Tuning the silver(I) complexes of 3-(2-pyridyl)pyrazole-based ligands: Syntheses and crystal structures of the complexes, as well as theoretical investigations on the coordination abilities of the ligands

Article abstract of DOI:10.1016/j.molstruc.2006.12.026

In our efforts to investigate the influences of different pendant aromatic groups and the spatial position of N donors in 3-(2-pyridyl)pyrazole-based ligands on the structures of their metal complexes, five structurally related ligands: 1-[3-(2-pyridyl)py

Full text of DOI:10.1016/j.molstruc.2006.12.026

Journal of Molecular Structure 843 (2007) 66–77
www.elsevier.com/locate/molstruc
Tuning the silver(I) complexes of 3-(2-pyridyl)pyrazole-based
ligands: Syntheses and crystal structures of the complexes, as well
as theoretical investigations on the coordination abilities of the ligands
Chun-Sen Liu, Jian-Rong Li, Ru-Qiang Zou, Jiang-Ning Zhou, Xue-Song Shi,
*
Jun-Jie Wang, Xian-He Bu
Department of Chemistry, Nankai University, Tianjin 300071, People’s Republic of China
Received 14 October 2006; received in revised form 17 December 2006; accepted 19 December 2006
Available online 10 January 2007
Abstract
In our efforts to investigate the influences of different pendant aromatic groups and the spatial position of N donors in
3-(2-pyridyl)pyrazole-based ligands on the structures of their metal complexes, five structurally related ligands: 1-[3-(2-pyridyl)pyra-
zol-1-ylmethyl]benzene (L1), 1-[3-(2-pyridyl)pyrazol-1-ylmethyl]naphthalene (L2), 8-[3-(2-pyridyl)pyrazol-1-ylmethyl]quinoline (L3),
3-[3-(2-pyridyl)pyrazol-1-ylmethyl]pyridine (L4) and 4-[3-(2- pyridyl)pyrazol-1-ylmethyl]pyridine (L5), have been used to react with
AgClO4 to form five Ag(I) complexes, [Ag(L1)2](ClO4) (1), [Ag(L2)2](ClO4) (2), [Ag(L3)(HL3)](ClO4)2(CH3CN) (3), {[Ag(L4)](ClO4)}2
(4), and {[Ag(L5)](ClO4)} (5). The structural differences of these complexes may be attributed to the coordination geometries or N
1
donor position of the pendant aromatic groups in ligands L1–L5. Also, the result reveals that various intra- and/or inter-molecular weak
interactions, such as pꢀ ꢀ ꢀp stacking, C–Hꢀ ꢀ ꢀp and C–Hꢀ ꢀ ꢀO H-bonding interactions, play important roles in the formation of 1–5,
especially in the aspect of linking the multi-nuclear discrete subunits or low-dimensional entities into high-dimensional frameworks.
Moreover, the coordination behaviors of ligands L1–L5 have been briefly evaluated by DFT calculations.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: 3-(2-Pyridyl)pyrazole-based ligands; Ag(I) complexes; Crystal structures; DFT calculations
1. Introduction
[5,6]. Indeed, in addition to coordination bonding [7,8], some
weak intra- or inter-molecular interactions, such as H-bond-
ing [9–13] and pꢀ ꢀ ꢀp stacking [14–16] also affect the final
structures of coordination complexes, and they may further
link discrete subunits or low-dimensional entities into high-
dimensional supramolecular networks [3–6].
The synthesis of multi-nuclear discrete or infinite coordi-
nation architectures has attracted great interest in coordina-
tion and supramolecular chemistry due to their intriguing
structures and potential applications as functional materials
[1–3]. The formation of these coordination architectures
depends mainly on the combinations of two factors includ-
ing the coordination geometry of metal ions and the nature
of ligands [4]. However, the methodologies to use transition
metal ions as connecting nodes to hold together organic
ligands in predefined patterns within self-assembled oligo-
meric or polymeric aggregates still remains a great challenge
Ward et al. has initially reported many coordination
architectures of 3-(2-pyridyl)pyrazole and its derivative
ligands [17]. In our recent work,
a
series of
3-(2-pyridyl)pyrazole-based ligands have been also used to
construct complexes with various structures including mul-
ti-nuclear discrete molecules as well as one-dimensional
(1D) and two-dimensional (2D) coordination polymers
exhibiting interesting properties [18]. In order to further
investigate the coordination architectures of such ligands,
five structurally related 3-(2-pyridyl)pyrazole-based ligands,
*
Corresponding author. Tel.: +86 22 23502809; fax: +86 22 23502458.
E-mail address: buxh@nankai.edu.cn (X.-H. Bu).
0022-2860/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.12.026

C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
67
1-[3-(2-pyridyl)pyrazol-1-ylmethyl]benzene (L1), 1-[3-(2-
pyridyl)pyrazol-1-ylmethyl]naphthalene (L2), 8-[3-(2-pyridyl)
pyrazol-1-ylmethyl]quinoline (L3), 3-[3-(2-pyridyl)pyrazol-
1-ylmethyl]pyridine (L4) and 4-[3-(2-pyridyl)pyrazol-1-yl-
methyl]pyridine (L5), have been synthesized (Chart 1), and
their reactions with AgClO4Æ H2O offered five complexes,
[Ag(L1)2](ClO4) (1), [Ag(L2)2](ClO4) (2), [Ag(L3)(HL3)]
(ClO4)2(CH3CN) (3), {[Ag(L4)](ClO4)}2 (4) and {[Ag(L5)]
procedures. All the other reagents for synthesis were com-
mercially available and used as received or purified by stan-
dard methods prior to use. Melting points were measured
on an X-4 micro melting point detector without further
correction. Elemental analyses (C, H, and N) were per-
formed on a Perkin-Elemer 240C analyzer and IR spectra
were measured on a Tensor 27 OPUS (Bruker) FT-IR spec-
trometer with KBr pellets. 1H NMR spectra were recorded
on a Bruker AC-P500 spectrometer (300 MHz) at 25 °C in
CDCl3 with tetramethylsilane as the internal reference.
(ClO4)} (5). These complexes have different structures,
1
showing the influences of the coordination geometries of
the pendant groups in L1–L5 ligands. Furthermore, DFT
theoretical calculations have also been carried out for briefly
estimating the coordination abilities of such ligands.
2.2. Syntheses of ligands
The ligands L1–L5 were prepared by modified literature
procedures [18,20]. The reactions of 3-(2-pyridyl)pyrazole
with benzyl chloride, 1-(chloromethyl)naphthalene, 8-bro-
momethylquinoline, 3-(chloromethyl)pyridine hydrochloride
(3-picolyl chloride hydrochloride) and 4-(chloromethyl)pyr-
idine hydrochloride (4-picolyl chloride hydrochloride),
respectively, in benzene as well as in the presence of NaOH
2. Experimental
2.1. Materials and general methods
3-(2-Pyridyl)pyrazole [19a,19b,19c] and 8-bromomethyl-
quinoline [19d] were synthesized according to the reported
n
and Bu4NOH, gave ligands L1–L5. It should be pointed
out that L1 along with its related metal complexes has been
synthesized and reported by us [18a] and others [20c], mean-
while, L2 and its Cu(II), Zn(II) and Cd(II) complexes
[18b,18c] as well as L3 and its Cu(II) complex [18d] have also
been documented in our previous work. Also, the structure
of the copper acetate complex [18d] of L3 is similar to the
Ag(I) complex 3 described in this work.
N
N
N
L1
For L4, yield: ꢁ30%. Mp.: 78–80 °C. 1H NMR
(300 MHz, CDCl3): d 5.54 (s, 2H), 6.95 (d, J = 2.4 Hz,
1H), 7.05 (d, J = 6.9 Hz, 1H), 7.18–7.23 (m, 2H), 7.59
(d, J = 2.4 Hz, 1H), 7.60–7.74 (m, 2H), 7.95 (d,
J = 7.8 Hz, 1H), 8.58–8.64 (m, 2H). IR (cmꢂ1): 3111w,
1594s, 1494m, 1458m, 1432s, 1355m, 1271m, 1247m,
1057m, 1030m, 994m, 789vs, 756s, 704m. Anal. Calcd for
C14H12N4: C, 71.17; H, 5.12; N, 23.71. Found: C, 71.23;
H, 4.98; N, 23.92%.
N
N
N
L2
For L5, yield: ꢁ30%. Mp: 81–83 °C. 1H NMR
(300 MHz, CDCl3): d 5.43 (s, 2H), 7.01 (d, J = 2.4 Hz,
1H), 7.08 (d, J = 6.3 Hz, 2H), 7.21–7.25 (m, 1H), 7.51
(d, J = 2.4 Hz, 1H), 7.71–7.77 (m, 1H), 7.95 (d,
J = 7.8 Hz, 1H), 8.56–8.59 (m, 2H), 8.64–8.66 (m, 1H).
IR (KBr, cmꢂ1): 2890w, 2790w, 1592s, 1566m, 1487s,
1458s, 1399m, 1277m, 1220vs, 1049s, 991m, 800m, 759s,
620m. Anal. Calcd for C14H12N4: C, 71.17; H, 5.12;
N, 23.71. Found: C, 70.95; H, 5.24; N, 23.91%.
N
N
N
N
L3
N
N
N
N
2.3. Synthesis of complexes 1–5
L4
All measurements were performed based on the crystal
samples.
[Ag(L1)2](ClO4) (1). The reaction of L1 (0.1 mmol) with
AgClO4ÆH2O (0.1 mmol) in MeOH (10 ml) for a few min-
utes afforded the yellow solid, which was then filtered.
The resulted solution was kept at room temperature in the
dark. Yellow single crystals were obtained by slow evapora-
tion of the solvent after several days. Yield: ꢁ40%. IR
N
N
N
N
L5
Chart 1.

68
C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
Table 1
Crystallographic data and structure refinement summary for complexes 1–5
1
2
3
4
5
Chemical formula
Formula weight
Crystal system
Space group
C
677.89
30H26AgClN6O4
C38H30AgClN6O4
778.00
C38H32AgCl2N9O8
921.50
C28H24Ag2Cl2N8O8
887.20
Triclinic
Pꢂ1
C14H12AgClN4O4
443.60
Monoclinic
P2(1)/c
10.892(3)
11.940(3)
22.380(7)
90
92.642(5)
90
2907.3(15)
4
Orthorhombic
Pna2(1)
14.585(5)
16.620(5)
13.782(4)
90
Monoclinic
P2(1)/c
15.946(3)
17.292(3)
14.140(3)
90
107.101(3)
90
3726.6(12)
4
Monoclinic
P2(1)/c
13.162(2)
8.1298(1)
14.888(2)
90
90.348(3)
90
1593.1(4)
4
˚
a (A)
7.700(3)
9.264(3)
11.609(4)
91.763(5)
99.740(5)
102.660(5)
794.3(5)
1
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
90
90
3
˚
V (A)
3340.7(19)
4
1.547
0.735
0.946
Z
D (g cmꢂ3
)
1.549
0.832
1.004
1.642
0.752
0.723
1.855
1.464
1.040
1.850
1.460
1.013
l (mmꢂ1
GOF
)
T (K)
Ra/wRb [I > 2r(I)]
293(2)
0.0570/0.1318
293(2)
0.0456/0.0582
293(2)
0.0422/0.0563
293(2)
0.0308/0.0705
293(2)
0.0322/0.0654
a
R = R(iF0j-jFCi)/RjF0j.
2
2
2
1=2
b
wR ¼ ½RwðjF 0j ꢂ jF Cj Þ =RwðF 20Þꢃ
.
(cmꢂ1): 3134w, 1600s, 1569w, 1498s, 1456w, 1434s, 1372w,
1358w, 1333w, 1236s, 1101vs, 959w, 774s, 722s, 705w,
621m, 460w. Anal. Calcd for C30H26AgClN6O4: C, 53.15;
H, 3.87; N, 12.40. Found: C, 52.87; H, 4.06; N, 12.01.
[Ag(L2)2](ClO4) (2). Yellow single crystals of 2 were
obtained by the similar method as described for 1 except
for L2 replacing L1. Yield: ꢁ50%. IR (cmꢂ1): 3110w,
3041w, 1592s, 1563br, 1512w, 1459s, 1401m, 1385m,
Fig. 1. View of (a) the coordination environment of Ag(I) in 1 and (b) the 1D chain formed by the intermolecular C–Hꢀ ꢀ ꢀp and pꢀ ꢀ ꢀp interactions (partial
H atoms and ClOꢂ4 omitted for clarity).

C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
69
1357m, 1326m, 1276w, 1233s, 1151m, 1113w, 1092m, 1053s,
2.5. Calculation details
993m, 959w, 860w, 793s, 776vs, 743s, 723m, 621m, 533w,
420w. Anal. Calcd for C38H30AgClN6O4: C, 58.66; H,
3.89; N, 10.80. Found: C, 58.34; H, 3.91; N, 11.05.
[Ag(L3)(HL3)](ClO4)2(CH3CN) (3). Mixing L3
(0.1 mmol) and AgClO4ÆH2O (0.1 mmol) in a mixed solu-
tion of MeOH and H2O (v/v = 1:1) to obtain yellow solid
which was filtered and washed with acetone and dried in
air. Single crystals were obtained by slow diffusion of
Et2O into the acetonitrile solution of the solid. Yield:
ꢁ40%. IR (cmꢂ1): 3105w, 3022w, 2841w, 1690vs, 1506s,
1468vs, 1143vs, 1097s, 864s, 780s, 623s. Anal. Calcd for
C38H32AgCl2N9O8: C, 49.53; H, 3.50; N, 13.68. Found:
C, 49.21; H, 3.41; N, 14.05.
The molecular mechanics optimization of the ligands
L1–L5 was carried out by DFT based on the structures
obtained from the crystallographic data and the termina-
tion condition is that the RMS gradient is below
0.01 kcal/mol. Then the Gaussian 03 set of programs was
applied to perform quantum-chemical computation of the
MM+-optimized ligands [24]. The MM+-optimized ligands
were further fully optimized using density functional theory
(DFT) method with B3LYP exchange-correlation func-
tional [25] and 6-31G (d, p) basis set, respectively. Also,
to ensure that the stationary points located on the potential
energy surfaces were minima, the vibrational frequency
calculations were done.
{[Ag(L4)](ClO4)}2 (4). Similar synthetic procedure as
for 3 was used except that L3 was replaced by L4, giving
yellow single crystals. Yield: ꢁ40%. IR (cmꢂ1): 3147w,
1602s, 1523w, 1504w, 1434s, 1361m, 1321w, 1242s,
1197m, 1080vs, 767s, 708w, 622s. Anal. Calcd for C28H24
Ag2Cl2N8O8: C, 37.91; H, 2.73; N, 12.63. Found: C,
38.01; H, 2.83; N, 12.24%.
3. Results and discussion
3.1. Synthesis and general characterizations
Complexes 1–5 were prepared by the reaction of
AgClO4ÆH2O and ligands L1–L5 under similar conditions.
The IR spectra for the five complexes show absorption
bands resulting from the skeletal vibrations of the aromat-
ic rings in 1600–1400 cmꢂ1 region, and the characteristic
bands of perchlorate anions at ꢁ620 and ꢁ1100 cmꢂ1. It
should be noted that, due to the coordination of the
{[Ag(L5)](ClO4)} (5). Similar synthetic procedure as
1
for 3 was also used except that L3 was replaced byL5,
and 5 was obtained as yellow single crystals. Yield:
ꢁ30%. IR (cmꢂ1): 3167w, 1595m, 1499w, 1429s, 1360m,
1324m, 1240m, 1078vs, 780s, 718w, 621s, 474w. Anal. Calcd
for C14H12AgClN4O4: C, 37.91; H, 2.73; N, 12.63. Found:
C, 37.50; H, 2.71; N, 12.32%.
Caution! Although we have met no problems in handling
perchlorate salt during this work, these should be treaded
cautiously owing to their potential explosive nature.
Table 2
˚
Selected bond distances (A) and angles (°) for complexes 1–5
Complex 1
Ag(1)–N(5)
Ag(1)–N(2)
2.253(4)
2.360(4)
Ag(1)–N(3)
Ag(1)–N(6)
2.275(4)
2.416(4)
2.4. X-ray crystallographic studies of 1–5
N(5)–Ag(1)–N(3)
N(3)–Ag(1)–N(2)
N(3)–Ag(1)–N(6)
146.05(16)
72.31(15)
132.47(15)
N(5)–Ag(1)–N(2)
N(5)–Ag(1)–N(6)
N(2)–Ag(1)–N(6)
123.83(14)
71.20(15)
116.32(13)
X-ray single-crystal diffraction data for complexes 1–5
were collected on a Bruker Smart 1000 CCD diffractometer
˚
Complex 2
Ag(1)–N(5)
Ag(1)–N(6)
N(5)–Ag(1)–N(2)
N(2)–Ag(1)–N(6)
N(2)–Ag(1)–N(3)
at 293(2) K with Mo–Ka radiation (k = 0.71073 A). The
2.293(5)
2.370(5)
138.46(17)
130.74(17)
71.81(13)
Ag(1)–N(2)
Ag(1)–N(3)
N(5)–Ag(1)–N(6)
N(5)–Ag(1)–N(3)
N(6)–Ag(1)–N(3)
2.302(3)
2.371(3)
71.44(17)
129.21(18)
125.03(18)
program SAINT [21] was used for integration of the dif-
fraction profiles. Semi-empirical absorption corrections
were applied using SADABS program [22]. All the struc-
tures were solved by direct methods using the SHELXS
program of the SHELXTL [23] package and refined by
full-matrix least-squares methods with SHELXL. Metal
atoms in each complex were located from the E-maps,
and other non-hydrogen atoms were located in successive
difference Fourier syntheses and refined with anisotropic
thermal parameters on F2. The hydrogen atoms of the
ligands were generated theoretically onto the specific atoms
and refined isotropically with fixed thermal factors. Crys-
tallographic data and experimental details for structural
analyses are summarized in Table 1. These crystallographic
data files in CIF format were deposited in Cambridge Crys-
tallographic Data Center (CCDC Nos. 606061–606065 for
1–5). These data can be obtained from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; Fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk.
Complex 3
Ag(1)–N(5)
Ag(1)–N(6)
N(5)–Ag(1)–N(2)
N(2)–Ag(1)–N(6)
N(2)–Ag(1)–N(1)
2.257(3)
2.401(3)
153.28(11)
111.39(10)
70.86(11)
Ag(1)–N(2)
Ag(1)–N(1)
N(5)–Ag(1)–N(6)
N(5)–Ag(1)–N(1)
N(6)–Ag(1)–N(1)
2.275(3)
2.422(3)
71.88(11)
135.49(11)
102.49(10)
Complex 4
Ag(1)–N(4)
Ag(1)–N(3)
N(4)–Ag(1)–N(2)
N(2)–Ag(1)–N(3)
2.191(2)
2.342(2)
131.75(9)
72.13(8)
Ag(1)–N(2)
2.305(2)
N(4)–Ag(1)–N(3)
156.06(9)
Complex 5
Ag(1)–N(4)#1
Ag(1)–N(2)
N(4)#1–Ag(1)–N(1)
N(1)–Ag(1)–N(2)
2.183(3)
2.395(3)
159.98(11)
72.19(9)
Ag(1)–N(1)
2.257(3)
N(4)#1–Ag(1)–N(2)
127.81(10)
Symmetry code for 5: #1 ꢂx + 3/2, y ꢂ 1/2, ꢂz + 1/2.

70
C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
pyridyl rings of ligands, the strong absorption band at
ꢁ1575 cmꢂ1 resulting from the skeletal vibrations of the
aromatic rings of the free ligands blue-shifted to
ꢁ1600 cmꢂ1 in the complexes. The results of elemental
analysis are in agreement with the theoretical requirements
of these complexes.
3.2. Crystal structures
[Ag(L1)2](ClO4) 1. The crystal structure of 1 consists of
discrete [Ag(L1)2]+ and ClOꢂ4 . The perspective view of 1 is
shown in Fig. 1a and the selected bond distances and
angles are listed in Table 2. The coordination geometry
Fig. 2. View of (a) the coordination environment of Ag(I) in 2, (b) the 1D chain arrayed by the intermolecular p ꢀ ꢀ ꢀ p interactions and (c) the 2D network
formed through inter-chain C–H ꢀ ꢀ ꢀ O H-bonding interactions (partial naphthalene rings, H atoms, and ClOꢂ4 anions omitted for clarity).

C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
71
˚
around the Ag(I) center could be described as a distorted
tetrahedron with the bond angles ranging from 71.20(2)°
to 146.05(2)°. All the Ag–N bond distances [2.253(4)–
separation and dihedral angle are 3.520, 3.486 A, and 2.2°,
respectively (Fig. 2b) [27]. Furthermore, the adjacent 1D
chains were linked together to form a quasi-2D network
through the inter-chain C–H ꢀ ꢀ ꢀ O bonding between the
O atoms of the free ClOꢂ4 and H atoms of pyridine or pyr-
azole rings of distinct L2 ligands (C(12)–H(12) ꢀ ꢀ ꢀ O(3A))
and (C(35)–H(35) ꢀ ꢀ ꢀ O(4B)) (Fig. 2c). The separations of
C(12) ꢀ ꢀ ꢀ O(3A) and C(35) ꢀ ꢀ ꢀ O(4B) are 3.253 and
˚
2.416(4) A] fall into the normal ranges for such coordina-
tion complexes (see Table 2) [26]. L1 adopts N,N-bidentate
chelating coordination mode to form two five-membered
chelating cycles (Ag–N–C–C–N) with Ag(I) center, namely,
Ag(1)–N(2)–C(10)–C(11)–N(3) and Ag(1)–N(5)–C(25)–
C(26)–N(6) with the N–Ag–N angles of 72.31(2)° for
N(2)–Ag(1)–N(3)° and 71.20(2)° for N(5)–Ag(1)–N(6),
respectively.
˚
3.410 A, with the angles for C(12)–H(12) ꢀ ꢀ ꢀ O(3A) and
C(35)–H(35) ꢀ ꢀ ꢀ O(4B) of 151.98° and 173.81°, respectively
(symmetry code A = ꢂx + 1, ꢂy + 1, ꢂ0.5 + z; B =
ꢂx + 0.5, y ꢂ 0.5, z ꢂ0.5, see Table 3) [29].
It should be noted that, due to the flexibility of the meth-
ylene group, the phenyl group of L1 can turn freely to offer
a suitable space for intermolecular edge-to-face C–H ꢀ ꢀ ꢀ p
interaction with the pyridyl–pyrazole ring of another L1
ligand from the adjacent [Ag(L1)2]+ units [d = 2.7989 and
[Ag(L3)(HL3)](ClO4)2(CH3CN) 3. Complex 3 consists of
a discrete [Ag(L3)(HL3)]2+, two ClO4ꢂ and one CH3CN
molecule (Fig. 3a). Similar to 1 and 2, in 3, the coordina-
tion geometry of Ag(I) is also a distorted tetrahedron coor-
dinated by four N donors of two distinct L3 ligands. All the
´
˚
2.8489 A; A = 166.99° and 169.04°; d and A stand for the
˚
Ag–N bond distances [2.257(3)–2.422(3) A] are in the nor-
H ꢀ ꢀ ꢀ p separations and C–H ꢀ ꢀ ꢀ p angles in the C–H ꢀ ꢀ ꢀ p
patterns, respectively]. Additionally, the adjacent discrete
[Ag(L1)2]+ units are arranged into a one-dimensional
(1D) chain by the combination of the weak intermolecular
C–H ꢀ ꢀ ꢀ p interaction mentioned above and pꢀ ꢀ ꢀp interac-
tions between the pyridyl–pyrazole ring of one L1 and
pyridine ring of another distinct L1 with the closest
mal range for such analogous complexes [26] and the bond
angles around each Ag(I) range from 70.86(1)° to
153.28(1)° (see Table 2). L3 also adopts N,N-bidentate che-
lating coordination mode with Ag(I) center forming five-
membered cheating cycles in which the N–Ag–N angles
are 70.85(1)° for N(2)–Ag(1)–N(1)° and 71.89(1)° for
N(5)–Ag(1)–N(6). However, L3 does not use the N donor
of its quinoline ring to coordinate to the Ag(I) center in
the course of the formation of 3, even though its electron
density of N donor was much higher than those of 3-(2-
pyridyl)pyrazole of L3 (see below, Scheme 1), which may
be due to the steric hindrance of the quinoline ring. It
should be pointed out that in each mononuclear unit
[Ag(L3)(HL3)]2+ of 3, N(8) donor of quinoline ring in L3
is protonated for the charge balance of the whole complex
(Fig. 3a) and presents a strong hydrogen-bonding interac-
˚
centroid–centroid distances of 3.580 A, and the average
˚
interplanar separation of 3.440 A and the dihedral angle
of 1.5°, respectively (Fig. 1b) [27,28].
[Ag(L2)2](ClO4) 2. The crystal structure of 2 consists of
[Ag(L2)2]+ and uncoordinated ClOꢂ4 , which has a similar
coordination geometry to that of 1. The perspective view
of the mononuclear entity in 2 with atomic labeling is given
in Fig. 2a and the selected bond distances and angles are
also listed in Table 2. Each Ag(I) center is four-coordinated
by four N donors of pyridyl–pyrazole rings from two L2
ligands, then giving a distorted tetrahedral geometry. All
˚
the Ag–N bond distances [2.293(5)–2.371(3) A] are within
Table 3
the normal range expected for such coordination bond dis-
tances and angles around each Ag(I) center ranging from
71.44(2)° to 138.46(2)° (see Table 2) [26]. Moreover, the
Ag–N distances formed by N(3) and N(6) of the pyridine
˚
Hydrogen–bonding geometry (A, °) for complexes 2–5
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
2
C(12)–H(12)ꢀ ꢀ ꢀO(3A)
C(35)–H(35)ꢀ ꢀ ꢀO(4B)
3
0.930
0.930
2.403
2.484
3.253
3.410
151.98
173.81
˚
˚
rings [Ag–N(3) = 2.371(3) A and Ag–N(6) = 2.370(5) A]
are a little longer than those formed by N(2) and N(5) of
˚
the pyrazole rings [Ag–N(2) = 2.302(3) A and Ag–
N(5) = 2.293(5) A]. Similar to 1, in 2, L also adopts
C(7)–H(7A)ꢀ ꢀ ꢀO(1A)
C(34)–H(34A)ꢀ ꢀ ꢀO(3A)
C(2)–H(2B)ꢀ ꢀ ꢀO(2B)
C(8)–H(8C)ꢀ ꢀ ꢀO(4C)
N(8)–H(8A)ꢀ ꢀ ꢀO(5D)
4
0.930
0.930
0.930
0.930
0.860
2.517
2.535
2.585
2.542
1.975
3.349
3.200
3.462
3.414
2.766
148.92
128.73
157.27
156.19
152.42
2
˚
N,N-bidentate chelating coordination mode to form two
five-membered Ag–N–C–C–N cycles [Ag(1)–N(2)–C(14)–
C(15)–N(3) and Ag(1)–N(5)–C(33)–C(34)–N(6) with the
N–Ag–N angles of N(2)–Ag(1)–N(3) = 71.81(1)° and
N(5)–Ag(1)–N(6) = 71.44(2)°, respectively].
However, different from 1, in 2, all the aromatic rings
are almost parallel to each other to form a suitable space
for intermolecular p ꢀ ꢀ ꢀ p interactions between the
pyridyl–pyrazole and naphthalene rings from other L2
ligands (Fig. 2b). Thus, the adjacent [Ag(L2)2]+ units are
arranged into 1D chain through the p ꢀ ꢀ ꢀ p interactions.
The closest centroid–centroid distance, average interplanar
C(2)–H(2A)ꢀ ꢀ ꢀO(4A)
C(11)–H(11A)ꢀ ꢀ ꢀO(2B)
C(12)–H(12A)ꢀ ꢀ ꢀO(2C)
C(13)–H(13A)ꢀ ꢀ ꢀO(3C)
5
0.930
0.930
0.930
0.930
2.540
2.498
2.600
2.590
3.450
3.173
3.395
3.321
166.08
129.61
143.80
135.89
C(8)–H(8A)ꢀ ꢀ ꢀO(2A)
0.930
2.515
3.381
154.78
Symmetry code for 2: A ꢂx + 1, ꢂy + 1, z ꢂ 0.5, B ꢂx + 0.5, y ꢂ 0.5,
z ꢂ 0.5; for 3: A ꢂx + 1, y ꢂ 0.5, ꢂz + 0.5, B ꢂx + 1, ꢂy, ꢂz, C ꢂx + 1,
ꢂy, ꢂz + 1, D x, y ꢂ 1, z; for 4: A ꢂx, ꢂy + 1, ꢂz, B 1 ꢂ x, ꢂy + 1, 1 ꢂ z,
C ꢂx, ꢂy + 1, 1 ꢂ z; for 5: A x + 0.5, ꢂy + 0.5, z + 0.5.

72
C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
Fig. 3. View of (a) the coordination environment of Ag(I) in 3 with the intramolecular p ꢀ ꢀ ꢀ p interactions, (b) the 1D chain constructed via C–H ꢀ ꢀ ꢀ
O H-bonding with l4-ClOꢂ bridging mode and (c) the 2D network formed through inter-chain p ꢀꢀꢀ p interactions (partial H atoms and ClOꢂ4 omitted for clarity).
4

C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
73
Scheme 1. The optimized conformations for 3-(2-pyridyl)pyrazole and L1–L5 showing the calculated electron density distributions for N donors (H atoms
omitted for clarity).
tions with the O(5D) atom of the uncoordinated ClOꢂ4 [the
dihedral angle being 3.658, 3.565 A, and 3.1°, respectively
(Fig. 3c) [27].
˚
N(8) ꢀ ꢀ ꢀ O(5D) and H(8A) ꢀ ꢀ ꢀ O(5D) separations are 1.975
˚
and 2.766 A, N(8)–H(8A) ꢀ ꢀ ꢀ O(5D) angle is 152.42°, sym-
Complexes 1–3 have similar subunit and metal coordi-
nation geometries, however, their stacking patterns in the
crystals are obviously different: 1 forms a linear 1D chain
through intermolecular C–H ꢀ ꢀ ꢀ p and p ꢀ ꢀ ꢀ p stacking
interactions, while 2 and 3 are 2D network via intermolec-
ular C–H ꢀ ꢀ ꢀ O H-bonding and p ꢀ ꢀ ꢀ p interactions. These
results indicate that the different pendant aromatic groups
in L1–L3 ligands may greatly influence the stacking mode
of their complexes in the solid state.
metry code D = x, y ꢂ 1, z see Table 3]. Moreover, in 3, the
centroid–centroid separations, interplanar separations and
dihedral angles between the pyridyl–pyrazole and quinoline
rings from adjacent L3 ligands are falling into 3.595–3.618,
˚
3.448–3.583 A, and 2.4–13.3°, respectively, showing the
obvious existence of the intramolecular p ꢀ ꢀ ꢀ p interactions
(see also Fig. 3a) [27].
Different from 1 and 2, an interesting feature of 3 resides
in the unique l4-ClOꢂ bridging mode, to link the
{[Ag(L4)](ClO4)}2 4. The structure of 4 consists of a cen-
trosymmetric dinuclear [Ag2(L4)2]2+ unit and two ClO4ꢂ. The
dinuclear [Ag2(L4)2]2+ cation (Fig. 4a) comprises two ligand
L4 and two Ag(I) ions. Each Ag(I) center takes a slightly
distorted trigonal planar geometry formed by three N
donors, two from the pyridyl–pyrazole ring of one L4, and
one from the pendant pyridine ring of another L4. All the
Ag–N bond distances and bond angles around each Ag(I)
center are in the normal range of such complexes
4
[Ag(L3)(HL3)]2+ cationic units to form an extended 1D
chain through C–H ꢀ ꢀ ꢀ O bonding interactions between
the O atoms of ClOꢂ4 and H atoms of the pyridine, pyra-
zole, and quinoline rings of distinct L3 ligands (Fig. 3b).
The separations of C(7) ꢀ ꢀ ꢀ O(1A), C(34) ꢀ ꢀ ꢀ O(3A),
C(2) ꢀ ꢀ ꢀ O(2B), and C(8) ꢀ ꢀ ꢀ O(4C) are 3.349, 3.200, 3.462,
˚
and 3.414 A with the angles for C(7)–H(7A) ꢀ ꢀ ꢀ O(1A),
C(34)–H(34A) ꢀ ꢀ ꢀ O(3A),
C(2)–H(2B) ꢀ ꢀ ꢀ O(2B),
and
˚
C(8)–H(8C) ꢀ ꢀ ꢀ O(4C) of 148.92°, 128.73°, 157.27°, and
156.19°, falling into the normal range of the C–H ꢀ ꢀ ꢀ O
bonding respectively (symmetry code A = ꢂx + 1,
y ꢂ 0.5, 0.5 ꢂ z; B = 1 ꢂ x, ꢂy, ꢂz; C = 1 ꢂ x, ꢂy, 1 ꢂ z
also see Table 3) [29].
[2.191(2)–2.342(2) A and 72.13(8)–156.06(9)° region,
respectively,] (Table 2) [26]. Meanwhile, each uncoordinated
ClOꢂ4 anion shows Ag ꢀ ꢀ ꢀ O weak coordination with the
Ag(I) centers (the Ag ꢀ ꢀ ꢀ O distances being 2.933 and
˚
3.183 A).
In addition, the quinoline rings of L3 form the intermo-
lecular p ꢀ ꢀ ꢀ p interactions with the pyridyl–pyrazole rings
from adjacent molecules, which further assemble the adja-
cent 1D chains into quasi-2D network, with the centroid–
centroid separation, average interplanar separation and
In addition, the adjacent discrete dinuclear [Ag2(L4)2]2+
units are assembled into a 1D chain by the combination of
the weak face-to-face p ꢀ ꢀ ꢀ p stackings (closest centroid–
˚
centroid separation of 3.758 A between the pyridyl–pyra-
zole rings) and the C–H ꢀ ꢀ ꢀ O H-bonding interactions

74
C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
Fig. 4. View of (a) the coordination environment of Ag(I) in 4 with the intramolecular Agꢀ ꢀ ꢀO weak interactions, (b) the 1D chain formed by the
intermolecular C–Hꢀ ꢀ ꢀO H-bonding and pꢀ ꢀ ꢀp interactions between dinuclear subunits and (c) the 2D network formed through inter-chain C–Hꢀ ꢀ ꢀO H-
bonding interactions (partial H atoms and ClOꢂ4 omitted for clarity).
between O atoms of the ClOꢂ4 anions and H atoms of the
pyridyl–pyrazole as well as pendant pyridine rings of
distinct L4 ligands [C(2)–H(2A) ꢀ ꢀ ꢀ O(4A) and (C(11)–
H(11A) ꢀ ꢀ ꢀ O(2B)) (Fig. 4b). The separations of
C(2) ꢀ ꢀ ꢀ O(4A) and C(11) ꢀ ꢀ ꢀ O(2B) are 3.450 and
H(12A) ꢀ ꢀ ꢀ O(2C) and C(13)–H(13A) ꢀ ꢀ ꢀ O(3C)] with the
˚
separations of 3.395 and 3.321 A for C(12) ꢀ ꢀ ꢀ O(2C) and
C(13) ꢀ ꢀ ꢀ O(3C) and the angles of 143.80° and 135.89° for
C(12)–H(12A) ꢀ ꢀ ꢀ O(2C) and C(13)–H(13A) ꢀ ꢀ ꢀ O(3C),
respectively (symmetry code C = ꢂx, ꢂy + 1, 1 ꢂ z see also
Table 3) (Fig. 4c) [29].
˚
3.173 A, with the angles for C(2)–H(2A) ꢀ ꢀ ꢀ O(4A)
and C(11)–H(11A) ꢀ ꢀ ꢀ O(2B) of 166.08° and 129.61°,
respectively (symmetry code A = ꢂx, ꢂy + 1, ꢂz and
B = ꢂx + 0.5, y ꢂ 0.5, z ꢂ 0.5 see also Table 3) [29]. Also,
the adjacent 1D chains were further linked to form a quasi-
2D network through the intermolecular C–H ꢀ ꢀ ꢀ O bond-
ing interactions between O atoms of the ClOꢂ4 anions and
{[Ag(L5)](ClO4)} 5. Different from 4, the crystal
1
structure of 5 consists of ClOꢂ4 and 1D chain cations
{[AgL5]+} (Fig. 5a and b). In the cationic chain, there
1
is only one crystallographic independent Ag(I) center
which, similar to 4, adopts a distorted trigonal planar
coordination geometry finished by three N donors, two
from the pyridyl–pyrazole ring of one L5 and one from
H
atoms of the pendant pyridine rings [C(12)–

C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
75
Fig. 5. View of (a) the coordination environment of Ag(I) in 5, (b) the 1D chain structure with the intra-chain Agꢀ ꢀ ꢀO weak interactions and (c) the 2D
network formed through inter-chain C–Hꢀ ꢀ ꢀO hydrogen-bonding interactions (partial H atoms and ClOꢂ4 omitted for clarity).
the pendant pyridine ring of another L5. The free ClO4ꢂ
N–Ag–N angles in 72.19(9)–159.98(1)°. L5 coordinates
to the Ag(I) centers adopting N,N-bidentate chelating
and terminal bridging modes, then resulting in an infinite
helical chain with the intramolecular Ag ꢀ ꢀ ꢀ Ag separation
anions show weak coordination with Ag(I) centers with
˚
the Ag ꢀ ꢀ ꢀ O distances of 2.944 and 3.024 A, respectively.
˚
The Ag–N bond distances [2.183(3)–2.395(3) A] fall in
˚
the expected range for such complexes [26] and the
of 7.787 A.

76
C.-S. Liu et al. / Journal of Molecular Structure 843 (2007) 66–77
Furthermore, the adjacent 1D chains are linked together
aromatic groups. Meanwhile, various intra- or inter-molec-
ular weak interactions, such as H-bonding, C–H ꢀ ꢀ ꢀ p and
p ꢀ ꢀ ꢀ p interactions, also play important roles in the forma-
tion of 1–5, especially in the aspect of linking the discrete
subunits or low-dimensional entities into high-dimensional
supramolecular networks. Moreover, the coordination
behaviors of L1–L5 ligands have been briefly investigated
by DFT calculations and the results indicate that electron
density or spatial position of coordinated N donors in
the pendant aromatic groups of L1–L5 ligands may jointly
affect the final crystal structures, which offer us an effective
means to construct unique supramolecular complexes with
tailored structures.
to form a quasi-2D network through the co-effects of
the weak Ag ꢀ ꢀ ꢀ O interaction aforementioned and the
C–H ꢀ ꢀ ꢀ O H-bonding interactions between O atoms of the
free ClOꢂ4 anions and H atoms of the pendant pyridine
rings [C(8)–H(8A) ꢀ ꢀ ꢀ O(2A)] with the separation of
˚
3.381 A for C(8) ꢀ ꢀ ꢀ O(8A) and the angle of 154.78° for
C(8)–H(8A) ꢀ ꢀ ꢀ O(2A), respectively (symmetry code
A = x + 0.5, ꢂy + 0.5, z + 0.5 see also Table 3) (Fig. 5c) [29].
In comparing with 4, 5 does not form discrete structure
but a 1D helical chain, which may be ascribed to the differ-
ent positions of N donors in the pendant pyridine rings of
L4 and L5 because the electron density of the three N
donors are almost the same with each other based upon
those theoretical results (see Scheme 1 and discussion
below). In fact, the electron density and spatial positions
of the coordinated N donor as well as the steric hindrance
of the different aromatic pendant groups of ligands L1–L5
may jointly affect the final crystal structures of 1–5.
Acknowledgements
This work was supported by the National Natural
Science Funds for Distinguished Young Scholars of
China (No. 20225101) and NSFC (Nos. 20373028 and
20531040).
3.3. Theoretical computational results
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In order to explore the underlying relationship between
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L5 ligands and the spatial structures of their complexes
from the standpoint of electronic effect, ab initio and
density functional theory (DFT) calculations of the five
ligands L1–L5, as well as 3-(2-pyridyl)pyrazole for com-
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tries of the coordinated ligands in 1–5 were carried out
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same with each other and the different crystal structures
of them (diunclear structure for L4 and 1D helical chain
for L5) obviously result from the different positions of
its N donors in the pyridine rings.
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