Synthesis and structures of dinuclear Silver(I) and Copper(II) complexes of a semirigid naphthalene-bridged bipyrazolyl ligand

Article abstract of DOI:10.1007/s10870-013-0444-8

Reactions of a semirigid bipyrazole, 2,7-bis(4′-methylene-1H- 3′,5′-diphenylpyrazole) naphthalene (H₂L) with Ag(I) or Cu(II) salts yielded four dinuclear complexes, namely, [Ag₂(H ₂L)₂(NO₃)₂] (1), [Ag ₂(H₂L)₂](ClO₄)₂ (2), [Ag₂(H₂L)₂](BF₄)₂ (3), and [Cu₂(H₂L)₂Cl₄] (4). X-ray analysis illustrates that the three Ag(I) complexes are structurally similar and exhibit a rectangular shape, while the Cu(II) complex features an intramolecular π-stacking between two naphthalene-moieties and is much more compressed compared with those Ag(I) complexes. Two different conformations, namely cis, cis- and trans, trans-, have been observed for this bipyrazolyl ligand in its Ag(I) and Cu(II) complexes, respectively. Graphical Abstract: A semirigid naphthalene-bridged bipyrazole and its four dinuclear silver(I) or copper(II) complexes have been prepared and the crystal structures of the metal complexes have been studied by X-ray diffraction.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10870-013-0444-8

J Chem Crystallogr (2013) 43:448–454
DOI 10.1007/s10870-013-0444-8
ORIGINAL PAPER
Synthesis and Structures of Dinuclear Silver(I) and Copper(II)
Complexes of a Semirigid Naphthalene-Bridged Bipyrazolyl
Ligand
•
•
•
Peng-Cheng Duan Rui-Wen Jin Zi-Xuan Wang
Guang Yang
Received: 15 January 2013 / Accepted: 10 July 2013 / Published online: 23 July 2013
Ó Springer Science+Business Media New York 2013
Abstract Reactions of a semirigid bipyrazole, 2,7-bis
(40-methylene-1H-30,50-diphenylpyrazole) naphthalene (H2L)
with Ag(I) or Cu(II) salts yielded four dinuclear complexes,
namely, [Ag2(H2L)2(NO3)2] (1), [Ag2(H2L)2](ClO4)2 (2),
[Ag2(H2L)2](BF4)2 (3), and [Cu2(H2L)2Cl4] (4). X-ray analysis
illustrates that the three Ag(I) complexes are structurally similar
and exhibit a rectangular shape, while the Cu(II) complex
features an intramolecular p-stacking between two naphtha-
lene-moieties and is much more compressed compared with
those Ag(I) complexes. Two different conformations, namely
cis, cis- and trans, trans-, have been observed for this bipy-
razolyl ligand in its Ag(I) and Cu(II) complexes, respectively.
complicated way than a single pyrazole does upon binding to
metals, as demonstrated in several recent publications [4, 5].
It has been becoming clear that the separation distance and
relative orientation between two pyrazolyl moieties are two
key structure-determining factors among others to dictate the
assembling of the bipyrazoles and metal ions.
We have recently reported the syntheses and structures of
a series of semi-rigid C4-linked bipyrazolyl ligands, as well
as their metal complexes (Scheme 1) [6–8]. As one might
readily see, this type of bipyrazoles can be easily shaped to
meet the requirement of assembling; 3,5-substituents of
pyrazolyl ring and the central spacer are the locations which
can be modified or replaced if need be. Following up with our
previous work, we designed and prepared a new bipyrazolyl
ligand with a naphthalene group as the linker (H2L,
Scheme 2), which is structurally similar to H2L1 (Scheme 1)
and others reported previously [6].
Keywords Crystal structure ꢀ Bipyrazole ꢀ
Dinuclear complex ꢀ Silver ꢀ Copper
Introduction
Replacement of the m-xylylene group in H2L1 with a
naphthalene-2,7-dimethylene linker yielded a new bipy-
razole (H2L) with a longer distance between two pyrazolyl
moieties. In the meantime the relative orientation for them
in H2L remains almost the same as in H2L1. Herein we
report the synthesis of the new bipyrazole—2,7-bis
(40-methylene-1H-30,50-diphenylpyrazole)-naphthalene (H2L),
together with the crystal structures of its Ag(I) or Cu(II)
complexes, namely [Ag2(H2L)2](NO3)2 (1), [Ag2(H2L)2]
(ClO4)2 (2), [Ag2(H2L)2](BF4)2 (3), and [Cu2(H2L)2Cl4] (4).
The use of bipyrazoles has attracted immense attention in
recent years in the field of construction of metal–organic
frameworks (MOFs) and discrete supramolecularassemblies
[1–5]. Bipyrazole, in which two pyrazolyl moieties are
bridged via an organic linker, behave in a much more
Electronic supplementary material The online version of this
article (doi:10.1007/s10870-013-0444-8) contains supplementary
material, which is available to authorized users.
P.-C. Duan ꢀ R.-W. Jin ꢀ G. Yang (&)
College of Chemistry and Molecular Engineering,
Zhengzhou University, Zhengzhou 450001, China
e-mail: yang@zzu.edu.cn
Experimental
Materials and Physical Measurements
Z.-X. Wang
Key Laboratory for Special Functional Materials of the Ministry
of Education, Henan University, Kaifeng 475004, China
Silver salts were purchased from Alfa Aesar and other
commercially available reagents used without further
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J Chem Crystallogr (2013) 43:448–454
449
Scheme 1 Three types of
bipyrazoles previously reported
by us
Scheme 2 Synthetic route for
the bipyrazole—H2L
purification. The bipyrazolyl ligand 2,7-bis(40-methylene-
1H-30,50-diphenylpyrazole)naphthalene (H2L) was pre-
pared according to the synthetic route shown in Scheme 2.
IR spectra were recorded on a Nicolet Impact 420 FT-IR
spectrometer as KBr pellets in the range of 500–4,000
cm-1. C, H, N and S microanalyses were determined on a
White precipitate was obtained after tert-butyl alcohol
being removed with rotary evaporation, which was dis-
solved in CHCl3, and washed with water for several times
to remove inorganic salts. The resulted solution was dried
by anhydrous magnesium sulfate. Then the residue was
recrystallized from THF–methanol to give the desired
product as blocks. Yield: 75 %.
1
Flash EA 1112 elemental analyzer. H NMR spectra were
recorded on a Bruker DPX-400 spectrometer. Lumines-
cence spectra were measured on a PTI Fluorimeter utilizing
a photomultiplier to measure light intensity and Xe-lamp as
radiation source.
1H NMR (400 MHz, CDCl3): d = 3.587–3.603 (d, 4H,
–CH2–), 5.604–5.637 (t, 2H, –CH–), 7.284–7.942 (m, 26H,
Ph and naphthyl) ppm.
Step C The obtained bis-diketone was dissolved in CHCl3
(50 mL), a solution of hydrazine (80 % N2H4ꢀH2O, 0.8 mL)
in methanol (8 mL) was added slowly. The mixture was
refluxed for 12 h and then the solvent removed off under
reduced pressure, the residue was recrystallized from THF–
methanol to give the desired product as needles. Yield: 70 %.
Syntheses
Preparation of 2,7-Bis(40-methylene-1H-30,50-
diphenylpyrazole)naphthalene
Step A A mixture of N-bromosuccinimide (2.50 g,
14.08 mmol), 2,7-dimethylnaphthalene (1.00 g, 6.4 mmol),
AIBN (0.10 g, 0.58 mmol) in carbon tetrachloride
(100 mL) was stirred at reflux for 10 min after which the
mixture was cooled to 0 °C, the precipitated succinimide
was filtered off and the filtrate evaporated under reduced
pressure. The residue was recrystallized from absolute
ether to give the desired product as a white solid. Yield:
85 %.
1H NMR (400 MHz, DMSO): d = 4.186 (s, 4H, –CH2–),
7.20–7.75 (m, 26H, Ph and naphthyl) ppm. IR (KBr pellet):
3205(s), 3049(s), 2923(m), 1633(w), 1604(m), 1494(s),
1445(s), 1292(w), 1264(w), 1220(m), 1171(m), 974(s),
916(m), 837(m),763(s), 696(s) cm-1. MS: m/z = 593.4
[M ? H]?.
Synthesis of [Ag2(H2L)2](NO3)2 (1)
1H NMR (400 MHz, CDCl3): d = 4.67 (s, 4H,
–CH2Br), 7.52–7.85 (m, 6H, naphthyl) ppm.
A solution of AgNO3 (0.01 mmol, 1.7 mg) in CH3CN
(4 mL) was layered on the surface of a solution of H2L
(0.01 mmol, 6 mg) in THF (2 mL) in a test tube. Colorless
crystals were obtained in 70 % yield within three days.
Anal. Calc. for C42H32AgN5O3ꢀ1.5CH3CNꢀTHF (894.5)
(%): C 65.74; H 4.97; N 10.17, Found: C 65.46; H 5.07; N
10.32. IR (KBr pellet): 3432(vs), 2924(w), 1635(m),
Step B Potassium (0.19 g, 4.9 mmol) was dissolved in
tert-butyl alcohol (50 mL), to this solution, dibenzoylme-
thane (1.19 g, 5.3 mmol), 2,7-di(bromomethyl)naphthalene
(0.77 g, 2.45 mmol) and KI (0.5 g) were added succes-
sively. The mixture was refluxed for 72 h under nitrogen.
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J Chem Crystallogr (2013) 43:448–454
1491(w), 1425(m), 1384(m) (NO3-), 1303(w), 1128(m),
evaporate slowly to produce colorless blocks in 30 % yield
within one week.
1036(w), 982(m), 918(w), 835(w), 768(w), 695(s) cm-1
.
Anal. Calc. for C42H32AgBF4N4ꢀ1/2CH3CNꢀTHFꢀ
1.5H2O (907.06) (%): C 62.23; H 4.94; N 6.95, Found: C
62.34; H 4.69; N 6.93. IR (KBr pellet): 3423(vs), 3060(w),
2922(w), 1707(m), 1636(m), 1561(w), 1481(w), 1450(m),
1384(w), 1200(w), 1113(s)(BF4-), 980(w), 929(w), 836(m),
Synthesis of [Ag2(H2L)2](ClO4)2 (2)
This complex was prepared in a similar way as for 1, using
AgClO4 (0.01 mmol, 2.3 mg) instead of the AgNO3. Yield:
75 %.
773(m), 702(s), 619(w) cm-1
.
Anal. Calc. for C42H32AgClN4O4ꢀ2H2OꢀTHF (908.19)
(%): C 60.83; H 4.88; N 6.17, Found: C 61.17; H 4.72; N
6.03. IR (KBr pellet): 3426(vs), 3051(w), 2991(w),
1636(s), 1564(w), 1499(w), 1452(m), 1384(w), 1296(m),
1113(vs)(ClO4-), 964(m), 921(w), 768(m), 698(s), 621(s) cm-1.
Synthesis of [Cu2(H2L)2Cl4] (4)
This complex was prepared in a similar way as for 1, using
CuCl2 (0.01 mmol, 1.7 mg) instead of the AgNO3. Yield:
80 %.
Anal. Calc. for C42H32CuCl2N4 (727.18) (%): C 69.37;
H 4.44; N 7.70,Found: C 69.15; H 4.58; N 7.51. IR (KBr
pellet): 3424(vs), 3053(w), 2923(w), 1634(m), 1557(w),
1482(s), 1450(s), 1385(w), 1293(m), 1179(s), 1130(m),
1074(w), 906(w), 834(w), 769(m), 697(vs), 624(w),
Synthesis of [Ag2(H2L)2](BF4)2 (3)
A solution of AgBF4 (0.03 mmol, 5.7 mg) in CH3CN
(2 mL) was mixed with a 2 mL of THF solution of H2L
(0.03 mmol, 18 mg). The resulting solution was allowed to
584(w) cm-1
.
Table 1 Crystallographic data
and structure refinement for 1,
2, 3 and 4
1ꢀ2THFꢀ6CH3CN
2ꢀ2THFꢀ6CH3CN
3
4
Formula
C104H98Ag2N16O8 C104H98Ag2Cl2N14O10 C84H64Ag2B2F8N8 C42H32Cl2CuN4
Mr
1915.72
1990.62
1574.79
727.18
Crystal system
Crystal group
Monoclinic
P21/c
Monoclinic
C2/m
Monoclinic
C2/c
Triclinic
P-1
˚
a (A)
13.075(3)
26.306(5)
18.806(6)
18.775(4)
26.360(5)
12.949(3)
27.321(9)
13.142(3)
27.915(11)
11.018(2)
12.568(3)
13.641(3)
82.92(3)
66.69(3)
73.98(3)
1667.2(6)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
132.846(18)
131.76(3)
121.36(3)
˚
V (A)
4742(2)
2
4780.4(28)
2
8559(5)
4
Z
T (K)
Dcalcd (Mg/m3)
153(2)
153(2)
153(2)
153(2)
1.342
1.350
1.222
1.449
m (mm-1
)
0.479
0.531
0.519
0.854
F (000) (e)
hkl range
1984
2008
3200
750
-17 B h B 17
-35 B k B 36
-19 B l B 25
40,326
-25 B h B 21
-33 B k B 35
-15 B l B 17
20,396
-25 Bh B =33
-15 B k B 13
-33 B l B 29
16,052
-14 B h B 14
-15 B k B 16
-17 B l B 17
15,719
Refl. collected
Refl. unique
12,499
[Rint = 0.0476]
6,523 [Rint = 0.0427] 7,758
[Rint = 0.1039]
546
7,533
[Rint = 0.0471]
Param. refined
Restrains
568
403
442
4
138
564
0
Final R indices
R1 = 0.0859
wR2 = 0.2163
1.188
R1 = 0.0535
wR2 = 0.1209
1.022
R1 = 0.0976
wR2 = 0.2917
1.006
R1 = 0.0603
wR2 = 0.1373
0.972
[I [ 2r]
GoF (F2)
Dqfin(max,
min)eA
1.139, -1.174
2.101, -0.949
1.453, -1.250
0.738, -0.524
-3
˚
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J Chem Crystallogr (2013) 43:448–454
451
X-ray Crystal Structure Determination
crystals of 3 were obtained by slow evaporation of a
mixture of AgBF4 and bipyrazole.
Diffraction intensities were collected at 153(2) K on a Rigaku
The microanalyses demonstrated the molar ratio of
metal to ligand is 1:1 for all of the four complexes. The IR
spectra of these complexes showed the characteristic peaks
of the anions (NO3-, ClO4-, or BF4-; Figs. S6–S8).
Saturn 724 ? CCD diffractometer with graphite-monochro-
˚
mated Mo–Ka radiation (0.71073 A). Absorption corrections
were applied using the multiscan program. The structures
were solved by direct methods and refined by least squares
techniques using the SHELXS-97 and SHELXL-97 programs
[9]. All non-hydrogen atoms were refined with anisotropic
displacement parameters expect for the disorder solvents;
hydrogen atoms were generated geometrically. SQUEEZE
program in PLATON was used in the refinement of 3 to cope
with the unidentifiable solvent molecules [10]. A phenyl
group and the tetrafluoroborate anion in 2 and the perchlorate
anions in 3 are disorder and were modeled by splitting them
into two parts, each with the site occupancy factor of 0.5 or
0.25. The high wR2 values for compound 1 and 3 may pos-
sibly originate from the highly disordered solvent molecules.
The crystal data and the selected bond lengths and angles for
these complexes are listed in Tables 1 and 2, respectively.
Crystal Structure Description
The solvated complex, 1ꢀ2THFꢀ6CH3CN, crystalizes in the
monoclinic space group of P21/c. The asymmetric unit con-
sistsofone Ag atom, one bipyrazole, one nitrate, two halvesof
THF molecules and three CH3CN molecules (Fig. S10).
1 actually exists as a dinuclear molecular rectangle of
M2L2 type, which is generated by a symmetric operation of
inversion on the asymmetric unit of 1. As shown in Fig. 1,
the Ag(I) atom is linearly two-coordinated by two pyraz-
olyl N2 atoms in a cis-fashion. The bipyrazolyl ligand, in
the cis, cis-conformation (Scheme 3), behaves as a l2-N,N0
bridge linking two Ag(I) atoms. The shape of 1 resembles
that of [Ag2(H2L1)2](NO3)2, H2L1 being a bipyrazole
similar to H2L, however, with m-xylylene as the linker
between two pyrazolyl moieties [6]. The rectangle thus
formed possesses a rather large cavity as exemplified by
Results and Discussion
Synthesis and Characterization
˚
the intramolecular AgꢀꢀꢀAg distance of 8.264(3) A, which
1
is much longer than that [5.825(3) A] in [Ag2(H2L )2]
˚
Complexes 1, 2 and 4 were prepared by slow diffusion of
solutions of metal salts into a solution of ligand, while the
(NO3)2. The nearest distance between Ag and O atom from
Table 2 Selected bond
˚
distances (A) and bond angles
(°) for 1, 2, 3 and 4
Complex 1
Ag(1)–N(1) 2.117(3)
N(3)–Ag(1)#1 2.117(3)
C(13)–N(3)–Ag(1)#1 135.7(3)
N(4)–N(3)–Ag(1)#1 118.2(2)
Complex 2
N(1)–Ag(1)–N(3)#1 165.93(13)
N(2)–N(1)–Ag(1) 118.3(2)
Ag(1)–N(1) 2.130(2)
O(3)–Cl(1)–O(2) 109.0(5)
O(3)–Cl(1)–O(1) 109.1(4)
O(2)–Cl(1)–O(1) 110.1(5)
C(1)–N(1)–Ag(1) 135.25(17)
N(2)–N(1)–Ag(1) 118.76(15)
N(1)#1–Ag(1)–N(1) 165.61(11)
Complex 3
Ag(1)–N(1) 2.147(7)
N(1)–Ag(1)–N(3)#1 170.5(3)
C(7)–N(1)–Ag(1) 134.0(7)
N(2)–N(1)–Ag(1) 120.8(6)
N(4)–C(36)–C(28) 106.4(7)
N(4)–C(36)–C(37) 121.2(7)
Ag(1)–N(3)#1 2.156(7)
C(29)–N(3)–Ag(1)#1 133.4(6)
N(4)–N(3)–Ag(1)#1 120.8(6)
Complex 4
Cu(1)–N(1) 2.008(3)
Cu(1)–N(3) 2.009(3)
Cu(1)–Cl(2) 2.232(13)
Cu(1)–Cl(1) 2.266(12)
C(9)–N(1)–Cu(1) 135.2(2)
N(1)–Cu(1)–N(3) 91.41(12)
N(1)–Cu(1)–Cl(2) 89.27(9)
N(3)–Cu(1)–Cl(2) 158.96(10)
N(1)–Cu(1)–Cl(1) 141.48(10)
N(3)–Cu(1)–Cl(1) 93.53(9)
Cl(2)–Cu(1)–Cl(1) 98.98(5)
N(2)–N(1)–Cu(1) 118.8(2)
Symmetry codes: 1 #1) -x ? 1,
-y, -z ? 1; 2 #1) x, -y ? 1, z;
3 #1) -x ? 1, y, -z ? 1/2
N(4)–N(3)–Cu(1) 117.5(2)
C(36)–N(3)–Cu(1) 135.3(3)
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J Chem Crystallogr (2013) 43:448–454
Fig. 1 Ball-and-stick diagram of 1, showing the coordination envi-
ronment around the Ag atom and the cis, cis-conformation of the
l2-bridging bipyrazolyl ligand. The solvent molecules have been
˚
omitted for clarity. Selected distances (A) and angles (°): Ag1–N1 =
2.117(3), Ag1–N3a = 2.117(3); N1–Ag–N3a = 165.93(13). Symme-
try code: a) -x ? 1, -y, -z ? 1
˚
nitrate is 2.895(8) A, indicative of no coordination to
Fig. 2 The intermolecular C–Hꢀꢀꢀp interactions in 1, involving the
metals. However, H-bonding is found between O atom of
naphthalene rings and the phenyl groups
nitrate and pyrazole N atoms, with OꢀꢀꢀN distances being
˚
2.934(6) and 2.981(6) A (Fig. 1).
One of the two solvated THF molecules is located
within the cavity, which is disordered to two opposite
positions with the distance of AgꢀꢀꢀO(THF) being
Extensive p–p interactions are observed in the crystal
structure of 1, which may contribute to the formation or
stabilization of the present structure. Within the dinuclear
complex, it can be clearly found that some of phenyl H
atoms are pointing to the faces of naphthalene. The dis-
tances of H(phenyl)ꢀꢀꢀC(naphthalene) for bipyrazole in 1
˚
2.733(13) A.
The complexes 2 and 3 crystalize in the monoclinic
space groups, C2/m and C2/c, respectively. Their structures
are similar to that of 1, therefore no further discussion is
made of these complexes (Figs. S13–S16).
˚
fall in the range of 2.559(5)–2.952(3) A, indicative of the
presence of C–Hꢀꢀꢀp interactions (Fig. S11) [11]. Moreover,
˚
A few rectangular dinuclear silver complexes of M2L2
type, based on the bipyrazole ligands and various metals,
have been recently reported by us [6–8]. The sizes of these
rectangular structures can be defined by their intramolec-
ular AgꢀꢀꢀAg distances, which are 5.825(3), 8.264(3),
we noticed that the HꢀꢀꢀH distances are 2.673(1) A between
two phenyl groups from two bipyrazoles within 1, implying
some kind of weak interactions. However, the orientation
and the centroid separation for the phenyl groups are
somehow different from the well-defined face-to-face p
stacking and the edge-to-face C–Hꢀꢀꢀp interaction (Fig. S12)
[12, 13]. Between neighboring dinuclear rectangles exist the
C–Hꢀꢀꢀp interactions, as evident by the fact that one naph-
thalene H atom points to a phenyl ring of an adjacent
dinuclear complex with the shortest distance of H(naphtha-
1
˚
8.898(2) and 12.153(2) A for [Ag2(H2L )2](NO3)2, [Ag2(H2L)2]
(NO3)2, [Ag2(H2L2)2](BF4)2 and [Ag2(H2L3)2](ClO4)2
(Scheme 1), respectively. It is worthy of note that except
[Ag2(H2L1)2](NO3)2, all other three complexes hold solvent
molecules in their cavities, indicating a longer linker
between the two pyrazolyl moieties of the bipyrazoles leads
˚
lene)ꢀꢀꢀC(phenyl) being 2.66(3) A (Fig. 2).
Scheme 3 Three possible
conformations of the
bipyrazole—H2L
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J Chem Crystallogr (2013) 43:448–454
453
to a larger cavity within the complex, which is inclined to
show the inclusion phenomena.
involving the phenyl H atoms and the naphthalene faces are
observed in 4, as evident by the distances of H(phenyl)ꢀꢀꢀC
(naphthalene) for bipyrazole falling in the range of
The complex 4 crystalizes in the triclinic P-1 space
group. The asymmetric unit consists of one Cu(II) atom,
one ligand and two chloride ions, which is related to its
other half by a crystallographically imposed inversion
center located midway between two metals in the dinuclear
complex 4 (Fig. S17).
The Cu(II) atom is four-coordinated by two Cl- ions and
two pyrazolyl N2 atoms from two ligands in a N2Cl2 geom-
etry between tetrahedron and square planar. The ligand, in
the trans, trans-conformation, acts as a l2-N,N0 bridge
linking the two Cu(II) atoms in 4, as depicted in Fig. 3. This
trans, trans-conformation has not been observed for its
analogue—H2L1, a m-xylylene bridged bipyrazole, while the
cis, cis- and the cis, trans-conformations for this ligand have
been reported in our previous paper [6].
˚
2.676(3)–2.769(4) A. Interestingly, the two naphthalene
rings in 4 are parallel with a face-to-face distance of
˚
3.484(4) A, revealing the presence of intramolecular offset
pꢀꢀꢀp stacking interaction (Fig. S18) [12], which together
with other structural determinants (e.g. the coordination
geometry of Cu2?) may contribute to the formation of the
somewhat compressed structure compared with that of 1.
The intermolecular distance of CuꢀꢀꢀCl between two
˚
adjacent molecules is 3.114(15) A, generating a 1D chain
along [011] direction if this weak CuꢀꢀꢀCl bond is taken into
consideration, as shown in Fig. 4.
Luminescence Spectra
Intramolecular hydrogen bonds of Npz-HꢀꢀꢀCl are pre-
The solid-state luminescent spectra were recorded for the
ligand and silver complexes at room temperature. Upon
excitations at 350, 350, 288 and 223 nm for H2L, 1, 2, and
3, the emission maxima are observed at 420, 478, 338 and
˚
sented with NꢀꢀꢀCl distances of 3.013(4) and 3.070(4) A.
Similar to 1, the intramolecular C–Hꢀꢀꢀp interactions
H2L
1
2
3
Fig. 3 Ball-and-stick diagram of 4, showing the coordination envi-
ronment around the Cu atom and the trans, trans-conformation of the
l2-bridging bipyrazolyl ligand. The intramolecular H-bonds of
˚
Npz–HꢀꢀꢀCl are represented as dashed lines. Selected distances (A)
300
350
400
450
500
550
and angles (°): Cu1–N1 = 2.008(3), Cu1–N3 = 2.009(3), Cu1–
Cl2 = 2.232(1), Cu1–Cl1 = 2.266(2); N1–Cu1–Cl2 = 89.27(9),
N1–Cu1–N3 = 91.41(12), N3–Cu1–Cl1 = 93.53(9), Cl1–Cu1–
Wavelength/nm
Cl2 = 98.98(5),
158.96(10). Symmetry code: a) -x ? 2, -y ? 1, -z
N1–Cu1–Cl1 = 141.48(10),
N3–Cu1–Cl2 =
Fig. 5 Solid-state luminescent spectra of H2L, 1, 2, and 3 at room
temperature
Fig. 4 A chain formed by
molecules of 4 through the weak
intermolecular CuꢀꢀꢀCl bonds
123

454
J Chem Crystallogr (2013) 43:448–454
416 nm, respectively (Fig. 5). Since the structures of 1, 2
and 3 are similar, the variation on the emission maximum
seems to be related with the different anions presented in
the structures.
diagrams showing the pꢀꢀꢀp interactions in 1 and 4 are
provided as supplementary material.
CCDC 918864–918867 contain the crystallographic data
for the complexes 1, 2, 3 and 4. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
Conclusion
Acknowledgments This work has been supported by the NSF of
China (Nos. 21071126 and J1210060).
In this paper, a semi-rigid naphthalene-2,7-dimethylene-
bridged bipyrazole together with its four Ag(I) or Cu(II)
complexes were prepared and characterized. X-ray analy-
ses revealed a novel trans, trans-conformation of the
bipyrazole in its Cu(II) complex, besides the more common
cis, cis-conformation observed in its Ag(I) complexes and
others reported previously with similar bipyrazolyl ligands.
Extensive pꢀꢀꢀp interactions are found in the structures,
involving the 3,5-diphenyl substituents of pyrazole and the
naphthalene rings. Compared with the analogue bipyrazole
with m-xylylene as the linker between two pyrazolyl
moieties, the one reported in this paper possesses a longer
separation distance here, which results in a larger void
within the rectangular dinuclear complex. Further research
to use this bipyrazole in construction of new architectures
is underway in our laboratory.
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123