3D supramolecular networks based on hydroxyl-rich Schiff-base copper(II) complexes

Article abstract of DOI:10.1016/j.poly.2018.06.001

Reactions of the Schiff base ligand OH-C₆H₄-CH[dbnd]NC(CH₂OH)₃ (H₄L) with copper(II) salts in various reaction media afforded complexes [Cu₄(H₂L)₄]·MeOH (1·MeOH), [Cu<

Full text of DOI:10.1016/j.poly.2018.06.001

Accepted Manuscript
3D supramolecular networks based on hydroxyl-rich Schiff-base copper(II)
complexes
Katerina N. Lazarou, Aikaterini Savvidou, Catherine P. Raptopoulou, Vassilis
Psycharis
PII:
S0277-5387(18)30317-6
https://doi.org/10.1016/j.poly.2018.06.001
POLY 13208
DOI:
Reference:
Polyhedron
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Received Date:
19 April 2018
Please cite this article as: K.N. Lazarou, A. Savvidou, C.P. Raptopoulou, V. Psycharis, 3D supramolecular networks
based on hydroxyl-rich Schiff-base copper(II) complexes, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.
2018.06.001
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3D supramolecular networks based on hydroxyl-rich Schiff-base
copper(II) complexes†
Katerina N. Lazarou, Aikaterini Savvidou, Catherine P. Raptopoulou* and Vassilis
Psycharis*
Institute of Nanoscience and Nanotechnology, NCSR “Demokritos”, 15310 Aghia Paraskevi,
Athens, Greece
† This work is dedicated to our dearest friend and colleague Prof. Spyros P. Perlepes on the
occasion of his 65th birthday and in recognition of his enormous contribution to the
development of Inorganic Chemistry.
*Corresponding author: Tel: +30 210 6503346; Fax: +30 210 6519430
E-mail address: c.raptopoulou@inn.demokritos.gr (Dr. C.P.Raptopoulou)
E-mail address: v.psycharis@inn.demokritos.gr (Dr. V. Psycharis)
1

Abstract
Reactions of the Schiff base ligand OH-C6H4-CH=NC(CH2OH)3 (H4L) with copper(II) salts
in various reaction media afforded complexes [Cu4(H2L)4]·MeOH (1·MeOH),
[Cu2(O2CMe)2(H3L)2] (2), [Cu4(H2L)4(H2O)2]·1.5dmf (3·1.5dmf), [Cu4(H2L)4(H2O)]·MeOH
(4·MeOH) and [Cu4(H2L)4]2·2H2O·7MeOH (5·2H2O·7MeOH). Compounds 1, 3 and 4 consist
of neutral tetranuclear entities in which the CuII ions are coordinated by the tridentate Schiff
base ligands, forming a tetranuclear Cu4O4 cubane-like configuration. Compound 5 contains
similar cubane-like tetranuclear entities which are further linked through the hydroxyl groups
of the ligands thus forming dimers of cubanes. Compound 2 contains a neutral dinuclear
entity in which the CuII ions are bridged through the Schiff base and the acetate ligands,
comprising distorted Cu2O2 core. The Schiff base ligand adopts five different coordination
modes and two deprotonation states in the structures of 1-5 acting simultaneously as chelating
and bridging agent between the metal ions. The lattice structures of 1-5 exhibit interesting 3D
networks based on hydrogen bonded metal clusters and they are studied with Hirshfeld
Surface analysis methods.
Keywords: copper(II) complexes, cubane structures, Schiff base ligands, crystal structures,
supramolecular networks, Hirshfeld surface analysis
2

1. Introduction
Porous coordination polymers, widely known as metal-organic frameworks (MOFs), have
been the major subject of materials chemistry during the last decades. In many cases, these
materials exhibit intricate and beautiful crystal structures. The main feature of MOFs is the
porosity which makes them the organic-inorganic hybrid analogs of zeolites and therefore
have found several applications such as storage and separation of gases, drug delivery,
catalysis, and functional materials (e.g. sensors, luminescent and magnetic materials) [1-3].
The formation of MOFs is based on the covalent interactions between the metal ions and the
donor atoms of the ligands. However, the presence of noncovalent interactions, such as
hydrogen bonding and π-π interactions are very important for the stability of MOFs, and most
importantly for the formation of supramolecular networks based on organic and/or hybrid
organic-inorganic building units. Noncovalent interactions control vital biological processes
in living systems with the most important ones being the proteins' structure and functionality.
Supramolecular networks based on various nuclearity metal complexes have been the major
subject of crystal engineering and have been extensively studied. The building blocks of these
networks are held together via noncovalent interactions with the most important being
hydrogen bonds, although other type of interactions such as halogen, chalcogen and pnicogen
interactions have gained attention recently. Supramolecular metal networks based on n-π*, π-
π stacking, π-cation, π-anion and hydrophobic interactions have been also reported [4-6].
Such materials have been examined for potential applications in separation technology and
catalysis based on host-guest chemistry principles [7-9].
Schiff bases can be easily prepared by reaction of amines with aldehydes or ketones [10,11].
The major advantage of this class of organic molecules is the large number of ligands that can
be prepared by choosing various starting materials with the desired functional sidegroups.
Therefore, Schiff base ligands have been extensively used for the synthesis of 3d, 3d/4f and 4f
complexes in order to study their physical properties [12-17] and in many cases exhibit
catalytic and significant biological activity [18,19].
3

One of our research projects aims in the use of Schiff base ligands, that contain
simultaneously chelating and bridging groups, in 3d and 3d/4f chemistry. Salicylaldehyde,
among other aldehydes, and polyalcohol amines, such as tris(hydroxymethyl)aminomethane,
are used to prepare ligand H4L used in the present study. H4L has been widely used in
transition metal chemistry [20-28]. Our recent results in Schiff bases chemistry involve
tetranuclear MnIII complexes with zig-zag chain structure, trinuclear and octanuclear FeIII
complexes, as well as heptanuclear heterometallic CuII/LnIII complexes [29-31].
We present herein the synthesis, spectroscopic and crystallographic characterization of CuII
complexes with H4L, i.e. the tetranuclear complexes with cubane structure
[Cu4(H2L)4]·MeOH
(1·MeOH),
[Cu4(H2L)4(H2O)2]·1.5dmf
(3·1.5dmf)
and
[Cu4(H2L)4(H2O)]·MeOH (4·MeOH), the dinuclear complex [Cu2(O2CMe)2(H3L)2] (2), and
the dimer of cubanes complex [Cu4(H2L)4]2·2H2O·7MeOH (5·2H2O·7MeOH). We discuss in
detail the supramolecular networks formed from 1-5 due to noncovalent interactions by using
Hirshfeld surface analysis method.
2. Experimental
2.1. General and spectroscopic measurements
All manipulations were performed under aerobic conditions using materials as received
(Aldrich Co). All chemicals and solvents were of reagent grade. Elemental analysis for
carbon, hydrogen, and nitrogen was performed on a Perkin Elmer 2400/II automatic analyzer.
Infrared spectra were recorded as KBr pellets in the range 4000 - 400 cm-1 on a Bruker
Equinox 55/S FT-IR spectrophotometer.
2.2. Compound preparations
2.2.1. OH-C6H4-CH=NC(CH2OH)3, H4L.
Solid tris(hydroxymethyl)aminomethane (10 mmol, 1.210 g) was dissolved in MeOH (15 mL)
to afford a colorless solution. A colorless solution of salicylaldehyde (10 mmol, 1.053 mL) in
4

MeOH (15 mL) was then added to afford a final yellow solution which was stirred at ~45 oC
for one hour. The final solution was evaporated to dryness under vacuum to yield a yellow
product which was extracted by n-hexane (5 mL). The final yellow precipitate was dried
under vacuum overnight. (Yield: 2.18 g, 96.9 %). C11H15NO4 requires: C, 58.66; H, 6.71; N,
6.22 %. Found: C, 58.42; H, 6.67; N, 6.19 %. FT-IR (KBr pellets, cm-1): 3320(br,s), 3062(w),
3029(w), 2978(m), 2936(m), 2885(m), 2820(m), 1637(vs), 1608(s), 1556(s), 1535(s),
1514(m), 1487(vs), 1456(s), 1424(m), 1395(s), 1382(m), 1366(m), 1340(s), 1306(s), 1279(m),
1225(s), 1189(s), 1153(s), 1132(s), 1101(vs), 1059(vs), 1028(vs), 982(vs), 943(s), 919(s),
893(s), 870(s), 846(m), 800(s), 776(m), 765(vs), 737(s), 648(s), 629(s), 568(s), 567(s), 546(s),
490(s), 477(s), 442(s), 420(s).
2.2.2. [Cu4(H2L)4]·MeOH (1·MeOH) and [Cu4(H2L)4]2·2H2O·7MeOH (5·2H2O·7MeOH) in
mixture.
Solid H4L (0.3 mmol, 0.068 g) was added to a green solution of [Cu2(O2CMe)4]·2H2O (0.15
mmol, 0.060 g) in MeOH (10 mL). The color of the solution immediately changed to dark
o
green. The final solution was stirred under heating at ~40 C for half hour and left for slow
evaporation. X-ray quality blue crystals of 1·MeOH and light blue crystals of 5·2H2O·7MeOH
were formed after 10 days. The crystals were separated manually under the microscope.
2.2.3. [Cu4(H2L)4]·MeOH (1·MeOH)
A yellow solution of H4L (0.3 mmol, 0.068 g) in MeOH (5 mL) was added to a green solution
of Cu(acac)2 (0.30 mmol, 0.079 g) in dmf (20 mL) which was stirred under heating at ~90 oC.
The resulting dark green solution was refluxed for 3 h and after cooled at r.t. was layered with
Et2O. X-ray quality blue crystals of 1·MeOH were formed after 3 weeks. The identity of the
crystals was confirmed by unit cell determination (a = b = 17.414(1), c = 16.751(1) Å, α = β =
γ = 90 o, V = 5079 Å3). The crystals were filtered off and dried under vacuum. (Yield: 0.056 g,
~65 %). The solid was analyzed as solvent free. C44H52Cu4N4O16 requires: C, 46.07; H, 4.57;
5

N, 4.88 %. Found: C, 45.88; H, 4.54; N, 4.85 %. FT-IR (KBr pellets, cm-1): 3413(br,s),
2912(w), 2873(w), 2828(w), 1625(vs), 1603(s), 1543(s), 1473(s), 1448(s), 1399(m), 1385(m),
1338(m), 1300(vs), 1254(m), 1206(m), 1160(m), 1129(m), 1083(m), 1029(s), 980(w),
936(w), 915(m), 875(m), 770(s), 683(s), 633(m), 586(m), 489(m), 454(m).
2.2.4. [Cu2(O2CMe)2(H3L)2] (2)
Solid H4L (0.3 mmol, 0.068 g) was added to a green solution of [Cu2(O2CMe)4]·2H2O (0.15
mmol, 0.060 g) in MeOH (8 mL). The color of the solution immediately changed to dark
o
green. The final solution was stirred under heating at ~40 C for half hour and left for slow
evaporation. A blue precipitate was filtered after one week and the light blue filtrate was left
for slow evaporation. X-ray quality light blue crystals of 2 were formed after one month,
which were filtered off and dried under vacuum. (Yield: 0.065 g, ~63 %). C26H34Cu2N2O12
requires: C, 45.02; H, 4.94; N, 4.04 %. Found: C, 44.83; H, 4.91; N, 4.01 %. FT-IR (KBr
pellets, cm-1): 3321(br,s), 2912(w), 2869(w), 1621(vs), 1601(s), 1542(s), 1472(s), 1446(s),
1396(m), 1371(m), 1340(s), 1302(vs), 1251(m), 1199(s), 1156(s), 1132(s), 1090(s), 1054(s),
1035(vs), 993(w), 980(w), 940(w), 915(m), 900(w), 878(m), 885(m), 824(m), 786(m), 765(s),
740(m), 684(s), 635(w), 584(s), 548(m), 485(m), 462(m), 415(m).
2.2.5. [Cu4(H2L)4(H2O)2]·1.5dmf (3·1.5dmf).
A yellow solution of H4L (0.30 mmol, 0.068 g) in dmf (6 mL) was added to a turquoise
solution of Cu(acac)2 (0.30 mmol, 0.079 g) in dmf (20 mL). The immediately formed green
solution was refluxed for 3 h and left for slow evaporation. X-ray quality blue crystals of
3·1.5dmf were formed after 2 months, which were filtered off and dried under vacuum.
(Yield: 0.053 g, ~60 %). The solid was analyzed as solvent free. C44H56Cu4N4O18 requires: C,
44.67; H, 4.77; N, 4.73 %. Found: C, 44.49; H, 4.74; N, 4.70 %. FT-IR (KBr pellets, cm-1):
3553(s), 3477(s), 3414(s), 1638(s), 1617(vs), 1578(s), 1553(s), 1533(s), 1462(w), 1413(m),
6

1384(m), 1355(s), 1275(s), 1189(s), 1020(s), 937(s), 782(s), 684(m), 653(w), 613(s), 480(m),
455(s).
2.2.6. [Cu4(H2L)4]·MeOH (1·MeOH) and [Cu4(H2L)4(H2O)]·MeOH (4·MeOH) in mixture.
Solid H4L (0.3 mmol, 0.068 g) was added to a green solution of [Cu2(O2CMe)4]·2H2O (0.15
mmol, 0.060 g) in MeOH (13 mL). The color of the solution immediately changed to dark
o
green. The final solution was stirred under heating at ~40 C for half hour and left for slow
evaporation. After two days the vial was closed and left undisturbed to afford blue crystals of
1·MeOH and light-blue needle-like crystals of 4·MeOH. The identity of 1·MeOH was
confirmed by unit cell determination (a = b = 17.035(3), c = 16.840(5) Å, α = β = γ = 90 o, V
= 4886 Å3). The crystals were separated manually under the microscope.
2.3. Single crystal X-ray crystallography
Crystals of 1·MeOH (0.41 × 0.43 × 0.57 mm), 2 (0.07 × 0.07 × 0.54 mm), 3·1.5dmf (0.14 ×
0.41 × 0.45 mm) and 4·MeOH (0.04 × 0.04 × 0.26 mm) were taken from the mother liquor
o
o
o
and immediately cooled to -83 C (1·MeOH), -93 C (2) and -113 C (3·1.5dmf and
4·MeOH). The few isolated crystals of 5·2H2O·7MeOH were destroyed into the cryo-
crystallography oil (Paratone-N) and were mounted in capillaries. Most of them showed poor
diffraction ability at lower 2θ angles which made them unsuitable for data collection.
Repeating efforts to improve the quality of the crystals of 5 proved unsuccessful thus the 'best'
quality crystal (0.08 × 0.08 × 0.32 mm) was used to establish the gross structure of 5.
Collimators of appropriate size were used for each studied crystal i.e. 0.8 for 1 and 2, 0.5 for 3
and 5 and 0.3 for 4. Diffraction measurements for all structures were made on a Rigaku R-
AXIS SPIDER Image Plate diffractometer using graphite monochromated Cu Kα radiation.
Data collection (ω-scans) and processing (cell refinement, data reduction and Empirical
absorption correction) were performed using the CrystalClear program package [32]. The
structures were solved by direct methods using SHELXS-97 and refined by full-matrix least-
7

squares techniques on F2 with SHELXL ver.2014/6 [33]. Important crystallographic and
refinement data for 1·MeOH, 2, 3·1.5dmf and 4·MeOH are listed in Table 1. Hydrogen atoms
were either located by difference maps and were refined isotropically or were introduced at
calculated positions as riding on bonded atoms. All non-hydrogen atoms were refined
anisotropically. Plots of the structure were drawn using the Diamond 3 program package [34].
Crystallographic data for 5·2H2O·7MeOH: C80H84Cu8N8O32, fw = 2177.87, triclinic, P-1, a =
10.8953(2), b = 16.6292(3), c = 17.4705(3) Å, α = 116.322(1), β = 90.301(1), γ = 93.192(1) o,
V = 2831.13(9) Å3, Z = 1, 14463 reflections collected of which 4699 were used for the
refinement of 438 parameters.
Table 1. Crystallographic data for 1·MeOH, 2, 3·1.5dmf and 4·MeOH.
1·MeOH
C45H56Cu4N4O17
1179.09
3·1.5dmf
C48.5H66.5Cu4N5.5O19.5
1292.73
4·MeOH
C45H58Cu4N4O18
1197.11
2
C26H34Cu2N2O12
693.63
Formula
Fw
Space group
a (Å)
I41/a
P21
C2/c
P-1
17.0529(3)
17.0529(3)
16.8166(3)
90
7.1096(1)
18.8623(3)
10.3396(2)
90
24.5751(4)
16.2214(3)
18.3146(3)
90
10.3714(2)
15.0019(3)
17.5737(3)
68.150(1)
b (Å)
c (Å)
α (ο)
8

β (ο)
90
90
105.711(1)
90
129.894(1)
90
74.349(1)
71.783(1)
γ (ο)
V (Å3)
Z
4890.29(19)
1334.77(3)
5601.54(18)
2373.89(8)
4
2
4
-113
2
-113
T (oC)
Radiation
ρcalcd, g cm-3
-83
-93
Cu Kα (1.54178 Å) Cu Kα (1.54178 Å)
Cu Kα (1.54178 Å)
1.533
Cu Kα (1.54178 Å)
1.675
1.601
2.603
1.726
2.591
µ, mm-1
2.368
130
2.707
143.5
214
120
657
2θmax (°)
130
387
parameters refined
461
reflections
collected/unique
/used
22600/2361
/2361
18009/4330
/4330
30801/4686
/4686
36140/6626/
6626
Rint
0.0370
0.0438
0.0323
0.0628
(∆/σ)max
0.043
0.656/ -0.257
2303
0.001
0.374/-0.486 e/Å3
4183
0.065
1.255/-0.462 e/Å3
4425
0.001
1.556/-1.303
4314
(∆ρ)max/( ∆ρ)min (e/Å3)
Reflections with
I>2σ(I)
a
R1 [I>2σ(I)]
0.0330
0.0897
0.0337
0.0902
0.0307
0.0760
0.0319
0.0396
0.1134
0.0414
0.0414
0.0765
0.1871
0.1127
0.2431
a
wR2 [I>2σ(I)]
R1a (for all data)
wR2a (for all data),
0.0898
2
a w=1⁄[σ2(Fo2)+(αP)2+bP] and P = (max Fo ,0)+2Fc2)/3, (a = 0.0451, b = 11.7273 (1); a = 0.0367, b = 0.5167
(2); a = 0.0635, b = 16.7529 (3); a = 0.1347, b = 0.0000 (4)),
2 2
R1 = Σ(|Fo|-|Fc|)/Σ(|Fo|) and wR2 = {Σ[w(Fo2-Fc2)2]/Σ[w(Fo ) ]}1/2.
3. Results and Discussion
9

3.1 Synthesis and infrared characterization
The reaction of two equivalents of H4L with one equivalent of [Cu2(O2CMe)4]·2H2O in
MeOH gave a dark green solution which was left for slow evaporation to afford mixture of
blue crystals of 1 and light-blue crystals of 5. The same reaction mixture, albeit more diluted,
gave after slow evaporation, mixture of blue crystals of 1 and light-blue crystals of 4.
Complexes 1 and 4 consist of neutral cubane entities, [Cu4(H2L)4] and [Cu4(H2L)4(H2O)]
respectively, whereas complex 5 consists of two cubanes [Cu4(H2L)4] linked through two long
Cu-OH bonds involving the pendant alkoxo groups of the Schiff base ligands. A more
concentrated reaction mixture, initially gave a blue precipitate which was filtered off and then
afforded light-blue crystals of the dinuclear complex 2 after slow evaporation. It is evident
that a multitude of products can be isolated from the respective reaction solution depending
on their solubility. Complexes 1, 4 and 5 contain tetranuclear cubane entities, constructed
from the Schiff base ligands only, whereas the acetates are involved only in the structure of
the dinuclear complex 2. Therefore, it was attempted to prepare the cubane complexes by
using other copper(II) salts following 'rational' synthetic procedures. By using Cu(acac)2 as
the metal source, the cubane complex 1 was isolated in pure form, from the 1:1
[Cu(acac)2]/H4L molar ratio reaction in MeOH/dmf. The same reaction in dmf afforded
another cubane complex, [Cu4(H2L)4(H2O)2], 3.
The IR spectra of 1, 2 and 3 which were isolated in pure form were recorded. All spectra
exhibit broad bands at ~3400 cm-1 attributed to the ν(OH) vibrations due to the presence of
the alkoxo groups of the Schiff base ligands. The ν(C=N) and ν(C-O) stretching vibrations of
the Schiff base ligands are observed at ~1620 and ~1350 cm-1. The stretching vibrations of the
α-substituted aromatic ring are observed as set of peaks in the 1600-1400 cm-1 region and the
out-of-plane CH deformation vibrations at ~760 cm-1. The νas(C=O) and νs(C=O) vibrations
of the acetates in 2 are also expected in the 1600-1400 cm-1 region. Both acetates present
different coordination modes, one behaves as monoatomic bridge asymmetrically coordinated
to the two metal ions and the second behaves as monodentate ligand and also participates in
10

strong hydrogen bonding (vide infra). The peaks at 1597 and 1373 cm-1 (∆ = 224 cm-1) can be
attributed to the νas(C=O) and νs(C=O) vibrations of the monodentate acetate, and these at
1538 and 1340 cm-1 (∆ = 198 cm-1) can be attributed to the νas(C=O) and νs(C=O) vibrations
of the monoatomic bridge [35].
3.2. Description of the structures
Compound 1 crystallizes in the tetragonal space group I41/a. The structure consists of neutral
tetranuclear entities, [Cu4(H2L)4] which possess four-fold rotoinversion symmetry, and one
solvate methanol molecule per formula unit, which occupy ca. 9% of the unit cell volume
(~445 Å3). The cubane structure of 1 has been previously reported and will be discussed
briefly [36,37]. The CuII ions are coordinated by the tridentate Schiff base ligands, forming a
tetranuclear Cu4O4 cubane-like configuration. The charge balance is achieved by doubly
deprotonation of the Schiff base i.e. of the phenolato hydroxyl group and one of the terminal
hydroxyl groups of the ligand. The CuII ion adopts a CuNO4 distorted square-pyramidal
coordination environment (Figure S1, Table S1). The hydroxyl groups of the Schiff base
ligands play three roles in the present structure. O(1) is deprotonated and is coordinated to
Cu(II) ions, O(3) configures the intracluster arrangement of the four coordinated Schiff bases
through the intramolecular O(3)-H(3O)···O(4) hydrogen bonds whereas the lattice structure of
1 is developed through the intermolecular O(2)-H(2O)···O(3) hydrogen bonds (Figure 1a,
Table 2). Each cubane unit is linked though these hydrogen bonds with four neighboring
cubanes in a distorted tetrahedral arrangement thus acting as 4-connected node (Figure 1a).
The 3D architecture of compound 1 is based on these tetrahedra, which form layers through
corner sharing parallel to the (001) plane. These layers are stacked along c axis and two
successive layers are rotated by 90o with respect to each other and interpenetrate. The
channels formed between the layers are filled by the solvent molecules.
11

Figure 1. (a) A cubane, shown with dark gray bond color, with its four neighbors connected
through hydrogen bonds [O(2)-H(2O)···O(3) dashed orange lines) and forming a distorted
tetrahedron, indicated by the pink dashed lines (b) The 3D architecture of tetrahedra of
cubane units in the structure of compound 1. Red dots among the layers indicate the site of
lattice solvent methanol molecules.
The molecular structure of 2 consists of neutral dinuclear entities [Cu2(O2CMe)2(H3L)2]
(Figure 2) with the copper atoms coordinated with one acetate and one Schiff base ligands
each presenting different coordination modes. One of the Schiff base ligands, possessing
O(4), N(1) and O(1) atoms (Figure 2), chelates to Cu(2) through the phenolato oxygen O(4),
the imino nitrogen N(1) and one of the terminal hydroxyl groups O(1). The second ligand
chelates to Cu(1) in a similar manner, through O(24), N(21) and O(21) atoms and in addition
the phenolato oxygen O(24), serves as bridge to Cu(2) (Figure 2, Scheme 1). One of the
acetate ligands (the one defined by O(51) and O(52) atoms) coordinates to Cu(1) with O(51)
oxygen in a monodentate fashion whereas the second (the one possessing O(41) and O(42)
atoms) serves as monodentate bridge between the two metal ions, through the O(41) atom.
The abovementioned coordination of both type of ligands around the CuII ions promotes the
formation of a distorted rhombic Cu2O2 core [Cu(1)-O(41)-Cu(2)-O(24)-Cu(1)]. The
Cu(1)···Cu(2) distance is 3.4244(9) Å. The coordination environment of each CuII ion is
square pyramidal (the trigonality index τ is 0.115 for Cu(1) and 0.153 for Cu(2)). The apical
12

position of each square pyramid is occupied by O(41) and O(24) for Cu(1) and Cu(2)
respectively, with distances Cu(1)-O(41) = 2.496(3) Å and Cu(2)-O(24) = 2.856(3) Å; the
latter is close to the sum of the van der Waals radii and can be characterized as weak bond.
The bridging phenolato and carboxylato oxygen atoms are asymmetrically coordinated to the
CuII ions (Cu(1)-O(24) = 1.897(3) Å, Cu(2)-O(24) = 2.856(3) Å; Cu(2)-O(41) = 1.947(3) Å,
Cu(1)-O(41) = 2.496(3)Å). The Cu-O and Cu-N bond distances in the basal plane are in the
range 1.897(3)-1.997(3) Å for Cu(1) and 1.875(3)-1.968(3) Å for Cu(2) (Table S2). The
angles within the basal plane are in the range 82.6(1)-95.3(1) o for Cu(1) and 82.9(1)-96.3(1) o
o
for Cu(2), whereas those involving the apical positions are in the range 89.7(1)-97.8(1) for
o
Cu(1) and 78.8(1)-99.9(1) for Cu(2). As the acetate ligands are both deprotonated, charge
balance considerations reveal that the Schiff base ligands in 2 are mono-deprotonated only at
the phenolato oxygen atom thus the three protonated hydroxyl groups are available for
hydrogen bonding interactions. Two intra-molecular hydrogen bonds, O(1)-H(1O)···O(52)
and O(22)-H(22O)···O(4), contribute to the stabilization of the dinuclear entities (Figure 2,
Table 2) and five intermolecular hydrogen bonding interactions create the 3D supramolecular
network (Table 2). The intermolecular hydrogen bonding interactions are divided into two
groups; those which promote chain formation by the dinuclear entities along the a-axis [O(2)-
H(2O)···O(24), O(21)-H(21O)···O(42) and C(2)-H(2B)···O(51), intrachain ones, Figure 3,
Table 2] and those which promote the three-dimensional development of the lattice network
[O(3)-H(3O)···O(42), O(23)-H(23O)···O(52), interchain ones, Figure 3, Table 2]. The
dinuclear units along the chain axis, the a crystallographic one, interact further through π-π
interactions (Figures 11b and 11g).The lattice structure of 2 is dense and robust as there are
no voids left for solvate incorporation.
13

Figure 2. Partially labeled plot of compound 2. Dashed cyan lines indicate intramolecular
hydrogen bonds. The thermal ellipsoids are shown at 50% probability. Only hydroxyl
hydrogen atoms are shown for clarity.
14

Figure 3. The 3D network in the lattice structure of 2 due to hydrogen bonding interactions.
(a) chain formed along a-axis. (b) 3D arrangement of chains. Orange dashed lines indicate
interchain O(2)-H(2O)···O(24), O(21)-H(21O)···O(42) and C(2)-H(2B)···O(51) hydrogen
bonding interactions and magenta dashed lines indicate O(3)-H(3O)···O(42), O(23)-
H(23O)···O(52) interchain ones. Cyan dashed lines indicate intracluster hydrogen bonding
interactions.
The molecular structure of 3 is shown in Figure 4. The compound crystallizes in the
monoclinic space group C2/c. The structure consists of neutral tetranuclear entities,
[Cu4(H2L)4(H2O)2] which possess two-fold symmetry, and solvate dmf molecules which fill
ca. 18% of the unit cell volume (~1015 Å3). The CuII ions are coordinated by the tridentate
Schiff base ligands, forming a tetranuclear Cu4O4 cubane-like configuration similar to 1. The
intramolecular Cu···Cu distances are in the range 3.1445(8)-3.649(2) Å (Table S3). Two of
the CuII ions (Cu(1) and Cu(1*)) present CuNO5 distorted octahedral coordination
environment and the other two metal ions (Cu(2) and Cu(2*)) present CuNO4 square
pyramidal coordination with trigonality index τ 0.13. The sixth atom in the coordination
sphere of Cu(1) and Cu(*') ions is an aqua ligand, with the O(1w) forming a rather weak bond
equal to 2.820(3) Å . The Cu-O and Cu-N bond distances in the equatorial plane of the Cu(1)
ion, with the distorted octahedron coordination fall in the range 1.905(2)-1.947(2) Å, whereas
those involving the apical positions within the cubane cage are longer due to Jahn-Teller
distortion (2.668(2) Å for Cu(1)-O(2)*, Table S3). The respective bond distances within the
basal plane of the Cu(2) ion, with square pyramidal coordination geometry fall in the range
1.913(2)-1.951(2) Å, whereas a much longer Cu-O bond distance is observed in the apical
position (2.526(3) Å for Cu(2)-O(12)*). The bond angles within the tetragonal plane of the
o
distorted octahedron around Cu(1) and Cu(1') are in the range 83.7(1)-95.4(1) , and those
involving the apical positions are in the range 70.1(1)-114.0(1) o. The respective angles within
15

o
the basal plane of the square pyramidal Cu(2) and Cu(2') are in the range 84.6(1)-95.5(1) ,
whereas those involving the apical position are in the range 73.4(1)-122.7(1) o.
The lattice structure of 3 is stabilized by an extensive network of intra- and inter-molecular
hydrogen bonding interactions. One intra-molecular hydrogen bonding interaction of the
hydroxyl terminal group O(13)-H(13O)···O(1) together with those formed among the water
molecules and the oxygen atoms of the terminal hydroxyl groups O(1w)-H(1wA)···O(11) and
O(1w)-H(1wB)···O(3) promote the stability of the cubane structure (Figure 4) . The cubane
units through hydrogen bonding interactions involving the protonated hydroxyl groups O(3)-
H(3O)···O(13) promote the formation of chains parallel to the c-axis (Figure 5a). These
chains are further linked through hydrogen bonds O(14)-H(14O)···O(1w) involving the
hydroxyl groups of the Schiff base as well as the coordinated water molecules, thus creating
an overall 3D supramolecular network (Figure 5b, Table 2).
Figure 4. Partially labeled plot of the cubane structure of 3. Dashed cyan lines indicate
O(13)-H(13O)···O(1), O(1w)-H(1wA)···O(11) and O(1w)-H(1wB)···O(3) intramolecular
16

interactions. The thermal ellipsoids are at 50% probability. Symmetry: (*) -x, y, 0.5-z.
Hydrogen atoms have been omitted for clarity.
Figure 5. The 3D network in the lattice structure of 3 due to hydrogen bonding interactions.
(a) chains of cubane units parallel to the c-axis and (b) linkage of the chains into 3D network.
Orange dashed lines indicate O(3)-H(3O)···O13 and magenta lines indicate O(14)-
H(14O)···O(1W) interchain ones. Cyan dashed lines indicate intracluster hydrogen bonding
interactions.
The molecular structure of 4 is shown in Figure 6. It consists of neutral tetranuclear entities,
[Cu4(H2L)4(H2O)], and MeOH solvate molecules which fill 3.5% of the unit cell volume (~83
Å3). The CuII ions are coordinated by the tridentate Schiff base ligands, forming a tetranuclear
17

Cu4O4 cubane-like configuration similar to 1 and 3. The intramolecular Cu···Cu distances are
in the range 3.165(2)-3.507(1) Å (Table S4). Two of the CuII ions (Cu(1) and Cu(2)) present
CuNO5 distorted octahedral coordination environment and the other two metal ions (Cu(3)
and Cu(4)) present CuNO4 square pyramidal coordination with trigonality index τ 0.13 and
0.11, respectively. The sixth coordination site at Cu(1) is completed by a protonated –CH2OH
group of the Schiff base ligand (O(3), Figure 6), whereas in the case of Cu(2) is an aqua
ligand (O1w, Figure 6). The Cu-O and Cu-N bond distances in the equatorial plane of the
distorted octahedron fall in the range 1.899(5)-1.957(5) Å, whereas those involving the apical
positions are much longer due to Jahn-Teller distortion (2.589(4) and 2.712(4) Å for Cu(1)
and 2.735(6) and 2.757(5) Å for Cu(2), Table S4). The respective bond distances within the
basal plane of the square pyramidal coordination geometry fall in the range 1.901(5)-1.946(5)
Å, whereas a much longer Cu-O bond distance is observed in the apical position (2.622(4) Å
for Cu(3) and 2.557(5) Å for Cu(4), Table S4). The bond angles within the tetragonal plane of
the distorted octahedron around Cu(1) and Cu(2) are in the range 82.3(2)-96.7(2) o, and those
involving the apical positions are in the range 67.7(2)-116.5(2) o. The respective angles within
o
the basal plane of the square pyramidal Cu(3) and Cu(4) are in the range 83.4(2)-95.9(2) ,
whereas those involving the apical position are in the range 69.8(2)-122.2(2) o.
An extensive network of intra and inter cluster hydrogen bonds is also observed in the lattice
structure of compound 4 (Figure 7). The configuration of ligands within the cubane units is
due to an extensive intracluster hydrogen bonds interactions involving the protonated and
deprotonated hydroxyl terminal groups of the ligands O(3)-H(3O)···O(31), O(13)-
H(13O)···O(33), O(24)-H(24O)···O(11) and those involving the hydrogen atoms of
coordinated water molecule as well, O(1w)-H(1wA)···O(1) and O(1w)-H(1wA)···O(14). Each
cubane cluster interacts from one side with a neighboring one through the O(23)-
H(23O)···O(4) hydrogen bonds and from the other side with another one through the
hydrogen bonds involving the lattice methanol solvent molecules, O(1M)-H(1OM) ···O(13)
and O(33)-H(33O)···O(1M) (Figure 7, Table 2), thus forming chains parallel to the [0,1,1]
18

direction. The chains interact through O(4)-H(4O)···O(1w), O(34)-H(34O)···O(24) and
O(14)-H(14O)···O(3) and build the 3D architecture of compound 4 (Figure 7).
Figure 6. Partially labeled plot of the cubane structure of 4. Only hydroxyl and water
hydrogen atoms are shown for clarity. Dashed cyan lines indicate O(3)-H(3O)···O(31), O(13)-
H(13O)···O(33), O(24)-H(24O)···O(11), O(1w)-H(1wA)···O(1) and O(1w)-H(1wA)···O(14)
intramolecular interactions. The thermal ellipsoids are at 50% probability.
19

Figure 7. The 3D network in the lattice structure of 4 due to hydrogen bonding interactions.
(a) chains of cubane units parallel to the [011] crystallographic direction and (b) linkage of
the chains into 3D network. Orange dashed lines indicate O(23)-H(23O)···O(4), O(1M)-
H(1OM)···O(13), O(33)-H(33O)···O(1M) and magenta lines indicate O(4)-H(4O)···O(1W),
O(34)-H(34O)···O(24) and O(14)-H(14O)···O(3) interchain ones. Cyan dashed lines indicate
intracluster hydrogen bonding interactions.
20

The Schiff base ligands in the cubane structures 1 and 3 are in the doubly deprotonated form
at the phenolato oxygen and one of the hydroxyl groups. These ligands behave as tridentate
µ3-κ3O:κO':κN and bind to the metal ions through the phenolato oxygen, the imino nitrogen
and the deprotonated hydroxo oxygen atoms. The latter is also coordinated to two
neighboring CuII ions, acting as triple bridge between the metal ions, and occupies the oxygen
sites of the Cu4O4 cubane structure (Scheme 1). Also in 4, three of the ligands behave as
tridentate µ3-κ3O:κO':κN as in 1 and 3, and the forth behaves as tetradentate µ3-
κ3O:κO':κO'':κN coordinated to a CuII ion through the phenolato oxygen, the imino nitrogen,
of the protonated hydroxo oxygen and the deprotonated hydroxo oxygen atom which also
bridges two neighboring CuII ions. Finally the Schiff base ligands in 2 are mono deprotonated
at the phenolato oxygen atom and present two different coordination modes, chelating
through the phenolato oxygen, the imino nitrogen and the protonated hydroxyl group, and
bidentate µ2-κ2O:κO':κN, coordinated to the adjacent CuII ion through the bridging phenolato
oxygen atom. The molecular structure of 5 is shown in Figure S2. The structure consists of
two cubane-like Cu4O4 entities, similar to those in 1, which are linked through long Cu-OH
bond distances. The compound crystallizes in the triclinic space group P-1 and is
centrosymmetric. The data have been collected from a poorly diffracting crystal and they are
useful in deriving the connectivity of compound 5 only. The unit cell contains one cubane
dimer, two water and seven methanol solvate molecules. The Schiff base ligands in 5 are also
doubly deprotonated as in 1 and 4 and present two different coordination modes. Three of the
ligands behave as tridentate µ3-κ3O:κO':κN as in 1 and 4, and the forth behaves as tetradentate
µ4-κ3O:κO':κO'':κN, coordinated to a CuII ion from a neighboring cubane unit through a
protonated hydroxyl group, thus creating the cubane dimers.
21

Scheme 1. Coordination modes of the Schiff base ligand in 1-5.
Table 2. Hydrogen bonding interactions in the structures of 1·MeOH, 2, 3·1.5dmf and
4·MeOH.
Interaction
D···A (Å) H···A (Å) D-H···A (o)
1·MeOH
Symmetry operation
Intramolecular
O(3)-H(3O)···O(4)
O(2)-H(2O)···O(3)
2.667
2.712
1.986
Intermolecular
2.027 167.5
171.5
-0.75+y, -0.25-x, 0.75-z
-0.25-y, 1.25+x, 0.25+z
2
Intramolecular
O(1)-H(1O)···O(52)
O(22)-H(22O)···O(4)
2.580
2.828
1.745
2.023
172.4
160.3
x, y, z
x, y, z
Intermolecular
22

O(21)-H(21O)···O(42)
O(2)-H(2O)···O(24)
C(2)-H(2B)···O(51)
O(3)-H(3O)···O(42)
O(23)-H(23O)···O(52)
2.709
2.822
3.246
2.780
2.786
1.872
2.024
2.473
1.957
1.989
174.0
158.5
134.6
166.3
158.1
-1+x, y, z
1+x, y, z
1+x, y, z
2-x, -0.5+y, -z
x, y, 1+z
3·1.5dmf
Intramolecular
O(13)-H(13O0···O(1)
2.637
1.931
1.987
2.086
178.3
-x, y, 0.5-z
x, y, z
O(1w)-H(1wA)···O(11) 2.804
170.4
177.0
O(1w)-H(1wB)···O(3)
2.894
x, y, z
Intermolecular
O(3)-H(3O)···O(13)
2.690
2.739
1.953
2.142
167.9
171.9
-x, 1-y, 1-z
O(14)-H(14O)···O(1w)
-0.5+x, 0.5-y, -0.5+z
4·MeOH
Intramolecular
O(3)-H(3O)···O(31)
O(13)-H(13O)···O(33)
O(24)-H(24O)···O(11)
O(1w)-H(1wA)···O(1)
2.696
2.704
2.668
2.797
1.86
1.87
1.84
1.98
2.06
170.6
x, y, z
x, y, z
x, y, z
x, y, z
x, y, z
171.4
170.7
154
O(1w)-H(1wB)···O(14) 2.758
162
Intermolecular
O(23)-H(23O)···O(4)
2.729
1.90
2.54
1.9
169.4
-x+1, -y+1, -z
x, y-1, z
O(1m)-H(1Om)···O(13) 3.019
117.4
147.1
165.5
161
O(33)-H(33O)···O(1m)
O(4)-H(4O)···O(1w)
O(34)-H(34O)···O(24)
O(14)-H(14O)···O(3)
2.709
2.668
2.704
2.691
-x+1, -y+1, -z+1
x-1, y, z
1.85
1.92
1.88
-x+1, -y+1, -z+1
-x+1, -y+2, -z
161.0
3.3 Hirshfeld surface analysis
The crystal packing and the intermolecular interactions of structures 1, 2, 3 and 4 are further
studied by the Hirshfeld Surface (HS) analysis method tools [38]. In Figure 8a the HS for
compound 1 decorated with dnorm property is presented. Figure 8b and 8c present the
23

fingerprint plots with the contribution for all the interactions and only for O···H interactions
respectively, for the same compound. In Figure 8c and in analogous Figures in the rest of the
text (Figures-9d, 9e, 10c, 10d, 11f and 11g ) the contributions from all the interactions in the
respective fingerprint plots are within the gray area beneath the respective type of
interactions, which are indicated with the colored area. The green lines [39] correspond to the
di + de distances which are equal to the sums of the van der Waals (vdW) radii [40] of the
corresponding pairs of atoms involved in the specific interaction and so all the points for each
type of interaction which are located within the cyan area indicate strong interactions i.e.
di+de sums with values smaller than sum of the corresponding vdW radii. The analysis of
fingerprint plots give 47.2, 29.9 and 17.4 % contributions from H···H, O···H/H···O and
C···H/H···C interactions respectively for compound 1. The strongest contribution comes from
the O···H/H···O type of interactions and the red spots B1 and B1´ in Figure 8a indicate the
acceptor O(3) and the H(2O) atom of the donor O(2) atoms respectively, in the O(2)-
H(2O)···O(3) hydrogen bonds. Through these interactions other parts of molecules are coming
closer, as the one indicated with faint red spots on the dnorm HS and are enclosed by the black
and gray circles in Figure 8a, which correspond to the acceptor O(2) (B2 points) and to H(8)
hydrogens (B2’ points) of the C(8) donor atoms in the C(8)-H(8)···O(2)i hydrogen bonds
[(i):0.5-x, 0.5-y, 1.5-z; C(8)-H(8) ···O(2) i: 0.85, H(8) ···O(2) i: 2.64, C(8)···O(2) i:3.412, C(8)-
H(8)-O(2):152o] respectively. Both of these interactions contribute at the spikes B and B’ in
Figures 8b and 8c. In Figure 8b, A indicate the contribution of H···H conduct points and C/C’
the C···H/H···C ones respectively. Based on fingerprint plot analysis for compound 3, the
contribution for H···H, C···H/H···C, O···H/H···O type of interactions are 47.9, 25.3 and 18.6
% respectively (Figure 9c). In the dnorm presentation (Figure 9a) of HS for compound 3 the
intense red spots B1 and B2 correspond to the acceptor atoms O(13) and O(1W) and the
primed ones B1´ and B2´ correspond to the hydrogen atoms of donors O(3) and O(14), of the
following hydrogen bonds O(3)-H(3O)···O(13) and O(14)-H(14O)···O(1w). These hydrogen
bond interactions contribute to the spikes observed in the fingerprint plots at points B and B’
24

(Figure 9c and d) and are quite strong as the most of the points lie in the area bellow the green
line (Figure 9d) . These interactions bring closer other parts of the clusters such as B3
[acceptor atom O(14)] and B3´ [hydrogen H(3) of the donor atom C(3)] through the weak
hydrogen bond C(3)-H(3)···O(14). Also H(11A) and H(22) hydrogen atoms of C(11) and
C(22) carbon atoms interact with the phenyl ring C(21)…C(26) and C(1)…C(6) respectively
resulting in C-H···π interactions, indicated with the circled areas in the HS decorated with
Shape index (Figure 9b), where the complementary hollows (red) and bumps (blue) areas are
parts of the HSs where neighboring molecules touching each other through C-H···π
interactions [41]. The asymmetry distribution of points in the area of donors conduct points
and more specifically at points B´´ (Figures 9c and 9d), in comparison to those of the
acceptors is indicative that at these points contribute different molecules i.e. those of lattice
solvents (B´´ red poind in Figure 9a). For compound 4, the contribution for H···H,
C···H/H···C, O···H/H···O type of interactions are 57.6, 19.9 and 19.9 % respectively
(Figure 10b).
In the dnorm representation (Figure 10a) the hydrogen bonds O(4)-
H(4)···O(1W), O(14)-H(14)···O(3) and O(23)-H(23)···O(4) give the red intense spots B1,
B2, and B3 for the acceptor oxygen atoms O(1W) , O(3) and O(4) and the B1´, B2´, and
B3´ ones for the corresponding hydrogen atoms of the donors O(4), O(14) and O(23)
respectively. These hydrogen bond interactions contribute to the spikes observed in the
fingerprint plots at points B and B’ (Figure 10b and c) and are quite strong as the most of the
points lie in the cyan area below the green line (Figure 10c). The points B5 and B4’ in Figure
10a) indicate the O13 (acceptor) and H33O (hydrogen of donor O33 atom) for the hydrogen
bonds O1M-H10M···O13 and O33-H33O···O1M respectively. For this structure the C-H···π
type of interactions contribute effectively as indicated with the presence of points at the cyan
area below the green line in Figure 10d.
The basic building block for the 3D structures of compounds 1, 3 and 4 are the structural units
with a cubane core and depending on the presence of water molecules (two in the case of
compound 3 and one in the case of compound 4) or not (compound 1) present different
25

packing arrangements, but all of them have a common characteristic. More specifically the
atoms O(3) (Figure S1, point B1 in Figure 8a) for compound 1, O(13) and O(1W) (Figure 4,
points B1 and B2 in Figure 9a) for compound 3 and O(3) and O(1W) (Figure 6, points B1
and B2 in Figure 10a) for compound 4, all of them are distributed around the middle of each
cluster and act as donors in the respective intracluster interactions (Table 2) and in parallel as
acceptors for the intercluster ones (Table 2). In all three clusters the donor atoms are the
oxygen atoms from non coordinated hydroxyl terminal groups of the Schiff base. In the case
of compound 1 these groups participate only in intercluster interactions but in the case of
compounds 3 and 4, they interact with the lattice solvent molecules (points B´´ and B4´, B5 in
Figures 9a and 10a respectively). Concluding the Sciff base used for this study could be used
as structural units to engineer lattices which could act simple as hosts ( compound 1) or as
functionalized host lattices (compound 3 and 4).
Figure 8. Hirshfeld surface analysis plots for compound 1. (a) HS decorated with dnorm
property. B1 and B2 points indicate the acceptor O(3) and O(2) atoms in the O(2)-
H(2O)···O(3) and C(8)-H(8)···O(2) hydrogen bonds respectively. B1’ and B2’ indicate the
hydrogen atoms H(2O) and H(8) in the respective hydrogen bonds. Fingerprint plots : (b) for
all type of interactions and (c) decomposed ones only for O···H/H···O type of interactions .
A (in (b)) indicate H···H conduct points. B and B’ (in (b) and (c)) indicate the areas of
contribution of conducts to the acceptor atoms and respective conducts to the Hydrogen atoms
26

bonded to the donor ones in the O···H/H···O type of interactions. C and C’ indicate the
analogous areas for C···H/H···C interactions.
Figure 9. Hirshfeld surface analysis plots for compound 3. (a) HS decorated with dnorm
property. B1, B2 and B3 indicate the acceptor O(13), O(1W) and O(14) atoms in the O(3)-
H(3O)···O(13) , O(14)-H(14O)···O(1W) and C(3)-H(3)···O(14) hydrogen bonds respectively
and B1’, B2’ and B3’ indicate the hydrogen atoms H(3O), H(14O) and H(3) in the same
hydrogen bonds. (b) HS decorated with Shape index. The white and pink ellipses indicate the
weak C···H/H···C interactions of C-H···π type i.e. C(11)- H(11A) and C(22)- H(22) with the
phenyl ring C(21)…C(26) and C(1)…C(6) respectively. Fingerprint plots: (c) for all type of
interactions, and decomposed ones (d) for O···H/H···O and (e) for C···H/H···C type of
interactions. A in (c) indicate areas of H···H conduct points. B, B’ [in (c), (d)] and C, C’ [in
(c), (e)] indicate areas with conducts to the acceptor atoms (unprimed ones) and areas (the
27

primed ones) with conducts to Hydrogen atoms of O···H/H···O and C···H/H···C type of
interactions respectively.
Figure 10. Hirshfeld surface analysis plots for compound 4. (a) HS decorated with dnorm
property. B1, B2 and B3 indicate the acceptor O(1W), O(3) and O(4) in the O(4)-
H(4)···O(1W), O(14)-H(14)···O(3) and O(23)-H(23)···O(4) hydrogen bonds respectively.
B1’, B2’ and B3’ indicate the hydrogen atoms H(4O), H(14O) and H(23O) in the respective
hydrogen bonds. B5 and B4’ indicate the O13 (acceptor) and H33O (hydrogen of donor O33
atom) for the following hydrogen bonds O1M-H10M···O13 and O33-H33O···O1M.
Fingerprint plots: (b) for all type of interactions and decomposed ones (c) for O···H/H···O
and (d) for C···H/H···C type of interactions. A in c) indicate areas of H···H conduct points.
28

B, B’ [in (b), (c)] and C, C’ [in (c), (d)] indicate areas with conducts to the acceptor atoms
(unprimed ones) and areas (the primed ones) with conducts to Hydrogen atoms of
O···H/H···O and C···H/H···C type of interactions respectively.
The basic structural units in compound 2 are the dinuclear complexes shown in Figure 3 and
present differences in their intermolecular interactions with respect to the other three
compounds studied in the present work. Based on fingerprint plot analysis of HS for
compound 2 the contribution for H···H, O···H/H···O, C···H/H···C and C···C type of
interactions are 58.6, 28.9, 6.2 % and 2.8 % respectively (Figure 11e). Figure 11a and 11b
present two views of the HS for compound 2 decorated with dnorm values and the intense red
points B1, B2, B3, B4 and B5 correspond to the acceptor oxygen atoms and the primed one
B1´, B2´, B3´, B4´ and B5´ to the hydrogen atoms of the donors for the hydrogen bonds
O(21)-H(21O)···O(42), O(2)-H(20)···O(24), C(2)-H(2B)···O(51), O(3)-H(30)···O(42) and
O(23)-H(230)···O(52). These hydrogen bond interactions contribute to the spikes observed in
the fingerprint plots at points B and B’ (Figure 11e and f) and are quite strong as the most of
the points lie in the cyan area below the green line (Figure 11f). In this case only the O(24)
(B2 point) act as an acceptor atoms from the hydroxyl groups of the Schiff base and all other
acceptor oxygen atoms belong to the deprotonated acetate oxygen atoms (O42, O51 and O52,
Figure 2). The views of HS presented in Figures 11a and 11b are along –a and along a axis
respectively, so these views present the dinuclear units down and opposite to direction of the
stacking axis (Figure 3a). Figures 11c and 11d present the HS of compound 2 decorated with
Shape index, and are the same views as those presented in Figures 11a and 11b. The circles in
Figures 11c and 11d indicate areas on the HSs with the characteristic blue and red triangles
for π···π interactions (Figure 11g).
29