Synthesis and characterization of N,N′,C-bound organotellurium(IV) and organomercury(II) derivatives

Article abstract of DOI:10.1016/j.ica.2018.08.016

We report the synthesis and characterization of the first examples of organotellurium (IV)/organomercury(II) derivatives of N,N′,C-chelating aryldiamine ligand, 2-{Me₂NCH₂CH₂N(Me)CH₂}C₆H₄Br (20). The dichalcogenides, [2-{Me₂NCH₂CH₂N(Me)CH₂}C₆H₄Se]₂ (24) and [2-{Me₂NCH₂CH₂N(Me)CH₂}C₆H₄Te]₂ (25), were prepared by treatment of the corresponding Grignard reagent (21)/organolithium reagent (22) in THF with selenium or tellurium, respectively. Compounds [2-{Me₂NCH₂CH₂N(Me)CH₂}C₆H₄]₂Se (26) and [2-{Me₂NCH₂CH₂N(Me)CH₂}C₆H₄]Te(S₂CN(CH₂CH₃)₂ (27) were synthesized by the reaction of 21/22 with Se(dtc)₂ in 2:1 or Te(dtc)₂ (dtc = diethyldithiacarbamate) in 1:1 ratio at room temperature. In contrast, the reaction of 21 with TeI₂ afforded an unexpected protonated derivative, [2-{(Me₂NH)CH₂CH₂N(Me)CH₂}C₆H₄TeI]⁺(I)^? (28a). Similarly, the halogenation reactions of 25 with chlorine gas or a solution of bromine in THF afforded protonated derivatives, [2-{(Me₂NH)CH₂CH₂N(Me)CH₂}C₆H₄TeCl₃]⁺(Cl)^? (29a) and [2-{(Me₂NH)CH₂CH₂N(Me)CH₂}C₆H₄TeBr₃]⁺(Br) ^? (30a), respectively. The organomercury precursors; 2-{Me₂NCH₂CH₂N(Me)CH₂}C₆H₄HgCl_0.54/Br_0.46 (31) and 2-{Me₂NCH₂CH₂N(Me)CH₂}C₆H₄HgBr (32), were obtained by the reaction of 21 with HgCl₂ and HgBr₂ in dry THF, respectively. The metathetical reaction of 31with silver azide afforded air- and moisture-stable organomercury azide, 2-{Me₂NCH₂CH₂N(Me)CH₂}C₆H₄HgN₃ (33) in 87% yield. The transmetallation reaction of 31 with TeBr₄ led to isolation of known o-formylphenyltellurenyl bromide. All the derivatives were characterized by various spectroscopic techniques such as ¹H, ¹³C, ⁷⁷Se, ¹²⁵Te, ¹⁹⁹Hg NMR spectroscopy, elemental analysis, ES-MS and HRMS studies.

Full text of DOI:10.1016/j.ica.2018.08.016

Accepted Manuscript
Research paper
Synthesis and Characterization of N,N’,C-bound Organotellurium(IV) and Or-
ganomercury(II) Derivatives
Puspendra Singh, Anand K. Gupta, Sagar Sharma, Harkesh B. Singh, Ray J.
Butcher
PII:
S0020-1693(18)30680-7
https://doi.org/10.1016/j.ica.2018.08.016
ICA 18416
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
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Revised Date:
Accepted Date:
4 May 2018
14 August 2018
14 August 2018
Please cite this article as: P. Singh, A.K. Gupta, S. Sharma, H.B. Singh, R.J. Butcher, Synthesis and Characterization
of N,N’,C-bound Organotellurium(IV) and Organomercury(II) Derivatives, Inorganica Chimica Acta (2018), doi:
https://doi.org/10.1016/j.ica.2018.08.016
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Synthesis and Characterization of N,N’,C-bound
Organotellurium(IV) and Organomercury(II) Derivatives
Puspendra Singha,b, Anand K. Guptaa, Sagar Sharmac, Harkesh B. Singha,*, Ray J.
Butcherd
aDepartment of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076,
India
bDepartment of Chemistry, Dr. Shakuntala Misra National Rehabilitation University
Lucknow, Uttar Pradesh, 226017, India
cPhysical Sciences Division, Institute of Advanced Study in Science & Technology,
Paschim Boragaon, Guwahati-781035, Assam, India
dDepartment of Chemistry, Howard University, Washington DC20059, USA
Abstract
We report the synthesis and characterization of the first examples of organotellurium
(IV)/organomercury(II)
derivatives
of
(20).
N,N’,C-chelating
aryldiamine
ligand,
2-
{Me2NCH2CH2N(Me)CH2}C6H4Br
The
dichalcogenides,
[2-
{Me2NCH2CH2N(Me)CH2}C6H4Se]2 (24) and [2-{Me2NCH2CH2N(Me)CH2}C6H4Te]2 (25),
were prepared by treatment of the corresponding Grignard reagent (21)/organolithium reagent
(22) in THF with selenium or tellurium, respectively. Compounds [2-
{Me2NCH2CH2N(Me)CH2}C6H4]2Se
(26)
and
[2-
1

{Me2NCH2CH2N(Me)CH2}C6H4]Te(S2CN(CH2CH3)2 (27) were synthesized by the reaction of
21/22 with Se(dtc)2 in 2:1 or Te(dtc)2 (dtc = diethyldithiacarbamate) in 1:1 ratio at room
temperature. In contrast, the reaction of 21 with TeI2 afforded an unexpected protonated
derivative, [2-{(Me2NH)CH2CH2N(Me)CH2}C6H4TeI]+(I)– (28a). Similarly, the halogenation
reactions of 25 with chlorine gas or a solution of bromine in THF afforded protonated
derivatives, [2-{(Me2NH)CH2CH2N(Me)CH2}C6H4TeCl3]+(Cl)– (29a)
{(Me2NH)CH2CH2N(Me)CH2}C6H4TeBr3]+(Br)– (30a), respectively. The organomercury
and
[2-
precursors;
2-{Me2NCH2CH2N(Me)CH2}C6H4HgCl0.54/Br0.46
(31)
and
2-
{Me2NCH2CH2N(Me)CH2}C6H4HgBr (32), were obtained by the reaction of 21 with HgCl2 and
HgBr2 in dry THF, respectively. The metathetical reaction of 31with silver azide afforded air-
and moisture-stable organomercury azide, 2-{Me2NCH2CH2N(Me)CH2}C6H4HgN3 (33) in 87%
yield. The transmetallation reaction of 31 with TeBr4 led to isolation of known o-
formylphenyltellurenyl bromide. All the derivatives were characterized by various spectroscopic
1
techniques such as H, 13C, 77Se, 125Te, 199Hg NMR spectroscopy, elemental analysis, ES-MS
and HRMS studies.
Keywords: Pincer Ligand, Organotellurium, Organomercury, Crystal Structure, DFT
1. Introduction
The last decade has witnessed a continuous growth in the development of pincer
complexes [1]. The complexes have received a lot of attention mainly due to their involvement in
catalysis [2], stabilization of low-valent compounds of main group elements [3] and isolation of
reactive intermediates [4]. Generally, the unstable and novel low-valent main group derivatives
have been stabilized with the help of tridentate pincer ligands. For example, the isolation of only
2

three stable organotellurium cations, [{2,6-(Me2NCH2)2C6H3}Te]+(PF6)-, (3) [5], [{2,6-
2+
-
(Me2NCH2)2C6H3}TeO]2 (PF6)2 , (4) [6] and [{2,6-{O(CH2CH2)2NCH2}2C6H3}Te]22+(Hg2Cl6)2-
, (6) [7] has been achieved using substrates (1&5) where the tellurenium/oxotelluronium cations
are stabilized by intramolecular Te∙∙∙N coordination (Chart 1). Subsequently, a few more crystal
structures of analogous organoselenium cations have been reported, e.g. [{2,6-
(Me2NCH2)2C6H3}Se]+(X)-, (X = PF6 [5], Cl, Ph2SbCl4 [8], Br [9], Cl0.44/Br0.56 [10]).
Interestingly, Kersting and DeLion succeeded in isolating the chalcogenols by ortholithiation of
7 followed by Se/Te insertion and hydrolysis with HCl [11]. Further, the oxidation of tellurol, 2-
hydrotelluro-N1, N3-diisopropylisophthalamide, in presence of base, afforded cyclic product,
N,2-diisopropyl-3-oxo-2,3-dihydrobenzo[d][1,2]tellurazole-7-carboxamide (9). Similarly, Zade
et al. have reported the synthesis of a related product, e.g. 5-tert-butyl-2-methyl-7-
(methylcarbamoyl)benzisotellurazol-3(2H)-one (10) [12]. The attempted synthesis of the
respective dichalcogenide led to facile cyclisation and isolation of 10. This benzisotellurazole
can be considered as a tellurium analogue of well-known antioxidant 2-phenyl-1,2-
benzisoselenazol-3(2H)-one, commonly referred as Ebselen [13]. Recently, Singh and co-
workers have reported the tellurenate esters, 14 and 15 and hypervalent
diorganyldiacyloxytellurane 16 through the intermediacy of tellurenyl hydroxide 12 and
diorganotelluriumdihydroxide 13 [14]. The ester groups act as an electrophilic trap for
aryltellurenyl hydroxide and are stabilised due to the presence of strong secondary bonding
Te∙∙∙O intramolecular interactions (Chart 1). Selvakumar et al. have focused on OCO and OCN
type pincer ligands to investigate the unprecedented sensitivity of secondary bonding interaction
(SBI) towards intramolecular steric force present in 2,6-disubstituted arylchalcogen compounds
[15]. The study revealed that the isolation of unstable intermediates as their cyclised form,
3

synthesis of heterocycles and spirocycles by the induction of steric stress at the molecular scale
is very productive [15].
In continuation of our studies on intramolecularly coordinated organochalcogens, we now
report here the first examples of organotellurium(IV) and organomercury(II) compounds derived
from cis-pincer N,N’,C- tridentate 2-{Me2NCH2CH2N(Me)CH2}C6H4Br (20) ligand. As
compared to the trans-pincer (N,C,N) ligands, the chemistry of the cis-pincer ligands bearing
main group derivatives is limited to only organolithium [16] and organotin [17] derivatives.
During our investigations on the cis-pincer ligand, one example of diorganodiselenide, [2-
{Me2NCH2CH2N(Me)CH2}C6H4Se]2 has been described by Mugesh et al. as glutathione
peroxidise mimetics [18]. In addition to this, there have been two more reports on serendipitous
formation of N,N’,C-bound tellurium (IV) derivatives [N,N’,C-bound TeCl3 (18) [19a] and
N,N’,C-bound TeBr3 (19) [19b] which were isolated while attempting coordination of
TeCl4/TeBr4 with 17. The cis-pincer complexes of 20 with transition metal (Ti [20], Ta [21], W
[22], Rh [23], Ir [23], Ni [24], Pd [25], Pt [23], Cu [26], Ag [26], and Au [26]) complexes have
been extensively studied.
4

Chart 1. Representatives of organotellurium cationic and neutral species with trans- pincer
ligands.
5

2. Experimental
2.1. Caution
The reactions involving mercury compounds and their azide derivative were carried out
in a well-ventilated fume hood with proper precautions due to their hazardous nature.
2.2. Materials and methods
Solvents were dried and distilled by standard procedures. Selenium, tellurium,
mercury(II) chloride, mercury(II) bromide, bromine, iodine were purchased from Aldrich.
Magnesium metal, sodium azide and silver nitrate were purchased from Sisco Research
Laboratories, India. 2-{Me2NCH2CH2N(Me)CH2}C6H4Br (20) [16a], TeI2 [27], Se(dtc)2 [28] and
Te(dtc)2 [28] were prepared according to literature procedures. Chlorine gas was generated by
treating KMnO4 with conc. HCl. Silver azide was freshly prepared by reacting of NaN3 and
1
AgNO3 in water. Melting points were recorded in capillary tubes and are uncorrected. The H,
77
13C, Se and 125Te NMR spectra were recorded on a Varian VXR 400 spectrometer. Chemical
shifts cited were referenced to TMS (1H, 13C) as internal and Me2Se (77Se) as external standard.
The 125Te NMR spectra were recorded on Bruker AMX 400 instruments with dimethyl telluride
(Me2Te) as reference. Electron spray mass spectra (ESI-MS) were performed on a Q-Tof micro
(YA-105) mass spectrometer. Mass spectra were obtained with a Platform II single quadrupole
mass spectrometer (Micromass, Altrincham, UK) using a CH3CN mobile phase. Elemental
analyses were performed on a Carlo-Erba model 1106 elemental analyzer. IR spectra were
recorded as KBr pellets on a Nicolet Impact 400 and Perkin FT-IR spectrometer.
2.3. Synthetic procedures
2.3.1. Synthesis of [2-{Me2NCH2CH2N(Me)CH2}C6H4E]2 (E = Se (24); Te (25)
6

In a 100-mL two-necked flask, magnesium (0.15 g, 6.17 mmol) was taken up in 15 mL of
anhydrous THF. To this, compound 20 (1.10 mL, 5.34 mmol) was added drop-wise with
constant stirring under reflux conditions. The stirring was continued until the completion of the
reaction as indicated by the disappearance of magnesium. Selenium (0.43 g, 5.34 mmol) or
tellurium powder (0.68 g, 5.34 mmol) was added to the reaction mixture in portions over a
period of 15 min. After 2 h of stirring, the solution was poured into a 50 mL solution of NH4Cl in
water which was kept open for 2 hr for aerial oxidation. The product was extracted with ether
(2x50 mL). The ether solution was washed with water and the organic layer was separated, dried
over sodium sulfate and evaporated under vacuum to give yellow dense liquid of 24/25
respectively.
Data For 24; Yield 0.85 g (59%); 1H NMR (400 MHz, CDCl3) δ 2.22 {6 H, s, H-11, 12,
N(CH3)2}, 2.23 (3 H, s, H-8, NCH3), 2.42-2.52 (4 H, m, H-9, 10, N-CH2-CH2-N), 3.51 (2 H, s,
H-7, C6H4–CH2–N), 7.29-7.36 (4 H, m, H-2–5, C6H4); 13C NMR (100.6 MHz, CDCl3) δ 42.47 (s,
C-8), 45.73 (s, C-11), 45.80 (s, C-12), 55.06 (s, C-9), 57.32 (s, C-10), 62.9 (s, C-7), 126.94 (s, C-
3), 128.11 (s, C-4), 128.15 (s, C-5), 128.20 (s, C-2), 129.07 (s, C-1), 138.80 (s, C-6); 77Se NMR
(76.3 MHz, CDCl3) δ 425.6. HRMS 543.1508 [M]+
.
1
For 25; Yield 1.56 g (46%); H NMR (400 MHz, CDCl3) δ 2.18{6 H, s, H-11, 12,
N(CH3)2}, 2.23 (3 H, s, H-8, NCH3), 2.50-2.57 (4 H, m, H-9, 10, N-CH2-CH2-N), 3.61 (2 H, s,
H-7, C6H4–CH2–N), 6.97-6.98 (2 H, m, H-3, 4, C6H4), 7.08 (1 H, m, H-5, C6H4), 7.95 (1 H, d, H-
2, C6H4); 13C NMR (100.6 MHz, CDCl3) δ 40.73 (s, C-8), 45.59 (s, C-11), 45.74 (s, C-12), 54.12
(s, C-9), 57.03 (s, C-10), 65.37 (s, C-7), 112.82 (s, C-1), 126.30 (s, C-3), 128.14 (s, C-4, 5),
139.00 (s, C-2), 140.89 (s, C-6); 125Te NMR (126.3 MHz, CDCl3) δ 347.3.
2.3.2. Synthesis of [2-{Me2NCH2CH2N(Me)CH2}C6H4]2Se (26)
7

Method (a)
To a freshly prepared Grignard solution of 20 (0.5 mL, 2.6 mmol) in THF, was added a
o
solution of Se(dtc)2 (0.375 g, 1.00 mmol) in the same solvent at -72 C. Then, the mixture was
stirred for 14 h to complete the reaction. The solution was poured into 50 mL water. The product
was extracted with ether (4 x50 mL). The ether solution was washed with water and the organic
layer was separated, dried over sodium sulfate and evaporated under vacuum to give an orange
coloured dense liquid. The dense liquid was further purified by flash column chromatography by
using 30% of ethyl acetate and petroleum-ether (40-60) which afforded orange coloured dense
liquid of 26 (0.25g, 54% yield).
Method (b)
To a solution of 20 (0.5mL, 2.6 mmol) in dry hexane (10 mL), was added a 1.6 M
solution of n-butyllithium in hexane (3.4 mL, 5.5 mmol) via syringe under N2 at room
temperature. This was stirred for 2h at room temperature and allowed to settle. The solvent was
removed by syringe and the white lithiated precipitate was dissolved in dry THF (20 mL). This
was added to a solution of Se(dtc)2 (0.488 g, 1.3 mmol) at -72 oC. Then the mixture was stirred
for 14 h to complete the reaction. Further workup of the reaction mixture and purification as
1
described in method (a) afforded a dense liquid of 26 (0.31 g, 67% yield). H NMR (400 MHz,
CDCl3) δ 2.24 (3 H, s, H-8, NCH3), 2.33{6 H, s, H-11, 12, N(CH3)2}, 2.60 (4 H, m, H-9, 10, N-
CH2-CH2-N), 3.53 (2 H, s, H-7, C6H4–CH2–N), 7.30-7.88 (4 H, m, H-2–5, C6H4); 13C
NMR(100.6 MHz,CDCl3) δ 41.47 (s, C-8), 44.68 (s, C-11, 12), 53.81 (s, C-9), 56.12 (s, C-11,
10), 61.89 (s, C-7), 126.07 (s, C-3), 127.25 (s, C-4, 5), 127.73 (s, C-2), 128.17 (s, C-1), 137.72
(s, C-6);77Se NMR (76.3 MHz, CDCl3) δ 422.2 ppm.
2.3.3. Synthesis of [2-{Me2NCH2CH2N(Me)CH2}C6H4]Te{S2CN(CH2CH3)2} (27)
8

Compound 27 was also prepared following the method (a) by using Te(dtc)2 (1.10 g, 2.6
1
mmol) in place of Se(dtc)2. The isolated compound was a dense liquid (0.28g, 60% yield). H
NMR (400 MHz, CDCl3) δ 1.27 {3 H, t, SCN(CH2CH3)2}, 1.34 {3 H, t, SCN(CH2CH3)2}, 2.30
{6 H, s, H-11, 12, N(CH3)2}, 2.53 (3 H, s, H-8, NCH3), 2.68 (4 H, m, H-9, 10, N-CH2-CH2-N),
3.50 (2 H, s, H-7, C6H4–CH2–N), 3.95 {2 H, q, SCN(CH2CH3)2}, 4.04 {2 H, q,
SCN(CH2CH3)2}7.13 (2 H, m, H-3, 4, C6H4), 7.31 (1 H, m, H-5, C6H4), 7.77 (1 H, d, H-2, C6H4);
125Te NMR (126.3 MHz, CDCl3) δ 1083.3 ppm; ES-MS m/z (relative intensity, nature of peak)
321
{Me2NCH2CH2N(Me)CH2}C6H4}2Te+OH]+.
2.3.4. Synthesis of [2-{(Me2NH)CH2CH2N(Me)CH2}C6H4TeI]+(I)– (28a)
(30,
[2-{Me2NCH2CH2N(Me)CH2}C6H4Te]+);
529
(100,
[{2-
To a freshly prepared Grignard solution of 20 (1 mL, 5.34 mmol) in THF, was added TeI2
(2.01 g, 5.34 mmol). Then the mixture was stirred for 12 h to complete the reaction. The
resulting solution was poured into 50 mL water. The product was extracted with chloroform
(4x50 mL). The chloroform solution was washed with water and the organic layer was separated,
dried over sodium sulfate, and filtered to give an orange coloured solution. The solution was
o
concentrated to 5 mL under vacuum. The solution was cooled in freeze at 0 C for 24 h to give
needle shaped crystals of 28a (0.45 g, 15% yield). The crystals were separated by decantation
1
and washed with hexane. M.p. 197-198 °C. H NMR (DMSO-d6) δ 2.74 (3 H, s, H-8, NCH3),
2.88 {6 H, s, H-11, 12, N(CH3)2}, 3.25 (2 H, m, H-10, N-CH2-CH2-N), 3.41 (2 H, m, H-9, N-
CH2-CH2-N)), 4.15 (2 H, s, H-7, C6H4–CH2–N), 7.28 (3 H, m, H-3–5, C6H4), 7.84 (1 H, d, H–2,
C6H4); 13C NMR (100.6 MHz, DMSO-d6) δ 43.10 (s, C-11, 12), 43.67 (s, C-8), 51.67 (s, C-10),
52.87 (s, C-9), 64.56 (s, C-7), 116.82 (s, C-1), 127.34 (s, C-3), 127.69 (s, C-4), 129.32 (s, C-5),
9

137.44 (s, C-2), 139.23 (s, C-6); ES-MS m/z (relative intensity, nature of peak) 449 (22, [M]+);
321 (90, [M-I]+); 125Te NMR (126.3 MHz, DMSO-d6) δ 1249.
2.3.5. Synthesis of [2-{(Me2NH)CH2CH2N(Me)CH2}C6H4TeCl3]+(Cl)– (29a)
To a 25 mL dry THF solution of 25 (1.35 g, 2.11 mmol), was passed, freshly prepared
dry Cl2 gas for 30 min. at 60 °C to afford a white ppt. of 29a. The precipitate obtained was
recrystallized from DMSO solvent to give colourless crystal of 29a (0.73 g, 74% yield). M.p.
1
186-188 °C. H NMR (400 MHz, CD3OD) δ 2.84 (3 H, s, H-8, NCH3), 2.98 {6 H, s, H-11, 12,
N(CH3)2}, 3.72 (4 H, m, H-9, 10, N-CH2-CH2-N), 4.48 (2 H, s, H-7, C6H4–CH2–N), 7.52 (3 H,
m, H-3–5, C6H4), 7.65 (1 H, d, H–2, C6H4); 13C NMR (100.6 MHz, DMSO-d6) δ41.96 (s, C-11),
42.70 (s, C-12), 43.42 (s, C-8), 50.82 (s, C-10), 51.05 (s, C-9), 61.79 (s, C-7), 128.13 (s, C-1),
130.29 (s, C-3), 131.03 (s, C-4), 131.95 (s, C-5), 139.40 (s, C-2), 145.24 (s, C-6); 125Te NMR
(126.3 MHz, DMSO-d6) δ 1363.1.
2.3.6. Synthesis of [2-{(Me2NH)CH2CH2N(Me)CH2}C6H4TeBr3]+(Br)–(30a)
To a 25 mL dry THF solution of 25 (1.70 g, 2.67 mmol), was added drop-wise Br2 (0.43
g, 2.67 mmol) solution in the same solvent for 15 min. at 60 °C to afford a yellow precipitate of
30a (1.14 g, 67% yield). The precipitate obtained was recrystallized from DMSO solvent to give
yellow crystals of 30a. M.p. 171 °C. ES-MS m/z (relative intensity, nature of peak) 479 (40, [M-
Br]+); 417 (100, [M-Br+OH]+); 125Te NMR (126.3 MHz, DMSO-d6) δ 1438.7; Anal. Calcd. for
C12H19N2Te Br3.HBr: C, 22.54; N, 4.38; H, 3.15. Found C, 23.10; N, 5.42, H, 3.05.
2.3.7.Synthesis of [2-{Me2NCH2CH2N(Me)CH2}C6H4]HgCl0.54/Br0.46(31)
To a freshly prepared Grignard solution of 20 (1.1 mL, 5.34 mmol) in THF, was added a
solution (15 mL) of HgCl2 (0.35 g, 2.06 mmol) in the same solvent and the reaction mixture was
stirred further for 12 h. The reaction mixture was concentrated to 5 mL under vacuum. The
10

residue was treated with water and the resulting aqueous solution was extracted with chloroform.
The organic layer was separated and dried over sodium sulphate. The resulting solution was
o
filtered, concentrated to 5 mL and cooled to 0 C to give colourless rhomboidal crystals of 31
(0.68g, 30% yield). M.p. 162 °C. FT-IR (KBr) 3041, 2982, 2963, 2949, 2841, 2825, 2791,
1448, 1434 1297, 1020, 962, 929, 798, 773, 744 cm-1; 1H NMR (400 MHz, CDCl3) δ 2.03 ({6 H,
s, H-11, 12, N(CH3)2}, 2.48 (4 H, br, H-9, 10, N-CH2-CH2-N), 2.55 (3 H, s, H-8, NCH3), 3.55, (2
H, s, H-7, C6H4–CH2–N), 7.14-7.23 (3 H, m, H-3–5, C6H4), 7.43 (1 H, d, H–2, C6H4); 13C NMR
(100.6 MHz, CDCl3) δ 43.43 (s, C-8), 45.73 (s, C-11, 12), 53.42 (s, C-9), 57.66 (s, C-10), 63.82
(s, C-7). 127.14 (s, C-3), 127.61 (s, C-4, 5), 128.85 (s, C-1), 137.57 (s, C-2), 143.82 (s, C-6);
199Hg NMR (400 MHz, CDCl3) -879.6, -996.1; HRMS 429.1008 (100, [M-Br]+), 473.0479 (60,
[M-Cl]+); Anal. Calcd. for C12H19N3HgCl: C, 33.73; N, 6.56; H, 4.48. Found C, 32.16; N, 6.19;
H, 4.51.
2.3.8. Synthesis of [2-{Me2NCH2CH2N(Me)CH2}C6H4]HgBr(32)
Compound 32 was prepared from HgBr2 (0.11 g, 5.34 mmol) and a freshly prepared
Grignard solution of 20 (1.1 mL, 5.34 mmol) in a similar way described for 31.It afforded
colourless rectangular shaped crystals of 32 (0.96 g, 38% yield). M.p. 151-152 °C. 1H NMR (400
MHz, CDCl3) δ 2.02 {6 H, s, H-11, 12, N(CH3)2}, 2.39 (4 H, br, H-9, 10, N-CH2-CH2-N), 2.54
(3 H, s, H-8, NCH3), 3.55, (2 H, s, H-7, C6H4–CH2–N), 7.16-7.24 (3 H, m, H-3–5, C6H4), 7.43 (1
H, d, H–2, C6H4); Anal. Calcd. for C12H19N3HgBr: C, 30.55; N, 5.94; H, 4.06. Found C, 30.37;
N, 6.08; H, 3.88.
2.3.9. Synthesis of [2-{Me2NCH2CH2N(Me)CH2}C6H4]HgN3 (33)
To a solution of 31 (0.24 g, 0.50 mmol) in 10 mL chloroform, was added 5 mL solution
of silver azide (0.60 g, 4.00 mmol) in methanol. The reaction mixture was stirred at room
11

temperature for 12 h and the precipitate filtered off. The filtrate was concentrated by removing
1
the solvent under vacuum to afford a crystalline solid of 33 (0.19 g, 87% yield). H NMR (400
MHz, CDCl3) δ 2.06 {6 H, s, H-11, 12, N(CH3)2}, 2.40 (4 H, br, H-9, 10, N-CH2-CH2-N), 2.57
(3 H, s, H-8, NCH3) 3.55 (2 H, s, H-7, C6H4–CH2–N), 7.16-7.20 (3 H, m, H-3–5, C6H4), 7.40 (1
H, d, H–2, C6H4); 13C NMR (100.6 MHz, CDCl3) δ 43.74 (s, C-8), 45.67 (s, C-11, 12), 53.55 (s,
C-9), 58.06 (s, C-10), 64.06 (s, C-7), 127.18 (s, C-3), 127.83 (s, C-4), 128.94 (s, C-5), 137.72 (s,
C-1), 143.62 (s, C-6); FT-IR (KBr) 2827, 2055 (HgN3), 1450, 1297, 1030, 964, 800, 745 cm-1;
HRMS m/z (Calculated 458.1241), 458.1235 [M+Na]+; Anal. Calcd. for C12H19HgN3: C, 33.22;
N, 16.14; H, 4.41. Found C, 33.41; N, 12.84; H, 4.05.
2.3.10. X-Ray Crystallographic Study
The single crystal X-ray diffraction measurements were performed on an Oxford
Diffraction Gemini diffractometer and Rigaku Saturn 724 diffractometer. The data were
corrected for Lorentz, polarization, and absorption effects. The structures were
determined by routine heavy-atom methods using SHELXS 97 [29] and Fourier methods
and refined by full-matrix least squares with the non-hydrogen atoms anisotropic and
hydrogen with fixed isotropic thermal parameters of 0.07 Å using the SHELXL 97 [29]
program. The hydrogen atoms were partially located from difference electron density
maps, and the rest were fixed at predetermined positions. Scattering factors were from
common sources [30]. The details of crystal data and structure refinement for 28a-30a
and 31-33 are given in Table 1. CCDC-1814430 (28a), CCDC-1814428 (29a), CCDC-
12

1814425 (30a), CCDC-1814429 (31), CCDC-1814431 (32) and CCDC-1814427 (33
)
contain the supplementary crystallographic data for this paper.
Table 1 Crystallographic Data and Refinement Details for 28a, 29a, 30a, 31, 32 and 33.
Compound
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
28a
C12H20I2N2Te
573.70
29a
30A
31
32
33
C12H19HgN5
433.91
C12H20Cl4N2Te C12H20Br4N2Te C12H19Br0.45Cl0.55HgN2 C12H19BrHgN2
461.70
Monoclinic
P21/c
639.54
Monoclinic
P21/c
447.34
Monoclinic
P21/n
471.79
Monoclinic
P21/n
Monoclinic
P21/c
Triclinic
P-1
11.0462(11)
15.3693(16)
10.1845(11)
90
16.8680(11)
7.7538(5)
13.5941(10)
90
17.1102(9)
7.9362(4)
14.0464(7)
90
10.1848(5)
9.5247(5)
14.3746(7)
90
10.2034(2)
9.5432(2)
14.4962(4)
90
9.2245(7)
9.4152(8)
9.4569(7)
89.764(7)
69.016(7)
79.020(7)°
750.99(11)
2
b (Å)
c (Å)
 (°)
 (°)
99.366(10)
90
100.865(7)
90
102.493(5)
90
98.762(5)
90
98.632(2)
90
 (°)
V (Å3)
1706.0(3)
4
1746.1(2)
4
1862.20(16)
4
1378.15(12)
4
1395.55(6)
4
Z
D(calcd) (Mg/m3)
T (K)
2.234
1.756
2.281
2.156
2.246
1.919
123(2)
123(2)
173(2)
123(2)
123(2)
296(2)
Range of (deg)
Abs coeff (mm-1)
Obsdreflens[I >]
Final R1 [I > 2(I)]
wR2 indices [I >]
Data/Restr./Param.
Goodness of fit F2
4.06 to 67.70
42.049
6.30 to 75.74
18.990
2.96 to 28.28
10.171
3.14 to 35.02
12.556
4.97 to 75.69
22.941
4.80 to 75.57
18.311
3351
3578
4609
5629
2809
3012
0.0844
0.0553
0.0543
0.0635
0.0431
0.0415
0.2234
0.1306
0.0935
0.0756
0.0928
0.0782
3351/6/157
1.055
3578/0/175
1.102
4609/1/178
1.060
5629/8/159
0.985
2809/0/148
1.064
3012/0/166
1.030
2.3.11. Computational Details
All density functional theory (DFT) calculations were performed with the aid of
Gaussian 09 suite of quantum chemical programs [31]. The geometries of the compounds
28-33 were optimized with B3LYP functional [32] by employing 6-311+G(d) basis set for
H,C,N and Lanl2dz basis set for Cl, Br, Te and Hg. The optimized geometries were
confirmed as minima by the frequency calculations on the optimized geometries. Natural
Bond Orbital (NBO) analysis [33] and Atoms in Molecules (AIM) [34] calculations were
performed using the DFT -optimized structures at the same level of theory. AIM
calculations were performed with the help of Multiwfn software [35] and the computed
structures of the compounds were visualized with ChemCraft program [36]
.
13

3. Results and discussion
3.1. Synthesis
The precursor, 2-{Me2NCH2CH2N(Me)CH2}C6H4Br (20) was prepared by following the
reported procedure [16]. Lithiation of 20 was carried out with an excess of n-BuLi (1:2 ratio) at -
78 °C followed by the addition of Se that afforded a viscous liquid of N1-(2-
(butylselanyl)benzyl)-N1,N2,N2-trimethylethane-1,2-diamine (23), instead of the expected
1
diaryldiselenide, [2-{Me2NCH2CH2N(Me)CH2}C6H4Se]2 (24). The H NMR spectrum of 23
exhibited some more peaks along with the peaks for the butyl group. To purify 23, it was
derivatized by complexing with HgCl2 that afforded [2-{Me2NCH2CH2N(Me)CH2}C6H4SeBu-
n]HgCl2 (For experimental details, molecular structure and spectra, see Supporting Information
pages S3-S10) [37]. To avoid the formation of the undesired product 23, alternatively, Grignard
route was used. A freshly prepared Grignard reagent, 2-{Me2NCH2CH2N(Me)CH2}C6H4MgBr
(21) in THF, was treated with Se/Te followed by oxidative workup to provide 24/ [2-
{Me2NCH2CH2N(Me)CH2}C6H4Te]2 (25) as major products. Compound 24 was isolated in
better yield (59%) compared with the reported lithiation route (42%) [18]. Compounds [2-
{Me2NCH2CH2N(Me)CH2}C6H4]2Se
{Me2NCH2CH2N(Me)CH2}C6H4]Te(S2CN(CH2CH3)2 (27) were synthesized by the reaction of
21/22 with Se(dtc)2 in 2:1 and Te(dtc)2 in 1:1 ratio at room temperature (dtc =
(26)
and
[2-
diethyldithiacarbamate). Similarly, the reaction of 21 with TeI2 leads to the formation of an
orange solid of [2-{(Me2NH)CH2CH2N(Me)CH2}C6H4Tel]+(I)– (28a). Compounds, 23-27 were
isolated as viscous liquids and all attempts to solidify these were unsuccessful. In order to study
the Te∙∙∙N intramolecular interactions in the solid state, halogen derivatives were prepared (vide
infra). The reactions of 25 with halogenating agents; chlorine gas or a THF solution of bromine,
14

in 1:1 or 1:3 molar ratio led to isolation of corresponding organotellurium halides as viscous
liquids and in no case the desired solids; LTeCl/LTeBr/LTeCl3(29)/LTeBr3(30) (L= 2-
{Me2NCH2CH2N(Me)CH2}C6H4), could be isolated. However, when an excess of the
halogenating agent was added to 25 in THF, it led to immediate precipitation of white and
yellow powdered solids of [2-{(Me2NH)CH2CH2N(Me)CH2}C6H4TeCl3]+(Cl)– (29a)/ [2-
{(Me2NH)CH2CH2N(Me)CH2}C6H4TeBr3]+(Br)– (30a), respectively (Scheme 1). Compounds
28a, 29a and 30a have low solubility in common organic solvents, however, these could be
crystallized from DMSO. The initial characterization by IR spectroscopy indicated the presence
of NH stretching frequency at 3440 cm-1 for 30a indicating protonation of one of the amine
nitrogen atoms. This was further confirmed by single crystal X-ray studies (vide infra). The
solubility behaviors of 28a and 29a with 30a indicated that these were also protonated (vide
infra). Attempted deprotonation of these to obtain the corresponding neutral organotellurium
halides (28-30) by treatment with saturated aqueous NaHCO3 solution or aqueous NaOH (10%)
were unsuccessful.
Alternatively, to circumvent the facile protonation, it was planned to use organomercury
derivatives as precursors for the isolation of 28-30 by transmetallation reaction with TeI2, TeCl4,
and
TeBr4
respectively.
For
this,
organomercurial
compound
2-
{Me2NCH2CH2N(Me)CH2}C6H4HgCl (31), was prepared by the treatment of LMgBr with
HgCl2. Complex 31 was co-crystallized with complex 2-{Me2NCH2CH2N(Me)CH2}C6H4HgBr
(32). The co-crystallisation was confirmed by elemental analysis, HRMS, 199Hg NMR and X-ray
structure determination (vide infra). Recently, similar co-crystallisation of the organomercury
chloro- and bromo-derivatives has been observed in the case of {2,6-
(Me2NCH2)2C6H3}HgCl0.70/Br0.30 [38]. Pure complex 32 could be prepared by using HgBr2 in
15

place of HgCl2. Both the complexes 31 and 32 are highly soluble in common organic solvents
and are crystalline in nature. The reaction of 32 with TeBr4 led to the isolation of o-
formylphenyltellurenyl bromide [39]. This probably forms by the protonation of amine nitrogen
atom followed by hydrolysis (Scheme S2, see Supporting Information page S4) [40]. The azide
derivative 33 was synthesizedby the metathesis of 31 with silver azide.
Scheme 1. Synthesis of organochalcogen (23-30, 28a-30a) and organomercury (31-33)
derivatives. Conditions: (i) Mg, I2, THF; (ii) n-BuLi, Et2O, 3h, -78 °C; (iii) Se/Te, 6 h, room
temperature (rt), [O2]; (iv) Se(dtc)2 (2:1)/[Te(dtc)2 (1:1), Et2O, 12h, rt; (v) TeI2, THF, 2h, 60 °C;
(vi) Cl2/Br2, THF, 2h, 60 °C (vii) HgCl2/HgBr2, 6h, rt (viii) AgN3, CHCl3, 12h, rt.
3.2. Spectroscopic Studies
3.2.1. NMR Spectroscopic Studies
16

The complexes were characterized by 1H, 13C, 77Se, 125Te, 199Hg NMR spectroscopy. The
1H NMR spectrum of the organoselenium and tellurium complexes showed sharp singlet and
1
triplet for C(aryl)CH2N and NCH2CH2N protons. Interestingly, the H NMR spectra of 31, 32
and 33 exhibit broad peaks for all the three sets of CH2 protons and the NMe2 group appeared as
singlet. The broad peaks may be due to plausible dynamic coordination of –NMe2 in the solution
state. A possible fluxional process could be an association-dissociation process involving the
Hg–NMe2 bond, a phenomenon which has been observed in other NN’C-bound metal complexes
[20, 23b]. The 77Se NMR spectra of 24 and 26 exhibited peaks at 425 and 422 ppm, respectively
and the chemical shift values are in the range reported for diaryldiselenide and diarylselenide
[41]. The 125Te NMR chemical shifts for 25, 27, 28a, 29a and 30a appear at 347, 1083, 1249,
1363 and 1439 ppm, respectively. The signal observed at  = 1083 ppm in the 125Te NMR
spectrum of 27 is shifted upfield relative to that observed for 28a ( = 1249 ppm), 29a ( = 1363
ppm) and 30a ( = 1439 ppm). This trend can be ascribed to the presence of electron
withdrawing iodo, chloro and bromo groups at the Te center in 28a, 29a and 30a, respectively.
The 199Hg NMR signals for 31 and 32 are shifted upfield relative to Ph2Hg (-745 ppm) [42]. The
shifts may be attributed to +I effect of the amino groups. The 199Hg NMR spectrum of 31 showed
two peaks at -966 and -879 ppm for complexes 31 and 32, respectively confirming the co-
crystallisation of 31 with 32.
3.2.2.Mass Spectrometric Studies
ES-MS of 27 showed three intense peaks at m/z 193, 321 and 529, which were assigned
to [2-{(Me2NH)CH2CH2N(Me)CH2}C6H5]+, [2-{Me2NCH2CH2N(Me)CH2}C6H4Te]+, and [{2-
{Me2NCH2CH2N(Me)CH2}C6H4}2Te+OH]+ respectively. For complex 28a, sets of peaks for
molecular ions [M]+ and [M-I]+ were observed at m/z 449 and 321 respectively. Similarly, the
17

ES-MS of 30a showed five sets of peaks for [2-{Me2NCH2CH2N(Me)CH2}C6H4TeBrOH]+, at
m/z
416;
[2-{Me2NCH2CH2N(Me)CH2}C6H4Te]+,
at
m/z
321;
[2-
[2-
[2-
{Me2NCH2CH2N(Me)CH2}C6H4TeBr2]+,
{Me2NCH2CH2N(Me)CH2}C6H4TeBrNa]+,
at
at
m/z
478;
and
m/z
423;
{Me2NCH2CH2N(Me)CH2}C6H4TeO]+, at m/z 337. The HRMS of 31 and 32 exhibited
molecular ion peaks at m/z 429.1008 and 473.0479, respectively. The peak observed at m/z
458.1235 corresponds to complex 33 [M+Na]+ (see Supporting Information, for ES-MS and
HRMS spectra). It is worth noting that similar to cations of 3 and 6, the cation of 28a is stable
and prominently observed in the mass spectrum.
3.3. Crystal structures
3.3.1. Molecular Structure of 28a
The molecular geometry around the tellurium(II) atom is distorted T-shaped (Fig. 1). The
distance between Te and N1 is 2.426(15) Å and is close to the calculated value of 2.570 Å
(Table 2). The Te∙∙∙N1 distance is much less than the sum of the van der Waals radii, Σ
rvdw (Te,N), 3.61 Å [43]. The tellurium atom in 28a is strongly coordinated by N1 atom
whereas N2 atom is protonated. The Te∙∙∙N1 distances are longer than those observed for
[2,6-{O(CH2CH2)2NCH2}2C6H3Te]+ (2.372 Å) [6] and shorter than that observed for [2,6-
2+
{Me2NCH2}2C6H3TeO]2
(2.475 Å)[7]. The lattice of 28a molecule exhibits
intermolecular C–H···I and N–H···I H-bonding interactions, which give rise to a 2-D
supramolecular motif that extends along the crystallographic a-axis. (Fig. S44, see
Supporting Information page S42).
3.3.2.Molecular Structures of 29a and 30a
18

The primary geometry around the Te(IV) atoms in these organotellurium trihalides is
trigonal bipyramidal with a stereochemically active lone pair (Fig. 2 and 3). Two halogen atoms
occupy the axial positions with an X–Te–X (X = Cl and Br) bond angle of 173.21(5)° and
173.97(2)° in 29a and 30a, respectively. Interatomic Te∙∙∙N(1) distances (d(Te∙∙∙N1) 2.437(4) Å
in 29a and 2.463(4) Å in 30a) are short enough to imply the presence of attractive intramolecular
Te∙∙∙N secondary bonding interactions but larger than that found in 17 [d(Te∙∙∙N1) 2.321(3) Å]
[19a] and 19 [d(Te∙∙∙N1) 2.359(3) Å] [19b]. There are no Te∙∙∙N2 close intermolecular contacts in
molecules 29a & 30a, though in the case of 18 [d(Te∙∙∙N2) 2.732(3)Å] [19a] and 19 [d(Te∙∙∙N2)
2.793(3)Å] [19b] such interactions are reported. The N1∙∙∙Te–X2 angles [X = Cl; 169.1(1)° and
X = Br; 170.2(1)] are also greater than the [(N1∙∙∙Te–Cl2)160.9(8)°] [19a] and [(N1∙∙∙Te–
Br2)164.1(8)°] angles [19a]. Complexes 29a and 30a show C–H∙∙∙halogen and N–H∙∙∙halogen H-
bonding interactions which possess the required linearity (~160.86°) and donor-acceptor distance
{interatomic d(H∙∙∙halogen, ~2.7190Å)}. These intermolecular interactions lead to
supramolecular assembly into two-dimensional motifs (see Supporting Information page S43-
S44).
19

Fig. 1 Molecular structure of 28a showing 50% probability displacement ellipsoids and
the atom numbering scheme. Selected bond distances (Å) and angles (°) are shown in
Table 2.
20

Fig. 2 Molecular structure of 29a showing 50% probability displacement ellipsoids and
the atom numbering scheme. Selected bond distances (Å) and angles (°) are shown in
Table 2.
Fig. 3 Molecular structure of 30a showing 50% probability displacement ellipsoids and the atom
numbering scheme. Selected bond distances (Å) and angles (°) are shown in Table 2.
21

Table 2: Comparison of the experimentally obtained structural parameters (bond distances and bond angles) with that computed for compounds 28a, 29a, and 30a.a
28a
29a
Exp.
30a
Exp.
Calc
Calc.
2.131
Exp.
Calc.
2.139
Bond
C1 Te
Te 1
2.145(17)
2.148
C1–Te
2.114(5)
C1–Te
2.122(5)
distances (Å)
2.8564(15)
2.959
Te – Cl1
Te – Cl2
2.5267(13)
2.4496(13)
2.4784(14)
2.437(4)
2.639
2.580
2.684
2.504
1.814
Te – Br1
Te – Br2
2.6493(7)
2.5946(6)
2.6731(7)
2.463(4)
2.28(2)
2.888
2.754
2.836
2.553
2.004
N1 Te
2.426(15)
2.428
2.570
2.213
Te – Cl3
Te – Br3
H2B∙∙∙I2
N1 Te
N1 Te
N2-H2B ∙∙∙Cl4
N1–Te Cl2
1.998
N2-H2NA∙∙∙Br4
N1–Te r2
Bond
N1 Te 1
C1 Te 1
169.0(3)
94.9(5)
171.05
96.96
169.08(12) 167.76
170.15(10) 169.18
angles (°)
C1– Te – Cl1
C1–Te – Cl2
C1–Te – Cl3
Cl1–Te – Cl3
84.69(14)
93.20(15)
88.52(14)
173.21(5)
90.70
92.90
90.85
171.68
C1–Te–Br1
C1–Te – Br2
C1–Te – Br3
Br1–Te – Br3
88.94(15)
94.87(15)
85.18(15)
173.97(2)
92.27
95.09
92.06
172.30
aThe optimized geometrical parameters are obtained at the B3LYP level of theory and 6-311+g(d), lanl2dzbasis set.
3.3.3. Molecular Structures of 31, 32 and 33
Organomercury(II) halides 31 (Fig. 4), and 32 (Fig. 5) crystallize in monoclinic crystal
system, however, mercury(II) azide 33 (Fig. 6) crystallizes in a triclinic crystal system.
Interestingly, in 31 the Hg atom is bonded to both Cl/Br with occupancies of 0.55:0.45 (vide
infra). All the three organomercury compounds exhibit coordination with both the N atoms and
have a non-linear structure rather than the distorted square planar geometry reported for [2-
(Me2NCH2)C6H4]HgCl [44]. The Hg∙∙∙N distances [Hg∙∙∙N1/Hg∙∙∙N2 2.680(4)/2.635(5) Å in 31,
2.690(6)/2.636(6) Å in 32 and 2.656(5)/2.699(6) Å in 33] are considerably shorter than the sum
of the van der Waals radii for Hg and N [Σrvdw (Hg, N), 3.05 Å] and greater than the sum of the
covalent radii for Hg and N[Σrcov(Hg,N), 2.03 Å] [43]. The C-Hg-X (X = Cl, Br, N(11)) bond
angles for 31, 32 and 33 are deviated from the linear geometry with bond angles of 167.8(7)°,
168.1(2)° and 172.6(3)°, respectively. The angle observed in 33 is smaller than the reported
22

value in [2-(Me2NCH2)C6H4]HgN3 (175.3(2)° [45]. The deviation in C-Hg-Cl/Br bond angle is
close to that reported for pentafluorophenylmercury chloride when it forms complexes with both
DMSO and DMF, 169.7(2)°[46]. It is clearly evident that the higher deviation of C-Hg-X [X =
Cl, Br, N(11)] bond angle is due to the stronger coordination of the both the amine nitrogen
atoms to mercury. The covalent nature of the azide is indicated by N3-N4 (1.096(9) Å) bond
length, which is shorter than N4-N5 1.173(9) Å bond distance. The covalent azide 33 shows a
bent trans configuration with an N3-N4-N5 bond angle of 172.9(9)°. The bent unit has different
N-N bond lengths. One of these bonds of azide i.e. (N3-N4) is found to be significantly shorter
than a typical N-N single bond (1.44 Å), while the other bond (N4-N5) is slightly longer than the
N≡N triple bond (1.098 Å). The Hg∙∙∙N(1) bond length in 33 is 2.656(6) Å and is close to those
reported by Klapötke et al.[47]. The packing diagram reveals the presence of a weak
intermolecular metallophilic interaction (Hg∙∙∙Hg) between two Hg atoms in crystal lattices of
33, [3.940(5)] Å (Fig. S48 see Supporting Information pageS46). The distance of 3.940(5) Å is
slightly smaller than the sum of the van der Waals radii for Hg∙∙∙Hg (Σrvdw= 3.96 Å) [43c]. These
intermolecular interactions are longer than the Hg∙∙∙Hg distances reported for [{2,6-
(Me2NCH2)2(p-t-Bu)C6H2]HgN3 (3.92Å)[45].
23

Fig. 4 Molecular structure of 31 showing 50% probability displacement ellipsoids and the
atom numbering scheme. Selected bond distances (Å) and angles (°) are shown in Table
3.
24

Fig. 5 Molecular structure of 32 showing 50% probability displacement ellipsoids and the
atom numbering scheme. Selected bond distances (Å) and angles (°) are shown in Table
3.
Fig. 6 Molecular structure of 33 showing 50% probability displacement ellipsoids and the
atom numbering scheme. Selected bond distances (Å) and angles (°) are shown in Table
3.
Table 3: Comparison of the experimentally obtained structural parameters (bond distances and bond angles) with
that computed for compounds 31, 32 and 33a
31
32
33
Exp.
2.078(5)
Calc.
2.230
Exp.
2.068(7)
Calc.
2.240
Exp.
2.062(7)
Calc.
2.224
Bond
Distances
Å)
C1 Hg
C1 Hg
C1 Hg
Hg Cl
N1 Hg
N2 Hg
C1 Hg
Cl
2.4164(15) 2.525
Hg r
N1 Hg
N2 Hg
2.467(8)
2.690(6)
2.636(6)
2.657
2.734
2.812
N1 Hg
N2 Hg
N Hg
2.656(6)
2.699(6)
2.108(6)
2.728
2.800
2.237
2.680(4)
2.635(5)
167.8(7)
2.728
2.797
166.77 C1 Hg
Bond
Angles (°)
168.1(2) 165.77 C1 Hg–
172.6(3) 173.21
Br
N3
N1 Hg
N2
70.22(13)
69.21
N1 Hg
N2
70.72(18) 68.88
N1 Hg
N2
69.52(17) 69.16
aThe optimized geometrical parameters are obtained at the B3LYP level of theory and 6-311+g(d), lanl2dz basis set.
25

3.4. DFT Calculations
In order to gain insight into the structure and nature of bonding in the synthesized
organotellurium and organomercury compounds, DFT calculations were carried out. The
optimized geometries of the compounds 28 33 showed good agreement with
-
experimentally determined X-ray crystal structures. A comparison of the experimentally
obtained structural parameters (bond distances and bond angles) with the bond parameters
of optimized geometries is shown in Table 2 and Table 3. To examine whether the
coordination mode of N donor atoms can be a contributing factor in obtaining
organotellurium compounds as salts, we investigated the coordination mode of potentially
tridentate, cis-pincer (N1,N2,C) ligand with Te. For this purpose, we optimized the
geometries of unprotonated forms of 28a
,
29a and 30a with the nitrogen atoms directed
29 and 30
towards Te for possible coordination), which have been represented as 28
,
,
respectively. The optimized geometries with corresponding Te∙∙∙N distances are shown in
Fig. S49. The optimized geometries revealed that the terminal N2 atoms do not involve in
strong coordination with Te. For instance, in 28, the terminal N2 has Te∙∙∙N2 distance of
3.669 Å, which is larger than sum of van der Waals radii of Te and N (3.61 Å) and thus,
does not coordinate with Te. Further, in 29 and 30, the terminal N2 atoms coordinate very
weakly with Te. The Te∙∙∙N2 bond distance and its Wiberg bond index in 29 are 3.046 Å
and 0.076, respectively, while the Te∙∙∙N1 bond distance is very short (2.514 Å), with
very a high Wiberg bond index of 0.263. This indicates a preferential coordination of Te
with N1 over terminal N2 donor atom. The coordination of terminal N2 with Te in
organotellurium compounds is so weak that the secondary bonding interaction energy for
the Te∙∙∙N1 interaction is more than 7 times (44.1 kcal/mol for 29 and 40.8 kcal/mol for
26

30, see Fig. S50) as large as for the Te∙∙∙N2 interaction (ETe N2 is 6.5 kcal/mol in 29 and
∙∙∙
ETe N2 is 5.8 kcal/mol in 30, see Fig S50). This is probably due to formation of very stable
∙∙∙
T-shaped/ trigonal bipyramidal geometry around central Te with 3c-4e (N-Te-X) bond.
Compound 27 is 10-Te-3 system whereas 29 and 30 are 12-Te-5 system, instead of 12-
Te-4/14-Te-6 systems which would have formed with the coordination of N2 [48]. The
hydrolysis of 28, having weakly acidic TeI group, even with traces of water is probably
facilitated by no coordination/very weak coordination of N2 with Te in 29
N2 acts as a proton sponge. Unlike organotellurium compounds, in organomercury
derivatives (31 33) both the donor N atoms of ligand coordinate to Hg with equivalent
-30. In a way,
-
ease (as evident from the similar Hg-N1 and Hg-N2 bond distances and WBI indices in
Table S1) and thereby have both the nitrogen atoms coordinated to Hg.
The nature of M∙∙∙N (M = Te, Hg) interaction in 28a, 29a, 30a 31, 32 and 33 was
studied with the aid of Natural Bond Orbital (NBO) analysis (Fig. 7). It has been earlier
reported in literature that Te/Se∙∙∙N/O interactions can include both electrostatic as well
covalent contributions [49,50]. We have calculated the electrostatic interaction (Eel)
energy for Te∙∙∙N interaction from their respective atomic charges assuming a point
charge model. The net atomic charges on Te and N in 28a-30a calculated by the natural
population analysis (NPA) are shown in Table S2 (see Supporting Information, page
S49). The NPA negative charges on N and positive charges on Te atoms clearly show
the significance of electrostatic interaction between them. The calculated electrostatic
interaction energy of 108.5 kcal/mol and 87.0 kcal/mol for Te∙∙∙N interaction in Te(IV)
compounds 29a and 30a was at least twice as compared with Eel of 35.8 kcal/mol for
Te(II)∙∙∙N interaction in 28a. This is clearly due to the higher net positive NPA charge on
27

Te(IV). Moreover, the higher value of Eel in 29a as compared with 30a is due to the high
electronegativity of the Cl atom attached to Te in 29a. The covalent contribution for the
Te∙∙∙N interaction was determined using NBO second order perturbation energies. The
NBO second order perturbation energies ENBO(Te N) for 28a, 29a and 30a were 30.9, 44.1
∙∙∙
and 39.2 kcal/mol, respectively. The origin of this interaction is due to the donation of
electron density from the lone pair of electrons on N (lp(N)) to the antibonding orbital of
Te-X bond (σ*(Te-X)) i.elp(N)
σ*(Te-X) interaction. The Wiberg bond indices (WBI)
for the Te∙∙∙N interaction are displayed in Table S1. Among the organotellurium
compounds, it is lowest for 28a (0.212) and highest for 29a (0.278). This is in line with
the shortest Te∙∙∙N distance of 2.504 Å and highest ENBO(Te N) interaction energy of 44.1
∙∙∙
kcal/mol for 29a. For organomercury compounds (31-33) the electrostatic energy
contribution for the Hg∙∙∙N interactions is significant, which ranged from 68.9-84.0
kcal/mol. The second order perturbation energies {ENBO(Hg N)} from NBO analysis
∙∙∙
revealed that the Hg∙∙∙N interaction arise from orbital interaction between lp(N)

σ*(Hg-
C) orbital as well from lp(N)
12.5 kcal/mol.
lp*(Hg) orbital interaction and ENBO(Hg N) varies from 8.1-
∙∙∙
The nature of N∙∙∙Te and Hg∙∙∙N interaction in 28a, 29a, 30a 31, 32 and 33 was also
studied from a topological point of view with the help of Atoms in Molecules analysis.
The important parameters obtained from the AIM calculation for the Te∙∙∙N and Hg∙∙∙
interaction are listed in Table S2. The presence of a bond critical point (bcp) for Te∙∙∙
N
N
and Hg∙∙∙N interaction clearly showed the existence of Te∙∙∙N and Hg∙∙∙N interactions. In
the case of organotellurium compounds, the electron density for the Te∙∙∙N interaction
(Te∙∙∙N) varied from 0.044-0.054 a.u (Table S2). The positive values of Laplacian of
28

electron density (2ρTe N) at the bcp, suggests a dominant electrostatic character for the
∙∙∙
Te∙∙∙N interaction. The negative values of local energy density (HTe N) point toward
∙∙∙
covalent character of Te∙∙∙N interaction, however, the relatively lower magnitude of HTe
∙∙∙
N
signifies dominant electrostatic contribution to the Te∙∙∙N interaction. For the
organomercury compounds 31 33, the values of electron density for the weak Hg∙∙∙
-
N
interactions lies in the range of 0.025-0.030 a.u. The positive values of Laplacian of
electron density (2ρHg N) and relatively low values of local energy density (HHg N) at the
∙∙∙
∙∙∙
bcp suggest a dominant electrostatic character for the Hg∙∙∙N interaction. In addition, for
compound 33, which possess a Hg-N(azide) bond, the electron density at bcp for this
bond is relatively high with a value of 0.074 a.u. Also, the large and negative value of
HHg-N(-0.0166 a.u) clearly suggests a dominant covalent character for the Hg-N azide
bond.
(a)
(b)
(c)
Fig. 7 NBO overlap diagram for (a) for lp(N)
σ*(Te-I) donor-acceptor interaction in 28a and
(b,c) lp(N)
σ*(Hg-C) donor-acceptor interactions for both the N1 and N2 atoms in 31.
29