Construction of heterometallic and mixed-valence copper(I/II) chloride π-complexes with 1,2,4-triazole allyl-derivative

Article abstract of DOI:10.1016/j.ica.2019.119012

Copper(I) coordination compounds with allyl-derivatives of various heterocycles are an interesting subject of current research, however, the possibility of exploiting a second metal cation (i.e. obtaining heterobimetallic complexes) as a tool for crystal

Full text of DOI:10.1016/j.ica.2019.119012

Accepted Manuscript
Construction of Heterometallic and Mixed-Valence Copper(I/II) Chloride π-
Complexes with 1,2,4-Triazole Allyl-Derivative
Oleh R. Hordiichuk, Yurii I. Slyvka, Vasyl V. Kinzhybalo, Evgeny A.
Goreshnik, Tamara J. Bednarchuk, Oleksandr Bednarchuk, Jarosław Jedryka,
Iwan Kityk, Marian G. Mys'kiv
PII:
S0020-1693(19)30666-8
https://doi.org/10.1016/j.ica.2019.119012
119012
DOI:
Article Number:
Reference:
ICA 119012
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
14 May 2019
8 July 2019
10 July 2019
Please cite this article as: O.R. Hordiichuk, Y.I. Slyvka, V.V. Kinzhybalo, E.A. Goreshnik, T.J. Bednarchuk, O.
Bednarchuk, J. Jedryka, I. Kityk, M.G. Mys'kiv, Construction of Heterometallic and Mixed-Valence Copper(I/II)
Chloride π-Complexes with 1,2,4-Triazole Allyl-Derivative, Inorganica Chimica Acta (2019), doi: https://doi.org/
10.1016/j.ica.2019.119012
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Construction of Heterometallic and Mixed-Valence Copper(I/II) Chloride π-
Complexes with 1,2,4-Triazole Allyl-Derivative
Oleh R. Hordiichuka, Yurii I. Slyvkaa, Vasyl V. Kinzhybalob, Evgeny A. Goreshnikc,
Tamara J. Bednarchukb, Oleksandr Bednarchukb, Jarosław Jedrykad, Iwan Kitykd,e, Marian G.
Mys’kiva,*
aDepartment of Inorganic Chemistry, Ivan Franko National University of Lviv, Kyryla I Mefodiya 6,
79005 Lviv, Ukraine
bInstitute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-
422 Wrocław, Poland
cDepartment of Inorganic Chemistry and Technology,“Jožef Stefan” Institute, Jamova 39, 1000,
Ljubljana, Slovenia
dInstitute of Optoelectronics and Measuring Systems, Faculty of Electrical Engineering,
Czestochowa University of Technology, Czestochowa, Poland
eInstitute of Solid State Physics, Eastern European University, Voli 6, Lutsk, Ukraine
*Corresponding author. Tel.: +380322394506; e-mail: marian.myskiv@lnu.edu.ua (M. G. Mys’kiv)
Highlights:
 A family of heterometallic and mixed-valence copper(I) π-complexes studied
 New synthetic routes explored & crystal structures construction details discussed
 Magnetic properties of coordination compounds studied and discussed
 Laser stimulated non-linear optics studied
Abstract: Copper(I) coordination compounds with allyl-derivatives of various
heterocycles are the interesting subject of current research, however, the possibility of
exploiting a second metal cation (i.e. obtaining heterobimetallic complexes) as a tool
for crystal engineering of copper(I) π-complexes was virtually uninvestigated. In this
work we report the synthesis, structure, magnetic and non-linear optical properties of
a family of heterometallic (CuI – AgI, CuI – ZnII, CuI – FeII) and mixed-valence (CuI –
CuII) copper(I) η2-π-complexes with an 3-allylsulfanyl-4-allyl-5-phenyl-4H-1,2,4-
triazole (L). The structures of obtained complexes can be considered as consisting of
two subunits: cationic organometallic moiety formed by Cu(I) ions, and anionic
inorganic fragments. The anionic part, formed by the second metal cation, determines
the dimensionality of a crystal structure – it either connects two copper(I) ions in a

bridging mode within the organometallic moiety leading to the 0D structure (in the
case of CuI – ZnII & CuI – FeII), or links cationic organometallic dimers into the 1D
ladder (CuI – AgI & CuI – CuII). Magnetic properties of mixed-valence Cu(I/II) and
heterometallic Cu(I)/Fe(II) coordination compounds were studied and discussed.
Separate studies have been done for the laser stimulated nonlinear optics.
Keywords: copper(I); η2-interaction; heterometallic; 1,2,4-triazole; allyl derivative;
crystal structure.
1. Introduction
Copper(I) π-coordination compounds with allyl-derivatives of various
heterocycles are becoming more and more appealing objects for modern
interdisciplinary research in view of catalytic, anticancer, photoluminescent,
ferroelectric and nonlinear optical properties of such compounds [1–12]. Adding the
conformationally flexible allyl group (which forms the strongly directed
Cu(I)‒(C═C) interaction) into a rigid heterocyclic core enables both chelating and
bridging functions for a ligand simultaneously and creates vast opportunities for
crystal structure engineering. By virtue of new synthetic approaches, based on allyl-
substituted azoles, a number of π-complexes with unknown or unstable in a free state
Cu(I) salts (CuHSO4, Cu2SiF6, Cu(NH2SO3) etc) have been obtained and unique
2-
inorganic fragments (such as the first case of Cu(I) – F(SiF6 ) interaction) have been
discovered [13–18].
We wondered whether it would be possible to incorporate other metal-based
fragments into the structure while preserving π-coordination of Cu(I). This would
enrich possibilities for purposeful control of composition and crystal structure
through the choice of a metal cation with an appropriate electronic configuration and
coordination geometry [19–21]. Obviously, the presence of a second metal ion in a
structure can lead to distinct from such of monometallic Cu(I) π-complexes
properties, which might emerge either due to the nature of an ion (e.g. paramagnetism
of Fe ions), or because of the ion’s structural role in a complex. There are numerous
literature reports on the exceptional properties of heterometallic complexes which

rely on the interplay between distinct coordination centers formed by different metal
ions [21–25]. However, heterometallic Cu(I) π-complexes remain virtually
unexplored, while they might be of a significant importance in view of catalytic,
optical and biological properties.
Organometallic complexes containing Cu are particularly interesting for the
laser stimulated nonlinear optical properties [26, 27]. Organometallic compounds are
fundamentally different from typical organic NLO chromophores because of a variety
of possible optical transitions they may exhibit: charge transfers from ligand to metal
and from metal to ligand, intra-molecular charge transfer, and d-d electronic
transitions [28]. These transitions as well as transitions present in an organic system
depend on the interaction of metal d-orbitals with the electronic system of the ligand.
In the end, it leads to an enhancement of the third order susceptibility (χ(3)) and
optimization of a chromophore for NLO applications [29].
We succeeded to obtain and to study a series of unique heterobimetallic CuI –
AgI, CuI – ZnII, CuI – FeII and mixed-valence CuI – CuII complexes with an 1,2,4-
triazole
allyl-derivative:
[Cu2(L)2Ag2Cl4]
(1),
[CuI2(L)2CuII Cl6]
(2),
2
[Cu2(L)2ZnCl4]∙2CH3CN (3) and [Cu2(L)2FeCl4]∙2CH3CN (4) (were L – is 3-
allylsulfanyl-4-allyl-5-phenyl-4H-1,2,4-triazole). According to the Cambridge
Structural Database, there have been no π-complexes of Cu(I) with any allyl-
derivatives containing silver or zinc and there has been only one structure containing
iron chloride [30]. The compound 2 is the first example of mixed-valence CuI – CuII
complexes with 1,2,4-triazole allyl-derivatives.
In this report, we demonstrate how the incorporation of a second metal ion into
the Cu(I) π-complex leads to the rearrangement of the crystal structure and thus can
be used as a tool for crystal engineering. The influence of the second metal ion on
physical properties is illustrated by magnetic and non-linear optical properties of the
complexes.
2. Experimental section
2.1. Materials and instrumentation

Unless mentioned otherwise, all chemicals were obtained from commercial
1
sources and used without further purification. The NMR experiments: H NMR (500
13
MHz), C{1H} NMR (125 MHz) for 1,2,4-triazole L were recorded on a Bruker
Avance 500 MHz NMR spectrometer. The chemical shifts are reported in ppm
1
13
relative to the residual peak of the deuterated CD3CN for the H and C{1H} NMR
spectra. The infrared (IR) spectra were recorded on the Bruker IFS-88 spectrometer
for 2-4 and on FT-IR Spectrum BX-II (Perkin Elmer) for L in nujol mulls. EDS
analyses for 3 and 4 were performed using Tecnai G2 F20 X-TWIN equipment (see
supplementary materials). Diffraction data for 2 were collected on an Agilent Gemini
A four-circle diffractometer equipped with an Atlas CCD detector. Diffraction data
for 1, 3 & 4 were collected on an Agilent Xcalibur four-circle diffractometer
equipped with an Atlas CCD detector.
2.2. Synthesis of the Organic Ligand
Ligand L (3-allylsulfanyl-4-allyl-5-phenyl-4H-1,2,4-triazole) was obtained in
several steps in accordance with the reported method [31] as described on Scheme 1.
1
Ligand (L): H NMR (CD3CN, 500 MHz) δH 7.68 – 7.58 (2H, m), 7.58 – 7.47 (3H,
m), 6.05 – 5.86 (2H, m), 5.32 – 5.16 (2H, m), 5.11 (1H, d, J = 10.1 Hz), 4.85 (1H, d,
J = 17.2 Hz), 4.65 – 4.54 (2H, m), 3.83 (2H, d, J = 7.1 Hz). 13C NMR (CD3CN, 126
MHz) δC 155.8, 150.8, 133.4, 132.4, 130.2, 128.9, 128.5, 128.4, 127.4, 118.1, 117.4,
116.9, 46.6, 36.2. IR (Nujol, cm-1): 411w, 432w, 475w, 495w, 530m, 563m, 587m,
603m, 700vs, 770vs, 855w, 877m, 920s, 936s, 979m, 996m, 1024m, 1075m, 1108w,
1137w, 1160w, 1201s, 1232m, 1257w, 1285w, 1298w, 1324m, 1353m, 1371m,
1387m, 1424vs, 1438m, 1460vs, 1475s, 1525w, 1580m, 1605m, 1635m, 1651m,
1702m, 1773vw, 1821vw, 1847w, 1897w, 1960w, 1980vw, 2024vw, 2341w, 2362w,
2548vw, 2612vw, 2711vw, 2853w, 2932m, 2976m, 3010m, 3082m.

O
O
N H
EtOH, H SO
2
C H NCS
2
4
4
3
5
NH
NH2
NH
NH
NH
PhCOOEt
PhCOOH
n-PrOH,
C H ,


EtOH,

6
6
Ph
Ph
S
O
NH
NH
NH
aq. NaOH,
then HCl
Ph

C H Cl, KOH
3 5
N
N
N
Ph
Ph
S
SH
EtOH,

N
S
N
N
Scheme 1. The ligand L synthesis
2.3. Synthesis of the [Cu2(L)2Ag2Cl4] (1)
Crystals of the heterometallic complex 1 were obtained under conditions of the
alternating-current electrochemical technique starting from the acetonitrile solution of
L and copper(II) chloride on silver electrodes. A solution of L (3.0 mmol, 0.771 g)
and CuCl2·2H2O (1.0 mmol, 0.171 g) in 3.0 mL of acetonitrile was prepared. The
prepared green solution was placed into a small 3 mL test-tube and then silver-plates
electrodes in cork were inserted. By the application of alternating current (frequency
50 Hz) of 0.55 V for 3-4 days good quality colourless single crystals of 1 in a very
small amount appeared on silver electrodes.
2.4. Synthesis of the [CuI2(L)2CuII Cl6] (2)
2
Crystals of the mixed-valence complex 2 were obtained by slow evaporation of
the acetonitrile solution of ligand L and copper(II) chloride. For this, the solution of
L (1.79 mmol, 0.46 g) and CuCl2·2H2O (1.79 mmol, 0.305 g) in 5.0 mL of
acetonitrile was prepared. By slow evaporation of the obtained solution for 3 days
good quality black crystals of 2 appeared. The yield was 89%. M.p. 166 ºC.
IR (Nujol, cm-1): 410w, 413w, 419w, 425vw, 430w, 433vw, 440w, 442w, 451w,
472w, 486w, 491vw, 495vw, 497w, 502w, 512w, 527vw, 543w, 546w, 548w, 556w,
564w, 580w, 585w, 588w, 595w, 597w, 605w, 632vw, 645vw, 661w, 666w, 669w,
672w, 687w, 699s, 704s, 718m, 740m, 769m, 783s, 802w, 877m, 879m, 887m,
907m, 918s, 942s, 956m, 965m, 990m, 1011m, 1036w, 1075m, 1161w, 1187w,
1197w, 1214m, 1247m, 1264m, 1292m, 1331m, 1333m, 1368m, 1400m, 1413m,
1418m, 1446s, 1483s, 1544m, 1577w, 1606m, 1609m, 1632m, 1638m, 1646m,
1649m.

2.4. Synthesis of the [Cu2(L)2ZnCl4]∙2CH3CN (3)
Method A: Crystals of 3 were obtained starting from acetonitrile solution of the
same organic ligand and the mixture of copper(II) and zinc(II) chlorides. For this the
solution of L (3.0 mmol, 0.771 g) and CuCl2·2H2O (1.0 mmol, 0.171 g) and ZnCl2
(1.0 mmol, 0.136 g) in 5.4 mL of acetonitrile was prepared. A copper wire was
wrapped into a spiral of 1 cm diameter. A straight copper wire was placed inside the
spiral. These copper electrodes were inserted in a cork and immersed in the above-
mentioned solution. Synthesis was performed using alternating current of 50 Hz,
voltage (0.60 V) was applied to both wire electrodes. Colourless crystals of
compound 3 appeared on the electrodes) in a dozen of minutes. The yield was about
90%. M.p. 147 ºC.
Method B: Crystals of 3 were obtained starting from acetonitrile solution of the
L and the copper(II) chlorides on zinc electrodes. For this the solution of L (3.0
mmol, 0.771 g) and CuCl2·2H2O (1.0 mmol, 0.171 g) in 5.4 mL of acetonitrile was
prepared. Two zinc plates were inserted in a cork and immersed in the above-
mentioned solution. Synthesis was performed using alternating current of 50 Hz,
voltage (0.15 V) was applied to both wire electrodes. Colorless crystals of compound
3 appeared on the electrodes in one day. The yield was about 78%. M.p. 146-147ºC.
IR (Nujol, cm-1): 408w, 414w, 416w, 428w, 444w, 447w, 449w, 460w, 478w, 481w,
490w, 499vw, 506w, 512m, 519w, 522w, 539w, 544w, 550vw, 561vw, 570w, 578w,
580m, 583m, 586w, 594w, 602w, 604w, 642w, 645w, 661w, 665w, 673w, 683w,
689m, 701s, 720m, 735m, 766m, 771m, 785s, 793m, 813w, 853w, 872m, 893m,
927s, 949m, 961m, 990m, 1013m, 1035w, 1057w, 1073w, 1100w, 1145m, 1160m,
1194m, 1215m, 1241m, 1255m, 1295m, 1327m, 1355m, 1365s, 1401m, 1414s,
1429s, 1446s, 1486s, 1546m, 1577w, 1610w, 1637w, 1641w, 1644m.
2.4. Synthesis of the [Cu2(L)2FeCl4]∙2CH3CN (4)
Crystals of 4 were obtained under the similar to 3 reaction conditions, using
FeCl3 instead of ZnCl2. For this a solution of L (2.0 mmol, 0.514 g) and CuCl2·2H2O
(1.0 mmol, 0.171 g) and FeCl3·6H2O (1.5 mmol, 0.346 g) in 5.4 mL of acetonitrile
was prepared. With the application of alternating current (frequency 50 Hz) of 0.56 V

for 12 hours good-quality colourless crystals of 4 appeared on the copper electrodes.
The yield was about 85%. M.p. 165 ºC.
IR (Nujol, cm-1): 410w, 414vw, 416vw, 422w, 430w, 435w, 445w, 449vw, 460w,
466w, 472w, 484w, 491w, 499vw, 506w, 513w, 518w, 528w, 536w, 542w, 550vw,
560w, 565w, 570w, 573w, 577w, 582m, 599m, 602m, 690m, 700s, 722m, 737m,
764m, 785s, 792m, 873m, 893m, 927s, 945m, 962m, 988m, 994s, 1008w, 1012m,
1075w, 1100w, 1149m, 1159m, 1192m, 1242m, 1250m, 1257m, 1295m, 1325m,
1352m, 1367m, 1399m, 1415m, 1420m, 1425m, 1439s, 1446s, 1486s, 1536m,
1546m, 1578w, 1610m, 1640w, 1632m, 1645m.
2.5. Single crystal X-ray diffraction studies
The collected diffraction data for 1-4 were processed with CrysAlis Pro [32]
program. The structures were solved by ShelXT and refined by least squares method
on F2 by ShelXL with the following graphical user interface of OLEX2 [33–35]. In 3
and 4 structure, bonded allyl group (C23 and C24) as well as Cu(2) atom are
disordered over two sites with the occupancy ratios of 0.534(6) : 0.466(6) (3) and
0.521(6) : 0.479(6) (4), while uncoordinated allyl group (C26, C27 and C28) is
disordered over two sites with an occupancy ratio of 0.850(7) : 0.150(7) (3) and
0.804(7) : 0.196(7) (4). Atomic displacements for non-hydrogen atoms (except
disordered carbon atoms of uncoordinated allyl group with lower s.o.f. and the atoms
of disordered solvent molecules in 3 & 4) were refined using an anisotropic model.
Hydrogen atoms were placed on geometrically calculated positions and refined as
riding atoms with relative isotropic displacement parameters. The crystal parameters,
data collection, and the refinement are summarized in Table 1.
Table 1. Selected crystal data and structure refinement parameters of 1-4
Crystal data
1
2
3
4
CCDC number
Empirical
1914906
1914892
1914893
1914894
C28H30Ag2Cl4Cu2N6S2 C28H30Cl6Cu4N6S2 C28H30Cl4Cu2N6S2Zn, C28H30Cl4Cu2N6S2Fe,
formula
2(C2H3N)
931.06
2(C2H3N)
921.54
F. w. (g·mol-1) 999.32
981.56
triclinic,
Crystal system,
monoclinic,
monoclinic,
monoclinic,
P1

space group
a (Å)
P21/c
P21/n
P21/n
8.948(3)
9.680(3)
10.165(4)
93.25(3)
101.26(3)
95.72(3)
856.6(5)
1
9.485(3)
10.042(4)
19.001(5)
90.0
10.775(4)
15.452(5)
23.266(6)
90.0
10.795(4)
15.510(6)
23.233(8)
90.0
b (Å)
c (Å)
α (º)
β (º)
103.34(3)
90.0
92.70(3)
90.0
92.70(3)
90.0
γ (º)
V (Å3)
1761.0(10)
2
3869(2)
4
3886(2)
4
Z
µ (mm-1)
F(000)
2.815
2.988
2.124
1.871
492
980
1888
1872
0.48 × 0.26 × 0.21
0.45 × 0.23 × 0.19
0.62 × 0.39 × 0.33
0.45 × 0.36 × 0.21
Crystal size
(mm)
Crystal color
Calculated
density, g/cm3
Data collection
Radiation type,
wavelength,
λ(Å)
colourless
1.937
black
1.851
colourless
1.598
colourless
1.575
Mo Ka, 0.71073
Mo Ka, 0.71073 Mo Ka, 0.71073
Mo Ka, 0.71073
Temperature, K 100
150
100
100
Used in
4500
4213
9934
10156
refinement
reflections
R[F2 > 2σ(F2 )] 0.0313
0.0254
0.0320
0.0328
wR(F2 )
0.0861
0.0584
0.0749
0.0788
GooF = S
Δρmax/Δρmin
(e Å3 )
1.067
1.047
1.059
1.053
1.541/-0.863
0.478/-0.567
0.716/-0.522
0.703/-0.713
3. Results and discussion
3.1. Peculiarities of synthesis
Compounds reported herein are unique of their kind, therefore there has been no
standard algorithm for their synthesis. Widely used approach for Cu(I) π-complexes
synthesis is the alternating current electrochemical method [15,31,36] which is based
on the reduction of Cu(II) to Cu(I) on copper electrodes in a solution in the presence
of a ligand. Since the method had proved to be highly effective and yielding high-

quality single crystals, we decided to try to adapt it to synthesize heterometallic Cu(I)
π-complexes. In order to obtain the CuI – AgI complex [Cu2(L)2Ag2Cl4] (1) copper
electrodes were replaced by silver ones and electrochemical alternating current
reduction of CuCl2 in the acetonitrilic solution of the ligand L was carried out. A few
high-quality single crystals appeared on the electrodes in several days. To synthesize
the CuI – ZnII complex [Cu2(L)2ZnCl4]∙2CH3CN (3) two alternative synthetic routes
may be used. According to the first method, ZnCl2 was dissolved in acetonitrile
together with CuCl2 and the ligand L, and alternating current was applied to copper
electrodes. The complex 3 crystallized in a dozen of minutes with a high yield. By the
second route, zinc electrodes instead of copper ones were used and the acetonitrilic
solution contained only CuCl2 and ligand L. In the case of CuI – FeII joint
electrochemical reduction of Cu(II) and Fe(III) chlorides was carried out in the
acetonitrilic solution of the corresponding salts in the presence of the ligand L and
copper electrodes. After applying alternating current the solution became colourless
in several minutes and a large amount of crystals [Cu2(L)2FeCl4]∙2CH3CN grew
shortly. The mixed-valence complex [CuI2(L)2CuII Cl6] (2) was obtained by slow
2
evaporation of the acetonitrilic solution of ligand L and copper(II) chloride.
Particularly interesting is the fact that the reduction of Cu(II) to Cu(I) occurs
spontaneously in the air even in the absence of metallic copper, what indicates a large
driving force towards formation of the Cu(I) organometallic units which are
discussed in the next paragraph.
3.2. Crystal structures descriptions
Structures of the complexes 1-4 may be considered as consisting of two
subunits – the cationic organometallic core and an anionic inorganic fragment. The
two parts are joined via the μ2-Cl ion (Fig. 1, 3 & 4). The organometallic part in all
complexes is represented by the {Cu2(L)2}2+ dimers which are formed due to the
chelating-bridging coordination behavior of the ligand L. The formation of similar
organometallic moieties has been previously observed in copper(I) halides π-
complexes with the ligand L [31]. Only the 3-thioallyl group of the ligand L is
coordinated, while the second one (4-allyl, N-bounded) remains inactive with respect
to Cu(I) but has some contribution to the structure formation due to the weak

interactions. Two possible reasons for why the second allyl group is noncoordinated –
electronic and steric ones – have been proposed [31]. The dimeric moieties contain a
six-membered ring comprised of two pairs of [NN] triazole fragments and two
Cu(I) cations. In all complexes the π-coordinated Cu(I) cation adopts a close to a
trigonal pyramidal coordination environment (2N, (C═C) + Cl) (Tables 2 & 3). The
corresponding four-coordinate geometry indexes τ4 [37] are 0.87 (1), 0.80 (2),
0.83/0.83 (3) and 0.84/0.83 (4). The basal plane of the coordination arrangement
consists of two N(tr) atoms and the η2-allyl group. The axial site is occupied by a Cl
ion that is part of anionic inorganic fragments which are different for every complex
and are described below. The C═C bond of the η2-allyl group is elongated because of
π-coordination in accordance with the Dewar – Chatt – Duncanson model [38,39].
Figure 1. The part of crystal (a) and infinite organometallic chains (b) in 1 structure.
Symmetry codes: (i) 1–x, 1–y, 1–z; (ii) 2–x, 1–y, 1–z.
In the structure of 1 inorganic part is represented by almost flat and
centrosymmetric {Ag2Cl4} subunit (Fig. 1), which is apically bonded to the two
copper(I) ions through bridging Cl1 ions. Thus, {Cu2(L)2} dimers are stitched
through {Ag2Cl4} bridges into the infinite ladder-like chain extended in [100]
crystallographic direction. The heterometallic complex 1 is isostructural to a
previously studied copper(I) bromide π-complex [Cu2(L)2Cu2Br4] with the same
ligand L [31], thus revealing the crystallochemical interchangeability of the anionic

inorganic fragments (silver(I) chloride and copper(I) bromide moieties) (Fig. 2).
Interestingly, in the case of copper(I) chloride π-complex with the ligand L of the
same stoichiometry, the anionic inorganic part is organized differently, leading to a
0D structure [31]. The distance between steps within the chain in [100] direction
makes up 6.261(1) Å in the case of 1, which is much smaller than the same step
length (6.616(1) Å) in the earlier studied isostructural copper(I) bromide
[Cu2(L)2Cu2Br4] π-complex [31] (Fig. 2).
Table 2
Selected interatomic distances and angles for crystals 1 & 2.
Distance
(Å)
(Å)
Distance
(Å)
(Å)
1
2
1
2
Cu1—Cl1
Cu1—N1
Cu1—N2i
Cu1—m [a]
C4—C5
N1—N2
N1—C2
Angle
2.501(1)
2.048(3)
2.005(2)
1.993(3)
1.370(4)
1.394(3)
1.315(4)
(º)
2.819(1)
1.977(2)
1.982(2)
1.936(2)
1.365(3)
1.391(2)
1.315(2)
(º)
Ag1—Cl1
Ag1—Cl2
Ag1—Cl2ii
Cu2—Cl1
Cu2—Cl2
Cu2—Cl3
Cu2—Cl3ii
Angle
2.426(1)
2.480(1)
2.688(1)
2.1982(7)
2.235(1)
2.2712(9)
2.326(1)
(º)
(º)
1
2
1
2
N1—Cu1—N2i
N1—Cu1—Cl1
N2i—Cu1—Cl1
N1—Cu1—m
N2i—Cu1—m
Cl1—Cu1—m
109.71(10) 111.37(6)
95.09(8) 94.40(6)
100.15(8) 91.42(6)
Cu1—Cl1—Ag1 98.40(4)
Cl1—Ag1—Cl2
Cu1—Cl1—Cu2
Cl1—Cu2—Cl2
Cl1—Cu2—Cl3
Cl2—Cu2—Cl3
114.94(4)
105.68(2)
96.94(3)
94.04(3)
159.17(2)
111.0(1)
126.9(1)
108.7(1)
115.99(8)
131.24(8)
95.89(6)
[a] m – middle point of C4=C5 bond.

Figure 2. Two isostructural copper(I) π-complexes: heterometallic [Cu2(L)2Ag2Cl4]
(1) and [Cu2(L)2Cu2Br4] [31].
Replacement of a monovalent metal in the anionic {Me2Cl4}2– fragment by
copper(II) ion leads to a modification of the inorganic subunit due to an appearance
of the distorted square environment (τ4 = 0.31) of Cu(II) ion by inclusion of one more
terminal chloride ion to the metal surrounding in structure 2. Despite some
modification of inorganic part, the centrosymmetric {Cu2Cl6}2– anion is apically
bonded through μ2-Cl ions to Cu(I) of the dimers, forming similar 1D-ladder (Fig. 3).
The terminal Cl2 ion is remote from the nearest metallic center by 3.488(1) Å, which
is too long for Cu—Cl interaction [40].

Figure 3. The structure of heterovalent π-complex 2. Symmetry codes: (i) 1–x, –y, 1–
z; (ii) 2–x, 1–y, 1–z.
π-Complexes 3 and 4 are isostructural. The structures of these compounds
implement a different construction principle - the inorganic part is represented by a
tetrahedral anion {MeCl4}2- (Me = Zn(II) or Fe(II)), which binds two copper(I) ions
of the {Cu2(L)2}2+ dimer in a bridging mode. Copper(I) ion adopts close to a trigonal
pyramid coordination environment. The tendency of L, like allylsubstituted 1,3,4-
thiadiazole [18], to form centrosymmetric {Cu2(L)2}2+ fragments leads to disordering
of Cu2 ion and π-bonded to it allyl group over two sites (Fig. 4). One of the chlorine
ion of the {MeCl4}2- anion presumably interacts with the electron deficient aromatic
system of the 1,2,4-triazole ring via the anion-π-interaction [41] with a distance of
3.514(2) Å. The anion-π-interactions may have a directing effect on the mutual
orientation of the anionic inorganic {MeCl4}2- part with respect to the organometallic
cationic dimeric {Cu2(L)2}2+ moiety.
Figure 4. The molecular structure of heterometallic π-complexes 3 & 4. Disordered
noncoordinated allyl groups with lower s.o.f. are omitted for clarity.
Table 3
Selected interatomic distances and angles for crystals 3 & 4.

Distance
(Å)
(Å)
Distance
(Å)
(Å)
3
4
3
4
Cu1—Cl1
Cu1—N11
Cu1—N22
Cu1—m1 a
C14—C15
Cu2A—Cl2
Cu2A—N12
Cu2A—N21
Angle
2.4878(9) 2.483(1)
Cu2A—m2A a
C24A—C25A
Cu2B—Cl2
Cu2B—m2B
Me—Cl1 b
Me—Cl2
1.965(6)
1.351(6)
2.815(4)
1.959(6)
2.297(1)
1.972(6)
1.341(6)
2.817(6)
1.953(6)
2.338(1)
2.008(2)
1.985(2)
1.953(2)
1.367(3)
2.540(4)
2.018(6)
2.043(6)
(º)
2.011(2)
1.985(2)
1.954(2)
1.371(3)
2.531(4)
2.018(6)
2.039(6)
(º)
2.3040(7) 2.3444(8)
2.2586(9) 2.294(1)
2.2679(9) 2.304(1)
Me—Cl3
Me—Cl4
Angle
(º)
(º)
3
4
3
4
N11—Cu1—N22
N11—Cu1—Cl1
N22—Cu1—Cl1
N11—Cu1—m1
N22—Cu1—m1
Cl1—Cu1—m1
N12—Cu2A—N21
N12—Cu2A—Cl2
110.68(7) 110.59(7) N21—Cu2A—Cl2
98.5(2)
98.8(2)
128.7(3)
113.7(3)
102.5(3)
97.42(5)
95.61(6)
97.51(5)
96.14(6)
N12—Cu2A—m2A 129.3(3)
N21—Cu2A—m2A 113.4(3)
114.48(6) 114.34(6) Cl2—Cu2A—m2A
128.16(6) 127.86(6) Cu1—Cl1—Me
102.40(6) 102.76(6) Cl1—Me—Cl2
102.6(3)
118.62(4) 117.56(4)
107.69(3) 107.05(3)
111.69(4) 111.00(4)
110.74(4) 111.46(4)
108.1(2)
98.4(2)
108.4(2)
98.6(2)
Cu2A—Cl2—Me
Cl1—Me—Cl3
[a] m1, m2А and m2B – middle points of C14=C15, C24A=C25A and
C24B=C25B bonds; [b] Me – Zn(II) or Fe(II).
Considering the design of the copper(I) chloride π-complexes with L, it is also
advisable to take into account the two previously studied structures: [Cu2(L)2Cl2] and
[Cu2(L)2(ClCuCl)2] [31]. The complex [Cu2(L)2Cl2] with two terminal chloride ions
may be regarded as the main building block (MB). An addition of two CuCl units to
this block leads to a formation of 0D [Cu2(L)2(ClCuCl)2] complex with two linear
ClCuCl subunits (Fig. 5). In the case of incorporation of two CuCl2 units to the MB,
the last ones are connected by copper(II) chloride linkers into 1D-ladder. The
addition of two AgCl units to the MB has similar effect. The inclusion of ZnCl2 or
FeCl2 units to the MB leads to the loss of MB’s centrosymmetry and tetrahedral
{MeCl4}2- anions serve as a bridge between the Cu(I) centers of MB.

Figure 5. The construction principles of copper(I) π-complexes with L.
3.3. Magnetic properties measurements.
Magnetic measurements were performed using commercial Quantum design
MPMS 5 SQUID magnetometer setup. Measurements performed on a sufficient
amount of single crystals of substances 2 and 4 stuffed and tightly sealed in a gelatin
capsule. Magnetic susceptibility curves were recorded within the 1.8 – 300 K
temperature range and magnetic fields of 0.5 T for complex 2 and 0.1 T for complex
4, respectively. Magnetization curves at the lowest T = 1.72 K for both samples were
recorded in fields up to 5 T.

Figure 6. Temperature variation of inverse molar magnetic susceptibility (panels a
and b) and the effective magnetic moment (panels c and d) for complexes 2 and 4.
Solid lines were obtained from the modified Curie-Weiss equation. Insets show low
temperature magnetic susceptibility (insets to panels a and b) and magnetization
isotherms at 1.72 K (panels c and d). Full and empty symbols in the latter insets
represent data points in increasing (full) and decreasing (empty) magnetic field
measurement sequences.
Temperature dependent inverse magnetic susceptibilities χ-1(T) of complexes 2
and 4 are depicted in Fig.6.(a,b). As expected for both compounds χ-1(T) decreases
with T in congruence with Curie-Weiss (CW) theory for compound 4, while for 2
there is a significant departure from linearity in χ-1(T) below 150 K, possibly caused
by the CEF splitting. To include these deviations, a modified CW equation
was used to fit the experimental data (see solid line in Fig.6.(a,b))
with the following parameters µeff = 2.52 µB and 5.58 µB; θp = 0.2 K and 0.8 K for
the substance 2 and 4, respectively. Both values of θp hint on a very weak
ferromagnetic character of magnetic interactions. The values of effective moment µeff

are in good correspondence with those reported in the literature 5.1 µB for tetrahedral
Fe(II) complexes [38, 39] and 2.54 µB for the case of divalent copper ion in
tetrahedral coordination environment [44]. In temperatures below 30 K χ(T)
dependencies for both compounds show immense increase due to the increasing
strength of short range interactions or possible magnetic impurities. The variation of
the effective moment (µeff
) with temperature is shown in panels c,d to Fig.6.
It is apparent that the magnetic moment for the Fe(II) complex is nearly independent
3
of temperature and remains close to the expected d6(e3t2 ) state with a perceptible
orbital contribution. Temperature change of µeff for complex 2 shows a monotonous
decrease with T, changing from 2.6 µB at RT to 2.1 µB at 35 K, due to continuous
change of the ligand environment on the contraction of the crystal lattice upon
cooling. This might be especially the case, since the tetrahedral environment of
Cu(II) ion is distorted at room temperature. Moreover, the shortest distance between
magnetic Cu(II) ions is approximately 3.42 Å and these ions are connected in a Cu2-
Cl3-Cu2 chain that could bridge the exchange interactions. In order to check on any
metamagnetic behavior, magnetization isotherms were recorded at 1.8 K (see insets
to panels c,d). Experimental data collected in magnetic fields of growing and
diminishing strength showed typical paramagnetic behavior and did not reveal any
anomalies or hysteretic behavior up below H= 5 T.
3.4. Nonlinear optical effects
Fig. 7 shows the dependences of the THG for complexes 3 and 4 versus the
laser stimulated two beam coherent power densities treatment at wavelength 1064
nm using 7 ns pulse laser duration with pulse frequency repetition about 10 Hz. More
details are described in the ref. [45].

4
3
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
20
40
60
80
100
120
2
E[J/m ]
Figure 7. Dependence of the THG versus the photoinducing energy density at
fundamental wavelength 1064 nm.
The photoinduced regime was carried out up to 3 min. by two coherent beams
split in the space at power density tuned continuously up to 110 J/m2. At power
densities about 120 J/m2 there occurs some sample’s destruction. The existing NLO
maxima were achieved almost at the same photoinduced energy densities. After they
decreased drastically at higher energy densities. This may be caused by the
excitations of a higher level and partial overheating which favors the sample heating
up to 20 K. Below this energy density, the THG magnitudes relaxed to initial states
within 2-3 min. without a significant irreversible changes. So, there appears a very
good opportunity to operate by tripling of the initial frequency. One can see that for
the compound 3 (without iron) the THG signal is higher comparing to the compound
4. This difference may be attributed to the fact that the 3d-localized Fe states might
be an additional source of the third order hyperpolarizabilities due to the high
localization of Fe states. They also have a huge potential for the good nonlinear
optics [46], however they are more sensitive to the coordination by ligands than Cu.
This may be a principal goal of further research.
4. Conclusions

To sum up, we presented a family of novel Cu(I) heterobimetallic
[Cu2(L)2Ag2Cl4] (1), [Cu2(L)2ZnCl4]∙2CH3CN (3), [Cu2(L)2FeCl4]∙2CH3CN (4) and
mixed-valence [CuI2(L)2CuII Cl6] (2) π-coordination compounds. We developed a
2
new approach for the synthesis of heterometallic copper(I) π-complexes based on the
alternating-current electrochemical method used for copper(I)-olefine compounds.
Mixed-valence complex 2 crystallized from the acetonitrile solution of L and
copper(II) chloride during the spontaneous reduction of Cu(II) to Cu(I) in the air even
in the absence of metallic copper or another reducing agent. This fact confirms a
large motive force towards the formation of copper(I) organometallic moieties with
the ligand L, and hence a high stability of Cu(I) towards oxidation in this
coordination environment. The structures of 1-4 can be represented as being
constructed from two subunits: the cationic organometallic moiety {CuI2(L)2}2+,
which is formed by two η2-π-coordinated copper(I) ions and two pairs of N atoms of
triazole cycles, and an anionic inorganic fragment. In all complexes, the second metal
cation is incorporated in the form of anionic halide fragments without perturbing
significantly the organometallic core. At the same time, the dimensionality of the
discussed crystal structures is determined exactly by this anionic subunit. Tetrahedral
2–
2–
ZnCl4 or FeCl4 anion joins two copper(I) ions in a bridging mode within the
organometallic moiety leading to 0D structures (3 & 4), while in the case of 1 & 2,
{Ag2Cl4}2– and {CuII Cl6}2– fragments connect {CuI2(L)2}2+ cations into 1D ladder.
2
Comparison of the presented herein heterometallic complexes with previously studied
copper(I) π-complexes with the ligand L reveals the crystallochemical
interchangeability of anionic inorganic fragments (silver(I) chloride and copper(I)
bromide moieties). We have discovered also laser stimulated third order NLO
maxima that were achieved almost at the same photoinduced energy densities. After
they decreased drastically at higher energy densities. Magnetic properties studies of
mixed-valence Cu(I/II) (2) and heterometallic Cu(I)/Fe(II) (4) coordination
compounds yielded the following parameters µeff = 2.52 µB (θp = 0.2 K) and
µeff = 5.58 µB (θp = 0.8 K),
respectively; both values of paramagnetic Curie
temperatures hint on very weak character of magnetic interactions of ferromagnetic
(positive) type. The THG signal is higher for 3, than for 4, that may be attributed to

the fact that the 3d-localized Fe states might be an additional source of the third order
hyperpolarizabilities. In the conclusion, the interplay between copper(I), other metals
and organic ligands may serve as a powerful tool for tuning magnetic and non-linear
optical properties, and its study may be a subject of future research.
Appendix A. Supplementary data
CCDC 1914906, 1914892, 1914893 and 1914894 contain the supplementary
crystallographic data for this paper. Copies of the data can be obtained free of charge
filling the corresponding form on https://www.ccdc.cam.ac.uk/structures/? page of
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK.
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