu(μ-OH)(μ-pdz)2Cu and
Cu(μ-COO)(μ-H2O)Cu (Cu⋯Cu distances are 3.175 and 3.324 Å, respectively). Magnetic coupling
phenomena were detected for every type of cluster by susceptibility measurements of 1, 3 and 4. For
binuclear clusters A in 1, the intracluster antiferromagnetic exchange interactions lead to a diamagnetic
ground state (J = −17.5 cm−1; g = 2.1). Strong antiferromagnetic coupling is relevant also for type B,
which consequently results in a diamagnetic ground state (J1 = −110 cm−1; J2 = −228 cm−1, g = 2.07). For
pentanuclear clusters of type C in 4, the exchange model is based on a strongly antiferromagnetically
coupled central linear trinuclear Cu3 group (J1 = −125 cm−1) and two outer Cu centers weakly antiferro-
magnetically coupled to the terminal Cu ions of the triad (J2 = −12.5 cm−1).
Received 17th January 2014,
Accepted 21st March 2014
DOI: 10.1039/c4dt00174e
www.rsc.org/dalton
Introduction
The study of metal–organic framework (MOF) structures
adopted by linkage of polynuclear metal ion clusters is a
special topic in coordination and materials chemistry and
aInorganic Chemistry Department, Taras Shevchenko National University of Kyiv,
Volodimirska Street 64/13, Kyiv 01601, Ukraine. E-mail: dk@univ.kiev.ua
bInstitut für Anorganische Chemie, Universität Leipzig, Johannisallee 29,
D-04103 Leipzig, Germany
cDepartement für Chemie und Biochemie, Universität Bern, Freiestrasse 3,
CH-3012 Bern, Switzerland. E-mail: liu@iac.unibe.ch
crystal engineering, and has attracted rapidly growing interest
during the last decade.1 In view of framework topologies,2 the
design of such solids offers a particularly successful approach.
It allows to avoid the common limitations for the node connec-
tions imposed by the typical coordination numbers,3 and
therefore a diversity of extremely highly-connected frameworks
became accessible by propagation of coordination geometries
established by polynuclear clusters.4 An even more important
aspect considers the utility of the latter for functionalization of
the MOFs towards specific applications in magnetism and
catalysis,5 while imprinting the inherent properties of the
dInstitute of Organic Chemistry, Murmanskaya Str. 4, Kyiv 253660, Ukraine
eDepartment of Chemistry, Memorial University of Newfoundland,
St. John’sA1B 3X7, Canada
†Electronic supplementary information (ESI) available: Details for organic syn-
thesis and characterization; IR spectra, TGA and thermo-XRPD patterns; X-ray
structure refinement. CCDC 967343–967348. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c4dt00174e
8530 | Dalton Trans., 2014, 43, 8530–8542
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Table 1 Bridging coordination of non-chelating pyridazines towards Cu(II) ionsa
Complex
co-Bridge(s)
μ-OH, μ-sac-N,O
μ-Cl (×2)
Cu⋯Cu/Å
3.360
Structural pattern and magnetic features
Ref.
[Cu(OH)(sac)(μ-pdz)]n
[Cu(μ-pdz)Cl2]n
1D chain of triply bridged Cu2+ ions;
strong AFM, μeff (RT) = 0.99 μB
22
3.378
1D chain of triply bridged Cu2+ ions;
μeff (RT) = 1.5–1.7 μB; low-temperature AF coupling
1D chain of triply bridged Cu2+ ions; strong AFM,
μeff (RT) = 1.08 μB
20a, 23
19
[Cu(OH)(μ-pdz)(NO3)]n
[Cu3(μ-pdz)4(pdz)2(μ-NO3)2(NO3)4]
μ-OH, μ-NO3-O,O′
μ-NO3-O,O
3.322
3.406
Triple bridges [M(μ-pdz)2(μ-NO3)M];
Discrete trinuclear; strong AFM, μeff (RT) = 1.51 μB
Discrete trinuclear, triple bridges [M(μ-pdz)2(μ-OH)M]
1D chain of triply bridged Cu2+ ions
Discrete binuclear cluster with triply bridged Cu2+ ions
Discrete tetranuclear cluster
15, 19
[Cu3(OH)2(μ-bpdz)3(H2O)2{CF3CO2}2]2+
[Cu(OH)(pp)](H2NSO3)·H2O
[Cu2(OH){TMA}(L)(H2O)]
[Cu4(OH)2{ATC}2(L)2(H2O)2]·H2O
[Cu4(OH)2{TDC}3(L)2(H2O)2]·7H2O
[Cu5(OH)2{BDC}4(L)2(H2O)2]·5H2O
μ-OH
μ-OH
3.236
3.394
3.075
3.272
3.334
3.175
13
14a
This work
This work
This work
This work
μ-OH, μ-RCO2-O,O′
μ3-OH
μ3-OH
μ-OH
The same
Discrete pentanuclear cluster with a trinuclear
triply-bridged skeleton M{(μ-pdz)2(μ-OH)M}2
The same
[Cu5(OH)2{HO-BDC}4(L)2(H2O)2]·6H2O
μ-OH
3.187
This work
a sac = saccharinate; bpdz = 4,4′-bipyridazine; pp = pyridazino[4,5-d]pyridazine; L = 1,3-bis(pyridazin-4-yl)adamantane; BDC = isophthalate;
HO-BDC 5-hydroxyisophthalate; TDC thiophene-2,5-dicarboxylate; TMA benzene-1,3,5-tricarboxylate; ATC adamantane-1,3,5-
tricarboxylate.
=
=
=
=
clusters into the extended lattices.6 Therefore, the development as hydroxo,10,13,19 halogenido,20 nitrato,15 isothiocyanato,10,21
of polynucleating ligand systems, which combine the abilities and saccharinato,22 and actually all of the reports for pyrid-
for generation of polynuclear fragments7 and their further inte- azine bridges between 3d-metal ions consider such a multiple
gration into the framework, has received a special value.8
heteroligand linkage, which is best illustrated by a Cu(II) series
Different types of azole and azine 1,2-dinitrogen donors are (Table 1). Thus a promising approach towards the develop-
applicable to assemble clusters of variable nuclearity and ment of nanosized molecular magnets may rely on a synergism
establish pathways for magnetic exchange between paramag- of the ligands in multicomponent systems24 based upon
netic metal ions, cf. copper(II) and cobalt(II). In this series, the bifunctional pyridazines, which could be well suited for the
pyridazine linker is a particular paradigm, while offering a synthesis of extended frameworks incorporating polynuclear
large magnetic superexchange interaction and thus mediating cluster units.
magnetic exchange most efficiently in comparison with corres-
In this work we report the construction of unprecedented
ponding phthalazine, 1,2,4-triazole, 1,2,4-triazolate and discrete di-, tetra- and pentanuclear copper(II)/pyridazine clus-
pyrazolate analogs.9 The ability of pyridazine to generate poly- ters and their integration into the 3D MOFs structures by the
nuclear complexes with tunable spin states of the metal ions is concerted action of representative di- and tricarboxylate
also known.10 The attractiveness of polypyridazinyl ligands, linkers (H2BDC = isophthalic acid; H2HO-BDC = 5-hydroxy-
however, was limited until now because of their low chemical isophthalic acid; H2TDC = thiophene-2,5-dicarboxylic acid;
accessibility. Actually, the preparative chemistry involving pyri- H3TMA = trimesic acid; H3ATC = adamantane-1,3,5-tricarb-
dazine relies on only one general method which is applicable oxylic acid) and prototypical pyridazine tecton 1,3-bis(pyrida-
for facile functionalization of different substrates, namely a zin-4-yl)adamantane (L) (Scheme 1), which features a double
very simple click reaction11 involving inverse electron demand ligand functionality established at a rigid alicyclic molecular
cycloadditions of 1,2,4,5-tetrazine.12 Recent developments platform.
have made this key intermediate readily available,12,13 thus
offering flexible pathways towards pyridazine ligands.13,14
A
second potential drawback one might find is the inherent
coordination ability of pyridazine.13–16 It manifests a pro-
nounced affinity towards d10 Cu(I) and Ag(I) ions, commonly
generating either single, double or triple bridges between the
metallic centres involved in the desired and peculiar poly-
nuclear and polymeric motifs.14,17 In the case of divalent
d-metal ions, bridging coordination of this electron deficient
and low basic ligand (pKa = 2.24 for pyridazine vs. pKa = 5.25
for pyridine) is less characteristic and predictable, compared
with a simple monodentate pyridine-like function.15,18 Never-
theless, double coordination of pyridazine may be stabilized
using suitable complementary short-distance co-bridges, such
Scheme 1 Synthesis of the bis-pyridazine ligand by
functionalization of the adamantane core.
a stepwise
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donors. The function of the carboxylate is most important for
compounds 4 and 5, providing expansion of the trinuclear
[Cu3(μ-pdz)4(μ-OH)2] skeleton to a pentanuclear architecture.
Results and discussion
Structure of the coordination compounds
All the compounds adopt 3D framework structures based upon Especially close structural relationships may be found for
multinuclear heteroligand clusters, which represent topologi- binuclear (A) and tetranuclear (B) motifs. Doubling the cluster
cal net nodes and thus provide a primary factor for the compli- nuclearity is made possible by elimination of the carboxylate
cated connectivities. Three types of the observed clusters, such bridge and a simple dimerization along the Cu–OH sides with
as binuclear in 1, tetranuclear in 2, 3 and pentanuclear units formation of two edge-sharing [Cu3(μ3-OH)] fragments. Such a
in 4 and 5 (Scheme 2), originate from a combination of three “dimer”, often encountered for different combinations of brid-
kinds of ligand bridges (pyridazine, hydroxo and carboxylate), ging ligands, is particularly characteristic of the hydroxocopper
while preserving a common simple submotif in the form of Cu systems.25 Further intercluster connection with generation of
ions linked by a double pdz/OH bridge. This suggests perfect frameworks occurs by the interplay of bipyridazine (as a
compatibility of μ-pdz and μ-OH linkers, which are commonly bitopic linker between the clusters, establishing three or four
concomitant and act in a synergetic manner.10,13,19 In fact, the Cu–N bonds) and dicarboxylate bridges (TDC2− (3), BDC2− (4),
significance of the hydroxo bridges is most crucial for the HO-BDC2− (5)), which are equally important in view of the
present systems since the bidentate coordination of pyridazine resulting topologies. This is contrary to the tricarboxylate
itself is less applicable for the chemistry of transition metal (TMA3− (1), ATC3− (2)) frameworks. Trifunctional anions, as
dications, as stated above. In this view, the clusters demon- the three-coordinated nodes, provide an additional origin of
strate a clear structural hierarchy, which implies a basic hydroxo- connectivity and generate distinct planar Cu-carboxylate sub-
copper(II) core, pyridazine co-bridges, auxiliary carboxylate topologies, further pillared with bitopic bipyridazine ligands
ligands and additional monodentate pyridazine and aqua (Table 2).
A simpler binuclear cluster A was observed in [Cu2(μ-OH)-
{TMA}(L)(H2O)] (1), with an unprecedented mixed-ligand pdz/
OH/carboxylate triple bridge connecting two Cu ions at very
short distances of Cu1⋯Cu2A 3.0746(6) Å and Cu1⋯Cu2B
3.1270(7) Å (for two orientations of the disordered fragment).
The environments of metal ions are complete with monoden-
tate carboxylate and pyridazine groups and aqua ligands
(Fig. 1, Table 3). As was indicated by the values of Addison τ
parameters,26 the geometries of the coordination polyhedra
are intermediate between idealized trigonal-bipyramidal (τ = 1)
and square-pyramidal (τ = 0) extremes: for orientation A, τ =
0.66 (Cu1) and 0.39 (Cu2A); for orientation B, τ = 0.53 (Cu1)
and 0.32 (Cu2B).
The low nuclearity of the cluster is likely a consequence of
topology limitations imposed by the rigid trigonal triple-
charged TMA3− connector: the planar Cu/carboxylate subtopo-
logy in the form of a hexagonal net (Fig. 1b) clearly implies a
three-fold coordination of the hydroxocopper nodes and their
complementary charge of +3 [e.g. Cu2(μ-OH)]. The bipyridazine
ligands are accommodated on both axial sides of this plane,
and they connect pairs of clusters at a distance of 13.56 Å and
Scheme 2 Three kinds of polynuclear Cu/OH/pyridazine clusters,
expand the structure in a third dimension as pillars between
the successive hexagonal layers. The result is a rare binodal
three- and five-connected {63}{69·8} net (three-letter notation is
representing the structures of the reported complexes: A – binuclear
motif in 1; B – tetranuclear clusters in 2 and 3; C – pentanuclear units in
4 and 5, with a central trinuclear hydroxo/pyridazine core.
Table 2 Highly-connected topologies of MOFs 1–5
Complex
Cluster type
Ligand coordination
Dimensionality
Net nodes (coordination)
Schläfli symbol
Topological type
1
2
3
4
5
A
B
B
C
C
3
3
3
4
4
2D → 3Da
2D → 3Da
3D
3D
3D
[Cu2(μ-OH)] (5), TMA (3)
[Cu4(μ3-OH)2] (8), ATC (3)
[Cu4(μ3-OH)2] (6)
{63}{69·8}
tcj-3,5-Ccc2
tfz-d (UO3)
pcu (α-Po)
bct
{43}2{46·618·84}
{412·63}
[Cu5(μ-OH)2] (10)
{312·428·55}
{312·428·55}
[Cu5(μ-OH)2] (10)
bct
a Dimensionality of the Cu/carboxylate subtopology and the overall dimensionality of the resulting heteroligand frameworks.
8532 | Dalton Trans., 2014, 43, 8530–8542
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Table 3 Selected bond distances (Å) and angles (°) for [Cu2(μ-OH)-
{TMA}(L)(H2O)] (1)a
Cu1–O3
Cu1–N4i
Cu1–N1
Cu1–O7ii
2.0418(18)
2.043(2)
2.053(2)
O3–Cu1–N1
O3–Cu1–O7ii
N4i–Cu1–O7ii
N1–Cu1–O7ii
O3–Cu1–N4i
N4i–Cu1–N1
89.10(8)
115.76(8)
89.91(9)
84.24(7)
91.75(9)
173.85(9)
2.1577(16)
Disordered fragment
Orientation A
Cu1–O1A
Orientation B
Cu1–O1B
Cu2B–O1B
Cu2B–O6iii
Cu2B–O8ii
Cu2B–O2B
Cu2B–N2B
1.873(3)
1.906(3)
1.946(2)
1.984(2)
1.991(3)
2.207(4)
1.913(3)
1.895(4)
1.9264(19)
1.9307(18)
1.952(4)
2.262(4)
Cu2A–O1A
Cu2A–O5iii
Cu2A–O4
Cu2A–O2A
Cu2A–N2A
O1A–Cu1–N4i
O1A–Cu1–N1
91.62(12)
93.80(12)
87.56(13)
88.78(14)
155.29(11)
178.92(17)
88.73(14)
109.02(13)
95.32(13)
108.89(16)
O1B–Cu1–N4i
O1B–Cu1–N1
86.79(12)
96.27(12)
88.57(13)
91.98(12)
159.17(9)
178.52(14)
87.98(15)
104.15(12)
96.68(12)
110.43(16)
O1A–Cu2A–O5iii
O1A–Cu2A–O4
O5iii–Cu2A–O4
O1A–Cu2A–O2A
O1A–Cu2A–N2A
O5iii–Cu2A–N2A
O4–Cu2A–N2A
Cu2A–O1A–Cu1
O1B–Cu2B–O6iii
O1B–Cu2B–O8ii
O6iii–Cu2B–O8ii
O1B–Cu2B–O2B
O1B–Cu2B–N2B
O6iii–Cu2B–N2B
O8ii–Cu2B–N2B
Cu2B–O1B–Cu1
a Symmetry codes: (i) −0.5 + x, −0.5 + y, z; (ii) x, −y, 0.5 + z; (iii) x, 1 −
y, 0.5 + z.
Fig. 1 (a) Binuclear cluster in the environment of carboxylate and pyri-
dazine ligands in the structure of 1; (b) 2D Cu/carboxylate subtopology
in the form of hexagonal net, with the pyridazine-N donors accommo-
dated at two sides of the plane. Only one orientation of the disordered
cluster is shown.
tcj-3,5-Ccc2), which appears to be very open and, therefore,
two identical nets interpenetrate (Fig. 2). That is a class IIa
ˉ 27,28
interpenetration, Z = 2, with a full symmetry element 1.
Fig. 2 Interpenetration of two inversion-related 3D frameworks
(marked with blue and grey bonds) in the structure of 1. The hydroxo-
copper-carboxylate layers are orthogonal to the drawing plane.
A comparable morphology of the framework is observed for
the aliphatic analog of trimesic acid, 1,3,5-adamantanetri-
carboxylate (ATC3−) in [Cu4(μ3-OH)2{ATC}2(L)2(H2O)2]·H2O (2).
That is a first coordination polymer generated by this ligand
and we introduce ATC3− as a novel geometrically rigid tripodal
linker, potentially complementing and expanding the chem-
istry of functional frameworks based upon TMA3− (such as
HKUST-1).29 Both metal ions adopt typical Jahn–Teller poly-
hedra in the form of square pyramids (Cu1; Addison para-
meter26 τ = 0.18) or axially elongated octahedra (Cu2) (Table 4),
with pyridazine-N donors positioned at the equatorial planes.
In the metal–carboxylate subtopology, the net nodes exist as the
above six-connected tetranuclear clusters [Cu4(μ3-OH)2] and
three-connected ATC3− (in 1 : 2 proportion), giving rise to a 2D
structure of the CdI2 or Mg(OH)2 type (Kagomé dual net,
{43}2{46·66·83}, three-letter notation “kgd”) (Fig. 3). Pairs of
bipyridazine ligands, as double links, interconnect the clusters
from the successive layers (separated at 12.83 Å), yielding a 3D
eight- and three-coordinated framework, with a Schläfli point
symbol {43}2{46·618·84} (tfz-d, topological type of UO3)
(Table 2). There are a limited number of structural precedents
for such a linkage, most of which also incorporate polynuclear
cluster nodes and trigonal TMA3− links.30
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Table 4 Selected bond distances (Å) and angles (°) for tetranuclear
complexes 2 and 3a
[Cu4(μ3-OH)2{ATC}2(L)2(H2O)2]·H2O (2)
Cu1–O1
Cu1–O2
Cu1–N4iv
Cu1–N1
Cu1–O1w
1.931(2)
1.952(3)
2.026(3)
2.068(3)
2.359(3)
Cu2–O6ii
Cu2–O5iii
Cu2–O1
Cu2–N2
Cu2–O1i
1.948(3)
1.953(3)
1.962(2)
2.016(3)
2.423(2)
O1–Cu1–O2
O1–Cu1–N4iv
O2–Cu1–N4iv
O1–Cu1–N1
O2–Cu1–N1
N4iv–Cu1–N1
O1–Cu1–O1w
N4iv–Cu1–O1w
N1–Cu1–O1w
167.55(11)
94.38(12)
93.50(12)
86.13(12)
86.29(12)
178.20(13)
100.77(10)
90.72(12)
87.49(11)
O6ii–Cu2–O5iii
O6ii–Cu2–O1
O5iii–Cu2–O1
O6ii–Cu2–N2
O5iii–Cu2–N2
O1–Cu2–N2
O6ii–Cu2–O1i
O1–Cu2–O1i
N2–Cu2–O1i
85.36(12)
97.84(11)
176.64(12)
173.27(12)
90.36(12)
86.36(12)
99.00(10)
85.52(10)
86.53(11)
Cu1–O1–Cu2
Cu1–O1–Cu2i
114.38(12)
120.24(12)
Cu2–O1–Cu2i
94.48(10)
[Cu4(μ3-OH)2{TDC}3(L)2(H2O)2]·7H2O (3)
Cu1–O1
Cu1–O1i
Cu1–O2
Cu1–O8ii
Cu1–O5iv
Cu1–N1
1.920(2)
2.352(2)
1.942(11)
1.952(2)
1.959(12)
2.052(3)
Cu2–O1
Cu2–O6
Cu2–N4iii
Cu2–N2
Cu2–O10
1.919(2)
1.968(2)
2.007(3)
2.058(3)
2.236(2)
O1–Cu1–O2
O1–Cu1–O8ii
O2–Cu1–O8ii
O1–Cu1–N1
O2–Cu1–N1
O8ii–Cu1–N1
O5iv–Cu1–N1
O1–Cu1–O1i
N1–Cu1–O1i
160.6(3)
97.53(10)
84.5(4)
88.00(10)
90.8(4)
174.25(11)
83.1(3)
85.37(9)
94.72(10)
O1–Cu2–O6
O1–Cu2–N4iii
O6–Cu2–N4iii
O1–Cu2–N2
O6–Cu2–N2
N4iii–Cu2–N2
O1–Cu2–O10
O6–Cu2–O10
N2–Cu2–O10
172.67(10)
91.96(10)
87.77(11)
88.41(10)
89.29(10)
159.51(12)
93.71(9)
93.25(10)
90.06(10)
Cu1–O1–Cu1i
Cu2–O1–Cu1
94.63(9)
120.57(12)
Cu2–O1–Cu1i
110.79(10)
a Symmetry codes for 2: (i) −x, 2 − y, 1 − z; (ii) −1 + x, y, z; (iii) 1 − x,
1 − y, 1 − z; (iv) x, y, −1 + z. For 3: (i) 1 − x, 2 − y, −z; (ii) −0.5 + x, 2.5 −
y, −0.5 + z; (iii) 1.5 − x, 0.5 + y, 0.5 − z; (iv) −x, 2 − y, −z.
Fig. 3 (a) Tetranuclear cluster in 2 showing the hydrogen bonding
interactions with μ3-OH and aqua ligands; (b) Cu/carboxylate topology
in the form of six- and three-connected CdI2-like network. Note the
intrinsic topological significance of the tricarboxylate linker. Symmetry
codes: (i) –x, 2 − y, 1 − z; (ii) −1 + x, y, z; (iii) 1 − x, 1 − y, 1 − z; (iv) x, y,
−1 + z.
Similar tetranuclear net nodes are also observed for
[Cu4(μ3-OH)2{TDC}3(L)2(H2O)2]·7H2O (3). However, substitution
of the carboxylate portion of the structure for dibasic thiophene-
dicarboxylate leads to simplification of the entire array. This
concerns the elimination of three-connected nodes and an
increased carboxylate/cluster ratio (3 : 1), which in effect
increases the dimensionality of the carboxylate subconnectiv-
ity, existing in the form of a primitive cubic net (pcu, Schläfli
point symbol {412·63}). The bipyridazine bridges did not gene-
rate additional intercluster links, but rather repeat the existing
links already established by the TDC2− bridges. In this way,
four out of six topological links are doubled as a result of the
concerted action of both sorts of ligands (Fig. 4). Two CuII ions
HO-BDC2−, n = 6), are more complicated and they include
pentanuclear net nodes (Fig. 4). The present open-chain
centrosymmetric Cu5 units are unprecedented yet comprising
a central trinuclear core [Cu3(μ-OH)2(pdz)4] built up with two
triple bis-pyridazino/hydroxo bridges, which itself is known for
copper(II)13 and cobalt(II)10 pyridazine complexes. These units
are extended to the pentanuclear pattern by connecting two
Cu3 ions as annexes through carboxylate bridges and distal
aqua ligands (Fig. 5). These outer ions have a typically dis-
torted [4 + 2] octahedral coordination, whereas the environ-
ment geometry of Cu2 is close to a square pyramid with N3 in
the apex position, with Addison parameters26 τ = 0.41 (4a at
296 K), τ = 0.37 (4b at 105 K) and τ = 0.42 (5) (Table 5).
adopt square-pyramidal environments (Addison parameters26
are 0.23 for Cu1 and 0.22 for Cu2) (Table 4).
τ
The structures of the two isotypic compounds,
[Cu5(μ-OH)2{X}4(L)2(H2O)2]·nH2O (4: X = BDC2−, n = 5; 5: X =
8534 | Dalton Trans., 2014, 43, 8530–8542
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Fig. 4 (a) Primitive cubic framework of 3 viewed down the b direction
showing interconnection of heteroligand carboxylate/pyridazine planes
by additional carboxylate linkers. (b) The heteroligand planes with
double organic bridges between the tetranuclear clusters constituting
the framework nodes.
Fig. 5 (a) Pentanuclear centrosymmetric clusters observed in 4 and 5.
Note the compressed octahedral geometry around the Cu1 ion. (b)
Mode of interconnection of the clusters by dicarboxylate links. Sym-
metry codes: (i) −x, −y, 2 − z; (ii) 0.5 − x, 0.5 + y, 2.5 − z; (iii) −0.5 + x,
−0.5 − y, −0.5 + z; (iv) −1 + x, y, z; (v) −0.5 − x, 0.5 + y, 2.5 − z.
The most striking features of the local coordination geome-
tries are the appreciably compressed octahedral environments
adopted by the central Cu1 ions lying on the centre of inver-
sion. For both of the compounds, these involve two pairs of
long “equatorial” Cu–N bonds (2.1733(18)–2.300(2) Å)
accompanied by two very short “axial” Cu–O1 bonds (1.901(2)–
1.9086(16) Å). The only documented example of the [Cu{(μ-OH)-
(μ-pdz)2Cu}2] pattern, in a 4,4′-bipyridazine complex, also
implies such a kind of coordination octahedron adopted by
the central Cu ion (Cu–O 1.887(2); Cu–N 2.146(2)–2.340(3) Å).13
Although these observations are suggestive of Jahn–Teller com-
pression (indicating the unusual {d(z2)} electronic ground state
of Cu1 ions), the present geometries, most likely, may be
attributed to the dynamic disorder of an axis of Jahn–Teller
elongation and consequent librational effects.31 First, the
examination of complex 4 at different temperatures (4a: 296 K,
4b: 105 K, using the same single crystal) reveals an appreciable
temperature dependence of the Cu1–N bond lengths. Being
actually equivalent at r.t. (2.221(2) × 2 and 2.252(2) × 2 Å), two
pairs of bonds became essentially differentiated upon cooling
(2.1733(18) × 2 and 2.300(2) × 2 Å) (Table 5). Second, mean-
square displacement amplitude (MSDA)32 analysis clearly indi-
cates the presence of librational disorder involving all four
Cu1–N bonds, at both temperatures (for Cu1–O1, Cu1–N1 and
Cu1–N4 bonds, <d2> (×104 Å2) = 11(11), 95(12) and 78(12) at
296 K, and 9(8), 74(11) and 41(10) at 105 K, respectively), with
the corresponding <d2> values being particularly high at r.t.
Importantly, the bonds adopted by Cu2 and Cu3 ions are actu-
ally temperature invariant (Table 5). The application of such
an approach towards “compressed” coordination geometry of
Cu2+ ions was extensively discussed by Halcrow.31
The fact that the cluster units accommodate in total eight
carboxylate and four pyridazine groups allows a very high, up
to twelve, connectivity at the net nodes.4 The latter is
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Table 5 Selected bond distances (Å) and angles (°) for pentanuclear
complexes 4 and 5a
[Cu5(μ-OH)2{BDC}4(L)2(H2O)2]·5H2O (4a, 296 K)
Cu1–O1
Cu1–N1
Cu1–N4
1.9086(16) × 2
2.221(2) × 2
2.252(2) × 2
Cu3–O10iv
Cu3–O6v
Cu3–O7
Cu3–O4
Cu3–O8
Cu3–O2
1.9085(17)
1.9593(19)
1.9614(16)
1.9685(18)
2.482(2)
Cu2–O1
Cu2–O3
Cu2–O2
Cu2–N2
Cu2–N3iii
1.8800(17)
1.9286(18)
2.0040(18)
2.195(2)
2.733(2)
2.224(2)
[Cu5(μ-OH)2{BDC}4(L)2(H2O)2]·5H2O (4b, 105 K)
Fig. 6 Thermal variation of χmT for 1 (the solid line is drawn based on
the Bleaney–Bowers equation).
Cu1–O1
Cu1–N1
Cu1–N4
1.9162(15) × 2
2.300(2) × 2
2.1733(18) × 2
Cu3–O10iv
Cu3–O6v
Cu3–O7
Cu3–O4
Cu3–O8
Cu3–O2
1.9139(16)
1.9616(16)
1.9615(14)
1.9715(16)
2.4799(18)
2.7019(18)
value originates from a minor paramagnetic phase; this is
reflected in the Curie tail as seen in the χm(T) plot (Fig. S24†).
The inverse magnetic susceptibility curve (Fig. S25†) shows
a linear behavior in the temperature range of 50 to 300 K,
which results in a Weiss constant θ = −37 K, in good agree-
ment with the negative slope of the χmT versus T curve. We can
use the following isotropic Hamiltonian to describe the
intracluster magnetic exchange interactions:
Cu2–O1
Cu2–O3
Cu2–O2
Cu2–N2
Cu2–N3iii
1.8784(15)
1.9245(15)
2.0093(16)
2.1671(19)
2.227(2)
[Cu5(μ-OH)2{HO-BDC}4(L)2(H2O)2]·6H2O (5)
Cu1–O1
Cu1–N1
Cu1–N4
1.901(2) × 2
2.138(3) × 2
2.344(3) × 2
Cu3–O8
1.915(2)
1.927(2)
1.949(2)
1.964(2)
2.541(3)
2.667(3)
Cu3–O6iv
Cu3–O4
H ¼ ꢀ2JðS1S2Þ
Cu3–O10v
Cu3–O11v
Cu3–O2
Cu2–O1
Cu2–O3
Cu2–O2
Cu2–N2
Cu2–N3ii
1.882(2)
1.933(2)
2.000(3)
2.154(3)
2.230(3)
The magnetic susceptibility data were least-squares fit to
the Bleaney–Bowers equation36 for isotropic exchange in the
Cu(II) pair. A good simulation of the data is achieved with J =
−17.5 cm−1 (g = 2.1). The fact that compound 1 shows a very
complex bonding pattern with a heteroligand pyridazine/OH/
carboxylate triple bridge connecting the two Cu(II) ions pre-
vents a detailed structure–property correlation, and thus the
experimentally determined J parameter comprises all possible
exchange pathways between the spin centers.
a Symmetry codes for 4: (iii) −0.5 + x, −0.5 − y, −0.5 + z; (iv) −1 + x, y, z;
(v) −0.5 − x, 0.5 + y, 2.5 − z. For 5: (ii) x, 0.5 − y, 0.5 + z; (iv) −x, −0.5 +
y, 0.5 − z; (v) 1 + x, y, z.
decreased in view of the generation of two double carboxylate
links. This produces only a six-connected cluster/carboxylate
subtopology (primitive cubic net), while further cross-linking
of the nodes by bipyridazine ligands yields a rarely encoun-
tered33 uninodal ten-coordinated framework with a Schläfli
point symbol {312·428·55} (identified by a “bct” notation in the
Reticular Chemistry Structure Resource database).34
The χmT(T) plot of a polycrystalline sample of [Cu4(μ3-
OH)2{TDC}3(L)2(H2O)2]·7H2O (3) (scaled per Cu4 unit) exhibits
strongly decreasing χmT values on cooling, starting from
0.34 cm3 K mol−1 at 300 K and approaching a zero value
around 90 K (Fig. 7). The high temperature χmT values are
much smaller than the spin-only value of 1.5 cm3 K mol−1 for
Magnetic properties
Compounds 1, 3 and 4, representing the cluster types A, B and
C, respectively, were selected for an investigation of their mag-
netic properties. The χmT(T) plot of a polycrystalline sample of
[Cu2(μ-OH){TMA}(L)(H2O)] (1) (scaled per Cu2 unit) exhibits
decreasing χmT values on cooling, starting from 0.91 cm3
K
mol−1 at 300 K and approaching a value of 0.05 cm3 K mol−1 at
1.9 K (Fig. 6). This plot is typical of intracluster antiferro-
magnetic exchange interactions leading to a diamagnetic
ground state. This behaviour may be compared with simpler
binuclear systems sustained by the mixed hydroxo + syn–syn
carboxylate bridge between the Cu ions, which exhibit a strong
ferromagnetic coupling.35 The small low temperature χmT (1)).
Fig. 7 Thermal variation of χmT for 3 (solid line is a fit according to eqn
8536 | Dalton Trans., 2014, 43, 8530–8542
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chelating pyridazine is involved, a fact which would principally
ask for two different exchange parameters, say J2 and J3. This
would result in six energy levels in the function of three J para-
meters.25b However, in view of the rather smooth curve of the
χmT(T) plot one can understand that any trials to fit the data
to a three parameter model are not conclusive due to overpara-
metrization. Next, it clearly turned out best to fix the J1 par-
ameter to a reasonable value of −110 cm−1; this coupling
strength results from an analogous core structure25a and then
using eqn (2), the experimental data were fitted satisfactorily
in the temperature range 300–30 K with J2 = −228 cm−1 (g =
2.07). Both values of the coupling constants express the fairly
strong antiferromagnetic intracluster coupling which conse-
quently results in a diamagnetic ground state. One has to bear
in mind, however, that the J2 parameter now represents an
average coupling value on the wing sides.
The χmT(T) and χm(T) plots of a polycrystalline sample of
[Cu5(μ-OH)2{BDC}4(L)2(H2O)2]·5H2O (4) (scaled per Cu5 unit)
are shown in Fig. 8. The high-temperature χmT value of
1.75 cm3 K mol−1 is smaller than the spin-only value of
2.06 cm3 K mol−1 for five non-interacting spins with S = 1/2
(g = 2.2) and they decrease to a value approaching zero at 2 K.
Both are indicative of strong antiferromagnetic exchange inter-
actions within the pentameric unit.
A structural analysis reveals that the central Cu3 subunit
involves Cu1 bound to two equivalent inversion related Cu2
via two bridges, hydroxo and pyridazine. The pyridazine
bridges can be considered to be orthogonal connections,
because of the short–long bonds to Cu2 and Cu2′ within each
pair. Cu–O connections to the bridging OH− groups are short
and since the Cu–OH–Cu angle (114.3°) is large, one would
anticipate strong antiferromagnetic exchange between Cu1
and the two Cu2 atoms through these bridges (equatorial–
equatorial connections). The Cu2–Cu3 connection is really just
a 1,3-carboxylate with short contacts to both copper centers
(the aqua O2 donor is just bonded to Cu2 with a short contact,
whereas the secondary Cu3–O2 interactions are only very distal
and weak, Table 6). Therefore both Cu2 atoms are going to be
Scheme 3 {Cu4(μ3-OH)2} core fragment of 3 and the corresponding
magnetic coupling scheme.
four non-interacting spins with S = 1/2 (g = 2.0) which is due to
strong intracluster antiferromagnetic exchange interactions.
The low temperature χmT values indicate a diamagnetic
ground state of the tetranuclear complex.
Given the butterfly-type arrangement of the tetranuclear
cluster fragment (Scheme 3) and leaving aside the asymmetry
of the bonding pattern on the wings, we can use it as an
approximation which is justified below. The following iso-
tropic Hamiltonian describes the intracluster magnetic
exchange interactions [eqn (1)]:
H ¼ ꢀ2J1ðS2S2iÞ ꢀ 2J2ðS1S2 þ S1S2i þ S2S1i þ S2iS1iÞ ð1Þ
This model approximates the [Cu4] core with a rhombic
symmetry while differentiating two magnetic exchange path-
ways, namely Cu2–Cu2i (J1) vs. Cu1–Cu2, Cu1–Cu2i, Cu2–Cu1i,
Cu2i–Cu1i (J2). Consequently, this Hamiltonian gives rise to
six spin states comprising the total spin values (ST) of 2, 1, 0
with the corresponding energy levels in terms of the magnetic
coupling constants as given below:
1
2
1
2
E1ðST ¼ 2Þ ¼ ꢀ J1 ꢀ 2J2
E2ðST ¼ 1Þ ¼ ꢀ J1 þ 2J2
1
E3ðST ¼ 1Þ ¼ ꢀ J1
2
3
E4ðST ¼ 1Þ ¼ þ J1
2
1
2
E5ðST ¼ 0Þ ¼ ꢀ J1 þ 4J2
3
E6ðST ¼ 0Þ ¼ þ J1
2
Applying these energy values to the van Vleck equation
gives the following analytical expression [eqn (2)]:
χm ¼ 2Nβ2g 2=kTðA=BÞ;
A ¼ 5expðꢀE1=kTÞ þ expðꢀE2=kTÞ þ expðꢀE3=kTÞ
þ expðꢀE4=kTÞ
ð2Þ
B ¼ 5expðꢀE1=kTÞ þ 3expðꢀE2=kTÞ þ 3expðꢀE3=kTÞ
þ 3expðꢀE4=kTÞ þ expðꢀE5=kTÞ þ expðꢀE6=kTÞ
To reiterate at this stage, the linking pattern at the wing
Fig. 8 Thermal variation of χm and χmT for 4 (the solid lines are a fit to
sides of the {Cu4(μ3-OH)2} core differs since on two sides a the data).
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Table 6 Crystal data for [Cu2(μ-OH){TMA}(L)(H2O)] (1), [Cu4(μ3-OH)2{ATC}2(L)2(H2O)2]·H2O (2), [Cu4(μ3-OH)2{TDC}3(L)2(H2O)2]·7H2O (3),
[Cu5(μ-OH)2{BDC}4(L)2(H2O)2]·5H2O (4a and 4b) and [Cu5(μ-OH)2{HO-BDC}4(L)2(H2O)2]·6H2O (5)
1
2
3
4a
4b
5
Formula
T, K
C
213
27H26Cu2N4O8
C62H78Cu4N8O19
296
C54H66Cu4N8O23S3
173
C68H72Cu5N8O25
296
C68H72Cu5N8O25
105
C68H74Cu5N8O30
296
M
661.60
Monoclinic
C2/c, 8
24.8536(18)
10.8716(7)
18.6837(14)
90
101.581(8)
90
4945.5(6)
1.783
1493.48
1545.49
Monoclinic
P21/n, 2
13.3933(4)
9.9035(3)
23.7661(8)
90
98.036(2)
90
3121.39(17)
1.530
1719.04
Monoclinic
P21/n, 2
10.0517(7)
18.4855(9)
19.1143(13)
90
104.721(5)
90
3435.1(4)
1.613
1719.04
Monoclinic
P21/n, 2
10.0322(6)
18.4439(9)
19.0354(12)
90
104.897(5)
90
3403.8(3)
1.627
1801.05
Monoclinic
P21/c, 2
10.0552(5)
18.7840(8)
19.1757(9)
90
104.829(2)
90
3501.2(3)
1.591
Crystal system
Space group, Z
a/Å
b/Å
c/Å
α
β
Triclinic
ˉ
P1, 1
11.1208(9)
11.5078(10)
13.8841(13)
83.981(6)
67.507(6)
62.065(5)
1444.3(2)
1.541
γ
V/Å3
μ(Mo-Kα)/mm−1
Dc/ g cm−3
1.777
25.96
1.717
26.94
1.644
27.10
1.662
28.54
1.677
28.54
1.708
27.48
°
θmax
/
Meas/ Unique reflns
Rint
Parameters refined
16 964/4789
0.041
433
15 505/6248
0.061
419
29 009/6862
0.085
477
28 251/8582
0.042
502
29 556/8509
0.046
502
31 226/8020
0.088
502
R1 [I > 2σ(I)]
0.033
0.084
0.917
0.44, −0.78
0.055
0.098
0.916
0.58, −0.59
0.049
0.104
0.990
0.59, −0.51
0.036
0.095
0.965
0.64, −1.10
0.032
0.081
0.901
0.54, −0.55
0.047
0.104
1.010
0.47, −0.53
wR2 [all data]
Goof on F2
Max, min peak/e Å−3
antiferromagnetically coupled to Cu3, but with a much until a temperature of 260 °C. In the range 260–340 °C, with a
smaller J value. The corresponding magnetic coupling scheme DTG peak maximum at 300 °C, it decomposes (−29.7%) with
is given as
dehydration (m/z 18) and release of CO2 (m/z 44) due to decarb-
oxylation. This is accompanied by a loss of crystallinity at
260 °C, as evidenced by PXRD patterns. The stability of the ali-
phatic analog 2 is comparable. Dehydration starts at 160 °C,
and above 220 °C it was accompanied by decarboxylation
which results in one unresolved stage of 12.3% weight loss in
the range of 160–270 °C (maximum at 250 °C). The PXRD
patterns are also indicative of the dehydration process
(160–170 °C) since the interlayer spacing is sensitive to elimin-
ation of the guest molecules located between the coordination
layers. Disintegration of the structure was observed at 230 °C.
Complex 3 experiences partial dehydration above 60 °C, with
the release of 5 water molecules in the temperature range of
60–170 °C (5.60% observed; 5.82% calculated). This results in
a phase transition at 170 °C, and at 195 °C the compound gets
amorphous due to decomposition with the release of CO2. For
the closely related 4 and 5, disintegration of the frameworks
occurs at an identical temperature of 235 °C. However, due to a
more hydrophobic nature of the isophthalate framework in 4,
vs. the 5-hydroxyisophthalate analog 5, the initial dehydration
in the first case proceeds more readily. The TG curve indicates
two insufficiently separated stages at 110–200 °C and
200–250 °C, with a total weight loss of 7.3% corresponding
to the release of coordinated and outer sphere water mole-
cules (calculated 7.32%). Further thermal decomposition pro-
ceeds at 270–340 °C. In the case of 5, the dehydration begins at
160 °C. Progressive release of water molecules (m/z 18) coincides
with beginning of decarboxylation (m/z 44) at 265 °C. The
weight loss of 8.5% in the temperature range 160–260 °C
corresponds to the elimination of 8 water molecules (calculated
8.0%).
J2
J1
J1
J2
Cu3ꢀꢀCu2ꢀꢀCu1ꢀꢀCu2iꢀꢀCu3i
and the isotropic Hamiltonian is
H ¼ ꢀ2J1ðS1S2 þ S1S2iÞ ꢀ 2J2ðS2S3 þ S2iS3iÞ
The exchange model is therefore based on a strongly anti-
ferromagnetically coupled central linear trinuclear Cu3 group,
with the Cu3 centers weakly antiferromagnetically coupled to
the terminal coppers (Cu2) of the triad.
In the data fitting J1 and J2 were represented as a ratio
(J1/J2) and after varying the ratio, fitting the data, and observing
and minimizing the fitting coefficient, a satisfactory fit was
obtained using MAGMUN4.11.37 This program calculates the
total spin states and their energies based on the exchange
Hamiltonian, and determines the fitted parameters internally
through weighted non-linear least squares procedures. The
optimum ratio was found to be J1/J2 = 10, with the best fit para-
meters at J1 = −125(3) cm−1, J2 = −12.5(3) cm−1 and g = 2.18,
providing the eminently sensible model based on the
regression statistics and the structure.
Thermal stability
The thermal behavior of compounds 1–5 was examined by
complementary TG/DTA-MS and temperature-dependent
powder X-ray diffractometry (TD PXRD) techniques. With the
exception of complex 4, the stages of dehydration and further
weight losses due to the thermal destructions are not separ-
ated and proceed above 150 °C, with the crystallization of an
inorganic product (CuO) observed above 350 °C. Compound 1
is somewhat more stable. It does not show any weight loss
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IR spectra
1,3,5-tricarboxylic acid was synthesized in 62% yield by the
Koch–Haaf carboxylation of 1,3,5-adamantanetriol with 100%
HCOOH in a 15% oleum medium.42 The 1,2,4,5-tetrazine was
prepared and freshly purified by sublimation as described
previously.13,14c
The IR spectra of complexes 1–5 exhibit strong and broad
absorption bands in the region of 3230–3500 cm−1, which are
attributed to the ν(OH) vibrations of the aqua and hydroxo
ligands. Bands at 2850–2933 cm−1 correspond to ν(CH)
vibrations of adamantane and aromatic moieties. The absorp-
tions for the carbonyl group, ν(CO), appear as very strong
bands at 1590–1627 cm−1 (see the Experimental section). The
absence of bands at 1730–1690 cm−1, where ν(CO) of COOH is
expected to appear, confirms full deprotonation of the poly-
carboxylate ligands in 1–5.38 Strong absorption bands at
1358–1382 cm−1 are characteristic of all the compounds; they
could be assigned to ν(CN) of the pyridazine rings.39
Synthesis
of
1,3-bis(pyridazin-4-yl)adamantane
(L)
(Scheme 1). A solution of 1.24 g (15.1 mmol) 1,2,4,5-tetrazine
and 1.26 g (6.8 mmol) 1,3-diethynyladamantane43 in 40 ml of
dry 1,4-dioxane was stirred at 90 °C over a period of 25 h. The
reaction proceeded smoothly and the evolution of dinitrogen
gas ceased after 15–16 h. The precipitate was filtered off,
washed with 1,4-dioxane and diethyl ether and dried in air. It
was dissolved in boiling methanol and the solution was de-
colorized by 15 min reflux with charcoal, then it was filtered
and evaporated yielding 1.41 g (71%) of a colorless crystalline
product. 1H NMR (400 MHz, dmso-d6): δ 9.38–9.28 (m, 2H),
9.06 (d, J = 5.4 Hz, 2H), 7.58 (dd, J = 5.5, 2.6 Hz, 2H), 2.42–2.32
(m, 2H), 2.10 (s, 2H), 1.98 (t, J = 3.7 Hz, 8H), 1.82 (d, J = 3.5 Hz,
2H). Anal. Calcd for C18H20N4: C, 73.94; H, 6.90; N, 19.17.
Found: C, 74.06; H, 6.88; N, 19.04.
Conclusions
The present results are important for providing innovative
strategies for the construction of extended coordination lat-
tices incorporating polynuclear metal–organic clusters. A com-
bination of pyridazine, carboxylate and hydroxo ligands is
especially well suited for sustaining coordination patterns of
different nuclearities and connectivities: this kind of bridges Preparation of the coordination compounds
reveals a perfect compatibility and they readily complement
The complexes were prepared under hydrothermal conditions
each other and act in a synergistic manner. In cooperation
with μ-carboxylate and, especially μ-hydroxo groups, pyridazine
typically behaves as a short-distance diatomic bridge. There-
fore, the present heteroligand system unites and extends the
structural and functional potential of such common types of
organic and inorganic bridges for the generation of discrete
polynuclear arrangements of metal ions. At the same time, a
multiplication of the ligand functionality, as it occurs for di-
and tricarboxylate and bipyridazine ligands, allows the inte-
gration of the clusters into polymeric arrays, which could be
anticipated for a broad range of transition metal ions and
different kinds of organic linkers. Our study suggests also a
new approach and attractive preparative sequence towards
bridge-head heteroaryl C-functionalization of adamantane,
which could find wider applications for the development of
multivalent geometrically rigid molecular building blocks
incorporating “nanodiamond scaffolds”.40 Moreover, the study
of magnetic properties of coordination network compounds is
a very topical issue in the field of molecular magnetism.41 In
the present case, the magnetic susceptibility data for clusters
1, 3 and 4 reveal substantial antiferromagnetic coupling
strengths, however, with varying ratios of the coupling para-
meters. In particular, common to all three structure types A, B
and C is the quite complex nature of bonding patterns includ-
ing heteroligand multiple bridges connecting the spin centers,
which prevents a discussion of more detailed structure–prop-
erty correlations.
as follows. A mixture of the starting compounds and distilled
water were placed in a 20 mL Teflon-lined stainless steel auto-
clave, stirred for 10–30 min, and heated at 140 °C for 40–70 h
in an oven, with further cooling to room temperature. In each
case, the excess of bipyridazine ligand was essential for partial
hydrolysis of Cu(II) ions and generation of the desired hydroxo-
bridged species. Under these conditions and absence of di- or
tricarboxylate components, the reactions of Cu(OAc)2·H2O and
the bipyridazine ligand did not afford insoluble products.
Synthesis of [Cu2(μ-OH){TMA}(L)(H2O)] (1). A mixture of
6.8 mg (0.034 mmol) Cu(OAc)2·H2O, 3.1 mg (0.015 mmol) tri-
mesic acid and 10.0 mg (0.034 mmol) ligand in
a
1 : 0.44 : 1 molar ratio with 4 mL water was stirred for 30 min
in a Teflon vessel, and then it was heated at 140 °C for 70 h.
Slow cooling to r.t. over a period of 48 h (cooling rate 2.5 °C
h−1) afforded a pure product as green prisms, which were
washed with 3 mL of water and dried in air for 1 h (yield:
7.9 mg, 80%). Anal. Calcd for C27H26Cu2N4O8: C, 49.01; H,
3.96; N, 8.47. Found: C, 48.89; H, 4.01; N, 8.35. IR (KBr discs,
selected bands, cm−1): 568w, 717s, 761m, 977w, 1022w, 1091w,
1359vs, 1407m, 1433s, 1558vs, 1607vs, 2852w, 2900m,
3233mbr, 3409m.
Synthesis of [Cu4(μ3-OH)2{ATC}2(L)2(H2O)2]·H2O (2). The
compound was prepared in a similar manner, starting with
6.8 mg (0.034 mmol) Cu(OAc)2·H2O, 3.5 mg (0.013 mmol) ada-
mantane-1,3,5-tricarboxylic acid, 10.0 mg (0.034 mmol) ligand
(1 : 0.38 : 1 molar ratio) and 4 mL of water. Small green pris-
matic crystals of the product were obtained in 80% yield. Anal.
Calcd for C62H78Cu4N8O19: C, 49.86; H, 5.26; N, 7.50. Found:
C, 50.03; H, 5.19; N, 7.59. IR (KBr discs, selected bands, cm−1):
Experimental
All starting materials were chemicals of reagent grade and 568w, 710m, 832w, 1084w, 1209w, 1274m, 1328s, 1358vs,
used as received without further purification. Adamantane- 1442w, 1590vs, 2850m, 2930s, 3044m, 3269mbr, 3471mbr.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 8530–8542 | 8539

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Paper
Dalton Transactions
Synthesis of [Cu4(μ3-OH)2{TDC}3(L)2(H2O)2]·7H2O (3). An X-Ray crystallography
equimolar mixture of 5.0 mg (0.025 mmol) Cu(OAc)2·H2O,
4.3 mg (0.025 mmol) 2,5-thiophenedicarboxylic acid, 7.4 mg
(0.025 mmol) ligand were placed in a Teflon vessel, and 5 mL
of water was added. The mixture was stirred for 30 min and
then it was heated at 140 °C for 24 h. Small blue prisms of the
pure product were obtained in 60% yield after slow cooling to
r.t. for a period of 72 h. Anal. Calcd for C54H66Cu4N8O23S3: C,
41.96; H, 4.30; N, 7.25. Found: C, 42.11; H, 4.22; N, 7.37. IR
(KBr discs, selected bands, cm−1): 556w, 689w, 774m, 808w,
973w, 1022w, 1072w, 1111w, 1314s, 1358vs, 1452w, 1527s,
1561s, 1597vs, 2852m, 2913m, 3407sbr.
The diffraction data were collected with graphite-monochro-
mated Mo-Kα radiation (λ = 0.71073 Å) (Table 6). Measure-
ments for 1 at 213 K and for 4 (4a: 296 K, 4b: 105 K) were
made using a Stoe Image Plate Diffraction System, φ oscil-
lation scans (numerical absorption correction using X-RED
and X-SHAPE).44 Measurements for 2, 3 and 5 were performed
at 173 K on a Bruker APEXII CCD area-detector diffractometer
(ω scans). The data were corrected for Lorentz-polarization
effects and for the effects of absorption (multi-scans method).
The structures were solved by direct methods and refined by
full-matrix least-squares on F2 using the SHELX-97 package.45
Synthesis of [Cu5(μ-OH)2{BDC}4(L)2(H2O)2]·5H2O (4).
A
The CH-hydrogen atoms were added geometrically, with Uiso
=
mixture of 6.8 mg (0.034 mmol) Cu(OAc)2·H2O, 5.7 mg
(0.034 mmol) isophthalic acid, 10.0 mg (0.034 mmol) ligand,
all in an equimolar ratio, and 4 mL of water was stirred for
10 min and then heated at 140 °C for 24 h in a Teflon vessel.
After cooling to r.t. for a period of 72 h, large blue-green crystals
of the pure product were collected by filtration (yield: 9.3 mg, or
80%, based on Cu). Anal. Calcd for C68H72Cu5N8O25: C, 47.51;
H, 4.22; N, 6.52. Found: C, 47.59; H, 4.19; N, 6.63. IR (KBr discs,
selected bands, cm−1): 548w, 716m, 748m, 806w, 1084w, 1156w,
1268w, 1368s, 1390vs, 1450m, 1476w, 1560s, 1622vs, 2856m,
2922m, 3400sbr, 3456sbr.
Synthesis of [Cu5(μ-OH)2{HO-BDC}4(L)2(H2O)2]·6H2O (5).
The compound was prepared similarly as for 4 from a mixture
of 6.8 mg (0.034 mmol) Cu(OAc)2·H2O, 6.2 mg (0.034 mmol)
5-hydroxyisophthalic acid and 10.0 mg (0.034 mmol) ligand,
giving large blue-green prisms (yield 75%). Anal. Calcd for
C68H74Cu5N8O30: C, 45.34; H, 4.14; N, 6.22. Found: C, 45.47;
H, 4.13; N, 6.39. IR (KBr discs, selected bands, cm−1): 558w,
646w, 678w, 721s, 777s, 985m, 1001m, 1021m, 1102w, 1128w,
1195m, 1218w, 1265m, 1280m, 1296m, 1382vs, 1420s, 1449m,
1.2Ueq (C) and OH-hydrogen atoms were located and included
with fixed d (O–H) = 0.85 Å and Uiso = 1.5Ueq (O). Part of the
solvate water molecules in 2–4 is disordered. They were refined
anisotropically and the hydrogen atoms were not added. In 1,
the binuclear cluster is equally disordered over two positions
(Cu ion, μ-OH and aqua ligand; one of the pyridazine cycles is
also disordered adopting two orientations). Attempted refine-
ments in space groups of lower symmetry did not afford an
ordered model. This fragment was freely refined anisotropi-
cally and the hydrogen atoms were added as stated above with
partial contributions of 0.5. In 3, one of the TDC2− ligands is
equally disordered over two positions across a center of inver-
sion. The disorder was resolved without restraints in geometry,
but with restrained parameters for thermal motion of the
carbon atoms. The topological analysis was performed using
TOPOS 4.046 and Graphical visualization of the structures was
made using the program Diamond 2.1e.47
1472m, 1545s, 1593s, 1627s, 2856m, 2899m, 2933s, 3370sbr, Acknowledgements
3500s, 3586m.
Financial support by Deutsche Forschungsgemeinschaft, grant
Measurements
KR 1675/4-3 (HK and KVD) and by the Swiss National Science
Foundation (grant 200021-147143) is gratefully acknowledged.
Thermogravimetric/differential thermal analysis mass spectro-
metry (TG/DTA-MS) was performed on a Netzsch F1 Jupiter
device connected to an Aeolos mass spectrometer. The sample
was heated at a rate of 10° min−1. The temperature-dependent
X-ray measurements were carried out on a Stoe STADIP with a
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