Thiosemicarbazonates of copper: Crystal structures of [(furan-2-acetaldehyde-N-phenyl-thiosemicarbazonato)][bis(triphenylphosphine)]copper(I) and [bis(furan-2-formaldehyde-N-phenyl-thiosemicarbazonato)]copper(II)

Polyhedron 152 (2018) 49–54

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Thiosemicarbazonates of copper: Crystal structures of [(furan-2-acetaldehyde-N-phenyl-thiosemicarbazonato)][bis (triphenylphosphine)]copper(I) and [bis(furan-2-formaldehyde-Nphenyl-thiosemicarbazonato)]copper(II) Tarlok S. Lobana a,⇑, Mani Kaushal a, Rajneet K. Virk a, Isabel Garcia-Santos b, Jerry P. Jasinski c a

Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, India Departamento de Quimica Inorganica, Facultad de Farmacia, Universidad de Santiago, 15782 Santiago, Spain c Department of Chemistry, Keene State College, Keene, NH 03435-2001, USA b

a r t i c l e

i n f o

Article history: Received 30 April 2018 Accepted 7 June 2018 Available online 18 June 2018 Keywords: Furan-2-formaldehyde-N1-phenyl thiosemicarbazone Triphenylphosphine Copper(I) Copper(II) X-ray crystallography

a b s t r a c t Equimolar reactions of furan-2-formaldehyde-N1-phenylthiosemicarbazone [(C4H3O)(H)C2@N3-N2(H)C1(@S)-N1HPh; HftscN-Ph)] and furan-2-acetaldehyde-N1-phenylthiosemicarbazone; [(C4H3O)(CH3) C2@N3-N2(H)-C1(@S)-N1HPh, HaftscN-Ph] with Cu(OAc)(PPh3)2 in methanol has yielded N,S-chelated CuI complexes, [Cu(j2-N,S-ftscN-Ph)(PPh3)2] 1 and [Cu(j2-N,S-aftscN1-Ph)(PPh3)2] 2. Similarly, reactions of Cu(OAc)2
H2O with HftscN-Ph and HaftscN-Ph in 1:2 M ratio (Cu:L) in acetonitrile-methanol (1:1, v/v) has yielded N,S-chelated CuII complexes, [Cu(j2-N,S-ftscN-Ph)2] 3 and [Cu(j2-N,S-aftscN-Ph)2] 4. These complexes have been characterized using elemental analysis, IR, UV–Vis, X-band ESR (3, 4), and single crystal X-ray crystallography (2, 3). ESR spectroscopy has supported axial symmetry of complex 3 confirmed by X-ray crystallography, while it revealed rhombic environments for complex 4. Complexes 1 and 2 represent rare examples of CuI in the domain of coordination chemistry of furan based anionic thiosemicarbazones in which the thio-ligands bind as anions in N3,S-chelation mode. Ó 2018 Elsevier Ltd. All rights reserved.

1. Introduction Coordination chemistry of thiosemicarbazones {R1R2C2@N3N2(H)-C1(@S)N1R3R4} constitutes an important class of N, S-donor thio-ligands which have been used for the synthesis, bonding properties, structures, analytical chemistry, and pharmacological applications [1–8]. Heterocyclic thiosemicarbazones, {R1R2C2@N3N2(H)-C1(@S)-N1HR3}, bearing R1 group as furan (C4H3O) or thiophene (C4H3S) rings with different R2 and R3 groups (Chart 1), have given rise to six types of coordination arrangements (types A to F, Chart 2) in their copper(I)/silver(I) complexes with triphenylphosphine as a co-ligand involving j1-S bonding (B, C, D), m-S-bridging (A, D), N,S-chelating (E) and N,S-chelating-cum-S-bridging (F) [9–15]. The m-S-bridging was observed in dinuclear complexes, [Ag2Cl2(l-S-Httsc-NH2)2(PPh3)2]
2CH3CN [9], [Cu2Br2(l-S-HttscNH2)2(PPh3)2]
2H2O [10], (type A) and [M2X2(l-S-L)2(j1-S-L)2] ⇑ Corresponding author. E-mail address: [email protected] (T.S. Lobana). https://doi.org/10.1016/j.poly.2018.06.022 0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.

{M = Cu, X = Cl, Br, L = Hftsc-NPh [13], M = Ag, X = Cl, L = HttscNMe [11]} (type D). Mono-coordination by thio-ligands (j1-S bonding) is shown by several halogen bridged complexes, [M2(lX)2(j1-S-L)2(PPh3)2] {M = Cu, X = I, L = Hftsc-NH2, Httsc-NH2 [10], M = Cu, X = Cl, Br, I, L = Httsc-NR3 [12], Hftsc-NR3 [13], R3 = Me, Et; M = Ag, X = Cl, Br, L = Httsc-NMe [11]} (type B), three coordinate complexes, [CuX(j1-S-L)2] {X = Cl, Br, I; L = Httsc-NPh [12], X = I, L = Hftsc-NPh [13]}(type C) and type D complexes [11,13]. The N, S-chelation was observed in mononuclear complexes, [Cu(N, S-L) (PPh3)2] (type E) {L(as anion) = ttsc-NR3, R3 = Me, Et, Ph) [14]}, and finally N, S-chelation-cum-S-bridging in dinuclear complexes, [Cu2(l3-N,S-attsc-NR3)2 (Ph3P)2] (R3 = Me, Et, Ph) 14], and [Ag2(l3-N,S-Hftsc-NH2)2(Ph3P)2](NO3)2 (type F) [9]. In this paper, reactions of furan based thio-ligands, HftscN-Ph and HaftscN-Ph (Chart 1) with [Cu(OAc)(PPh3)2] and Cu2(OAc)4
2H2O are investigated and the products studied using various analytical and structural techniques. The basic purpose was to obtain CuI/CuII complexes with furan based thiosemicarbazones as anions and to explore the possibility of coordination by furan ring to the metal centre, if any.

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S 4

5

1

3 3

6

2

N

2

1

NHR3

N H

C

X

C

R2

R2 H H H H Me

X S S S S S

R3 H Me Et Ph Et

Abbrev. Httsc-NH2 Httsc-NMe Httsc-NEt Httsc-NPh Hattsc-NEt

X R2 S Me O H O H O H O H O Me

R3 Ph H Me Et Ph

Abbrev. Hattsc-NPh Hftsc-NH2 Hftsc-NMe Hftsc-NEt Hftsc-NPh

Ph

Haftsc-NPh

Chart 1. The thio-ligands under purview.

S S

X M P

P M

S

X

S

P

M X

M

X

M

P

X

A

S

S

C

B N

S

X M S

S

P

S

M S

X

S M

M N

D

P E

P M

S

P

N

F

Chart 2. Types of coordination arrangements (A–F) shown by complexes.

2. Experimental 2.1. Materials and techniques Copper(II) acetate monohydrate, N-phenyl thiosemicarbazide, triphenylphosphine, furan-2-form aldehyde and furan-2-acetaldehyde were procured from Aldrich Sigma Ltd. The thio-ligands (HftscN-Ph and HaftscN-Ph) were prepared by the condensation of furan-2-formaldehyde and furan-2-acetaldehyde with a respective thiosemicarbazide as previously reported [14]. The starting compound [Cu(OAc)(PPh3)2] was prepared by reacting copper(II) acetate with a fourfold excess of triphenylphosphine [16]. The melting points were determined with a Gallenkamp electrically heated apparatus. The IR spectra were recorded using KBr pellets with a VARIAN FT-IR 670 spectrophotometer in the 4000–400 cm1 range. Elemental analysis (CHNS) were carried out using the THERMO FINNIGAN FLASH technique. The UV–Vis spectra of the compounds were recorded in chloroform with the help of a UV-1601 PC Shimadzu spectrophotometer. The X-band ESR (9.4 GHz) spectra were obtained from Universidad de Santiago, Spain. 2.2. Synthesis of complexes 2.2.1. Synthesis of [Cu(j2:N,S-ftscN-Ph)(PPh3)2] (1) To a solution of thio-ligand, HftscN-Ph (0.019 g, 0.077 m mol) in methanol (15 mL) was added solid [Cu(OAc)(PPh3)2] (0.050 g, 0.077 m mol) and contents were stirred for a period of 1 h. A clear yellow solution formed was allowed to evaporate at room temperature. It gave a yellow solid of stoichiometry, [Cu(j2-N,S-ftsc-NPh) (PPh3)2] 1. Yield: 0.050 g, 78%, m.p. 106–108 °C. Anal. Calc. for C48H40CuN3OP2S: C, 69.27; H, 4.81; N, 5.05; S, 3.85. Found: C, 69.02; H, 4.88; N, 5.02; S, 3.56. Main IR bands (KBr, cm1): m (N1AH) 3363 m; m(CAH), 2970 w, 2926 w, 2889 w; m(C@N), 1597 s; m(C@C), 1547 m, 1522 s; d(CAH), 1491 s, 1473 s, 1432 w, 1384 w, 1371 w; m(CAO), 1311 s; 1243 m, 1190 m, 1149 m; m(PACPh), 1101 m; 952 w; m(CAS) 888 w, 832 m; 757 w, 725 m, 694 w,

654 m, 621 m, 571 w, 517 w, 465 m. Electronic absorption spectrum, CHCl3, kmax/nm, e/L mol1 cm1: [105 M] 261(7.73  104), 338 (4.02  104), 379 (2.42  104). 2.2.2. Synthesis of [Cu(j2:N,S-aftscN-Ph)(PPh3)2] (2) To a solution of thio-ligand, HaftscN-Ph (0.020 g, 0.077 mmol) in methanol (15 mL) was added solid [Cu(OAc)(PPh3)2] (0.050 g, 0.077 mmol) and contents were stirred for a period of 1 h. A clear yellow solution formed was allowed to evaporate at room temperature. It gave yellow crystals of stoichiometry, [Cu(j2-N,S-aftscNPh)2] 2. Yield: 0.039 g, 60%, m.p. 155–160 °C. Anal. Calc. for C49H42CuN3OP2S: C, 69.54; H, 4.96; N, 4.96; S, 3.78. Found: C, 69.51; H, 4.79; N, 4.96; S, 3.84. Main IR bands (KBr, cm1): m(N1AH), 3419 m; m(CAH), 3051 w; m(C@N), 1595 m; m(C@C) + d (CAH), 1522 m, 1475 m, 1433 s, 1417 s; 1309 m, 1244 w; m(CAO), 1182 s, m(PACPh), 1093 s; 1029 w; m(CAS), 815 m; 746 m, 721 m, 695 s, 541 m, 510 m. Electronic absorption spectrum, CHCl3, kmax/nm, e/L mol1 cm1: [105 M] 259(8.06  104), 332 (6.37  104), 373 (3.73  104). 2.2.3. Synthesis of [Cu(j2:N,S-ftscN-Ph)2] (3) To a solution of Cu(OAc)2
H2O (0.050 g, 0.25 mmol) in acetonitrile (10 mL) was added a solution of thio-ligand, HftscN-Ph (0.123 g, 0.50 mmol) in methanol (10 mL) and mixture was stirred for 1 h. A clear dark green solution formed was allowed to evaporate at room temperature. It gave dark green crystals of stoichiometry, [Cu(j2-N,S-ftsc-NPh)2] 3. Yield: 0.095 g, 69%, m.p. 122–124 °C. Anal. Calc. for C24H20CuN6O2S2: C, 52.22; H, 3.63; N, 15.23; S, 11.60. Found: C, 51.38; H, 3.57; N, 14.94; S, 11.37. Main IR bands (KBr, cm1): m(N1AH) 3407 m, 3354 m; m(CAH), 3150 w, 3118 w, 3046 m; m(C@N), 1599 s; m(C@C) + d(CAH), 1529 s, 1495 s, 1468 s, 1432 s, 1386 m, 1350 m; m(CAO), 1316 s; 1248 s, 1181 m, 1148 m 1090 m, 1053 m, 1015 m, 948 w; m(CAS) 868 s; 832 m, 742 s, 691 m, 593 m, 531 w, 498 m. Electronic absorption spectrum, CHCl3, kmax/nm, e/L mol1 cm1: [105 M] 244(3.62  104), 302 (3.19  104); [103 M] 560–740 (390–32).

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2.2.4. Synthesis of [Cu(j2-N,S-aftscN-Ph)2]
CH3OH (4) To a solution of [Cu(OAc)2]
H2O (0.050 g, 0.25 mmol) in acetonitrile (10 mL) was added a solution of thio-ligand, HaftscN-Ph (0.130 g, 0.50 mmol) in methanol (10 mL) and mixture was stirred for 1 h. A clear dark green solution formed was allowed to evaporate at room temperature. It gave dark green solid of stoichiometry, [Cu(j2-N,S-aftscN-Ph)2] 4. Yield: 0.099 g, 68%, m.p. 136–138 °C. Anal. Calc. for C26H24CuN6O2S2
CH3OH: C, 52.98; H, 4.57; N, 13.74; S, 10.47; found: C,52.00; H, 4.14; N, 14.20; S, 10.28. Main IR bands (KBr, cm1): m(N1AH) 3308 m; m(CAH), 3126 m, 3069 m, 3005 w, 2965 w, 2922 w; m(C@N), 1588 s, 1543 s; m(C@C) + d (CAH), 1496 s, 1434 s, 1364 m; m(CAO), 1313 s; 1257 m, 1227 m, 1189 m, 1116 m, 1084 m, 1060 m, 917 w, 884 w, 846 w; m (CAS), 820 m; 746 m, 690 m, 670 w, 588 m, 505 m, 473 w. Electronic absorption spectrum, CHCl3, kmax/nm, e/L mol1 cm1: [105 M] 259(2.71  104), 340 (2.56  104); [103 M] 542–730 (490–57). 2.3. X-ray crystallography A single crystal was mounted on a glass fiber and used for data collection with a Agilent Eos (Gemini), Agilent Technologies, {2; 173(2) K; 3, 293(2)} equipped with graphite monochromated Cu Ka (k = 1.54184 Å). The data recorded for compounds were processed with CrysAlisPro (data collection) and CrysAlisPro RED (cell refinement and data reduction). The structures were solved by direct methods using Superflip, refined by full-matrix least-squares techniques against F2 using SHELXL-97 and molecular graphics from OLEX 2. The data were corrected for Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. Atomic scattering factors were taken from International Tables for Crystallography. Table 1 gives crystal data of complexes 2 and 3 [17–23].

3. Results and discussion 3.1. Synthetic comments and IR spectroscopy Reactions of furan-2-formaldehyde-N1-phenylthiosemicarbazone (HftscN-Ph) and furan-2-acetaldehyde-N1-phenylthiosemicarbazone (HaftscN-Ph) with Cu(OAc)(PPh3)2 and Cu(OAc)2
H2O in acetonitrile-methanol/methanol have yielded complexes of stoichiometry, [Cu(j2:N,S-ftscN-Ph)(PPh3)2] 1, [Cu(j2:N,S-aftscN-Ph) (PPh3)2] 2, [Cu(j2:N,S-ftscN-Ph)2] 3, and [Cu(j2-N,S-aftscN-Ph)2]
CH3OH 4. The acetate anion is involved in deprotonation of thioligands (AN2-H moiety), and yielded CuI and CuII complexes (see Chart 3). In these complexes, the thio-ligands coordinate as anions in N3,S-chelation mode, as observed with analogous thiophene based thiosemicarbazones [14]. The complexes are highly soluble in chloroform, methanol, dichloromethane and acetonitrile. It is added here that complex 3 has also been reported by Jian et al. [24,25] using a different procedure by reacting copper(II) chloride and HftscN-Ph thio-ligand in THF medium involving washings with water. However, work described in the present paper provides complementary information about complex 3, specifically with respect to synthesis, spectroscopy (UV–Vis and ESR), and improved X-ray crystal data. The IR spectral bands of complexes are placed in the experimental section. In the uncoordinated thio-ligands, Hftsc and Haftsc, the m(N2-H) band appears at 3128 and 3155 cm1 respectively which disappeared in complexes 1–4 and it supported that these ligands are coordinating as anions to the copper metal centre. Complexes did show m(N1AH) bands of AN1HPh moiety in the range 3308–3419 cm1 which are at different positions relative to those of the free ligands (Hftsc, 3294 cm1 and Haftsc, 3459 cm1). The m(CAS) bands of the free ligands (Hftsc, 885 cm1 and Haftsc, 757 cm1) shifted to the region 815–888 cm1 in

Table 1 Crystal data for complex 2 and 3. T (K)

Complex 2, 173(2) K

Complex 3, 293(2) K

Empirical formula M k (Å) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm3) l (mm1) F(0 0 0) Reflections collected Unique reflections Data/restraints/parameters Reflns. With [I > 2r(I)] R Indices R1 wR2 R indices (all data) R1 wR2 Largest difference in peak and hole (e Å3)

C49H42CuN3OP2S 846.39 1.54184 Monoclinic P21/n

C24H20CuN6O2S2 552.12 1.54184 Orthorhombic Pbcn

15.0586(4) 16.3809(4) 17.4710(5) 90 103.367(3) 90 4192.85(19) 4 1.341 2.238 1760 31 064 7958 (Rint = 0.0477) 7958/0/515 7164

20.8180(4) 15.0425(2) 7.5313(2) 90 90 90 2358.46(8) 4 1.555 3.261 1132 16 097 2288 (Rint = 0.0418) 2288/0/160 2049

0.0368 0.0978

0.0402 0.1096

0.0408 0.1015 0.497, 0.357

0.0442 0.1135 0.626, 0.390

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PPh3

Cu Cu(OAc)(PPh3)2

S

Ph3P 1, 2

N3

S

N3

-AcOH H 2

O

C

3

N

2

N

N1HPh

1

2

O

C R2

C S

Cu(OAc)2 -AcOH

R2 = H, Me

N

2

1

N

C

N1HPh S

N3

S

R2

3

=

Cu N3

S 3, 4

Chart 3. Schematic formation of complexes 1, 2, 3 and 4.

complexes. The m(PACPh) bands of complexes 1 and 2 in the region 1093–1101 cm1 support the presence of the coordinated Ph3P in these complexes [14].

3.2. Crystal structures Crystal data are given in Table 1 while important bond parameters of respective complexes are given in Table 2. Complex 2 crystallized in monoclinic system with space group P21/n, while Table 2 Important bond distances (Å) and bond angles (°) in complexes 2 and 3. [Cu(2-N,S-aftscN1-Ph)(PPh3)2] 2

[Cu(2-N,S-ftscN-Ph)2] 3

Cu1AN1 Cu1AS1 Cu1AP1 Cu1AP2 S1AC1 S1ACu1AN1 S1ACu1AP1 S1ACu1AP2 N1ACu1AP1 N1ACu1AP2 P1ACu1AP2

Cu1AN1 Cu1AN1a Cu1AS1 Cu1AS1a S1AC1 S1ACu1AN1 S1aACu1AN1a N1ACu1AS1a N1aACu1AS1a S1ACu1AS1a N1ACu1AN1a

2.0886(14) 2.3177(5) 2.2356(5) 2.2682(5) 1.7367(18) 85.96(4) 107.795(18) 102.562(18) 122.33(4) 105.11(4) 124.314(18)

2.0114(19) 2.0115(19) 2.2862(5) 2.2862(5) 1.741(2) 96.43(5) 96.43(5) 83.57(5) 83.57(5) 180.0 180.0

Fig. 1. Molecular structure of [Cu(j2-N,S-aftsc-NPh)(PPh3)2] 2 with atomic numbering scheme.

complex 3 crystallized in the orthorhombic system with space group Pbcn. The crystal structure of complex 2 (Fig. 1) shows that the aftsc-NPh anion (after deprotonation of AN2H moiety of Haftsc-NPh) chelates to CuI ion through its N3,S – donor atoms and the remaining two sites are occupied by two PPh3 ligands. The CuAS bond distance of 2.3177(5) Å is somewhat longer than that (2.2956(6) Å) recorded in the thiophene based analogous CuI complex, [Cu(j2-N3,S-ttsc-NPh)(PPh3)2] (see Chart 1 for thioligand) [14]. The difference in bond length is attributed to somewhat weaker interaction of the anionic ligand in complex, [Cu (j2-N3,S-aftsc-NPh)(PPh3)2] 2, in conformity with different R1 rings in two cases. However, the longer CuAS bond distance leads to the relatively shorter CuAP bond distances [2.2356(5); 2.2682(5) Å] in 2 versus 2.2642(6) and 2.2845(6) Å in [Cu(j2-N3,S-ttsc-NPh) (PPh3)2] [14]. The CuAN bond distance of 2.0886(14) Å is longer in 2 as compared with 2.0608(19) Å reported in literature [14]. The CAS bond distance of 1.7367(18) Å is very similar to that {1.743(2) Å} found in literature [14] and is in between that of a CAS single and C@S double bonds (1.81 and 1.62 Å, respectively), indicating a partial double bond character [26]. The angles around Cu vary in the range, 85.96(4) to 124.314(18)°, with the bite angle NACuAS being the shortest and PACuAP being the largest. This range is similar to that {84.55(6)–122.97(2)°} observed in literature [14] (Fig. 2). In complex 3, copper(II) is bonded to two S and two N donor atoms of two thio-ligands at equal CuAS bond distances of 2.2862(5) Å each and likewise nearly equal CuAN bond distances of 2.0114(19) and 2.0115(19) Å. In view of absence of competing PPh3 ligands, both these distances are expectedly shorter than those in 2 and literature [14], as discussed above. The CAS bond

Fig. 2. Molecular structure of [Cu(j2-N,S-ftsc-NPh)2] 3 with atomic numbering scheme.

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distance of 1.741(2) Å is, however, similar to that found in 2. Both the SACuAN bite angles are equal (83.57(5)° each), and similar to that shown by complex 2. The NACuAN and SACuAS bond angles are exactly 180.00°. Other NACuAS bond angles {96.43(5)° each} are bigger than SACuAN bite angles (83.57(5)° each).

1

0

Intensity(a.u)

In order to obtain electronic absorption bands in the UV region, 105 M solutions of complexes 1–4 in CHCl3 (Fig. 3) were used and for observing d–d transitions for CuII complexes 3 and 4, 103 M solutions of complexes (Fig. 4) were used. Complexes 1 and 2 have shown three absorption bands at 259–261; 332–338 and 373–379 nm assigned to the p ? p⁄, n ? p⁄ and MLCT transitions (metal to ligand charge transfer transitions) respectively. Similarly complexes 3 and 4 have shown absorption bands at 244–259 and 302–340 nm, which are assigned to p ? p⁄ and n ? p⁄ transitions respectively. These latter complexes have shown weak absorption in a continuous manner in the region, 550–750 nm which are due 2 to d–d transitions of 3d9 CuII metal centre {2B1(dx2-y2) Eg(dxz, dyz)} (Fig. 4). Only complexes 3 and 4, as expected, were found to be ESR active, confirming the presence of divalent copper in these complexes [27–30]. The ESR signals expected in the parallel and the perpendicular regions involving coupling from 63Cu (I = 3/2) nucleus are not observed probably due to the dipolar broadening induced by the closest neighbors in the crystal lattice. Figs. 5 and 6 depict the respective ESR spectra of complexes 3 and 4, which

5000

-5000

-10000

-15000

-20000 2600

2800

3000

3200

3400

3600

3800

4000

Magnetic field(gauss) Fig. 5. The ESR spectrum of [Cu(j2-N,S-ftsc-NPh)2] 3.

30000

20000

10000

Intensity(a.u.)

3.3. UV–Vis and ESR spectroscopy

10000

0

-10000

-20000

Absorbance

-30000

Complex 1

-40000 2600

Complex 2

0.5

Complex 3

2800

3000

3200

3400

3600

3800

4000

Magnetic field(gauss) Fig. 6. The ESR spectrum of [Cu(j2-N,S-aftsc-NPh)2] 4.

Complex 4

0

230

330

430

530

630

Wavelength (nm) Fig. 3. Electronic absorption spectrum of complexes 1–4 at 105 M in chloroform.

Absorbance

1

Complex 1

0.5

Complex 2 Complex 3 Complex 4

0

450

550

650

750

850

Wavelength (nm) Fig. 4. Electronic absorption spectrum of complexes 1–4 at 103 M in chloroform.

is similar to that reported earlier for CuII [30]. The ESR spectrum of complex 3 shows two signals with gII = 2.137 in the parallel region, and g\ = 2.048 in the perpendicular region (Fig. 5). This spectral pattern supports square planar geometry with gII > g\ > 2, which implies that 2B1 is the ground state of copper(II) in this complex. The single crystal X-ray crystallography has shown that CuN2S2 core of complex 3 makes a square planar geometry with trans NACuAN and SACuAS angles of 180.0° and z-axis passing through copper metal center. Thus this complex 3 can be regarded to have axial symmetry. The ESR spectrum of complex 4 has shown three g1, g2 and g3 values, calculated as: g1 = 2.120, g2 = 2.078, g3 = 2.050 (Fig. 6). The presence of methyl substituent at C2 position of aftsc-NPh anion is likely to affect the square plane of CuN2S2 core of complex 4 (see Chart 3). The presence of methyl groups at C2 carbon close to N3 is expected to affect trans NACuAN bond angle and this might change environments along NACuAN and SACuAS angles. With z-axis passing through copper metal center, the environments along three axes are likely to be different and this introduces asymmetry in the environments surrounding CuII metal centre (rhombic environments) [27–30]. This is reflected in the ESR spectrum of complex 4 (Fig. 6). 4. Conclusion The thio-ligands Hftsc and Haftsc have yielded two types of complexes depending on the starting metal salts and all have

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thio-ligands as anions. Interestingly complexes 1 and 2 represent rare examples of CuI in the domain of coordination chemistry of furan based anionic thiosemicarbazones in which the thio-ligands bind as anions in N3,S-chelation mode. In this context, there are a few examples of nickel(II) with furan based thiosemicarbazones coordinating as anion through N3,S and O,N3,S – coordinating as donor atoms [31]. However, the furan ring coordination to the copper metal centre was not observed in complexes unlike that observed in case of nickel(II) complexes [31]. A series of CuI complexes bearing thiophene based anionic thiosemicarbazones were recently reported as the first examples [14]. Acknowledgements Financial assistance from the Department of Science and Technology DST, India for the X-ray diffractometer grant to the department and Emeritus Scientist Grant [21(0904)/12-EMR-II] to T.S. Lobana, from the Council of Scientific and Industrial Research (CSIR, India) are gratefully acknowledged. JPJ acknowledges the NSF-MRI program [Grant No. CHE-1039027] for funds to purchase of the X-ray diffractometer. Appendix A. Supplementary data CCDC 1454665 and 1454666 contains the supplementary crystallographic data for (2) and (3). These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving. html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. References [1] T.S. Lobana, R. Sharma, G. Bawa, S. Khanna, Coord. Chem. Rev. 253 (2009) 977. [2] E.B. Seena, M.R.P. Kurup, Polyhedron 26 (2007) 829. [3] A.D. Naik, P.A.N. Reddy, M. Nethaji, A.R. Chakravarty, Inorg. Chim. Acta 349 (2003) 149.

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