Structure and Bonding of 1,2,4-Triazole Thiones Derived from Nitron

DOI: 10.1016/j.molstruc.2020.129682

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Journal of Molecular Structure (2021)

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Sambade, David

Collins, Cameron

Parkin, Gerard

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Article abstract of DOI:10.1016/j.molstruc.2020.129682

The molecular structures of two 1,2,4-triazole thiones derived from Nitron, namely Nitron(S) and Nitron(S)^Me, have been determined by single crystal X-ray diffraction. Comparison with the structure of Nitron indicates that the formation of the thiones is accompanied by a shortening of the C–N bond within the 5-membered ring that is opposite to the thione group, and a lengthening of the exocyclic C–N bond. Analysis of the structures of Nitron, Nitron(S) and Nitron(S)^Me, together with hypothetical versions in which the phenyl substituents are replaced by hydrogen, indicates that these changes are in accord with bond order differences predicted by natural bond orbital methods. A similar evaluation of the thione groups of Nitron(S) and Nitron(S)^Me indicates that the C–S bonds are composed of both covalent and ionic components and are best described by a combination of resonance structures that feature C[dbnd]S double and C–S single bonds.

Full text of DOI:10.1016/j.molstruc.2020.129682

Journal of Molecular Structure 1231 (2021) 129682

Contents lists available at ScienceDirect

Journal of Molecular Structure

journal homepage: www.elsevier.com/locate/molstr

Structure and Bonding of 1,2,4-Triazole Thiones Derived from Nitron

David Sambade, Cameron Collins, Gerard Parkin^∗

Department of Chemistry, Columbia University, New York, New York 10027, USA

a r t i c l e i n f o

a b s t r a c t

Article history:

The molecular structures of two 1,2,4-triazole thiones derived from Nitron, namely Nitron(S) and

Nitron(S)^Me, have been determined by single crystal X-ray diffraction. Comparison with the structure of

Nitron indicates that the formation of the thiones is accompanied by a shortening of the C–N bond within

the 5-membered ring that is opposite to the thione group, and a lengthening of the exocyclic C–N bond.

Analysis of the structures of Nitron, Nitron(S) and Nitron(S)^Me, together with hypothetical versions in

which the phenyl substituents are replaced by hydrogen, indicates that these changes are in accord with

bond order differences predicted by natural bond orbital methods. A similar evaluation of the thione

groups of Nitron(S) and Nitron(S)^Meindicates that the C–S bonds are composed of both covalent and

Received 13 October 2020

Revised 22 November 2020

Accepted 25 November 2020

Available online 28 November 2020

ionic components and are best described by a combination of resonance structures that feature C S dou-

ble and C–S single bonds.

1. Introduction

2. Results and discussion

We are currently interested in the application of heterocyclic

nitrogen compounds that feature exocyclic C=S thione functional

groups (Figure 1). In particular, we have focused attention on 5-

membered imidazole-2-thiones [1–3] that have been employed

as both ligands [4,5] and as components of (i) multidentate bis-

and tris(mercaptoimidazolyl)hydroborato ligands [6–12] and (ii)

metallaboratranes [13,14]. Metal complexes of imidazole-2-thiones

[15] are of speciﬁc interest because they provide catalytic sys-

tems for a wide variety of transformations [16,1 7]. In addition,

imidazole-2-thiones have been incorporated into bidentate and

pincer ligands which also have catalytic properties [18,19,20]. Fur-

thermore, imidazole-2-thiones themselves are also of relevance be-

cause they may be employed for the synthesis of N-heterocyclic

carbenes, [21] an important class of molecules [22]. Closely related

to imidazole-2-thiones are 1,2,4-triazole thiones, which are a class

of molecules that are of utility for the synthesis of heterocyclic

compounds, [23] and which also have important biological activ-

ities, [24] as illustrated by the inhibition of metallo-β-lactamases.

[25] As such, there is continued interest in developing the synthe-

ses of new 1,2,4-triazole thiones, [26] and so here we extend our

studies to the synthesis, structural characterization, and analysis of

the bonding of this class of molecules.

A variety of approaches exist for the synthesis of 1,2,4-triazole

thione derivatives, [23,26] some of which include the use of

thiosemicarbazides, thiocyanates and CS₂as the source of the

thione moiety. The thione moiety of 1,2,4-triazole thione may also

be installed by using elemental sulfur in the presence of a base,

[27,28] a method that has likewise been employed for the syn-

thesis of 1,3-disubstituted imidazole-2-thiones [29]. A more re-

cent extension of this approach involves the direct addition of el-

emental sulfur to a molecule that can generate a divalent car-

bon center. In this regard, Nitron, i.e. (1,4-diphenyl-1,2,4-triazol-

4-ium-3-yl)-phenylazanide, which is spectroscopically and struc-

turally characterized as a mesoionic compound, [30–34] exhibits

reactivity that is in accord with its so-called N-heterocyclic car-

bene tautomer [30,35]. As such, treatment of Nitron with sulfur

has been shown to result in the formation of the thione compound,

Nitron(S) (Scheme 1). [30,36,37] To extend this class of compound,

we sought to replace the hydrogen on the phenylamino group by a

methyl group. This transformation may be achieved by deprotona-

tion of Nitron(S) with MeLi,[38] followed by methylation with MeI

to afford Nitron(S)^Me(Scheme 2).

The molecular structure of Nitron(S)^Mehas been determined by

X-ray diffraction, as illustrated in Figure 2. For comparison, that

of the precursor, Nitron(S), has also been determined (Figure 3)

and the metrical data are presented in Table 1 and Table 2, to-

gether with those for Nitron and related derivatives. Examination

of these data indicates that the metrical details associated with

both the heterocyclic ring and the exo C–S (d₁) and C–N (d₇) bonds

(Figure 4) are very similar for Nitron(S) and Nitron(S)^Me. As an il-

∗

Corresponding author

E-mail address: parkin@columbia.edu (G. Parkin).

https://doi.org/10.1016/j.molstruc.2020.129682

D. Sambade, C. Collins and G. Parkin

Journal of Molecular Structure 1231 (2021) 129682

Table 1

Selected bond lengths of Nitron(S)^Rand related derivatives.^a

d₃/A

d₄/A

d₅/A

d₆/A

d₇/A

d₂/A

Ref

Nitron(S)

Nitron(S)^Me

1.356(4)

1.3566(18)

1.340(3)

1.326

1.396(4)

1.4008(16)

1.394(3)

1.409

1.298(4)

1.3000(17)

1.306(3)

1.357

1.383(4)

1.3831(17)

1.384(3)

1.413

1.370(4)

1.3831(18)

1.379(3)

1.315

1.358(4)

1.3702(18)

1.357(3)

1.327

this work

Nitron(Se)

Nitron (molecule #1)^b

1.328

1.401

1.351

1.437

1.345

1.306

[Nitron(H)][Cl]

mtaz^Me,Bu

1.317(2)

1.335(3)

1.344(2)

1.347(2)

1.3906(18)

1.399(3)

1.3803(19)

1.3757(19)

1.310(2)

1.301(3)

1.293(2)

1.294(2)

1.392(2)

1.365(4)

1.360(2)

1.354(2)

1.345(2)

1.388(3)

1.3717(19)

1.368(2)

1.358(2)

1.374(3)

–

^t,NBu^t

mtaz^Me

26a

mtaz^Me,Bz

–

(a) See Figure 4 for labeling scheme.

(b) Two crystallographically independent molecules in the asymmetric unit.

Fig. 1. Imidazole thiones and 1,2,4-triazole thiones.

Scheme 2

lustration, the shortest bond within each ring is the C–N bond (d₄)

that is opposite the thione moiety, while the other bond lengths

are much more comparable to each other. Thus, the d₄C–N bond

of Nitron(S) is 1.298(4) A, whereas the other bonds within the

ring are in the range 1.356(4) A to 1.396(4) A, with an average of

1.376 A. The structures of Nitron(S) and Nitron(S)

are also com-

pared with those of other 5-membered heterocyclic thione deriva-

tives in Table 2 [29b,39–44]. These data indicate that the C–S bond

lengths of Nitron(S) and Nitron(S)^Meare comparable to those in

Fig. 3. Molecular structure of the thione, Nitron(S). A minor component of a disor-

dered phenyl group is omitted for clarity.

Table 2

C–S and adjacent C–N bond lengths in 5-membered heterocyclic thione com-

pounds.

Fig. 2. Molecular structure of the thione, Nitron(S)^Me

d(C–S)/A

d(C–N)/A

Ref.

Nitron(S)

Nitron(S)^Me

mtaz^Me,Bu

1.668(3)

1.6656(14)

1.689(3)

1.6765(15)

1.6705(17)

1.671(3)

1.683(8)

1.671(2)

1.670(3)

1.356(4)

1.3566(18)

1.335(3)

1.344(2)

1.347(2)

1.374(4)

1.358(10)

1.361(3)

1.368(3)

1.370(4)

1.3831(18)

1.388(3)

1.3717(19)

1.368(2)

1.377(4)

1.361(10)

1.373(2)

1.371(3)

this work

^t,NBu^t

mtaz^Me

26a

mtaz^Me,Bz

mim^Ph

mim^Ar

ꢀ

ꢀꢀ

ꢀ

(a) Ar = 4-Me-C₆H₂-2,6-(CHPh₂)₂.

ꢀꢀ

(b) Ar = C₆H₃-2,6-Prⁱ₂

Scheme 1

D. Sambade, C. Collins and G. Parkin

Journal of Molecular Structure 1231 (2021) 129682

Fig. 4. Labeling scheme for heterocyclic bonds in 1,2,4-triazole derivatives.

Fig. 6. Geometry optimized structures of simpliﬁed counterparts of Nitron and its

derivatives in which the phenyl groups are replaced with hydrogen.

Table 3

Fig. 5. Geometry optimized structures of Nitron and its derivatives.

Selected bond lengths for geometry optimized structures.

d₂/A

d₃/A

d₄/A

d₅/A

d₆/A

d₇/A

d₁/A

other 1,2,4-triazole thiones and 1,3-imidazole thiones, as are the

adjacent C–N bond lengths.

Nitron(S)

Nitron(S)^Me

Nitron

1.671

–

1.370

1.374

1.324

1.347

1.357

1.355

1.319

1.344

1.396

1.388

1.372

1.401

1.385

1.387

1.366

1.397

1.304

1.303

1.366

1.305

1.308

1.382

1.304

1.386

1.387

1.455

1.401

1.377

1.380

1.435

1.381

1.401

1.402

1.343

1.381

1.388

1.344

1.385

1.366

1.382

1.290

1.368

1.381

1.373

1.285

1.386

It is also pertinent to compare the structures of the thiones

with Nitron. In this regard, examination of the data in Table 1 in-

dicates that the most noticeable structural differences are that (i)

the exo C–N bond in the thione is signiﬁcantly longer than in Ni-

tron, while (ii) the C–N bond opposite to the thione moiety (d₄) is

shorter than the corresponding bond in Nitron. None of the hete-

rocyclic ring bonds in the thiones, however, are as long as the d₅

C–N bond in Nitron.

Nitron^NHC

–

Nitron(S)^∗

1.669

1.670

–

Nitron(S)^Me∗

Nitron^∗

Nitron^NHC∗

–

a,b

(a) Nitron^NHCrefers to the N-heterocyclic carbene tautomer of Nitron.

(b) Nitron^∗, Nitron^NHC∗and Nitron(S)^R∗refer to molecules in which the phenyl sub-

stituents are replaced by hydrogen.

To analyze these differences in more detail, the structures of

Nitron(S)^Rand Nitron were analyzed computationally, with geom-

etry optimized structures of Nitron(S)^Rand Nitron presented in

Figure 5 and selected bond lengths in Table 3. Signiﬁcantly, the

geometry optimized structures reproduce the differences observed

experimentally, with the C–N (d₄) bond length being shorter in the

thiones than in Nitron [45,46]. In order to facilitate the analysis,

calculations have also been performed on counterparts in which

the phenyl groups are replaced by hydrogen (and are labeled with

^∗), and the metrical data for these counterparts also compare fa-

vorably with the complete molecules.

in Nitron(S)^∗. These changes are reﬂected in the principal reso-

nance structures for Nitron^∗and Nitron(S)^∗, which are summarized

in Figure 7. Thus, the dominant resonance structure of Nitron^∗pos-

sesses single and double bonds respectively for d₄and d₇(39.0 %),

[47] whereas that for Nitron(S)^∗possesses double and single bonds

respectively for d₄and d₇(Figure 7) [48]. Furthermore, considera-

tion of all of the resonance structures indicates that 79.4 % of the

resonance structures of Nitron^∗possess both a single C–N (d₄) het-

erocyclic bond and a double C=N (d₇) exocyclic bond, while the

converse is observed for the thione, Nitron(S)^∗, with the majority

(62.7%) of the resonance structures possessing a heterocyclic C=N

(d₄) double bond and an exocyclic C–N (d₇) single bond. In ad-

dition, more than 93 % of all resonance structures of Nitron(S)^∗

possess an exocyclic C–N (d₇) single bond. These resonance struc-

Examination of the bond orders derived from natural bond

orbital (NBO) analyses supports the observed structural changes

(Table 4). Speciﬁcally, the exocyclic d₇C–N bond order in Nitron^∗

is reduced considerably from 1.83 to 1.07 in Nitron(S)^∗, while the

trans d₄C–N heterocyclic bond order increases from 1.11 to 1.66

D. Sambade, C. Collins and G. Parkin

Journal of Molecular Structure 1231 (2021) 129682

Table 4

NBO derived bond orders.

Bond order

d₄

d₁

d₂

d₃

d₅

d₆

d₇

Nitron(S)

Nitron(S)^Me

Nitron

1.8188

1.1150

1.1016

1.8270

1.9441

1.3174

1.3274

1.4931

1.5980

1.0172

1.1147

1.0003

1.0331

1.0226

1.1365

1.0002

1.8959

1.9149

1.0675

1.8926

1.6565

1.6450

1.1142

1.8186

1.0435

1.0346

1.0331

1.0803

1.2225

1.2161

1.0517

1.0747

1.0662

1.0865

1.0546

1.0556

1.1407

1.402

1.0434

1.0333

1.8482

1.0268

1.0658

1.0933

1.8341

1.0723

1.8118

–

Nitron^NHC

–

Nitron(S)^∗

1.5097

Nitron(S)^Me∗

1.5008

Nitron^∗

–

1.2433

1.3828

Nitron^NHC∗

a,b

(a) Nitron^NHCrefers to the N-heterocyclic carbene tautomer of Nitron.

(b) Nitron^∗, Nitron^NHC∗and Nitron(S)^R∗refer to molecules in which the phenyl substituents are

replaced by hydrogen.

Table 5

NLMO composition and atomic charges (Q) for C–S moieties of Nitron(S)^R

and Nitron(S)^R∗

σ–orbital

π–orbital

Q_C/e

Q_S/e

σ_%C

σ_%S

π_%C

π_%S

Nitron(S)

60.71

60.62

61.17

61.15

39.29

39.38

38.83

38.85

28.35

28.47

27.66

27.36

71.65

71.53

72.34

72.64

0.21

0.19

–0.22

–0.23

Nitron(S)^Me

Nitron(S)^∗

Nitron(S)^Me∗

structurally related 1,2,4-triazole thiones [26a] and 1,3-imidazole

thiones (Table 2), are shorter than the average value for struc-

turally characterized compounds with C–S single bonds (1.804 A),

[52] but longer than C=S double bonds in compounds such as car-

bon disulﬁde (1.554 A, [53] 1.54 A, [54] 1.5532 A [55] and 1.558 A

[56]), thioformaldehyde (1.611 A), [57] thioaldehydes [e.g. 1.588(11)

A, [58] 1.602(7) A, [58] 1.602(5) A [59]], and thioketones [e.g. 1.626

A, [60] 1.658 A, [60] 1.628(2) A, [61], 1.639(2) A, [61] 1.605(4) A,

[62] 1.665(8) A, [62] 1.661(5) A, [63] 1.630(9) A, [63] and 1.636(9)

A [64]]. Support for the observation that the C–S bonds in Ni-

tron(S) and Nitron(S)^Meare longer than those in compounds with

well deﬁned C=S double bonds is provided by the fact that the

C–S bond orders are 1.82 and 1.81, with signiﬁcant ionic compo-

nents of 0.57 and 0.56, respectively. These data suggest that the

bonding in these compounds is best described by a combination

of resonance structures that feature C=S double and C–S single

bonds [65]. Furthermore, calculations on Nitron(S)^∗, in which the

phenyl groups have been replaced with hydrogen, indicate that

while the dominant resonance structure features a C=S double

bond, components with C–S single bonds also play a signiﬁcant

role (Figure 7). Speciﬁcally, resonance structures with C=S double

bonds contribute 44.5% to the overall bonding description, while

those with C–S single bonds contribute 52.3%. This situation con-

trasts markedly with that for thioformaldehyde, for which the C=S

doubly bonded resonance structure contributes 96.4% to the over-

all description of the molecule [2]. The different bonding situations

between thioformaldehyde and the 1,2,4-triazole thiones deriva-

tives is clearly a consequence of the participation of the lone pairs

on the adjacent nitrogen atoms in the heterocyclic compounds.

Examination of the natural localized molecular orbitals (NL-

MOs) for the thione group indicates that the π-bond is heavily

localized on the sulfur atom, such that it bears a negative charge

(Figure 8, Figure 9 and Table 5). This observation is in accord with

calculations on 1,3-imidazole-2-thiones and selones which indicate

that the HOMO is largely localized on the chalcogen, in accord with

zwitterionic character [66–69].

Fig. 7. Dominant resonance structures (> 10 %) for Nitron^∗(top), Nitron^NHC∗(cen-

ter) and Nitron(S)^∗(bottom).

tures for Nitron^∗are in accord with representations for Nitron that

present it with cationic amidinium and anionic amidate fragments,

with the latter comprising the exo NPh moiety [49,50].

While the d₄and d₇bond orders, and the resonance structures,

of the thione derivatives differ considerably from those of Nitron

and Nitron^∗, they are comparable to those of the N-heterocyclic

carbene tautomers, Nitron^NHC[51] and Nitron^NHC∗(Table 4). For

example, the dominant resonance structures of both Nitron^NHC∗

and Nitron(S)^∗contain a C=N (d₄) double bond and an exocyclic C–

N (d₇) single bond, while the converse is observed for Nitron^∗. This

aspect of the similarity of the resonance structures of Nitron^NHC∗

and Nitron(S)^∗is in accord with the notion that the latter may be

viewed as an adduct between an N-heterocyclic carbene and a sul-

fur atom.

Another aspect of the structures of Nitron(S) and Nitron(S)^Me

that merits discussion is the nature of the thione interaction. In

this regard, the C–S bond lengths of 1.668(3) A and 1.6656(14)

A, respectively, which are similar to the values observed in

D. Sambade, C. Collins and G. Parkin

Journal of Molecular Structure 1231 (2021) 129682

Fig. 8. NLMOs pertaining to the thione moiety of Nitron(S).

3. Summary

Fig. 9. NLMOs pertaining to the thione moiety of Nitron(S)^Me

In summary, the 1,2,4-triazole thiones derived from Nitron,

namely Nitron(S) and Nitron(S)^Me, exhibit signiﬁcant structural dif-

ferences relative to Nitron. Speciﬁcally, for each compound, the

heterocyclic C–N bond that is opposite to the thione moiety is

shorter than the corresponding bond in Nitron, whereas the ex-

ocyclic C–N bond is longer. Analysis of the compounds by using

natural bond orbital methods are in accord with the experimental

observations, and indicate that the bond order for the heterocyclic

C–N bond that is opposite to the thione group for each compound

is larger than that in Nitron, while that for the exocyclic C–N bond

is smaller than in Nitron. A similar analysis of the thione groups

indicates that the C–S bonds are composed of both covalent and

ionic components and are best described by a combination of reso-

nance structures that feature C=S double and C–S single bonds. As

such, the bonding contrasts markedly with that for thioformalde-

hyde, for which the C=S doubly bonded resonance structure con-

tributes 96.4% to the overall description of the molecule, and this

difference is attributed to participation of the lone pairs on the ad-

ters. ¹H NMR chemical shifts are reported in ppm relative to SiMe₄

(δ = 0), and were referenced with respect to the protio solvent im-

purity (δ = 7.16 for C₆D₅H, δ = 1.94 for CD₂HCN and δ = 1.72 for

C₄D₇HO) [71]. Infrared spectra were recorded on a Perkin Elmer

Spectrum Two spectrometer in attenuated total reﬂectance (ATR)

mode, and are reported in reciprocal centimeters. Nitron(S) was

prepared by the literature method [30], and crystals suitable for

X-ray diffraction were obtained from benzene/pentane. All other

reagents were obtained commercially and used as received.

4.2. X-ray structure determinations

X-ray diffraction data were collected on

a Bruker Apex II

diffractometer. The structures were solved by using direct meth-

ods and standard difference map techniques, and were reﬁned

by full-matrix least-squares procedures on F²with SHELXTL (Ver-

sion 2014/7) [72]. Crystallographic data have been deposited with

the Cambridge Crystallographic Data Centre (CCDC #2035263-

2035264).

jacent nitrogen atoms of Nitron(S) and Nitron(S)^Me

4. Experimental section

4.1. General considerations

4.3. Computational details

All manipulations were performed using

combination of

glovebox, high vacuum and Schlenk techniques under either an ar-

gon or nitrogen atmosphere, unless otherwise stated [70]. Solvents

were puriﬁed and degassed by standard procedures. NMR spec-

tra were recorded on Bruker 300 DRX, Bruker AVIII 300, Bruker

AVIII 400SL, Bruker AVIII 400, and Bruker AVIII 500 spectrome-

Calculations were carried out using DFT as implemented in the

Jaguar 8.9 (release 15) suite of ab initio quantum chemical pro-

grams [73]. Geometry optimization calculations were performed

with the B3LYP density functional using the LACVP^∗∗basis set. Nat-

ural bond orbital (NBO) and natural resonance theory (NRT) calcu-

D. Sambade, C. Collins and G. Parkin

Journal of Molecular Structure 1231 (2021) 129682

lations[74] were performed with NBO 6.0 [75] as implemented in

the Jaguar suite of programs.

[4] (a) J.G. Melnick, G. Parkin, Cleaving mercury-alkyl bonds: A functional

model for mercury detoxiﬁcation by MerB, Science 3 1 7 (2007) 225–227;

(b) J.G. Melnick, K. Yurkerwich, G. Parkin, Synthesis, structure, and reac-

tivity of two-coordinate mercury alkyl compounds with sulfur ligands:

Relevance to mercury detoxiﬁcation, Inorg. Chem. 48 (2009) 6763–6772;

molecular structure of the tris (2-mercapto-1-tolylimidazolyl)hydroborato

zinc(2–mercapto–1–tolylimidazole) complex, {[Tm^p-Tol]Zn(mim^p-Tol)}[ClO₄]:

4.4. Synthesis of Nitron(S)^Me

A stirred solution of Nitron(S) (1.215 g, 3.53 mmol) in THF

(ca. 30 mL) under nitrogen was treated with MeLi (2.4 mL of 1.6

M in Et₂O, 3.84 mmol), resulting in the immediate evolution of

methane. The mixture was allowed to stir at room temperature

for 10 minutes, after which MeI (ca. 0.23 mL, 3.69 mmol) was

added via syringe. After stirring the mixture for 1 hour, the volatile

components were removed in vacuo to afford a viscous orange oil,

which was dissolved in CH₂Cl₂(ca. 20 mL) and treated slowly with

H₂O (ca. 4 mL) with stirring. The organic layer was separated and

ﬁltered in air. The volatile components were removed from the so-

lution in vacuo to yield an off-white residue, which was dissolved

in C₆H₆(ca. 20 mL) and then lyophilized to afford Nitron(S)^Me

as a free-ﬂowing powder (1.161 g, 3.24 mmol, 92%). Crystals suit-

able for X-ray diffraction were obtained by allowing a solution of

Nitron(S)^Mein hot methanol to cool slowly. ¹H NMR (THF-d₈): 3.26

[s, 3H of {C₂N₃(C₆H₅)₂(S)(N(CH₃)(C₆H₅))}], 6.88 [m, 3H], 7.07 [m,

2H], 7.14–7.23 [m, 5H], 7.29 [m, 1H], 7.43 [m, 2H], 8.34 [m, 2H].

¹H NMR (CD₃CN): 3.25 [s, 3H of {C₂N₃(C₆H₅)₂(S)(N(CH₃)(C₆H₅))}],

6.92 [m, 3H], 7.12 [m, 2H], 7.20–7.24 [m, 2H], 7.26–7.30 [m, 3H],

7.43 [m, 1H], 7.55 [m, 2H], 8.10 [m, 2H]. ¹H NMR (C₆D₆): 2.85 [s,

3H of {C₂N₃(C₆H₅)₂(S)(N(CH₃)(C₆H₅))}], 6.38 [m, 2H], 6.63 [m, 1H],

6.70–6.96 [two m, 7H], 7.04 [m, 1H], 7.25 [m, 2H], 8.74 [m, 2H]. IR

(cm^–1): 3062 (w), 2926 (w), 1960 (w), 1887 (w), 1580 (s), 1493 (s),

1458 (m), 1435 (m), 1383 (s), 1325 (m), 1299 (m), 1280 (m), 1175

(m), 1153 (m), 1089 (m), 1066 (m), 1024 (m), 991 (m), 971 (m), 915

(m), 870 (m), 845 (w), 761 (s), 737 (m), 718 (m), 692 (vs), 661 (m),

649 (m), 615 (m), 580 (m), 547 (m), 487 (m), 452 (m), 410 (w).

•••

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Declaration of competing interest

There are no conﬂicts of interest to declare.

CRediT authorship contribution statement

David Sambade: Conceptualization, Investigation, Writing

original draft. Cameron Collins: Investigation. Gerard Parkin: Con-

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ceptualization, Writing - original draft, Funding acquisition.

Acknowledgements

This research was supported by the U. S. Department of Energy,

Oﬃce of Science, Oﬃce of Basic Energy Sciences, Catalysis Science

Program under Awards DE-SC0019204 and DE-FG02-93ER14339.

Supplementary materials

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Supplementary material associated with this article can be

found, in the online version, at doi:10.1016/j.molstruc.2020.129682.

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