Search for the shortest intermetallic Tl—Tl contacts: Synthesis and characterization of Thallium(I) coordination polymers with several mono- and bis-cyanoximes

Article abstract of DOI:10.1016/j.ica.2020.119597

Five new Tl(I) coordination compounds based on aryl monocyanoximes, such as phenylcyanoxime – HPhCO, 1, 2-fluorophenylcyanoxime – H(2F-PhCO, 2, 3-fluorophenylcyanoxime – H(3F-PhCO), 3, of TlL composition, and aryl biscyanoximes, such as 1,3-cyanoxime (benzene) – H₂(1,3-BCO, 4 and 1,4-cyanoxime (benzene) – H₂(1,4-BCO), 5 of Tl₂L stoichiometry were synthesized and characterized using spectroscopic methods, thermal stability studies, and X-ray analysis. All obtained complexes represent coordination polymers of different complexity, ranging in dimensionality from 1D in Tl(2F-PhCO) to 3D in Tl₂(1,3-BCO). The most interesting feature of all synthesized complexes is the formation of Tl₂O₂ rhombs: non planar and non-centrosymmetric in Tl(PhCO), and planar and centrosymmetric in the other three compounds. These rhombi are interconnected, forming zigzag and ladder-type polymers in which very short thallophilic Tl—Tl distances were observed. Thus, in the structure of Tl₂(1,3-BCO) the closest distance between metal centers was found to be 3.670 ?. This is the second shortest on-record intermetallic contact in non-organometallic and non-cluster, but Werner type complexes, and is close to that in metallic thallium: 3.456 ?. In all five new coordination polymers the central atom has a stereo-active 6 s² lone pair that significantly distorts the shape of the coordination polyhedron of Tl(I). The first time, Tl–O vibrations in Tl₂O₂ rhombs were observed in Raman spectra of the obtained complexes. Thermal analysis studies evidenced stability of all complexes, but Tl(PhCO), to ～200 °C. The Tl₂(1,3-BCO) compound demonstrates properties of the high energy compound, and violently exothermically decomposes at ～255 °C with the release of a significant amount of kinetic energy. The final product of anaerobic decomposition of all studied Tl-cyanoximates is metallic thallium sponge.

Full text of DOI:10.1016/j.ica.2020.119597

InorganicaChimicaActa508(2020)119597
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journal homepage: www.elsevier.com/locate/ica
Research paper
Search for the shortest intermetallic Tl—Tl contacts: Synthesis and
characterization of Thallium(I) coordination polymers with several mono-
and bis-cyanoximes
Scott Curtisa, Brett Lottesa, Daniel Robertsona, Sergey V. Lindemanb, Nikolay Gerasimchuk.a,⁎
a Missouri State University, Department of Chemistry, Temple Hall 456, Springfield, MO 65897, United States
b Department of Chemistry, Marquette University, Milwaukee, WI 53233, United States
A R T I C L E I N F O
A B S T R A C T
Keywords:
Five new Tl(I) coordination compounds based on aryl monocyanoximes, such as phenylcyanoxime – HPhCO, 1, 2-
fluorophenylcyanoxime – H(2F-PhCO, 2, 3-fluorophenylcyanoxime – H(3F-PhCO), 3, of TlL composition, and
aryl biscyanoximes, such as 1,3-cyanoxime (benzene) – H2(1,3-BCO, 4 and 1,4-cyanoxime (benzene) – H2(1,4-
BCO), 5 of Tl2L stoichiometry were synthesized and characterized using spectroscopic methods, thermal stability
studies, and X-ray analysis. All obtained complexes represent coordination polymers of different complexity,
ranging in dimensionality from 1D in Tl(2F-PhCO) to 3D in Tl2(1,3-BCO). The most interesting feature of all
synthesized complexes is the formation of Tl2O2 rhombs: non planar and non-centrosymmetric in Tl(PhCO), and
planar and centrosymmetric in the other three compounds. These rhombi are interconnected, forming zigzag and
ladder-type polymers in which very short thallophilic Tl—Tl distances were observed. Thus, in the structure of
Tl2(1,3-BCO) the closest distance between metal centers was found to be 3.670 Å. This is the second shortest on-
record intermetallic contact in non-organometallic and non-cluster, but Werner type complexes, and is close to that
in metallic thallium: 3.456 Å. In all five new coordination polymers the central atom has a stereo-active 6 s2 lone
pair that significantly distorts the shape of the coordination polyhedron of Tl(I). The first time, Tl–O vibrations in
Tl2O2 rhombs were observed in Raman spectra of the obtained complexes. Thermal analysis studies evidenced
stability of all complexes, but Tl(PhCO), to ∼200 °C. The Tl2(1,3-BCO) compound demonstrates properties of the
high energy compound, and violently exothermically decomposes at ∼255 °C with the release of a significant
amount of kinetic energy. The final product of anaerobic decomposition of all studied Tl-cyanoximates is me-
tallic thallium sponge.
Thallium(I) coordination polymers
Cyanoxime ligands
X-ray analysis
Thermal analysis
Electronic spectra
Raman spectra
1. Introduction
component of ‘hydrogen economy’ [32–34].
Coordination polymers have attracted a fair deal of attention for
In recent years, there has been an upturn in research on a subset of
macromolecules known as coordination polymers [1–4]. They can take
on a variety of morphologies, being divided according to their di-
mensionality into 1D, 2D and 3D polymers, with different properties
and potential applications. Thus, one-dimensional columnar, zigzag
chains, ladder-type, or stacks, are interesting from the standpoint of
electrical conductivity [5–8], while two-dimensional sheets of co-
ordination polymers are interesting for catalysis applications [9–11]
and magnetic coupling/ordering [12,13]. A specific type of three-di-
mensional coordination polymers, known as metal–organic frameworks
(MOFs), contains large lattices that are mostly empty scaffolds with
pores for potential application for gas sorption [14–31]. These struc-
tures can accommodate the most important gas, H2, which is the key
their optical and elastic properties, as well as their potential for use in
molecular electronics [35], and in certain cases, have even been shown
to have antimicrobial properties [36]. A number of coordination poly-
mers that have been synthesized have been shown to exhibit electro-
luminescence [37], which has garnered attention with regard to the use
of the transition metals for coordination polymers with this property,
owing to the energy of the triplet state that the metals exhibit [38–42].
Substantial attention with regard to coordination polymers has been
given to the transition metals [43–52] with the main group elements
largely disregarded recently. Of particular interest in the main group
metals is a small cluster of 5p and 6p elements, specifically Tl, Pb, Sb,
and Bi, that can exist in two accessible oxidation states which are two
electrons apart. Thallium, however, has shown a unique ability among
⁎ Corresponding author.
E-mail address: NNGerasimchuk@MissouriState.edu (N. Gerasimchuk.).
https://doi.org/10.1016/j.ica.2020.119597
Received 1 December 2019; Received in revised form 14 March 2020; Accepted 16 March 2020
Availableonline28March2020
0020-1693/©2020ElsevierB.V.Allrightsreserved.

S. Curtis, et al.
InorganicaChimicaActa508(2020)119597
its group to form coordination polymers [53,54]. This element is of
particular interest with regards to 1D coordination polymers, because of
the propensity for ‘electron-hopping’ between metal centers, as Tl exists
in two oxidation states, Tl1+ and Tl3+. Such electrical properties may
be of use, leading to potential applications in electronics [53]. In this
case, very short intermetallic distances would be required for electrical
conductivity via electron hopping [55].
additional purification. Melting points were determined with the help
of pre-calibrated apparatus with urea and naphthalene standards
DigiMelt in an open capillary, and reported without correction.
2.2. Synthesis of ligands and Tl(I) Complexes.
The preparation of compounds reported in this study is outlined in
Scheme 2 for both organic ligands and their Tl(I) complexes, with some
details for typical syntheses presented below.
In recent years, there has been a discovery of a number of oxime-
based Tl coordination polymers [53,54], each possessing the 1D motif
of Tl atoms with short intermetallic distances, of potential interest in
electrical applications. Oximes are ionizable ligands and readily form
compounds of TlL composition which excludes the necessity for counter
ions commonly present in other types of coordination polymers con-
taining transition metals. Oximes, and their specific subclass – cya-
noximes NCeC(]NOH)eR – are known to form 1D and 2D coordina-
tion polymers with Ag(I) and Tl(I) [56]. In addition to a series of mono-
cyanoximes [57], bis-cyanoximes are of interest in the formation of
coordination polymers as well, and their use has been studied in recent
years [58,59]. It should be noted that, though Tl is widely known for its
high toxicity, other no less toxic, elements in binary GaAs, selenides,
tellurides of Pb and Cd, and halogenides of Hg are already widely used
in enclosed electronic devices [53]. Lastly, Tl(I) was found to be a very
valuable component of luminescent heterometallic polymeric com-
plexes, with heavy metals such as Pb [60], Au [95] and especially Pt
[61–66]. Coordination polymers of Tl(I) with short intermetallic dis-
tances represent precursors for these systems especially when me-
tallophilic interactions [67,68] play role in shaping the geometry of
complexes formed. Coordination polymers itself represent vigorously
developing area of modern inorganic chemistry research due to re-
markable range of applications [69].
In this work, we report the synthesis and detailed characterization
of four Tl complexes with two mono-cyanoximes such as phenylcya-
noxime, NCeC(]NOH)eC6H5 (further as H(PhCO)), NCeC(]NOH)
eC6H4F (later as H(2F-PhCO)), and with two isomeric bis-cyanoximes
1,3-biscyanoxime benzene (later as H2(1,3-BCO)) and 1,4-bis-cya-
noxime benzene (later as H2(1,4-BCO)) structures, which are shown in
Scheme 1. The latter ligands, due to their 120° or 180° angle in mutual
orientation of ionizable cyanoxime groups, offer better possibilities for
the formation of extended coordination polymers in which close me-
tal–metal separation can be achieved.
2.3. Syntheses of mono- and bis-cyanoximes
H(PhCO). Preparation of this ligand was carried out using benzyl-
cyanide, NC-CH2-C6H5 and commercially-available amylnitrite C5H11
-
ONO in isopropanol, according to published procedures [53,71]. Phy-
sical parameters such as m.p., TLC Rf value, and 1H, 13C{1H} NMR
spectra, match those reported for this cyanoxime.
H(2F-PhCO) and H(3F-PhCO) [72]. These isomeric mono-
substituted arylcyanoximes were prepared in similar fashion and only
one prep for the first one will be given in detail. Thus, 0.182 g
(7.91 mM) of thinly sliced Na metal was dissolved at 25 °C in i-PrOH
(100 ml) under a N2 atmosphere in a 250 ml capacity three-neck flask.
Following dissolution of the metal, 10 ml of a 7.90 mM of 2-fluor-
ophenylacetonitrile in isopropanol was added, dropwise, within
2–3 min, to the first solution. The gaseous methylnitrite CH3-ONO
generated in situ was bubbled through the mixture within ∼20 min, at
room temperature under a N2 blanket (Associated content: Electronic
Supporting Materials, ESI 2). At this stage, the reaction mixture gained
a bright-yellow color. The reaction flask was closed and left in a re-
frigerator overnight at +4 °C. The solvent was removed under reduced
pressure using the rotovap, and the obtained yellow sludge was further
dried at room temperature by an oil pump. The foamy solid residue was
dissolved in 30 ml of H2O to form a caustic yellow solution which was
dropwise acidified with HCl (1:5 by volume) to pH ∼ 4, then saturated
with solid NaCl to form brine. White powdery cyanoxime H(2F-PhCO)
precipitated shortly, and was filtered, washed with cold water dried
over P4O10 in a vacuum desiccator. The yield of the H(2F-PhCO) is 74%,
m.p. = 118 °C; Rf = 0.28 in the 1:4 ehtylacetate/hexane mobile phase.
1H NMR in dmso-d6, ppm: 14.22 for OH (broad singlet 1H); aromatic:
7.68 (m, 1H), 7.57 (m 1H), 7.38(m, 1H), 7.32(m, 1H). According to
both 1H and 13C{1H} NMR spectra this cyanoxime represents single syn-
isomer (ESI 3 and 4). IR spectrum in KBr disk, cm−1: 3257 – ν(OH);
3085,3009 – ν(CeH, arom); 2234 – ν(C^N); 1493,1462 – ν(C]C);
2. Experimental part
2.1. General considerations
1056, 972 – ν(NeO). UV–visible spectrum (in EtOH): 228 nm
(ε = 7200), CN group; 302 nm (ε = 8900), oximino/aryl fragment.
High resolution mass-spectrometry for C8H5FN2O calculated: 165.1444
(for M + 1), found 165.0963.
The yield for H(3F-PhCO) was 51%, white powder, m.p. = 115 °C,
and Rf = 0.14 in 1:4 ethylacetate/hexane mobile phase. The 1H NMR in
dmso-d6, ppm: 14.11 for OH (singlet, 1H); aromatic region: 7.79
(doublet, 1H); 7.74–7.18 (meta-, 3H). UV-spectrum in methanol, π-π
Precursors for cyanoximes, such as phenyl-acetonitrile C6H5-
CH2CN, 2-fluorophenyl-acetonitrile, and substituted 1,3- and 1,4-
phenyl-diacetonitriles of C6H4(CH2CN)2 formula were purchased from
Sigma-Aldrich. All other chemicals and solvents – i-PrOH, NaNO2,
H2SO4, and HCl, which were purchased from Fisher Scientific, with
sodium metal from Fluka, were of sufficient quality, and used without
Scheme 1. Chemical formulas of the five reported cyanoximes with their abbreviations.
2

S. Curtis, et al.
InorganicaChimicaActa508(2020)119597
Scheme 2. General synthesis of aryl-cyanoximes and their Tl salts.
transitions: 224 nm (ε = 8150; cyano-group), 304 nm (ε = 7770; oxi-
mino group). IR spectrum in KBr disk, cm−1: 3254 – ν(OH); 3085,2976
– ν(CeH, arom); 2250,2201 – ν(C^N); 1585,1490 – ν(C]C); 1073,
1009 – ν(NeO). High resolution mass-spectrometry for C8H5FN2O cal-
culated: 165.1444 (for M + 1), found 165.0791. The 13C{1H} spectra
showed double set of signals indicating presence of two diastereomers
(ESI 5), which was earlier confirmed by the crystal structure of this
compound existing as 60:40% mixture of syn- and anti-isomers re-
spectively [54].
Syntheses of bis-cyanoximes H2(1,3-BCO) and H2(1,4-BCO) were
analogous, and a general procedure used for the preparation of both
compounds, as follows. Thus, 2.00 g (9.3 mM) of aryl-bis-acetonitrile
(Scheme 2A) were dissolved in 50 ml of isopropanol. In a separate Er-
lenmeyer flask with 100 ml of the same solvent thinly sliced metallic
sodium, 0.428 g (18.6 mM) was dissolved under a N2 gas protection to
form a clear solution. After mixing both solutions, a flow of colorless,
gaseous, CH3ONO (ESI 2) bubbled for 35 min through the mixture,
which immediately changed color from clear to bright yellow. The flask
was closed and placed into the refrigerator at +4 °C overnight. The
solvent was removed using the rotovap at +40 °C to form a yellow
sludge that was further dried using an oil pump at room temperature. A
foamy solid residue then was dissolved in distilled water to form a
yellow solution, and then dropwise acidified to pH ∼ 3 with 25% HCl
until a fine, milky-white solid precipitated. The bis-cyanoxime was
filtered, washed with cold water, and dried in a vacuum desiccator
charged with CaCl2 and H2SO4(c).
group), 122.45, 127.98, 131.24 (oxime carbon), 130.84, 130.90; minor
component: 115.77 (CN group), 126.03, 128.55, 133.09 (oxime
carbon), 130.56, 128.65. For 1,3-BCO the UV spectra, λmax, nm (ε,
cm−1 × M−1): in methanol 2258 nm (2600), ethanol 2259 nm (6840),
n-propanol 2260 nm (4160).
The yield for 1,4-BCO was 47%; m.p. = 197 °C (with decomposi-
tion); Rf = 0.26. Analysis for C10H6N4O2·H2O calculated (found, %): C
51.73 (52.28), H 3.47 (3.57), N 24.13 (23.36). IR spectrum (KBr disk;
cm−1): 3508 ν(OeH), 3324 ν(CeH), 2239 ν(C^N), 1624 (ν(C]N),
1516, 1421, 1409 ν(C]C), 973 ν(NeO), 468 (δ (C]C)). NMR 1H
spectrum (δ ppm): 7.82 (singlet, 2H phenyl group), 13.98 (H, oxime,
singlet). The 13C{1H} NMR spectrum (δ ppm): 110.30 (CN-group),
131.90 (oxime carbon), 130.98 (ipso-carbon), 126.78 (phenyl group
carbon). For 1,4-BCO the UV spectra, λmax, nm (ε, cm−1 × M−1): me-
thanol 2297 nm (3480), ethanol 2300 nm (5370), n-propanol 2302 nm
(3870).
2.4. Synthesis of Tl(I) cyanoximates
Tl complexes of each cyanoxime were synthesized by adding the
solid cyanoxime in small aliquots to a 95 °C aqueous solution of Tl2CO3,
as depicted in Scheme 2 (ESI 6 and 7). All Tl-cyanoximates are light
stable and non-hygroscopic compounds, soluble in water upon heating
and insoluble in common organic solvents such as alcohols, acetone,
ether, EtOAc, CH2Cl2 and CHCl3, but dissolve in polar donor solvents
such as DMF, DMSO, and pyridine. All Tl(I) derivatives of the mono-
cyanoximes give a very good elemental analyses data, contrary to the
bis-cyanoximates in which carbon content for an unknown reason was
off (see below).
The yield for 1,3-BCO was 34%; m.p. = 193 °C (decomposition);
Rf = 0.42 using 9 : 1 chloroform–methanol mobile phase. Analysis for
C
10H6N4O2·0.5H2O calculated (found %): C 53.81 (54.54), H 3.16
(3.16), N 25.10 (24.76). IR spectrum (KBr disk; cm−1, tentative as-
signments): 1021 ν(NeO), 3293 ν(OeH), 1700 ν(CeN), 1403, 1254,
1232 ν(CeC), 2260 ν(C^N). The NMR 1H spectrum (complicated, due
to presence of two diastereoisomers, δ ppm): 14.07 (minor narrow
singlet oxime), 13.96 (main narrow singlet), 8.00 (multiplet, 1H, be-
tween two cyanoxime groups), 7.83–7.80 (multiplet, 2H, at ortho-po-
sitions to cyanoxime groups), 7.66–7.61 (multiplet, 1H, at meta-position
to cyanoxime groups). The 13C{1H} NMR spectrum, δ ppm (double set
of signals due to presence of two isomers) main component: 110.29 (CN
The Tl(PhCO) appears as very fine long and thin lemon-yellow
needles (ESI 8 and 9).
The Tl(2F-PhCO) represents orange-yellow needles. Elemental
analyses calculated (found), %: C − 26.14 (26.02); H − 1.10 (0.95); N
− 7.62 (7.59) [71]. The IR spectrum (ATR method, cm−1): ν(CeH) −
3080; ν(C^N) − 2205; ν(C]C) − 1494; ν(CNO) − 1105; ν(NeO) −
995.
The Tl(3F-PhCO) represents bright-yellow needled. Elemental ana-
lysis calculated (found), %: C – 26.14 (26.11), H – 1.10 (0.91); C – 7.62
3

S. Curtis, et al.
InorganicaChimicaActa508(2020)119597
Table 1
Crystal and refinement data for studied in this work Tl-cyanoximates.
Parameter
Tl2(1,3-BCO)
Tl2(1,4-BCO)
Tl(PhCO)
Tl(2F-PhCO)
Tl(3F-PhCO)
Formula
C10H4N4O2Tl2
620.91
120(2)
0.71073
Monoclinic
C 2/c
a = 21.672 (4)
b = 7.8698 (13)
c = 6.9082(11)
α = 90
β = 98.487(2)
γ = 90
1165.3(3)
4
C5H2N2OTl
310.46
120(2)
0.71073
Triclinic
C8H5N2OTl
349.51
120(2)
0.71073
Orthorhombic
P bca
a = 15.1903(8)
b = 6.8828(3)
c = 32.513(3)
α = 90
β = 90
γ = 90
3302.1(18)
8
2.812
19.511
2496
C8H4N2OTlF
367.5
100(2)
1.54178
Monoclinic
P 21/c
a = 4.1126(4)
b = 6.5823(5)
c = 30.905(2)
α = 90
β = 93.595(4)
γ = 90
834.96(12)
4
C8H4N2OTlF
735.00
100(2)
0.71073
Orthorhombic
P n a 21
F.W., g/mol
Temperature
Wavelength, λ
Crystal System
Space group
Unit cell, Å/°
P-1
a = 3.9696(15)
b = 6.672(2)
c = 11.149(4)
α = 83.551(5)
β = 82.254(5)
γ = 89.516(5)
290.73(17)
2
a = 14.1040(17)
b = 3.7562(8)
c = 30.905(2)
α = 90
β = 90
γ = 90
Cell volume, Å3
Z
1679.1(5)
4
D (Calc), Mg/m3
3.539
27.619
1080
3.546
27.675
270
2.924
37.017
656
2.908
19.210
1312
Abs. μ (mm−1
)
F(0 0 0)
Cryst. Size, mm
Θ Range
0.10 × 0.08 × 0.06
1.90–30.51°
h: −30 to 30
k: −11 to 11
l: −9 to 9
8280
0.1 × 0.06 × 0.04
1.86–26.20°
h: −4 to 4
k: −8 to 8
l: −13 to 13
3208
0.5 × 0.06 × 0.05
1.85–25.24°
h: −17 to 17
k: −8 to 8
l: −38 to 38
2894
0.62 × 0.26 × 0.06
1.90–30.51°
h: −4 to 4
k: 0 to 7
l: 0 to 34
5056
0.080 × 0.080 × 0.280
2.89–27.52°
h: 0 to 17
k: 0 to 4
l: 0 to 40
1261
Index Ranges
Reflections total
Independent Refl.
1757
1158
1952
1204
1261
[R(int) = 0.0474]
99.20%
[R(int) = 0.0418]
99.40%
[R(int) = 0.1013]
99.80%
[R(int) = 0.0483]
91.20%
[R(int) = 0.0691]
71.5%
Completeness, %
Absorption Method
Semi-empirical
0.7464/0.3027
1757/0/83
1.073
Semi-empirical
0.7453/0.4122
1158/0/70
1.035
Semi-empirical
0.2094/0.0645
2894/190/217
1.038
Numerical
0.2148/0.0165
1204/0/60
1.04
Semi-empirical
0.3090/0.0750
1261/334/236
1.59
Tmax. and Tmin.
D/R/P**
GOF on F2
Final R values [I > 2σ(I)]
R1 = 0.0388,
wR2 = 0.0813
R1 = 0.0480,
wR2 = 0.0862
4.628/−2.785
830.2 (71.2)
3D
R1 = 0.0402,
wR2 = 0.0972
R1 = 0.0464,
wR2 = 0.0998
4.161/−2.118
205.8 (70.8)
2D
R1 = 0.0655,
wR2 = 0.1344
R1 = 0.1058,
wR2 = 0.1554
3.145/−1.864
2200.3 (66.6)
2D
R1 = 0.0740,
wR2 = 0.1949
R1 = 0.0740,
wR2 = 0.1949
3.439/−3.288
586.2 (70.2)
1D
R1 = 0.0702,
wR2 = 0.1234
R1 = 0.0887,
wR2 = 0.1254
4.076/−2.977
1162.3 (69.2)
3D
R Indices (all data)
Largest Peak/Hole, e− Å3
Volume Taken, Å3 (%)
Dimensionality
* – Refinement Method Full-matrix least-sq. on F2 ** – listing of Data, Restraints, and Parameters.
(7.53). The IR spectrum: ν(CeH) − 3080; ν(C^N) − 2201; ν(C]C) −
1493; ν(CNO) − 1109.
The Tl2(1,3-BCO) is a dark yellow powder. It is soluble in water at
elevated temperatures and insoluble in EtOAc. Anal. Calc. (Found): C:
19.34 (19.98); H: 0.65 (0.7); N: 9.02 (9.17). IR (ATR, cm−1): ν(CN):
2207; ν(C]C): 1441, 1250, 1244; ν(NeO): 1032.
The Tl2(1,4-BCO) is a bright yellow powder. Anal. Calc. (Found): C:
19.34 (19.50); H: 0.65 (0.60); N: 9.02 (8.77). IR (ATR, cm−1): ν(CN):
2207; ν(C]C): 1396, 1311; ν(NeO): 978.
Safety Note: Although no difficulties or accidents have ever occurred in
many years of laboratory work, extreme care should be taken when working
with Tl salts because of their high toxicity, water solubility, and the ready
absorption through the skin of aqueous Tl2CO3 solutions. Wearing of pro-
tective gloves is absolutely necessary, while face masks are not, due to very
low volatility of ionic thallium(I) compounds.
X-Ray Crystallography. Selected crystals of these complexes were
placed into the CryoLoop, or MiTeGen plastic loops and then attached
to the copper pin positioned on the goniometer head of the Bruker
APEX2 diffractometer, equipped with a SMART CCD area detector. The
data sets were measured at temperatures below 150 K. The intensity
data for Tl(PhCO), Tl2(1,3-BCO) and Tl2(1,4-BCO) were collected in ω
scan mode, using the Mo tube (Kα radiation; λ = 0.71073 Å) with a
highly oriented graphite monochromator. The intensities were in-
tegrated from four series of 364 exposures each, covering 0.5° in ω at 10
to 60 s of exposure time, with the total data set being a sphere.
We should note that two out of five studied crystalline compounds
were difficult samples for single crystal analysis. There were poor
quality thin, needle habitus crystals of Tl(2F-PhCO) and its isomeric Tl
(3F-PhCO) which also turned out to be twinned or multi-domain
specimen, yet poor diffractors (ESI 10). We were lucky to reliably de-
termine their crystal and molecular structures, albeit low precision of
bonds length to
0.01 Å. These two structures generated several A
and B-type alerts that we explained in their checkCIF reports. Very
small and poor quality needles of Tl(2F-PhCO) were studied using a
more intense Cu tube (Kα radiation; λ = 1.54178 Å). Still, the best
selected for studies specimen was the rotational twin crystal. Successful
structure solution and refinement was carried using twin law
[−1 0 0 0 −1 0 1 0 1] and BASF 0.241. It was not possible to make a
reasonable refinement of atoms in this structure in anisotropic ap-
proximation without structure of getting imploded and having non-
positive-definites (NPDs). Therefore, all non-H atoms and Tl centers
were chosen to be in isotropic approximation. Similarly, the best se-
lected crystal of Tl(3F-PhCO) complex also turned out to be multi-
component specimen, but was successfully refined as an inversion twin
with BASF 0.618 using just two most intense domains. It was not pos-
sible to make a reasonable refinement of atoms in this structure in
freely in anisotropic approximation without structure of getting im-
ploded and having non-positive-definites (NPDs). In order to avoid the
overuse of SIMU, DELU commands we applied ISOR 0.001 restraint and
RIGU instruction to keep fully converged structure reasonable.
Thallium atoms in the structure appeared with normal thermal para-
meters. In summary, non-single crystalline specimen used for these
studies and approximated as twins contained other smaller domains
that contributed into overall electron density count. As such, we ob-
served some 3–4 electrons “ripples” next to Tl atoms, as well as some
holes of about the same magnitude of charge. Location of both is the
very close proximity to thallium centers and does not have chemical
meaning.
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InorganicaChimicaActa508(2020)119597
help of Bruker Vertex S70 spectrophotometer.
3. Results and discussion
3.1. Preparation of compounds and crystals growth.
X-Ray-suitable crystals of TlL (L = PhCO−, 2F-PhCO−) and Tl2L
(L = 1,3-BCO2−, 1,4-BCO2−) were grown from the mother liquors
upon slow cooling in a thermostat within several days. Thus, im-
mediately after the reaction between Tl2CO3 with solid HL (or H2L) to
complete CO2 evolution, the reaction mixture was hot-filtered at 95 °C
into long test tubes, already positioned in the large Dewar flask filled
with water at that temperature (ESI 6 and 7). These test tubes, with
mother liquors, being well insulated from surrounding in 4l of pre-
heated to 95 °C water, were left undisturbed for 5 days. When the
system was opened, long needles of Thallium(I) cyanoximates were
filtered using gravity filtration and paper filters, and air dried. Crystals
of Tl(PhCO), Tl2(1,3-BCO) and Tl2(1,4-BCO) suitable for X-ray analysis
were harvested right away, while selection of single crystals of Tl
(PhCO) and Tl(2F-PhCO) was a challenging task, due to their high
propensity for twinning. In fact, the best specimen of the latter complex
selected for studies was a pseudo-merohedral twin, containing two
components at 24% and 76% contribution.
3.2. Crystal Structures.
Structure of Tl(PhCO). The crystal structures of two TlL complexes
(L = 2Cl-PhCO− and 4Br-PhCO−) represent uncommon examples of
the double-stranded columnar coordination polymers, in which linear
arrays of Tl+ ions exhibit short intermetallic distances. The distance
between π-π interacting haloaryl groups reflects their ‘thickness’ and
affects Tl—Tl separations. Thus, the smallest halogen atom in size,
provides the closest inter-thallium distances. In light of that finding, it
was very interesting to synthesize the Tl+ complex with unsubstituted
arylcyanoxime – H(PhCO) – oxime. We postulated that the absence of
any halogen atoms at the phenyl group should provide the closest
distances between unsubstituted phenyl groups, and will lead to the
shortest Tl—Tl separations. This turned out not to be the case: the
molecular structure of the Tl(PhCO) is shown in Fig. 1 and exhibits two
crystallographically different cyanoxime anions which are differently
connected to Tl+. Because of the uniqueness of this structure we de-
scribe it in detail.
The molecular structure and numbering scheme of a single dimeric
unit of Tl(PhCO) is shown in Fig. 1A. This complex crystallizes in the
orthorhombic crystal system, and two projections of the unit cell con-
tent are presented in Fig. 1B,C, while crystallographic information is
shown in Table 1. The values of bond lengths and valence angles in the
complex are given in the ESI 18. The crystal structure of Tl(PhCO) re-
presents a highly unusual case of one-dimensional coordination poly-
mers, comprised of a non-centrosymmetric dimer with anions in the
trans-anti configuration [79] with two phenylcyanoxime anions PhCO−
in the structure having different geometries: one is non-planar, while
the other one is practically planar. The ligand, that has the shortest
Tl2–O1 and Tl1–O1 bonds, is in non-planar configuration similar to that
in the structure of the uncomplexed phenylcyanoxime reported recently
[80]. The anion is arguably in the nitroso-form judging the shorter
O1–N1 bond than N1–C1 in the fragment (ESI 18). In the non-planar
anion there are two planar fragments in the structure of the anion: the
cyanoxime and phenyl groups joined together at the C1 atom (Fig. 1).
The dihedral angle between the two planar fragments C4-C3-C1-N1 and
C8-C3-C1-N1 is 14.3°. The second phenylcyanoxime anion is planar,
with the value of the dihedral angle between the cyanoxime plane and
phenyl group equal at 3.7°. This particular anion has less of the nitroso-
character: N3–O2 = 1.310 Å and C9–N3 = 1.320 Å (ESI 18). The
crystal packing diagram for this complex is also unusual. The structure
of Tl2O2 rhomb is unconventional too, when compared to those in our
Fig. 1. A – Molecular structure and numbering scheme of the asymmetric unit
(ASU) in the structure of Tl(PhCO). B – Organization of the one-dimensional
coordination polymer in the structure of Tl(PhCO). Two orthogonal views: B –
normal to [100] plane; C – normal [0 1 0] plane showing slightly “slipped” π-π
interactions. Arrows indicate asymmetric dimers.
The space group determination in all cases was done with the aid of
XPREP software [73]. The absorption correction was performed, using
values from face-indexed crystals and numerical values obtained from
the set of images recorded with the video-microscope (ESI 11), followed
by the SADABS program that was included in the Bruker AXS software
package [73–76]. All structures were solved by direct methods, and
refined by least squares on weighted F2 values for all reflections, using
the SHELXTL program. The structures reported herein did not have
apparent errors, and are well refined. Crystal and refinement data can
be found in Table 1, while selected bond lengths and angles are pre-
sented in appropriate places in the ESI sections 18,20,27,31. For
drawings were using the ORTEP 3v2 [77,78] and Mercury software
packages [79]. Thermal ellipsoids in all figures are drawn at their 50%
probability level. All four crystal structures have been deposited into
the CCDC: 1,969,209 for Tl(PhCO), 1,969,208 for Tl(2F-PhCO),
1,990,393 for Tl(3F-PhCO), 1,969,206 for Tl2(1,3-BCO) and 19,690,007
for Tl2(1,4-BCO).
Thermal analysis. The TG analysis was performed on the TA
Instrument Q-600, in an alumina crucible, under pure nitrogen flow, in
the range between 30 and 1000 °C at 100
2 ml/min, and a heating
rate ranging from 10 °C/min. The crucible was calcined prior to each
experiment using the propane torch (ESI 44). Data of the TG analyses
were processed using the TA Universal Analysis software package.
Spectroscopy. Diffusion reflectance spectra of all obtained com-
plexes in solid state in the range of 300–850 nm were recorded with the
help of CARY Bio 100 equipped with integrating sphere (from
Labsphere), while electronic spectra in aqueous solutions were obtained
with an HP 8453 spectrophotometer. The IR spectra of Tl(I) cyanox-
imates were recorded using grinded pure samples of complexes on a
Bruker ATR X80 spectrometer, since pressing KBr pellets with thallium
complexes leads to the metathesis reaction between Tl(I) and Br−
anion. The Raman spectra of these compounds were obtained with the
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InorganicaChimicaActa508(2020)119597
Fig. 3. Fragment of crystal structure of Tl(2F-PhCO): A – one cyanoxime and
several closest Tl(I) centers, B – important bond length in the anion connected
to the neighboring Tl(I) atoms, C – the same fragment, only metal centers ex-
pressed as van-der-Waals spheres emphasizing metallophilic interaction. H-
atoms are omitted for clarity. Symmetry codes for positions: #1 is 2 − x; ½ + y;
½ − z, #1_1 is 1 + x; ½ − y; ½ + z. #1_2 is 1 − x; ½ + y; ½ − z, #1_3 is
1 + x; ½ − y; 2 + z, and for #1_4 is x; ½ − y; ½ + z.
Fig. 2. Intermetallic distances in Tl(PhCO): A – the least obstructed view of the
1D zig-zag chain in the structure showing all four closest Tl—Tl distances; B –
the same arrangement suitably turned to show Tl atoms as wan-der-Waals
spheres. H-atoms are omitted for clarity. Symmetry codes for 1: 1 − x, 1 − y,
1 − z; for _1: ½ + x, ½ − y, 1 − z.
planar. Cyanoxime is in the nitroso form judging from bond lengths as
follows: C7–N1 = 1.408 Å, N1–O1 = 1.335 Å (ESI 18). The crystal
structure of this complex represents a truly 1D coordination polymer
with the ‘building block’ as centrosymmetric [Tl(2F-PhCO)]2 units
containing the planar cyanoxime anion with an inversion center in the
middle of a dimer (Fig. 4A). Geometries of the cyanoxime anion in the
ASU, as well as intermetallic distances between the closest neighboring
Tl atoms, are presented in Fig. 4. There are also short thallophilic in-
teractions in the structure (Fig. 3C).
previous studies of Tl-cyanoximes [81–84]. There are two crystal-
lographically different Tl(I) atoms (Figs. 1 and 2). Each has its own
unusual zig-zag 1D pattern (ESI 13–16). Examination of the coordina-
tion polyhedron reveals an unconventional and, in fact very rare,
structure, with regard to the Tl and O atom connectivity. Thallophilic
interactions are clearly visible in the structure (Fig. 2B).
Examination of the coordination polyhedron of Tl(2F-PhCO) reveals
its essentially trigonal pyramidal structure (Fig. 3A and B). The shortest
The geometry of intermetallic distances in the structure of Tl(PhCO)
is shown in Fig. 2, while peculiarities of polymer formation are depicted
in ESI 14. Two non-centrosymmetric Tl(PhCO) dimers are joined to-
gether by O1 and O2 atoms of the oxime groups, which act as two
different bridges (Fig. 2). Thus, O1 atoms form two short contacts be-
tween Tl1 and Tl2 centers, while O2 atoms form three slightly longer
bonds, with two Tl1 and one Tl2 cations (ESI 14). The distance Tl2_7 –
O2 = 3.518 Å is significantly longer than any reasonable chemical bond
and represents an electrostatic contact (ESI 16). The resultant Tl2O2O’
polyhedron is a highly distorted trigonal bipyramid. Some interaction
between the Tl atoms and N atoms from the cyano-groups were ob-
served being both within, and between, the polymer chains, which
extend structure into puckered sheets. The intra-columnar contact
(Tl2–N4) of shortest distance is 3.325 Å, while the shortest inter-co-
lumnar Tl–N distance is 3.021 Å [72]. Organization of polymeric col-
umns structure is shown in ESI 12 and 15. Further details of crystal
packing in this highly unusual structure of Tl(PhCO) complex are pre-
sented in ESI 16. The rarity of the observed crystal structure of this
complex is such that there are only a few other structures known that
somewhat resemble Tl(PhCO) [87].
Fig. 4. Fragment of the crystal structure of Tl(2F-PhCO) showing two pro-
spective views of isolated 4-unit cells extended along a-direction (A) and b-
direction (B). The formation of the centrosymmetric dimers Tl2L2 is indicated
with a blue arrow. Weak F—H interactions are marked with a grey arrow. H-
atoms are omitted for clarity. (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this article.)
Structure of Tl(2F-PhCO). The molecular structure and numbering
scheme for this compound are shown in Fig. 3 with the most essential
bonds and angles presented in ESI 17. The anion in this complex adopts
trans-anti (with respect to the oxime group) geometry and is practically
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InorganicaChimicaActa508(2020)119597
Fig. 5. Molecular structure and principal atoms numbering scheme for Tl(3F-
PhCO) (A) and view of the unit cell content along b-direction showing lack of
center of center of symmetry and stabilizing lattice short CeH—F contacts (B).
Tl–O bond length in Tl2O2 rhomb is 2.595 Å (Tl1–O11) with the second
being 2.670 Å (Tl1–O1), and another Tl1—O1 distance in the closest
ASU unit being 2.645 Å. The O–Tl–O angles in the Tl2O2 rhomb are
77.24° and 101.37° (ESI 19). The [Tl(2F-PhCO)]2 dimeric units are
forming a ladder-type column due to bonding between the Tl1 center
and the O1 atom of the similarly aligned neighboring unit (Fig. 4). That
1D extension is also quite well stabilized by ‘slipped’ π-π stacking in-
teractions between fluoro-phenyl groups (Fig. 5B). In addition, weak,
but stabilizing, F—H(phenyl group) interactions between columns are
also present (Fig. 4A) at a distance of 2.875 Å. In line with previously
determined TlL structures [54,58,88] and other structures presented
here, there is a long, non-bonding interaction, most likely of electro-
static nature, between the Tl atoms and the nitrogen atoms of the CN-
group. These are intra-columnar Tl1—N2 electrostatic contacts Tl1–N2
at 3.160 Å.
Structure of Tl(3F-PhCO). Structure of this compound is also quite
unique and differs entirely from its analogous and isomeric complex Tl
(2F-PhCO) described above. First of all there are two crystal-
lographically different metal centers and fluorinated cyanoxime anions
(Fig. 5A). This situation is somewhat similar to tha structure of Tl
(PhCO) discussed above. Secondly, this complex crystallizes in non-
cenrtrosymmetric space group Pna21 (Table 1). Then, there is no for-
mation of Tl2O2 rhombs, but instead the cyanoxime exhibits rare “side-
on” coordination which we previously observed only in one case of Tl(I)
pyridine-based cyanoxime [57]. There are two zig-zag chains of Tl1—
Tl2—Tl1—Tl2 atoms running parallel a-dimension (Fig. 5B). Both
chains are on a top of each other forming an unusual “thallium ladder”
with bent at 135.7 and 134.5° (Fig. 6) with very pronounced metallo-
philic interactions were observed in this structure. Each Tl center has
severely distorted octahedral environment with clearly identifiable
place for stereoactive 6 s2 lone pair (ESI 21). Octahedrons of metal
atoms both for Tl1 and Tl2 are fused by the face forming infinite chain.
Further details of this truly unique structure can be seen in ESI 22. Both
cyanoximes are practically planar and are in the nitroso form judging
shorter NeO than CeN bonds in that fragment (ESI 20).
Fig. 6. Two different prospective views of partial unit cell content showing
geometry of metal atoms in one chain of a “thallium ladder”: A – space filling
representation indicating very close contacts, and B – angles between atoms.
Structure of Tl2(1,3-BCO). The 1,3-BCO bis-cyanoxime ligand has a
complex 1H and 13C NMR signature which evidences the rather rich
stereochemistry of this seemingly simple compound [89]. Restricted
rotation around CeC bonds between cyanoxime fragments and the
phenyl ring, as well as the presence of syn- and anti- geometrical iso-
mers, are responsible for such conformational richness, explained in ESI
26. In the studied Tl2(1,3-BCO) complex, ligand’s diastereomer 9 is
present. The ligand is in the oxime- form (ESI 27), and is not planar,
with a small dihedral angle of 11.99° between the cyanoxime fragment
and the aromatic ring. One 1,3-biscyanoxime anion, and its closest Tl
centers, are presented in Fig. 7A, while the shortest intermetallic dis-
tances are shown in Fig. 7C. The bis-cyanoxime acts as bridging ligand
(Fig. 8A). Organization of crystal structure and packing into crystal can
be viewed in Fig. 8B. There are non-planar and non-centrosymmetric
rhombs formed in the structure of Tl2(1,3-BCO) (ESI 23). As such, it
should be especially noticed, the overall structural motif is not the
double-stranded “ladder-type” as that for Tl(2F-PhCO)! It is much more
complex and can be explained as an interconnected system of both
types of planar and non-planar Tl2O2 rhombuses (ESI 24 and 25). Thus,
the structure of Tl2(1,3-BCO) also represents an inter-tangled puckered
sheets of Tl2O2 units with the cyanoxime anions acting as a tridentate
bridge between Tl atoms via O atoms (Fig. 8A). Slipped ‘π-π stacking’
interactions with shortest contact at ∼3.95 Å align aromatic rings,
which helps in crystal packing (ESI 23). Thus, the structure represents
elegant pleated sheets, which, via additional Tl—O contact, are ex-
tended into the 3D framework. Details of intermetallic Tl—Tl distances
in the structure are shown in Fig. 7C where short thallophilic
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InorganicaChimicaActa508(2020)119597
Fig. 7. A – Fragment of crystal structure of Tl2(1,3-BCO) showing one bis-cy-
anoxime and closest metal centers; B – the shortest intermetallic distances in
the complex; C – a slightly rotated similar view with metal ions expressed as
van-der-Waals spheres emphasizing metallophylic interactions.
Fig. 9. A – The GROW fragment in the structure of Tl2(1,4-BCO) showing the
atomic numbering scheme (the inversion center is in the middle of the phenyl
ring with respective symmetry codes for #1 position as: −x, −y, −z), and
perspective view of several unit cells in the structure of Tl2(1,4-BCO) showing
organization of the crystal lattice: B – view along a-direction presenting the
formation of Tl2O2 rhombs, C – view along b-direction displaying the formation
of ladder-type motif and slipped π-π stacking interactions (arrow). H-atoms are
omitted for clarity.
Examination of the coordination polyhedron of Tl in the molecule
reveals a T-shaped arrangement of the surrounding O atoms, with the
true structure being of a highly distorted trigonal pyramidal geometry
(ESI 28 and 29). The shortest Tl1–O1 bond is 2.561 Å, with the other
two metal–oxygen distance also being shorter than the sum of ionic
radii of these elements and implying certain degree of covalency in
chemical bonding (Fig. 7A).
Structure of Tl2(1,4-BCO). The bis-cyanoxime ligand in this struc-
ture is present as trans-anti-diastereomer 10 (ESI 30 and 32). The
atomic numbering scheme for the dianion is shown in Fig. 9A. The li-
gand is in the oxime form as evident from C1–N1 and N1–O1 bonds
being 1.300 Å and 1.393 Å, respectively (ESI 31). The ligand adopts a
practically planar structure, with a dihedral angle of 7.77° between the
ring and the cyanoxime fragment. Similarly to the Tl(2F-PhCO) and
Tl2(1,3-BCO) complexes described above, there is a formation of dis-
tinct centrosymmetric and planar Tl2O2 rhombs (Fig. 9B and C). Every
CeNeO fragment in the complex has three short Tl1–O1 bonds geo-
metry, which is given in Fig. 10A. The shortest O1–Tl1 distance is
2.559 Å, with the other two being less than 2.7 Å, and all three shorter
than the sum of ionic radii of involved elements. The geometry of in-
termetallic distances in this complex is displayed in Fig. 10B and 10C,
with the shortest Tl—Tl metallophylic contact determined to be
3.784 Å. The overall structure motif is columnar (Fig. 9B and C), but
with additional Tl1—O contacts, a ‘ladder-type’ 2D polymer is formed
(Fig. 9B). There are two Tl2O2 rhombs, slightly different in geometry,
and the Tl–Tl–Tl angle is 98.72° in the zig-zag chain of the ‘ladder’ (ESI
34). Further details of geometry in this arrangement can be viewed in
Fig. 8. A – The ASU in the structure of Tl2(1,3-BCO) showing atomic numbering
scheme and formation of planar centrosymmetric Tl2O2 rhomb, B – fragment of
crystal structure of Tl2(1,3-BCO showing details of crystal packing with view
along c-direction.
interactions were observed as well. The shortest distance was found to
be 3.670 A, which amounted to metallophylic interactions. The shortest
Tl1—N2 interatomic distance of an intra-columnar nature is 3.541 Å,
and the shortest distance between the columns is 3.142 Å. These can be
considered only as electrostatic interactions, with no bonding occurring
between Tl and the cyano group.
A remarkable property of the Tl2(1,3-BCO) crystal structure is the
presence of a large pore/channel within its lattice. The pore is large,
∼6.55 Å across, and potentially these pores may be able to hold a
variety of gases with smaller kinetic diameters. That variety includes
gases such as H2, SO2, CO2, CH4, and other greenhouse gases [72], and
this case represents the first example of porous crystal structures based
on cyanoximes. No attempts to measure the surface area inside the
channel were made at this stage, but are considered for future work
using the BET method.
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InorganicaChimicaActa508(2020)119597
been confirmed by Raman spectroscopy, upon comparison of spectra of
uncomplexed, solid cyanoximes with spectra of TlL. Thus, a pronounced
low frequency shift in the range 2250–2100 cm−1 was detected for the
nitrile group (ESI 37, 39, 41 and 43). Also, for the first time, we were
able to identify and assign νsym and νasym Tl–O vibrations in the range of
150–50 cm−1 associated with the Tl2O2 rhombs described above (ESI
36, 38, 40 and 42).
3.4. Electronic spectra: absorption and emission.
All synthesized complexes are yellow in color, and demonstrate
single absorbance at ∼400 nm, due to the n → π* transition in the ni-
troso-chromophore, both in solutions and in solid state
[20,30,48,50,97]. When ground powdery samples of TlL and Tl2L’
(L = mono- and L’ = bis cyanoximes), are excited at 380 nm, all solid
compounds are strongly emissive, with red-shifted for ∼30 nm single
band for Tl(2F-PhCO) and Tl2(1,3-BCO), and with the most re-
presentative spectrum shown in Fig. 11.
The emission is very bright, and presented some difficulty in ob-
taining non-truncated spectra, even at the smallest emission/excitation
slits, and the lowest integration time of 0.1 s allowed by our fluori-
meter. Emission spectra for Tl(PhCO) and Tl2(1,4-BCO) contain two
poorly-resolved bands (ESI 44–47).
3.5. Thermal analysis
Pure organic ligands – cyanoximes – are much less thermally stable
than their Tl(I) complexes as we determined studying their TG/DSC
properties under pure argon atmosphere. Thus, H(PhCO) melts at
130.2 °C followed by rapid decomposition, while H2(1,3-BCO) and
H2(1,4-BCO) melt at 135.1° and 149.6 °C respectively. The latter bis-
cyanoximes decompose at 15-19° higher temperatures.
Fig. 10. Fragment of crystal structure of Tl2(1,4-BCO): A – one cyanoxime and
several closest Tl(I) centers showing their bonds and angles, B – important bond
length in the anion connected to the neighboring Tl(I) atoms, C – only closest
metal centers expressed as van-der-Waals spheres emphasizing metallophilic
interaction.
There was found to be a very distinct difference between the
thermal properties of the Thallium(I) mono-cyanoximates and bis-cya-
noximates. The former complexes melt with quickly followed decom-
position, while the latter complexes exhibit strongly exothermic and
violent decomposition. The least thermally-stable compound was de-
termined to be Tl(PhCO), which melts with decomposition at 157 °C,
while Tl(2F-PhCO) melts at 204 °C, and then quickly begins decom-
posing at 226 °C. Thallium bis-cyanoximates Tl2(1,3-BCO) and Tl2(1,4-
BCO) are more thermally-stable, and undergo rapid decomposition at
262 °C and 283 °C respectively. The most interesting finding is that
Tl2(1,3-BCO) violently decomposes at once (ESI 48 and 49) with a
considerable magnitude of the exo-effect, demonstrating the properties
of a heat-activated, high energy compound [98]. In this context it
should be noted that other heavy metals salts containing also toxic lead
(II) and mercury(I,II) are widely used in specific applications for high-
energy compounds [70,100–102], and discovery similar properties for
thallium(I) Werner-type complex was, actually, a surprise. Also, release
of kinetic energy upon decomposition of Tl2(1,3-BCO) leads to dis-
location of the crucible from the thermal analyzer balance pan. Thus,
the enthalpy of rapid decomposition of a sample of this complex -
ESI 24. The π-π stacking is important for the stabilization of this
structural motif: the ring-ring separations between the centroids of
aromatic fragments in the lattice are 3.970 Å, which are longer than
those in other complexes reported here (Fig. 9C). However, it turned
out to be sufficient packing in this particular compound. The polymer
phenyl rings lie roughly in the same plane and are spaced at a distance
of 6.672 Å. The same kind of Tl—N long and electrostatic interactions
between Tl atoms and N atoms of the cyano groups, as seen in struc-
tures of Tl(PhCO), Tl(2F-PhCO) and Tl2(1,3-BCO) are also present, as
seen in Tl2(1,4-BCO), but to a lesser extent. The shortest Tl-N interac-
tion, found only within the sheets, is 3.224 Å. The coordination poly-
hedron of Tl(I) can be best described as a distorted trigonal pyramid
(ESI 33).
A plot of intermetallic Tl—Tl distances vs. the size of the halogen
atom in Tl(I) cyanoximates is displayed in ESI 35. Lastly, the geometry
and motifs of all thallium(I) cyanoximates that contain Tl2O2 rhombs,
known and studied thus far, are summarized in Table 2.
In summary, based on our findings we can present observed binding
modes of cyanoximes in their Tl(I) complexes as it is shown in Scheme
3. Interesting multidentate bridging ability of these new anionic ligands
was found and will allow us to move with preparation of heterometallic
complexes.
within several seconds - is 175
15 kJ/mol. Further details of the
thermal behavior of that complex are presented in ESI 50–53 explaining
this rare phenomenon. Interestingly, similar behavior was not observed
for the analogous Tl2(1,4-BCO) complex, and silver(I) cyanoximates of
AgL composition [99,103], despite a great chemical similarity between
monovalent Ag and Tl. However, we recently found several other Cu(II)
cyanoximes-based compounds which exhibit properties of high energy
compounds. [99] The final product of complexes’ thermal decomposi-
tion in an inert atmosphere (N2) is metallic thallium, which appears as
fine shiny sponge (Fig. 12; ESI 54).
3.3. Spectroscopic properties.
Vibrational spectra. Involvement of the nitrile group of cyanox-
imes due to conjugation in the overall electronic structure of Tl-com-
plexes was postulated in early works [96,98]. However, only now has it
4. Conclusions.
In summary of the conducted investigation, we report:
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InorganicaChimicaActa508(2020)119597
Table 2
Specific details of geometry around metal centers in studied Tl-arylcyanoximates and in some other complexes with different types of ligands. The shortest distance is
indicated in bold italic type font.
Complex
Tl—O arrangement
Tl—Tl distances, Å
Reference
Thallium(0)
Metallic thallium
hexagonal close packed
3.456, a, hexagonal
3.438, a, hexagonal
3.362, I-centered cube
[86]
[87]
[87]
Thallium(I)
Tl(PhCO)
Non-centrosymmetric, non-
planar Tl2O2 rhombs forming
2D polymer
4.042 (inner dimer)
4.194, 4.033,
3.770
This work
Tl(2Cl-PhCO)
Tl(4Br-PhCO)
Tl(2F-PhCO)
Centrosymmetric Tl2O2
rhombs forming 1D columns
centrosymmetric Tl2O2
rhombs forming 1D columns
centrosymmetric Tl2O2
rhombs forming 2D polymer
4. 184 (inner dimer)
4.440, 3.838
4. 097 (inner dimer)
4.435, 4.058
4.114 (inner dimer)
4.113, 4.301, 3.950
3.748
[85]
[50]
this work
Tl(3F-PhCO)
Tl2(1,3-BCO)
metal ladder, no of Tl2O2
double-stranded
presence of both
centrosymmetric and non-
centrosymmetric, non-planar Tl2O2 rhombs
forming complex 3D network
centrosymmetric Tl2O2
3.802, 3.846 (intra strand)
3.756 (inter strand)
4.214 (intra dimer)
4.160, 4.282
this work
this work
3.670
Tl2(1,4-BCO)
4.330 (intra dimer)
this work
rhombs forming 2D polymer
3.970, 3.967
3.784
3.67
3.63
3.99
3.76
3.152
3.180
Tl+(thalla-dicarbollide)−
Tl(C5(CH2-Ph)5)**
Tl(C5H5)**
[Tl(C5(1,3-t-Bu2)]2**
[Tl6{SiMe2}(N-t-Bu)6]***
*
metallophilic Tl—Tl
metallophilic Tl—Tl
metallophilic Tl—Tl
metallophilic Tl—Tl dimer
metallophilic Tl—Tl
two edge sharing cubes
[88]
[89]
[90]
[91]
[92]
Thallium(II)
Tl2{Si(t-Bu3)2}***
Tl2{Si(SiMe3)3}2***
linear, with direct Tl-Tl bond
linear, with direct Tl-Tl bond
2.97
2.914
[93]
[94]
* – thallium anionic ligand: dicarbollide, [3,1,2-TlC2Me2B9H9]−; ** – cyclopentadiene (Cp) based compounds; *** – organosilyl derivatives.
Fig. 11. Reflectance and emission spectra of solid sample of Tl2(1,3-BCO);
T = +25 °C.
planar and non-centrosymmetric Tl2O2 dimers in the structure of Tl
(PhCO), and side-on coordination of the nitroso-groups in Tl(3F-
PhCO).
The finding of a spacious, ∼6.5 Å wide channel in the structure of
Tl2(1,3-BCO) complex which allows its further exploration for po-
tential gas sorption purposes.
•
Scheme 3. Observed bridging binding modes in studied coordination polymers
of Tl(I).
Tabulation of all known Tl(I) structures with cyanoximes that con-
tain Tl2O2 rhombs.
•
Preparation of five new Tl(I) coordination polymers based on two
groups of anionic ligands: mono- and bis-cyanoximes.
Determination of five crystal structures of new compounds with a
new interesting finding: the unexpected formation of unusual non-
•
•
Spectroscopic characterization of all obtained compounds, and de-
tection of low-frequency Tl–O vibrations, the first time.
One compound - Tl2(1,3-BCO) – demonstrated properties of a high
•
•
10

S. Curtis, et al.
InorganicaChimicaActa508(2020)119597
Fig. 12. A – thermal analysis traces in usable temperature range for a sample of high-energy Tl2(1,3-BCO); B – actual microscope photograph of the alumina crucible
after thermal decomposition reaction, showing metallic thallium sponge.
energy compound.
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115.
Declaration of Competing Interest
[8] J. Berry, Extended Metal Atoms Chains, third ed.,, Springer Science and Business
Media Inc, 2005.
[9] Y. Wang, J. Mao, X.M. Liang, Y.D. Deng, X. Bao, Chem. Rev. 119 (3) (2019)
1806–1854.
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L. Ohrstrom, M. O’Keeffe, M.P. Suh, J. Reedijk, CrystEngComm 14 (2012) 3001.
[11] M. Tran, K. Kline, Y. Qin, Y. Shen, M.D. Green, S. Tongaya, Appl. Phys. Rev. 6
(2019) 041311.
[12] J. López-Cabrelles, S. Mañas-Valero, I.J. Vitórica-Yrezábal, P.J. Bereciartua,
J.A. Rodríguez-Velamazán, J.C. Waerenborgh, B.J. Vieira, D. Davidovikj,
P.G. Steeneken, H.S.J. van der Zant, G. Mínguez Espallargas, E. Coronado, Nat.
Chem. 10 (10) (2018) 1001.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgement
NG is very grateful to Dr. K.V. Domasevitch for the data collection
and preliminary structure determination for Tl(PhCO), to Dr. Nigam
Rath for the data collection for Tl(3F-PhCO), and to Ms. Victoria Barry
for invaluable technical help during the manuscript preparation. Also,
NG and SC thank the College of Natural and Applied Sciences for their
ongoing support of the X-ray diffraction laboratory. DR and SC are
thankful to the MSU Graduate College for financial support during work
on this project.
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Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2020.119597.
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