Synthesis and assessment of compounds trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,4-diamine and trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,4-diamine as hosts for potential xylene and ethylbenzene guests

Article abstract of DOI:10.1007/s10847-019-00883-0

In this work, two novel compounds, trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,4-diamine 1 and trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,4-diamine 2, were designed and successfully synthesized in our laboratories, and assessed for their host potential in the presence of potential xylene (Xy) isomer and ethylbenzene (EB) guests. Host 1 successfully formed complexes with all four of o-Xy, m-Xy, p-Xy and EB, while 2 only clathrated p-Xy and EB. Equimolar guest/guest competition experiments showed that hosts 1 and 2 possess very similar selectivities for these guests [p-Xy (73.9%) > EB (13.0%) > m-Xy (8.1%) > o-Xy (5.0%) and p-Xy (71.3%) > EB (20.2%) > m-Xy (6.0%) > o-Xy (2.5%) for 1 and 2, respectively]. Single crystal diffraction analyses revealed striking geometry changes for the sulfur host analogue: while the tricyclic fused ring system of the oxygen host remained planar when guest was absent or present, this fused system of the sulfur analogue experienced a dramatic geometry change from buckled (in the absence of guest) to planar (in guest presence). This observation explained the selectivity similarities of both hosts in the presence of these guests. Additionally, the relative thermal stabilities of the four complexes with host 1 were assessed by employing thermal analyses, and the results of these correlated exactly with the selectivity order, since the onset temperature of the guest release processes (T_on) was in the order p-Xy (88.0?°C) > EB (70.9?°C) > m-Xy (59.7?°C) > o-Xy (46.2?°C). T_on values also explained the significant preference of host 2 for p-Xy (115.5?°C) relative to EB (76.6?°C), respectively.

Full text of DOI:10.1007/s10847-019-00883-0

Journal of Inclusion Phenomena and Macrocyclic Chemistry
https://doi.org/10.1007/s10847-019-00883-0
ORIGINAL ARTICLE
Synthesis and assessment of compounds trans-N,N′-bis(9-phenyl-9-
xanthenyl)cyclohexane-1,4-diamine and trans-N,N′-bis(9-phenyl-9-
thioxanthenyl)cyclohexane-1,4-diamine as hosts for potential xylene
and ethylbenzene guests
Benita Barton1 · Daniel V. Jooste1 · Eric C. Hosten1
Received: 12 November 2018 / Accepted: 17 January 2019
© Springer Nature B.V. 2019
Abstract
In this work, two novel compounds, trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,4-diamine 1 and trans-N,N′-bis(9-
phenyl-9-thioxanthenyl)cyclohexane-1,4-diamine 2, were designed and successfully synthesized in our laboratories, and
assessed for their host potential in the presence of potential xylene (Xy) isomer and ethylbenzene (EB) guests. Host 1 suc-
cessfully formed complexes with all four of o-Xy, m-Xy, p-Xy and EB, while 2 only clathrated p-Xy and EB. Equimolar
guest/guest competition experiments showed that hosts 1 and 2 possess very similar selectivities for these guests [p-Xy
(73.9%)>EB (13.0%)>m-Xy (8.1%)>o-Xy (5.0%) and p-Xy (71.3%)>EB (20.2%)>m-Xy (6.0%)>o-Xy (2.5%) for 1 and
2, respectively]. Single crystal diffraction analyses revealed striking geometry changes for the sulfur host analogue: while
the tricyclic fused ring system of the oxygen host remained planar when guest was absent or present, this fused system of
the sulfur analogue experienced a dramatic geometry change from buckled (in the absence of guest) to planar (in guest pres-
ence). This observation explained the selectivity similarities of both hosts in the presence of these guests. Additionally, the
relative thermal stabilities of the four complexes with host 1 were assessed by employing thermal analyses, and the results
of these correlated exactly with the selectivity order, since the onset temperature of the guest release processes (Ton) was in
the order p-Xy (88.0 °C)>EB (70.9 °C)>m-Xy (59.7 °C)>o-Xy (46.2 °C). Ton values also explained the significant prefer-
ence of host 2 for p-Xy (115.5 °C) relative to EB (76.6 °C), respectively.
Keywords Xylene · Ethylbenzene · Host–guest chemistry · Supramolecular chemistry · Xanthenyl systems
Introduction
guest mixtures [3, 4], drug-delivery system enhancement
[5], chemo- and bio-sensing [6, 7], as well as the detection
of cationic and anionic analytes in the environment [8].
Several host compounds display selectivity when presented
with mixed guests, thus forming a complex that contains
more of one guest than the other [3, 4, 9]. The employment of
host–guest chemistry for the separation of isomers is therefore
a burgeoning field since this separation may be challenging for
many industrially-relevant isomers by more conventional means
(fractional distillations and crystallizations) owing to physical
property similarities. For example, o-, m- and p-xylene (o-, m-
and p-Xy), and ethylbenzene (EB), known as the C8 aromatic
fraction, are obtained as a mixture from crude oil distillation [4]
due to similarities in their boiling points (144.5, 139.1, 138.2
and 136.2 °C, respectively [9]). These compounds, indepen-
dently, are of significant commercial importance—for exam-
ple, the para-isomer is used extensively for the manufacture
Host–guest chemistry is that branch of chemistry that com-
prises interrelating host and guest molecules, via non-cova-
lent interactions, during inclusion compound formation [1,
2]. The applications of this field of chemistry is far-reaching,
and include the separation of isomers through simple host
recrystallization techniques from both chiral and achiral
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10847-019-00883-0) contains
supplementary material, which is available to authorized users.
* Benita Barton
benita.barton@mandela.ac.za
1
Department of Chemistry, Nelson Mandela University, PO
Box 77000, Port Elizabeth 6031, South Africa
Vol.:(0123456789)
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
X
X
of polyesters and polyethylene terephthalates [10]. Hence,
due to their separation being inherently problematic, numer-
ous researchers have recently spent considerable capacity on
investigating alternative separation strategies. As such, extrac-
tive processes [10, 11], zeolites [12–14], metal–organic frame-
works (MOFs) [4, 15, 16] and carbon molecular sieves [17]
have all shown potential in addressing this problem. Kawahata
and co-workers [18], furthermore, employed an adamantane-
based acyclic host compound to selectively include p-Xy from
the C8 aromatic fraction.
1) PhMgBr
2) H
OH
O
3: X = O
4: X = S
5: X = O
6: X = S
HClO4
In this work, we report on the synthesis and assessment
of two novel crystalline materials, namely trans-N,N′-bis(9-
phenyl-9-xanthenyl)cyclohexane-1,4-diamine 1 and trans-
N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,4-diamine
2, for their host ability in the presence of potential guests
o-Xy, m-Xy, p-Xy and EB (Scheme 1). We designed these
solid compounds for these solvents upon the knowledge
that xanthenyl and thioxanthenyl systems typically afford
immensely effective host materials when incorporated into
the host molecular structure. As examples, related N,N′-
bis(9-phenylxanthen-9-yl)ethylenediamine and/or its thio
derivative displayed enhanced selectivity when recrystal-
lized from various mixtures of the C8 aromatics [19], dih-
aloalkanes [20, 21] and pyridine/methylpyridines [22]. All
successfully-formed crystalline materials were analysed by
means of extensive single crystal diffraction (SCXRD) and
thermal analyses (TA), and we report on these findings here.
X
H2N
NH2
ClO4
1 and 2
7: X = O
8: X = S
Scheme 2 Synthetic pathway towards compounds 1 and 2
alcohols 5 and 6 after acidic workup. These were treated
with perchloric acid to yield the perchlorate salt derivatives
7 and 8 as crystalline solids which, upon the addition of
trans-1,4-diaminocyclohexane, yielded the desired com-
pounds 1 and 2 in reasonable yield (45%).
Results and discussion
Assessment of the host potential of 1 and 2
when recrystallized from each of the four organic
solvents
Synthesis of potential hosts 1 and 2
The title compounds were synthesized from xanthone 3 or
thioxanthone 4 (Scheme 2) by means of a standard Grignard
addition reaction with phenylmagnesium bromide to afford
Table 1 summarises the host:guest (H:G) ratios of the crys-
talline solids obtained after independently recrystallizing 1
Scheme 1 Molecular structures
of novel hosts trans-N,N′-
bis(9-phenyl-9-xanthenyl)
cyclohexane-1,4-diamine 1
and trans-N,N′-bis(9-phenyl-
9-thioxanthenyl)cyclohexane-
1,4-diamine 2, and guests
o-xylene (o-Xy), m-xylene
(m-Xy), p-xylene (p-Xy) and
m-Xy
o-Xy
X
X
ethylbenzene (EB)
NH
HN
1: X = O
2: X = S
p-Xy
EB
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
and 2 from each of the xylene and ethylbenzene solvents,
and analysing these by means of 1H-NMR spectroscopy.
trans-N,N′-Bis(9-phenyl-9-xanthenyl)cyclohexane-1,4-di-
amine 1 proved to be a highly efficient host material for these
aromatic compounds, clathrating each one with 1:1 H:G ratios
(Table 1). The thio derivative 2, however, fared less well and
only formed complexes with p-Xy and EB, but also with 1:1
H:G ratios. o- and p-Xy were not included by 2 in this way.
hosts would display selectivity when presented with equi-
molar mixed guests. We therefore prepared various combi-
nations of binary, ternary and quaternary mixtures of the
guests, where each one was present in equimolar quantities,
and dissolved and recrystallized the hosts from these mix-
tures. Owing to overlapping guest/guest resonance signals
in the 1H-NMR spectra, GC–MS was considered to be the
more prudent analytical method here for the crystalline sol-
ids that formed in this way. Table 2 contains a summary of
the results so-obtained, where the preferred guest is pro-
vided in bold font face for ease of comparison. Experiments
were conducted in duplicate, and percentage estimated
standard deviations (% e.s.d.’s) are provided in the table in
parentheses.
Guest/guest competition experiments
Selectivity of 1 and 2 in the presence of equimolar mixtures
of the guests
Since both 1 and 2 formed complexes with some or all four
Host 1 displayed remarkable selectivity when recrystal-
lized from o-Xy/p-Xy and m-Xy/p-Xy mixtures, includ-
ing significantly more p-Xy in both cases (95.1 and
89.2%, respectively) (Table 2). These results suggest that
host–guest chemistry employing this host is certainly fea-
sible for the separation of p-Xy from both o- and m-Xy.
More ambivalent behaviour, however, was noted when the
guest mixtures were o-Xy/m-Xy and o-Xy/EB, where o-Xy
was discriminated against in each instance (32.5, 26.5%).
A mixture comprising m-Xy and EB afforded a complex
rich in the latter guest (66.8%), while the inclusion com-
pound emanating from a p-Xy/EB combination contained
of the guests, we subsequently investigated whether these
Table 1 H:G ratios of solids
Guest
Host 1
Host 2
formed after recrystallization
of 1 and 2 from each proposed
guest solvent
o-Xy
m-Xy
p-Xy
EB
1:1
1:1
1:1
1:1
1:0a
1:0a
1:1
1:1
aThe guest was not included by
the host
Table 2 Results of the
competition experiments of
1 and 2 when recrystallized
from various equimolar guest
mixtures
o-Xy m-Xy p-Xy EB
Host 1
Overall
Host 2
Overall
(% e.s.d.)
H:G ratio (% e.s.d.)
H:G ratio
X
X
X
X
32.5:67.5
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
0.0:0.0
N/A
1:0
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
(0.5)
X
X
4.9:95.1
4.3:95.7
(0.1)
(0.2)
X
26.5:73.5
6.9:93.1
(1.0)
(0.3)
X
X
10.8:89.2
10.3:89.7
(0.9)
(0.1)
X
33.2:66.8
23.0:77.0
(1.1)
(0.2)
X
X
X
X
85.0:15.0
75.2:24.8
(0.7)
(0.4)
X
X
X
X
5.7:10.2:84.1
3.3:8.4:88.3
(0.4):(1.3):(0.9)
(0.2):(0.3):(0.1)
X
X
X
X
6.3:78.9:14.8
3.2:74.7:22.1
(0.4):(0.3):(0.1)
(0.2):(0.6):(0.7)
X
X
X
15.6:27.4:57.0
4.5:19.5:76.0
(1.3):(0.2):(1.5)
(0.3):(0.5):(0.2)
X
X
7.6:79.8:12.6
6.3:73.1:20.6
(0.9):(0.2):(0.8)
(0.0):(0.0):(0.1)
X
5.0:8.1:73.9:13.0
2.5:6.0:71.3:20.2
(0.7):(0.0):(0.7):(0.0)
(0.5):(0.3):(0.3):(0.5)
Ratios were determined using GC–MS
Experiments were conducted in duplicate for confirmation purposes with % e.s.d.’s provided in parentheses
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
considerably more of the xylene (85.0%). When 1 was
recrystallized from a mixture of all three xylenes, the host
remained decidedly selective for the para isomer, with
the least favoured isomer being o-Xy [p-Xy (84.1%) > m-
Xy (10.2%)> o-Xy (5.7%)]. Complexes arising from other
ternary solvent combinations, o-Xy/p-Xy/EB, o-Xy/m-Xy/
EB and m-Xy/p-Xy/EB, comprised increased amounts of
p-Xy when it was present (78.9 and 79.8%, respectively),
while EB was the preferred guest in the absence of this
isomer (EB, 57.0%). The host was also subjected to all
four guests simultaneously, and the mixed crystal result-
ing from this experiment, once more, showed an increased
amount of p-Xy. The host selectivity order for these guests
was therefore noted as p-Xy (73.9%)>EB (13.0%)>m-Xy
(8.1%) > o-Xy (5.0%).
90:10, 80:20, 60:40, 50:50, 40:60, 20:80 and 10:90. The
crystals that formed in each case were analysed via GC–MS
to determine the mole fraction of the preferred guest present
(Z), while mother liquors were also analysed in the same
way (X). A plot of Z vs. X provided the selectivity behaviour
of the host as the guest concentration varied. In this way,
Fig. 1a–k were obtained (since 2 did not form an inclusion
compound when recrystallized from an equimolar mixture
of o- and m-Xy, this guest/guest competition experiment was
not carried out here). Note that the straight-line plot in each
figure is theoretical and represents a host that does not dis-
play any selectivity.
In all of these figures, hosts 1 and 2 are selective for the
preferred guest over the entire concentration range and there-
fore the host preference is unrelated to the guest concentra-
tion; only the extent of this selectivity is affected by the
guest concentration.
Given that neither o-Xy nor m-Xy were clathrated in the
single solvent experiments with host 2, it was unsurpris-
ing that when this host was recrystallized from an equi-
molar mixture of these two solvents, no inclusion was
observed (Table 2). However, for all other guest combina-
tions (with both hosts 1 and 2), mixed complexes were
formed in which the overall H:G ratio was consistently
1:1. Notable also is that, whenever host 2 was recrystal-
lized from a solvent mixture containing either p-Xy and/or
EB, the only two guests that formed inclusion compounds
with this host in single solvent experiments, guests that
were not clathrated in these single solvent experiments
were also found in the host crystal. For example, binary
mixtures o-Xy/p-Xy and m-Xy/p-Xy afforded complexes
with 95.7 and 89.7% p-Xy, while 93.1 and 77.0% EB were
found in complexes that crystallized from o-Xy/EB and
m-Xy/EB. A p-Xy/EB mixture afforded a complex that
was rich in p-Xy (75.2%). Once more, the three xylenes
were mixed and host 2 recrystallizing from this mixture
contained a significant amount of p-Xy [p-Xy (88.3%)>m-
Xy (8.4%) > o-Xy (3.3%)]. Clearly, in this instance, 2 was
somewhat more selective for p-Xy compared with 1 (88.3
vs. 84.1%). The remaining combinations of guests pro-
vided results for 2 that followed a similar trend to those
for 1. In fact, it was remarkable that the guest preference
of hosts 1 and 2 in every experiment correlated exactly,
and it was only the observed quantities of each guest in
the crystals that changed somewhat. The host 2 selectivity
order when presented with all four guests was therefore
p-Xy (71.3%) > EB (20.2%) > m-Xy (6.0%) > o-Xy (2.5%).
For experiments containing p-Xy in the binary mixture,
1 displayed significant selectivity for this guest even when
present in low concentrations: when the mother liquors con-
tained 10.6 (p-Xy/o-Xy), 9.1 (p-Xy/m-Xy) and 11.5% (p-
Xy/EB) p-Xy, resultant mixed complexes already possessed
72.0, 54.7 and 47.7% of this guest, respectively (Fig. 1b, d
and f). The poorest selectivity for this host was observed
in the EB/m-Xy experiment, where only 17.4% of EB was
found in the crystal when the mother liquor contained 11.8%
EB (Fig. 1e). This was followed by the m-Xy/o-Xy (Fig. 1a)
and EB/o-Xy (Fig. 1c) experiments (mother liquors contain-
ing 10.4 and 10.6% of m-Xy and EB afforded crystals with
17.8 and 31.8% of these guests, respectively).
Once more, as with 1, host 2 showed enhanced selec-
tivities for p-Xy in the p-Xy/o-Xy (Fig. 1g) and p-Xy/m-Xy
(Fig. 1i) experiments when mother liquors contained low
concentrations of this guest: in the first of these, a 9.9% p-Xy
concentration in the mother liquor furnished crystals with
89.9% of this guest while, in the second, a 10.5% concen-
tration afforded a mixed complex with 60.7% p-Xy. These
experiments reveal that host 2 is, in fact, more selective than
1 for p-Xy when competing with o- and m-Xy. The selectiv-
ity of 2 for EB in the EB/o-Xy (Fig. 1h) experiment was
low initially (at 21.2% of this guest in the mother liquor,
the complex that crystallized only contained 28.8% EB),
but increased abruptly at 39.9% EB concentration (crystals
now contained 91.3% EB). EB/m-Xy (Fig. 1j) and p-Xy/EB
(Fig. 1k) experiments revealed moderate and similar host
selectivities for EB and p-Xy, respectively.
Selectivity of 1 and 2 when recrystallized from binary guest
mixtures with varying guest concentrations
In summary, both hosts 1 and 2 are immensely selective
for p-Xy when this guest competes with o- or m-Xy, and this
selectivity is present even when low concentrations of p-Xy
are present in the recrystallizing mixture. Furthermore, in
these conditions, 2 displays superior selectivity compared
with 1.
In order to determine whether the selectivities of hosts 1
and 2 are guest-concentration dependent, we subsequently
performed host recrystallizations from binary guest 1/guest
2 (G1/G2) mixtures with G1:G2 molar ratios approximating
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
(a) Host 1: m-Xy vs o-Xy
(b) Host 1: p-Xy vs o-Xy
1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Experimental Data
Experimental Data
0.1
0
Line of No Selectivity
Line of No Selectivity
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
X(m-Xy)
X(p-Xy)
(c) Host 1: EB vs o-Xy
(d) Host 1: p-Xy vs m-Xy
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Experimental Line
Experimental Data
Line of No Selectivity
Line of No Selectivity
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
X(p-Xy)
X(EB)
Fig. 1 Host selectivity profiles for the a m-Xy/o-Xy, b p-Xy/o-Xy, c EB/o-Xy, d p-Xy/m-Xy, e EB/m-Xy, f p-Xy/EB competition experiments
with host 1, and g p-Xy/o-Xy, h EB/o-Xy, i p-Xy/m-Xy, j EB/m-Xy, k p-Xy/EB competition experiments with host 2
deposited at the Cambridge Crystallographic Data Centre
(CCDC reference numbers 1: 1876416, 2: 1876417, 1·o-
Xy: 1876418, 1·m-Xy: 1876419, 1·p-Xy: 1876420, 1·EB:
1876421, 2·p-Xy: 1876422 and 2·EB: 1876423).
Single crystal X‑ray diffraction (SCXRD) analyses
of apohosts 1 and 2, and their complexes
with the xylenes and EB
Tables 3 (apohosts) and 4 (complexes) contain the rel-
evant crystallographic data for these crystalline materials.
Apohost 1 crystallized in the monoclinic crystal sys-
tem and C2/c space group, while this was different for 2
(triclinic, P − 1) (Table 3). The cyclohexyl moiety of 1
displayed some disorder, and this is illustrated in Fig. 2a,
which depicts the geometry of this molecule in the absence
of guest. Furthermore, and for comparative purposes, Fig. 2b
is also provided for 2. Striking geometry differences between
these two compounds are immediately apparent. As an
example, it is clearly evident that the fused tricyclic unit of
the xanthenyl host 1 is virtually planar, whilst 2 has the fused
system significantly buckled. Figure 3a, b are stereoviews
that further highlight these differences in three dimensions.
An analysis of the data provided in Table 4 indicates that all
complexes formed by both 1 and 2 crystallize in the triclinic
Apohosts 1 and 2, as well as the 1·o-Xy, 1·m-Xy, 1·p-Xy,
1·EB, 2·p-Xy and 2·EB complexes were subjected to SCXRD
analyses. These X-ray studies were performed at 200 K using
a Bruker Kappa Apex II diffractometer with graphite-mon-
ochromated Mo Kα radiation (λ=0.71073 Å). APEXII [23]
was used for data collection and SAINT [23] for cell refine-
ment and data reduction. The structures were solved using
SHELXT-2018/2 [24] and refined by least-squares proce-
dures using SHELXL-2018/3 [25] with SHELXLE [26] as
a graphical interface. All non-hydrogen atoms were refined
anisotropically, and the carbon-bound hydrogen atoms were
added in idealized geometrical positions in a riding model.
The nitrogen-bound H atoms were located on a difference
Fourier map and refined freely. Data were corrected for
absorption effects using the numerical method implemented
in SADABS [23]. These structures were subsequently
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
(f) Host 1: p-Xy vs EB
(e) Host 1: EB vs m-Xy
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Experimental Data
Experimental Data
Line of No Selectivity
Line of No Selectivity
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
X(p-Xy)
X(EB)
(g) Host 2: p-Xy vs o-Xy
(h) Host 2: EB vs o-Xy
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Experimental Data
Experimental Line
Line of No Selectivity
Line of No Selectivity
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
X(EB)
X(p-Xy)
Fig. 1 (continued)
crystal system and P−1 space group. Additionally, the crys-
tals of 1 with o-, m- and p-Xy experience isostructural host
packing while this is different only in 1·EB. The host packing
for both 2 p-Xy and 2 EB is also isostructural. Figure 4a–c are
views of the unit cells for 1·p-Xy (which is also representative
of both 1·o-Xy and 1·m-Xy), 1·EB and 2·p-Xy (representative
of 2·EB) along the c, a and b axes, respectively.
Fig. 5c, the two molecules have been overlaid and it is sur-
prising to note that the geometries of both the oxygen and
sulfur analogues are near identical. This possibly explains
why these two hosts displayed very similar selectivities in
the equimolar mixed solvent experiments.
The guests in the complexes of 1 all experience π–π
stacking interactions with the host, measuring between
approximately 4 and 5.9 Å, and are therefore all rela-
tively weak. Interactions of the CH–π type are also pre-
sent between 1 and o-Xy [(host)CH⋯π(guest) and (guest)
CH⋯π(host), 2.87 Å, 171° and 2.89 Å, 130°], m-Xy [(host)
CH⋯π(guest), 3.00 Å, 160°] and both disordered compo-
nents of EB [(host)CH⋯π(guest), 2.84 Å, 160° and (guest)
CH⋯π(host), 3.00 Å, 149° for the major component, and
(host)CH⋯π(guest), 2.88 Å, 176° for the minor compo-
nent]. This interaction type is absent in the complex with
p-Xy. Other short contacts, dominated by interactions
of the guest methyl hydrogens with aromatic carbons or
hydrogens, are also observable.
All of the guests in the crystals of both 1 and 2 display
disorder, with the exception of that in 2·p-Xy. In both 1·o-Xy
and 2·EB, the disorder is around an inversion point, while
the methyl moieties of the guest in 1·p-Xy exhibit rotational
disorder and, in 1·m-Xy, the guest is disordered around a
symmetry element.
Interestingly, while the geometry of the tricyclic fused
ring system of host 1 in all of its complexes remained virtu-
ally planar, as it was in the apohost material, the presence
of guest in the two complexes with 2 (2·p-Xy and 2·EB)
enforced a dramatic geometry change in the fused system
compared with apohost 2, that is, from buckled to planar.
Figure 5a, b were prepared from the 1·p-Xy and 2·p-Xy
crystal data, where this observation can be clearly seen. In
The interaction types experienced by the two guests
that are clathrated by 2 are comparable to those of 1,
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
(i) Host 2: p-Xy vs m-Xy
(j) Host 2: EB vs m-Xy
1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Experimental Data
Experimental Data
0.1
0
Line of No Selectivity
Line of No Selectivity
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8 1
X(EB)
X(p-Xy)
(k) Host 2: p-Xy vs EB
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Experimental Data
Line of No Selectivity
0
0.2
0.4
0.6
0.8 1
X(p-Xy)
Fig. 1 (continued)
differential scanning calorimetric (DSC), thermogravimetric
(TG) and its derivative (DTG) traces. The temperatures at
which the various thermal events occured are summarized
in Table 5.
including each of π–π stacking, CH⋯π types [2·p-Xy: (host)
CH⋯π(guest), 2.99 Å, 168°; 2·EB: (guest)CH⋯π(host),
2.72 Å, 171° and (host)CH⋯π(guest), 2.87 Å, 179°], and
various other short contacts.
The theoretical and expected mass losses after heating
each of the six complexes are in close agreement (Table 5).
Furthermore, when one considers the DSC traces in each of
the figures, it is clear that the guest release process occurs in
a clear and single step. The onset temperature for this release
event, Ton, estimated from the DTG trace, is a measure of
the relative thermal stabilities of the complexes. Gratify-
ingly, for host 1, this stability order correlates precisely with
what was observed in the competition experiments, and p-Xy
(88.0 °C)>EB (70.9 °C)>m-Xy (59.7 °C)>o-Xy (46.2 °C)
was noted. Additionally, p-Xy and EB guests were released
from crystals of host 2 from 115.5 to 76.6 °C, respectively,
and this is also in accordance with this host’s selectivity
order. These thermal data therefore explain the selectivity
orders of both hosts.
We also considered the nature of the guest accommoda-
tion in each complex by removing the guest from the pack-
ing calculation and determining the remaining voids using a
1.2 Å probe radius. Figure 6a–c clearly illustrate that all of
these guests experience similar constricted-channel occupa-
tion within the host crystals.
Hence, owing to similarities in both the nature of the
host–guest interactions and guest accommodation in each
of the complexes, possibly as a result of the non-polar nature
of each of the guests, we consequently analysed the inclu-
sion compounds by means of thermal analyses in order to
understand the selectivity orders displayed by hosts 1 and 2.
Thermal analyses of the complexes of hosts 1 and 2
After heating each of the complexes of hosts 1 and 2 at
10 °C min−1 from 40 to 300 °C, the thermograms provided
in Fig. 7a–f were obtained. Each of these is an overlay of the
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Table 3 Crystallographic data for apohosts 1 and 2
Host 1
in the presence of guests, although the fused system remains
planar in 1, a dramatic geometry change from buckled to
flat was noted for 2. Each of the six complexes crystallized
in the triclinic crystal system and P − 1 space group, and
all guests in complexes with both hosts 1 and 2 experience
similar host–guest interactions as well as guest accommoda-
tion types (constricted channel). Thermal analyses, however,
revealed the reasons for the selectivity order of host 1 since
this correlated exactly with the relative thermal stabilities
of the complexes as obtained from the onset temperatures
of the guest release processes (Ton) [p-Xy (88.0 °C)>EB
(70.9 °C)>m-Xy (59.7 °C)>o-Xy (46.2 °C)]. Finally, these
thermal experiments also explained the overwhelming pref-
erence of host 2 for p-Xy relative to EB, where observed Ton
values were 115.5 and 76.6 °C, respectively. This work has
shown that the potential to separate these guest types using
host–guest chemistry as an alternative separation methodol-
ogy is certainly a viable one.
Host 2
Chemical formula
Formula weight
Crystal system
C44H38N2O2
626.76
Monoclinic
C2/c
C44H38N2S2
658.88
Triclinic
P−1
Space group
µ (Mo-Kα)/mm−1
0.075
0.194
a/Å
b/Å
c/Å
α/°
16.3737(6)
8.8244(4)
23.3404(9)
90
7.3856(4)
8.7989(5)
13.3269(7)
99.867(2)
94.472(2)
97.751(2)
840.88(8)
1
β/°
93.025
90
3367.7(2)
4
γ/°
V/Å3
Z
D (calc)/g cm−3
1.236
1.301
348
200
F(000)
Temp./K
1328
200
Restraints
Nref
3
4200
0
4201
Experimental
Npar
243
221
R1
wR2
S
0.0466
0.1325
1.03
0.0359
0.0990
1.02
General methods
Melting points (uncorrected) were obtained using a Stu-
art SMP10 melting point apparatus. Infrared spectra were
recorded on a Bruker Tensor 27 Fourier Transform Infrared
Spectrometer, while 1H- and 13C-NMR spectra were obtained
by employing a 400 MHz Bruker Avance Ultrashield Plus
400 Spectrometer using CDCl3 as deuterated solvent. Thermal
experiments were carried out using a Perkin Elmer STA6000
Simultaneous Thermal Analyser and analysed using Perkin
Elmer Pyris 13 Data Analysis software. Samples were placed
in open ceramic pans and an empty ceramic pan was used
as reference. High purity nitrogen gas was the purge gas,
and samples were heated at 10 °C min−1 from 40 to 300 °C.
GC–MS experiments were carried out using an Agilent
7890A gas chromatograph fitted with an Agilent 5975C VL
mass spectrometer, equipped with a Cyclosil-B column. Com-
plexes were dissolved in dichloromethane for these analyses.
θ min–max/°
Tot. data
Unique data
Observed data [I>2.0 sigma (I)]
Rint
Dffrn measured fraction θ full
Min. resd. dens. (e/Å3)
Max. resd. dens. (e/Å3)
2.5, 28.3
36,295
4200
3210
0.020
0.999
− 0.23
0.27
2.4, 28.4
39,831
4201
3723
0.020
0.998
− 0.21
0.34
Conclusion
Novel host materials, trans-N,N′-bis(9-phenyl-9-xanthenyl)
cyclohexane-1,4-diamine 1 and trans-N,N′-bis(9-phenyl-
9-thioxanthenyl)cyclohexane-1,4-diamine 2, were facilely
synthesized from xanthone and thioxanthone in adequate
yield. Host 1 clathrated each of the components of the C8
aromatic fraction of crude oil, o-, m- and p-Xy, and EB, all
with 1:1 host:guest ratios. Host 2 proved more selective
towards these guests and only formed complexes with p-Xy
and EB (H:G 1:1). Equimolar guest/guest competition experi-
ments furnished very similar host selectivity orders of p-Xy
(73.9%)>EB (13.0%)>m-Xy (8.1%)>o-Xy (5.0%) and p-Xy
(71.3%)>EB (20.2%)>m-Xy (6.0%)>o-Xy (2.5%) for both
1 and 2, respectively. SCXRD analyses of each of the apo-
hosts revealed that the fused tricyclic ring system of the oxy-
gen derivative experiences a planar geometry, while that of
the sulfur analogue is significantly more buckled. However,
Syntheses of hosts 1 and 2
trans-N,N′-Bis(9-phenyl-9-xanthenyl)
cyclohexane-1,4-diamine 1 (X=O)
Host compound 1 was readily synthesized from xanthone 3
(Scheme 1): this ketone was subjected to a standard Grig-
nard addition reaction of phenylmagnesium bromide to
afford the alcohol 5, and this product treated with perchloric
acid in order to prepare the perchlorate salt 7, according to a
published procedure [27]. To a solution of trans-1,4-diami-
nocyclohexane (1.2374 g, 10.84 mmol) in dichloromethane
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Table 4 Crystallographic data for 1·o-Xy, 1·m-Xy, 1·p-Xy, 1·EB, 2·p-Xy and 2·EB
1·o-Xy
1·m-Xy
1·p-Xy
1·EB
2·p-Xy
2·EB
Chemical formula
C44H38N2O2⋅C8H10 C44H38N2O2⋅C8H10 C44H38N2O2⋅C8H10 C44H38N2O2⋅C8H10 C44H38N2S2⋅C8H10 C44H38N2S2⋅C8H10
Formula weight
Crystal system
732.92
Triclinic
P − 1
732.92
Triclinic
P − 1
732.92
Triclinic
P − 1
732.92
Triclinic
P − 1
765.04
Triclinic
P − 1
765.04
Triclinic
P − 1
Space group
µ (Mo-Kα)/mm−1
0.073
0.073
0.075
0.074
0.168
0.167
a/Å
b/Å
c/Å
α/°
8.7311(9)
9.0959(10)
13.9973(14)
89.115(5)
78.416(5)
66.517(5)
996.21(19)
1
8.8204(4)
9.0584(4)
13.9326(6)
88.492(2)
77.234(2)
67.166(2)
998.41(8)
1
8.7500(7)
8.9935(7)
13.7413(12)
89.636(4)
79.311(4)
67.507(4)
979.26(14)
1
8.9672(5)
14.0662(8)
16.1106(8)
101.958(2)
97.690(2)
90.581(2)
1968.62(19)
2
9.0090(4)
9.0426(5)
14.2327(8)
80.324(3)
71.666(2)
70.002(2)
1031.87(9)
1
8.9901(5)
9.0958(5)
14.1804(7)
80.469(2)
72.633(2)
70.146(2)
1038.25(10)
1
β/°
γ/°
V/Å3
Z
D (calc)/g cm−3
F(000)
Temp./K
Restraints
Nref
1.222
390
200
0
1.219
390
200
0
1.243
390
200
0
1.237
780
200
119
1.231
406
200
0
1.224
406
200
0
4729
4982
4874
9816
5098
5165
Npar
283
283
257
564
258
282
R1
wR2
S
0.0467
0.1334
1.03
0.0432
0.1169
1.04
0.0432
0.1084
1.03
0.0462
0.1207
1.01
0.0412
0.1088
1.03
0.0454
0.1206
1.03
θ min–max/°
Tot. data
Unique data
2.4, 28.0
23,927
4729
2.4, 28.4
31,537
4982
2.5, 28.4
24,993
4874
2.2, 28.4
47,519
9816
2.4, 28.3
38,689
5098
2.4, 28.4
54,387
5165
Observed data [I>2.0
3671
4116
3616
6758
4176
4563
sigma (I)]
Rint
0.028
0.994
0.017
0.999
0.029
0.998
0.026
0.999
0.020
1.000
0.020
0.999
Dffrn measured fraction
θ full
Min. resd. dens. (e/Å3)
Max. resd. dens. (e/Å3)
− 0.18
0.32
− 0.19
0.29
− 0.21
0.26
− 0.20
0.29
− 0.37
0.31
− 0.40
0.33
(30 mL) was added salt 7 (3.8763 g, 10.87 mmol) also in
dichloromethane (150 mL). The reaction was allowed to
stir at room temperature for 15 min before triethylamine
(2.5 mL, 1.8150 g, 17.94 mmol) was added to the reaction
mixture which brought about a colour change from yellow
to colourless. The solution was then allowed to stir for a
further 30 min at room temperature before being washed
with water and dried over anhydrous Na2SO4. The solvent
was removed under reduced pressure which afforded trans-
N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,4-diamine 1
(3.0301 g, 4.84 mmol, 45%) as an off-white solid with no
further purification required, mp 267–274 °C; vmax (solid)/
cm−1 3306 (NH), 3071 (ArCH), 2918 (alkyl CH), 2851
(alkyl CH) and 1602 (Ar C=C); δH(CDCl3)/ppm 0.66–0.76
(4H, m, CH2), 0.99–1.01 (4H, m, CH2), 1.65 (2H, s, NH),
2.11 (2H, s, CH) and 6.89–7.36 (26H, m, Ar); δC(CDCl3)/
ppm 34.23 (CH2), 51.6 (NHCH), 59.7 (CPh), 115.9 (ArC),
Fig. 2 Geometries of molecules of a apohost 1 and b apohost 2
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Fig. 3 Stereoviews highlighting the geometrical differences of molecules of a apohost 1 and b apohost 2
Fig. 4 Unit cells for a 1·p-Xy (also representing 1·o-Xy and 1·m-Xy), b 1·EB and c 2·p-Xy (also representing 2·EB)
122.8 (quaternary ArC), 126.3 (ArC), 126.5 (ArC), 127.3
(ArC), 127.8 (ArC), 128.0 (ArC), 130.0 (ArC), 150.6 (qua-
ternary ArC) and 150.8 (quaternary ArC) [Found: C, 84.03;
H, 6.04; N, 4.40. C44H38N2O2 requires C, 84.38; H, 6.12;
N, 4.47%].
8.08 mmol) also in dichloromethane (80 mL) and triethyl-
amine (1.5 mL, 1.089 g, 10.76 mmol), which effected a col-
our change from red–orange to faint yellow, trans-N,N′-bis(9-
phenyl-9-thioxanthenyl)cyclohexane-1,4-diamine (2.3631 g,
3.59 mmol, 45%) was obtained as an off-white solid, mp
246–252 °C; vmax (solid)/cm−1 3306 (NH), 3071 (ArCH),
2918 (alkyl CH), 2851 (alkyl CH) and 1602 (Ar C=C);
δH(CDCl3)/ppm 0.66–0.76 (4H, m, CH2), 1.04–1.05 (4H,
m, CH2), 1.66 (2H, s, NH), 2.14 (2H, s, CH) and 6.99–7.39
(26H, m, Ar); δC(CDCl3)/ppm 34.2 (CH2), 52.2 (NHCH),
66.3 (CPh), 125.2 (ArC), 125.5 (ArC), 126.6 (ArC), 126.7
(ArC), 127.6 (ArC), 128.7 (ArC), 130.9 (quaternary ArC),
131.0 (ArC), 139.0 (quaternary ArC) and 148.0 (quaternary
ArC) [this host was recrystallized from p-xylene which
trans-N,N′-Bis(9-phenyl-9-thioxanthenyl)
cyclohexane-1,4-diamine 2 (X=S)
In a similar fashion to 1, host 2 was synthesized from thi-
oxanthone 4 via the same sequence of reactions to afford
the alcohol 6 and then the perchlorate salt 8 [27]. As
before, and using trans-1,4-diaminocyclohexane (0.9191 g,
8.05 mmol) in dichloromethane (30 mL), salt 8 (3.0114 g,
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Fig. 5 The geometry of a host 1 and b host 2 in their complexes with p-Xy; c an overlay of a, b showing the very similar geometry of these hosts
in these complexes
Fig. 6 Calculated voids for a 1·p-Xy (also representing 1·o-Xy and 1·m-Xy), b 1·EB and c 2·p-Xy (also representing 2·EB)
afforded a 1:1 H:G complex with this solvent; found: C,
81.96; H, 6.62; N, 3.42; S, 8.27. C44H38N2S2·C8H10 (1:1)
requires C, 81.64; H, 6.32; N, 3.66; S, 8.38%].
Assessment of the host potential of 1 and 2
when recrystallized from each of the four organic
solvents
Hosts 1 and 2 were recrystallized from o-Xy, m-Xy, p-Xy
and EB by dissolving the host (0.08 g) in an excess of each
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Fig. 7 Overlaid DSC, TG and DTG traces for a 1·o-Xy, b 1·m-Xy, c 1·p-Xy, d 1·EB, e 2·p-Xy and f 2·EB
of the guest solvents (0.8 g) in glass vials. These vessels
were lidded and allowed time for crystallization to occur
(between 24 and 36 h). The crystals were collected by vac-
uum filtration, washed with petroleum ether (40–60 °C) and
dried in the vacuum filtration funnel for 1 to 2 min. Host
recovery in this way was typically 70%. 1H-NMR spectros-
copy was used to determine whether complexation had been
successful and, if so, the H:G ratios through the integration
of relevant host and guest resonance signals. These data are
summarized in Table 1.
Selectivity of 1 and 2 in the presence of equimolar
mixtures of the guests
Binary, ternary and quaternary combinations of the guests
were mixed together in equimolar proportions (the com-
bined guest mass was 0.8 g), and each of the hosts (0.08 g)
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
5. Huang, D., Wu, D.: Biodegradable dendrimers for drug delivery.
Mater. Sci. Eng. C 90, 713 (2018)
Table 5 Temperatures of the various thermal events experienced by
complexes with hosts 1 and 2
6. Iskierko, Z., Noworyta, K., Piyush, S.S.: Molecular recognition
by synthetic receptors: application in field-effect transistor based
chemosensing. Biosens. Bioelectron. 109, 50 (2018)
Complex
Ton (°C)
Tp (°C)
Theoretical
Observed
mass loss
(%)
mass loss (%)
7. Cai, H., Huang, Y., Li, D.: Biological metal–organic frameworks:
structures, host–guest chemistry and bio-applications. Coord.
Chem. Rev. https://doi.org/10.1016/j.ccr.2017.12.003
8. Manandhar, E., Wallace, K.J.: Host–guest chemistry of pyrene-
based molecular receptors. Inorg. Chim. Acta 381, 15 (2012)
9. Nassimbeni, L.R., Marivel, S., Su, H., Weber, E.: Inclusion of
picolines by a substituted binaphthyl diol host: selectivity and
structure. RSC. Adv. 3, 25758 (2013)
1·o-Xy
1·m-Xy
1·p-Xy
1·EB
2·p-Xy
2·EB
46.2
59.7
88.0
70.9
115.5
76.6
84.7
93.1
132.9
98.0
149.3
107.3
14.5
14.5
14.5
14.5
13.9
13.9
14.2
14.5
14.7
14.2
14.2
11.5
10. Seo, C.H., Kim, Y.H.: Separation of ethylbenzene and p-xylene
using extractive distillation with p-dinitrobenzene. Sep. Purif.
Technol. 209, 1 (2019)
Ton
is the onset temperature of guest release, estimated from the
DTG, and Tp the temperature at which the rate at which this release is
highest, also estimated from the DTG
11. Yang, H., Hu, Y.: Separation of para-xylene and meta-xylene by
extraction process using aqueous cyclodextrins solution. Chem.
Eng. Process. 116, 114 (2017)
12. Hong, S., Kim, D., Richter, H., Moon, J., Choi, J.: Quantitative
elucidation of the elusive role of defects in polycrystalline MFI
zeolite membranes on xylene separation performance. J. Membr.
Sci. 569, 91 (2019)
recrystallized from these mixtures. The crystallization ves-
sels were lidded, and the crystals that formed after 24 to
36 h were treated as in the single solvent experiments, but
analysed by GC–MS owing to guest/guest resonances over-
lapping in the 1H-NMR spectra. Guest peak areas on each
GC trace were compared in order to obtain the relative guest/
guest quantities, and these results are summarized in Table 2.
Overall H:G ratios were determined by means of 1H-NMR
spectroscopy.
13. Khabzina, Y., Laroche, C., Perez-Pellitero, J., Farrusseng, D.:
Xylene separation on a diverse library of exchanged faujasite
zeolites. Microporous Mesoporous Mater. 247, 52 (2017)
14. Hasan, M.M.F., First, E.L., Floudas, C.A.: Discovery of novel
zeolites and multi-zeolite processes for p-xylene separation using
simulated moving bed (SMB) chromatography. Chem. Eng. Sci.
159, 3 (2017)
15. Gao, B., Huang, M., Zhang, Z., Yang, Q., Bao, Z.: Hybridization
of metal–organic framework and monodisperse spherical silica
for chromatographic separation of xylene isomers. Chin. J. Chem.
Eng. https://doi.org/10.1016/j.cjche.2018.06.016
Selectivity of 1 and 2 when recrystallized
from binary guest mixtures with varying guest
concentrations
16. Belarbi, H., Boudjema, L., Shepherd, C., Ramsahye, N., Trens, P.:
Adsorption and separation of hydrocarbons by the metal organic
framework MIL-101(Cr). Colloids. Surf. A 520, 46 (2017)
17. Ma, Y., Zhang, F., Yang, S., Lively, R.P.: Evidence for entropic
diffusion selection of xylene isomers in carbon molecular sieve
membranes. J. Membr. Sci. 564, 404 (2018)
Here, each host (0.08 g) was dissolved in binary guest mix-
tures (combined guest mass 0.8 g) in which the molar guest
ratios were varied between 90:10 and 10:90. The vials were
treated as in the equimolar mixed guest experiments, and
both the crystals which formed (Z) and the mother liquor
from which these formed (X) were analysed, as before, by
means of GC–MS experiments to afford the selectivity pro-
files in Fig. 1a–k.
18. Kawahata, M., Hyodo, T., Tominaga, M., Yamaguchi, K.: Separa-
tion of p-xylene from aromatic compounds through specific inclu-
sion by acyclic host molecule. CrystEngComm. 20, 5667 (2018)
19. Barton, B., Caira, M.R., de Jager, L., Hosten, E.C.: N,N′-Bis(9-
phenyl-9-thioxanthenyl)ethylenediamine: highly selective host
behavior in the presence of xylene and ethylbenzene guest mix-
tures. Cryst. Growth Des. 17, 6660 (2017)
20. Barton, B., de Jager, L., Hosten, E.C.: An investigation of the
complexation of host N,N′-bis(9-phenyl-9-thioxanthenyl)ethylen-
ediamine with dihaloalkanes guests. J. Incl. Phenom. Macrocycl.
Chem. 89, 105 (2017)
Acknowledgements Financial support is acknowledged from the Nel-
son Mandela University and the National Research Foundation (NRF).
21. Barton, B., Jager, L., Hosten, E.C.: A comparison of the behaviour
of two closely related xanthenyl-derived host compounds in the
presence of vaporous dihaloalkanes. J. Incl. Phenom. Macrocycl.
Chem. 92, 181 (2018)
References
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bis(9-phenyl-9-thioxanthenyl)ethylenediamine for pyridine and
the methylpyridine guests—a competition study. Supramol. Chem.
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