Structure and photoluminescence of silver(i) trinuclear halopyrazolato complexes

Article abstract of DOI:10.1039/c4dt01978d

Five halogen substituted pyrazolates, 4-chloro-3,5-diisopropylpyrazole (4-Cl-3,5-iPr₂pzH), 4-bromo-3,5-diisopropylpyrazole (4-Br-3,5-iPr₂pzH), 4-iodo-3,5-diisopropylpyrazole (4-I-3,5-iPr₂pzH), 4-chloro-3,5-diphenylpyrazole

Full text of DOI:10.1039/c4dt01978d

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Structure and photoluminescence of silver(I)
trinuclear halopyrazolato complexes†
Yui Morishima,a David James Youngb and Kiyoshi Fujisawa*a
Cite this: Dalton Trans., 2014, 43,
15915
Five halogen substituted pyrazolates, 4-chloro-3,5-diisopropylpyrazole (4-Cl-3,5-iPr2pzH), 4-bromo-3,5-
diisopropylpyrazole (4-Br-3,5-iPr2pzH), 4-iodo-3,5-diisopropylpyrazole (4-I-3,5-iPr2pzH), 4-chloro-3,5-
diphenylpyrazole (4-Cl-3,5-Ph2pzH), and 4-bromo-3,5-diphenylpyrazole (4-Br-3,5-Ph2pzH), were con-
veniently prepared by halogenation of the appropriate pyrazoles with N-halosuccinimides (NXS) (X = Cl,
Br, and I) followed by complexation of the pyrazolate anions with silver(I) nitrate. Single crystal X-ray analy-
sis revealed either dimeric trinuclear {[Ag(μ-4-X-3,5-R2pz)]3}2 (R = iPr, X = Cl, Br, and I) or trinuclear
[Ag(μ-4-X 3,5-R2pz)]3 (R = iPr, X = I; R = Ph, X = Cl, R = Ph, X = Br) structures, the latter held together
with argentophilic interactions (Ag⋯Ag interactions) that could also be observed in the Raman spectra.
The electronegativity of the halogen substituent could be correlated with the strength of the Ag⋯Ag
interaction and the wavelength of solid-state photoluminescence. All complexes were emissive on UV
irradiation at low temperatures, with the colour of emission from the diisopropyl substituted analogues
red shifted by the halogens in the order Cl (red) > Br (orange) > I (yellow). Emission from the diphenyl
substituted analogues was dominated by the extended aromatic system and was largely invariant to the
halogens.
Received 1st July 2014,
Accepted 25th August 2014
DOI: 10.1039/c4dt01978d
www.rsc.org/dalton
Introduction
Metal pyrazolato complexes have been studied for over 100
years.1,2 Early studies suggested that silver(I) pyrazolate existed
as a polymeric 1D chain [Ag(pz)]n (pz = pyrazolate anion,
C3H3N2−).3 Subsequent ab initio powder XRD evidence indi-
cated that silver(I) pyrazolate could exist as either a coordi-
nation polymer [Ag(pz)]n with an intermolecular Ag⋯Ag
distance of 3.27 Å or as a dimeric trinuclear {[Ag(pz)]3}2 struc-
ture with an intermolecular Ag⋯Ag distance of 3.43 Å, depend-
ing on the method of synthesis.4 The pyrazolate ligand bridges
silver(I) ions in a N–Ag–N linear coordination mode,1,5 with
additional stabilization of the silver(I) ions provided by argen-
tophilic interactions (Ag⋯Ag interactions).6
Fig. 1 Different structures of silver(I) pyrazolato complexes; left: poly-
nuclear, center: trinuclear, right: tetranuclear.7–9
ring (Fig. 1).7–9 The first single crystal X-ray diffraction charac-
terization of a dimeric trinuclear complex with the 3,5-diphe-
nylpyrazolate ligand ({[Ag(μ-3,5-Ph2pz)]3}2) was reported by
Fackler and co-workers in 1989.10 Since then, many silver(I)
pyrazolato structures have been characterized (see Table 1).9,11–21
The dimeric trinuclear (hexanuclear) structure is stabilized by
intermolecular argentophilic interaction(s).4,9–13,15–17,19–21
The silver(I) 3,5-diisopropylpyrazolato complex ({[Ag(μ-3,5-
iPr2pz)]3}2) displays two intermolecular argentophilic inter-
actions (Fig. 2, left).11 Introducing a bromine at the 4-position
of the pyrazolate ligand yields the silver(I) 4-bromo-3,5-diiso-
propylpyrazolato complex ({[Ag(μ-4-Br-3,5-iPr2pz)]3}2) with
three intermolecular argentophilic interactions (Fig. 2,
middle).11 Nitration of the 4-position of the pyrazolate ion
and subsequent complexation yields the trinuclear silver(I) 3,5-
Silver(I) pyrazolato complexes form polynuclear, trinuclear,
and tetranuclear structures, depending on the method of syn-
thesis and the nature of the substituents on the pyrazolate
aDepartment of Chemistry, Ibaraki University, Mito 310-8512, Japan
bSchool of Science, Monash University, 47500 Bandar Sunway, Selangor D.E.,
Malaysia. E-mail: kiyoshif@mx.ibaraki.ac.jp
†Electronic supplementary information (ESI) available: X-ray crystallographic
and refinement data for complexes [Ag(L1Cl)]2, [Ag(L1I)], [Ag(L1I)]2, and
[Ag(L5Cl)] (Table S1); experimental details for [Ag(L1Br)]2, [Ag(L5H)]2, and
[Ag(L5Br)]; IR, far-IR and Raman spectra for L1 and L5 complexes (Fig. S1);
emission wavelengths at variable temperatures (Table S2). CCDC 993077,
993079, 993080 and 993082. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c4dt01978d
This journal is © The Royal Society of Chemistry 2014
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Table 1 Bond distances (Å) and angles (°) for trinuclear and dimeric trinuclear complexes {[Ag(μ-pz)]3}1 or 2
Ag–N (range)
N–Ag–N (range)
Intra Ag⋯Ag (range)
Inter Ag⋯Ag (shortest)
References
{[Ag(μ-3,5-iPr2pz)]3}2
2.048(3)–2.088(3)
2.055(12)–2.097(11)
2.053(4)–2.094(4)
2.064(8)–2.117(7)
2.061(6)–2.116(6)
2.073(4)–2.106(4)
2.088(8)–2.101(8)
2.054(10)–2.122(10)
2.13(2)–2.24(2)
2.028(51)–2.049(46)
2.058(11)–2.111(10)
2.095(7)–2.147(6)
2.072(5)–2.128(5)
2.081(5)–2.095(6)
2.097(7)–2.138(6)
2.081(3)–2.096(3)
2.076(3)–2.084(3)
2.086(3)–2.093(4)
2.084(8)–2.095(8)
2.098(4)–2.112(4)
2.102(3)–2.115(3)
2.087(11)–2.142(10)
2.074(6)–2.120(6)
2.073(9)–2.092(9)
2.013(2)–2.101(2)
170.21(13)–177.68(13)
169.4(5)–172.0(5)
168.61(16)–172.89(16)
173.4(3)–179.2(3)
171.3(2)–172.9(3)
171.17(17)–172.30(16)
176.3(3)–177.2(3)
170.1(4)–178.4(4)
172.1(7)–177(1)
3.324–3.489
3.3927(16)–3.5445(16)
3.413–3.489
3.3975(12)–3.4461(18)
3.4007(8)–3.4428(10)
3.35–3.52
3.4547(18)–3.5421(14)
3.43–3.63
3.414(6)–3.449(6)
3.318(9)–3.388(11)
3.333–3.470
3.458–3.585
3.296–3.529
3.3719(7)–3.4586(8)
3.382–3.458
3.440–3.541
3.392–3.493
3.413–3.489
3.394–3.448
3.460–3.498
3.443–3.491
3.655–3.702
2.9870(4)
3.1003(17)
3.0438(5)
—
3.2049(7)
2.9712(14)
—
11
{[Ag(μ-4-Cl-3,5-iPr2pz)]3}2
{[Ag(μ-4-Br-3,5-iPr2pz)]3}2
[Ag(μ-4-I-3,5-iPr2pz)]3
This work
11
This work
This work
{[Ag(μ-4-I-3,5-iPr2pz)]3}2
{[Ag(μ-3,5-Ph2pz)]3}2
12
[Ag(μ-4-Cl-3,5-Ph2pz)]3
[Ag(μ-4-Br-3,5-Ph2pz)]3
{[Ag(μ-pz)]3}2
This work
13
4
—
3.431(4)
3.230(13)
3.2027(16)
3.524(1)
—
{[Ag(μ-3,5-Me2pz)]3}2
—
14
13
13
11
9
13
15–17
17
17
17
18
18
19
20
21
21
{[Ag(μ-3-Ph-5-Me-pz)]3}2
{[Ag(μ-3-o-Cl-Phpz)]3}2
[Ag(μ-4-NO2-3,5-iPr2pz)]3
[Ag(μ-3-iPr-5-tBupz)]3
174.5(4)–178.7(4)
176.5(3)–178.4(3)
170.52(19)–178.20(18)
177.5(2)–179.2(2)
171.7(3)–176.7(3)
172.01(12)–177.69(13)
177.78(10)–178.62(10)
166.94(16)–172.99(15)
174.1(4)–179.3(3)
177.7(2)–178.5(1)
176.8(1)–178.9(1)
166.1(4)–176.1(4)
170.7(2)–174.9(2)
172.3(4)–178.2(4)
171.26(9)–173.86(9)
—
{[Ag(μ-4-Br-3-tBupz)]3}2
{[Ag(μ-3,5-(CF3)2pz)]3}2
{[Ag(μ-3-(CF3)-5-Me-pz)]3}2
{[Ag(μ-3-(CF3)-5-tBu-pz)]3}2
[Ag(μ-3-(C3F7)-5-tBupz)]3
[Ag(μ-4-Cl-3,5-(CF3)2pz)]3
[Ag(μ-4-Br-3,5-(CF3)2pz)]3
{[Ag(μ-2-{3(5)-pz}py)]3}2
{[Ag(μ-3,5-(iPrSCH2)2pz)]3}2
[Ag(μ-3,5-(p-F-PhSCH2)2pz)]3
{[Ag(μ-4-Ph-3,5-(PhSCH2)2pz)]3}2
3.142(3)
3.2037(4)
3.3553(4)
3.4804(7)
—
—
—
3.227(2)
3.041(1)
—
3.453–3.700
3.468–3.564
3.486–3.629
3.2435(3)
1.52 V)27 and luminescent silver(I) materials are, therefore, an
attractive target with potential applications in light-emitting
devices.
We now report the influence of halogen substituents at the
4-position of the pyrazolate ligands on the structures and lumi-
nescence properties of the corresponding silver(I) complexes.
We also report a convenient and versatile synthetic route to
these ligands. Halogenation of pyrazoles can be achieved
with Cl2, NaOCl/CH3COOH, Br2, Br2/CH3COOH, I2/KI/Na2CO3,
I2/NaI/CH3COONa, I2/(NH4)2[Ce(NO3)6], I2/LiN(CH(CH3)2)2,
I2/H2O2, KICl2, I2/NaI/Na2CO3, I2/NaI/K2CO3, I2/HIO3, and
ICl.28–30 These reagents are, however, toxic and corrosive and
halogenations often require high temperatures and long reac-
tion times. We therefore investigated the use of the more con-
veniently handled N-halosuccinimides31 as an alternative and
achieved good yields at room temperature with simple product
isolation.
Silver(I) 3,5-diisopropylpyrazolato complexes bearing chlor-
ine ([Ag(L1Cl)]2) and iodine ([Ag(L1I)]n (n = 1 or 2)) at the
4-position were synthesized together with the corresponding
3,5-diphenyl analogue bearing chlorine ([Ag(L5Cl)]). The struc-
tures of [Ag(L1H)]2, [Ag(L1Br)]2, [Ag(L5H)]2, and [Ag(L5Br)]
have been previously reported.10–13 Their resynthesis
here allows a systematic study of the influence of halogen at
the 4-position on the structural and emissive properties of
these complexes.
Fig. 2 Schematic diagram of trinuclear complexes indicating inter-
actions;11 left: {[Ag(μ-3,5-iPr2pz)]3}2, center: {[Ag(μ-4-Br-3,5-iPr2pz)]3}2,
right: {[Ag(μ-4-NO2-3,5-iPr2pz)]3}2. : silver(I) ion, : pyrazolate ion,
O atom of NO2 substituent, • • •: Ag–O contacts.
:
diisopropyl-4-nitropyrazolato complex ([Ag(μ-4-NO2-3,5-iPr2pz)]3)
without any intermolecular argentophilic interactions.11 In
this case, the oxygen atoms of the NO2 coordinate with an
adjacent silver(I) ion, forming a dimeric structure (Fig. 2,
right).
Silver(I) pyrazolato trinuclear complexes (Ag3) can exhibit
luminescence,16,22 self-assembly,23 and remarkable π acid/base
interactions.24,25 Luminescent transition-metal complexes are
an attractive research area because of their potential appli-
cations in display devices and chemosensors.26 The silver(I)
3,5-bis(trifluoromethyl)pyrazolato
complex
({[Ag(μ-3,5-
(CF3)2pz)]3}2) exhibits efficient UV→blue internal conversion
1
attributable to LMMCT absorption below 290 nm at 77 K and
3MM emission from a Ag⋯Ag excited state.16 This emission is
highly temperature dependent and influenced by π–π inter-
action with aromatic solvents.25 There are, however, relatively
few published investigations of luminescent silver(I) pyrazolato
complexes correlating emission with the nature of the substi-
tuents on the pyrazolate ring. Silver(I) is the most stable of the
Group 11 ions (standard reduction potential E0 (V versus NHE
Experimental
Materials
(normal hydrogen electrode)); Cu2+ + e− = Cu+: 0.159 V, Ag2+
+
The preparation and handling of all the complexes were per-
e− = Ag+: 1.98 V, Au+ + e− = Au: 1.83 V and Au3+ + 3e− = Au: formed under an argon atmosphere using standard Schlenk
15916 | Dalton Trans., 2014, 43, 15915–15928
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tube techniques. Dichloromethane was carefully purified by Preparation of ligands
distillation from phosphorous pentoxide under an argon
atmosphere.32 Tetrahydrofuran and diethyl ether were distilled
4-Cl-3,5-iPr2pzH (L1Cl-H). A solution of N-chlorosuccini-
from sodium benzophenone ketyl under an argon atmos- mide (5.28 g, 39.5 mmol) in acetone (60 cm3) was added drop-
phere.32 Super-dehydrated n-hexane was purchased from Wako wise to
solution of L1H-H (5.00 g, 32.8 mmol) in
a
Pure Chemical Ind. Ltd and deoxygenated by purging with dichloromethane (20 cm3) over 15 min. After stirring for
argon gas. Deuteriochloroform was obtained from Cambridge 5 hours, the solvent was evaporated under vacuum and the
Isotope Laboratories, Inc. Other reagents are commercially resulting solid was extracted with hexane (100 cm3) to remove
available and were used without further purification. The 3,5- succinimide. The filtrate was then washed with H2O, dried
diisopropyl-1-pyrazole (3,5-iPr2pzH = L1H-H) and 3,5-diphenyl- over anhydrous magnesium sulfate and evaporated under
1-pyrazole (3,5-Ph2pzH = L5H-H) were prepared by published vacuum to provide a white powder that was recrystallized from
methods.33 The 4-halo-3,5-diphenyl-1-pyrazoles (4-X-3,5- acetonitrile at 0 °C. Colorless crystals (4.98 g, 26.7 mmol, yield
Ph2pzH = L5X-H) were synthesized by halogenation of the 81%) were filtered and dried under vacuum. IR (KBr, cm−1):
corresponding pyrazole using N-halosuccinimides (NXS) by a 3166vs (N–H), 3094vs (N–H), 2973vs (C–H, aliphatic), 2932vs
modification of a literature method.31 Although the synthesis (C–H, aliphatic), 2884vs (C–H, aliphatic), 2811vs (C–H, ali-
of 4-halo-3,5-dimethyl-1-pyrazoles using N-halosuccinimides phatic), 1574s (CvN), 1487s, 1469s, 1447s, 1422w, 1387m,
has been reported, the synthesis of the corresponding 4-halo- 1366s, 1335m, 1310m, 1276vs, 1170m, 1143m, 1112s, 1078vs,
3,5-diisopropyl-1-pyrazoles (4-X-3,5-iPr2pzH = L1X-H) using 1051m, 1011vs, 961w, 923w, 884m, 733w, 711w, 682w, 621w,
these reagents has not been previously published.31g Some of 588m, 539w, 500w, 469w. Raman (solid, cm–1): 3170w (N–H),
the chemical properties of [Ag(L1H)]2, [Ag(L1Br)]2, [Ag(L5H)]2, 3090w (N–H), 2975vs (C–H, aliphatic), 2912vs (C–H, aliphatic),
and [Ag(L5Br)] have been previously reported.10–13 These com- 2873vs (C–H, aliphatic), 2758w, 2719w, 2587w, 1569w (CvN),
pounds were remade here to allow a more detailed comparison 1484m, 1466m, 1450s, 1421s, 1388w, 1368w, 1336m, 1307s,
of their spectroscopic properties with those of the new 1278m, 1182w, 1145w, 1113m, 1081m, 1062m, 1001w, 962m,
members in the series. Pyrazolate anions were obtained by 926w, 881s, 685w, 635s, 588w, 543s, 503m, 460w, 429w, 359w,
1
the reaction of the corresponding pyrazoles with 1 equiv. of 281m, 239m, 190w. H-NMR (CDCl3, 500 MHz): δ 1.30 (d, J =
sodium hydride in diethyl ether at room temperature for 7.0 Hz, 12H, CHMe2), 3.07 (sept, J = 7.0 Hz, 2H, CHMe2), 10.19
1–2 hours.9
(s, br, 1H, NH). 13C-NMR (CDCl3, 125 MHz): δ 21.4 (CHMe2),
25.9 (CHMe2), 104.9 (C–Cl), 150.3 (pz-C3,5). Anal. Calc. for
C9H15ClN2: C 57.90, H 8.10, N 15.01; Found: C 57.78, H 8.17,
Measurements
IR spectra (4000–400 cm−1) were recorded on KBr pellets using N 14.96.
JASCO FT/IR-6300 spectrophotometer. Raman spectra
a
4-Br-3,5-iPr2pzH (L1Br-H). This ligand was prepared by a
(4000–50 cm−1) were measured in solid-disks on a JASCO procedure analogous to that used for L1Cl-H using 2.28 g
RFT600 spectrophotometer with a 500 mW YAG laser. Far-IR (15.0 mmol) of L1H-H. Colorless crystals (2.33 g, 10.1 mmol,
spectra (800–150 cm−1) were recorded on CsI pellets using a yield 67%) were isolated from acetonitrile at 0 °C. IR (KBr,
JASCO FT/IR 6200 spectrophotometer. Abbreviations used in cm−1): 3158vs (N–H), 3085vs (N–H), 2968vs (C–H, aliphatic),
the description of vibration data are as follows: vs, very strong; 29 328vs (C–H, aliphatic) 2873vs (C–H, aliphatic) 2810vs (C–H,
s, strong; m, medium; w, weak. 1H and 13C NMR spectra aliphatic), 2362w, 1570s (CvN), 1484s, 1468s, 1420w, 1382m,
(500 MHz and 125 MHz respectively) were obtained on a 1364s, 1334m, 1309m, 1299m, 1270s, 1169m, 1143m, 1111s,
Bruker AVANCE-500 NMR spectrometer at room temperature 1071s, 1051m, 1041s, 1009vs, 925w, 883m, 835m, 731w, 703w,
1
(298 K) in CDCl3. H and 13C chemical shifts were reported as 620w, 581m, 490w. Raman (solid, cm−1): 3167w (N–H), 2972vs
δ values relative to residual solvent peaks. Some 13C NMR (C–H, aliphatic), 2913vs (C–H, aliphatic), 2871vs (C–H, ali-
signals for [Ag(L5Br)] were not observed due to the low solubi- phatic), 2765w, 2716w, 1570w (CvN), 1465s, 1447s, 1420s,
lity of this complex. Electronic absorption spectra (solution 1390w, 1369w, 1335w, 1306m, 1272m, 1181w, 1112m, 1076m,
and solid, 200–800 nm) were recorded on a JASCO V-560 1053w, 1002w, 961m, 882s, 625s, 515m, 494m, 368m, 277m,
1
spectrophotometer. Solid samples (mulls) for spectroscopy 224m. H-NMR (CDCl3, 500 MHz): δ 1.30 (d, J = 7.0 Hz, 12H,
that were prepared by finely grinding microcrystalline material CHMe2), 3.06 (sept, J = 7.0 Hz, 2H, CHMe2), 10.92 (s, br, 1H,
into powders with a mortar and pestle and then adding NH). 13C-NMR (CDCl3, 125 MHz): δ 21.6 (CHMe2), 26.5
mulling agents (poly(dimethylsiloxane), viscosity 10 000) (CHMe2), 91.0 (C–Cl), 151.5 (pz-C3,5). Anal. Calc. for
(Aldrich) were uniformly spread between quartz plates. Lumi- C9H15BrN2: C 46.77, H 6.54, N 12.12; Found: C 46.50, H 6.53,
nescence spectra were recorded on a JASCO FP-6500 (solid, N 12.03.
300–750 nm) spectrofluorometer. Low temperature electronic
4-I-3,5-iPr2pzH (L1I-H). This ligand was prepared by a pro-
absorption and luminescence spectra were recorded using cedure analogous to that used for L1Cl-H, using 1.27 g
solid samples cooled with a liquid nitrogen cooled cryostat (8.34 mmol) of L1H-H. Colorless crystals (1.34 g, 4.82 mmol,
(CoolSpeK) from Unisoku Scientific Instruments (Osaka, yield 58%) were isolated from acetonitrile at 0 °C. IR (KBr,
Japan). The elemental analyses (C, H, and N) were performed cm−1): 3151vs (N–H), 3068vs (N–H), 2966vs (C–H, aliphatic),
by the Chemical Analysis Center of Ibaraki University.
2930vs (C–H, aliphatic), 2870vs (C–H, aliphatic), 2802vs (C–H,
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aliphatic), 1560m (CvN), 1480s, 1463s, 1416w, 1382m, 1364s, Preparation of complexes
1330w, 1294w, 1265s, 1167w, 1110m, 1071s, 1032s, 1007vs,
960w, 924w, 885m, 730w, 701w, 617w, 574m, 486w. Raman
(solid, cm−1): 3155w (N–H), 2968vs (C–H, aliphatic), 2928vs (265 mg, 1.27 mmol) in tetrahydrofuran (10 cm3) was added
(C–H, aliphatic), 2909vs (C–H, aliphatic), 2870vs (C–H, dropwise to suspension of silver(I) nitrate (217 mg,
{[Ag(μ-4-Cl-3,5-iPr2pz)]3}2 ([Ag(L1Cl)]2). A solution of NaL1Cl
a
aliphatic), 2758w, 2716w, 1556w (CvN), 1462s, 1446s, 1.28 mmol) in tetrahydrofuran (10 cm3) over 15 min. The reac-
1416s, 1388m, 1369m, 1333m, 1305m, 1267m, 1251m, tion was protected from light, and after stirring for 16 hours,
1186w, 1149w, 1112m, 1075m, 1042w, 1000w, 960m, 927w, the solvent was evaporated under vacuum. The resulting solid
881s, 688w, 620s, 575w, 499s, 473w, 446w, 386w, 351m, 304m, was extracted with dichloromethane (40 cm3) to remove
1
277m, 208m. H-NMR (CDCl3, 500 MHz): δ 1.30 (d, J = 7.0 Hz, sodium nitrate. The filtrate was evaporated under vacuum to
12H, CHMe2), 3.03 (sept, J = 7.0 Hz, 2H, CHMe2), 11.32 provide a white powder that was recrystallized from hexane at
(s, br, 1H, NH). 13C-NMR (CDCl3, 125 MHz): δ 21.9 (CHMe2), −15 °C. Colorless crystals (154 mg, 0.0874 mmol, yield 41%)
27.7 (CHMe2), 59.2 (C–Cl), 153.9 (pz-C3,5). Anal. Calc. for were filtered and dried under vacuum. IR (KBr, cm−1): 2965vs
C9H15IN2: C 38.86, H 5.44, N 10.07; Found: C 38.70, H 5.42, (C–H, aliphatic), 2929 (C–H, aliphatic), 2868s (C–H, aliphatic),
N 10.08.
1505m (CvN), 1455m, 1383s, 1364s, 1299w, 1280m, 1261m,
4-Cl-3,5-Ph2pzH (L5Cl-H). N-Chlorosuccinimide (1.81 g, 1146s, 1115m, 1092s, 1044m, 1034m, 921w, 880w, 802m,
13.6 mmol) and L5H-H (3.00 g, 13.6 mmol) were dissolved in 558w. Far-IR (CsI, cm−1): 670w, 658w, 598m, 579s (C–Cl), 559s,
acetonitrile (20 cm3) and stirred for 3 hours at 70 °C. The 511m (Ag–N), 441w, 375vs, 350s, 293vs, 276s, 256vs, 194w,
solvent was evaporated under vacuum and the resulting solid 176w. Raman (solid, cm−1): 2971vs (C–H, aliphatic), 2912vs
was extracted with chloroform (40 cm3) to remove succinimide. (C–H, aliphatic), 2869vs (C–H, aliphatic), 2758w, 2714w,
The filtrate was washed with H2O, dried with anhydrous mag- 1495m (CvN), 1445s, 1430m, 1368s, 1304m, 1283m, 1182w,
nesium sulfate and evaporated to provide a white powder that 1152w, 1110m, 1053w, 958m, 882s, 745w, 729w, 707w, 655m,
was recrystallized from chloroform at 0 °C. Colorless crystals 599w, 573s (C–Cl), 511m (Ag–N), 427w, 337w, 269m, 197m
1
(0.645 g, 2.53 mmol, yield 19%) were filtered and dried under (Ag⋯Ag). H-NMR (CDCl3, 500 MHz): δ 1.41 (d, J = 7 Hz, 72H,
vacuum. IR (KBr, cm−1): 3197m (N–H), 3158m (C–H, aliphatic), CHMe2), 3.13 (sept, J = 7 Hz, 12H, CHMe2). 13C-NMR (CDCl3,
1604w, 1581w, 1561m, 1492m (CvN), 1472m, 1440m, 1385m, 125 MHz): δ 22.2 (CHMe2), 28.4 (CHMe2), 103.9 (C–Cl), 155.6
1311w, 1293w, 1257m, 1210w, 1134s, 1074m, 1025m, 1003w, (pz-C3,5). UV–Vis (solution, cyclohexane, λmax/nm (ε/cm–1 mol–1
990m, 957vs, 915m, 767vs, 721m, 693vs, 659m, 581m, 539m, dm3)): 226 (30 400). UV–Vis (solid, nujol, nm): 225. Emission
482w. Raman (solid, cm−1): 3067m (C–H, aromatic), 1606vs, (solid, 299 K, λmax/nm): 312, 373.5, 620, 721 (ex. 280 nm). Anal.
1556m (CvN), 1517m, 1448m, 1427m, 1395m, 1296w, 1262w, Calc. for C54H84Ag6Cl6N12: C 36.82, H 4.81, N 9.54; Found:
1221w, 1180w, 1161m, 1033w, 1003m, 993s, 845w, 770w, 706w, C 36.68, H 4.70, N 9.46.
671m, 618w, 553w, 506w, 485w, 405w, 361w, 347w, 287m,
[Ag(μ-4-I-3,5-iPr2pz)]3 ([Ag(L1I)]) and {[Ag(μ-4-I-3,5-iPr2pz)]3}2
1
245m, 220m. H-NMR (CDCl3, 500 MHz): δ 7.41 (t, J = 7.2 Hz, ([Ag(L1I)]2). This complex was prepared by a procedure analo-
2H, p-Ph), 7.46 (t, J = 7.2 Hz, 4H, m-Ph), 7.81 (s, br, 4H, o-Ph), gous to that used for [Ag(L1Cl)]2, substituting NaL1I (540 mg,
10.93 (s, br, 1H, NH). 13C-NMR (CDCl3, 125 MHz): δ 106.3 1.80 mmol). Colorless crystals (376 mg, 0.326 mmol, yield
(pz-C4), 126.0 (p-Ph), 127.9 (m-Ph), 129.1 (o-Ph). Anal. Calc. for 54%) were isolated from dichloromethane–hexane at −15 °C.
C15H11ClN2: C 70.73, H 4.35, N 11.00; Found: C 71.07, H 4.41, Both [Ag(μ-4-I-3,5-iPr2pz)]3 and {[Ag(μ-4-I-3,5-iPr2pz)]3}2 were
N 11.06.
obtained from the same solution. Attempts to separate these
4-Br-3,5-Ph2pzH (L5Br-H). This ligand was prepared by a complexes from one another were not successful (see Syn-
procedure analogous to that used for L5Cl-H, using 3.00 g thesis). These colorless crystals were filtered and dried under
(13.6 mmol) of L5H-H (3.00 g, 13.6 mmol). Colorless crystals vacuum. IR (KBr, cm−1): 2963vs (C–H, aliphatic), 2925vs (C–H,
(1.63 g, 5.45 mmol, yield 40%) were isolated from chloroform aliphatic), 2864s (C–H, aliphatic), 1498s (CvN), 1456s, 1429m,
at 0 °C. IR (KBr, cm−1): IR (KBr, cm−1): 3200m (N–H), 3059w 1381m, 1362s, 1301m, 1276m, 1169m, 1141s, 1104s, 1089s,
(C–H, aromatic), 1604w, 1580m, 1560m, 1489s (CvN), 1468s, 1038s, 922w, 877w, 724w, 583w, 551m, 503w. Far-IR (CsI,
1449s, 1392m, 1332w, 1312w, 1293w, 1255s, 1219w, 1210w, cm−1): 653w, 641w, 598w, 582w, 554w, 534m (C–I), 499m (Ag–
1150w, 1121s, 1074m, 1025m, 1001w, 981m, 958vs, 917m, N), 483w, 454m, 387s, 364w, 337m, 246vs, 192vs. Raman
757vs, 718m, 695vs, 660m, 575s, 513s. Raman (solid, cm−1): (solid, cm−1): 2961s (C–H, aliphatic), 2907v (C–H, aliphatic),
3068m (C–H, aliphatic), 1607vs, 1553m (CvN), 1517m, 2877s (C–H, aliphatic), 2864s (C–H, aliphatic), 2751w, 2710w,
1447m, 1423m, 1396m, 1294w, 1258w, 1186w, 1158m, 1032w, 1478m (CvN), 1442s, 1368s, 1306m, 1276m, 1174m, 1146m,
1002s, 984s, 844w, 768w, 669m, 618w, 525w, 479w, 405w, 1110m, 1085m, 1037s, 958m, 879s, 711w, 636s, 531s (C–I),
361w, 324w, 258m, 241m, 221w. 1H-NMR (CDCl3, 500 MHz): 498m (Ag–N), 456w, 373m, 338w, 269m, 227m, 196w (Ag⋯Ag).
δ 7.42 (t, J = 6.9 Hz, 2H, p-Ph), 7.46 (t, J = 6.9 Hz, 4H, m-Ph), 1H-NMR (CDCl3, 500 MHz): δ 1.43 (d, J = 7.1 Hz, 36H, CHMe2),
7.78 (s, br, 4H, o-Ph), 11.05 (s, br, 1H, NH). 13C-NMR (CDCl3, 3.20 (sept, J = 7.1 Hz, 6H, CHMe2). 13C-NMR (CDCl3, 125 MHz):
125 MHz): δ 91.7 (pz-C4), 128.2 (m-Ph), 129.0 (o-Ph), 129.2 δ 22.7 (CHMe2), 29.7 (CHMe2), 56.3 (C–I), 159.6 (pz-C3,5). UV–
(p-Ph), Anal. Calc. for C15H11BrN2·1/4(CHCl3): C 55.65, H 3.48, Vis (cyclohexane, λmax/nm (ε/cm–1 mol–1 dm3)): 229.5 (35 000).
N 8.51; Found: C 55.64, H 3.50, N 8.65.
UV–Vis (nujol, nm): 230.5. Emission (solid, 299 K, λmax/nm):
15918 | Dalton Trans., 2014, 43, 15915–15928
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Table 2 Selected distances (Å) for {[Ag(L1X)]}1 or 2 and {[Ag(L5X)]}1 or 2 complexes
pz-C4⋯pz-C4 short distancesa
Ag⋯X short distances
References
{[Ag(μ-3,5-iPr2pz)]3}2 {[Ag(L1H)]}2
{[Ag(μ-4-Cl-3,5-iPr2pz)]3}2 {[Ag(L1Cl)]}2
{[Ag(μ-4-Br-3,5-iPr2pz)]3}2 {[Ag(LBr)]}2
[Ag(μ-4-I-3,5-iPr2pz)]3 [Ag(L1I)]
{[Ag(μ-4-I-3,5-iPr2pz)]3}2 {[Ag(L1I)]}2
{[Ag(μ-3,5-Ph2pz)]3}2 {[Ag(L5H)]}2
[Ag(μ-4-Cl-3,5-Ph2pz)]3 [Ag(L5Cl)]
[Ag(μ-4-Br-3,5-Ph2pz)]3 [Ag(L5Br)]
5.52–5.91
4.99(3)–5.39(2)
5.31–5.53
11
This work
11
This work
This work
12
This work
13
3.3677(12) (X = I)
3.5043(7), 3.5698(8) (X = I)
6.13(1)–7.56(1)
5.18–6.27
3.345(4), 3.395(4), 3.448(4) (X = Cl)
3.208 (X = Br)
a pz-C4⋯pz-C4 short distance: the distance between C4 of adjacent pyrazolates.
314, 363.5, 621, 700 (ex. 280 nm). Anal. Calc. for crystals to detector distance was ca. 45 mm. Data were col-
C27H42Ag3I3N6: C 28.08, H 3.67, N 7.28; Found: C 27.85, H lected using 0.5° intervals in φ and ω to a maximum 2θ value
3.53, N 7.28.
of 55.0°. A total of 744 oscillation images were collected. The
[Ag(μ-4-Cl-3,5-Ph2pz)]3 ([Ag(L5Cl)]). This complex was pre- highly redundant data sets were reduced using CrystalClear
pared by a procedure analogous to that used for [Ag(L5H)]2, and corrected for Lorentz and polarization effects.34,35 An
substituting NaL5Cl (107 mg, 0.385 mmol). Colorless crystals empirical absorption correction was applied for each complex.
(61.4 mg, 0.0566 mmol, yield 44%) were isolated from dichloro- Structures were solved by direct methods (SIR9736 or SIR9237).
methane at −25 °C. IR (KBr, cm−1): 3063m (C–H, aromatic), The position of the silver(I) ions and their first coordination
3025m (C–H, aromatic), 2963m, 1950w, 1883w, 1807w, 1760w, sphere were located from a direct method E-map; other non-
1685w, 1603m, 1577m, 1463s (CvN), 1438s, 1407w, 1323m, hydrogen atoms were found in alternating difference Fourier
1297m, 1261s, 1191m, 1144s, 1096s, 1073s, 1030s, 916m, syntheses,38 and least-squares refinement cycles and during
867w, 800s, 766s, 731m, 696vs, 604m, 586m, 509w (Ag–N), the final cycles were refined anisotropically (CRYSTALSTRUC-
477m, 436w. Far-IR (CsI, cm−1): 619m, 605vs, 588m (C–Cl), TURE).34,39 Refinement was carried out by a full matrix least-
556w, 509s (Ag–N), 498w, 479s, 434s, 404m, 389m, 357m, squares method on F2. All calculations were performed using
320m, 299m, 290m, 265s, 236w, 223s, 154m. Raman (solid, the CrystalStructure program. Crystallographic data and struc-
cm−1): 3068m (C–H, aromatic), 1605vs, 1578w, 1521s, 1466w ture refinement parameters including the final discrepancies
(CvN), 1440s, 1409s, 1324m, 1299m, 1276w, 1182w, 1158w, (R and Rw) are listed in Tables S1 (ESI†). Solvent molecules
1034w, 1004s, 991s, 969w, 844w, 768w, 698w, 675m, 619m, were highly disordered in the structure of [Ag(L1Cl)]2 and
1
582w (C–Cl), 510w (Ag–N), 406w, 360w, 287w. H-NMR (CDCl3, these atoms were refined isotropically. There were also some
500 MHz): δ 7.18 (t, J = 7 Hz, 12H, m-Ph), 7.31 (t, J = 7 Hz, 6H, disorder in the isopropyl groups (C31 and C41) of [Ag(L1Cl)]2
p-Ph), 7.58 (d, J = 7 Hz, 12H, o-Ph). 13C-NMR (CDCl3, and (C21 and C39) in [Ag(L1I)]2. Large solvent accessible voids
125 MHz): δ 106.2 (pz-C4), 127.9 (o-Ph), 129.0 (m-Ph), 128.9 were observed in the structure of [Ag(L1I)]. They are presum-
(p-Ph), 131.8 (Ph-C1), 151.2 (pz-C3,5). UV–Vis (solution, CH2Cl2, ably filled with severely disordered isopropyl groups, which
λmax/nm (ε/cm–1 mol–1 dm3)): 242 (93 100). UV–Vis (solid, could not be modeled by the present analysis. Observed reflec-
nujol, nm): 249. Emission (solid, 299 K, λmax/nm): 320.5, 634.5 tions were too low for [Ag(L5Cl)] and so a 2 sigma cutoff was
(ex. 280 nm). Anal. Calc. for C45H30Ag3Cl3N6: C 49.83, H 2.79, applied for this calculation. The absolute structures were
N 7.75; Found: C 49.72, H 2.75, N 7.69.
deduced based on Flack parameters40 of 0.25(8) refined using
3956 Friedel pairs for [Ag(L1I)] and 0.06(3) refined using 3170
Friedel pairs for [Ag(L5Cl)]. Additional refinement details are
contained in the CIF files (ESI†). Instrument parameters,
crystal data, and data collection parameters for all the com-
plexes are summarized in Table S1.† Selected bond distances
are listed in Tables 1 and 2.
Crystal structure determination
Single crystals of [Ag(L1Cl)]2, [Ag(L1I)], and [Ag(L1I)]2 for X-ray
analysis were obtained by recrystallization at −15 °C from
hexane and dichloromethane/hexane solutions, respectively.
Single crystals of [Ag(L5Cl)] for X-ray analysis were obtained
from dichloromethane at −25 °C.
Diffraction data were measured on a Rigaku mercury diffr-
actometer using graphite monochromated Mo Kα (λ
0.71070 Å) radiation at low temperature (−65 °C for [Ag-
(L1Cl)]2, −83 °C for [Ag(L1I)] and [Ag(L1I)]2, and at −70 °C for
=
Results and discussion
Synthesis
[Ag(L5Cl)]). All crystals were mounted on the tip of glass fibers The ligand syntheses are depicted in Scheme 1 and gave pure
using highly viscous oil. The unit cell parameters of each product in each case. The reactions of L1H-H and L5H-H with
crystal were determined using CrystalClear from 6 images. The the three different N-halosuccinimides (NXS, X = Cl, Br, and I)
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Scheme 1 Synthesis of ligands.
in appropriate solvents led to isolation of only the desired
products L1Cl-H, L1Br-H, L1I-H, L5Cl-H, and L5Br-H.
This method is more convenient than using the traditional
reagents listed above and more straightforward than ultrasonic
halogenation with NXS which requires specialized instrumen-
tation.31d,e,f
Scheme 2 Synthesis of complexes.
All of the seven complexes, prepared as depicted in
Scheme 2, gave satisfactory elemental analyses. The reactions
of silver(I) nitrate with the sodium salts of the five different
halogen substituted pyrazoles NaL1Cl, NaL1Br, NaL1I, NaL5Cl,
NaL5Br and two different non-substituted pyrazoles NaL1H
and NaL5H in appropriate solvents led to the isolation of
products [Ag(L1Cl)]2, [Ag(L1Br)]2, [Ag(L1I)]n, [Ag(L5Cl)],
[Ag(L5Br)], and [Ag(L1H)]2 and [Ag(L5H)]2, respectively.
[Ag(L1I)]n was obtained in two polymorphs. Both complexes
were obtained by recrystallization from the same solvent and
could not be separated. All complexes were stable when
shielded from light.
Structural characterization
Single-crystal X-ray structural analyses were performed on com-
pounds [Ag(L1Cl)]2, [Ag(L1I)], [Ag(L1I)]2, and [Ag(L5Cl)].
Diffraction data for the known silver(I) complexes [Ag(L1H)]2,
[Ag(L1Br)]2, [Ag(L5H)]2, and [Ag(L5Br)] were used for
comparison.10–13 The perspective drawings of these complexes
are given in Fig. 3 for [Ag(L1Cl)]2, Fig. 4 for [Ag(L1I)], Fig. 5 for
[Ag(L1I)]2, and Fig. 6 for [Ag(L5Cl)]. Selected bond distances,
intramolecular and intermolecular Ag⋯Ag distances, and
bond angles are summarized in Tables 1 and 2.
There are alternative, published protocols for synthesizing
silver(I) pyrazolato complexes. One method involves using
silver(I) oxide.8,11,15–18,21,23 However, this reaction needs to be
heated for some hours. The reaction of sodium pyrazolate with
silver(I) nitrate was therefore selected for our study.
{[Ag(μ-4-Cl-3,5-iPr2pz)]3}2 [Ag(L1Cl)]2 exists as a dimeric
trinuclear with three intermolecular argentophilic interactions
(Ag1⋯Ag4, 3.1003(17); Ag2⋯Ag5, 3.1298(15); Ag3⋯Ag6, 3.1051
(16) Å). These distances are significantly shorter than twice
Bondi’s van der Waals radius (3.44 Å = 1.72 Å × 2), indicating
Fig. 3 Left side: molecular structure of [Ag(L1Cl)]2, showing Ag⋯Ag intermolecular interactions (green lines), 50% displacement ellipsoids, and the
selected atom labeling scheme. Right side: packing diagram (ball and stick) of [Ag(L1Cl)]2, showing Ag⋯Ag intermolecular interactions (green lines).
Hydrogen atoms and solvent molecules are omitted for clarity. Color code: Ag, red; N, blue; Cl, orange.
15920 | Dalton Trans., 2014, 43, 15915–15928
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Fig. 4 Left side: molecular structure of [Ag(L1I)], showing 50% displacement ellipsoids and the selected atom labeling scheme. Right side: packing
diagram (ball and stick) of [Ag(L1I)], showing Ag⋯I weak interactions (dashed green lines). Symmetry operators: X + 1/2, −Y + 1/2, Z. Hydrogen atoms
are omitted for clarity. Color code: Ag, red; N, blue; I, violet.
Fig. 5 Left side: molecular structure of [Ag(L1I)]2, showing Ag⋯Ag intermolecular interactions (green lines), 50% displacement ellipsoids, and the
selected atom labeling scheme. Right side: packing diagram (ball and stick) of [Ag(L1I)]2, showing Ag⋯I weak interactions (dashed green lines).
Symmetry operators: −X + 2, −Y + 1, −Z + 1. Hydrogen atoms and solvent molecules are omitted for clarity. Color code: Ag, red; N, blue; I, violet.
Ag⋯Ag interaction.41 Moreover, the planes formed by the two
{[Ag(μ-4-Br-3,5-iPr2pz)]3}2 [Ag(L1Br)]2 also exists as a
Ag3N6 metallacycles completely overlap. The short distances dimeric trinuclear with three intermolecular argentophilic
between C4 atoms of adjacent pyrazolates (referred to as interactions.11 The intramolecular argentophilic interactions
pz-C4⋯pz-C4) for this dimer are in the range 4.99(3) to 5.39(2) in [Ag(L1Cl)]2 are only slightly weaker than those in
Å (Fig. 3 and Table 2). By comparison, the parent [Ag(L1H)]2 [Ag(L1Br)]2 (the average of three distances (Å) for [Ag(L1Cl)]2 is
has two intermolecular argentophilic interactions (Ag⋯Ag, 3.47 (ranging from 3.3927(16) to 3.5445(16)), while for
2.9870(4) Å) and the planes are only slightly overlapped.11 [Ag(L1Br)]2 it is 3.45 (ranging from 3.413 to 3.489)) but the
The pz-C4⋯pz-C4 distances in this complex are 5.52 and 5.91 Å intermolecular argentophilic interactions in [Ag(L1Cl)]2 are
– much longer than those of [Ag(L1Cl)]2 (Table 2) despite the significantly stronger than those in [Ag(L1Br)]2 (the average
relative bulk of chlorine versus hydrogen. We attribute this to value of three distances (Å) for [Ag(L1Cl)]2 is 3.11 (ranging
the relatively high electronegativity of chlorine that withdraws from 3.1003(17) to 3.1298(15)), while for [Ag(L1Br)]2 it is 3.23
electron density from the coordinating N and thus strengthens (ranging from 3.044 to 3.408)) (Table 1). The dimeric trinuclear
the intermolecular argentophilic interactions.
units of [Ag(L1Cl)]2 and [Ag(L1Br)]2 are structurally very
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Fig. 6 Left side: molecular structure of [Ag(L5Cl)], showing 50% displacement ellipsoids and the selected atom labeling scheme. Right side:
packing diagram (ball and stick) of [Ag(L5Cl)], showing Ag⋯Cl weak interactions (dashed green lines). Symmetry operators: X + 1/2, −Y + 1/2, Z.
Hydrogen atoms and solvent molecules are omitted for clarity. Color code: Ag, red; N, blue; Cl, orange.
similar. However, the packing of these dimers is quite is reduced. This is in contrast to the better overlap and shorter
different with [Ag(L1Cl)]2 units packed parallel to one another Ag⋯Ag contacts observed when comparing the parent
(Fig. 3), and [Ag(L1Br)]2 dimers packed perpendicular to adja- [Ag(L1H)]2 with the bulkier [Ag(L1Cl)]2.
cent dimers and parallel to diagonal dimers (data not shown).
The solid-state structures of 3,5-diphenylpyrazolato silver(I)
Two polymorphs of {[Ag(μ-4-I-3,5-iPr2pz)]3}n [Ag(L1I)]n (n = 1 complexes {[Ag(μ-4-X-3,5-Ph2Pz)]3}n (n = 1 or 2) (X = H and Br)
or 2) were prepared from the same reaction. {[Ag(μ-4-I-3,5- have been reported by Fackler, Raptis, and co-workers.10,12,13
iPr2pz)]3}n exists as a mixture of trinuclear metallacycles {[Ag(μ-3,5-Ph2Pz)]3}2 ([Ag(L5H)]2) has only one intermolecular
([Ag(L1I)]) (Fig. 4) with no close Ag⋯Ag contacts and the argentophilic interaction and exists as a dimeric trinuclear
corresponding dimeric trinuclear metallacycle ([Ag(L1I)]2) (Ag⋯Ag′, 2.9712(14) Å). By comparison, only soft–soft, Ag⋯X
(Fig. 5) with two argentophilic interactions (Ag1⋯Ag2′, 3.2049(7) interactions are observed for [Ag(μ-4-Cl-Ph2Pz)]3 ([Ag(L5Cl)])
Å) (Table 1). The structure of [Ag(L1I)]2 is similar to that of and [Ag(μ-4-Br-3,5-Ph2Pz)]3 ([Ag(L5Br)]) which exist as weakly
[Ag(L1H)]2 but with additional weak Ag⋯I interactions to bound 1D polymers (Fig. 6). No intermolecular argentophilic
neighbouring dimers. Similarly, one of the silver(I) ions of interactions were observed for these halogenated analogues,
monomeric [Ag(L1I)] interacts with one of the iodine substitu- as was the case for [Ag(L1I)]. The intermolecular distances in
ents of an adjacent [Ag(L1I)] unit, yielding a 1D polymer of tri- [Ag(L5Cl)] are 3.345(4) Å (Ag1⋯Cl41), 3.395(4) Å (Ag2⋯Cl41),
nuclear metallacycles. The distance between Ag1 and I1′ and 3.448(4) Å (Ag3⋯Cl41). The corresponding (Ag⋯Br) inter-
(symmetry operators: X + 1/2, −Y + 1/2, Z) is 3.3677(12) Å molecular distance in [Ag(L5Br)] is 3.208 Å (Table 2). Again,
(Fig. 4 and Table 2), which is shorter than the sum of Bondi’s these Ag⋯X contacts are shorter than the sum of Bondi’s van
van der Waals radii of Ag and I atoms (1.72 + 1.98 = 3.70 Å)41 der Waals radii of Ag and Cl (1.72 + 1.75 = 3.47 Å) and Ag and
and can be considered as a soft acid (Ag(I) ion), soft base Br (1.72 + 1.85 = 3.57 Å). Raptis and co-workers suggest that
(I substituent) interaction. The distances between Ag and I on the bromine substituent in [Ag(L5Br)] increases the π-acidity of
adjacent [Ag(L1I)]2 dimers are 3.5043(7) (Ag2-I2′) and 3.5698(8) the Ag3 face13 and it seems reasonable to us that this effect
(Ag3-I2′) Å (symmetry operators: –X + 2, Y + 1/2, −Z + 1/2) would be even greater for the chlorine analogue. The electron
(Fig. 5 and Table 2). Therefore, [Ag(L1I)]2 also exists as a withdrawing phenyl substituents of L5 also enhance this
loosely bonded 1D polymer in the solid state.
π-acidity as opposed to the electron release isopropyl substitu-
Not unexpectedly, as the 4-position halogens increase in ents of L1.13
size (Bondi’s van der Waals radii Cl (1.75 Å) < Br (1.85 Å) < I
In summary, a comparison of the four dimeric trinuclear
(1.98 Å))41 the overlap between Ag3N6 planes decreases. The L1 complexes ([Ag(L1H)]2, [Ag(L1Cl)]2, [Ag(L1Br)]2, and
three short pz-C4⋯pz-C4 distances in [Ag(L1Cl)]2, [Ag(L1Br)]2, [Ag(L1I)]2) revealed two intermolecular argentophilic inter-
and [Ag(L1I)]2 range from 4.99(3) to 5.39(2) Å, from 5.31 to actions for the complexes in which the substituent X = H and
5.53 Å, and from 6.13(1) to 7.56(1) Å, respectively (Table 2). I, and three intermolecular argentophilic interactions for X =
Finally, a comparison of Ag⋯Ag contacts as the halogens Cl and Br. This pattern does not correlate with the size of the
become larger reveals that the intermolecular argentophilic halogen substituents, but can be explained by the influence
interactions weaken, and distortion of the trinuclear structure of the more electronegative halogens on the metal. Only in
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Table 3 Selected IR, far-IR, Raman data of the complexes (cm−1
)
Far-IR
Raman
IR
ν(CvN)
ν(Ag–N)
ν(C–X)
ν(CvN)
ν(Ag–N)
ν(C–X)
ν(Ag⋯Ag)
Reference
[Ag(L1H)]2
[Ag(L1Cl)]2
[Ag(L1Br)]2
[Ag(L1I)]n
[Ag(L5H)]2
[Ag(L5Cl)]
[Ag(L5Br)]
1517
1505
1498
1498
1470
1463
1462
478
511
505
499
508
509
488
—
1516
1495
1499
1478
1464
1466
1465
477
511
506
498
510
510
488
—
207
197
186
196
244
—
9
579
545
534
—
588
549
573
533
531
—
582
546
This work
This work
This work
This work
This work
This work
—
[Ag(L1I)]2 were Ag⋯I interactions observed. By contrast, the suggests that the intermolecular Ag⋯Ag interactions and weak
solid-state structures of the 3,5-diphenylpyrazolato complexes Ag⋯X interactions observed in the solid state are not retained
[Ag(L5Cl)] and [Ag(L5Br)] are dominated by Ag⋯X, rather than in solution, or at least are not long-lasting relative to the NMR
by Ag⋯Ag interactions. Only in [Ag(L5H)]2 were Ag⋯Ag inter- timescale. Similarly, there were no differences in the NMR
molecular interactions observed. These results point to the spectra of the two polymorphs of [Ag(L1I)]n, or between
subtle interplay of electronic, more so than steric influences of [Ag(L1I)] and [Ag(L1I)]2, again suggesting the absence (or
the 3, 5 and 4 substituents that promote weak interactions only transitory existence) of these weak interactions in
with one another.
solution.
IR, far-IR, and Raman spectra of the L1 and L5 silver(I) com-
plexes are reproduced in Fig. S1 (see the ESI†) and selected
Spectroscopy
1
The H and 13C NMR signals of the ligands are quite different vibrational data are listed in Table 3. The CvN stretching
in chemical shifts from those of the trinuclear metallacycle vibrations in the L1 silver(I) complexes are shifted to
silver(I) pyrazolato complexes indicating that Ag–N coordi- ca. 1505 cm−1 (1517–1498 cm−1
)
from ca. 1563 cm−1
nation is retained in solution. The simplicity of the latter (1577–1556 cm−1) of the corresponding pyrazolate anions. The
Fig. 7 Electron absorption spectra (left: L1 complexes, right: L5 complexes: (a) solid (nujol), (b) solution, CH3CN: [Ag(L1H)]2, cyclohexane:
[Ag(L1Cl)]2, [Ag(L1Br)]2, [Ag(L1I)]n, CH2Cl2: [Ag(L5H)]2, [Ag(L5Cl)], and [Ag(L5Br)]); red: H, green: Cl, orange: Br, purple: I.
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Fig. 8 Emission spectra of L1 complexes at variable temperatures at 280 nm irradiation (aqua: 299 K, blue: 173 K, purple: 83 K).
halogen substituents exhibit a relatively small influence on
All Ag–N stretching vibrations were observed in the region
this vibration in the order I (1498 cm−1 in [Ag(L1I)]n) = Br 520 cm−1 to 480 cm−1 as expected.9,42 The Ag–N stretching
(1498 cm−1 in [Ag(L1Br)]2) < Cl (1505 cm−1 in [Ag(L1Cl)]2) < H vibrations were observed in the region 520 cm−1 to
(1517 cm−1 in [Ag(L1H)]2) which does not correlate with the 480 cm−1 9,42
and, for the L1 complexes, in the order
,
electronegativity of the substituents. The C–X stretching H (478 cm−1 in [Ag(L1H)]2) < I (499 cm−1 in [Ag(L1I)]n) < Br
vibrations could be observed in the far-IR spectra of (505 cm−1 in [Ag(L1Br)]2) < Cl (511 cm−1 in [Ag(L1Cl)]2)
[Ag(L1Cl)]2, [Ag(L1Br)]2, and [Ag(L1I)]n, at 579, 545, and which correlates with the electronegativity of the sub-
534 cm−1, respectively.42 These results are in agreement with stituent. No trend was identified for the corresponding L5
C–X bond distances (1.722(14) to 1.75(3) Å in [Ag(L1Cl)]2, 1.88 complexes.
to 1.90 Å in [Ag(L1Br)]2,11 and 2.072(9) to 2.102(8) Å in
[Ag(L1I)]n).
Raman spectroscopy revealed Ag⋯Ag stretching vibrations
for all complexes in which intermolecular argentophilic inter-
The same trend was seen in the corresponding vibrational actions were observed in the X-ray crystal structures, and for
spectra of the L5 silver(I) complexes. The CvN stretching two L5 complexes ([Ag(L5Cl)] and [Ag(L5Br)]) for which close
vibrations are shifted to ca. 1465 cm−1 (1462–1470 cm−1) from contacts were not observed. The frequency of these vibrations
ca. 1492 cm−1 (1495–1489 cm−1) of the corresponding pyrazo- was consistent with the bond distances: 207 cm−1 [Ag(L1H)]2
late anions and the CvN stretching vibrations are in the order (2.987 to 2.995 Å),11 197 cm−1 [Ag(L1Cl)]2 (3.1003(17) to
Br (1462 cm−1 in [Ag(L5Br)]) ≤ Cl (1463 cm−1 in [Ag(L5Cl)]) < 3.1298(15) Å), 186 cm−1 [Ag(L1Br)]2 (3.044 to 3.408 Å),11
H (1470 cm−1 in [Ag(L5H)]2). Similarly, the C–X stretching 196 cm−1 [Ag(L1I)]2 (3.2049(7) Å), 244 cm−1 [Ag(L5H)]2
vibrations were in agreement with the C–X distances, 588 cm−1 (2.9712(14) Å).12
for [Ag(L5Cl)]2 (1.742(9) to 1.768(11) Å) and 549 cm−1 for
[Ag(L1Br)] (1.870(12) to 1.889(12) Å).13
Electronic absorption spectra for the L1 and L5 complexes
acquired as Nujol suspensions and in solution are given in
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Fig. 9 Emission spectra of L5 complexes at variable temperatures at 280 nm irradiation (aqua: 299 K, blue: 173 K, purple: 83 K).
Fig. 7. These spectra were quite similar in both media. The
Omary and coworkers previously reported large thermo-
two polymorphs of [Ag(L1I)]n gave only one peak in solution or chromic shifts in the luminescence of trinuclear pyrazolato
in the solid state. These results suggest that the absorption metallacycle complexes of Cu, Ag, and Au.16 New, higher
bands do not arise from the intermolecular argentophilic energy emissions appeared in these compounds concomitant
interactions but from chromophores in the trinuclear metalla- with the disappearance of lower energy bands upon cooling,
cycles. DFT calculations reported by Omary and co-workers for resulting in dramatic colour changes from orange at 285 K to
similar coinage metal trinuclear pyrazolato metallacycle com- green at 77 K for the gold(I) trinuclear complex and from blue
plexes point to a transition from a filled orbital with strong (77 K) to UV emission (4 K) for the corresponding silver(I)
ligand character to a vacant molecular orbital mainly associ- trinuclear complex. No such “startling” change in the emission
ated with the trinuclear moiety.16 In our study, the order of the frequency was observed with our compounds (Fig. 8, 9 and
electronic absorption band maxima match the order of Ag–N Table S2†). However, temperature dependent emission at
bond lengths; 221 nm in [Ag(L1H)]2 (2.048(3) to 2.088(3) Å), 280 nm irradiation in the solid state at variable temperatures
225 nm in [Ag(L1Cl)]2 (2.055(12) to 2.097(11) Å), 227.5 nm in (299, 173, and 83 K) was observed.
[Ag(L1Br)]2 (2.053(4) to 2.094(4) Å), 230.5 nm in [Ag(L1I)]n
(2.061(6) to 2.117(7) Å) (Table 1). This correlation is consistent somewhat different from that of the halogenated analogues
with the Omary and co-workers proposition.16
(Fig. 8). The more intense emission spectra of [Ag(L1H)]2 at
The emission spectrum of [Ag(L1H)]2 in the solid state was
The electronic absorption bands for the L5 complexes were 83 K exhibited a vibronic structure around 345 nm and
much broader, presumably because of overlapping π–π* tran- 690 nm, while no vibronic progression was observed for the
sition bands associated with the phenyl substituents on the halogenated analogues at the same temperature. The latter
ligands and little structural information could be deduced displayed visible emission under UV lamp irradiation at
from these data.
liquid nitrogen temperatures and the colour of this
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emission correlated with the electronegativity of the halogen with the electronegativity of the halogen substituents and a
substituent: ([Ag(L1Cl)]2 red, [Ag(L1Br)]2 orange, [Ag(L1I)]n similar relationship was observed for the emission wavelength
yellow).
of the L1 complexes, pointing to a Ag–Ag excited state as pre-
By contrast, the emission spectra of L5 complexes at 83 K viously proposed. Emission from the L5 complexes was domi-
were dominated by intense emission bands from ca. 400 to nated by the extended π-system of this chromophore. Our
600 nm with the parent [Ag(L5H)]2 appearing more yellowish ongoing study will focus on this correlation of the electronic
than blue under UV lamp irradiation at liquid nitrogen temp- influences of the substituent on structure and emission
eratures (Fig. 9). Some vibrational structure was observed in colour tuning with a view to chemosensing and display
the parent and halogenated analogues and it seems reasonable applications.
to suggest that extended conjugation provided by the two
phenyl groups has red shifted the intense blue band observed
in the corresponding diisopropyl analogues.
Acknowledgements
This research was supported in part by the Ministry of Edu-
cation, Culture, Sports, Science and Technology (Scientific
Conclusion
Research on Innovative Areas “Stimuli-responsive Chemical
Four new silver(I) complexes {[Ag(μ-4-X-3,5-R2-pz)]3}n (R = iPr,
Species for the Creation of Functional Molecules” (25109505))
X = Cl, n = 2: [Ag(L1Cl)]2; R = iPr, X = I, n = 1: [Ag(L1I)], n = 2:
and by the Iwatani Naoji Foundation’s Research Grant.
[Ag(L1I)]2; R = Ph, X = Cl, n = 1: [Ag(L5Cl)]) have been syn-
thesized and structurally characterized together with the pre-
viously reported {[Ag(μ-4-X-3,5-R2pz)]3}n (R = iPr, X = H, n = 2:
[Ag(L1H)]2; R = iPr, X = Br, n = 2: [Ag(L1Br)]2; R = Ph, X = H, n = 2:
References
[Ag(L5H)]2; R = Ph, X = Br, n = 1: [Ag(L5Br)]). In the diisopro-
pyl (L1) analogues, two argentophilic interactions in
[Ag(L1H)]2 and [Ag(L1I)]2 and three in [Ag(L1Cl)]2 and
1996, 147, 247–297; (b) G. La Monica and G. A. Ardizzoia,
[Ag(L1Br)]2 were observed in the Raman spectra and X-ray
structures and relative strengths correlated with the electrone-
gativity of the halogens. Only silver(I) ion (soft acid) and iodide
ion (soft base) soft–soft interactions were observed in the X-ray
1 (a) A. P. Sadimenko and S. S. Basson, Coord. Chem. Rev.,
Prog. Inorg. Chem., 1997, 46, 151–238; (c) L. A. Oro,
M. A. Ciriano and C. Tejel, Pure Appl. Chem., 1998, 70, 779–
788; (d) M. A. Halcrow, Dalton Trans., 2009, 2059–2073;
(e) J. Pérez and L. Piera, Eur. J. Inorg. Chem., 2009, 4913–
structure of [Ag(L1I)]. Fewer argentophilic interactions were
4925; (f) A. Mohamed, Coord. Chem. Rev., 2010, 254, 1918–
observed in the corresponding diphenyl (L5) analogues. Only
1847; (g) M. Viciano-Chumillas, S. Tanase, L. J. de Jongh
one Ag⋯Ag contact was observed for X = H, [Ag(L5H)]2,
and J. Reedijk, Eur. J. Inorg. Chem., 2010, 3403–3418;
but only Ag⋯X contacts were observed for X = Cl and Br
(h) S. Fustero, M. Sánchez-Roselló, P. Barrio and A. Simón-
([Ag(L5Cl)] and [Ag(L5Br)]), in contrast to their L1 counterparts
(Fig. 10).
All complexes exhibited solid-state photoluminescence at
visible wavelengths at liquid nitrogen temperatures. The
strength of the argentophilic interactions could be correlated
Fuentes, Chem. Rev., 2011, 111, 6984–7034; (i) J.-P. Zhang,
Y.-B. Zhang, J.-B. Lin and X.-M. Chen, Chem. Rev., 2012,
112, 1001–1033.
2 E. Buchner, Chem. Ber., 1889, 22, 2165–2167.
3 (a) H. Okkersen, W. L. Groeneveld and J. Reedijk, Recl.
Trav. Chim. Pays-Bas, 1973, 92, 945–953; (b) J. G. Vos and
W. L. Groeneveld, Transition Met. Chem., 1979, 4, 137–141.
4 N. Masciocchi, M. Moret, P. Cairati, A. Sironi,
G. A. Ardizzoia and G. L. Monica, J. Am. Chem. Soc., 1994,
116, 7668–7676.
5 (a) S. Trofimenko, Chem. Rev., 1972, 72, 497–509;
(b) S. Trofimenko, Chem. Rev., 1993, 93, 943–980;
(c) S. Trofimenko, Scorpionates – The Coordination Chemistry
of Polypyrazolylborate Ligands, Imperial College Press,
London, 1999; (d) C. Pettinari and R. Pettinari, Coord.
Chem. Rev., 2005, 249, 525–543; (e) C. Pettinari and
R. Pettinari, Coord. Chem. Rev., 2005, 249, 663–691;
(f) F. Marchetti, C. Pettinari and R. Pettinari, Coord. Chem.
Rev., 2005, 249, 2909–2945; (g) C. Pettinari, Scorpionates II:
Chelating Borate Ligands, Imperial College Press, London,
2008.
6 (a) M. A. Omary, T. R. Webb, Z. Assefa, G. E. Shankle and
Fig. 10 Schematic diagram of the synthesized complexes.
15926 | Dalton Trans., 2014, 43, 15915–15928
H. H. Patterson, Inorg. Chem., 1998, 37, 1380–1386;
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
(b) M. A. Rawashdeh-Omary, M. A. Omary and 26 (a) M. Formica, V. Fusi, L. Giorgi and M. Micheloni, Coord.
H. H. Patterson, J. Am. Chem. Soc., 2000, 122, 10371–10380.
7 G. Yang and R. G. Raptis, Inorg. Chim. Acta, 2007, 360,
2503–2506.
Chem. Rev., 2012, 256, 170–192; (b) D.-L. Ma, V. P.-Y. Ma,
D. S.-H. Chan, K.-H. Leung, H.-Z. He and C.-H. Leung,
Coord. Chem. Rev., 2012, 256, 3087–3113.
8 U. J. Scheele, M. Georgiou, M. John, S. Dechert and 27 R. Parson, in Standard Potentials in Aqueous Solution, ed.
F. Meyer, Organometallics, 2008, 27, 5146–5151.
9 K. Fujisawa, Y. Ishikawa, Y. Miyashita and K. Okamoto,
Inorg. Chim. Acta, 2010, 363, 2977–2989.
10 H. H. Murray, R. G. Raptis and J. P. Fackler Jr., Inorg.
Chem., 1988, 27, 26–33.
11 H. V. R. Dias and H. V. K. Diyabalanage, Polyhedron, 2006,
25, 1655–1661.
12 A. A. Mohamed, L. M. Pérez and J. P. Fackler Jr., Inorg.
Chim. Acta, 2005, 358, 1657–1662.
13 G. Yang, P. Baran, A. R. Martínez and R. G. Raptis, Cryst.
Growth Des., 2013, 13, 264–269.
14 N. Masciocchi, P. Cairati and A. Sironi, Powder Diffr., 1998,
13, 35–40.
15 H. V. R. Dias, S. A. Polach and Z. Wang, J. Fluorine Chem.,
2000, 103, 163–169.
16 M. A. Omary, M. A. Rawashdeh-Omary, M. W. A. Gonser,
O. Elbjeirami, T. Grimes and T. R. Cundari, Inorg. Chem.,
2005, 44, 8200–8210.
A. J. Bard, R. Parsons and J. Jordan, Marcel Dekker,
New York, 1985, pp. 1–12.
28 L. E. Ochando, J. M. Amigó, J. Rius, D. Louër, Ch. Fontenas
and J. Elguero, J. Mol. Struct., 2001, 562, 11–17.
29 (a) M. K. Ehlert, A. Storr and R. C. Thompson,
Can. J. Chem., 1992, 70, 1121–1128; (b) M. I. Rodríguez-
Franco, I. Dorronsoro, A. I. Hernández-Higueras and
G. Antequera, Tetrahedron Lett., 2001, 42, 863–865;
(c) S. J. Garden, J. C. Torres, S. C. de S. Melo, A. S. Lima,
A. C. Pinto and E. L. S. Lima, Tetrahedron Lett., 2001, 42,
2089–2092; (d) R. E. Sammelson and J. E. Casida, J. Org.
Chem., 2003, 68, 8075–8079; (e) M. M. Kim, R. T. Ruck,
D. Zhao and M. A. Huffman, Tetrahedron Lett., 2008, 49,
4026–4028; (f) S. Guillou, O. Nesmes, M. S. Ermolenko and
Y. L. Janin, Tetrahedron, 2009, 65, 3529–3535; (g) S. Guillou,
F. J. Bonhomme, M. S. Ermolenko and Y. L. Janin, Tetrahe-
dron, 2011, 67, 8451–8457; (h) E. Salanouve, S. Guillou,
M. Bizouarne, F. J. Bonhomme and Y. L. Janin, Tetrahedron,
2012, 68, 3165–3171.
17 H. V. R. Dias, C. S. P. Gamage, J. Keltner,
H. V. K. Diyabalanage, I. Omari, Y. Eyobo, N. R. Dias, 30 Y. L. Janin, Chem. Rev., 2012, 112, 3924–3958.
N. Roehr, L. McKinney and T. Poth, Inorg. Chem., 2007, 46, 31 (a) D. R. Sliskovic, B. D. Roth, M. W. Wilson, M. L. Hoefle
2979–2987.
and R. S. Newton, J. Med. Chem., 1990, 33, 31–38;
(b) Y. R. Huang and J. A. Katzenellenbogen, Org. Lett., 2000,
2, 2833–2836; (c) A. S. Paulson, J. Eskildsen, P. Vedsø and
M. Begtrup, J. Org. Chem., 2002, 67, 3904–3907;
(d) H. A. Stefani, C. M. P. Pereira, R. B. Almeida,
R. C. Braga, K. P. Guzen and R. Cella, Tetrahedron Lett.,
2005, 46, 6833–6837; (e) S. L. Jeon, J. H. Choi, B. T. Kim
and I. H. Jeong, J. Fluorine Chem., 2007, 128, 1191–1197;
(f) G. Li, R. Kakarla and S. W. Gerritz, Tetrahedron Lett.,
2007, 48, 4595–4599; (g) Z.-G. Zhao and Z.-X. Wang, Synth.
Commun., 2007, 37, 137–147.
18 C. V. Hettiarachchi, M. A. Rawashdeh-Omary, D. Korir,
J. Kohistani, M. Yousufuddin and H. V. R. Dias, Inorg.
Chem., 2013, 52, 13576–13583.
19 K. Singh, J. R. Long and P. Stavropoulos, J. Am. Chem. Soc.,
1997, 119, 2942–2943.
20 F. Meyer, A. Jacobi and L. Zsolnai, Chem. Ber., 1997, 130,
1441–1447.
21 A. C. Jahnke, K. Pröpper, C. Bronner, J. Teichgräber,
S. Dechert, M. John, O. S. Wenger and F. Meyer, J. Am.
Chem. Soc., 2012, 134, 2938–2941.
22 T. Grimes, M. A. Omary, H. V. R. Dias and T. R. Cundari, 32 W. L. F. Armarego and D. D. Perrin, Purification of Labora-
J. Phys. Chem. A, 2006, 110, 5823–5830.
23 J.-P. Zhang and S. Kitagawa, J. Am. Chem. Soc., 2008, 130,
907–917.
24 (a) H. V. R. Dias and C. S. P. Gamage, Angew. Chem., Int.
Ed., 2007, 46, 2192–2194; (b) S. M. Tekarli, T. R. Cundari
and M. A. Omary, J. Am. Chem. Soc., 2008, 130, 1669–1675;
(c) D. M. M. Krishantha, C. S. P. Gamage, Z. A. Schelly and
tory Chemicals, Butterworth-Heinemann, Oxford, UK, 4th
edn, 1997.
33 (a) N. Kitajima, K. Fujisawa, C. Fujimoto and Y. Moro-oka,
Chem. Lett., 1989, 18, 421–424; (b) N. Kitajima, K. Fujisawa,
C. Fujimoto, Y. Moro-oka, S. Hashimoto, T. Kitagawa,
K. Toriumi, K. Tatsumi and A. Nakamura, J. Am. Chem.
Soc., 1992, 114, 1277–1291.
H. V. R. Dias, Inorg. Chem., 2008, 47, 7065–7067; 34 J. R. Carruthers, J. S. Rollett, P. W. Betteridge, D. Kinna,
(d) V. N. Tsupreva, A. A. Titov, O. A. Filippov,
A. N. Bilyachenko, A. F. Smol’yakov, F. M. Dolgushin,
L. Pearce, A. Larsen and E. Gabe, CRYSTAL ISSUE 11,
Chemical Crystallography Laboratory, Oxford, UK, 1999.
D. V. Agapkin, I. A. Godovikov, L. M. Epstein and 35 J. W. Pflugrath, CRYSTALCLEAR Ver. 1.3, Acta Crystallogr.,
E. S. Shubina, Inorg. Chem., 2011, 50, 3325–3331. Sect. D: Biol. Crystallogr., 1999, 55, 1718–1725.
25 (a) M. A. Omary, O. Elbjeirami, C. S. P. Gamage, 36 A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano,
K. M. Sherman and H. V. R. Dias, Inorg. Chem.,
2009, 48, 1784–1786; (b) M. A. Rawashdeh-Omary,
C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori
and R. Spagna, J. Appl. Crystallogr., 1999, 32, 115–119.
M. D. Rashdan, S. Dharanipathi, O. Elbjeirami, P. Ramesh 37 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
and H. V. R. Dias, Chem. Commun., 2011, 47, 1160–
1162.
M. C. Burla, G. Polidori and M. Camalli, J. Appl. Crystal-
logr., 1993, 26, 343–350.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15915–15928 | 15927

View Article Online
Paper
Dalton Transactions
38 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, 40 H. D. Flack, Acta Crystallogr., Sect. A, 1983, 39, 876–
R. de Gelder, R. Israel and J. M. M. Smits, DIRDIF99, Tech- 881.
nical Report of the Crystallography Laboratory, University 41 A. Bondi, J. Phys. Chem., 1964, 68, 441–451.
of Nijmegen, The Netherlands, 1999.
42 K. Nakamoto, Infrared and Raman Spectra of Inorganic and
39 CRYSTALSTRUCTURE 4.0, Crystal Structure Analysis Package,
Rigaku and Rigaku/MSC, 2000–2010.
Coordination Compounds, John Wiley and Sons, Inc.,
New York, USA, 6th edn, 2009.
15928 | Dalton Trans., 2014, 43, 15915–15928
This journal is © The Royal Society of Chemistry 2014