Synthesis, characterization and structural analysis of new copper(II) complexes incorporating a pyridoxal-semicarbazone ligand

Polyhedron 30 (2011) 16–21

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Synthesis, characterization and structural analysis of new copper(II) complexes incorporating a pyridoxal-semicarbazone ligand Dragoslav Vidovic a,⇑, Aleksandra Radulovic b, Violeta Jevtovic c,⇑ a

Chemistry Research Laboratory, 13 Mansfield Road, Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK Department of Dental Prosthetic, School of Medicine, Department of Stomatology, Banja Luka, Bosnia and Herzegovina c Department of Chemistry, Faculty of Sciences, University of Novi Sad, 21000 Novi Sad, Trg D. Obradovica 3, Serbia b

a r t i c l e

i n f o

Article history: Received 6 July 2010 Accepted 21 September 2010 Available online 26 October 2010 Keywords: Cu(II) complexes Pyridoxal-semicarbazone Synthesis Structural analysis

a b s t r a c t The reaction between 3-hydroxy-5-hydroxymethyl-2-methyl-4-pyridinecarboxaldehyde semicarbazone (pyridoxal-semicarbazone or PLSC) and appropriate chloride, sulfate, nitrate or thiocyanate Cu(II) salts in water/alcohol mixtures resulted in the formation of new copper(II) complexes: [Cu(PLSC)Cl2] (1), [Cu(PLSC)(H2O)(SO4)]23H2O (2), [Cu2(PLSC)2(NCS)2](NCS)2 (3), [Cu(PLSC)(NO3)2(CH3OH)] (4) and [Cu(PLSC–2H]NH3H2O (5). The complexes were characterized by elemental analysis, conductometric measurements and IR spectroscopy, while complexes 1, 2, 3 and 4 were further characterized by single crystal X-ray diffraction. Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.

1. Introduction Cancer is undoubtedly one of the main health concerns facing our society and one of the primary targets regarding medicinal chemistry. Even though platinum-based complexes had been the primary focus of the research on chemotherapy agents [1–3], the interests in this field have shifted to non-platinum-based agents [4–11], in order to find different metal complexes with less side effects and similar, or better, cytotoxicity. Thus, a wide variety of metal complexes based on titanium, gallium, germanium, palladium, gold, cobalt, ruthenium and tin are being intensively studied as platinum replacements [4–11]. Furthermore, copper(II)-based complexes appear to be very promising candidates for anticancer therapy; an idea supported by a considerable number of research articles describing the synthesis and cytotoxic activities of numerous copper(II) complexes [12–15]. The choice of the coordinated ligand(s) seems to be as important as the choice of metal(s) because besides being the integral part of biologically active complexes these organic molecules (ligands) can exert biological activity on their own [16]. Complexes incorporating 3-hydroxy-5-hydroxymethyl-2-methylpyridine4-carboxaldehyde-3-methylisotiosemicarbazone (pyridoxal-thiosemicarbazone or PLTSC) ligand have been not only the focus of anticancer research in past several years [17–22] but also the ⇑ Corresponding authors. Tel.: +44 1865285137 (D. Vidovic), tel.: +381 214852750; fax: +381 21454065 (V. Jevtovic). E-mail addresses: [email protected] (D. Vidovic), [email protected] (A. Radulovic), [email protected] (V. Jevtovic).

inspiration for the synthesis of a new ligand based on pyridoxalsemicarbazide, i.e. 3-hydroxy-5-hydroxymethyl-2-methyl-4-pyridinecarboxaldehyde semicarbazide or PLSC. Recently, several research articles have been published reporting the synthesis and biological activity of transition metal complexes incorporating PLSC ligand [23–30], including a review article [29] and a PhD thesis [31]. Coordination chemistry of PLSC-based complexes proved to be very interesting as this ligand can exist in neutral, monoand dianionic forms depending on pH while its most predominant tridentate coordination mode, achieved through hydrazine nitrogen, phenolic and carbonyl oxygen atoms, allows it to be an excellent chelating ligand [31]. Furthermore, this ligand, based on semicarbazone and pyridoxal moieties (forms found in vitamin B6), has an enormous potential as a biologically active reagent as it has been demonstrated that transition metal complexes incorporating semicarbazones show biological activity. In particular, with the regard to biological importance, nickel(II) complexes with semicarbazone ligands show antibacterial activity [32], and copper(II) complexes containing semicarbazones have also displayed biological properties [33–35]. Additionally, several nickel(II) complexes with octadiensemicarbazones exhibit strong inhibitory activity against Staphylococcus aureus and Eschericia coli [36]. In vitro anticancer studies of several nickel(II) complexes with naphthaquinone semicarbazone and thiosemicarbazone on MCF7 human breast cancer cells revealed that semicarbazone nickel(II) complexes inhibited cell proliferation more actively than the thiosemicarbazone analogs [37]. Thus, we wish to report the synthesis and characterization of several Cu(II) complexes incorporating PLSC ligand namely [Cu(PLSC)Cl2] (1), [Cu(PLSC)(H2O)(SO4)]2.3H2O

0277-5387/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.09.022

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0

(2), [Cu2(PLSC)2(NCS)2](NCS)2 (3), [Cu(PLSC)(NO3)2(CH3OH)] (4) and [Cu(PLSC-2H]NH3H2O (5). The single crystal X-ray analyses for 1, 2, 3 and 4 are also reported. 2. Experimental 2.1. Reactants All commercially obtained reagent-grade chemicals were used without further purification, except for the ligand, which were prepared according to the previously described procedure [31]. 2.2. Measurements Elemental (C,H, and N) analysis of air-dried samples was carried out by standard micromethods in the Center for Instrumental Analysis, Faculty of Chemistry, Belgrade. Molar conductivities of the freshly prepared 1  103 M solution were measured on a Jenway 4010 conductivity meter. IR spectra (KBr disk) were recorded on a Thermo Nicolet (NEXUS 670 FT-IR) instrument. Magnetic susceptibility properties were measured using a magnetic susceptibility balance, Johnson Matthey Chemical Ltd. The X-ray analysis was performed at the University of Oxford Chemical Crystallography Service.

using graphite monochromated Mo Ka radiation (k = 0.71073 Å A). Data collection and cell refinement were carried out using DENZO and COLLECT [38,39]. The structures were solved with SIR-92 and refined using CRYSTALS [40,41]. In general, the hydrogen atoms were visible in the difference map. Therefore, they were positioned geometrically and refined in a separate hydrogen cycle (with soft restraints) before inclusion in the refinement using a riding model. The exception was the hydroxyl hydrogen atom of the disordered – CH2OH group of complex 1. In this case they were not visible in the difference map mainly due to the disordered nature of the entire – CH2OH group. For more information see the Supplementary information. Crystal data and details concerning data collection and structure refinement are given in Table 1. 2.4. Preparation of the complexes 2.4.1. [Cu(PLSC)Cl2], 1 To a warm methanol solution (10 cm3) containing 0.13 g (0.5 mmol) of PLSC2H2O 0.08 g (0.5 mmol) of CuCl2 was added and the mixture was left to react for about 15 min. Green solution was filtered and left to crystallize. After 25 h dark green crystals started to appear. Yield: 0.10 g (65%). Anal. Calc. for C10H16N4CuO4Cl2: C, 30.14; H, 3.37; N, 15.62. Found: C, 30.15; H, 3.38, N, 15.42%. Magnetic moment (l, BM): 1.85. IR [v (cm1) (KBr)]: 2800 (C@O), 1660 (NH+). kMeOH = 205 S cm2 mol1.

2.3. Crystal data collection and processing A single crystal of was mounted on a glass fibber in a random orientation. Data collection was performed at temperature 150 K on a computing data collection Nonius Kappa CCD diffractometer

2.4.2. [Cu(PLSC)(H2O)(SO4)]23H2O, 2 To a warm water solution (5 cm3) containing 0.13 g (0.5 mmol) PLSC2H2O 0.12 g (0.5 mmol) of CuSO45H2O was added resulting in complete dissolution of the ligand and the formation of green

Table 1 Summary of crystallographic data for 1, 2, 3 and 4. Identification code

1

2

3

4

Empirical formula Formula weight T (K) k (Å) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (Mg/m3) l (mm1) F(0 0 0) Crystal size (mm3) h Range for data collection (°) Index ranges

C9H12Cl2Cu1N4O3 357.66 150 K 0.71073 triclinic  P1

C18H34Cu2N8O19S2 857.73 150 K 0.71073 triclinic  P1

C22H24Cu2N12O6S4 807.8 150 K 0.71073 triclinic  P1

C10H16Cu1N6O10 443.82 150 K 0.71073 monoclinic P21/c

7.4735(3) 8.5925(3) 0.5331(4) 92.2071(19) 97.018(2) 108.4273(14) 634.76(4) 2 1.871 2.150 360 0.19  0.14  0.12 5.191–27.482 9 6 h 6 9 11 6 k 6 10 13 6 l 6 13 8218 2868 (0.075) 99.1 semi-empirical from equivalents 0.77 and 0.75 full-matrix least-squares on F2 2277/241/191 0.9118 R1 = 0.0471, wR2 = 0.0901 R1 = 0.0852, wR2 = 0.1043 1.47 and 1.45

9.2575(2) 9.5857(2) 17.1333(3) 83.7857(8) 82.9242(9) 85.7804(7) 1497.16(5) 2 1.903 1.660 880 0.21  0.15  0.09 5.124–27.511 11 6 h 6 12, 12 6 k 6 12 0 6 l 6 22 18 928 6800 (0.071) 99.0 semi-empirical from equivalents 0.85 and 0.74 full-matrix least-squares on F2 6800/0/443 0.9624 R1 = 0.0564, wR2 = 0.1156 R1 = 0.0850, wR2 = 0.1280 1.26 and 1.05

7.7686(2) 8.5400(3) 12.5363(4) 82.1120(15) 76.5427(15) 63.9438(14) 726.08(4) 1 1.847 1.816 410 0.20  0.18  0.11 5.198–27.573 10 6 h 6 10, 9 6 k 6 11, 16 6 l 6 16 11 358 3301 (0.121) 99.3 semi-empirical from equivalents 0.82 and 0.63 full-matrix least-squares on F2 2726/269/209 0.9545 R1 = 0.0871, wR2 = 0.2490 R1 = 0.1019, wR2 = 0.2641 1.12 and 1.47

8.5771(2) 10.1164(3) 19.0567(5)

Reflections collected Independent reflections (Rint) Completeness% Absorption correction Max. and min. transmission Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)

101.174(1) 1622.19(7) 4 1.817 1.417 908 0.19  0.12  0.06 5.166–27.464 11 6 h 6 11, 13 6 k 6 13, 24 6 l 6 24 27 890 3669 (0.046) 99.2 semi-empirical from equivalents 0.92 and 0.87 full-matrix least-squares on F2 3477/0/244 0.9991 R1 = 0.0505, wR2 = 0.1174 R1 = 0.0791, wR2 = 0.1266 0.88 and 1.09

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solution. The mixture was then left to crystallize. After about 10 h crystals started to appear which were then washed with water. Yield 0.10 g (71%). Anal. Calc. for C18H34Cu2N8O19S2: C, 25.21; H, 4.00; N, 13.06. Found: C, 25.27; H, 4.03; N, 13.13%. Magnetic moment (l, BM): 1.65. IR [v (cm1) (KBr)]: 2800 (C@O), 1656 1 (NH+), 618 (SO4). kMðH2 OÞ ¼ 197 Scm2 mol . 2.4.3. [Cu2(PLSC)2(NCS)2](NCS)2, 3 To a water solution (20 cm3) containing 0.08 g (0.5 mmol) of CuCl22H2O 0.13 g (0.5 mmol) of PLSC2H2O was added followed by 0.12 g (1.6 mmol) NH4NCS. Dark brown crystals started to form after a couple of hours, which were then washed with methanol. Yield: 0.10 g (54%). Anal. Calc. for C22H24Cu2N12O6S4: C, 32.71; H, 3.00; N, 20.82; S, 15.84. Found: C, 32.60; H, 3.07; N, 20.76; S, 15.69%. Magnetic moment (l, BM): 1.60. IR [v(cm1) (KBr)]: 1 2800 (NH+), 2122 (C@N), 1648 (C@O). kMðH2 OÞ ¼ 367 Scm2 mol . 2.4.4. [Cu(PLSC)(NO3)2(CH3OH)], 4 To a warm methanol solution (10 cm3) containing 0.13 g (0.5 mmol) of PLSC2H2O, 0.12 g (0.5 mmol) of Cu(NO3)23H2O was added. After 2 days green crystals were separated by filtration. Yield: 0.09 g (42%). Anal. Calc. for C10H16Cu1N6O10: C, 27.06; H, 3.63; N, 18.94. Found: C, 26.93; H, 3.65; N, 18.59%. Magnetic moment (l, BM): 1.83. IR [v (cm1) (KBr)]: 2800 (NH+), 1657 (C@O), 1382 (NO3). kMeOH = 140 S cm2 mol1.

a 1:1 and 1:2 electrolyte. Finally, due to its sparing solubility the molar conductivity of 5 was not measured. In the IR spectra of 1, 2, 3 and 4 there exist one or more peaks at about 2800 cm1 belonging to m(NH+) of pyridine nitrogen [17], which are, on the other hand, absent in the IR spectra for 5 due to the deprotonation of the pyridine ring. The carbonyl stretching frequency for the coordinated ligand for all the complexes is found to be lower for about 20 cm1 in comparison with the free ligand (1680 cm1), which is consistent with the coordination of the ligand through this carbonyl group [26]. 3.2. X-ray crystallography The molecular structure of 1, shown in Fig. 1, emphasizes the coordination of both chloride anions in the solid state which is opposite of what has been observed in solution. However, the propensity of this complex towards ionization in solution is evident by a substantial difference in the two Cu–Cl bond lengths (2.5753(14) and 2.248(16) Å for Cu1–Cl2 and Cu1–Cl3, respectively). The ligand, in its neutral but zwitterionic form, coordinates in the usual tridentate fashion creating, together with two chloride atoms, a slightly disordered square pyramidal geometry around the central copper cation, which is also confirmed by the value for the trigonality index (s) of 0.098 [46]. The Cl2–Cu1–Cl3 angle (105.65(6)°) represents the largest deviation from this geometry (see Table 2). The Cu1–O4, Cu1–N12 and Cu1–O15 bond distances

2.4.5. [Cu(PLSC–2H]NH3H2O, 5 To a warm water solution (20 cm3) containing 0.13 g (0.5 mmol) of PLSC2H2O, 0.12 g (0.5 mmol) of CuSO45H2O was added resulting in complete dissolution of the ligand. Then, 5 cm3 of NH3(aq) (28–30% NH3 in water) was added to the warm mixture resulting in the formation of gray-green precipitate. Yield: 0.11 g (73%). Anal. Calc. for C9H15N5CuO4: C, 33.90; H, 3.55; N, 21.40. Found: C, 33.66; H, 4.71; N, 21.84%. Magnetic moment (l, BM): 1.80. IR [v (cm1) (KBr)]: 1644 (C@O), 1137 (NH3). k(insoluble). 3. Results and discussion 3.1. Synthesis and characterization of Cu(II) complexes All the reported complexes (1 through 5) are crystalline solids, stable in air and at room temperature, and of characteristic green color for Cu(II) compounds with this class of ligands [42,43]. They are all soluble in water and in most common polar solvents except for 5, which is only sparingly soluble in water. The magnetic moment measurements confirmed that all of the reported complexes incorporate Cu(II), d9, cation. Lower leff values for 2 (1.65 BM) and 4 (1.60 BM) are consistent with dinuclear structures while the leff values for 1 (1.85 BM), 3 (1.83 BM) and 5 (1.80 BM) are consistent with mononuclear one-electron transition metal complexes [44]. The molar conductivity value for 1 (kMeOH = 205 S cm2 mol1) is typical for a 2:1 electrolyte [45] and even though this complex is neutral in the solid state it still shows propensity for losing the chloride ligands (see X-ray discussion below) in solution. Complex 1 2 has the molar conductivity value (kMðH2 OÞ ¼ 197 Scm2 mol ) substantially greater than for a 1:1 electrolyte, which can be explained by doubly charged cations and anions formed in solution. Based on 1 the molar conductivity value for 3 (kMðH2 OÞ ¼ 367 Scm2 mol ), this complex exists as a 3:1 electrolyte suggesting the formation of [(PLSC)Cu(NCS)Cu(PLSC)]3+[NCS]3 in which one of the bridging thiocyanate ligands is displaced by solvent. A great extent of nitrate ligand substitution by solvent is also observed for 4 as the molar conductivity value (kMeOH = 140 S cm2 mol1) falls between

Fig. 1. The molecular structure of complex 1.

Table 2 Selected bond lengths (Å) and angles (°) for 1. Bond lengths Cu(1)–Cl(2) Cu(1)–Cl(3) Cu(1)–O(4) Cu(1)–N(12) Cu(1)–O(15) O(4)–C(5) C(5)–C(10) C(10)–C(11) C(11)–N(12) N(12)–N(13) N(13)–C(14) C(14)–O(15)

Bond angles 2.5753(14) 2.2489(16) 1.906(3) 1.975(4) 1.986(3) 1.282(6) 1.426(7) 1.452(6) 1.282(7) 1.379(5) 1.347(7) 1.252(6)

Cl(2)–Cu(1)–Cl(3) Cl(2)–Cu(1)–O(4) Cl(3)–Cu(1)–O(4) Cl(2)–Cu(1)–N(12) Cl(3)–Cu(1)–N(12) O(4)–Cu(1)–N(12) Cl(2)–Cu(1)–O(15) Cl(3)–Cu(1)–O(15) O(4)–Cu(1)–O(15) N(12)–Cu(1)–O(15) Cu(1)–O(4)–C(5) O(4)–C(5)–C(10) C(5)–C(10)–C(11) C(10)–C(11)–N(12) C(11)–N(12)–Cu(1) C(11)–N(12)–N(13) Cu(1)–N(12)–N(13) N(12)–N(13)–C(14) N(13)–C(14)–O(15) C(14)–O(15)–Cu(1)

105.65(6) 98.22(12) 91.96(12) 94.03(14) 159.72(15) 90.00(15) 92.93(11) 93.79(11) 165.58(14) 80.09(15) 128.6(3) 127.0(4) 120.8(5) 123.0(5) 129.7(3) 118.5(4) 111.7(3) 114.4(4) 120.0(4) 113.4(3)

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(1.906(3), 1.975(4) and 1.986(3) Å, respectively) are in agreement with the similar bond lengths observed for the dibromide analog [23]. The value of 124.60° for the C6–N7–C8 bond angle indicates the presence of a proton on N7 as the value of about 118° for this angle has been observed for deprotonated forms of similar ligands [26,29]. Lastly, the zwitterionic form of this ligand has been confirmed by the presence of a proton on N17. It is worth nothing that the hydrogen atom on the disordered –CH2OH group has not been included in the final refinement. For more details see Supplementary information. Dimeric form of 2 is shown in Fig. 2 in which the phenolic oxygen atoms on adjacent molecules act as bridging atoms. The Cu–Cu distance of 3.596(1) Å is much longer than the sum of Cu(II) ionic radii (1.58 Å) [47] for five coordinate Cu2+ ions. Besides the bridging phenolic oxygen, the central copper atom in each molecule is surrounded by the usually coordinated tridentate ligand, water and sulfate molecules resulting in a disordered octahedral geometry around the metal center (see Table 3). The bond lengths formed between the central copper atom and the ligand (1.882(3), 1.968(4) and 1.945(3) Å for Cu1–O2, Cu1–N6 and Cu1–O9, respectively) are in excellent agreement with the corresponding values observed for 1. Long Cu–O distances (2.295(3) and 2.256(3) Å for Cu1–O19 and Cu101–O119, respectively) for sulfate anions confirm the tendency this complex to ionize in solution. Furthermore, the pyridine angle C12–N12–C14 (124.0(4)°) confirms the neutral but zwitterionic form of the coordinated ligand. As in the case of 2, complex 3 (Fig. 3) is dimeric in the solid state in which two thiocyanide anions act as bridging ligands while the other two reside outside the copper coordination sphere. It is, however, worth noting that the centroid of the dimmer in 3 lies on an inversion center i.e. the second part of the dimmer is generated by symmetry. The Cu–Cu distance (5.506(2) Å) is much longer than in 2 and certainly longer than the sum of ionic radii for six coordinate Cu(II) complexes (1.74 Å) suggesting that there is no bonding interaction between two copper centers. The square pyramidal geometry (s = 0.053), created by the tridentate ligand and two bridging

Table 3 Selected bond lengths (Å) and angles (°) for 2. Bond lengths Cu(1)–O(2) Cu(1)–N(6) Cu(1)–O(9) Cu(1)–O(18) Cu(1)–O(19) Cu(1)–O(102) O(2)–C(3) C(3)–C(4) C(4)–C(1) C(1)–N(6) N(6)–N(7) N(7)–C(8) C(8)–O(9)

Bond angles 1.882(3) 1.968(4) 1.945(3) 1.981(3) 2.295(3) 2.790(3) 1.305(5) 1.431(6) 1.465(6) 1.283(6) 1.370(5) 1.372(6) 1.266(5)

O(2)–Cu(1)–N(6) O(2)–Cu(1)–N(6) O(2)–Cu(1)–O(9) N(6)–Cu(1)–O(9) O(2)–Cu(1)–O(18) N(6)–Cu(1)–O(18) O(9)–Cu(1)–O(18) O(2)–Cu(1)–O(19) N(6)–Cu(1)–O(19) O(9)–Cu(1)–O(19) O(18)–Cu(1)–O(19) O(2)–Cu(1)–O(102) N(6)–Cu(1)–O(102) O(9)–Cu(1)–O(102) O(18)–Cu(1)–O(102) O(19)–Cu(1)–O(102) Cu(1)–O(2)–C(3) O(2)–C(3)–C(4) C(4)–C(1)–N(6) C(1)–N(6)–Cu(1) C(1)–N(6)–N(7) Cu(1)–N(6)–N(7) N(6)–N(7)–C(8) N(7)–C(8)–O(9)

91.17(14) 91.17(14) 171.38(14) 82.51(13) 93.30(13) 166.12(14) 91.56(12) 92.11(13) 98.98(13) 94.65(12) 93.98(13) 85.88(12) 81.66(12) 87.40(11) 85.56(11) 177.91(10) 126.8(3) 126.6(4) 121.5(4) 130.3(3) 119.3(4) 110.4(3) 114.6(4) 120.1(4)

thiocyanides, around each copper is very similar to the geometry found in 1 (see Table 4). Additionally, the bond lengths between the central copper and the ligand (1.898(6), 1.949(7) and 1.988(6) Å for Cu1–O5, Cu1–N9 and Cu1–O12, respectively) are in excellent agreement with the same parameters observed for 1 and 2. The value for the C15–N16–C17 bond angle (123.6(7)°) also confirms neutral, but zwitterionic, form of the ligand. The copper coordination sphere for 4 (Fig. 4) consists of the tridentate ligand, two nitrate anions and a molecule of ethanol. The bond angles C2–Cu1–O9 (166.87(12)°) and C18–Cu1–O24 (166.47(9)°) show the larges deviation from perfect octahedron.

Fig. 2. The molecular structure of complex 2.

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Fig. 3. The molecular structure of complex 3.

Table 4 Selected bond lengths (Å) and angles (°) for 3. Bond lengths Cu(1)–N(4)#2 Cu(1)–S(2) Cu(1)–O(5) Cu(1)–N(9) Cu(1)–O(12) O(5)–C(6) C(6)–C(7) C(7)–C(8) C(8)–N(9) N(9)–N(10) N(10)–C(11) C(11)–O(12)

Table 5 Selected bond lengths (Å) and angles (°) for 4.

Bond angles 1.929(7) 2.865(3) 1.898(6) 1.949(7) 1.988(6) 1.314(11) 1.424(12) 1.451(12) 1.290(11) 1.381(10) 1.345(11) 1.267(10)

N(4)#2–Cu(1)–S(2) N(4)#2–Cu(1)–O(5) S(2)–Cu(1)–O(5) N(4)#2–Cu(1)–N(9) S(2)–Cu(1)–N(9) O(5)–Cu(1)–N(9) N(4)#2–Cu(1)–O(12) S(2)–Cu(1)–O(12) O(5)–Cu(1)–O(12) N(9)–Cu(1)–O(12) Cu(1)–O(5)–C(6) O(5)–C(6)–C(7) C(6)–C(7)–C(8) C(7)–C(8)–N(9) C(8)–N(9)–Cu(1) C(8)–N(9)–N(10) Cu(1)–N(9)–N(10) N(9)–N(10)–C(11) N(10)–C(11)–O(12)

Bond lengths 95.4(2) 93.7(3) 94.9(2) 171.5(3) 90.7(2) 91.7(3) 92.2(3) 94.6(2) 168.3(3) 81.4(3) 125.3(6) 126.5(8) 121.9(8) 121.6(8) 130.0(6) 118.4(7) 111.6(5) 114.9(7) 120.1(7)

Fig. 4. The molecular structure of complex 4.

The bond lengths that the cationic copper center forms with the ligand (1.886(3), 1.917(3) and 1.985(3) Å for Cu1–O2, Cu1–N6 and Cu1–O9, respectively) do not differ from the analogous values found in the there previously discussed complexes. Also, the neutral form of the ligand in 4 is confirmed by the value for the C12–N13–C14 angle of 124.9(3)°, while the tendency of this complex to lose its nitrate ligands in solution is established by long Cu–O bond distances (2.408(3) and 2.783(3) Å fro Cu1–O18 and Cu1–O24, respectively) (see Table 5). It is worth also mentioning that molecular structures of 1, 2, 3 and 4 exhibit extensive H-bonding. As the unit cells of 1 and 4 does not contain any non-coordinated anions or solvent molecules the H-bonding network is predominantly formed between the PLSC ligand backbone of one molecule with coordinated anionic ligand (e.g. Cl and NO3) of the neighboring molecule(s). The asymmetric

Cu(1)–O(2) Cu(1)–N(6) Cu(1)–O(9) Cu(1)–O(18) Cu(1)–O(22) Cu(1)–O(24) O(2)–C(3) C(3)–C(4) C(4)–C(5) C(5)–N(6) N(6)–N(7) N(7)–C(8) C(8)–O(9)

Bond angles 1.886(3) 1.917(3) 1.985(3) 2.408(3) 1.945(3) 2.783(3) 1.292(4) 1.426(5) 1.451(5) 1.293(5) 1.370(4) 1.353(5) 1.271(5)

O(2)–Cu(1)–N(6) O(2)–Cu(1)–O(9) N(6)–Cu(1)–O(9) O(2)–Cu(1)–O(18) N(6)–Cu(1)–O(18) O(9)–Cu(1)–O(18) O(2)–Cu(1)–O(22) N(6)–Cu(1)–O(22) O(9)–Cu(1)–O(22) O(18)–Cu(1)–O(22) O(2)–Cu(1)–O(24) N(6)–Cu(1)–O(24) O(9)–Cu(1)–O(24) O(18)–Cu(1)–O(24) O(22)–Cu(1)–O(24) Cu(1)–O(2)–C(3) O(2)–C(3)–C(4) C(3)–C(4)–C(5) C(4)–C(5)–N(6) C(5)–N(6)–N(7) N(6)–N(7)–C(8) N(7)–C(8)–O(9) C(8)–O(9)–Cu(1) C(12)–N(13)–C(14)

92.42(12) 166.87(12) 82.31(12) 106.77(11) 86.85(11) 85.04(10) 90.54(11) 176.10(12) 94.26(11) 94.72(11) 80.72(10) 81.51(11) 86.59(10) 166.47(9) 96.48(10) 127.2(2) 126.2(3) 121.7(3) 122.3(3) 119.0(3) 115.1(3) 119.7(3) 110.8(2) 124.9(3)

unit of 3 contains a non-coordinating thiocyanide anion, which aids to the formation of the H-boding network. The three water molecules in the asymmetric unit of 4 play a key role in the formation of H-bonds in this molecule. For example, the O53 labeled water molecule uses its two hydrogen atoms as donors to form H-bonds with two NO3 groups found on separate neighboring molecules while at the same time it acts as an acceptor for amino and phenolic hydrogen atoms located on two additional neighboring molecules. Also, the O51 and O52 labeled water molecules form H-bonds with three and two neighboring molecules, respectively, for which NO3 groups act as hydrogen acceptors.

4. Conclusion The synthetic, magnetic and conductiometric properties of five copper complexes featuring PLSC ligand have been examined. Magnetic measurements were consistent with the presence of Cu(II), d9, ion which was confirmed by the structural parameters obtained by single crystal X-ray analysis of four of these complexes. However, the conductiometric measurements suggested that the solution states of these complexes were different than the corresponding solid state structures with the regard to dissociation of anionic ligands.

D. Vidovic et al. / Polyhedron 30 (2011) 16–21

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