Copper(I) and silver(I) coordination frameworks involving extended bipyridazine bridges

Article abstract of DOI:10.1039/b801231h

1,4-(Pyridazin-4-yl)benzene (bpph), a new N-donor tetradentate ligand, was prepared by inverse electron demand cycloaddition reacting 1,4-diethynylbenzene and 1,2,4,5-tetrazine. In combination with Cu(i) and Ag(i) ions, it affords coordination framework topologies that were dominated by assembly of dinuclear metal-pyridazine "secondary building blocks" [M₂(μ-pdz) ₂] supporting further polymeric connectivity. In structures [Cu ₂(bpph)(CH₃CN)₂{S₂O₆}] (1) and [Ag₆(bpph)₃(H₂O)₆{C ₆H₄(COO)₂}₂]C₆H ₄(COO)₂·4H₂O (8) interconnection of the dinuclear nodes occurs with anionic dithionate and isophthalate bridges, while [Ag₂(bpph){C₆H₅CO₂} ₂]·2H₂O (7) adopts a linear chain structure incorporating disilver(i) pyridazine units and terminal benzoate anions. [Cu₄(bpph)₅](BF₄)₄·4CHCl ₃ (2) has a 3D supramolecular structure involving polycatenation of the 2D "bilayer" metal-organic topologies built up of five-connected dinuclear nodes. Frameworks of [Ag(bpph){NO₃}]·CHCl ₃ (3) and [Ag(bpph){C₂F₅COO}] (5) exist as 2D square-grids nets supported with sets of tetra- and bidentate bipyridazine bridges, while closely related [Ag₄(bpph)₃{CF ₃COO}₄]·CH₃CN (4) is a 1D "ladder" polymer. The three-fold interpenetrated 3D diamondoid framework of [Ag₄(bpph)₃{CH₃SO ₃}₄]·2CHCl₃ (6) was based upon more complicated tetranuclear nodes [Ag₄(μ-pdz)₄(pdz) ₂]. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008.

Full text of DOI:10.1039/b801231h

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Copper(I) and silver(I) coordination frameworks involving extended
bipyridazine bridgesw
Anna S. Degtyarenko,a Pavlo V. Solntsev,a Harald Krautscheid,b
Eduard B. Rusanov,c Alexander N. Chernegac and Konstantin V. Domasevitch*a
Received (in Durham, UK) 23rd January 2008, Accepted 18th April 2008
First published as an Advance Article on the web 9th June 2008
DOI: 10.1039/b801231h
1,4-(Pyridazin-4-yl)benzene (bpph), a new N-donor tetradentate ligand, was prepared by inverse
electron demand cycloaddition reacting 1,4-diethynylbenzene and 1,2,4,5-tetrazine. In
combination with Cu(I) and Ag(I) ions, it affords coordination framework topologies that were
dominated by assembly of dinuclear metal–pyridazine ‘‘secondary building blocks’’ [M2(m-pdz)2]
supporting further polymeric connectivity. In structures [Cu2(bpph)(CH3CN)2{S2O6}] (1) and
[Ag6(bpph)3(H2O)6{C6H4(COO)2}2]C6H4(COO)2ꢀ4H2O (8) interconnection of the dinuclear nodes
occurs with anionic dithionate and isophthalate bridges, while [Ag2(bpph){C6H5CO2}2]ꢀ2H2O (7)
adopts a linear chain structure incorporating disilver(I) pyridazine units and terminal benzoate
anions. [Cu4(bpph)5](BF4)4ꢀ4CHCl3 (2) has a 3D supramolecular structure involving
polycatenation of the 2D ‘‘bilayer’’ metal–organic topologies built up of five-connected dinuclear
nodes. Frameworks of [Ag(bpph){NO3}]ꢀCHCl3 (3) and [Ag(bpph){C2F5COO}] (5) exist as 2D
square-grids nets supported with sets of tetra- and bidentate bipyridazine bridges, while closely
related [Ag4(bpph)3{CF3COO}4]ꢀCH3CN (4) is a 1D ‘‘ladder’’ polymer. The three-fold
interpenetrated 3D diamondoid framework of [Ag4(bpph)3{CH3SO3}4]ꢀ2CHCl3 (6) was based
upon more complicated tetranuclear nodes [Ag4(m-pdz)4(pdz)2].
short-distance 1,2-diazine bridges.10 The latter stabilize proxi-
mity of the metal centers and contribute to the formation of
Introduction
The concept of secondary building blocks offers new perspec-
complicated polynuclear patterns, as evidenced by character-
tive approaches towards designing of framework coordination
istic bi- and polynuclear clusters involving either double or
polymers.1 Exploitation of versatile polynuclear metal–
triple pyridazine bridges (Scheme 1).11 Some of the typical
organic ensembles as subunits of the framework structures allows
generation of unusual coordination topologies,2 synthesis of
M(m-pdz)M ensembles may retain a set of coordinatively
unsaturated positions at the multiple metal centers for inter-
porous materials with gas adsorption and catalytic proper-
action with an additional ligands or reaction substrates and
ties3,4 luminiscent and magnetic coordination polymers,5 and
they may be applicable for functionalization of the solid-state
functionalization of the framework towards interaction with
structure. Features of the metal–pyridazine coordination are
different substrates. The applicable secondary building blocks
especially relevant also from the design perspective, since all of
commonly involve short-distance bridges (hydroxo, oxo, tria-
zole,6 tetrazolate,7 carboxylate,4 and their combinations)
between set of metal ions that in total affords very favorable
coordination patterns dominating self-assembly processes.
Therefore the heteroaryl ligands with multiple N-donor sites
possess a special potential for the crystal design as may be
compared with a family of simpler connectors derived from
monodentate pyridine-N donors.8,9
In this respect, pyridazine is very efficient double nitrogen
donor ligand towards transition metal ions generating a
range of coordination compounds, in which it readily sustains
a Inorganic Chemistry Department, Kiev University, Volodimirska
Str.64, 01033 Kiev, Ukraine. E-mail: dk@univ.kiev.ua
b
´
Institut fur Anorganische Chemie, Universitat Leipzig, Linnestraße 3,
¨
D-04103 Leipzig, Deutschland
¨
c Institute of Organic Chemistry, Murmanskaya Str.4, 253660 Kiev,
Ukraine
w Electronic supplementary information (ESI) available: Details for
preparation procedures and crystal structure refinement. CCDC re-
ference numbers 685682–685689. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b801231h
Scheme 1 Representative polynuclear patterns adopted by pyridazine
ligands: (a) dimeric unit; (b) triply-bridged ‘‘triptycene-like’’ unit; (c)
spirane motif; (d) tetranuclear ‘‘figure eight’’ stabilized by additional
p–p stacking.
ꢁc
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these ensembles may be involved as the ‘‘secondary building
blocks’’ for generation of polymeric arrays.8 In this way, self-
assembly reactions between metal ions and bridging ligands
possessing multiple pyridazine donor sites provide a clear
scenario for construction of the solids integrating polynuclear
clusters as an origin of the framework connectivity.
Table 1 Selected bond distances (A) and angles (1) for complexes 1
and 2
[Cu2(bpph)(CH3CN)2{S2O6}] (1)
Cu1–N1
Cu1–N2a
2.047(2)
1.979(2)
Cu1–N3
Cu1–O1
1.958(2)
2.189(2)
In this context we have examined a new multidentate
N-donor 1,4-(pyridazin-4-yl)benzene, which combines abilities
for bridging of closely separated and very distal metal ions and
in this respect it unites the rich potential of small pyridazine
bridges and of longer nitrogen-donor connectors.
N1–Cu1–N3
102.48(8)
123.02(6)
123.47(8)
N1–Cu1–O1
N3–Cu1–O1
N2a–Cu1–O1
100.53(7)
102.02(7)
100.67(6)
N1–Cu1–N2a
N3–Cu1–N2a
a: ꢂx, 1 ꢂ y, 1 ꢂ z.
[Cu4(bpph)5](BF4)4ꢀ4CHCl3 (2)
Cu1–N5
Cu1–N9
Cu1–N3b
Cu1–N8a
2.071(3)
2.059(3)
2.005(3)
2.044(3)
Cu2–N1
Cu2–N6
Cu2–N7a
Cu2–N10
1.996(3)
2.036(3)
2.054(3)
2.067(3)
Results and discussion
Synthesis of the bis-pyridazine ligand was carried out follow-
ing a methodology for the inverse electron demand Diels–
Alder cycloaddition.12 Azadiene reactivity of substituted tetra-
zines allows preparation of different types of pyridazine
bridging ligands,13 while very uncommon use of the parent
1,2,4,5-tetrazine may provide a general convenient route to a
series of 3,6-unsubstituted species (Scheme 2). The latter are of
special interest as very useful polydentate ligands for copper(I)
and silver(I) ions, which possess an appreciable affinity towards
multiple N-donor heterocycles.10,14
N5–Cu1–N9
N5–Cu1–N3b
N5–Cu1–N8a
N9–Cu1–N8a
N3b–Cu1–N8a
N9–Cu1–N3b
98.94(13)
112.24(12)
108.84(12)
102.04(13)
117.37(12)
115.45(13)
N1–Cu2–N6
N1–Cu2–N10
N1–Cu2–N7a
N6–Cu2–N10
N6–Cu2–N7a
N10–Cu2–N7a
120.11(12)
113.55(13)
111.49(13)
96.61(13)
111.14(12)
101.56(13)
a: x, 1 + y, z; b: ꢂ1 + x, y, ꢂ1 + z.
Rational evolution of the dinuclear copper–pyridazine pat-
tern was observed in the structure of tetrafluoroborate
[Cu4(bpph)5](BF4)4ꢀ4CHCl3 (2). Weak coordinating properties
Thus, the structure of the 1,4-(pyridazin-4-yl)benzene
(bpph) coordination polymers was typically supported by
formation of dinuclear metal–pyridazine ensembles, which
provide further connectivity as a ‘‘secondary building block’’.
In the structure of dithionate complex [Cu2(bpph)(CH3CN)2-
{S2O6}] (1) pairs of the copper(I) ions were connected by
tetradentate organic bridges into chains. The ligand lies across
a center of inversion and the dithionate anion lies across a
twofold axis. Typical tetrahedral coordination of the metal
ions was completed with the dithionate oxygen atoms and
terminal acetonitrile ligands (Table 1). The dithionate groups
are coordinated and moreover, their bidentate-bridging func-
tion results in interconnection of the metal–organic chains and
generation of a flat 2D framework (Fig. 1). There are only two
precedents for coordination polymers based upon simple
copper(I)–pyridazine dimers, in a combination with octa-
molybdate or cyanide bridges.15 The manifestation of nucleophi-
ꢂ
of BF4 are reflected by elimination of the anions from the
metal environment and this makes possible to involve an
additional pyridazine bridge yielding a triptycene-like pattern,
lic properties of the S2O6 groups towards CuI cations is
2ꢂ
slightly unexpected and the complex 1 represents a first
example of such coordination. Very recently, dithionate
bridges were employed for the construction of Cu2+, Co2+
and Zn2+ coordination polymers.16
Fig. 1 Structure of [Cu2(bpph)(CH3CN)2{S2O6}] (1): (a) cross-
linking of dicopper/dipyridazine units by the dithionate anions; (b)
resulting 2D framework incorporating Cu/bipyridazine chains.
Scheme 2 Synthesis of the 1,4-(pyridazin-4-yl)benzene (bpph) invol-
ving cycloaddition of bifunctional ethyne and 1,2,4,5-tetrazine.
ꢁc
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which incorporates a pair of copper ions triply bridged by
pyridazine (Scheme 1(b)). This characteristic copper(I)–
pyridazine motif allows accommodation of two additional
ligands (such as acetonitrile or benzonitrile)17,18 completing
the tetrahedral environment of the metal ions. In the present
case these two additional coordination sites were occupied by
monodentate pyridazine-N donors (Fig. 2(a)) and therefore
the dicopper secondary building block could serve as an origin
of connectivity for generation of a five-connected framework.
The overall topology, however, is not an evident ‘‘pillared
honeycomb net’’ and it was dominated by a conformational
flexibility of the long organic connector. Thus, a primary
connectivity based upon entirely the m4-organic bridges is a
1D ‘‘ladder’’ motif, which was further interconnected by
N,N0-bidentate bipyridazine molecules yielding a five-connected
bilayer (Fig. 3). This topology itself has little precedent: it is
observed in [Ag(pz)2][Ag2(pz)5](PF6)3 (pz = pyrazine) com-
plex19 and several systems with 4,40-bipy and 4,40-bipy
di-N-oxide.20 Within the bilayer, the separation between two
interconnected layers is ca. 14.1 A and the bilayer has a
significant size of the internal channels (9 ꢃ 12 A, calculated
using PLATON21). Therefore, free space in such structure is
partially filled by parallel polycatenation22 of the bilayers
(Fig. 4), which in total occupy 57.5% of the crystal volume.21
The remaining space is filled with counter anions and guest
chloroform molecules.
Fig. 3 (a) 1D ‘‘ladder’’ motif of structure 2 assembled by linking of
the dicopper units by m4-bipyridazine bridges (one of two unique
tetradentate bipyridazine molecules lies across an inversion centre),
while additional bidentate ligands interconnect the ladders orthogonal
to the drawing plane; (b) resulting coordination bilayer involving five-
connected nodes.
Formation of the dimeric metal–pyridazine cycles was also a
well-predictable feature for silver(I) compounds and such the
coordination moieties may be best involved as ‘‘secondary
ꢂ
building blocks’’. Complexes with low nucleophilic NO3
,
CF3COOꢂ and C2F5COOꢂ anions were closely related to
the above examples and they illustrate utility of the coordina-
tion pattern for the generation of frameworks (Table 2). Thus,
in the nitrate compound [Ag(bpph){NO3}]ꢀCHCl3 (3) the
disilver–pyridazine chains remain as a clearly distinguishable
motif of the structure (Fig. 5). The nitrate groups are only
weakly coordinated (Ag–O 2.66, 2.69 A) and this makes
possible coordination of the extra pyridazine-N donors (unlike
simpler dimeric molecular units in the complex of parent
pyridazine [Ag(pdz){NO3}]2).23 This additional set of the
Fig. 2 Illustrative types of dinuclear units constituting the framework
nodes: (a) triple pyridazine bridge between the copper(I) ions in
structure 2; (b) combination of double pyridazine and carboxylate
bridges between silver ions in structure 4.
Fig. 4 Parallel polycatenation of the 2D bilayers in structure 2,
leaving only small channels (3 ꢃ 5 A) for housing of guest chloroform
molecules and counter anions.
ꢁc
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Table 2 Selected bond distances (A) and angles (1) for complexes 3–6
[Ag(bpph){NO3}]ꢀCHCl3 (3)
Ag1–N1
Ag1–N2a
Ag1–N3
2.350(3)
2.259(2)
2.352(3)
Ag1–O1
Ag1–O3
2.661(2)
2.691(3)
N1–Ag1–N3
102.76(9)
114.66(9)
128.16(8)
80.61(8)
N2a–Ag1–O1
N2a–Ag1–O3
N3–Ag1–O1
N3–Ag1–O3
O1–Ag1–O3
101.79(8)
127.22(9)
76.65(8)
88.66(8)
47.67(7)
N1–Ag1–N2a
N1–Ag1–O1
N1–Ag1–O3
N2a–Ag1–N3
a: ꢂx, 1 ꢂy, 2 ꢂ z.
130.49(9)
[Ag4(bpph)3{CF3COO}4]ꢀCH3CN (4)
Ag1–N1
Ag1–N4a
Ag1–O1
Ag1–O3
2.288(2)
2.317(2)
2.481(3)
2.401(3)
Ag2–N2
Ag2–N5
Ag2–N3a
Ag2–O2
2.347(2)
2.287(2)
2.304(2)
2.374(3)
N1–Ag1–N4a
N1–Ag1–O3
N1–Ag1–O1
N4a–Ag1–O1
N4a–Ag1–O3
O3–Ag1–O1
122.97(8)
122.88(10)
102.42(9)
93.55(9)
108.36(11)
97.33(12)
N5–Ag2–N3a
N5–Ag2–N2
N5–Ag2–O2
N3a–Ag2–N2
N3a–Ag2–O2
N2–Ag2–O2
127.43(8)
101.36(8)
103.71(11)
122.90(8)
93.71(11)
102.41(9)
a: 1 ꢂ x, 1 ꢂ y, 1 ꢂ z.
[Ag(bpph){C2F5COO}] (5)
Ag1–N1
Ag1–N2a
2.343(2)
2.304(3)
Ag1–N3
Ag1–O1
2.341(3)
2.388(2)
N1–Ag1–N3
N1–Ag1–N2a
N1–Ag1–O1
126.20(9)
113.36(9)
101.95(9)
N2a–Ag1–N3
N2a–Ag1–O1
N3–Ag1–O1
108.01(9)
113.85(9)
90.87(9)
a: ꢂx, ꢂy, 1 ꢂ z.
[Ag4(bpph)3{CH3SO3}4]ꢀ2CHCl3 (6)
Fig. 5 Closely related structure of 2D coordination frameworks 3 (a)
and 5 (b): cross-linking of the disilver/pyridazine chains by a set of
bidentate ligand molecules. Note differences in the coordination mode
of the m2-ligand, which allows tuning of the shape and size of the
resulting rectangular meshes of the framework. In these structures,
either bi- or tetradentate ligand molecules are situated across inversion
centres.
Ag1–N1
Ag1–N7a
Ag2–N2
Ag2–N5
Ag2–N9
Ag3–N6
2.202(7) Ag3–N4b
2.254(8)
2.250(8)
2.310(7)
2.341(10)
2.40(1)–2.58(1)
2.213(7) Ag4–N3b
2.306(7) Ag4–N8a
2.242(7) Ag4–N11c
2.338(9) Ag–O
2.255(8)
N1–Ag1–N7a
N2–Ag2–N9
N5–Ag2–N2
N5–Ag2–N9
166.8(3)
N6–A–g3–N4b
147.0(3)
of the ligand (Ag–Ag 16.03 A). That the coordination topol-
ogy is very sensitive to the steric volume of functionally almost
uniform counter anions was best illustrated by structure of
trifluoroacetate [Ag4(bpph)3{CF3COO}4]ꢀCH3CN (4). This
structure was also based upon ‘‘disilver chains’’ involving
organic ligands as m4-bridges. However, one of the carboxylate
anions was bidentate-bridging within the disilver unit (in this
respect the structure of the Ag2(pyridazine)2(m-CF3COO) frame-
work parallels the Cu2(pyridazine)3 unit observed in
structure 2), while a second trifluoroacetate group was mono-
dentate and terminal (Fig. 2(b)). Such bridging coordination of
the trifluoroacetate contributes to the proximity of two sliver ions
(Agꢀ ꢀ ꢀAg 3.279 A vs. 3.785 and 3.842 A for 5 and 3, respectively).
This may be compared with a very short argentophilic interac-
tion in dimeric silver(I) trifluoroacetate itself (2.973 A).25 Unlike
the nitrate (3) and pentafluoropropionate (5) structures, the
disilver unit in 4 retains only one coordinatively unsaturated
position for accommodation of an additional monodentate
pyridazine donor and thus it provides only a three-connected
node for the network. The latter is one-dimensional and exists in
the form of a ‘‘ladder’’ (Fig. 6).
98.1(3)
129.4(3)
124.4(3)
N3b–Ag4–N8a
N3b–Ag4–N11c
N8a–Ag4–N11c
129.3(3)
127.4(4)
99.1(4)
a: ꢂx, ꢂy, 1 ꢂ z; b: 1 ꢂ x, ꢂy, ꢂz; c: ꢂ1 + x, 0.5 ꢂ y, ꢂ0.5 + z.
bidentate organic ligands was employed for the cross-linking
of the chains and this yields a 2D ‘‘square-grid’’ polymeric
structure. The bidentate bpph group adopts slightly unex-
pected 2,20-like coordination, which allows to bridge Ag atoms
at a shorter distance of 13.71 A (cf. ca. 16 A for 1,10-bidentate
coordination) and to minimize the size of the square meshes.
The net nodes for such the framework are composed by
[Ag2(m-pdz)2(pdz)2] fragments, which are stabilized by a pair
of weak CHꢀ ꢀ ꢀN hydrogen bonds and itself are very charac-
teristic for silver–pyridazine or phthalazine coordination.24
A very comparable principle of the network architecture was
observed also for the [Ag(bpph){C2F5COO}] (5) complex
(Fig. 5(b)). Needs for incorporation of bulk pentafluoropropionate
groups effect augmentation of the net meshes, which was
achieved with 1,10-bridging mode of the bidentate molecules
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Complex [Ag4(bpph)3{CH3SO3}4]ꢀ2CHCl3 (6) reveals a
more complicated metal–ligand pattern composed with four
silver ions, four m-pyridazine moieties and two additional
monodentate pyridazine-N donors, in the form of ‘‘figure
eight’’ (Scheme 1(d)). The structure of such a tetranuclear
‘‘secondary building block’’ is very favorable since it allows
slipped p–p stacking interactions26 within the pairs of parallel
pyridazine cycles (Fig. 7). These interactions occur at distances
(centroid–centroid separations 3.58 and 3.64 A), which are
consistent with typical Agꢀ ꢀ ꢀAg contacts and in view of
combination of coordination and stacking interactions the
components afford a complementary system. A similar pattern
involving six m-pyridazine groups was observed also for a
simpler 4,40-bipyridazine ligand8 and in a mixed-ligand
pyridazine/3,5-bis(trifluoromethyl)pyrazolate complex.11a For the
resulting tetrasilver square, each of the edges was centered by
coordinating methanesulfonate groups, which bridge the ad-
jacent metal ions with very long Ag–O bonds. Thus pairs of
the m4-ligand molecules connect Ag4 ensembles into the di-
meric chains, while a set of bidentate organic bridges links the
chains into the very distorted diamondoid framework. This
adopts three-fold class Ia interpenetration27 where the iden-
tical nets are related by a single translation vector.
Another possibility for interconnection of the disilver sec-
ondary building blocks arises in a doubling of the anion
functionality, as it may be found from comparison of carboxy-
late structures 7 and 8. The simpler structural prototype was
provided by benzoate complex [Ag2(bpph){C6H5CO2}2]ꢀ2H2O
(7), which adopts a 1D chain-like array incorporating dis-
ilver(I) pyridazine units (Fig. 8). Each of the heterocyclic
termini is bidentate-bridging and the entire ligand is a tetra-
dentate bridge. The nucleophilic carboxylate anions are situ-
ated coplanar towards the disilver units and are coordinated in
a bidentate pseudochelate fashion (Ag–O 2.38, 2.67 A)
(Table 3), similarly to silver(I) acetate complex with phthalazine.28
This terminates any further coordination connectivity, while
the interchain interactions occur by means of hydrogen bond-
ing of the carboxylate groups with the solvate water molecules
(Oꢀ ꢀ ꢀO 2.67, 2.81 A).
Fig. 7 (a) Tetranuclear silver–pyridazine cluster providing the net-
work nodes in structure 6. Note the close parallel alignment of the
pairs of pyridazine cycles supporting weak slipped p–p stacking; (b)
Fragment of the polymer showing mode of cross-linking of the silver/
bipyridazine double chains by additional bidentate ligand molecules.
As a further step for construction of the framework, the
interconnection of the disilver–pyridazine chains may be
achieved by simple doubling the carboxylate function of the
counter-anion and this suggests utility of the above silver–
pyridazine–carboxylate array as a ‘‘supramolecular synthon’’.
In this way, the two-dimensional structure of the isophthalate
complex
[Ag6(bpph)3(H2O)6{C6H4(CO2)2}2]C6H4(CO2)2ꢀ
4H2O (8) was clearly derived from the 1D chains of parent
benzoate prototype, although only one of three unique silver
ions completely retains the above coordination environment
involving a pseudochelating carboxylate group (Ag1–O 2.43,
2.62 A) (Fig. 9). The second carboxylate group of the dianion
was coordinated monodentately, similarly to the silver phtha-
late complex with phthalazine,29 and the tetrahedral environ-
ment of the silver ion Ag2 was completed with a water
molecule, while the third silver ion coordinates two terminal
aqua ligands. The latter eliminates part of the carboxylate
bridges and this results in a formation of 3,4-connected flat
Fig.
6
One-dimensional
‘‘ladder’’
coordination
polymer
[Ag4(bpph)3{CF3COO}4]ꢀCH3CN (4). The bidentate bipyridazine li-
gand is situated across an inversion centre. Space within the rectan-
gular windows of the motif is populated by trifluoroacetate groups of
the adjacent ‘‘ladder’’.
cationic net (Schlafli symbol (4.62)2(42;62)) instead of the
¨
evident 4-connected neutral framework. Non-coordinated
ꢁc
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Table 3 Selected bond distances (A) and angles (1) for complexes 7
and 8
[Ag2(bpph){C6H5CO2}2]ꢀ2H2O (7)
Ag1–N1
Ag1–N2a
2.253(2)
2.335(2)
Ag1–O1
Ag1–O2
2.673(2)
2.379(2)
N1–Ag1–N2a
N1–Ag1–O1
N1–Ag1–O2
122.96(8)
92.92(8)
144.38(8)
N2a–Ag1–O1
N2a–Ag1–O2
O2–Ag1–O1
143.53(8)
92.52(8)
51.47(7)
a: ꢂx, ꢂy, 1 ꢂ z.
[Ag6(bpph)3(H2O)6{C6H4(CO2)2}2]C6H4(CO2)2ꢀ4H2O (8)
Ag1–N2
Ag1–N4
Ag1–O1
Ag1–O2
Ag2–N5
Ag2–N6a
2.342(3)
2.294(4)
2.431(4)
2.622(4)
2.333(4)
2.256(3)
Ag2–O4
Ag2–O7
Ag3–N1
Ag3–N3
Ag3–O5
Ag3–O6
2.321(3)
2.621(5)
2.298(4)
2.243(3)
2.471(4)
2.427(4)
Fig. 8 One-dimensional disilver/bipyridazine chain in the structure of
benzoate complex 7. The pyridazine ligands and disilver/pyridazine
dimers are situated across inversion centres.
N2–Ag1–N4
N2–Ag1–O1
N4–Ag1–O1
N4–Ag1–O2
O1–Ag1–O2
N5–Ag2–N6a
N5–Ag2–O4
N5–Ag2–O7
N6a–Ag2–O7
125.69(14)
85.07(13)
139.53(14)
96.47(12)
52.20(12)
123.54(14)
95.17(14)
115.01(19)
83.39(15)
N6a–Ag2–O4
O4–Ag2–O7
N1–Ag3–N3
N1–Ag3–O5
N1–Ag3–O6
N3–Ag3–O6
N3–Ag3–O5
O6–Ag3–O5
137.37(15)
96.65(18)
128.87(14)
133.57(14)
88.73(14)
125.76(14)
91.29(13)
82.98(14)
isophthalate dianions populate voids of the structure and are
involved in extensive hydrogen bonding.
Experimental
a: ꢂx, ꢂ1 ꢂ y, ꢂ1 ꢂ z.
All chemicals were of analytical grade and used as received
without further purification. Unsubstituted 1,2,4,5-tetrazine
was prepared following a detailed procedure described in a
supplementary publication.9
introduced as an intermediate layer. Slow interdiffusion of the
solutions over 15 d led to crystallization of orange–red plates
of the product (45 mg, 75%). Anal. for 1, C18H16Cu2N6O6S2.
Calc. (%): C, 35.82; H, 2.67; N, 13.93. Found (%): C, 35.70;
H, 2.49; N, 14.09.
Preparation of 1,4-(pyridazin-4-yl)benzene
A solution of 2.30 g (0.028 mol) 1,2,4,5-tetrazine and 1.76 g
(0.014 mol) 1,4-diethynylbenzene in 40 ml of dry dioxane was
stirred at 80 1C until evolution of nitrogen gas ceased (20–25 h).
The precipitate was filtered off, washed with dioxane and
diethyl ether and dried in air. Yield of practically pure colorless
crystalline product was 2.95 g (90%). The compound is spar-
ingly soluble in methanol and chloroform. 1H NMR (dmso-d6,
d/ppm, J/Hz): 8.08 (s, 4H, C6H4), 8.02 (d, 2H, 5-H-pdz, J =
5.21), 9.26 (d, 2H, 6-H-pdz, J = 5.21), 9.64 (s, 2H, 3-H-pdz).
Coordination compounds were synthesized reacting the
components in acetonitrile–chloroform solutions, using the
layering technique. Starting copper(I) compounds, dithionate
and tetrafluoroborate, were generated in a dilute acetonitrile
solution by reduction of corresponding copper(II) salts with an
excess of copper powder. Colorless solutions containing
[Cu(CH3CN)4]X (X = BF4, 1/2S2O6) are relatively air-stable
and they were used for preparation of coordination polymers
without isolation of individual copper(I) salts. Silver benzoate
and isophthalate complexes 7 and 8 were prepared from
aqueous solutions using a hydrothermal technique.
Complex [Cu4(bpph)5](BF4)4ꢀ4CHCl3 (2) (dark-red blocks)
was synthesized similarly, starting with an acetonitrile solution
of copper(I) tetrafluoroborate. Crystals of the compound
easily lose solvate chloroform molecules in air within minutes,
which was accompanied with a loss of crystallinity.
Preparation of [Ag(bpph){NO3}]ꢀCHCl3 (3)
A solution of AgNO3 (17.0 mg, 0.10 mmol) in 3 ml acetonitrile
was layered over the solution of ligand L (23.4 mg, 0.10 mmol)
in 8 ml chloroform. Light-yellow prisms of the product grew
on the walls of the tube as the reaction layers slowly inter-
diffused (14–15 d). The yield was 44.5 mg, 85%. The sample is
stable under the mother-liquor, but it loses the incorporated
solvent in air with loss of crystallinity. Anal. for 3,
C15H11AgCl3N5O3. Calc. (%): C, 34.41; H, 2.12; N, 13.38.
Found (%): C, 34.76; H, 2.31; N, 13.62.
Coordination polymers [Ag4(bpph)3{CF3COO}4]ꢀCH3CN
(4) (yellow blocks, yield 55%), [Ag(bpph){C2F5COO}] (5)
(pale yellow plates, yield 70%) and [Ag4(bpph)3{CH3SO3}4]ꢀ
2CHCl3 (6) (light-yellow prisms, yield 45%) were prepared
similarly starting with the corresponding silver(I) salts. Anal.
for 4, C52H33Ag4F12N13O8. Calc. (%): C, 38.38; H, 2.04; N,
11.19. Found (%): C, 38.12; H, 2.01; N, 11.03. Anal. for 5,
C17H10AgF5N4O2. Calc. (%): C, 40.42; H, 2.00; N, 11.09.
Found (%): C, 40.31; H, 1.83; N, 11.24.
Preparation of [Cu2(bpph)(CH3CN)2{S2O6}] (1)
A solution of 66.3 mg (0.2 mmol) CuS2O6ꢀ6H2O in 4 ml
acetonitrile was stirred with 127 mg (2 mmol) of copper
powder for 1 h, until a total discoloration of the solution
was observed. The solution was filtered and then layered over
the solution of the ligand (23.4 mg, 0.1 mmol) in 8 ml chloro-
form. 8 ml of a chloroform–acetonitrile mixture (1 : 1 v/v) was
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Fig. 9 (a) Three types of silver coordination environments in the
structure 8, one of which involves two terminal aqua ligands; (b)
resulting 2D coordination 3,4-connected net based upon interconnec-
tion of the disilver–pyridazine chains with isophthalate anions. One of
two unique bipyridazine ligands is situated across an inversion centre.
Preparation of [Ag2(bpph){C6H5CO2}2]ꢀ2H2O (7)
Silver(I) benzoate (32.1 mg, 0.14 mmol), ligand (16.4 mg,
0.07 mmol) and 6 ml of water were sealed in a Pyrex glass tube.
The mixture was heated at 180 1C in a glycerine-bath for 8 h and
then it was cooled to r.t. over 40 h. Large yellow–green crystals of
the complex were separated in an almost quantitative yield of
44.8 mg (94%). Anal. for 7, C28H24Ag2N4O6. Calc. (%): C,
46.18; H, 3.32; N, 7.70. Found (%): C, 46.52; H, 3.28; N, 7.84.
Isophthalate complex [Ag6(bpph)3(H2O)6{C6H4(CO2)2}2]ꢀ
C6H4(CO2)2ꢀ4H2O (8) (yellow plates, yield 85%) was prepared
in a similar way, starting with a mixture of silver acetate (20.0
mg, 0.12 mmol) and isophthalic acid (11.6 mg, 0.07 mmol).
Anal. for 8, C66H62Ag6N12O22. Calc. (%): C, 39.19; H, 3.09;
N, 8.31. Found (%): C, 39.45; H, 2.98; N, 8.47.
Crystallography
Crystallographic measurements were made using a Stoe Ima-
ging Plate Diffraction System (213 K, absorption corrections
using DIFABS) and Bruker APEX area-detector diffracto-
meter for 3, 6 and 7 (296 and 213 K, absorption corrections
by SADABS30) (Mo-Ka radiation, l = 0.71073 A). The
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structures were solved by direct methods using the program
SHELXS-97.31 The refinement and all further calculations
were carried out using SHELXL-97.31 The non-H atoms were
refined anisotropically, using weighted full-matrix least-
squares on F2 (Table 4). For all structures CH hydrogens were
added geometrically, OH hydrogen atoms of coordinated
water molecules were located and then fixed. In structure 2,
both unique solvate chloroform molecules are disordered, the
components of the disorder were refined isotropically and with
restraints in their geometry. In trifluoroacetate structure 4,
both independent CF3 groups show typical rotational dis-
order, which was resolved with fixed geometry and with partial
occupancies 0.5, 0.5 and 0.6, 0.4. Solvate acetonitrile molecule
was equally disordered over the center of inversion, it was
refined anisotropically and the CH3 hydrogen atoms were not
added. In 8, 2-aromatic carbon atom of the non-coordinated
isophthalate dianion occupies an inversion centre and there-
fore the entire anion is disordered over two partially over-
lapping positions. The disorder was resolved with fixed
geometry of carboxylate groups. Non-coordinated water mo-
lecules were also equally disordered, they were refined iso-
tropically and the hydrogen atoms were not added. Two
independent chloroform molecules in structure 6 were badly
disordered and therefore the remaining electron density was
modeled using Squeeze.21 One of the methanesulfonate anions
was equally disordered over two overlapping positions. It was
possible to resolve the disordering scheme with fixed geometry.
Graphical visualisation of the structures was made using the
Diamond program.32
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CCDC reference numbers 685682–685689.
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Conclusions
The study provides a novel tetradentate ligand system, which
is well suited for bridging of many metal ions and generation
of metal–organic polymer structures. Our results suggest
utility of the metal ion/pyridazine dimers as attractive
‘‘secondary building units’’ for the rational construction of
coordination framework solids. The very easy and general
synthetic route employed for preparation of the extended
bipyridazine ligand may find further applications for develop-
ing of multidentate organic building blocks for crystal design.
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Chem., Int. Ed. Engl., 1995, 34, 1895.
20 R. J. Hill, D.-L. Long, M. S. Turvey, A. J. Blake, N. R.
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1918 | New J. Chem., 2008, 32, 1910–1918