Tuning the inclusion properties and solid-state reactivity of second sphere adducts using conformationally flexible bidentate ligands

Article abstract of DOI:10.1021/acs.cgd.5b00272

Second-sphere coordination refers to any intermolecular interaction with the ligands directly bound to the primary coordination sphere of a metal ion. In this article, we have successfully applied the second-sphere coordination approach in the construction of versatile host frameworks that can accommodate various guest molecules. We have used a family of bidentate flexible molecules as second-sphere ligands, and the tetrachlorometalate anion [MCl₄]^2- (where M = Cu, Co, Cd, Zn, and Hg) as the primary coordination sphere to synthesize new second sphere adducts. By introducing an alkyl spacer -(CH₂)_n- (n = 1, 2, 3, 4) to bibenzylamine (L⁰), the ligands L¹, L², L³, and L⁴ with higher degree of flexibility were synthesized. Different guest molecules such as alcohol, acetic acid, acrylic ester, or acetonitrile can be included in the host framework self-assembling diprotonated L¹-L⁴ and [MCl₄]^2-, leading to a novel type of supramolecular assemblies: CH₃CH₂OH[L²]2H⁺·[CuCl₄]^2- (2), CH₃OH[L³]2H⁺·[MCl₄]^2- (3), CH₃COOH[L³]2H⁺·[CuCl₄]^2- (4), CH₂CHCOOCH₃'[L³]2H⁺·[MCl₄]^2- (5-7), CH₃CN·H₂O'[L⁴]2H⁺·[MCl₄]^2- (8-9), and CH₃OH'[L⁴]2H⁺·[MCl₄]^2- (10). L² forms the quasi-chelating charge-assisted N-H···Cl hydrogen bonds with [MCl₄]^2- that can transform in the solid-state to a chelated coordination complex following a mechanochemical dehydrochlorination reaction. By increasing the number of methylene groups, ligands L³ and L⁴ exhibit considerable conformational diversity due to the higher flexibility induced by the backbone chains. The -(CH₂)_n- spacer lengths of the ligands influences the structural dimensionality, and its solid-state mechanochemical reactivity preventing the transformation from salt [L^3-4]2H⁺·[MCl₄]^2- to the chelating coordination complex [(MCl₂)(L^3-4)]. Moreover, the thermal stability of the second sphere adducts has been monitored by thermogravimetric analyses and X-ray powder diffraction (PXRD). We demonstrate that some of the second sphere adducts are dynamic, showing reversible guest release/uptake involving crystalline-to-amorphous-to-crystalline phase transformations. QuantumMechanical (QM) demonstrate that ligands with backbone lengths longer than -(CH₂)₂- are reticent to react via dehydrochlorination reaction because of the backbone chain length, the symmetry and orientation of the frontier molecular orbitals (FMOs), while for the -(CH₂)₂-, the length and orientation of the FMOs is optimal for the reaction to occur.

Full text of DOI:10.1021/acs.cgd.5b00272

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)
Article
Tuning the Inclusion Properties and Solid-State Reactivity of Second
Sphere Adducts Using Conformationally Flexible Bidentate Ligands
Fang Guo, Xu Wang, Hong-yu Guan, Hai-Bin Yu, Lei Li, Shan-
Shan Chen, Antonino Famulari, and Javier Marti-Rujas
Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 11 May 2015
Downloaded from http://pubs.acs.org on May 11, 2015
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Crystal Growth & Design is published by the American Chemical Society. 1155
Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Tuning the Inclusion Properties and SolidꢀState
Reactivity of Second Sphere Adducts Using
Conformationally Flexible Bidentate Ligands
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fang Guoa*, Xu Wanga, Hongꢀyu Guana, Haiꢀbin Yua, Lei Lia, Shanꢀshan Chena, Antonino
Famulari,b and Javier MartíꢀRujasc*
a College of Chemistry, Liaoning University, Shenyang 110036, China.
b Dipartimento di Chimica Materiali e Ingegneria Chimica. ‘‘Giulio Natta’’, Politecnico di
Milano, Via L. Mancinelli 7, 20131 Milan, Italy.
c Center for Nano Science and Technology@Polimi, Istituto Italiano di Tecnologia, Via
Pascoli 70/3, 20133 Milano, Italy.
Corresponding Authors
*Fang Guo; Eꢀmail: fguo@lnu.edu.cn
*Javier MartíꢀRujas; Eꢀmail: javier.rujas@iit.it
1
ACS Paragon Plus Environment

Crystal Growth & Design
Page 2 of 42
1
2
3
4
Abstract
5
6
7
8
9
Secondꢀsphere coordination refers to any intermolecular interaction with the ligands directly
bound to the primary coordination sphere of a metal ion. In this article, we have
successfully applied the secondꢀsphere coordination approach in the construction of versatile
host frameworks that can accommodate various guest molecules. We have used a family of
bidentate flexible molecules as secondꢀsphere ligands, and the tetrachlorometalate anion
[MCl4]2ꢀ (where M = Cu, Co, Cd, Zn and Hg) as the primary coordination sphere to
synthesize new second sphere adducts. By introducing an alkyl spacer –(CH2)n– (n = 1, 2, 3,
4) to bibenzylamine (L0), the ligands L1, L2, L3 and L4, with higher degree of flexibility were
synthesized. Different guest molecules such as alcohol, acetic acid, acrylic ester or
acetonitrile can be included in the host framework selfꢀassembling diprotonated L1–L4 and
[MCl4]2–, leading to a novel type of supramolecular assemblies: CH3CH2OH ⊂
[L2]2H+·[CuCl4]2– (2), CH3OH⊂[L3]2H+·[MCl4]2– (3), CH3COOH ⊂[L3]2H+·[CuCl4]2– (4),
CH2CHCOOCH3⊂[L3]2H+·[MCl4]2– (5ꢀ7), CH3CN·H2O ⊂[L4]2H+·[MCl4]2– (8ꢀ9), and
CH3OH ⊂[L4]2H+·[MCl4]2– (10). L2 forms the quasiꢀchelating chargeꢀassisted N–H···Cl
hydrogen bonds with [MCl4]2– that can transform in the solidꢀstate to a chelated coordination
complex following a mechanochemical dehydrochlorination reaction. By increasing the
number of methylene groups, ligands L3 and L4 exhibit considerable conformational diversity
due to the higher flexibility induced by the backbone chains. The –(CH2)n– spacer lengths
of the ligands influences the structural dimensionality and its solidꢀstate mechanochemical
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment

Page 3 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
reactivity preventing the transformation from salt [L3ꢀ4]2H+•[MCl4]2– to chelating
coordination complex [(MCl2)(L3–4)]. Moreover, the thermal stability of the second sphere
adducts has been monitored by thermogravimetric analyses and Xꢀray powder diffraction
(PXRD). We demonstrate that some of the second sphere adducts are dynamic showing
reversible guest release/uptake involving crystallineꢀtoꢀamorphousꢀtoꢀcrystalline phase
transformations. Quantum\Mechanical (QM) demonstrate that ligands with backbone
lengths longer than –(CH2)2– are reticent to react via dehydrochlorination reaction because of
the backbone chain length, the symmetry and orientation of the frontier molecular orbitals
(FMOs), while for the –(CH2)2– the length and orientation of the FMOs is optimal for the
reaction to occur.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Keywords
Second Sphere Coordination, HostꢀGuest Superstructures, Conformational Flexible Ligands,
Hydrogen Bonding, SelfꢀAssembly, QuantumꢀMechanical Calculations, DFT Frontier
Molecular Orbitals.
Introduction
Chemical reactions carried out in the solid state induced by external stimuli are important to
gain insights on how chemical reactions occur.1,2,3,4,5,6,7,8,9,10 An important aspect is on the
ability to bring the reacting molecules into an optimal orientation and distance allowing the
3
ACS Paragon Plus Environment

Crystal Growth & Design
Page 4 of 42
1
2
3
4
5
6
7
8
9
reaction partners to interact and react. Molecular recognition is crucial to bring the reactants
together, but such control is often difficult in the solidꢀstate. Crystal engineering is one of
the most important routes to achieve molecular recognition by proper combination of
functional groups present in molecules or ions.11,12 One way to achieve selectivity and
effective binding of ions can be obtained by using the concept of second sphere
coordination.13
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Second sphere coordination was described by Alfred Werner over a century ago by
describing how the first coordination sphere of a transition metal complex can interact with
neutral or charged species to give a second sphere coordination. In the early 80’s studies
aimed to get insights into the nature of second sphere coordination were carried out,14,15,16,17
and more recently has been exploited to study metalꢀbased anion receptors.18,19,20 The first
sphere ligands can form secondꢀsphere adducts with the whole range of noncovalent bonding
interactions, such as electrostatic, hydrogen bonding, halogen bonding, charge transfer and
van der Waals interactions. The contribution of second sphere coordination has been
important in supramolecular chemistry,21 including biological recognition.22
Solidꢀstate chemistry knowledge of hybrid metal organic compounds (i.e., selfꢀassembled via
electrostatic interactions) is very important in order to design new functional materials.
However, the solid state chemistry of second sphere coordination has not been studied very
much. Only recently, second sphere coordination has demonstrated that is a suitable
approach to synthesize functional materials for gas adsorption,23 separation of metal
4
ACS Paragon Plus Environment

Page 5 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
ions24,25,26,27 for the extraction of auric anions using α–cyclodextrin,28 to study solidꢀstate
mechanochemical dehydrochlorination reactions,29 crystallineꢀtoꢀpolycrystalline reactions,30
and to form permanent porous networks showing singleꢀcrystalꢀtoꢀsingleꢀcrystal guest
exchange and ionic conductivity.31 Halogen bonds have been used in secondꢀsphere
coordination complexes to form 6,3ꢀnetworks.32
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Using large and flexible molecules having bulky groups can be a good crystal engineering
strategy to synthesize new hostꢀguest systems,33 because such molecules would not organize
efficiently and therefore alternative crystal packing modes (using molecule’s flexibility)
might be achieved by inclusion of guests with good size and shape complementarity.34
Our recent research has focused on the construction of new type of supramolecular
inclusion system that cooperatively utilizes secondary sphere coordination interactions, in
which a series of Nꢀbidentate flexible ligands have been designed as secondꢀsphere ligands
and selfꢀassembled with tetrahedral anions like [MCl4]2– (M = Cu, Co, Mn and Zn) as the
primary coordination sphere.35 Herein, we have used bibenzylamine (L0) as an organic
moiety, to which we introduced –(CH2)n– (n = 1, 2, 3, 4) alkyl chains on the bibenzylamine
ligand to synthesize a series of ligands L1–L4 differing only in the backbone chain separating
the two aromatic moieties (Scheme 1).
5
ACS Paragon Plus Environment

Crystal Growth & Design
Page 6 of 42
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Ligands used in this work (a); and cartoon showing the metals used as first
coordination sphere which are selfꢀassembled with ligands L1ꢀ4 via second coordination
sphere interactions (b).
The two N atoms in the flexible backbone can be protonated. They can act as hydrogen
bonding donors (outer sphere), playing a key role in the anion recognition of the primary
coordination sphere of tetrachlorometallates such as [MCl4]2–, but also might act as an
anchoring point for guests molecules. Moreover, the bulky phenyl rings may also act as
molecular recognition site and contribute to the formation of voids to accommodate
small/medium guests such as methanol, ethanol, acetic acid, acrylic ester or acetonitrile. In
6
ACS Paragon Plus Environment

Page 7 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
some complexes, the host structure upon heating, is robust enough to allow guest
release/uptake whilst maintaining their crystallinity or via an amorphous phase. Up to now,
studies of inclusion complexes involving thermal stability, solidꢀstate mechanochemical
dehydrochlorination reactivity, and their guest behavior selfꢀassembled via secondꢀsphere
coordination using bidentate ligands with different backbone lengths (i.e., the effect of
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
–(CH2)n– spacers) are uncommon.
Additionally, we provide Quantum Mechanical
calculations (QM) including methods for solid phases, which have been carried out to gain
information about the electronic density distribution of frontier molecular orbitals (FMOs) in
ligands L2ꢀL4 in order to better understand their solidꢀstate reactivity. The QM results
indicate that the orientation and symmetry of the HOMOs (which resulted concentrated
mainly at the N atoms) need to be considered as well as the backbone N–(CH2)n–N distance
in order to achieve dehydrochlorination reactions followed by chelation upon
mechanochemical grinding.
Experimental section
Materials and Methods. All chemicals were obtained from commercial sources and used
without further purification. IR spectra were obtained with a Perkin Elmer 100 FTꢀIR
1
spectrometer using KBr pellets. H NMR spectra were recorded on a MercuryꢀPlus 300
spectrometer (VARIAN, 300 MHz) at 25 ºC with TMS as the internal reference. Powder
7
ACS Paragon Plus Environment

Crystal Growth & Design
Page 8 of 42
1
2
3
4
Xꢀray diffraction were recorded using a D8 Bruker and D2 PHASER diffractometer (λ =
5
6
7
1.54056 Å).
8
9
Synthesis of ligands L1–L4
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Synthesis of L1: For the synthesis of L1, 8g (0.04 mol) of bibenzylamine were added into 40
mL ethanol, and slowly stirred at 40 ºC. Subsequently 1.62 g ((0.02 mol) 37 % purity)
formaldehyde was then continuously (2–3 drops) added into the mixture solution. The
reaction was stirred for 2 h, and the mixture was cooled to room temperature. The white
product was separated from ethanol, and then washed with distilled water. Recrystallization
using anhydrous ethanol dryied under vaccum conditions produced a white crystalline solid
1
6.8982 g, yield 84.95 %, m.p. 101–103ºC. H NMR (CDCl3, 300 MHz)
δ: 3.09 (2H, s, CH2);
3.61 (8H, s, CH2); 7.22ꢀ7.33 (20H, m, ArH).
Synthesis of L2: The synthesis of L2 was carried out by slowly adding 7 mL ethylene
diamine into a solution of 8 g NaOH and 20 mL distilled water. Then 30 mL of benzyl
chloride (2–3 drops) were continuously added into the mixture solution. The reaction was
heated to 95°C and stirred for 4 h, and then the mixture was cooled to room temperature. The
white product was separated from diethyl ether, and then washed with distilled water.
Recrystallisation using anhydrous ethanol dried under vaccum conditions resulted in white
crystals 12.43 g, yield 60.0%, m.p. 92ꢀ95ºC. 1H NMR (CDCl3, 300 MHz)δ: 2.60 (4H, s, CH2),
3.50 (8H, s, CH2), 7.23–7.28 (20H, m, Ar–H).
8
ACS Paragon Plus Environment

Page 9 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Synthesis of L3: Ligand L3 was prepared by adding 4.2 mL 1, 3ꢀpropanediamine into a
solution of 8g NaOH and 18 mL anhydrous ethanol. Then, 27.5 mL benzyl chloride (2–3
drops/s) were continuously added into the solution. The reaction was heated to 80°C and
stirred for 4 h, then cooled to room temperature. The white product was separated from
ethanol, and then washed with distilled water for several times. Recrystallization using
anhydrous ethanol dryied in vaccum conditions produced white needle crystals 14.06 g, yield
64.6 %, m.p. 50ꢀ51 ºC. 1HNMR (CDCl3, 300MHz) δ: 1.71 (2H, s, CH2), 2.38ꢀ2.42(4H, t,
CH2), 3.48 (8H, s, CH2), 7.21ꢀ7.28 (20H, m, ArꢀH).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Synthesis of L4: The synthesis of L4 was performed by adding 2 mL of 1,4ꢀbutanediamine
into a solution of 7 g NaHCO3 and 20 mL of distilled water. Then, 10 mL benzyl chloride
(2–3 drops) were continuously added into the solution. The reaction was heated to 95°C
and stirred for 8 h and cooled to room temperature. The white reaction product was
separated from the mixture solution, washed with ethanol and distilled water several times.
Drying in vacuum produced white needle crystals 4.87 g, yield 54.4 %, m.p. 138–140 ºC.
1HNMR (DMSO, 300MHz) δ: 1.39 (4H, s, CH2), 2.25 (4H, s, CH2), 3.45 (8H, s, CH2),
7.20ꢀ7.30 (20H, m, ArꢀH).
Synthesis of [L0]2H+·[CuCl4]2ꢀ (1)
0.050 g (0.00012 mol) L0 and 5 mL ethanol were placed in a 50 mL Erlenmeyer flask, then
0.5 mL concentrated hydrochloric acid and 0.050 g (0.00029 mol) CuCl2·2H2O were slowly
9
ACS Paragon Plus Environment

Crystal Growth & Design
Page 10 of 42
1
2
3
4
added and shaken until the contents were dissolved. The flask was allowed to stand for one
5
6
7
week at room temperature, giving rise to blue block crystal 1. M.p. 193ꢀ195°C.
8
9
Synthesis of CH3CH2OH ⊂ [L2]2H+·[CuCl4]2ꢀ (2)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
0.35 g (0.00083 mol) of L2 and 10 mL ethanol were placed in a 50 mL Erlenmeyer flask,
then 1 mL concentrated hydrochloric acid and 1 mL of prepared K2[CuCl4] were added
slowly and shaken until the contents were dissolved. The flask was left to stand for about
8ꢀ10 days at room temperature, giving rise to orange crystal 2. M.p. 173ꢀ178°C.
Synthesis of CH3OH⊂ [L3]2H+·[CuCl4]2ꢀ (3)
0.10 g (0.00023 mol) of L3 and 20 mL methanol were introduced into a 50 mL Erlenmeyer
flask, then 0.19 g of CuCl2·2H2O (0.0011 mol) and 1 mL concentrated hydrochloric acid
were slowly added and shaken until the contents were dissolved. The flask was left for
month at room temperature, giving rise to red block crystals 3. M.p. 174ꢀ185 °C.
Synthesis of CH3COOH ⊂ [L3]2H+·[CuCl4]2ꢀ (4)
0.10 g (0.00023 mol) of L3 and 10 mL acetic acid were placed into a 50 mL Erlenmeyer
flask, then 0.10 g of CuCl2·2H2O (0.00059 mol) and 2 mL concentrated hydrochloric acid
were slowly added and shaken until the contents were dissolved. The flask was allowed to
stand for 5 days at room temperature, giving rise to orangeꢀred crystals 4. M.p.151ꢀ159°C.
Synthesis of CH2CHCOOCH3 ⊂ [L3]2H+·[MCl4]2ꢀ (5ꢀ7) (M = Zn, Co, Hg)
0.10g (0.00023 mol) of L3 and 10 mL acrylic ester were placed into a 50 mL Erlenmeyer
flask, then 0.10 g ZnCl2 (0.00073 mol) and 2 mL of concentrated hydrochloric acid were
10
ACS Paragon Plus Environment

Page 11 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
slowly added and shaken until the contents were dissolved. The flask was left for about one
week at room temperature, giving rise to transparent block crystals 5. M. p. 244–255°C. The
same experiments were carried out using CoCl2·6H2O/HgCl2·2H2O yielding crystals 6 (m.p.
240ꢀ244°C) and 7 (m.p. 163–173°C).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Synthesis of CH3CN·H2O ⊂ [L4]2H+·[MCl4]2ꢀ (8ꢀ9) (M = Hg, Co)
0.10 g (0.00022 mol) of L4 and 4 ml dichloromethane and 20 ml acetonitrile were
placed into a 50 ml Erlenmeyer flask, and then 0.10 g HgCl2 (0.00037 mol) and 1 ml
concentrated hydrochloric acid were slowly added and shaken until the contents were
dissolved. The flask was allowed to stand overnight at room temperature, giving rise to
transparent block crystals 8. M.p. 106ꢀ115 °C. The same experiments were carried out
using CoCl2·6H2O to produce blue block crystals 9. M.p. 98ꢀ106°C.
Synthesis of CH3OH ⊂ [L4]2H+·[CdCl4]2ꢀ (10)
0.10 g (0.00022 mol) of L4 and 4 ml dichloromethane and 20 ml methanol were placed into a
50 mL Erlenmeyer flask, then 0.10 g CdCl2·2.5H2O (0.00044 mol) and 1 mL concentrated
hydrochloric acid were slowly added and shaken until the contents were dissolved. The
flask was allowed to stand overnight at room temperature, giving rise to transparent crystals
10. M.p.102ꢀ107 °C.
Crystallography
Single crystal data collection were performed on a Bruker P4 diffractometer with Mo Kα
radiation (λ = 0.71073 Å) and Bruker X8 Prospector APEXꢀII/CCD diffractometer equipped
11
ACS Paragon Plus Environment

Crystal Growth & Design
Page 12 of 42
1
2
3
4
with a microfocusing mirror (CuꢀKα radiation,
λ
= 1.54056 Å). The structures were
5
6
7
8
9
determined using direct methods and refined (based on F2 using all independent data) by
fullꢀmatrix leastꢀsquare methods (SHELXTL 97). Data were reduced by using the Bruker
SAINT software. All nonꢀhydrogen atoms were directly located from different Fourier maps
and refined with anisotropic displacement parameters. Guest molecules were well resolved
but disordered, with the thermal displacement parameters of some atoms being relatively
large, partly owing to the loose packing in the void and partly because the atomic positions
represent an average between the included guest molecules. The details of data collection,
data reduction and crystallographic data are summarized in ESI Tables S1 and S2.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Mecanochemistry
Liquidꢀassisted grinding (LAG) of 32 mg (0.047 mmol) of crystals 3 and 10.5 mg (0.094
mmol) of KOH in a 1:2 molar ratio, with the addition of 30 ꢁL of EtOH was performed.
Upon grinding, a color change from orange to brown was observed within 5 min. Then the
powder after grinding was recrystallized in anhydrous methanol.
Liquidꢀassisted grinding (LAG) of 29 mg (0.041 mmol) of crystals 10 and 4.6 mg (0.082
mmol) of KOH in a 1:2 molar ratio, with the addition of 30 ꢁL of anhydrous methanol was
carried out. Upon grinding, a color change from colorless to white was observed within 10
min. Then the powder after grinding was recrystallized in anhydrous methanol.
Results and Discussion
Structure description of complexes using L0 and L2: second sphere adducts 1 and 2.
In the absence of alkyl chain on the bibenzylamine ligand (L0), the bibenzylamine can
directly react with [CuCl4]2– anion to produce the secondꢀsphere coordination complex
12
ACS Paragon Plus Environment

Page 13 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
[L0]2H+·[CuCl4]2–(1). Crystal structure analysis reveals that the asymmetric unit in 1
comprises half [CuCl4]2– anion and one diprotonated L0 ligand. The [CuCl4]2– anion adopts
planar geometry, with the Cu–Cl bond lengths being 2.245 (1) Å and 2.279 (1) Å respectively.
Each [CuCl4]2– anion is surrounded by four protonated L0 through N–H···Cl interactions (i, ii)
and expanded into a linear hydrogen bonding chain along the crystallographic aꢀaxis (Fig. 1).
The second sphere adduct 1 does not include guest molecules.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1 Crystal structure of 1 showing the secondꢀsphere coordination formed by L0 and
[CuCl4]2ꢀanions. NꢀHꢁꢁꢁCl interactions (i, ii) showed as dashed lines.
Using L1 (one –CH2– spacer), no second sphere adduct was obtained. In fact, the reaction
between L1 and [MCl4]2– showed that the ligand L1 is unstable and decomposes into L0 and
subsequently forms complexes with [MCl4]2–.
However, when the N–CH2–N backbone was expanded by introducing an extra CH2
group to form the –(CH2)2– backbone, the ligand L2 was obtained. Xꢀray crystallography
reveals that L2 crystallized in the Pꢀ1 space group with half molecule in the asymmetric
unit.36 The intramolecular NꢁꢁꢁN distance is 3.766 Å. The diffusion of CuCl2·2H2O in
EtOH into a HCl/EtOH solution of L2 resulted in the second sphere adduct 2, in which the
host framework [L2]2H+·[CuCl4]2– includes EtOH guest molecules. Single crystal XRD
13
ACS Paragon Plus Environment

Crystal Growth & Design
Page 14 of 42
1
2
3
4
5
6
7
8
9
shows that there are two [CuCl4]2– dianions, two doubly protonated L2 and one EtOH
molecules in each asymmetric unit. The two protons in L2 are linked with the same
[CuCl4]2– anion through two charge assisted N–HꢁꢁꢁCl hydrogen bonds (i, ii), giving rise to a
quasiꢀchelating37 building block 1 (Fig 2a). The geometry of the [CuCl4]2– anion forms
highly distorted tetrahedral coordination environment with Cl atoms. The neighbouring
quasiꢀchelating building blocks further form a hydrogen bonded chain along the
crystallographic bꢀaxis through C–HꢁꢁꢁCl interactions (iii–v, Fig. 2a) and then expanded into a
cageꢀlike along cꢀaxis accommodating disordered ethanol (i.e., over two positions) guest
molecules (Fig. 2b).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Crystal structure of 2 showing the quasiꢀchelating hydrogen bonded chain along
the bꢀaxis via C–HꢁꢁꢁCl interactions (a). View along the cꢀaxis of the included ethanol
molecules (spacefilling) disordered over two positions (b).
Structure description of complexes using L3: second sphere adducts 3ꢀ7.
14
ACS Paragon Plus Environment

Page 15 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Structure description of CH3OH⊂ [L3]2H+·[MCl4]2ꢀ (3). The insertion of an extra
methylene in L2 formed a new ligand (L3). From single crystal Xꢀray diffraction data we
observed that the intramolecular NꢁꢁꢁN distance increased from 3.766 Å in L2 to 5.113 Å in
L3.37 The diffusion of a methanolic solution of CuCl2·2H2O into the HCl/MeOH solution of
L3, gave good quality single crystals of the second sphere adduct
CH3OH⊂[L3]2H+·[CuCl4]2ꢀ(3). Xꢀray crystallographic analysis reveals that 3 is monoclinic
(P21/c) with one dianion [CuCl4]2–, one doubly protonated L3 and one methanol molecule in
the asymmetric unit. One doubleꢀprotonated ligand L3 is linked with two different [CuCl4]2–
anions through N–HꢁꢁꢁCl interactions (i, ii), forming the nonꢀchelating dicationꢀdianion
building block which propagates along the bꢀaxis (Fig. 3a). Methanol molecules are trapped
in the concave region of the helical chain through the O–HꢁꢁꢁCl interaction (3.165(4) Å)
involving the hydroxyl groups and chloride atoms of [CuCl4]2– anions. The helical chains are
linked further by weak C–HꢁꢁꢁCl hydrogen bonds (iiiꢀv) along the cꢀaxis, constructing a 3D
structure (Fig. 3b).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
15
ACS Paragon Plus Environment

Crystal Growth & Design
Page 16 of 42
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. View along the bꢀaxis of the hydrogen bonding interactions (dashed lines) between
dianions, dications and solvent in 3 (a). View of the crystal packing of 3 accommodating
methanol guest molecules (b).
We note that 3 is not isostructural to other two second sphere adducts crystallized using L3
[HgCl4]2– and [ZnCl4]2– which also include methanol as a guest.37 This demonstrates the
structural diversity of this type of second sphere complexes (Fig. 4a,b,c).
16
ACS Paragon Plus Environment

Page 17 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. Different building blocks in crystals formed by L3 and metal chlorides in MeOH
solvent: (a) crystal 3; (b) different building blocks previously reported in second sphere
adducts (b) and (c).
Structure description of CH3COOH ⊂[L3]2H+·[CuCl4]2ꢀ (4). It is known that weak
interactions are crucial in the molecular selfꢀassembling outcome. The effect of the solvent
molecules can direct the crystallization affecting the stoichiometric ratio between the
selfꢀassembling building blocks (i.e., cations, anions and solvent molecules in this case).
The following example is a proof on how by replacing methanol for acetic acid in the
crystallization of L3 and [CuCl4]2– results in a completely different second sphere adduct.
This adduct was synthesized diffusing CuCl2⋅2H2O in acetic acid into a HCl/MeOH solution
containing ligand L3 to yield the salt CH3COOH ⊂[L3]2H+·[CuCl4]2– (4). The metal organic
hybrid complex 4 crystallizes in the monoclinic system in the P21/c space group, with two
independent doublyꢀprotonated L3 ligands, two [CuCl4]2– dianions and one acetic acid in the
asymmetric unit.
The two independent L3 ligands (labeled L3a, L3b) in the asymmetric unit interact with two
independent [CuCl4]2– dianions ([CuCl4]2– , CuCl4]2–b) through N–H···Cl interactions,
a
constructing two individual building blocks (Fig. 5a). In one of the building blocks, one
ligand L3a is connected with two independent [CuCl4]2– anions ([CuCl4]2– , CuCl4]2– )
a
b
17
ACS Paragon Plus Environment

Crystal Growth & Design
Page 18 of 42
1
2
3
4
5
6
through N–H···Cl interactions (i and ii); whereas in the other building block, the other ligand
L3b and the [CuCl4]2– anion via four N–H···Cl interactions (iii and iv) as shown in Fig. 5a.
a
7
8
9
The building blocks are alternately arranged along the cꢀaxis through C–H···Cl weak
interactions (v ꢀ ix) to build a 3D structure (Fig. 5b), with acetic acid guest molecules filling
the concave region through O–HꢁꢁꢁCl interactions (3.148 Å).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. Crystal structure of 4 showing the two different building blocks involving L3a and
L3b (a). Crystal packing in 4 showing the inclusion of acetic acid as guest molecule
(spacefilling).
Structure description of CH2CHCOOCH3 ⊂ [L3]2H+·[MCl4]2ꢀ (5ꢀ7). In order to test
the guest inclusion ability of the second sphere adducts selfꢀassembled using L3 we used
larger guest molecules such as acrylic ester. When acrylic ester was added into a mixture of
18
ACS Paragon Plus Environment

Page 19 of 42
Crystal Growth & Design
1
2
3
4
a
solution of HgCl2·2H2O/ZnCl2·2H2O/CoCl2·2H2O and L3 in HCl/EtOH, the
CH2CHCOOCH3 ⊂ [L3]2H+·[MCl4]2ꢀ (M = Zn, (5); M = Co, (6), M = Hg, (7) inclusion
complexes were formed. Since 5ꢀ7 are isostructural, the description of one (Zn) of the
structures will suffice for all. The crystal structure of 5 crystallizes in the monoclinic P21/n
space group, with one doublyꢀprotonated L3, one [ZnCl4]2ꢀ dianion and half acrylic ester in
each asymmetric unit. Each two L3 ligands and two [ZnCl4]2ꢀ dianions form a closed
hydrogen bonded network through four N–H···Cl hydrogen bonds (i, ii), forming the building
block (Fig. 6a). The neighboring building blocks are arranged nearly perpendicular giving a
linear hydrogen bonded chain through weak C–H···Cl interactions (iiiꢀvi) (Fig. S2 and 6b)
and further expanded into a 3D structure, in which the acrylic ester adopts planar
conformation and is accommodated inside the host framework formed by L3 and [MCl4]2ꢀ
dianions through C–H···O interaction (3.070(3) Å). For the isostructural [HgCl4]2– and
[CoCl4]2–ꢀ second sphere adducts see ESI.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
19
ACS Paragon Plus Environment

Crystal Growth & Design
Page 20 of 42
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 6. Single crystal structure of second sphere adduct 5. View of the building block
involving dianion and dications (a). Crystal packing showing the inclusion acrylic ester
guest molecules (spacefilling) (b).
Structure description of complexes using L4: second sphere adducts 8ꢀ10.
20
ACS Paragon Plus Environment

Page 21 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Structure description of CH3CN·H2O ⊂[L4]2H+·[MCl4]2ꢀ (8ꢀ9). To explore the guest
behavior of this family of flexible molecules, we synthesized a new bidentate ligand L4 with
longer –(CH2)4– backbone chain, and therefore higher conformational flexibility. The Xꢀray
crystal structure shows that in the asymmetric unit there is half molecule of L4. The
molecule crystallizes in the Pꢀ1 space group. The N–(CH2)4–N distance increased to
6.266(4) Å to give a longer backbone.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Addition of HgCl2/CoCl2 in a dichloromethane (DCM) solution containing L4 and
HCl/CNCH3 for four days, resulted in the isostructural second sphere adducts CH3CN·H2O
⊂[L4]2H+·[MCl4]2ꢀ (M = Hg, (8); M = Co, (9)). The two complexes crystallize in the
monoclinic P21/n space group, with one doublyꢀprotonated L4, one [HgCl4]2ꢀ dianion, one
acetonitrile and one water molecule in the asymmetric unit. It is an enclosed hydrogen
bonding interaction between L4 and [HgCl4]2–/[CoCl4]2– anion involving water molecules as
linker (Fig. 7a).
The second sphere adduct 8 has a building block that involves three types of hydrogen
bonds: the expected N–H···Cl interaction between N ligand and [HgCl4]2ꢀ/[CoCl4]2ꢀ (i),
N–H···O interaction between ligand and linker water molecules (ii), and O–H···Cl
interactions between water and [HgCl4]2ꢀ (iii). The acetonitrile molecule is encapsulated
and stabilized by O–H···N interactions (iv) between the other remaining unused hydrogen
atom of water and N atom of the CN group. Interestingly, the CH3CN molecules do not
play a primary role in the host hydrogen bond network and are somehow acting as templates
21
ACS Paragon Plus Environment

Crystal Growth & Design
Page 22 of 42
1
2
3
4
5
6
7
8
9
to fill the empty space, while water is more directly involved in the host framework bridging
the dication and dianion (Fig. 7a). The building blocks are further linked to each other
through C–H···Cl interactions (vꢀviii) along bꢀ and cꢀaxis, constructing a 3D structure as seen
in Fig. 7b, with the ligand molecules in a helical arrangement along cꢀaxis.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
22
ACS Paragon Plus Environment

Page 23 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Figure 7. Crystal structure of second sphere adduct 8 showing the main hydrogen bonds
between dications and dianions (i.e., the building block) (a). (b) Crystal packing in 8
displaying also the hydrogen bonds between adjacent building blocks (b). The included
acetonitrile guest molecules are shown as spacefilling model.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Structure description of CH3OH⊂[L4]2H+·[CdCl4]2– (10). Using the above same
conditions, the ligand L4 can react with CdCl2⋅2.5H2O in methanol to produce the complex
CH3OH⊂[L4]2H+·[CdCl4]2– (10). The complex crystallizes in the monoclinic P21/n space
group, with one doublyꢀprotonated L4, one [MCl4]2– dianion, one methanol in one
asymmetric unit. One protonated NH in L4 is connected with [CdCl4]2– dianion through
N–H···Cl interaction (i), the other protonated NH in L4 is linked with methanol molecule
through N–H···O interaction (ii). Then the methanol acts as link further connecting with
another [CdCl4]2– dianion through O–H···Cl hydrogen bonding (iii). The above three
hydrogen bonds comprise a new building block. The building blocks are further linked to a
linear chain along diagonal of acꢀaxis (Fig. 8a), and then expanded into a 3D structure
through C–H···Cl (iv) (Fig. 8b).
23
ACS Paragon Plus Environment

Crystal Growth & Design
Page 24 of 42
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 8. Single crystal structure of 10. View of the building block involving dication,
dianion and a water guest molecule (a); (b) Crystal packing showing the hydrogen bonding
interactions perpendicular to the crystallographic acꢀplane (b). Hydrogen bonds are shown as
dash lines.
Influence of ꢀ(CH2)nꢀ (n = 2, 3, 4) spacer lengths for inclusion property
The metal : ligand ratio can be an important parameter controlling the dimensionality of
the resultant second sphere adduct. Herein, the metal : ligand ratio is constant (1 : 1) in
crystals 2ꢀ10. Only 1 formed by L0 ligand give rise to the 1 : 2 ratio but does not show
guest inclusion (i.e., due to the ligand size). The tetrachlorometallate dianion adopts a
24
ACS Paragon Plus Environment

Page 25 of 42
Crystal Growth & Design
1
2
3
4
planar geometry in crystal 1, but forms various distorted tetrahedral [MCl4]2ꢀ dianions in 2ꢀ10
5
6
crystals. The alkyl chain length is an important factor determining the formation of
7
8
secondꢀsphere coordination giving rise to different guest molecules.
Such
9
versatility/flexibility allows keeping the 1:1 metal ratio even if the chain length increases
from 3.766 to 6.266 Å.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
QM calculations specific for solid state phases, particularly DFT approaches have
demonstrated that for the ligand with two methyl groups in the backbone, the stability is
higher than that with three methyl groups.37 Moreover, the conformational freedom
introduced by the addition of methylene groups has a strong influence in the conformational
flexibility of the ligand when it selfꢀassembles with the metal ions and solvent molecules.
In the second sphere adduct 1 containing L0 (i.e., without alkyl), only one nitrogen donor,
reacts with the dianion [CuCl4]2– through N–H···Cl interactions, constructing a linear second
sphere adduct without included guests. Interestingly, the ligand L1 (–(CH2)n– n = 1) is
unstable during the selfꢀassembling reaction with [MCl4]2–, and decomposes into L0 and
subsequently forms crystal 1.
In L2 the length between the two nitrogen atoms is ca. 3.76 Å, adopting a gauche
conformation in crystal 2 (Fig. 9a) and forms a quasiꢀchelating N–H···Cl hydrogen bond with
[MCl4]2–, including ethanol in the host framework.
By increasing the methylene chain length [(CH2)n (n = 3)], the distance between the two
nitrogen donors in L3 is ca. 5.11 Å. L3 exhibits higher conformational diversity due to the
higher flexibility of ligand. L3 adopts antiperiplanar conformation or gauche conformation
in this crystals (Fig. 9 b,c,d). The host framework takes different molecular arrangements to
fit the demands of the same guest species (methanol). In 3, methanol is not directly
25
ACS Paragon Plus Environment

Crystal Growth & Design
Page 26 of 42
1
2
3
4
5
6
7
8
involved in the connection between the ligand and [MCl4]2–. Additionally, acetic acid or
acrylic ester can also be included in the host cavity formed by L3 and [MCl4]2–, in which L3
adopts gauche conformation in crystal 4 (Fig 9e) and crystal 5ꢀ7 (Fig. 9f).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
With longer methylene chains ((CH2)n n = 4), acetonitrile and methanol molecules were
included in the host framework formed by L4 and [MCl4]2–, due to length increase of N···N
by (CH2)4 spacer (6.34 Å), the interaction with [MCl4]2– is through water molecules, and
acetonitrile. L4 also exhibit flexibility and can adopt gauche conformation in crystals 8ꢀ9
(Fig. 9g) whereas antiperiplanar conformation in crystal 10 (Fig 9 h).
Figure 9. Diversity in the conformations of L2ꢀL4 in crystals 2ꢀ10 viewed from the
projection of the Newmanꢀtype overlay of two nitrogen atoms: (a) L2 in crystal 2; (b) L3 in
crystal 3; (c,d) L3 in previous reported crystal structures; (e) L3 in crystal 4; (f) L3 in crystal
5ꢀ7; (g) L4 in crystal 8ꢀ9 (h) L4 in crystal 10.
Thermal stability of supramolecular adducts 1ꢀ10.
The thermal stability and the reversible/irreversible properties (guest behavior) of
complexes 2, 4 and 8 have been studied. The experimental PXRD patterns of complexes 1−10
are in agreement with the simulated diffraction patterns from their respective single crystal
structures (Fig. S6ꢀS13), thus confirming their phase purity.
26
ACS Paragon Plus Environment

Page 27 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
To begin with, we monitored the thermal stability of the second sphere adduct 2 which
contains L2. The release of the guest molecules has been monitored first by
thermogravimetrical analysis (TGA), which showed that crystal 2 exhibits an initial weight
loss (3.4 %) from RT to 137 °C, corresponding to the release of ethanol (calcd 3.5%).
Further heating leads to the loss of ligand. Second, we have monitored the thermal stability
of 2 by heating from RT to 150 °C by holding the sample at 100 °C for several hours. As
shown in Figure S14, the crystallinity is practically lost after 15 h at 100 °C but seems that at
120 °C there is somehow a reorganization as weak diffraction is observed. However, at
higher temperatures (i.e., 120ꢀ150 °C) the crystallinity is lost and the original crystalline
structure (2) is not restored after immersing the heated powders of 2 in EtOH for 24 h.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The structural stability of 4, formed using L3, was also monitored upon heating. We
found that heating complex 4 to 160 °C showed that after 140 °C, an amorphous phase is
obtained and did not return to the original structure when it was immersed in acetic acid (Fig.
S19). The structural transformation is probably too severe to allow the reconstruction of the
framework. TG analysis reveals that 4, the first weight loss (4.57 %) from 50°C to 170° C
corresponds to the release of acetic acid (calcd 4.46 %).
The investigation of reversible guest inclusion/release process of supramolecular second
sphere adducts including ligand L4 and [MCl4]2ꢀ shows an interesting result for the second
sphere adduct 8. The PXRD pattern of 8 shows that the positions and intensities of all peaks
shifted upon heating at 100 ºC, suggesting that the supramolecular host structure changed
upon CH3CN release whilst maintaining the crystallinity (see ESI). Powder XRD indicates
that a new phase is obtained at least for that period of heating time (as seen in Fig. 10d).
Interestingly, when we put the polycrystalline powder in acetonitrile/water for 72h, the original
structure was formed again (Fig. 10e).
TGA corroborates that 8, shows two distinct weight losses corresponding to the CH3CN
and water respectively. The weight loss (4.90 %) fits with the release of CH3CN molecules
27
ACS Paragon Plus Environment

Crystal Growth & Design
Page 28 of 42
1
2
3
4
5
6
7
8
9
from RT to 120 ºC (calcd. 4.82%) and the subsequent weight loss (2.32 %) from 120 to 170
ºC corresponds to the release of water molecules (calcd. 2.22%). We note that the PXRD
pattern obtained after 3 hours at 100 °C might be the one corresponding to the structure
containing only H2O (as shown by TG and by the fact that there is no presence of 8 as the
most intense peak at ca. 2ꢀtheta 12˚ is not present anymore Fig. 10d) and therefore, a
stepwise guest release is observed. The restoration of 8 occurs as it might be helped by the
presence of H2O in the crystal structure (Fig. 10e).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 10. Experimental PXRD patterns of 8: (a) Simulated PXRD from single crystal; (b) as
synthesized PXRD pattern; (c) sample heated at 100 ºC for 1h; (d) sample heated at 100 ºC
for 3h; (e) Immersing (d) sample in acetonitrile/water for 100 h. The diffraction peak
highlighted in red corresponds to the most intense peak of 8 that does not appear after being
heated to 100 ºC for 3 hours.
In order to corroborate the dynamic behavior of adducts including L4, we have prepared a
new second sphere complex that includes ethanol and water as a guest 8·EtOH·H2O (see
ESI). We demonstrate that if 8·EtOH·H2O is heated up to 100 ˚C for 1h, it becomes
1
amorphous upon guest release (i.e., corroborated by H NMR) but if it is immersed again in
28
ACS Paragon Plus Environment

Page 29 of 42
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
EtOH the desolvated adduct reverts to its initial structure as shown by PXRD (Figure 11).
Thus the dynamic behavior in a second sphere adduct is observed following a
crystallineꢀtoꢀamorphousꢀtoꢀcrystalline transformation which is reminiscent to some
coordination networks. 9,38,39,40 Such reconstruction of the original framework is indicative
of a certain structural memory retained in the amorphous phase, clearly demonstrating that
second sphere coordination adducts can be flexible and active upon external stimuli.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 11. (a) Simulated PXRD (100 K) of 8·EtOH·H2O; (b) Experimental PXRD (300 K)
of 8·EtOH·H2O. (c) PXRD (300 K) corresponding to single crystals of 8·EtOH·H2O heated
up to 100 ºC for 1h. (d) PXRD of the immersed amorphous phase obtained upon heating
8·EtOH·H2O to 100 ºC in EtOH for 24h (d).
Influence of –(CH2)n– (n = 2, 3, 4) spacer lengths on the solidꢀstate mechanochemical
dehydrochlorination reaction.
29
ACS Paragon Plus Environment