Cooperative metal-ligand influence on the formation of coordination polymers, and conducting and photophysical properties of Tl(i) β-oxodithioester complexes

Article abstract of DOI:10.1039/c8dt03694b

Eight novel Tl(i) β-oxodithioester complexes, [TlL]_n (1-8), with ligands, L = methyl-3-hydroxy-3-(2-furyl)-2-propenedithioate (L1), methyl-3-hydroxy-3-(2-thienyl)-2-propenedithioate (L2), methyl-3-hydroxy-3-(3-pyridyl)-2-propenedithioate (L3),

Full text of DOI:10.1039/c8dt03694b

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Cooperative metal–ligand influence on the
formation of coordination polymers, and
conducting and photophysical properties of Tl(I)
β-oxodithioester complexes†‡
Cite this: Dalton Trans., 2018, 47,
16264
Chote Lal Yadav,a Gunjan Rajput,b Krishna K. Manar,a Kavita Kumari,a
Michael G. B. Drewc and Nanhai Singh
*
a
Eight novel Tl(I) β-oxodithioester complexes, [TlL]n (1–8), with ligands, L = methyl-3-hydroxy-3-(2-furyl)-2-
propenedithioate (L1), methyl-3-hydroxy-3-(2-thienyl)-2-propenedithioate (L2), methyl-3-hydroxy-3-
(3-pyridyl)-2-propenedithioate (L3), methyl-3-hydroxy-3-(4-pyridyl)-2-propenedithioate (L4), methyl-3-
hydroxy-3-(9-anthracenyl)-2-propenedithioate (L5), methyl-3-hydroxy-3-(4-fluorophenyl)-2-propenedithio-
ate (L6), methyl-3-hydroxy-3-(4-chlorophenyl)-2-propenedithioate (L7) and methyl-3-hydroxy-3-(4-bromo-
phenyl)-2-propenedithioate (L8), were synthesized and thoroughly characterized by elemental analysis, and
IR, UV-Vis, 1H and 13C{1H} NMR spectroscopy, and their structures were ascertained by X-ray crystallography.
Complexes 1 and 2 crystallized in P21 and P212121 chiral space groups, respectively, and were studied using
Circular Dichroism (CD) spectra. Solid state structural analyses revealed that the β-oxodithioester ligands are
bonded to Tl(I) ions in (O, S) chelating and chelating–bridging modes, thereby forming different types of 1D
and 2D coordination polymeric structures. By considering the metal-assisted bonding interactions, various
coordination numbers of 5–8 and 10 are established around the metal centre. Except for 5 and 7a which
have Tl⋯Tl separations at 3.724(1) and 3.767(1), 3.891(1) Å respectively, the remaining complexes have no
Tl⋯Tl distances <4.0 Å. This indicates that the majority of structures contain only weak inter- and intra-
molecular thallophilic interactions. The structures of 1–8 highlight the role played by variations in substituents
in the dithioester unit in the structure and properties of the complexes. The multi-dimensional assembly in
these complexes rests on important non-covalent C–H⋯π (TlOSC3, chelate), C–H⋯X (X = F, Cl, O, N),
C–H⋯π, H⋯H and rare Tl⋯H–C intermolecular anagostic interactions. The Tl⋯H–C anagostic interactions
together with C–O⋯Tl and C–S⋯Tl interactions formed 7-, 11- and 12-membered chelate rings about the
metal centers. The anagostic interactions in 1, 2 and 7b were assessed by theoretical calculations. All the
complexes showed bright green luminescent emissions in solution and solid phases. Time-resolved emission
spectra revealed a triexponential decay curve and short mean lifetime for fluorescence behavior.
Received 12th September 2018,
Accepted 12th October 2018
DOI: 10.1039/c8dt03694b
rsc.li/dalton
unusual structures and properties due to their interesting
topologies and potential applications in optical, photo-, mole-
Introduction
Considerable attention has been devoted in recent years to the cular electrical and magnetic materials.1–5 In spite of their
synthesis of coordination polymers of transition metals with important optical and conducting properties and varied appli-
aDepartment of Chemistry, Institute of Science, Banaras Hindu University,
Varanasi-221005, India. E-mail: nsinghbhu@gmail.com, nsingh@bhu.ac.in
bDepartment of Chemistry, Ram Chandra Uniyal Government PG College,
Uttarkashi-249193, India
cDepartment of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK
†Part of the work was presented at ISACS: Challenges in Inorganic Chemistry,
April 10–13, 2017, Manchester, UK.
actions in 3, 4, 6 and 7b; Fig. S4: Temperature dependent pressed pellet conduc-
tivity plots for complexes 1–8; Fig. S5: Solid state CD spectra of complexes 1 and
2; Table S1: Crystallographic parameters for the ligand L5 and complexes 1–8;
Table S2: Selected bond lengths (Å) and angles (°) for complexes 1–4, 7b and 8;
Table S3: Selected bond lengths (Å) and angles (°) for complex 5; Table S4:
Selected bond lengths (Å) and angles (°) for complex 6; Table S5: Selected bond
lengths (Å) and angles (°) for complexes 7a; Table S6: Intermolecular interactions
of note in 3, 4 and 6, distances (Å) and angles (°). CCDC 1534939, 1534940,
1842767, 1566019, 1534943, 1534941, 1534942, 1842768, 1566020 and 1842769.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c8dt03694b
‡Electronic supplementary information (ESI) available: S1: Simulated and
experimental PXRD patterns for 1–8; Fig. S1: Simulated and experimental PXRD
patterns for 1–8; Fig. S2: (a) UV-Vis spectra of complexes as solid in nujol mull;
(b) and (c) their emission spectra in the solid phase; Fig. S3: Non-covalent inter-
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cations in materials chemistry and medical technology, coordi- Ag+ coinage metal ion. Furthermore, the presence of a stereo-
nation polymers of low valence p-block (Tl, Sn, and Pb) metal chemically active 6s2 lone pair with greater relativistic effects
ions with organic ligands including thiolato ligands have may induce the formation of coordination polymers through
received very little attention.6–10
Tl–O and Tl–S bonds with varied polarity and stability; (iii) a
Transition and main group metal dithiolates have been systematic variation in the steric and electronic properties and
extensively studied because of their rich structural diversity the presence of additional donor atoms (N, O, S, F, Cl, and Br)
and myriad applications.11,12 Complexes of thallium with 1,1- on the substituents may facilitate the generation of intra- and
dithioligands including dithiocarbamate having identical (S, S) intermolecular non-covalent and rare Tl⋯H–C anagostic and
donor atoms have been known for many years.8 Transition Tl⋯Tl metallophilic interactions in the organization of multi-
metal complexes of somewhat similar β-oxodithioester ligands dimensional assembly and (iv) the Tl(I) chromophore in the
with (O, S) hetero donor atoms have been sporadically extended rigid coordination polymeric structures and in part
reported.13 In comparison, despite their synthetic versatility metallophilic interactions may lead to enhanced luminescent
and practical applications, Tl(I) β-oxodithioester complexes and conducting properties of the complexes. Theoretical
have not been investigated until recently.
calculations were performed to support the rare Tl⋯H–C
Bearing these points in mind we were motivated to under- intermolecular anagostic interactions. Impressive photo-
take the investigation of the synthesis, crystal structures, and luminescence, lifetime measurements and semiconducting
luminescent and conducting properties of some novel Tl(I) characteristics of the complexes are also described in this con-
coordination polymers derived from potassium salts of func- tribution. Significant differences in the structural features of
tionalized β-oxodithioester ligands (Scheme 1). The important these complexes with those of previously reported8 Tl(I) dithio-
aspects of this work are: (i) the β-oxodithioesters display (O, S) carbamates are studied.
coordination and electron delocalization over the stable
6-membered chelate ring about the metal center. In compari-
son, the previously reported 1,1-dithiolates including dithio-
Experimental section
carbamates form strained 4-membered chelate rings via identi-
General methods and materials
cal (S, S) donor atoms. This difference in behavior may result
All the reactions were carried out in open air at ambient temp-
erature. The solvents were purified by standard procedures and
where necessary dried before use. All the commercially avail-
able reagents, TlNO3, 2-acetylfuran, 2-acetylthiophene (all from
Sigma-Aldrich), 3-acetylpyridine, 4-acetylpyridine, 9-acetyl-
anthracene (SPECTROCHEM), p-fluoroacetophenone, p-chloro-
acetophenone and p-bromoacetophenone (Avra Synthesis) were
used as received without further purification. Experimental
details of the elemental analysis (C, H, and N) and recording
of FT IR (as KBr discs), and 1H and 13C{1H} NMR in CDCl3/
DMSO-d6 on a JEOL ECZ500 MHz FT NMR spectrometer of the
ligands L1–L8 and complexes 1–8 have been described ear-
lier.8,13d (CH3)4Si (TMS) was used as an internal standard for
recording NMR spectra. CD spectra were collected on a JASCO
J-815 spectrophotometer. Diffuse reflectance, UV-visible absorp-
tion, and solution and solid phase emission spectra were
obtained using a Harrick Praying Mantis accessory on Shimadzu
UV-3600, Shimadzu UV-1800 and Fluorolog Horiba Jobin Yvon/
PerkinElmer LS–55 fluorescence spectrophotometers, respect-
ively, at room temperature. Fluorescence decay lifetimes were
recorded on an Edinburgh OB920 Fluorescence Spectrometer.
The pressed pellet temperature dependent conductivity measure-
ment was carried out on a Keithley 236 source measure unit. The
details on single crystal X-ray data are provided in the crystal dis-
cussion section and X-ray powder diffraction data were collected
using a Rigaku MultiFlex-600 system with Cu–Kα radiation (λ =
1.54056 Å) with a scan rate of 2° min−1 in the range 2θ = 5–50°.
in huge differences in their structure/bonding and physico-
chemical properties; (ii) the small and hard O atom having no
d orbitals and a distinctly soft character together with larger S
with more diffused p and d orbitals in the dithioester unit
lead to greater affinity for the large Tl(I) ion which lies in
between the hard and soft Lewis acids since its size and
charge are comparable to a hard K+ alkali metal ion and a soft
Synthesis of ligands (L1–L8)
The ligands methyl-3-hydroxy-3-(2-furyl)-2-propenedithioate
(L1), methyl-3-hydroxy-3-(2-thienyl)-2-propenedithioate (L2),
Scheme 1 Potassium salts (KL1–KL8) of β-oxodithioester ligands used
in this work.
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methyl-3-hydroxy-3-(3-pyridine)-2-propenedithioate (L3), methyl- solution was cooled, filtered off and dried using a vacuum
3-hydroxy-3-(4-pyridyl)-2-propenedithioate (L4), methyl-3-hydroxy- evaporator to yield the potassium salts of the ligands KL1–KL8
3-(9-anthracenyl)-2-propenedithioate (L5), methyl-3-hydroxy-3- as yellow to orange solid products.
(p-fluorophenyl)-2-propenedithioate (L6), methyl-3-hydroxy-3-
The complexes were obtained adopting the following
(p-chlorophenyl)-2-propenedithioate (L7) and methyl-3-hydroxy- general procedure. To a 15 mL stirred methanol solution of
3-(p-bromophenyl)-2-propenedithioate (L8) and their potass- the potassium salt of the ligand KL1 (0.24 g, 1 mmol), KL2
ium salts were prepared adopting previously reported meth- (0.25 g, 1 mmol) KL3 (0.25 g, 1 mmol), KL4 (0.25 g, 1 mmol),
ods13d (Scheme 2). To a solution of NaH (0.6 g, 25 mmol) dis- KL5 (0.35 g, 1 mol), KL6 (0.27 g, 1 mmol), KL7 (0.28 g,
solved in a DMF : hexane mixture (4 : 1; 20 mL) was added 1 mmol) or KL8 (0.35 g, 1 mmol) was gradually added a
(dropwise) 2-acetylfuran (1.10 g, 10.0 mmol) (for L1), 2-acetyl- 10 mL methanol : water (80 : 20) solution of TlNO3 (0.27 g,
thiophene (1.26 g, 10.0 mmol) (for L2), 3-acetylpyridine 1 mmol) and further stirred for 4–6 h. The reddish-brown
(1.20 g, 10.0 mmol) (for L3), 4-acetylpyridine (1.21 g, 10.0 mmol) solid formed was filtered off, washed with methanol, dried in
(for L4), 9-acetylanthracene (2.20 g, 10.0 mmol) (for L5), open air and dissolved in DMF to yield red-orange crystals
p-fluoroacetophenone (1.38 g, 10.0 mmol) (for L6), p-chloro- within 10 days.
acetophenone (1.54 g, 10.0 mmol) (for L7) or p-bromoaceto-
phenone (1.99 g, 10 mmol) (for L8) in DMF (20 mL) separately.
Characterization data
After stirring for 1 h in an ice bath under a N2 atmosphere, a 1 Yield: (0.314 g, 78%). M. P.: 172–175 °C. Anal. calcd for
solution of dimethyltrithiocarbonate (TTC)14 (1.38 g, 10 mmol) C8H7O2TlS2 (403.65): C 23.40, H 3.44%. Found: C 23.25,
was added slowly and the mixture was additionally stirred for H 3.48%. IR (KBr, cm−1): 1590 (νC–O), 1565 (νCvC), 1009 (νCvS).
another 10 h at room temperature. Excess NaH was neutralized 1H NMR (500.15 MHz, DMSO-d6, ppm): δ 2.30 (s, 3H, –SCH3),
by adding 0.1 M HCl (50 mL), and the product was extracted 6.45 (s, 1H, –CHvC–), 6.75–7.62 (m, 3H, C4H3O). 13C{1H}
with dichloromethane (3 × 50 mL), washed with brine solution NMR (125.03 MHz, DMSO-d6, ppm) δ 17.82 (–SCH3), 111.08
and water, concentrated and dried over anhydrous Na2SO4. (–CHvC–), 112.05, 113.39, 143.88, 156.80 (C4H3O), 169.08
The product was purified by silica gel (100–200 mesh) chrom- (vC–O–), 195.03 (–CvS). UV-Vis (DMSO, λmax (nm),
atography using hexane as the eluent to collect crystalline ε (M−1 cm−1)): 315 (1.52 × 103), 405 (1.25 × 104); (Nujol, λmax
yellow solids (for characterization data for L1–L8, see S1, ESI‡). (nm)): 292, 352 and 418.
2 Yield: (0.339 g, 81%). M. P.: 138–142 °C. Anal. calcd for
C8H7OTlS3 (419.71): C 22.89, H 1.68%. Found: C 22.58,
Syntheses of complexes 1–8
H 1.65%. IR (KBr, cm−1): 1578 (νC–O), 1516 (νCvC), 1020 (νCvS).
1H NMR (500.15 MHz, DMSO-d6, ppm): δ 2.30 (s, 3H, –SCH3),
For the syntheses of complexes, potassium salts of the ligands
6.97 (s, 1H, –CHvC–), 7.01–7.72 (m, 3H, C4H3S). 13C{1H} NMR
KL1–KL8 were obtained by the following procedure. To a
stirred 10 mL acetone solution of ligands L1 (0.22 g, 1 mmol),
(125.03 MHz, DMSO-d6, ppm)
δ 17.94 (–SCH3), 113.29
L2 (0.20 g, 1 mmol), L3 (0.21 g, 1 mmol), L4 (0.21 g, 1 mmol),
L5 (0.31 g, 1 mmol), L6 (0.24 g, 1 mmol), L7 (0.23 g, 1 mmol)
and L8 (0.29 g, 1 mmol) was added solid K2CO3 (0.21 g,
1.5 mmol) separately and in each case the reaction mixture
was additionally stirred for 4–5 h under reflux conditions. The
(–CHvC–), 126.79, 128.32, 129.64, 150.37 (C4H3S), 172.80
(vC–O–), 193.34 (–CvS). UV-Vis (DMSO, λmax (nm),
ε (M−1 cm−1)): 355 (6.24 × 103), 413 (0.62 × 104); (Nujol, λmax
(nm)): 296, 354 and 502.
3 Yield: (0.286 g, 69%). M. P.: 132–136 °C. Anal. calcd for
C9H8NOTlS2 (414.68): C 26.07, H 1.94, N 3.38%. Found: C
25.85, H 1.95, N 3.35%. IR (KBr, cm−1): 1595 (νC–O), 1534
(νCvC), 1024 (νCvS). 1H NMR (500.15 MHz, DMSO-d6, ppm):
δ 2.62 (s, 3H, –SCH3), 7.21 (s, 1H, –CHvC–), 7.51, 8.22, 8.67,
9.05 (m, 4H, C5H4N). 13C{1H} NMR (125.03 MHz, DMSO-d6,
ppm) δ 17.67 (–SCH3), 113.35 (–CHvC–), 123.42, 134.39,
136.94, 148.30, 150.23 (C5H4N), 176.77 (vC–O–), 195.13
(–CvS). UV-Vis (DMSO, λmax (nm), ε (M−1 cm−1)): 352 (9.11 ×
103), 398 (1.40 × 104); (Nujol, λmax (nm)): 287, 352 and 472.
4 Yield: (0.315 g, 76%). M. P.: 157–160 °C. Anal. calcd for
C9H8NOTlS2 (414.65): C 26.05, H 1.94, N 3.23%. Found:
C 25.90, H 2.05, N 3.30%. IR (KBr, cm−1): 1594 (νC–O), 1512
(νCvC), 1060 (νCvS). 1H NMR (500.15 MHz, DMSO-d6, ppm):
δ 2.33 (s, 3H, –SCH3), 7.03 (s, 1H, –CHvC–), 7.60–8.53 (m, 4H,
C5H4N). 13C{1H} NMR (125.03 MHz, DMSO-d6, ppm) δ 18.03
(–SCH3), 113.64 (–CHvC–), 121.42, 149.56, 150.26 (C5H4N),
175.95 (vC–O–), 198.95 (–CvS). UV-Vis (DMSO, λmax (nm),
ε (M−1 cm−1)): 323 (2.55 × 103), 415 (1.42 × 104); (Nujol, λmax
(nm)): 295, 355 and 530.
Scheme 2 General methodology for the synthesis of ligands L1–L8
and their potassium salts KL1–KL8.
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5 Yield: (0.349 g, 68%). M. P.: 219–223 °C. Anal. calcd for the CrysAlis program.16 The structures were solved by direct
C18H13OTlS2 (513.80): C 42.08, H 2.55%. Found: C 41.88, methods using SHELXS-9717 and refined on F2 by the full
H 2.62%. IR (KBr, cm−1): 1559 (νC–O), 1519 (νCvC), 1002 (νCvS). matrix least squares technique using SHELXL2016-6.18 Non-
1H NMR (500.15 MHz, DMSO-d6, ppm): δ 2.41 (s, 3H, –SCH3), hydrogen atoms were refined anisotropically and hydrogen
6.55 (s, 1H, –CHvC–), 741–8.43 (m, 9H, C14H9). 13C{1H} NMR atoms were geometrically fixed with thermal parameters equi-
(125.03 MHz, DMSO-d6, ppm)
δ 17.79 (–SCH3), 116.37 valent to 1.2 times that of the atom to which they were
(–CHvC–), 125.58, 125.69, 125.77, 127.07, 127.50, 128.61, bonded. In 7b the phenyl ring is disordered and two orien-
131.43, 141.76 (C14H9), 177.83 (vC–O–), 194.87 (–CvS). tations were refined with occupancies x and 1 − x. Diagrams
UV-Vis (DMSO, λmax (nm), ε (M−1 cm−1)): 310 (2.85 × 103), 380 for ligand L5 and all complexes were obtained using OLEX2,19a
(1.14 × 104); (Nujol, λmax (nm)): 295, 345 and 477.
Diamond19b and Mercury19c software. Crystallographic data for
6 Yield: (0.323 g, 75%). M. P.: 143–147 °C. Anal. calcd for 1–8 and L5 were deposited at the Cambridge Crystallographic
C10H8FOTlS2 (431.67): C27.82, H 1.87%. Found: C 27.78, Data Centre with reference numbers CCDC 1534939, 1534940,
H 1.92%. IR (KBr, cm−1): 1598 (νC–O), 1505 (νCvC), 1010 (νCvS). 1842767, 1566019, 1534943, 1534941, 1534942, 1842768,
1H NMR (500.15 MHz, DMSO-d6, ppm): δ 2.34 (s, 3H, –SCH3), 1566020 and 1842769, respectively.†
6.74 (s, 1H, –CHvC–), 7.15–7.85 (m, 4H, C6H4F). 13C{1H} NMR
(125.03 MHz, DMSO-d6, ppm)
δ 18.05 (–SCH3), 113.70
(–CHvC–), 125.37, 129.81, 130.31, 138.53 (C6H4F), 178.66
(vC–O–), 192.15 (–CvS). UV-Vis (DMSO, λmax (nm),
ε (M−1 cm−1)): 315 (0.26 × 104), 400 (1.67 × 104); (Nujol, λmax
(nm)): 292, 345 and 492.
Results and discussion
Synthesis and characterization
The reactions of
a methanol–water solution of TlNO3
and methanolic solutions of potassium salts of the
β-oxodithioester ligands, KL1–KL8, in an equimolar ratio
afforded the formation of air and moisture stable homoleptic
complexes [TlL]n 1–8 in good yields. All the complexes were in-
soluble in water and sparingly soluble in common organic sol-
vents such as dichloromethane, acetone, acetonitrile, ethanol
and methanol but soluble in DMSO and DMF due to their
polymeric nature. They were characterized by elemental ana-
7 Yield: (0.313 g, 70%). M. P.: 164–168 °C. Anal. calcd for
C10H8ClOTlS2 (448.13): C 26.80, H 1.80%. Found: C 26.76,
H 1.93%. IR (KBr, cm−1): 1588 (νC–O), 1490 (νCvC), 1011 (νCvS).
1H NMR (500.15 MHz, DMSO-d6, ppm): δ 2.30 (s, 3H, –SCH3),
7.04 (s, 1H, –CHvC–), 7.35–7.74 (m, 4H, C6H4Cl). 13C{1H}
NMR (125.03 MHz, DMSO-d6, ppm) δ 17.40 (–SCH3), 112.97
(–CHvC–), 127.89, 128.57, 133.91, 140.86 (C6H4Cl), 176.77
(vC–O–), 195.20 (–CvS). UV-Vis (DMSO, λmax (nm),
ε (M−1 cm−1)): 322 (1.45 × 103), 405 (9.48 × 103); (Nujol, λmax
(nm)): 291, 345 and 475.
8 Yield: (0.359 g, 73%). M. P.: 166–170 °C. Anal. calcd for
C10H8BrOTlS2 (492.59): C 24.38, H 1.64%. Found: C 26.33,
H 1.75%. IR (KBr, cm−1): 1583 (νC–O), 1488 (νCvC), 1006 (νCvS).
1H NMR (500.15 MHz, DMSO-d6, ppm): δ 2.35 (s, 3H, –SCH3),
7.09 (s, 1H, –CHvC–), 7.54–7.73 (m, 4H, C6H4Br). 13C{1H}
NMR (125.03 MHz, DMSO-d6, ppm) δ 17.97 (–SCH3), 113.48
(–CHvC–), 123.36, 129.42, 131.38, 141.75 (C6H4Br), 177.42
(vC–O–), 195.73 (–CvS). UV-Vis (DMSO, λmax (nm),
ε (M−1 cm−1)): 315 (1.44 × 103), 406 (1.20 × 104); (Nujol, λmax
(nm)): 288, 346 and 502.
1
lysis, and IR, UV-Vis, H and 13C{1H} NMR spectroscopy. Solid
state structural determination by X-ray crystallography revealed
their spectacular 1D and 2D coordination polymeric structures
displaying Tl⋯Tl and rare Tl⋯H–C intermolecular anagostic
interactions along with various interesting non-covalent inter-
actions. The anagostic interactions in 1, 2 and 7b were corro-
borated by theoretical calculations. The semiconducting beha-
viors of the complexes were investigated using diffuse reflec-
tance spectra. The phase purity of the bulk products 1–8 was
assessed by a comparison of the experimental PXRD patterns
with their respective simulated powder patterns obtained from
the single crystal data. The experimental and simulated PXRD
patterns matched well indicating the phase purity of the bulk
samples (Fig. S1, ESI‡). All the complexes showed bright green
luminescence characteristics in solution and solid phases; also
the luminescence lifetime decay profiles were studied.
Complexes 1 and 2 are chiral as confirmed by the CD spectra.
Theoretical calculations
Single point calculations were carried out using the Gaussian
03 program.15 Structures were investigated using the B3LYP
density functional together with basis sets LANL2DZ for Tl,
6-31+G* for S and 6-31G for the remaining atoms. Models were
taken from the crystal structures but with hydrogen atoms
given theoretical positions.
Spectroscopic characterization
In the IR spectra, complexes 1–8 display bands at 1559–1598;
1488–1565 and 1002–1060 cm−1 for the νCvO, νCvC and
νC–S vibrations, respectively, diagnostic of coordinated
X-ray structure determination
Single crystal X-ray diffraction data for the ligand L5 and com- β-oxodithioester ligands.13 In the 1H NMR spectra of the
plexes 2 and 5–8 were collected on an Oxford Diffraction ligands L1–L8, the –OH protons at δ 14.62–15.37 ppm are
X-Calibur CCD diffractometer using Mo Kα radiation at 150 K; absent in the complexes 1–8 due to keto–enol tautomerism.
1 and 3 on a Bruker D8 Quest SCM X-ray diffractometer at The position of the vinylic proton in the free ligands at
100 K and 4 on a Bruker AXS D8 Quest SC X-ray diffractometer δ 6.47–6.90 ppm and complexes at δ 6.45–7.21 ppm remains
at 295 K. Data reduction for L5 and 1–8 was carried out using almost unchanged. A comparison of the 1H NMR spectra of
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the methyl hydrogen atoms (–SMe) in 1, 2, 5, 6, and 7b; aro-
matic protons in 3, 4, 6, and 7a; and anthracene ring protons
in 5 with those observed in the parent ligands revealed no
noticeable shift in the corresponding protons. This obser-
vation indicates that the Tl⋯H–C intermolecular anagostic
interactions detected in the solid state from X-ray crystallogra-
phy (vide infra) do not persist in solution. The 13C{1H} NMR
resonances observed at δ 159.37–170.18 ppm for the C–OH
carbon in the free ligands are not observed in the complexes
due to stabilization of the keto form. The vinylic carbon of the
ligands showed a chemical shift in the δ 106.56–108.26 ppm
range; exceptionally in L5 the anthracene group is out of plane
and therefore acts as an electron withdrawing group, showing
Fig. 2 (a) UV-Vis absorption and (b) fluorescence spectra of complexes
1–8 in DMSO.
tures (Fig. 2a and Fig. S2a, ESI‡). In solution, the absorption
a
higher downfield shift of δ 115.17 ppm, while the
bands near 320–340 nm (ε = 2.85 × 103–6.24 × 103 M−1 cm−1
)
corresponding vinylic carbon in the complexes at
δ 111.08–116.37 ppm displays a downfield shift in the range
and 380–425 nm (ε = 1.14 × 104–1.42 × 104 M−1 cm−1) in all the
complexes are assigned to intraligand charge transfer (ILCT)
and metal perturbed ILCT transitions, respectively.21,22 The
presence of an additional weak broad absorption band at
500 nm in 1–8 originates most likely from Tl⋯Tl interactions.
This band is absent in the solution spectra thereby indicating
a lack of thallophilic interactions in the solution.
δ
4.52–6.12 ppm. The –CvS carbon located at
δ 215.92–219.27 ppm in the free ligands is upfield shifted at
δ 193.34–198.92 ppm in the complexes indicating metal–ligand
bonding. The –CvO carbon observed at δ 159.37–170.18 ppm
in the ligands is located at δ 169.08–177.83 ppm in the com-
plexes showing –CvO oxygen coordination.13 This indicates
that the keto form of the β-oxodithioester ligands is stabilized
in these complexes, as confirmed by the crystal structures
vide infra, instead of the more stable enolate form reported in
the transition metal complexes.13
The Tl(I) compounds are important from the view point of
their luminescent properties. Upon excitation at 380 nm in
DMSO solution, complexes 1–8 show an unstructured green
emission band in the range of 465–510 nm (Fig. 2b) with a
Stokes shift of 100–145 nm arising from the metal perturbed
ILCT state. When excited at 350 nm in the solid phase, all the
complexes show two to three unstructured emission bands
near 475 and 550 nm (Fig. S2b and 2c, ESI‡) emanating from
the ILCT and metal perturbed ILCT states,8,21 respectively,
because except for L5 and L6 the remaining ligands are non-
emissive in solution. L5 having a highly conjugated anthracene
moiety and L6 having a small and highly electronegative
F atom in the phenyl ring increasing conjugation due to a
mesomeric effect when excited at 360 and 380 nm, respect-
ively, show an unstructured intense broad emission band near
450 nm originating from the ILCT state. A larger red shifted
emission band observed near 550 nm with a Stokes shift of
∼200 nm in the solid state may be ascribed to Tl⋯Tl inter-
molecular interactions23 in the polymeric structures. Notably,
the stronger luminescence characteristics of 5 both in solid
and solution phases in comparison with the remaining com-
plexes may be attributed to the anthracene functionality on the
ligand which enhances the delocalization within the molecule.
Circular dichroism
Complexes 1 and 2 crystallized in chiral space groups; hence
their CD spectra were studied in DMSO solution. The CD
spectra of 1 and 2 show several deflections in the range of
386–430 nm as depicted in Fig. 1. The chirality of these com-
plexes probably originates from their asymmetric arrangement
about the metal center and/or the arrangement of monomeric
units in the left and right handed helical motifs in 1 and 2,
respectively.20 (See the crystal structure discussion vide infra.)
The chiral nature of these compounds was further established
using solid state CD spectra. As depicted in the ESI as Fig. S5,‡
the solid state CD spectra for 1 and 2 exhibited prominent
dichroic signals at 384 and 310 nm respectively.
Absorption and emission spectra
The UV-Vis absorption spectra of complexes 1–8 in DMSO
solution and as solid in nujol mull show virtually similar fea-
Lifetime evaluation
The fluorescence decay lifetime spectra24 (Fig. 3) were recorded
at room temperature in solution (λexc = 380 nm) and they
revealed a triexponential curve for all the complexes except 5.
The mean lifetime for 5 is remarkably longer at 9.79 ns when
compared with the remaining complexes which show
τm values in the range of 1.33–6.26 ns (Table 1). This unique
behavior of 5 is explained by the presence of a highly conju-
gated and bulky anthracene chromophore in the dithioester
ligand moiety and short Tl⋯Tl interactions.
Fig. 1 CD spectra of complexes 1 and 2 in DMSO.
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These values are in good agreement with the values derived
from Kubelka–Munk functions26 using the software package
available with a Shimadzu UV-3101PC spectrometer (Fig. 4c).
Optical band gaps in the range of 2.04–2.26 eV for the studied
compounds suggest the semiconductor behavior of complex-
es27a–d which is further supported by temperature dependent
pressed pellet conductivity measurements.27e,f The conduc-
tivities of all compounds range from 1.26 × 10−7 S cm−1 to 9.55
× 10−7 S cm−1 at room temperature (308 K). A steady increase
in the conductivity was observed with the increase in tempera-
ture as depicted in Fig. S4 (ESI‡).
Crystal structures
Single crystals of 1–8 were obtained by slow evaporation of the
solutions of compounds in DMF within a week and those of
ligand L5 and 7a were obtained in dichloromethane solutions
within two weeks. Crystallographic data and structure refine-
ment details for all crystals are given in Table S1 (ESI‡) and
selected bond distances and angles of 1–8 are given in Tables
S2–S5 (ESI‡).
Fig. 3 Fluorescence lifetime decay profiles of 1–8 in DMSO at room
temperature.
Table 1 Fluorescence decay lifetime data for complexes 1–8
The ORTEP diagram of L5 is presented in Fig. 5. The struc-
ture consists of two planar parts, the anthracene substituent
(atoms C(21) to C(34)) and atoms O(11) to C(17) show r.m.s.
deviations of 0.014 and 0.014 Å, respectively, and intersect at
an angle of 68.77(3)°. The ligand is in the enol form forming
intramolecular hydrogen bonds, O(11)–H⋯S(15), with O–H,
S⋯H and O⋯S distances of 0.82(2), 2.15(2) and 2.926(12) Å,
respectively, with a ∠O–H⋯S of 158(2)°.
The structures of complexes 1–8 contain Tl atoms with a
wide variety of bonding patterns. It is often difficult to assess
the nature of the coordination spheres because of the wide
range of bond lengths around the metal. Donor atoms within
3.5 Å of the metal are considered to be within the coordination
sphere but where it was thought relevant other atoms were
also considered. In addition to bonds to O and S, all structures
contained Tl⋯H contacts of note and these are considered
together in a separate section. Complexes 1, 2, 3, 4, 7b and 8
contained one TlL moiety in the asymmetric unit with dimen-
sions compared in Table S2 (ESI‡). Complexes 5, 6 and 7a con-
tained 2, 2, and 3 TlL moieties in the asymmetric unit with
dimensions shown in Tables S3, S4 and S5 (ESI‡) respectively.
The asymmetric units of complexes 1 and 2 derived from
Complex τ1 (α1)a
τ2 (α2)a
τ3 (α3)a
τm
χ2
b
1
2
3
4
5
6
7
8
0.22 ns
(68.95%)
0.95 ns
(72.67%)
1.07 ns
(81.91%)
0.84 ns
(68.75%)
10.21 ns
(83.30%)
0.97 ns
(81.10%)
1.02 ns
(78.38%)
0.83 ns
(70.93%)
33.59 ns
(16.68%)
3.41 ns
(21.10%)
2.93 ns
(13.94%)
2.28 ns
(25.32%)
7.71 ns
(16.70%)
4.36 ns
(9.88%)
2.27 ns
(19.48%)
1.98 ns
(27.17%)
3.51 ns
(14.37%)
14.16 ns
(6.23%)
10.67 ns
(4.15%)
9.78 ns
(5.93%)
—
6.26 1.13
2.29 1.15
1.73 1.13
1.73 1.07
9.79 1.18
4.71 1.16
1.46 1.22
1.33 1.09
38.76 ns
(9.02%)
10.11 ns
(2.13%)
10.83 ns
(1.90%)
a αi is the amplitude for the fluorescence lifetime τi. b The mean life-
time (τm) is calculated using the equation τm = ∑αiτi. τ is reported in
ns.
Diffuse reflectance spectra
The optical band gaps for 1–8 were determined using solid
state diffuse reflectance spectra (DRS) recorded against BaSO4 the β-oxodithioester ligands L1 and L2 having furyl and thienyl
as the reference at ambient temperature (Fig. 4a). The DRS substituents on the dithioester unit contains only one formula
shows that the studied complexes partly reflect the wave- unit (ORTEP diagram of 1 in Fig. 6).
lengths in the studied region, particularly up to ca. 700 nm
It is noteworthy that complexes 1 and 2 crystallize in mono-
which suggests that the corresponding energies are being used clinic and orthorhombic systems with P21 and P212121 chiral
by the complexes for excitation of electrons from the valence space groups, respectively. Such non-centrosymmetric chiral
to conduction bands. The band gaps were calculated by using space groups have been rarely found in Tl(I) complexes.20 It is
Planck’s relationship, Eband gap = hc/λ, where h is Planck’s con- worth noting that the cell dimensions of 1 and 2 are very
stant (4.135667516 × 10−15 eV s), c is the velocity of light similar apart from the fact that the c axis in 2 is doubled in
(2.998 × 108 m s−1) and λ is the wavelength (nm). The suitable length. The chirality is a result of solid state packing in both
wavelength for band gap determination was ascertained using structures given the fact that all starting compounds are
the first differential of the diffuse reflectance spectra achiral.
(Fig. 4b).12c,13d,25 Complexes 1–8 show optical band gaps of
2.16, 2.26, 2.04, 2.15, 2.16, 2.11, 2.16 and 2.15 eV, respectively. one ligand and one metal, in both structures the metal atom is
In both 1 and 2, while the asymmetric unit contains just
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Fig. 4 (a) Diffuse reflectance plots for solids 1–8 at room temperature using BaSO4 as the reference, (b) differentials of solid state absorbance of
complexes with respect to radiation energy inflection points which give the band gap values and (c) Kubelka–Munk function vs. energy plot for
complexes 1–8.
Fig. 5 X-ray crystal structure of ligand L5 with ellipsoids at 50% prob-
ability showing the atom numbering scheme. Hydrogen bond is shown
as a dotted line.
Fig. 6 The asymmetric unit of 1 with ellipsoids at 50% probability
showing the atom numbering scheme. Complexes 2–4, 7b and 8 have
similar asymmetric units.
seven-coordinated with a capped trigonal prismatic geometry
being bonded to five sulfur atoms and two oxygen atoms from bond lengths of 2.795(12) and 3.109(4) Å and a bite angle of
four different ligands. Thus in 1 the metal is chelated via 65.2(3)° shows the metal at 1.00(3) Å from the chelate plane,
O(11) and S(15) of the bidentate ligand to two ligands, and while the other ligand (symmetry operation: −1 + x, y, z) with
also via S(15) and S(16) from a third ligand and the coordi- dimensions of 3.271(17) and 3.191(5) Å and a bite angle of
nation is completed by S(15) from a fourth ligand, the latter 59.2(3)° shows the metal at 2.77(1) Å; so the bonds are almost
occupying a unique capping position; this arrangement is perpendicular to the chelate ring. A third bidentate interaction
1
2
illustrated in Fig. 7a. Despite the differences in space groups, is found from S(15) and S(16) (symmetry operation: (1 − x,
+
the arrangements around the metals are very similar although y, −z)) with Tl–S distances of 3.273(4) and 3.413(5) Å and a bite
the symmetry elements involved are perforce different and angle of 50.6(1)°. An additional bond is found for S(15) (1 − x,
1
2
indeed the dimensions are remarkably similar as clearly
+ y, −z) at 3.365(4) Å. There is also an interaction with a
shown in Table S2 (ESI‡). We discuss in detail here the dimen- methyl hydrogen atom H(17A) (−1 + x, 1 + y, z) from a fifth
sions in complex 1. It is interesting to note that of the two ligand at 3.33 Å as shown in Fig. 7a. In the two structures the
ligands chelating through O(11) and S(15), one with shorter closest Tl⋯Tl distances are 4.203(1) and 4.152(1) Å.
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Fig. 7 (a) Coordination environment in 1 formed by Tl–O and Tl–S bonding and Tl⋯H–C intermolecular anagostic interactions and (b) 2D net-like
coordination polymeric structure of 1; Tl⋯H–C anagostic interactions have been omitted for clarity. Complex 2 shows a similar structure.
1
2
1
2
together with S(15) and S(16) (symmetry element: − x, − y,
z) forming a four membered ring with distances 3.187(1) and
3.590(1) Å, respectively. The r.m.s. deviation of this TlS3O
moiety in the equatorial plane is 0.053 Å. The unique bond to
1
S(15) (12 − x, y, + z) in an axial position has a length of
2
3.024(1) Å. This axial S(15) atom bridges two Tl(1) atoms with a
∠Tl–S–Tl of 111.4(4)° in a μ3κ3-tridentate coordination mode
(Scheme 3) on the adjacent molecules forming a 1D open
Fig. 8 Formation of helical motifs along the b axis in 1 and 2 sustained
via bonding intermolecular interactions leading to chirality in their
supramolecular architectures.
As shown in Fig. 8, the monomeric units in 1 and 2 form
left and right handed helical20a motifs sustaining several
bonding intermolecular interactions.
In complexes 3 and 4 the cell dimensions are very similar
but the space groups Pccn and Iba2 are very different. In both
cases, the asymmetric unit consists of only one molecule. The
ORTEP diagrams for 3 are 4 are similar to that in Fig. 6. In 3
the metal is five-coordinate bonded to one oxygen and four
sulfur atoms in a coordination environment best considered as
a pentagonal bipyramid with one axial and one equatorial site
missing. Thus, the py(N) atoms in position
3 in the
β-oxodithioester ligand L3 is not involved in bonding to the
metal despite its strong donor character presumably because
of less flexibility of the pyridyl group directly attached to the
dithioester unit. However, it is involved in several inter- and
intramolecular interactions such as C–H⋯N and C–H⋯O.
The equatorial plane in 3 is occupied by two donor atoms
from each of the two ligands; atoms O(11) and S(15) at 2.724
Scheme 3 Structural representation of complexes 1–8 showing Tl⋯Tl,
Tl⋯H–C, chelating and chelating–bridging (μ2, μ3 and μ4) modes of
(3) and 2.893(1) Å, respectively, form a six-membered ring coordination.
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Fig. 9 1D open ladder-like coordination polymeric structure of
3
formed by the Tl–S intermolecular bonding. A similar polymeric struc-
ture is formed in 4.
Fig. 10 The asymmetric unit of 5 with ellipsoids at 50% probability
showing the atom numbering scheme.
ladder-like structure (Fig. 9). S(15) is therefore axial to one Tl
and equatorial to the other.
The arrangement in 4 is similar but the Tl(1)–S(16)$3 dis-
tance is significantly longer at 3.813(3) Å and there is a weak
interaction with a second oxygen atom O(11)$1 at 3.382(8) Å.
This latter interaction is not observed in 3 where the distance
is 4.666(9) Å.
Both structures contain two Tl⋯H–C contacts, one to a
methyl hydrogen atom on C(17) at distances of 3.43 and 3.44 Å
in approximately axial positions and another to the aromatic
hydrogen atom H(24) in 3 and H(25) in 4 at 3.34 and 3.39 Å,
respectively (Fig. 18).
The crystallographic asymmetric unit of 5 comprises two
independent Tl(1) and Tl(2) atoms which are connected to
each other at 3.724(5) Å forming a dimeric [TlL5]2 unit
showing significant thallophilic interactions.8,28–30 Both
metals are chelated by two L5 ligands in the arrangement
shown in Fig. 10. The distances shown in Table S3 (ESI‡) are
within the expected range.8,29,30 Both Tl atoms show one short
Fig. 11 The 1D polymeric chain structure of
Tl(1)⋯S(45) and Tl(2)⋯S(16) contacts between the [Tl(1)Tl(2)(L5)2] dimers.
5 formed through
Tl–O bond (2.651(5) and 2.572(5) Å) and one long Tl–O bond of 4.356(1) Å and 4.348(1) Å are too long to indicate thallo-
(2.848(5) and 2.904(6) Å) though the Tl–S distances fall within philic interactions.
a narrow range of 2.943(3)–3.086(2) Å.
Complexes 6, 7a, 7b and 8 derived from the dithioester
This structure is the only one of the eight Tl complexes that ligands L6, L7 and L8 containing F, Cl and Br substituents at
can be considered to be non-polymeric. Introduction of the the para position of the phenyl ring, respectively, display dis-
bulky anthracenyl substituent on the dithioester backbone tinctly different crystal packing and structural features because
obstructed the involvement of O(15), O(45) and S(11), S(41) of their different sizes and electronegativities.
atoms in the formation of a coordination polymeric structure
The asymmetric unit of 6, dimensions shown in Table S4
through effective Tl–O and Tl–S bonding thus imposing the (ESI‡), contains two TlL moieties (Fig. 12). The distance
low coordination numbers in 5 compared to those found in between the two independent Tl(1) and Tl(2) atoms is 4.098(1)
the other complexes. However, in addition to these four Å showing only weak thallophilic interaction. The arrange-
bonds, each Tl atom has an additional weak interaction with a ments around the two metals are very different: Tl(1) is
sulfur atom S(45)$1 for Tl(1) at 3.511(2) Å and S(16)$2 for Tl(2) bonded to one OS chelate, two SS chelates and an additional
at 3.557(2) Å forming a 1D polymeric chain structure (Fig. 11). –SMe moiety while Tl(2) is bonded to two OS chelates and two
The closest inter-dimer Tl(1)⋯Tl(1) and Tl(2)⋯Tl(2) distances sulfur atoms from different ligand molecules. Thus the O(11)
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2.57–2.63 Å which is at the limit of hydrogen bonding
behavior.
Remarkably when complex 7 is recrystallized from dichloro-
methane, crystals of 7a are obtained which have a distinctly
different structure from 7b. The crystallographic asymmetric
unit of 7a, dimensions shown in Table S5 (ESI‡), contains
three independent Tl(1), Tl(2) and Tl(3) atoms (Fig. 14). The
closest Tl(1)⋯Tl(2) and Tl(1)⋯Tl(3) intermetallic distances at
3.891(1) Å and 3.767(1) Å, respectively, are well within the
range for thallophilic interactions.8,28–30 The two L7 ligands
having a Cl substituent chelate Tl(1) and Tl(2) through O(51),
S(55) and O(11), S(15) at 2.760(14), 3.241(4) Å and 2.629(12),
3.137(4) Å, respectively. S(15) and S(55) simultaneously bridge
one Tl(1) and two Tl(3) atoms at 3.424(4), 3.139(4), and
3.297(4) Å and one Tl(1) and two Tl(2) atoms at 3.241(4), 3.283
(4), and 3.371(4) Å, respectively. Furthermore, O(11) bridges
Tl(2) and Tl(3) at 2.629(12) and 3.031(12) Å and O(31) bridges
Tl(3) and Tl(1) at 3.008(11) and 2.794(12) Å, respectively, result-
ing in the formation of a 2D coordination polymeric structure
showing the most spectacular arrangement of Tl atoms in a
wave-like fashion (Fig. 15). The aromatic hydrogen at the ortho
position H(23) of the benzene ring is involved in the rare
Tl(2)⋯H–C intermolecular anagostic interactions (Fig. 18).
Tl(1) and Tl(3) have no Tl⋯H interactions, and indeed they are
Fig. 12 The asymmetric unit of 6 with ellipsoids at 50% probability
showing the atom numbering scheme.
and S(15) chelate is bonded to both metal atoms as follows: the only thallium atoms in all the complexes 1–8 that have no
Tl(1)–O(11) (2.596(10) Å) and Tl(2)–O(11) (2.732(9) Å), and such interactions.
Tl(1)–S(15) (3.059(4)) and Tl(2)–S(15) (3.562(3) Å). A second
In the structure of 7b, there is only one TlL moiety in the
ligand chelates Tl(2) with Tl(2)–O(41) with a distance of asymmetric unit. The O and S atoms of ligand L7 coordinate
2.840(12) and Tl2–S(45) with a distance of 2.998(3) Å. An in μ2κ2-bidentate chelating/bridging and μ4κ4-tetradentate che-
additional atom S(45)$1 also bridges Tl(1) and Tl(2) with dis- lating/bridging modes, respectively, resulting in a net-like 2D
tances of 3.266(4) and 3.209(4) Å. The asymmetric unit follows coordination polymeric structure (Fig. 16). The chelating and
the μ3κ3-tridentate coordination mode forming a 2D polymeric bridging Tl–O and Tl–S distances at 2.87(3)–3.00(3) Å and
structure (Fig. 13); the bridging Tl–S distances are significantly 3.108(11)–3.306(10) Å, respectively, are within the range men-
longer than that of the chelating O(41) as it is not involved in tioned in the literature.8,29,30
bridging but instead forms C–H⋯O hydrogen bonds at 2.45 Å.
The asymmetric unit of 8 also contains only one formula
But Fig. 13 shows that S(15) primarily bridges Tl(1) atoms. It is unit. Here, the coordination number around Tl is increased to
to be noted that the fluorine atom at the para position of the 8 when Tl⋯H–C anagostic interactions are considered. L8 is
benzene ring forms C–H⋯F intermolecular hydrogen bonds at coordinated to the Tl atom via O(11) and S(15) donor atoms in
a μ2κ2-bidentate and μ3κ3-tridentate manner (Scheme 3), sim-
Fig. 14 The asymmetric unit of 7a with ellipsoids at 50% probability
Fig. 13 2D polymeric structure of 6 formed by Tl–O and Tl–S bonds.
showing the atom numbering scheme.
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Fig. 17 Open ladder-like 1D coordination polymeric structure of 8
formed by Tl–O and Tl–S bonds. The Tl⋯H–C anagostic bond is
omitted for clarity.
Tl–S and Tl–O inter- and intramolecular bonds is observed
(Fig. 17).
Fig. 15 2D coordination polymeric structure formed by Tl–O and Tl–S
bonds showing a wave-like arrangement of Tl atoms in 7a.
1–8 are unique examples of Tl(I) complexes with (O, S)
donor β-oxodithioester ligands exhibiting remarkable vari-
ations in their structures and bonding assisted by several inter-
actions in their networks.
The term agostic bonding was used for a 3c–2e covalent
bond formed where the C–H bond acts as a ligand to electron
seeking transition metal ions.28,31 The rare preagostic or ana-
gostic M⋯H–C bonding, largely electrostatic in nature, is
observed in planar organometallic and metal dithiolates
including dithiocarbamate complexes. Here, M = Ni(II), Pd(II),
Pt(II), Cu(II) and Rh(I) metal ions with d8/d9 electronic con-
figurations.32 The former is generally regarded to be mechanis-
tically important for the key step in C–H activation processes33
while the latter is recognized as a pre-stage to agostic bonding
and of broad general interest due to possible implications for
the mechanism of C–H activation.33
The striking feature of complexes 1–8 is the existence of
rare Tl⋯H–C intermolecular anagostic interactions in all struc-
tures. This interaction is facilitated by the fact that the coordi-
nation sphere around the metal of sulfur and oxygen atoms
contains an empty site. Crystal packing effects in addition to
steric and electronic properties of the substituents on the di-
thioester unit are elemental in bridging the hydrogen atom in
close vicinity of the metal centre. For the structures with one
metal in the asymmetric unit, namely 1, 2, 3, 4, 7b and 8, the
Tl⋯H–C distances, are in the range 3.24 to 3.47 Å8 with Tl⋯H–C
Fig. 16 2D net-like coordination polymeric structure of 7b formed by
Tl–O and Tl–S bonds; interactions are included. However, in this figure
H atoms are omitted for clarity.
ultaneously chelating one Tl(1) and bridging another neigh- angles of 118–135° (details in Table S2, ESI‡). These inter-
bouring Tl(I), respectively. These chelating and bridging con- actions involve a methyl hydrogen atom on C(17) and the
tacts lead to formation of a 1D coordination polymeric open hydrogen occupies a vacant approximately axial position in the
ladder-like structure (Fig. 17). The difference between the poly- metal coordination sphere. It is noted from Table S2 (ESI‡)
meric structure of 8 and the 2D structures of 6 and 7 (having that in structures 3 and 4, there is a second Tl⋯H interaction
F and Cl substituents) may be attributed to the larger size and and this involves aromatic hydrogen atoms H(24) and H(25),
smaller electronegativity of the Br substituent at the para position respectively. Structures 5, 6 and 7a have two or more metal
of ligand L8. The closest Tl(1)⋯Tl(1) contact of 4.605(1) Å between atoms in the asymmetric unit and the involvement of hydro-
the zig-zag chain of metal atoms with a ∠Tl(1)–Tl(1)–Tl(1) of gen atoms is necessarily more complicated. In 5 there are four
98.03(1)° shows a lack of metallophilic interaction. The chelat- protons around Tl(1), namely H(51), H(47A)$1, H(21) and
ing and bridging Tl–O and Tl–S distances at 2.869(16)–3.137(17) H(31)$3, participating in anagostic interactions at 3.30, 3.23,
Å and 2.989(6)–3.115(6) Å, respectively, are well within the lit- 3.50, and 3.34 Å, respectively, and one around Tl(2), namely
erature values,8,29,30 with the bridging distances longer than H(32)$1, at a distance of 3.22 Å. It is noted that two of the ana-
the chelating distances. An open ladder-like structure built on gostic interactions around Tl(1) are intramolecular in nature.
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The Tl⋯H–C angles involving Tl(1) are in the range of atoms. Tl(2) has just one such interaction with H(23)$5 at
136–158° considerably larger than that involving Tl(2) at 122°. 3.25 Å with an angle of 148°. These rare Tl⋯H–C inter-
Notably, these hydrogen atoms occupy coordination sites molecular anagostic interactions are illustrated in Fig. 18.
about the metal along with the closest donor atoms that are Considering these interactions as bonding, the effective
O(41) and S(45) atoms on the adjacent molecules in 5 and O(11) coordination number about the metal center in these
in both 6 and 7a from dithioester ligands forming spectacular complexes is enhanced. The Tl⋯H distances in these com-
7-, 11- and 12-membered chelate rings, respectively (Fig. 18).
plexes are somewhat longer than those found at 2.61–2.89 Å in
In structure 6, both of the independent thallium atoms Ni(II), Pd(II), Pt(II) and Cu(II) dithiocarbamate complexes32 but
have an interaction with hydrogen in an axial position, at 3.21 are well within the range of values of previously reported Tl(I)
and 3.21 Å with Tl⋯H–C angles of 132 and 139°, respectively. dithiocarbamate complexes.8 This may be ascribed to the
Complex 7a contains three metal atoms in the asymmetric unit larger size, high relativistic effects and stereochemically active
but Tl(1) and Tl(3) are not in close contact with hydrogen lone pair on the Tl(I) ion. The observed anagostic interactions
Fig. 18 Depiction of Tl⋯H–C intermolecular anagostic interactions in complexes 2, 3 and 4. Complexes 1, 7b and 8 show interactions similar to 2.
The formation of chelate rings around the Tl atom in 5, 6 and 7a shows Tl⋯H–C intermolecular anagostic interactions.
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in these complexes are in the order 6 > 5 > 2 > 7a > 1 > 3 > 4 >
7b > 8.
Conclusions
Single point calculations were carried out to assess the Eight new β-oxodithioester Tl(I) complexes were synthesized
energy of these Tl⋯H–C anagostic interactions. For 1 and 2, and fully characterized. These provide efficient examples of
we used two TlL asymmetric units connected by a simple complexes which highlight the effect of steric and electronic
translation and connected via Tl⋯H(methyl) interactions. properties of various substituents on the ligand backbone in
Calculations using the formula Energy of dimer = 2 × the development of interesting solid state structures. 1–8
monomer yielded the values −2.46 and −2.34 kcal mol−1
Similar calculations on 7b gave an energy difference of polymeric structures, interesting anagostic and C–H⋯π(TlOSC3,
−0.74 kcal mol−1
chelate) interactions along with several other hydrogen
.
portray unprecedented 1D and 2D ladder/net-like coordination
.
Apart from these direct Tl⋯H–C anagostic interactions, bonding, covalent and non-covalent interactions. These inter-
hydrogen atoms play an important role in generating actions proved crucial in the formation of two (1 and 2) chiral
C–H⋯π(MS2C, chelate) interactions. Tiekink and Zuckerman– Tl(I) complexes aligning as helices in their supramolecular
Schpector have described34 the important role of such inter- structure. The β-oxodithioester ligands are bonded to the Tl(I)
actions in transition and main group metal 1,1-dithiolates in centers in (O, S) chelating and chelating–bridging μ2, μ3 and μ4
facilitating the construction of multi-dimensional supramole- modes (Scheme 3). The structure of 7a is most intriguing as it
cular architectures.35 The structural features of this kind of contains three independent thallium atoms uniquely linked
interaction were defined by three dimensions, α the angle with each other forming a 2D wave-like polymeric structure. 5,
between the perpendicular to the ring and the H⋯CG vector 6 and 7a exhibited 7-, 11-, and 12-membered chelate rings via
(CG being the centroid of the four-membered MS2C ring), β (H, O, S) bonding and anagostic interactions about the metal
the CG⋯H–C angle and d the H⋯CG distance. The examples center. These anagostic interactions were assessed by theore-
with values of α < 20, β in the range of 110–180° and d tical calculations. Compared with the case of Tl(I) dithiocarba-
between 2.4 and 3.6 Å were found to define the C–H⋯π(MS2C, mates, identical (S, S) donor atoms forming strained 4-mem-
chelate) interactions of interest. The existence of such inter- bered chelate rings bond in the chelating–bridging mode in
actions in the main group metal complexes is less commonly the formation of a dimeric unit but not in a bridging fashion
observed as compared to transition metal complexes because in the coordination polymeric structures. All the complexes
of the lack of planarity.12,34 The stereochemically active 6s2 show bright green fluorescence emission in the solution and
lone pair with greater relativistic contribution of the Tl atom solid phases at room temperature originating from the metal
and formation of a highly delocalized 6-membered ring about perturbed intra-ligand charge transfer states and Tl⋯Tl inter-
the metal center in 5 together with crystal packing effects, actions. Particularly, the stronger luminescence characteristics
notably exhibits C–H⋯π(TlOSC3, chelate) interactions (Fig. 19). of 3, 4 and 5 are due to the presence of higher conjugation in
It is to be noted that in 5 intramolecular interactions between the pyridyl and anthracene moieties of the substituents and
hydrogen atoms of anthracene, H(21) with Tl(1) and H(61) conformational rigidity in the extended polymeric structures.
with Tl(2), are observed with α, β and d values of 1, 132°, The fluorescence lifetime of 5 is significantly higher than that
2.96 Å and 8, 129°, 3.21 Å, respectively.
of the remaining complexes due to greater steric bulk of the
Furthermore, the coordination polymeric structures of com- anthracene chromophore and the shorter Tl⋯Tl distance. DRS
plexes 1–8 were supported by important non-covalent inter- and temperature dependent pressed pellet conductivity
actions, H⋯H, C–H⋯π, C–H⋯π (TlOSC3, chelate), Tl⋯H–C measurements indicate the semiconducting behavior of com-
anagostic and C–H⋯X (X = N, O, F and Cl) hydrogen bond plexes 1–8. This study extends the scope of coordination poly-
interactions35 sustaining the multi-dimensional architecture mers derived from thallium metal with dithioester ligands for
of the complexes (Fig. S2.1–S2.2 and Table S6, ESI‡).
their intriguing structural features and possible applications
as luminescent and semiconducting materials.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We gratefully acknowledge financial support from the Science
and Engineering Research Board (SERB) for the project:
(SB/SI/IC-15/2014) and University Grants Commission (UGC),
New Delhi for the award of BSR Faculty Fellow (ref No. F.18-1
(BSR) 30 Dec 2016) to NS and UGC-SRF fellowship to CLY. GR
Fig. 19 Representation of C–H⋯π(TlOSC3, chelate) interactions in 5.
16276 | Dalton Trans., 2018, 47, 16264–16278
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Paper
acknowledges Department of Science and Technology (DST),
New Delhi for DST-INSPIRE Faculty fellowship (award ref no.
DST/INSPIRE/04/2016/000997). We are also thankful to
2014, 43, 4752–4761; (c) G. Rajput, M. K. Yadav,
M. G. B. Drew and N. Singh, Inorg. Chem., 2015, 54, 2572–
2579.
Department of Chemistry, Institute of Science, Banaras Hindu 13 (a) R. Saumweber, C. Robl and W. Weigand, Inorg. Chim.
University, UGC CAS-II for infrastructural facilities and
University of Reading, EPSRC (UK) for funds for the diffrac-
tometer used in the data collection of samples L5, 2 and 5-8.
Acta, 1998, 269, 83–90; (b) I. G. Orozco, J. G. L. Cortes,
M. C. O. Alfaro, R. A. Toscano, G. P. Carrillo and
C. A. Toledano, Inorg. Chem., 2004, 43, 8572–8576;
(c) I. G. Orozco, M. C. O. Alfaro, J. G. L. Cortes,
R. A. Toscano and C. A. Toledano, Inorg. Chem., 2006, 45,
1766–1773; (d) G. Rajput, M. K. Yadav, M. G. B. Drew and
N. Singh, Dalton Trans., 2015, 44, 5909–5916.
Notes and references
1 M. P. Suh, Y. E. Cheon and E. Y. Lee, Coord. Chem. Rev., 14 A. W. M. Lee, W. H. Chan and H. C. Wong, Synth.
2008, 252, 1007–1026. Commun., 1988, 18, 1531–1536.
2 O. M. Yaghi, M. Okeeffe, N. W. Ockwig, H. K. Chae, 15 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. Eddaoudi and J. Kim, Nature, 2003, 423, 705–714.
3 N. W. Ockwig, O. Delgado-Friedrichs, M. Okeeffe and
O. M. Yaghi, Acc. Chem. Res., 2005, 38, 176–182.
4 A. K. Cheetham, C. N. R. Rao and R. K. Feller, Chem.
Commun., 2006, 46, 4780–4795.
5 T. R. Cook, Y. R. Zheng and P. J. Stang, Chem. Rev., 2013,
113, 734–777.
6 F. Caruso, M. L. Chan and M. Rossi, Inorg. Chem., 1997, 36,
3609–3615.
7 (a) S. K. Dutta and M. W. Perkovic, Inorg. Chem., 2002, 41,
6938–6940; (b) P. D. McNaughter, S. A. Saah, M. Akhtar,
K. Abdulwahab, M. A. Malik, J. Raftery, J. A. M. Awudza and
P. O’Brien, Dalton Trans., 2016, 45, 16345–16353.
8 (a) V. Kumar, V. Singh, A. N. Gupta, M. G. B. Drew and
N. Singh, Dalton Trans., 2015, 44, 1716–1723;
(b) K. K. Manar, G. Rajput, M. K. Yadav, C. L. Yadav,
K. Kumari, M. G. B. Drew and N. Singh, ChemistrySelect,
2016, 1, 5733–5742; (c) L. Nilson and R. Hesse, Acta Chem.
Scand., 1969, 23, 1951–1965; (d) E. Elfwing, H. Anacker-
Eickhoff and R. Hesse, Acta Chem. Scand., Ser. A, 1976, 30,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr.,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam,
S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma,
G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski,
S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas,
D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford,
J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, L. Komaromi, R. L. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian 03,
Revision C.02, Gaussian, Inc., Wallingford CT, 2004.
335–339; (e) A. V. Ivanov, O. A. Bredynk, A. V. Gerasimenko, 16 Oxford Diffraction, CrysAlis CCD, RED, version 1.711.13,
O. N. Antzutkin and W. Forsling, Russ. J. Coord. Chem., copyright (1995–2003), Oxford Diffraction Poland Sp.
2006, 32, 339–349; (f) B. Krebs and A. Brommelhaus, 17 G. M. Sheldrick, SHELXS-97, Acta Crystallogr., Sect. A:
Angew. Chem., Int. Ed. Engl., 1989, 28, 1682–1683. Found. Crystallogr., 2008, A64, 112–122.
9 K. Ramasamy, V. L. Kuznetsov, K. Gopal, M. A. Malik, 18 G. M. Sheldrick, SHELXL2016–16, Program for Crystal
J. Raftery, P. P. Edwards and P. O’Brien, Chem. Mater., 2013,
25, 266–276.
Structure Refinement, University of Gottingen, Gottingen,
1997.
10 (a) N. O. Bodi, M. A. Malik, P. O’Brien and J. A. M. Awudza, 19 (a) O. V. Dolomanov, L. J. Bourhis, R. J. Gildea,
Dalton Trans., 2012, 41, 10497–10506; (b) J. R. Casto,
K. C. Molloy, Y. Liu, C. S. Lai, T. J. White and
E. R. T. Tiekink, J. Mater. Chem., 2008, 18, 5399–5405.
J. A. K. Howard and H. Puschmann, J. Appl. Crystallogr.,
2009, 42, 339–341; (b) K. Brandenburg, DIAMOND Crystal
Impact GbR, Bonn, Germany, 1999; (c) C. F. Macrae,
I. J. Bruno, J. A. Chisholm, P. R. Edgington, P. McCabe,
E. Pidcock, L. Rodriguez-Monge, R. Taylor, J. van de
Streek and P. A. Wood, J. Appl. Crystallogr., 2008, 41, 466–
470.
11 (a) D. Coucouvanis, Prog. Inorg. Chem., 1970, 11, 233–371;
(b) D. Coucouvanis, Prog. Inorg. Chem., 1979, 26, 301–469;
(c) G. Hogarth, Prog. Inorg. Chem., 2005, 53, 71–561;
(d) G. Hogarth, Mini-Rev. Med. Chem., 2012, 12, 1202–1215;
(e) E. R. T. Tiekink and I. Haiduc, Prog. Inorg. Chem., 2005, 20 (a) G. M. Davies, J. C. Jeffery and M. D. Ward, New J. Chem.,
54, 127–319; (f) P. J. Heard, Prog. Inorg. Chem., 2005, 53, 1–
69.
12 (a) A. Kumar, R. Chauhan, K. C. Molloy, G. K. Kohn,
2003, 27, 1550–1553; (b) E. Craven, E. Mutlu, D. Lundberg,
S. Temizdemir, S. Dechert, H. Brombacher and C. Janiak,
Polyhedron, 2002, 21, 553–562.
L. Bahadur and N. Singh, Chem. – Eur. J., 2010, 16, 4307– 21 (a) E. J. Fernandez, A. Laguna, J. M. Lopez-de-Luzuriaga,
4314; (b) V. Singh, R. Chauhan, A. N. Gupta, V. Kumar,
M. G. B. Drew, L. Bahadur and N. Singh, Dalton Trans.,
M. Monge, M. Montiel, M. E. Olmos and J. Perez,
Organometallics, 2004, 23, 774–782; (b) M. V. Childress,
This journal is © The Royal Society of Chemistry 2018
Dalton Trans., 2018, 47, 16264–16278 | 16277

View Article Online
Paper
Dalton Transactions
D. Millar, T. M. Alam, K. A. Kreisel, G. P. A. Yap, 29 (a) F. Wiesbrock and H. Schmidbaur, J. Am. Chem. Soc.,
L. N. Zakharov, J. A. Golen, A. L. Rheingold and
L. H. Doerrer, Inorg. Chem., 2006, 45, 3864–3877;
(c) F. Sabin and A. Vogler, Monatsh. Chem., 1992, 123, 705–
708.
2003, 125, 3622–3630; (b) D. Marcano, N. Gerasimchuk,
V. Nemykin and S. Silchenko, Cryst. Growth Des., 2012, 12,
2877–2889.
30 (a) H. Pritzkow and P. Jennische, Acta Chem. Scand., Ser. A,
1975, 29, 60–70; (b) B. E. Bosch, M. Eisenhawer,
B. Kersting, K. Kirschbaum, B. Krebs and D. M. Giolando,
Inorg. Chem., 1996, 35, 6599–6605; (c) H. Schmidbaur,
Angew. Chem., Int. Ed. Engl., 1985, 24, 893–1008.
22 (a) E. J. Fernandez, A. Laguna and J. M. Lopez-de-
Luzuriaga, Coord. Chem. Rev., 2005, 249, 1423–1433;
(b) A. Strasser and A. Vogler, Inorg. Chem. Commun., 2004,
7, 528–530; (c) V. J. Catalano, B. L. Bennett and H. M. Kar,
J. Am. Chem. Soc., 1999, 121, 10235–10236.
23 P. C. Ford and A. Vogler, Acc. Chem. Res., 1993, 26, 220–226.
24 (a) G. Krishnamoorthy, J. Mol. Biol., 2009, 393, 735–752;
(b) D. G. Cuttell, S. M. Kuang, P. E. Fanwick, D. R. McMillin
and R. A. Walton, J. Am. Chem. Soc., 2002, 124, 6–7;
(c) M. K. Singh, H. Pal, A. S. R. Koti and A. V. Sapre, J. Phys.
Chem., 2004, 108, 1465–1474; (d) D. M. Zink, T. Baumann,
J. Friedrichs, M. Nieger and S. Brase, Inorg. Chem., 2013,
52, 13509–13520; (e) J. Pospisil, I. Jess, C. Nather,
M. Necasa and P. Taborsky, New J. Chem., 2011, 35, 861–
864.
31 (a) M. Brookhart, M. L. H. Green and G. Parkin, Proc. Natl.
Acad. Sci. U. S. A., 2007, 104, 6908–6914; (b) H. V. Huynh,
L. R. Wong and P. S. Ng, Organometallics, 2008, 27, 2231–
2237; (c) J. Sabmannshausen, Dalton Trans., 2012, 41,
1919–1923; (d) K. A. Siddiqui and E. R. T. Tiekink, Chem.
Commun., 2013, 49, 8501–8503; (e) S. Scholer, M. H. Wahl,
N. I. C. Wurster, A. Puls, C. Hattig and G. Dyker, Chem.
Commun., 2014, 50, 5909–5911; (f) W. H. Bernskoetter,
C. K. Schauer, K. I. Goldberg and M. Brookhart, Science,
2009, 326, 553–556; (g) M. Stepien and L. Latos-Grazynski,
Acc. Chem. Res., 2005, 38, 88–98; (h) M. Teci, E. Brenner,
D. Matt, C. Gourlaouen and L. Toprt, Dalton Trans., 2015,
44, 9260–9268; (i) J. A. Harrison, A. J. Nielson, M. A. Sajjad,
G. C. Saunders and P. Schwerdtfeger, Eur. J. Inorg. Chem.,
2016, 64–77.
25 A. E. Morales, E. S. Mora and U. Pal, Rev. Mex. Fis. S, 2007,
53, 18–22.
26 J. Tauc, R. Grigorovici and A. Vancu, Phys. Status Solidi,
1966, 15, 627–637.
27 (a) X. Zhao, S. Zhang, J. Yan, L. Li, G. Wu, W. Shi, G. Yang, 32 (a) R. Angamuthu, L. L. Gelauff, M. A. Siegler, A. L. Spek
N. Guan and P. Cheng, Inorg. Chem., 2018, 57, 5030–5037;
(b) Y. Liu, F. Wei, S. N. Yeo, F. M. Lee, C. Kloc, Q. Yan,
H. H. Hng, J. Ma and Q. Zhang, Inorg. Chem., 2012, 51,
4414–4416; (c) T. Okubo, H. Anma, N. Tanaka, K. Himoto,
S. Seki, A. Saeki, M. Maekawa and T. Karuda-Sowa, Chem.
and E. Bouwman, Chem. Commun., 2009, 7, 2700–2702;
(b) B. Singh, M. G. B. Drew, G. K. Kohn, K. C. Molloy and
N. Singh, Dalton Trans., 2011, 40, 623–631; (c) A. N. Gupta,
V. Kumar, V. Singh, K. K. Manar, M. G. B. Drew and
N. Singh, CrystEngComm, 2014, 16, 9299–9307.
Commun., 2013, 49, 4316–4318; (d) P. I. Clemenson, Coord. 33 (a) W. Yao, O. Eisenstein and R. H. Crabtree, Inorg. Chim.
Chem. Rev., 1990, 106, 171–203; (e) G. Rajput, V. Singh,
A. N. Gupta, M. K. Yadav, V. Kumar, S. K. Singh, A. Prasad,
M. G. B. Drew and N. Singh, CrystEngComm, 2013, 15,
Acta, 1997, 254, 105–111; (b) J. L. Haller, M. J. Page,
S. A. Macgregor, M. F. Mohan and M. K. Whittlesey, J. Am.
Chem. Soc., 2009, 131, 4604–4605.
4676–4683; (f) G. Rajput, V. Singh, S. K. Singh, 34 (a) E. R. T. Tiekink and J. Z. Schpector, Chem. Commun.,
L. B. Prasad, M. G. B. Drew and N. Singh, Eur. J. Inorg.
Chem., 2012, 15, 3885–3891.
28 (a) P. Pyykko, Chem. Rev., 1997, 97, 597–636; (b) C. Janiak,
2011, 47, 6623–6625; (b) C. I. Yeo, S. N. A. Halim, S. W. Ng,
S. L. Tan, J. Z. Schpector, M. A. B. Ferreira and
E. R. T. Tiekink, Chem. Commun., 2014, 50, 5984–5986.
Coord. Chem. Rev., 1997, 163, 107–216; (c) C. H. Galka and 35 V. R. Thalladi, H. C. Weiss, D. Blaser, R. Boese, A. Nangia
L. H. Gade, Inorg. Chem., 1999, 38, 1038–1039.
and G. R. Desiraju, J. Am. Chem. Soc., 1998, 120, 8702–8710.
16278 | Dalton Trans., 2018, 47, 16264–16278
This journal is © The Royal Society of Chemistry 2018