Formation of a water-mediated assembly of two neutral copper(II) Schiff base fragments with a Cu2(NCS)4 moiety: Exploration of non-covalent C-H?π(bimetallo ring) interactions

Article abstract of DOI:10.1039/c7ce01473b

A water molecule is encapsulated in a dimeric assembly of a copper(ii) Schiff base complex with a Cu₂(NCS)₄ moiety. The structure has been confirmed by single crystal X-ray diffraction analysis. Thermogravimetric analysis has been performed to check the stability of the enclathrated water molecule. This theoretical study is devoted to analyzing the stabilization of the H₂O molecule in the cavity generated by the formation of the supramolecular dimer of the copper(ii) Schiff base moiety in the solid state. The Cu₂(NCS)₄ moiety exists as a bimetallic eight-membered ring, which behaves as a π-system establishing C-H?π interactions with two neighbouring copper(ii) Schiff base moieties. The molecular electrostatic potential (MEP) surface of the complex has been computed to rationalize the interaction from an electrostatic point of view.

Full text of DOI:10.1039/c7ce01473b

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Volume 18 Number 1 7 January 2016 Pages 1–184
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HIGHLIGHT
Tiddo J. Mooibroek, Antonio Frontera et al.
Towards design strategies for anion–π interactions in crystal engineering
rsc.li/crystengcomm

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Formation of a water mediated assembly of two neutral copper(II)
Schiff base fragments with Cu (NCS) moiety: Exploration of non-
2
4
covalent C-H···π(bimetallo ring) interactions
a
b
c
*c
Sourav Roy, Michael G. B. Drew, Antonio Bauzá, Antonio Frontera, Shouvik
*a
Chattopadhyay
a
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata - 700032, India.
Tel: +9133-2457-2941; E-mail:shouvik.chem@gmail.com
b
School of Chemistry, The University of Reading, P.O. Box 224, Whiteknights, Reading RG6 6AD,
United Kingdom,
c
Departamento de Química, Universitat de les Illes Balears, Crta. deValldemossa km 7.5, 07122
Palma, Baleares, Spain. E-mail: toni.frontera@uib.es
Abstract: A water molecule is encapsulated in a dimeric assembly of a copper(II) Schiff base
complex with a Cu (NCS) moiety. The structure has been confirmed by single crystal X-ray
2
4
diffraction analysis. Thermo-gravimetric analysis has been performed to check the stability of
the enclathrated water molecule. The theoretical study is devoted to analyze the stabilization
of the H O in the cavity generated by the formation of the supramolecular dimer of the
2
copper(II) Schiff base moiety in the solid state. Cu (NCS) moiety exists as a bimetallic eight-
2
4
membered ring, which behaves as a π-system establishing C-H···π interactions with two
neighbouring copper(II) Schiff base moieties. The molecular electrostatic energy (MEP) surface

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of the complex has been computed to rationalize the interaction from an electrostatic point of
view.
Keywords: Copper(II); Multimetallic; Schiff base; Enclathrated water; C-H···π interactions; DFT
studies.
Introduction
Mononuclear transition metal complexes with various salen type Schiff bases were
1
prepared by our group and many other groups since long. Many of such complexes were found
application in biological modelling experiment e.g. to mimic catechol oxidase, phenoxazinone
2
synthase, catalase etc. DNA binding and DNA cleavage activities of such complexes were also
3
explored. Non-covalent interactions (e.g. C-H···π, π···π, cation···π, anion···π etc.) in many such
4
complexes were investigated using various theoretical calculations. These mononuclear
complexes were used as ligand (i.e. metalloligand) by various groups to form many homo and
5
hetero polynuclear complexes. Presence of inner N O and outer O cavities, capable of
2
2
4
accommodating different metal ions, made N O donor salen type compartmental Schiff bases
2
4
6
more attractive for preparing polynuclear complexes in recent past. Several mixed valence
7
complexes were also prepared with these salen type compartmental ligands. Mononuclear
transition metal complexes with various potential N O donor salen type compartmental Schiff
2
4
bases could also be assembled by ammonium ion or water molecule, placed in the O cavity of
4
8
the ligand. However, this area has not been explored in detail till date.
In the present work, a potential N O donor compartmental Schiff base [N,N'-bis(3-
2
4
ethoxysalicylidene)propane-1,3-diamine] has been used to prepare a copper(II) complex using

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copper(II) acetate monohydrate. The Schiff base ligand encompasses a copper(II) ion in its
9
N O donor inner compartment, and two of these “ligand complexes” provide an octadentate
2
2
crown ether type coordination set (through the outer O compartments) to encapsulate a water
4
molecule. The complex crystallizes with a discrete Cu (NCS) moiety.
2
4
The energetic features of H O encapsulation via dimer formation have been studied by
2
means of DFT calculations and the Bader’s theory of atoms-in-molecules. Theoretical
calculations are important in terms of finding many unconventional and rare interactions which
can be very important in stabilizing the complex. The energy of C-H···π interaction between the
hydrogen atoms of the ligand and the π-system of the bimetallic eight-membered planar ring of
the Cu (NCS) moiety has also been investigated. To our knowledge, this is the first study
2
4
dealing with this unconventional C-H···π interaction that involves the π-system of a ring formed
by two μ -pseudohalide ligands and two copper(II) centers.
1,3
Results and Discussion
Synthesis
1
,3-diaminopropane was refluxed with 3-ethoxysalicylaldehyde in 1:2 ratio to form a
1
0
potential N O donor Schiff base ligand, H L, following the literature method. This Schiff base,
2
4
2
(H2L) on reaction with copper(II) acetate monohydrate and nickel(II) thiocyanate tetrahydrate,
respectively formed the complex, [(CuL) ⊂(H O)][Cu (μ -NCS) (NCS) ], in which copper(II) is
2
2
2
1,3
2
2
placed in the inner N O compartment of the ligand and a water molecule is trapped in the O
4
2
2
compartments of two adjacent CuL moieties. Formation of the complex is shown in Scheme 1.
On the other hand, use of copper(II) acetate monohydrate and sodium thiocyanate produced a

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trinuclear Cu/Na/Cu cationic unit and copper(I) thiocyanate anionic counterpart, the structure
1
1
of which was reported by a different group.
Scheme 1: Preparation of the ligand and the complex.
The ligand has been used by various groups to prepare varieties of di, tri and
+x
+y
+z
tetranuclear complexes of the types [(TrL)M] , [(TrL)M(LTr)] or [(TrL) M )] {Tr= any
2
2
1
1,12
transition metal M = any metal} (Table 1).
However, in no case, water molecule or any other
non-metallic cation is trapped in the outer O cavity of the ligand. Scheme 2 gathers all such X-
4
1
1,12
ray characterized complexes.
On the other hand, the present complex also possesses a
dinuclear cyclic Cu (NCs) unit in it. Formation of bimetallic eight-membered ring (Cu-N-C-S-Cu-
2
4
N-C-S-) of Cu (NCs) , therefore, deserves special attention from both synthetic inorganic
2
4
chemists and theoretical chemists as well and lead us to estimate the energy of C-H···π
interaction between the hydrogen atoms of the ligand and the π-system of this bimetallic eight-
membered planar ring.

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+x
Table 1: X-ray characterized di, tri and tetranuclear complexes of the types [(TrL)M] ,
+y
+z
[
(TrL)M(LTr)] or [(TrL) M )] {Tr= any transition metal, M= any metal} retrieved from
2 2
Cambridge Structural Database (CSD), version 5.38 updates (November 2016). H L = [N,N'-bis(3-
2
ethoxysalicylidene)propane-1,3-diamine].
Complex
CCDC code
LAVWEN
LAVWIR
YILHEI
Ref
12a
12a
12b
12c
12d
12d
11
[
(SCN)ClCd(L)Ni(DMF)2]
[
(SCN)(CH CO )Cd(L)Ni(CH OH) ]
3 2 3 2
[
(CH CN)Cu(L)(UO )(NO ) ]
3 2 3 2
[
Zn L(NCS)(OOCCH )(CH OH) ]
VIRJAJ
2
3
3
2
[
CuLZnCl2]
EXASIG
[
CuLZnBr2]
Na(CuL) ][Cu (μ -NCS) ]
3 n
EXATON
KEYWOC
ESOSAI
[
2
2
1,3
[
(CH CO ) Ni (L) Cd (NCS) ]
4
3
2 2
2
2
2
2
[
(DMSO) Ni(L)Cd(NCS)(μ1,3-SCN)Ni(DMSO)(L)Cd(NCS)2]
ESOSEM
FAKLOT
4
2
[
{(CH ) CO}Cu(L)Gd(NO ) ]
12e
3
2
3 3

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Scheme 2: X-ray characterized di, trinuclear and tetranuclear complexes with ligand H L, where,
2
H2L = [N,N'-bis(3-ethoxysalicylidene)propane-1,3-diamine].
Structure description
Single crystal X-ray diffraction analysis reveals that the complex crystallizes in triclinic
space group P . The molecular formula of the complex is [(CuL) ⊂(H O)][Cu (μ -NCS) (NCS) ].
2
2
2
1,3
2
2
It is to be noted here that an investigation has been done whether the crystallography could be
used to determine whether the three metal atoms could be identified as copper or nickel. We

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refined the structure with four combinations and obtained the following wR2 values (all data);
Cu1, Cu2, Cu3: 0.0998; Cu1, Cu2, Ni3: 0.1032; Ni1, Ni2, Cu3: 0.1008 and Ni1, Ni2, Ni3: 0.0985.
The R1 values with I > 2*sigma(I) are 0.0551, 0.0564, 0.0557, 0.0551 respectively. Clearly the
metal assignation from these values is problematic though it seems likely that the metal atoms
are either all copper or all nickel. However, tricoordinated nickel(II) is very much unusual,
especially with non-bulkier ligand, and therefore, all metal centres are identified as copper(II).
The moiety [(CuL) ⊂(H O)] consists of two neutral [CuL] parts which are strongly
2
2
hydrogen bonded with a water molecule encapsulated between the two. The hydrogen atoms
of the enclathrated water molecule are disordered and three sets of positions were used to
refine both hydrogen atoms with occupancies of 0.33(1) for each site. A perspective view of the
complex is shown in Figure 1. Important bond lengths and bond angles are listed in Table 2 and
Table 3 respectively.
Table 2: Selected bond lengths (Å) of the complex.
Cu(3)-S(2)
Cu(3)-N(1)
2.417(2)
1.871(3)
1.891(3)
1.913(2)
1.916(2)
1.974(2)
Cu(2)-N(23)
Cu(1)-N(53)
Cu(1)-O(41)
Cu(1)-N(49)
Cu(1)-O(61)
-
1.970(2)
1.986(3)
1.914(2)
1.968(2)
1.928(2)
-
a
Cu(3)-N(2)
Cu(2)-O(11)
Cu(2)-O(31)
Cu(2)-N(19)
a
Symmetry transformations: = -x, -y, 2-z.
Table 3: Selected bond angles (°) of the complex.
S(2)-Cu(3)-N(1)
112.06(9)
104.14(9)
143.78(12)
O(31)-Cu(2)-N(23)
O(41)-Cu(1)-O(61)
O(41)-Cu(1)-N(49)
90.55(9)
a
S(2)-Cu(3)-N(2)
N(1)-Cu(3)-N(2)
81.43(8)
a
91.31(10)

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O(11)-Cu(2)-O(31)
O(11)-Cu(2)-N(19)
O(11)-Cu(2)-N(23)
N(19)-Cu(2)-N(23)
O(31)-Cu(2)-N(19)
81.58(8)
92.24(9)
O(41)-Cu(1)-N(53) 170.30(10)
O(61)-Cu(1)-N(49) 169.60(10)
169.62(9)
96.41(10)
170.37(9)
N(49)-Cu(1)-N(53)
O(61)-Cu(1)-N(53)
96.64(10)
91.36(9)
-
-
a
Symmetry transformations: = -x, -y, 2-z.
H L is a potential N O donor compartmental Schiff base having inner N O and outer O
4
2
2
4
2
2
compartments with copper(II) occupying the inner N O cavity. The outer O compartment
2
2
4
remains vacant. Different small molecules (acting as guests) may be encapsulated (with the
help of hydrogen bonding interaction) in this vacant O compartment (acting as host). Thus
4
1
3
interesting host-guest complexes may be formed. In the present case, the outer O cavities of
4
two CuL moieties behave as host site to encapsulate water molecule (guest) leading to the
formation of a host-guest complex, [(CuL) ⊂(H O)]. In this unit, both copper(II) centers assume
2
2
square planar geometry. They [Cu(1) and Cu(2)] are coordinated with two imine nitrogen atoms
N(49), N(53) for Cu(1) and N(19), N(23) for Cu(2)] and two phenoxo oxygen atoms [O(41),
[
O(61) for Cu(1) and O(31),O(11) for Cu(2)] of the deprotonated Schiff bases. The copper(II)
centers are located almost exactly on the mean basal plane of the ligand cavity [deviation of
only 0.008Å for Cu(1) and 0.007Å for Cu(2)]. The trans angles O(61)-Cu(1)-N(49) and O(41)-
Cu(1)-N(53) are 169.6(1)° and 170.3(1)° respectively for Cu(1). For Cu(2), the trans angles O(11)-
Cu(2)-N(23) and O(31)-Cu(2)-N(19) are 169.6(1)° and 170.3(1)° respectively. These values
indicate slight distortion from perfect square planar geometry around copper(II) centers.
Saturated six membered chelate ring [Cu(1)–N(49)–C(50)–C(51)–C(52)–N(53)] has envelope
1
4
conformation with puckering parameters q = 0.567(4) Å; θ = 56.4(3)°;
φ = 166.6(4)°. Another

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saturated six membered chelate ring [Cu(2)–N(19)–C(20)–C(21)–C(22)–N(23)] has half-chair
1
4
conformation with puckering parameters q = 0.614(3) Å; θ = 116.3(3)°; φ = 30.5(3)°.
The moiety, [Cu (μ -NCS) (NCS) ], contains an eight-membered metallacyclic loop,
2
1,3
2
2
a
a
a
a
a
[
Cu(3)-S(2)-C(2)-N(2)-Cu(3) -S(2) -C(2) -N(2) ] {symmetry transformation; = -x, -y, 2-z}. The
a
copper(II) centers [Cu(3) and Cu(3) ] assume trigonal planar geometry being coordinated by one
a
a
a
nitrogen and one sulphur atom, [N(1) and S(2) for Cu(3) and N(1) and S(2) for Cu(3) ] of two
a
a
thiocyanate anions and one nitrogen atom [N(2) for Cu(3) and N(2) for Cu(3) ] of a symmetry
related thiocyanate anion. The distance between two copper(II) centers is 5.127(7) Å.
Figure 1: Perspective view of the complex with selective atom numbering scheme. Hydrogen
atoms (except the water hydrogens) have also been omitted for clarity. Only one fraction of
each disordered hydrogen atom of the enclathrated H O is shown for clarity. Symmetry
2
a
transformations: = -x, -y, 2-z.

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Theoretical Study
The theoretical study is devoted to analyze the stabilization of the H O molecule in the
2
cavity generated by the formation of the supramolecular dimer of the CuL complex in the solid
state. The molecular electrostatic energy (MEP) surface of the complex has been computed first
to rationalize the interaction from an electrostatic point of view (Figure 2). As expected the
surface shows a red colored isocontour at the region of the four coplanar oxygen atoms of the
ligand, indicating the MEP value is large and negative (–80 kcal/mol). Since the MEP values are
plotted onto the van der Waals surface, the plot also reveals that the size of the cavity is too
small to accommodate the H O molecule. The most positive region are located at the axial
2
positions of the square planar copper(II) atom (+33 kcal/mol).
Figure 2: Molecular electrostatic potential (MEP) surfaced of the complex (isosurface value
0
.002 a.u.). The MEP energies are selected points are also indicated in kcal/mol.
As aforementioned, the complex forms a supramolecular dimer that is able to
encapsulate H O. The interaction energy of this assembly has been computed considering first
2

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the formation of the dimer and then the interaction of the water (Figure 3) in order to evaluate
the different contributions separately. The dimerization energy is –8.5 kcal/mol and both CuL
moieties interact by means of π···π interactions involving both the aromatic and chelate rings,
along with other long range van der Waals interactions. The interaction of the water with the
dimer is weak (-0.9 kcal/mol) due to the compensating effect of (i) the energetically favourable
hydrogen bonds and the (ii) electrostatic repulsion between the lone pairs at the oxygen atom
and the negative surfaces of the CuL moieties. It should be mentioned that in the crystal
structure, the water molecule is disordered because the hydrogen atoms of H O may establish
2
hydrogen bonds with any of the eight oxygen atoms of the cavity. For the calculations, only one
of both orientations has been considered as shown in Figure 3c.
Figure 3: (a) Dimerization of the CuL complex. (b) Detail of the stacking interaction between
two CuL moieties (c) Interaction energy of H O with the CuL dimer. The water molecule has
2
been represented in space-filled model. Distance in Å.
The AIM analysis, has been used to study the complexion of the H O with the dimer. The
2
distribution of bond critical points (CP) and bond paths are represented in Figure 4, where the
ring and cage CPs have been omitted for the sake of clarity. The existence of a bond CP and
bond path connecting two atoms is an unambiguous evidence of interaction. The AIM

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distribution shows that four bond CPs connect both hydrogen atoms of water to four oxygen
atoms of the ligand, thus characterizing the bifurcated hydrogen bonds. Moreover, several
atoms of the aromatic ring of one CuL complex are inter-connected to the copper(II)-chelate
ring of another complex and vice-versa via five bond CPs, thus confirming the existence and
participation of this unconventional π···π(chelate ring) in the formation of the supramolecular
dimer.
Figure 4: AIM distribution of bond CPs (red spheres) and bond paths in the assembly of the
complex. Some bond CPs and bond paths involving the ethyl arms have been omitted for
clarity. The full distribution is shown in the ESI (Figure S1).
The role of the [Cu (NCS) ] moiety in the solid state of the complex has also been
2
4
analyzed. Interestingly, it establishes C-H···π interactions with two neighbouring CuL moieties
a
(
Figure 5a) where the π-system is a bimetallic eight-membered [Cu(3)-S(2)-C(2)-N(2)-Cu(3) -
a
a
a
a
S(2) -C(2) -N(2) ] {symmetry transformation; = -x, -y, 2-z} ring. Remarkably, two hydrogen
atoms of each organic ligand point to the middle of the ring leading to the formation of

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supramolecular trimers. To our knowledge, this is the first report describing this type
interaction involving two metal centers and two μ -bridging pseudohalide ligands. The
1
,3
interaction energy for the 1:1 complex is -3.5 kcal/mol (Figure 5b), which is remarkable for this
type of bonding. Moreover, the C-H···π distances are very short (2.43 and 2.99 Å, measured
from the hydrogen atoms to the mean plane). Finally, the AIM analysis of CPs and bond paths in
this C-H···π supramolecular complex has also been computed. It reveals that four hydrogen
atoms participate in the interaction that are connected to the sulfur and copper atoms of the
bimetallic ring and confirming the existence of the C-H···π(bimetallo ring) noncovalent bonding.
The interaction is further characterized by the presence of one ring CP (yellow sphere) as a
consequence of the formation of a supramolecular ring.
Figure 5: (a) X-ray fragment of the complex. Distances in Å. (b) AIM distribution of bond and
ring CPs (red and yellow spheres, respectively) and bond paths in the model of the complex.
The interaction energy is also indicated.

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Spectral and magnetic properties
A sharp band around 1610 cm due to azomethine (C=N) group is routinely noticed in
-
1
1
5
-1
-1
the IR spectrum of the complex. Two strong bands at 2083 cm and 2112 cm in IR spectrum
1
6
of the complex indicate the presence of end-to-end bridged thiocyanate. Band around 2929
-
1
17
cm in the IR spectrum of the complex is observed due to alkyl C-H bond stretching. A broad
-
1
band around 3432 cm in the IR spectrum of the complex is observed due to O-H bond
1
8
stretching of water molecule.
Electronic spectrum of the complex consists of four bands around 235 nm, 281 nm, 372
nm and 606 nm respectively. In general, square planar copper(II) complex is expected to exhibit
2
2
2
2
2
2
19
three bands corresponding to A ← B , B ← B and E ← B transitions. But in many
1g
1g
2g
1g
g
1g
cases, the long tail of strong inter-ligand charge transfer transitions hides some or all of these
bands. Broad absorption band around ~600 nm may be assigned to two superimposed
2
2
2
2
19
transitions B ← B and E ← B
The broad absorption ~372 nm may be assigned as ligand
2
g
1g
g
1g.
2
0
to metal charge transfer transition. Bands ~281 nm and ~235 nm may be assigned as ligand
*
*
21
centered π ←n and π ←π transitions respectively. Lack of any electronic transition at longer
wavelengths (over 650 nm) indicates a large crystal-field splitting as expected for Schiff base
2
2
complexes.
X-ray diffraction of powdered sample
The experimental PXRD pattern of the bulk product is in good agreement with the
simulated XRD pattern from single crystal X-ray diffraction results, indicating consistency of the
bulk sample. The simulated pattern of the complex is calculated from the single crystal

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structural data (cif) using the CCDC Mercury software. The experimental and simulated PXRD
patterns of the complex are shown in Figure 6.
Figure 6: Experimental and simulated PXRD patterns of the complex confirming purity of the
bulk material.
Thermo-gravimetric analysis
The thermal behaviour of the complex has been studied in a dynamic nitrogen
-
1
-1
atmosphere (100 mL min ) at a heating rate of 10°C min using thermo-gravimetric (TG)
technique. The thermo-gravimetric plot for the complex is given in Figure 7. The complex is
stable up to ~60 °C. A weight loss of 1.73% for the complex in the temperature range of 70-
1
00°C corresponds to loss of the enclathrated water molecule (calc. 1.82%). An exothermic

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peak is also observed in the corresponding DTA curve for the complex, as expected. The
dehydrated complex then decomposes ~250°C as indicated by huge weight loss in the TG curve.
Figure 7: Thermal analysis of the complex. Inset shows the highlighted blue rectangle.
Hirshfeld surface analysis
Hirshfeld surfaces of the complex, mapped over dnorm (range of -0.1 to 1.5 Å), shape
index and curvedness, are illustrated in Figure 8. Red spots on the dnorm surface (Figure 8)
indicate the interaction between sulphur and hydrogen atoms. O···H and N···H contacts are also
observed in the Hirshfeld surfaces as smaller visible spots of light colour indicating weaker and
longer contact. The intermolecular interactions appear as distinct spikes in the 2D fingerprint
plot are shown in Figure 9.

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Figure 8: Hirshfeld surfaces mapped with dnorm (left), shape index (middle) and curvedness
right) of the complex.
(
Figure 9: Fingerprint plot: Full (top left), resolved into H···S/S···H (top right), H···O/O···H (bottom
left) and H···N/N···H (bottom right) contacts contributed to the total Hirshfeld Surface area of
the complex.

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Concluding Remarks
Synthesis and characterization of a multi-metallic complex, [(CuL) ⊂(H O)][Cu (μ -
2
2
2
1,3
NCS) (NCS) ], has been described in this paper. This complex is unique in the sense that two
2
2
molecules of a simple Cu-salen type monomeric complex (CuL) are utilized in this complex to
trap a water molecule by strong H-bonding interactions. The energetic features of the dimer
formation and water molecule encapsulation have been studied by means of DFT calculations.
Bader’s theory of atoms-in-molecules has been used to characterise the interactions. On the
other hand, the π-system of the bimetallic eight-membered planar ring (Cu-N-C-S-Cu-N-C-S-Cu)
of the moiety [Cu (μ -NCS) (NCS) ] is also linked with the hydrogen atoms of CuL moieties by
2
1,3
2
2
unconventional C-H···π interaction. The energetic features of this interesting C-H···π interaction
has also been analysed with the help of DFT calculation. Remembering the various roles of
water in chemical and biological systems, the present findings may serve as a prototype for
synthesizing and stabilizing enclathrated water molecules in many other complexes.
Experimental Section
Nickel(II) thiocyanate tetrahydrate was prepared in our laboratory following the
2
3
literature method. All other materials were commercially available, reagent grade and used as
purchased from Sigma-Aldrich without further purification.
Synthesis
Synthesis of the complex [(CuL)2⊂(H O)][Cu (μ -NCS) (NCS) ]
2 2 1,3 2 2
A potential N O donor ligand, H L, was prepared by refluxing 3-ethoxysalicylaldehyde
2
4
2
(332 mg, 2 mmol) and 1,3-diaminopropane (0.13 mL, 1 mmol) in methanol for ca. 1 h. The

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ligand was not isolated and used directly for the synthesis of the complex. A methanol (10 mL)
solution of copper(II) acetate monohydrate (200 mg, 1.01 mmol) was added to the methanol
solution (20 mL) of H L. The resulting solution was stirred for 15 min. A methanol (20 mL)
2
solution of nickel(II) thiocyanate tetrahydrate (500 mg, 2.02 mmol) was added to the methanol
solution (20 mL) of H L. The resulting solution was stirred for 2 hr. Single crystals, suitable for X-
2
ray diffraction, were obtained after 3-4 days on slow evaporation of the solution in open
atmosphere.
Yield: 274 mg (52%); based on copper(II). Anal. Calc. for C H N Cu O S (FW =
4
4
50
6
3 9 2
-
1
1
061.67): C, 44.51; H, 4.06; N, 9.03; Found: C, 44.7; H, 3.8; N, 9.2%. FT-IR (KBr, cm ): 1610
-
1
-1
(
C=N); 2083, 2112 (NCS); 3432 (O-H); 2929 (C-H). UV-VIS [λmax(nm)] [εmax(Lmol cm )]
5
4
3
2
(
acetonitrile): 235 (2.4×10 ); 281 (6.7×10 ); 372 (19.9×10 ); 606 (5.9×10 ). ESI-MS (positive ion
+
+
mode, acetonitrile) m/z: 454.09 [Cu(L)Na] , 886.19 [{Cu(L)} Na] .
2
Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were performed using a Perkin
-
1
Elmer 240C elemental analyzer. IR spectrum in KBr (4500-500 cm ) was recorded with a Perkin
Elmer Spectrum Two spectrophotometer. Electronic spectrum in acetonitrile was recorded on a
Perkin Elmer Lambda 35 UV-visible spectrophotometer. Steady state photoluminescence
spectrum in acetonitrile was obtained in Shimadzu RF-5301PC spectrofluorometer at room
temperature. Time dependent photoluminescence spectrum was recorded using Hamamatsu
MCP photomultiplier (R3809) and was analyzed by using IBHDAS6 software. The emission in the
complex was tentatively attributed to intra-ligand transitions modified by metal coordination.

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exp −
t
Intensity decay profile was fitted to the sum of exponential series ( ) ∑i αi
I t =
(
)
τi
, where
αi was a factor representing the fractional contribution to the time resolved decay of the
component with a lifetime of τi. A bi-exponential function was used to fit the decay profile of
2
the complex, with obtaining χ close to 1. The intensity-averaged lifetime (τav) was determined
2
i
∑i αiτ
∑i αiτ
from the result of the exponential model using τav
=
, where α and τI are the pre-
i
i
exponential factors and excited state luminescence decay time associated with the i-th
component, respectively. The instrument was calibrated using metallic nickel. Powder X-ray
diffraction measurement was obtained on a Bruker D8 instrument with Cu K , (λ =1.5406 Å)
α
radiation. In this process, the complex was ground with a mortar and pestle to fine powders
which were then dispersed with alcohol onto a zero background holder (ZBH). The alcohol was
allowed to evaporate to provide an even coating of powder adhered to the sample holder.
Mass spectrum was recorded in acetonitrile on an XEVO G2QTof spectrometer (Waters) with an
electron spray ionization source. The TGA/DTA curves of the complex was recorded using a SDT
−1
Q600 TA instruments, with nitrogen as purge gas at a flow rate of 100 ml min . The complex
o
−1
was heated from 20 to 500 C at a rate of 10 °C min .
X-ray crystallography
Suitable single crystal of the complex was picked, mounted on a glass fibre and
diffraction intensities were measured with an Oxford Diffraction XCalibur diffractometer
equipped with Mo K radiation (λ =0.71073 Å, 50 kV, 40 mA) at an ambient temperature (150
α

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2
4
K). Data collection and reduction were performed with the Crysalis software. The structure of
2
the complex was solved by direct methods and refined by full-matrix least squares on F , using
2
5
the SHELXL-2016/6 package. Non-hydrogen atoms were refined anisotropically. Hydrogen
atoms attached with oxygen atoms were located by difference Fourier maps. All other
hydrogen atoms were placed in their geometrically idealized positions and constrained to ride
2
6
27
28
on their parent atoms. Programs used included PLATON, DIAMOND, ORTEP and
2
9
MERCURY. Details of crystallographic data and refinement are given in Table 4.
Table 4: Crystal data and refinement details of the complex.
Formula
Formula Weight
Temperature(K)
Crystal system
Space group
a(Å)
C H N Cu O S
44 50 6 3 9 2
1
061.67
50
1
Triclinic
P
1
2.4225(7)
3.0816(9)
5.8045(9)
b(Å)
1
1
c(Å)
α
(deg)
6
6.690(6)
2.340(5)
4.193(5)
2
β(deg)
7
γ(deg)
8
Z
-
3
d (g cm )
calc
1
1
.569
.562
-
1
μ(mm )
F(000)
1
094
Total Reflections
1
6054

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Unique Reflections
1
2604
Observed data [I >2σ (I)]
No. of parameters
R(int)
9
609
5
99
0
.028
R1, wR2 (all data)
R1, wR2 [I > 2 σ (I)]
0
0
.0803, 0.0998
.0551, 0.0921
Theoretical methods
The calculations of the non-covalent interactions were carried out using the Turbomole
.0 and the M06-2X/def2-TZVP level of theory. The interactions in the solid state were
evaluated using the crystallographic coordinates. This procedure and level of theory were
3
0
7
3
1
successfully used to evaluate similar interactions. The interaction energies were computed by
calculating the difference between the energies of isolated monomers and their assembly. The
interaction energies were calculated with correction for the basis set superposition error (BSSE)
3
2
by using the Boys–Bernardi counterpoise technique. The molecular electrostatic potential
3
3
surfaces were computed using the SPARTAN software. The Bader’s “atoms-in-molecules”
3
4
analysis were performed at the same level of theory, using the AIMAll program.
Hirshfeld surfaces
3
5
36
The Hirshfeld surface of the complex was determined using Crystal Explorer. The
normalized contact distance (dnorm) based on d and d was given by,
e
i
Error! Reference source not found.

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vdw
vdw
where ri and re are the van der Waals radii of the atoms. d and d represent the distances
e
i
from the point to the nearest nucleus external and internal to the surface respectively. The
dnorm values were mapped on to the Hirshfeld surface, where red colour is used to highlight
shorter contacts, white colour is used for contacts at distances around the vdW separation and
blue colour is used for longer contacts. 2D-fingerprint plots of Hirshfeld surface were also
shown as plots of d against d .
i
e
Notes and References
CCDC 1561200 contains the supplementary crystallographic data for the complex.
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