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Copper(II) complexes derived from di-2-pyridyl ketone N(4),N(4)-(butane-1,4-diyl)thiosemicarbazone: Crystal structure and spectral studies
Polyhedron 25 (2006) 1931–1938 www.elsevier.com/locate/poly
Copper(II) complexes derived from di-2-pyridyl ketone N(4),N(4)-(butane-1,4-diyl)thiosemicarbazone: Crystal structure and spectral studies Varughese Philip a
a,1
, V. Suni a, Maliyeckal R. Prathapachandra Kurup Munirathinam Nethaji b
a,*
,
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022, Kerala, India b Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Received 22 October 2005; accepted 12 December 2005 Available online 24 February 2006
Abstract Neutral copper(II) complexes with a tetradentate NNNS Schiff base have been synthesized using the ligand, di-2-pyridyl ketone N(4),N(4)-(butane-1,4-diyl)thiosemicarbazone (HL). A series of five binuclear complexes of HL with general stoichiometry CuLX [X = Cl (1), Br (2), NO3 (3), N3 (4) and SCN (5)], another dinuclear complex [Cu2LCl3] (6) with copper(II) chloride, and a tetranuclear complex [Cu4L4(SO4)2] (7) with copper(II) sulfate were also synthesized. The crystal structure of [Cu2L2(SO4)]2 Æ 3H2O has been determined by X-ray diffraction studies. Crystal analysis shows that the complex is tetranuclear with five coordinated copper centers. 2006 Elsevier Ltd. All rights reserved. Keywords: Thiosemicarbazone; Copper(II); X- ray crystal structure; Di-2-pyridyl ketone
1. Introduction Thiosemicarbazones belong to a group of thiourea derivatives and have emerged as an important class of sulfur donor ligands particularly for transition metal ions. Copper complexes with bis(thiosemicarbazone) ligands synthesized in the 1950s [1–3], have anticancer chemotherapeutic [4–6] and superoxide dismutase-like activity [7] and in the radiolabelled form have been used as positron emission agents for blood perfusion [8] and most recently tissue hypoxia [9,10]. The use of small magnetic centers has gained much interest because of the magnetic materials based on metal-cyano bridges [11]. In this study we have synthesized a novel tetranuclear copper(II) complex with sulfate bridging. The crystal structure revealed that the
compound is a rare example of a copper(II)–sulfato complex having a square pyramidal geometry around the copper(II) centers. Incorporation of the quadridentate ligand into the macrocyclic self assembled supramolecular structure is attractive for several reasons. There are only few examples of self-assembled systems [12]. The molecular structure reported here can add new dimensions to supramolecular chemistry. In this study we report the synthesis, magnetic and spectral studies of binuclear copper(II) complexes and the X-ray crystal structure of the tetranuclear copper(II) complex [Cu2L2(SO4)]2 (7) of the ligand di-2pyridyl ketone N(4),N(4)-(butane-1,4-diyl)thiosemicarbazone [13]. 2. Experimental
*
Corresponding author. Tel.: + 91 484 2575804; fax: +91 484 2577595. E-mail addresses: [email protected], [email protected] (M.R. Prathapachandra Kurup). 1 Permanent address: St. Thomas College, Kozhencherry, Kerala, India. 0277-5387/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2005.12.023
Di-2-pyridyl ketone (Fluka) and the copper(II) salts were used as received. The ligand HL was prepared by adapting the reported procedures [13,14].
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V. Philip et al. / Polyhedron 25 (2006) 1931–1938
2.1. Syntheses of complexes 2.1.1. Synthesis of [Cu2L2Cl2] (1), [Cu2L2Br2] (2), [Cu2L2(NO3)2] (3) and [Cu4L4(SO4)2] Æ 3H2O (7) The ligand HL (1 mmol) was dissolved in 20 ml of hot ethanol and the appropriate copper(II) salt (1 mmol) in the same solvent was added to it. The solution was heated under reflux for 2 h and then evaporated to a small volume. After cooling at room temperature, the dark blue crystals formed were isolated and dried under vacuum. 2.1.2. Synthesis of [Cu2L2(N3)2] (4) and [Cu2L2(SCN)2] (5) To a 20 ml hot ethanolic solution of the ligand HL (1 mmol) was added copper(II) acetate (1 mmol) in hot methanol. The solution was heated under reflux. To the refluxing solution, sodium azide or potassium thiocyanate were added in portions in the same molar ratio and further refluxed for 2 h. After cooling at room temperature, the dark blue crystals formed were isolated and dried under vacuum. 2.1.3. Synthesis of [Cu2LCl3] (6) The ligand HL (1 mmol) was dissolved in 20 ml of hot ethanol and CuCl2 Æ 2H2O (2 mmol) in the same solvent was added to it. The solution was heated under reflux for 2 h and then evaporated to a small volume. After cooling at room temperature, the dark blue crystals formed were isolated and dried under vacuum. 2.2. X-ray crystallography Single crystals of compound 7 suitable for X-ray diffraction studies were grown from its solution in a mixture of methanol and chloroform (1:1) by slow evaporation at room temperature in air. A single crystal of dimension 0.40 · 0.35 · 0.30 mm with P 1 symmetry was selected and mounted on a Bruker SMART APEX CCD diffractometer, equipped with a fine focus sealed tube X-ray source. The unit cell dimensions and intensity data were measured at 293 K. SMART software was used for data acquisition and SAINT software for data extraction [15]. Corrections for absorption were carried out by the SADABS method [16].
The whole structure was refined with SHELXL 97 [17] by the full-matrix least squares technique and the graphics tool was DIAMOND [18]. All non-hydrogen atoms were refined anisotropically, while the hydrogen atoms were treated with a mixture of independent and constrained refinements. 2.3. Physical methods Elemental analyses were carried out using a Heraeus Elemental Analyzer at the Regional Sophisticated Instrumentation Center, CDRI, Lucknow, India. Molar conductance measurements of the complexes were carried out in DMF solvent on a Century CC-601 digital conductivity meter with a dip type cell and platinum electrode. Approximately 103 M solutions were used. Magnetic moment measurements were carried out in the polycrystalline state on a Vibrating Sample Magnetometer at 5 kOe field strength. Infrared spectra were recorded on a Shimadzu DR 8001 series FTIR instrument as KBr pellets for spectra run from 4000 to 400 cm1, and using polyethylene for the range 500–100 cm1 in a Nicolet Magna 550 FTIR instrument. Solid-state reflectance spectra were recorded on Ocean Optics SD 2000 Fibre Optic Spectrometer. 3. Results and discussion Di-2-pyridyl ketone N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone (HL) interacts with copper(II) ions in the presence of anions, in the molar ratio 1:1:1 yielding complexes with the empirical formula [CuLX] where X = Cl, Br, NO3, N3, SCN. Analogously, the complexes [Cu2LCl3] (6) and [Cu4L4(SO4)2] (7) were obtained when the metal– ligand ratios were 2:1 and 1:1, respectively. Upon evaporation of the solvent, the complexes are precipitated as dark blue solids. These complexes are sparingly soluble in most non-polar solvents but soluble in DMF and DMSO giving non-conducting solutions [19]. Single crystals of the complex 7 suitable for X-ray diffraction were obtained by slow evaporation of its solution in a 1:1 mixture of methanol and chloroform in air at room temperature. The elemental analyses, molar conductance and magnetic susceptibility values are presented in Table 1. The magnetic susceptibility
Table 1 Colors, partial elemental analysis data, magnetic moments and molar conductivities of the Cu(II) complexes Compound
HL [CuLCl]2 (1) [CuLBr]2 (2) [CuL(NO3)]2 (3) [CuLN3]2 Æ H2O (4) [CuL(NCS)]2 (5) [Cu2LCl3] (6) [Cu2L2SO4]2 Æ 3H2O (7) a b
Color
yellow blue blue blue blue greenish yellow blue blue
Molar conductivity, 103 M DMF at 298 K. Magnetic susceptibility per copper atom.
Composition % found (calc) Carbon
Hydrogen
Nitrogen
62.10 47.16 42.40 43.48 45.37 46.94 35.75 43.80
5.56 4.02 3.56 3.77 3.86 3.81 3.07 4.30
22.43 16.65 14.92 18.88 26.94 19.42 12.27 15.60
(62.70) (46.94) (42.34) (44.08) (45.22) (47.26) (35.33) (44.13)
(5.46) (3.94) (3.55) (3.67) (4.03) (3.73) (2.94) (4.05)
(22.53) (17.11) (15.43) (19.28) (26.37) (19.45) (12.88) (16.08)
kMa
leffb (B.M.)
32 23 22 25 30 27 15
1.24 0.92 1.61 1.69 1.27 2.03 1.54
V. Philip et al. / Polyhedron 25 (2006) 1931–1938
values per copper atom are found to be less than the spin only value, indicating an exchange interaction between the copper centres. All complexes are reported to be paramagnetic at room temperature. 3.1. Molecular and crystal structures of the complex [Cu4L4(SO4)2] Æ 3H2O The structure of the tetranuclear complex [Cu4L4(SO4)2] Æ 3H2O is illustrated in Fig. 1 and the structural refinement parameters are given in Table 2. Selected bond lengths and bond angles are given in Tables 3 and 4. The structure contains four units comprising of two identical Cu(1)L outer units and two identical Cu(2)L inner units. In other words, it can be regarded as a dimeric structure of binuclear [Cu2L2SO4] units. The atom numbering scheme of the bimetallic unit is given in Fig. 1. Each copper atom in the outer unit is coordinated by a pyridyl nitrogen, azomethine nitrogen and thiolate sulfur of the thiosemicarbazone moiety and an oxygen of the bridging sulfato group. In addition to these, there is an additional Cu1– ˚, S3 bridging interaction at an apical distance of 2.942 A which renders a distorted (4 + 1) square pyramidal geometry around the Cu1 atoms. The Cu–Npyridyl bonds are ˚ farther away than Cu–Nimine bonds, denoting 0.0781 A the strength of the azomethine nitrogen coordination. The C(6)–N(3) bond length is slightly shorter than the cor˚ in the free ligand, responding bond distance of 1.308(4) A [13] indicating that there is no clear decrease in the double bond character on chelation. This can be attributed to the stabilization of the C–Nazomethine bond in the copper(II) complexes due to the presence of an important metal-
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Table 2 Crystal data and structural refinement parameters for the complex [Cu2L2(SO4)]2 Æ 3H2O Parameters
[Cu2L2(SO4)]2 Æ 3H2O
Empirical formula Formula weight (M) Temperature (T) K ˚) Wavelength (Mo Ka) (A Crystal system Space group Lattice constants ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) Volume, V (A Z Calculated density (q) (Mg m3) Absorption coefficient, l (mm1) F(000) Crystal size (mm) h Range for data collection Limiting Indices
C64H70Cu4N20O11S6 1741.96 293(2) 0.71073 triclinic P 1
Reflections collected Unique reflections Completeness to h Absorption correction Max and min transmission Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > r2(I)] R indices (all data) ˚ 3) Largest difference peak and hole (e A
11.225(6) 13.201(7) 14.558(7) 68.112(7) 67.786(7) 78.048(8) 1847.6(16) 2 1.614 1.382 924 0.40 · 0.35 · 0.30 1.60–27.46 13 6 h 6 13, 16 6 k 6 17, 18 6 l 6 18 19 156 7528 [Rint = 0.0201] 27.46 89.2% multiscan 0.6818 and 0.6078 full-matrix least-squares on F2 7528/0/623 1.079 R1 = 0.0335, wR2 = 0.0897 R1 = 0.0407, wR2 = 0.0944 0.471 and 0.438
Fig. 1. Molecular structure of [Cu2L2(SO4)]2 Æ 3H2O with the atom numbering scheme. Hydrogen atoms are omitted for clarity.
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V. Philip et al. / Polyhedron 25 (2006) 1931–1938
Table 3 ˚ ) of HL and [Cu2L2(SO4)]2 Æ 3H2O Selected bond lengths (A Bond length Cu(1)–S(1) Cu(1)–O(12) Cu(1)–N(1) Cu(1)–N(3) Cu(2)–S(3) Cu(1)–S(3) Cu(2)–O(11) Cu(2)–N(1A) Cu(2)–N(2A) Cu(2)–N(3A) S(1)–C(12) S(2)–O(11) S(2)–O(12) S(2)–O(13) S(3)–C(12A) N(3)–C(6) N(3A)–C(6A) N(3)–N(4) N(3A)–N(4A) N(4)–C(12) N(4A)–C(12A) N(5)–C(12) N(5A)–C(12A)
[Cu2L2(SO4)]2 Æ 3H2O
HL
1.671(4)
1.308(4) 1.308(4) 1.371(4) 1.371(4) 1.386(4) 1.386(4) 1.349(5) 1.349(5)
2.2771(12) 1.9322(15) 2.0274(18) 1.9493(17) 2.2871(12) 2.9417(15) 1.9386(13) 2.0225(17) 2.5958 1.9534(15) 1.745(2) 1.4967(13) 1.4886(14) 1.4449(15) 1.7423(18) 1.297(2) 1.304(2) 1.349(2) 1.349(2) 1.329(2) 1.330(2) 1.336(2) 1.337(2)
Table 4 Selected bond angles () of HL and [Cu2L2(SO4)]2 Æ 3H2O Bond angles S(1)–Cu(1)–O(12) S(1)–Cu(1)–N(1) S(1)–Cu(1)–N(3) O(12)–Cu(1)–N(1) O(12)–Cu(1)–N(3) N(1)–Cu(1)–N(3) S(3)–Cu(2)–O(11) S(3)–Cu(2)–N(1A) S(3)–Cu(2)–N(2A) S(3)–Cu(2)–N(3A) O(11)–Cu(2)–N(1A) O(11)–Cu(2)–N(2A) O(11)–Cu(2)–N(3A) N(1A)–Cu(2)–N(2A) N(1A)–Cu(2)–N(3A) N(2A)–Cu(2)–N(3A) N(3A)–Cu(2)–S(3) N(1A)–Cu(2)–S(3) N(4)–N(3)–C(6) N(4A)–N(3A)–C(6A) N(3)–N(4)–C(12) N(3A)–N(4A)–C(12A) N(5)–C(12)–N(4) N(5A)–C(12A)–N(4A) N(5)–C(12)–S(1) N(5A)–C(12A)–S(3)
HL
[Cu2L2(SO4)]2 Æ 3H2O
118.6(3) 118.6(3) 118.7(3) 118.7(3) 112.3(3) 112.3(3) 123.2(3) 123.2(3)
97.72(5) 164.20(4) 84.61(5) 96.22(6) 172.04(6) 80.60(6) 101.66(4) 164.61(4) 99.06 84.89(5) 93.63(5) 90.49 156.94(6) 82.47 80.27(6) 110.48 84.89(5) 164.61(4) 119.13(14) 119.09(14) 112.23(14) 112.50(13) 114.88(16) 114.19(14) 119.75(14) 119.91(13)
to-ligand p-back donation. The lengthening of the S(1)–C(12) bond from the corresponding bond distance in the free ˚ can be attributed to the delocalization ligand of 1.671(4) A of the negative charge on the N(3)–N(4)–C(12) system which is generated as a result of N(4)H deprotonation on complexation. The bond angles also are in conformity with
a distorted square pyramidal structure around the copper centres. Each copper atom in the inner subunit is also pentacoordinate with the bonds Cu(2)–S(3), Cu(2)–O(11), Cu(2)– N(1A), Cu(2)–N(3A) and Cu(2)–N(2A) adapting a distorted square pyramidal geometry with N(2A) of the third ligand moiety at the apical site. The pyridyl nitrogen N(1A), the imino nitrogen N(3A), and the thiolate sulfur S(3) atom, together with O(11) of the sulfato group, constitute the basal plane. The bond lengths in the basal plane agree with those found in copper(II) complexes containing thiosemicarbazones which act as uninegative tridentate ligands [20]. The bond lengths and bond angles reveal a distorted square pyramidal geometry around Cu(2). The unit cell-packing diagram of the complex viewed down the a-axis is given in Fig. 2. It can be observed that the molecules are packed in a two-dimensional manner parallel to the bc-plane. The adjacent tetrameric units are interconnected through hydrogen bonding interactions involving the oxygen atoms of the water molecules and the sulfato group. The assemblage of molecules in the respective manner in the unit cell is also assisted by the diverse p–p stacking, CH–p and ring–metal interactions as shown in Tables 5 and 6. The hydrogen bonding interactions are observed with donor–acceptor distances in the ˚ . The p–p interactions are rather range 2.8048–3.5360 A ˚ being the minimum distance between weak, with 3.3457 A the centroids. The p–p, CH–p, ring–metal and hydrogen bonding interactions stabilize the unit cell and point out the possibility for metalloaromaticity – a classic concept reviewed by Masui [21]. 3.2. Electronic spectra The electronic spectral data of the copper(II) complexes are given in Table 7. The UV–Vis spectra give much insight into the coordination geometry around the copper(II) ion. The broad band around 36 000 cm1 can be attributed to the p ! p* transition (pyridyl ring and the imine function) of thiosemicarbazone moiety. The shift of the p ! p* bands to the longer wavelength region in the complexes is the result of the C@S bond being weakened and the conjugation system being enhanced on complexation [22]. The pyridyl and imine function n ! p* band, centered around 29 100 cm1, overlaps and undergoes a small blue shift to ca. 31 500 cm1 on complexation indicating coordination via the pyridyl nitrogen with a reduction in intensity [23]. The ligand ! metal CT bands are found at 23 000– 26 000 cm1. The band near 26 000 cm1 in the complexes corresponds to S ! Cu(II) ligand to metal charge transfer bands. This band is in accordance with previous studies of copper(II) complexes with a similar type of ligand [24,25]. The pyridyl nitrogen N ! Cu(II) LMCT transitions are observed at 23 000 cm1. The spectra of the complexes exhibit weak d ! d bands centered around 16 000 cm1 for compounds 5 and 7. Such a feature is expected for square planar complexes [26]. For square planar complexes
V. Philip et al. / Polyhedron 25 (2006) 1931–1938
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Fig. 2. Unit cell packing diagram of [Cu2L2(SO4)]2 Æ 3H2O viewed down the ‘a’ axis. Table 5 H-bonding and p–p interaction parameters for [Cu2L2(SO4)]2 Æ 3H2O H-bonding Donor–H. . .A O(1) H(101) O(3) O(1) H(11) O(13) O(2) H(200) O(14) O(2) H(201) O(14) O(3) H(300) O(2) O(3) H(301) O(1) C(1A) H(1A) O(2) C(2) H(2) O(3) C(4) H(4) N(2) C(8A) H(8A) N(5) C(11A) H(11A) O(11) C(11A) H(11A) O(13) p–p interactions Cg(I)-Res(I) Cg(J) Cg(3)-[1] Cg(4)a Cg(3)-[1] Cg(7)a Cg(4)-[1] Cg(3)a Cg(4)-[1] Cg(5)a Cg(4)-[1] Cg(14)b Cg(5)-[1] Cg(4)a Cg(5)-[1] Cg(7)a Cg(7)-[1] Cg(3)a Cg(7)-[1] Cg(5)a Cg(7)-[1] Cg(14)b Cg(8)-[1] Cg(8)b Cg(14)-[1] Cg(4)b Cg(14)-[1] Cg(7)b Equivalent position codes a = x, y, z b = x, y, z
˚) D–H (A 0.69 0.87 0.73 0.75 0.75 0.64 0.95 0.93 0.95 0.94 0.95 0.95
˚) H A (A 2.19 1.94 2.10 2.24 2.09 2.17 2.56 2.45 2.49 2.62 2.59 2.59
˚) Cg–Cg(A 3.3457 3.3703 3.3457 3.3637 3.7415 3.3637 3.4142 3.3703 3.4142 3.6512 3.5172 3.7415 3.6512
˚) D–A (A 2.8715 2.8073 2.8048 2.9570 2.8287 2.7979 3.4637 3.3389 3.1139 3.5360 3.1619 3.5120
a () 14.65 15.37 14.65 14.37 5.18 14.37 15.00 15.37 15.00 04.10 0.00 05.18 04.10
D–H A () 171 175 163 161 168 170 160 159 123 164 118 164
b () 16.19 13.24 1.54 5.31 26.63 16.16 15.45 05.64 10.82 24.76 19.10 29.40 26.32
Cg(3) = Cu(1), S(1), C(12), N(4) Cg(4) = Cu(2), S(3), C(12A), N(4A) Cg(5) = Cu(1), S(1), C(12), N(4), N(3) Cg(7) = Cu(2), S(3), C(12A), N(4A), N(3A) Cg(8) = Cu(2), N(1A), C(5A), C(6A), N(3A) Cg(14) = N(1A), C(1A), C(2A), C(3A), C(4A), C(5A)
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Table 6 CH–p and ring–metal interaction parameters of [Cu2L2(SO4)]2 Æ 3H2O CH–p interactions X–H(I) Cg(J) C(4A)–H(4A) Cg(4)b C(4A)–H(4A) Cg(7)b C(8A)–H(8A) Cg(9)b C(10A)–H(10A) Cg(15)c C(15A)–H(15B) Cg(16)d C(16A)–H(16A) Cg(6)a Equivalent position codes a = x, y, z b = x, y, z c = x, 1 + y, z d = 1x, y, z
Ring–metal interaction Cg(I) Res(I) Me(J) Cg(3)-[1] ! Cu(1)e Cg(3)-[1] ! Cu(2)a Cg(4)-[1] ! Cu(1)3a Cg(5)-[1] ! Cu(1)e Cg(5)-[1] ! Cu(2)a Cg(7)-[1] ! Cu(1)a Equivalent position codes a = x, y, z e = x, y, 1 z
˚) H. . .Cg(A 3.3153 3.3660 2.8918 3.0467 3.3162 3.1225
X–H. . .Cg () 80.05 76.58 140.20 151.69 159.61 136.23
N
˚) X–Cg (A 3.2957 3.2826 3.6612 3.8815 4.1800 3.8890
S
C
N
X
N
C
M N
N
N N
Cg(4) = Cu(2), S(3), C(12A), N(4A) Cg(6) = Cu(1), N(1), C(5), C(6), N(3) Cg(7) = Cu(2), S(3), C(12A), N(4A), N(3A) Cg(9) = N(5), C(13), C(14), C(15), C(16) Cg(15) = N(2), C(7), C(8), C(9), C(10), C(11) Cg(16) = N(2A), C(7A), C(8A), C(9A), C(10A), C(11A)
M X
N C
S
C N N
Fig. 3. Tentative structure of compounds 1–5. ˚) Cg(I)–Me(J) (A b () 3.666 18.84 3.884 38.81 3.346 30.69 3.752 21.75 3.975 41.57 3.498 35.14 Cg(3) = Cu(1), S(1), C(12), N(4) Cg(4) = Cu(2), S(3), C(12A), N(4A) Cg(5) = Cu(1), S(1), C(12), N(4), N(3) Cg(7) = Cu(2), S(3), C(12A), N(4A), N(3A)
Cl N C
3.3. Infrared spectra A square pyramidal geometry can be assigned for 1–5 consisting of one of the pyridyl nitrogens, azomethine nitrogen, thiolate sulfur and the anion forming the basal plane, while the pyridyl nitrogen of the second ligand unit occupies the apical positions (Fig. 3) as reported by us before [25]. For compound 6 (Fig. 4), the terminal nature of the chlorine atoms indicates its structure to be similar to the copper(II) complex of a di-2-pyridyl ketone thiosemicarbazone prepared by Swearingen et al. [28]. Selected vibration bands of HL and its metal complexes are listed
Cl
N N
N Cu
with a dx2 y 2 ground state [27], three transitions are possible 2 dz 2 dx2 y 2 ; dxy dx2 y 2 and dxz ; dyz dx2 y 2 (2A1g B1g, 2 2 2 2 B2g B1g and B2g B1g). Since the four d orbitals lie very close together, each transition cannot be distinguished by their energy and hence it is very difficult to resolve the three bands into separate components.
Cu
C
N
S
Cl Fig. 4. Tentative structure of [Cu2LCl3] (6).
in Table 8. Since the compound contains a thioamide function, HL can exhibit thione–thiol tautomerism. The m(S–H) band at 2600 cm1 is absent in the spectrum of the ligand, indicating that it exists as the thione tautomer in the solid state. This is further supported by a medium band at 3049 cm1, indicative of the m(N–H) vibration. The absence of m(NH) in the spectrum of the complexes provides strong evidence for the ligand coordination around Cu(II) ion in its deprotonated form. The vibrations m(C@N) and d (C@S) contribute substantially to the bands at 1582 and 808 cm1, respectively, in the ligand. The band corresponding to azomethine nitrogen, m(C@N), shifts to higher energy on coordination due to the combination of m(C@N) with the newly formed m(N@C) bond which results
Table 7 Solid state electronic spectral data (cm1) for the copper(II) complexes Compound
d–d
CT
n ! p*
p ! p*
HL [CuLCl] (1) [CuLBr] (2) [CuL(NO3)] (3) [CuLN3] Æ 1/2H2O (4) [CuL(NCS)] (5) [Cu2LCl3] (6) [Cu2L2SO4]2 Æ 3H2O (7)
17857, 13947 sh 17094 w, 14534 sh 17793, 13263 sh 18050 sh, 14471 sh 16000 sh 17730, 14347 16025 sh
27473, 23475 sh, 22573 sh 25445 sh, 23310 s,b 25445 sh, 23584 s,b 25641sh, 22883 s,b, 25380 sh, 23041 s,b, 26246 s, 22624 s,b 25125 sh, 23809 s,b
30864, 29154 sh 32154 s, 32573 s, 31152 sh 32467 s,b, 31446 sh 32573 s,b 31446 s,b 31250 s, 31645 sh, 31152 sh
36231 sh, 35087 sh 32679 sh 34634 sh 38167 m 33112 sh
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Table 8 Tentative assignments of the selected IR bands (cm1) of the copper(II) complexes Compound
m(N–H)
m(C@N) + m(N@C)
m(C@S)
d(C@S)
m(Cu–N)
m(Cu–S)
m(Cu–Xa)
HL [CuLCl] (1) [CuLBr] (2) [CuL(NO3)] (3) [CuLN3] Æ 1/2H2O (4) [CuL(NCS)] (5) [Cu2LCl3] (6) [Cu2L2SO4]2 Æ 3H2O (7)
3049 m
1582 1593 1594 1599 1592 1593 1599 1593
1330 1289 1285 1278 1278 1295 1278 1296
808 784 780 789 784 787 789 784
409 412 411 410 419 411 406
336 325 328 334 325 328 332
320 250 445 312 318 310 303
a
s s s m s s m s
s w m m w m m m
m m w m w w m w
s s s m m s s
w m m w m m w
sh w m sh sh m m
X represents the anion Cl, Br, etc.
from the loss of the thioamide hydrogen from the thiosemicarbazone moiety [29–33]. The band at 808 cm1 shifts to lower wavenumbers in all complexes and this can be assigned to the d(C@S) vibration suggesting the change of bond order and strong electron-delocalization upon chelation [34]. Coordination of the pyridine nitrogen causes the out-of-the plane bending vibrational bands to shift from 600 cm1 to higher frequencies by 12–20 cm1 [20]. Compounds 1 and 6 showed sharp bands at 320 and 310 cm1, respectively, indicating terminally bonded rather than bridging chlorine ligands. A sharp band at 250 cm1 due to m(Cu–Br) vibrations is suggestive of terminally bonded bromine in 2. The ratio of m(Cu–Br)/m(Cu–Cl) is 0.77, which is consistent with the usual values obtained for the first row transition metals. For the nitrato complex (3), medium bands are observed at 1384, 1285 and 1013 cm1 corresponding to m4, m2 and m1, respectively, with a separation of 102 cm1, suggestive of terminally bonded monodentate nitrato groups [35]. The bands due to m3, m5 and m6 could not be assigned due to the richness of the spectrum. The m(Cu–N) of the complex is found at 445 cm1. The spectrum of complex 4 showed a strong band at 2042 cm1 due to the asymmetric m(N3) mode. The band
associated with the symmetric m(N3) mode is located at 1369 cm1. The band at 312 cm1 is assigned to the m(Cu–Nazide) mode. We have obtained three bands for compound 5, a strong sharp band at 2081 cm1, medium band at 787 cm1 and a weak band at 480 cm1 corresponding to m(CN), m(CS) and d(NCS), respectively. The intensity and band position indicates the unidentate coordination of the thiocyanate through the nitrogen atom. The sulfato complex 7 exhibits four fundamental vibrations: 970 cm1 due to m1, a medium band at 459 cm1 due to m2, medium and weak bands at 1243, 1181 and 1112 cm1 corresponding to m3, and medium and weak bands at 650, 615 and 575 cm1 due to m4, which are assigned to the bidentately coordinated sulfato group [35]. 3.4. EPR spectral investigations EPR parameters found for the complexes in the polycrystalline state (293 K) and in DMF at 293 and 77 K are presented in Table 9. The spectra in the polycrystalline state gave much information about the coordination geometry around the copper(II) ion. The complexes 1 and 3 revealed rhombic features. The compounds 2, 4, 5 and 7
Table 9 EPR spectral assignments of the copper(II) complexes Compound
State
Temperature (K)
[CuLCl] (1)
polycrystalline DMF DMF
298 298 77
[CuLBr] (2)
polycrystalline DMF
298 77
[CuL(NO3)] (3)
polycrystalline DMF DMF
298 298 77
polycrystalline DMF DMF
298 298 77
2.084
2.036
2.162
2.116
[CuL(NCS)] (5)
polycrystalline DMF
298 77
2.171 2.169
2.050 2.045
Cu2LCl3 (6)
DMF DMF
298 77
polycrystalline DMF DMF
298 298 77
[CuLN3] Æ 1/2H2O (4)
[Cu2L2SO4]2 Æ 3H2O (7)
gi
g1
g^
g2
g3
2.006
2.060
2.145
2.176
2.058
1.980
2.040
2.070
2.180
1.990
2.060
2.211
giso 2.101
2.124 2.093
2.063 2.066 2.110
2.076
2.090 2.020
2.061
2.151
2.060
2.180
2.051
2.789 2.080
1938
V. Philip et al. / Polyhedron 25 (2006) 1931–1938
showed an axial spectrum with well defined gi and g^ features. The variation in the g values indicates that the geometry of the compound is affected by the nature of the coordinating anions. The solution state EPR measurements in DMF at 298 K give isotropic spectra with well resolved hyperfine lines. The isotropic nature of the spectra is due to the tumbling motion of the molecules in DMF. The spectra of complexes showed clearly four well resolved hyperfine lines, which are due to the interaction of the electron spin with the copper nuclear spin (65Cu, I = 3/2). The A0 and g0 values show variations indicating dissimilar bonding character of the complexes. The EPR spectra of compounds 1, 3 and 6 in DMF at 77 K showed rhombic features with three g values g1, g2 and g3. However the azido complex (4) shows an axial spectrum. The g values for complexes in the solid state at 298 K and in DMF at 77 K are close to each other, which perceives that the geometry around the copper(II) ion is unaffected on cooling the solution to liquid nitrogen temperature. Acknowledgements The authors are thankful to the Regional Sophisticated Instrumentation Centre, CDRI, Lucknow, India, for the elemental analysis. M.R.P. Kurup is thankful to the Department of Science and Technology, Government of India, New Delhi for financial assistance. The authors also acknowledge DST IRPHA for X-ray data collection. Appendix A. Supplementary data Crystallographic data for 7 has been deposited at the Cambridge Crystallographic Centre with CCDC No. 272580. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 0 1223 336033; e-mail: [email protected]). Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2005.12.023. References [1] [2] [3] [4]
G.Z. Bahur, Anorg. Allg. Chem. 268 (1952) 351. G.Z. Bahur, Anorg. Allg. Chem. 273 (1953) 351. G.Z. Bahur, E.Z. Schieitzer, Anorg. Allg. Chem. 278 (1955) 136. J.P. Scovill, D.L. Klayman, C.F. Franchino, J. Med. Chem. 25 (1982) 1261. [5] P. Bindu, M.R.P. Kurup, T.R. Sathyakeerthy, Polyhedron 18 (1999) 321.
[6] B.S Garg, M.R.P. Kurup, S.K. Jain, Y.K. Bhoon, Transit. Met. Chem. 13 (1988) 309. [7] A. Wada, Y. Fujibayshi, A. Yokoyamma, Arch. Biochem. Biophys. 310 (1994) 1. [8] C.J. Mathias, M.J. Weich, M.E. Raichie, L.L. Lich, A.H. McGuire, K.R. Zinn, E. John, M.A. Green, J. Nucl. Med. 31 (1990) 351. [9] J.L.J. Dearling, J.S. Lewis, D.W. McCarthy, M.J. Welch, P.J. Blower, J. Chem. Commun. (1988) 2531. [10] J.L.J. Dearling, J.S. Lewis, G.E.D. Mullen, M.J. Welch, P.J. Blower, J. Biol. Inorg. Chem. 7 (2002) 249. [11] A.W. Christopher, P.A.G. Yap, N.P. Raju, J.E. Greedan, R.J. Crutchley, Inorg. Chem. 38 (1999) 2548. [12] H. Cheng, D. Chun-ying, F. Chen-jie, L. Yong-jiang, M. Qing-jin, J. Chem. Soc., Dalton Trans. (2000) 1207. [13] A. Usman, I.A. Razak, S. Chantrapromma, H.K. Fun, V. Philip, A. Sreekanth, M.R.P. Kurup, Acta Crystallogr. 58 (2002) c652. [14] J.P. Scovill, Phosphorous Sulfur Silicon 60 (1991) 25. [15] Siemens, SMART and SAINT, Area Detector Control and Integration Software, Siemens Analytical X-ray Instrunments Inc., Madison, WI, USA, 1996. [16] G.M. Sheldrik, SADABS, Program for Crystal Structure Refinement, University of Go¨ttingen, Go¨ttingen, Germany, 1993. [17] G.M Sheldrick, SHELXS-97 Program for the Solution of Crystal Structures, University of Go¨ttingen, Go¨ttingen, Germany, 1997. [18] K. Brandenburg, H. Putz, DIAMOND Version 3.0, Crystal Impact, GbR, Postfach 1251, D-53002 Bonn, Germany, 2004. [19] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81. [20] A. Sreekanth, M.R.P. Kurup, Polyhedron 22 (2003) 3321. [21] H. Masui, Coord. Chem. Rev. 957 (2001) 219. [22] I.-X. Li, H.-A. Tang, Yi-Zhi Li, M. Wang, L.-F. Wang, C.-G. Xia, J. Inorg. Biochem. 78 (2000) 167. [23] R.P. John, A. Sreekanth, M.R.P. Kurup, A. Usman, I.A. Razak, H.K. Fun, Spectrochim. Acta. 59A (2003) 1349. [24] M.A. Ali, D.A. Chowdhary, M. Nazimuddin, Polyhedron 3 (1984) 595. [25] V. Philip, V. Suni, M.R.P. Kurup, M. Nethaji, Polyhedron 24 (2005) 1133. [26] R.P. John, A. Sreekanth, V. Rajakannan, T.A. Ajith, M.R.P. Kurup, Polyhedron 23 (2004) 2549. [27] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., Elsevier, Amsterdam, 1984. [28] J.K. Swearingen, W. Kaminsky, D.X. West, Transit. Met. Chem. 32 (2002) 7. [29] M. Joseph, V. Suni, M.R.P. Kurup, M. Nethaji, A. Kishore, S.G. Bhat, Polyhedron 23 (2004) 3069. [30] A. Ali, M.T.H. Tarafdar, J. Inorg .Nucl .Chem. 39 (1977) 1785. [31] M.J.M. Campbell, Coord. Chem. Rev. 15 (1975) 279. [32] B.S. Garg, M.R.P. Kurup, S.K. Jain, Y.K. Bhoon, Transit. Met. Chem. 13 (1988) 247. [33] B.S. Garg, M.R.P. Kurup, S.K. Jain, Y.K. Bhoon, Transit. Met. Chem. 16 (1991) 111. [34] R. Mayer, in: M. Jansen (Ed.), Organosulfur Chemistry, Interscience, Newyork, 1967, p. 219. [35] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th ed., Wiley Interscience, New York, 1986.
Copper(II) complexes derived from di-2-pyridyl ketone N(4),N(4)-(butane-1,4-diyl)thiosemicarbazone: Crystal structure and spectral studies Varughese Philip a
a,1
, V. Suni a, Maliyeckal R. Prathapachandra Kurup Munirathinam Nethaji b
a,*
,
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022, Kerala, India b Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Received 22 October 2005; accepted 12 December 2005 Available online 24 February 2006
Abstract Neutral copper(II) complexes with a tetradentate NNNS Schiff base have been synthesized using the ligand, di-2-pyridyl ketone N(4),N(4)-(butane-1,4-diyl)thiosemicarbazone (HL). A series of five binuclear complexes of HL with general stoichiometry CuLX [X = Cl (1), Br (2), NO3 (3), N3 (4) and SCN (5)], another dinuclear complex [Cu2LCl3] (6) with copper(II) chloride, and a tetranuclear complex [Cu4L4(SO4)2] (7) with copper(II) sulfate were also synthesized. The crystal structure of [Cu2L2(SO4)]2 Æ 3H2O has been determined by X-ray diffraction studies. Crystal analysis shows that the complex is tetranuclear with five coordinated copper centers. 2006 Elsevier Ltd. All rights reserved. Keywords: Thiosemicarbazone; Copper(II); X- ray crystal structure; Di-2-pyridyl ketone
1. Introduction Thiosemicarbazones belong to a group of thiourea derivatives and have emerged as an important class of sulfur donor ligands particularly for transition metal ions. Copper complexes with bis(thiosemicarbazone) ligands synthesized in the 1950s [1–3], have anticancer chemotherapeutic [4–6] and superoxide dismutase-like activity [7] and in the radiolabelled form have been used as positron emission agents for blood perfusion [8] and most recently tissue hypoxia [9,10]. The use of small magnetic centers has gained much interest because of the magnetic materials based on metal-cyano bridges [11]. In this study we have synthesized a novel tetranuclear copper(II) complex with sulfate bridging. The crystal structure revealed that the
compound is a rare example of a copper(II)–sulfato complex having a square pyramidal geometry around the copper(II) centers. Incorporation of the quadridentate ligand into the macrocyclic self assembled supramolecular structure is attractive for several reasons. There are only few examples of self-assembled systems [12]. The molecular structure reported here can add new dimensions to supramolecular chemistry. In this study we report the synthesis, magnetic and spectral studies of binuclear copper(II) complexes and the X-ray crystal structure of the tetranuclear copper(II) complex [Cu2L2(SO4)]2 (7) of the ligand di-2pyridyl ketone N(4),N(4)-(butane-1,4-diyl)thiosemicarbazone [13]. 2. Experimental
*
Corresponding author. Tel.: + 91 484 2575804; fax: +91 484 2577595. E-mail addresses: [email protected], [email protected] (M.R. Prathapachandra Kurup). 1 Permanent address: St. Thomas College, Kozhencherry, Kerala, India. 0277-5387/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2005.12.023
Di-2-pyridyl ketone (Fluka) and the copper(II) salts were used as received. The ligand HL was prepared by adapting the reported procedures [13,14].
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V. Philip et al. / Polyhedron 25 (2006) 1931–1938
2.1. Syntheses of complexes 2.1.1. Synthesis of [Cu2L2Cl2] (1), [Cu2L2Br2] (2), [Cu2L2(NO3)2] (3) and [Cu4L4(SO4)2] Æ 3H2O (7) The ligand HL (1 mmol) was dissolved in 20 ml of hot ethanol and the appropriate copper(II) salt (1 mmol) in the same solvent was added to it. The solution was heated under reflux for 2 h and then evaporated to a small volume. After cooling at room temperature, the dark blue crystals formed were isolated and dried under vacuum. 2.1.2. Synthesis of [Cu2L2(N3)2] (4) and [Cu2L2(SCN)2] (5) To a 20 ml hot ethanolic solution of the ligand HL (1 mmol) was added copper(II) acetate (1 mmol) in hot methanol. The solution was heated under reflux. To the refluxing solution, sodium azide or potassium thiocyanate were added in portions in the same molar ratio and further refluxed for 2 h. After cooling at room temperature, the dark blue crystals formed were isolated and dried under vacuum. 2.1.3. Synthesis of [Cu2LCl3] (6) The ligand HL (1 mmol) was dissolved in 20 ml of hot ethanol and CuCl2 Æ 2H2O (2 mmol) in the same solvent was added to it. The solution was heated under reflux for 2 h and then evaporated to a small volume. After cooling at room temperature, the dark blue crystals formed were isolated and dried under vacuum. 2.2. X-ray crystallography Single crystals of compound 7 suitable for X-ray diffraction studies were grown from its solution in a mixture of methanol and chloroform (1:1) by slow evaporation at room temperature in air. A single crystal of dimension 0.40 · 0.35 · 0.30 mm with P 1 symmetry was selected and mounted on a Bruker SMART APEX CCD diffractometer, equipped with a fine focus sealed tube X-ray source. The unit cell dimensions and intensity data were measured at 293 K. SMART software was used for data acquisition and SAINT software for data extraction [15]. Corrections for absorption were carried out by the SADABS method [16].
The whole structure was refined with SHELXL 97 [17] by the full-matrix least squares technique and the graphics tool was DIAMOND [18]. All non-hydrogen atoms were refined anisotropically, while the hydrogen atoms were treated with a mixture of independent and constrained refinements. 2.3. Physical methods Elemental analyses were carried out using a Heraeus Elemental Analyzer at the Regional Sophisticated Instrumentation Center, CDRI, Lucknow, India. Molar conductance measurements of the complexes were carried out in DMF solvent on a Century CC-601 digital conductivity meter with a dip type cell and platinum electrode. Approximately 103 M solutions were used. Magnetic moment measurements were carried out in the polycrystalline state on a Vibrating Sample Magnetometer at 5 kOe field strength. Infrared spectra were recorded on a Shimadzu DR 8001 series FTIR instrument as KBr pellets for spectra run from 4000 to 400 cm1, and using polyethylene for the range 500–100 cm1 in a Nicolet Magna 550 FTIR instrument. Solid-state reflectance spectra were recorded on Ocean Optics SD 2000 Fibre Optic Spectrometer. 3. Results and discussion Di-2-pyridyl ketone N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone (HL) interacts with copper(II) ions in the presence of anions, in the molar ratio 1:1:1 yielding complexes with the empirical formula [CuLX] where X = Cl, Br, NO3, N3, SCN. Analogously, the complexes [Cu2LCl3] (6) and [Cu4L4(SO4)2] (7) were obtained when the metal– ligand ratios were 2:1 and 1:1, respectively. Upon evaporation of the solvent, the complexes are precipitated as dark blue solids. These complexes are sparingly soluble in most non-polar solvents but soluble in DMF and DMSO giving non-conducting solutions [19]. Single crystals of the complex 7 suitable for X-ray diffraction were obtained by slow evaporation of its solution in a 1:1 mixture of methanol and chloroform in air at room temperature. The elemental analyses, molar conductance and magnetic susceptibility values are presented in Table 1. The magnetic susceptibility
Table 1 Colors, partial elemental analysis data, magnetic moments and molar conductivities of the Cu(II) complexes Compound
HL [CuLCl]2 (1) [CuLBr]2 (2) [CuL(NO3)]2 (3) [CuLN3]2 Æ H2O (4) [CuL(NCS)]2 (5) [Cu2LCl3] (6) [Cu2L2SO4]2 Æ 3H2O (7) a b
Color
yellow blue blue blue blue greenish yellow blue blue
Molar conductivity, 103 M DMF at 298 K. Magnetic susceptibility per copper atom.
Composition % found (calc) Carbon
Hydrogen
Nitrogen
62.10 47.16 42.40 43.48 45.37 46.94 35.75 43.80
5.56 4.02 3.56 3.77 3.86 3.81 3.07 4.30
22.43 16.65 14.92 18.88 26.94 19.42 12.27 15.60
(62.70) (46.94) (42.34) (44.08) (45.22) (47.26) (35.33) (44.13)
(5.46) (3.94) (3.55) (3.67) (4.03) (3.73) (2.94) (4.05)
(22.53) (17.11) (15.43) (19.28) (26.37) (19.45) (12.88) (16.08)
kMa
leffb (B.M.)
32 23 22 25 30 27 15
1.24 0.92 1.61 1.69 1.27 2.03 1.54
V. Philip et al. / Polyhedron 25 (2006) 1931–1938
values per copper atom are found to be less than the spin only value, indicating an exchange interaction between the copper centres. All complexes are reported to be paramagnetic at room temperature. 3.1. Molecular and crystal structures of the complex [Cu4L4(SO4)2] Æ 3H2O The structure of the tetranuclear complex [Cu4L4(SO4)2] Æ 3H2O is illustrated in Fig. 1 and the structural refinement parameters are given in Table 2. Selected bond lengths and bond angles are given in Tables 3 and 4. The structure contains four units comprising of two identical Cu(1)L outer units and two identical Cu(2)L inner units. In other words, it can be regarded as a dimeric structure of binuclear [Cu2L2SO4] units. The atom numbering scheme of the bimetallic unit is given in Fig. 1. Each copper atom in the outer unit is coordinated by a pyridyl nitrogen, azomethine nitrogen and thiolate sulfur of the thiosemicarbazone moiety and an oxygen of the bridging sulfato group. In addition to these, there is an additional Cu1– ˚, S3 bridging interaction at an apical distance of 2.942 A which renders a distorted (4 + 1) square pyramidal geometry around the Cu1 atoms. The Cu–Npyridyl bonds are ˚ farther away than Cu–Nimine bonds, denoting 0.0781 A the strength of the azomethine nitrogen coordination. The C(6)–N(3) bond length is slightly shorter than the cor˚ in the free ligand, responding bond distance of 1.308(4) A [13] indicating that there is no clear decrease in the double bond character on chelation. This can be attributed to the stabilization of the C–Nazomethine bond in the copper(II) complexes due to the presence of an important metal-
1933
Table 2 Crystal data and structural refinement parameters for the complex [Cu2L2(SO4)]2 Æ 3H2O Parameters
[Cu2L2(SO4)]2 Æ 3H2O
Empirical formula Formula weight (M) Temperature (T) K ˚) Wavelength (Mo Ka) (A Crystal system Space group Lattice constants ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) Volume, V (A Z Calculated density (q) (Mg m3) Absorption coefficient, l (mm1) F(000) Crystal size (mm) h Range for data collection Limiting Indices
C64H70Cu4N20O11S6 1741.96 293(2) 0.71073 triclinic P 1
Reflections collected Unique reflections Completeness to h Absorption correction Max and min transmission Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > r2(I)] R indices (all data) ˚ 3) Largest difference peak and hole (e A
11.225(6) 13.201(7) 14.558(7) 68.112(7) 67.786(7) 78.048(8) 1847.6(16) 2 1.614 1.382 924 0.40 · 0.35 · 0.30 1.60–27.46 13 6 h 6 13, 16 6 k 6 17, 18 6 l 6 18 19 156 7528 [Rint = 0.0201] 27.46 89.2% multiscan 0.6818 and 0.6078 full-matrix least-squares on F2 7528/0/623 1.079 R1 = 0.0335, wR2 = 0.0897 R1 = 0.0407, wR2 = 0.0944 0.471 and 0.438
Fig. 1. Molecular structure of [Cu2L2(SO4)]2 Æ 3H2O with the atom numbering scheme. Hydrogen atoms are omitted for clarity.
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V. Philip et al. / Polyhedron 25 (2006) 1931–1938
Table 3 ˚ ) of HL and [Cu2L2(SO4)]2 Æ 3H2O Selected bond lengths (A Bond length Cu(1)–S(1) Cu(1)–O(12) Cu(1)–N(1) Cu(1)–N(3) Cu(2)–S(3) Cu(1)–S(3) Cu(2)–O(11) Cu(2)–N(1A) Cu(2)–N(2A) Cu(2)–N(3A) S(1)–C(12) S(2)–O(11) S(2)–O(12) S(2)–O(13) S(3)–C(12A) N(3)–C(6) N(3A)–C(6A) N(3)–N(4) N(3A)–N(4A) N(4)–C(12) N(4A)–C(12A) N(5)–C(12) N(5A)–C(12A)
[Cu2L2(SO4)]2 Æ 3H2O
HL
1.671(4)
1.308(4) 1.308(4) 1.371(4) 1.371(4) 1.386(4) 1.386(4) 1.349(5) 1.349(5)
2.2771(12) 1.9322(15) 2.0274(18) 1.9493(17) 2.2871(12) 2.9417(15) 1.9386(13) 2.0225(17) 2.5958 1.9534(15) 1.745(2) 1.4967(13) 1.4886(14) 1.4449(15) 1.7423(18) 1.297(2) 1.304(2) 1.349(2) 1.349(2) 1.329(2) 1.330(2) 1.336(2) 1.337(2)
Table 4 Selected bond angles () of HL and [Cu2L2(SO4)]2 Æ 3H2O Bond angles S(1)–Cu(1)–O(12) S(1)–Cu(1)–N(1) S(1)–Cu(1)–N(3) O(12)–Cu(1)–N(1) O(12)–Cu(1)–N(3) N(1)–Cu(1)–N(3) S(3)–Cu(2)–O(11) S(3)–Cu(2)–N(1A) S(3)–Cu(2)–N(2A) S(3)–Cu(2)–N(3A) O(11)–Cu(2)–N(1A) O(11)–Cu(2)–N(2A) O(11)–Cu(2)–N(3A) N(1A)–Cu(2)–N(2A) N(1A)–Cu(2)–N(3A) N(2A)–Cu(2)–N(3A) N(3A)–Cu(2)–S(3) N(1A)–Cu(2)–S(3) N(4)–N(3)–C(6) N(4A)–N(3A)–C(6A) N(3)–N(4)–C(12) N(3A)–N(4A)–C(12A) N(5)–C(12)–N(4) N(5A)–C(12A)–N(4A) N(5)–C(12)–S(1) N(5A)–C(12A)–S(3)
HL
[Cu2L2(SO4)]2 Æ 3H2O
118.6(3) 118.6(3) 118.7(3) 118.7(3) 112.3(3) 112.3(3) 123.2(3) 123.2(3)
97.72(5) 164.20(4) 84.61(5) 96.22(6) 172.04(6) 80.60(6) 101.66(4) 164.61(4) 99.06 84.89(5) 93.63(5) 90.49 156.94(6) 82.47 80.27(6) 110.48 84.89(5) 164.61(4) 119.13(14) 119.09(14) 112.23(14) 112.50(13) 114.88(16) 114.19(14) 119.75(14) 119.91(13)
to-ligand p-back donation. The lengthening of the S(1)–C(12) bond from the corresponding bond distance in the free ˚ can be attributed to the delocalization ligand of 1.671(4) A of the negative charge on the N(3)–N(4)–C(12) system which is generated as a result of N(4)H deprotonation on complexation. The bond angles also are in conformity with
a distorted square pyramidal structure around the copper centres. Each copper atom in the inner subunit is also pentacoordinate with the bonds Cu(2)–S(3), Cu(2)–O(11), Cu(2)– N(1A), Cu(2)–N(3A) and Cu(2)–N(2A) adapting a distorted square pyramidal geometry with N(2A) of the third ligand moiety at the apical site. The pyridyl nitrogen N(1A), the imino nitrogen N(3A), and the thiolate sulfur S(3) atom, together with O(11) of the sulfato group, constitute the basal plane. The bond lengths in the basal plane agree with those found in copper(II) complexes containing thiosemicarbazones which act as uninegative tridentate ligands [20]. The bond lengths and bond angles reveal a distorted square pyramidal geometry around Cu(2). The unit cell-packing diagram of the complex viewed down the a-axis is given in Fig. 2. It can be observed that the molecules are packed in a two-dimensional manner parallel to the bc-plane. The adjacent tetrameric units are interconnected through hydrogen bonding interactions involving the oxygen atoms of the water molecules and the sulfato group. The assemblage of molecules in the respective manner in the unit cell is also assisted by the diverse p–p stacking, CH–p and ring–metal interactions as shown in Tables 5 and 6. The hydrogen bonding interactions are observed with donor–acceptor distances in the ˚ . The p–p interactions are rather range 2.8048–3.5360 A ˚ being the minimum distance between weak, with 3.3457 A the centroids. The p–p, CH–p, ring–metal and hydrogen bonding interactions stabilize the unit cell and point out the possibility for metalloaromaticity – a classic concept reviewed by Masui [21]. 3.2. Electronic spectra The electronic spectral data of the copper(II) complexes are given in Table 7. The UV–Vis spectra give much insight into the coordination geometry around the copper(II) ion. The broad band around 36 000 cm1 can be attributed to the p ! p* transition (pyridyl ring and the imine function) of thiosemicarbazone moiety. The shift of the p ! p* bands to the longer wavelength region in the complexes is the result of the C@S bond being weakened and the conjugation system being enhanced on complexation [22]. The pyridyl and imine function n ! p* band, centered around 29 100 cm1, overlaps and undergoes a small blue shift to ca. 31 500 cm1 on complexation indicating coordination via the pyridyl nitrogen with a reduction in intensity [23]. The ligand ! metal CT bands are found at 23 000– 26 000 cm1. The band near 26 000 cm1 in the complexes corresponds to S ! Cu(II) ligand to metal charge transfer bands. This band is in accordance with previous studies of copper(II) complexes with a similar type of ligand [24,25]. The pyridyl nitrogen N ! Cu(II) LMCT transitions are observed at 23 000 cm1. The spectra of the complexes exhibit weak d ! d bands centered around 16 000 cm1 for compounds 5 and 7. Such a feature is expected for square planar complexes [26]. For square planar complexes
V. Philip et al. / Polyhedron 25 (2006) 1931–1938
1935
Fig. 2. Unit cell packing diagram of [Cu2L2(SO4)]2 Æ 3H2O viewed down the ‘a’ axis. Table 5 H-bonding and p–p interaction parameters for [Cu2L2(SO4)]2 Æ 3H2O H-bonding Donor–H. . .A O(1) H(101) O(3) O(1) H(11) O(13) O(2) H(200) O(14) O(2) H(201) O(14) O(3) H(300) O(2) O(3) H(301) O(1) C(1A) H(1A) O(2) C(2) H(2) O(3) C(4) H(4) N(2) C(8A) H(8A) N(5) C(11A) H(11A) O(11) C(11A) H(11A) O(13) p–p interactions Cg(I)-Res(I) Cg(J) Cg(3)-[1] Cg(4)a Cg(3)-[1] Cg(7)a Cg(4)-[1] Cg(3)a Cg(4)-[1] Cg(5)a Cg(4)-[1] Cg(14)b Cg(5)-[1] Cg(4)a Cg(5)-[1] Cg(7)a Cg(7)-[1] Cg(3)a Cg(7)-[1] Cg(5)a Cg(7)-[1] Cg(14)b Cg(8)-[1] Cg(8)b Cg(14)-[1] Cg(4)b Cg(14)-[1] Cg(7)b Equivalent position codes a = x, y, z b = x, y, z
˚) D–H (A 0.69 0.87 0.73 0.75 0.75 0.64 0.95 0.93 0.95 0.94 0.95 0.95
˚) H A (A 2.19 1.94 2.10 2.24 2.09 2.17 2.56 2.45 2.49 2.62 2.59 2.59
˚) Cg–Cg(A 3.3457 3.3703 3.3457 3.3637 3.7415 3.3637 3.4142 3.3703 3.4142 3.6512 3.5172 3.7415 3.6512
˚) D–A (A 2.8715 2.8073 2.8048 2.9570 2.8287 2.7979 3.4637 3.3389 3.1139 3.5360 3.1619 3.5120
a () 14.65 15.37 14.65 14.37 5.18 14.37 15.00 15.37 15.00 04.10 0.00 05.18 04.10
D–H A () 171 175 163 161 168 170 160 159 123 164 118 164
b () 16.19 13.24 1.54 5.31 26.63 16.16 15.45 05.64 10.82 24.76 19.10 29.40 26.32
Cg(3) = Cu(1), S(1), C(12), N(4) Cg(4) = Cu(2), S(3), C(12A), N(4A) Cg(5) = Cu(1), S(1), C(12), N(4), N(3) Cg(7) = Cu(2), S(3), C(12A), N(4A), N(3A) Cg(8) = Cu(2), N(1A), C(5A), C(6A), N(3A) Cg(14) = N(1A), C(1A), C(2A), C(3A), C(4A), C(5A)
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Table 6 CH–p and ring–metal interaction parameters of [Cu2L2(SO4)]2 Æ 3H2O CH–p interactions X–H(I) Cg(J) C(4A)–H(4A) Cg(4)b C(4A)–H(4A) Cg(7)b C(8A)–H(8A) Cg(9)b C(10A)–H(10A) Cg(15)c C(15A)–H(15B) Cg(16)d C(16A)–H(16A) Cg(6)a Equivalent position codes a = x, y, z b = x, y, z c = x, 1 + y, z d = 1x, y, z
Ring–metal interaction Cg(I) Res(I) Me(J) Cg(3)-[1] ! Cu(1)e Cg(3)-[1] ! Cu(2)a Cg(4)-[1] ! Cu(1)3a Cg(5)-[1] ! Cu(1)e Cg(5)-[1] ! Cu(2)a Cg(7)-[1] ! Cu(1)a Equivalent position codes a = x, y, z e = x, y, 1 z
˚) H. . .Cg(A 3.3153 3.3660 2.8918 3.0467 3.3162 3.1225
X–H. . .Cg () 80.05 76.58 140.20 151.69 159.61 136.23
N
˚) X–Cg (A 3.2957 3.2826 3.6612 3.8815 4.1800 3.8890
S
C
N
X
N
C
M N
N
N N
Cg(4) = Cu(2), S(3), C(12A), N(4A) Cg(6) = Cu(1), N(1), C(5), C(6), N(3) Cg(7) = Cu(2), S(3), C(12A), N(4A), N(3A) Cg(9) = N(5), C(13), C(14), C(15), C(16) Cg(15) = N(2), C(7), C(8), C(9), C(10), C(11) Cg(16) = N(2A), C(7A), C(8A), C(9A), C(10A), C(11A)
M X
N C
S
C N N
Fig. 3. Tentative structure of compounds 1–5. ˚) Cg(I)–Me(J) (A b () 3.666 18.84 3.884 38.81 3.346 30.69 3.752 21.75 3.975 41.57 3.498 35.14 Cg(3) = Cu(1), S(1), C(12), N(4) Cg(4) = Cu(2), S(3), C(12A), N(4A) Cg(5) = Cu(1), S(1), C(12), N(4), N(3) Cg(7) = Cu(2), S(3), C(12A), N(4A), N(3A)
Cl N C
3.3. Infrared spectra A square pyramidal geometry can be assigned for 1–5 consisting of one of the pyridyl nitrogens, azomethine nitrogen, thiolate sulfur and the anion forming the basal plane, while the pyridyl nitrogen of the second ligand unit occupies the apical positions (Fig. 3) as reported by us before [25]. For compound 6 (Fig. 4), the terminal nature of the chlorine atoms indicates its structure to be similar to the copper(II) complex of a di-2-pyridyl ketone thiosemicarbazone prepared by Swearingen et al. [28]. Selected vibration bands of HL and its metal complexes are listed
Cl
N N
N Cu
with a dx2 y 2 ground state [27], three transitions are possible 2 dz 2 dx2 y 2 ; dxy dx2 y 2 and dxz ; dyz dx2 y 2 (2A1g B1g, 2 2 2 2 B2g B1g and B2g B1g). Since the four d orbitals lie very close together, each transition cannot be distinguished by their energy and hence it is very difficult to resolve the three bands into separate components.
Cu
C
N
S
Cl Fig. 4. Tentative structure of [Cu2LCl3] (6).
in Table 8. Since the compound contains a thioamide function, HL can exhibit thione–thiol tautomerism. The m(S–H) band at 2600 cm1 is absent in the spectrum of the ligand, indicating that it exists as the thione tautomer in the solid state. This is further supported by a medium band at 3049 cm1, indicative of the m(N–H) vibration. The absence of m(NH) in the spectrum of the complexes provides strong evidence for the ligand coordination around Cu(II) ion in its deprotonated form. The vibrations m(C@N) and d (C@S) contribute substantially to the bands at 1582 and 808 cm1, respectively, in the ligand. The band corresponding to azomethine nitrogen, m(C@N), shifts to higher energy on coordination due to the combination of m(C@N) with the newly formed m(N@C) bond which results
Table 7 Solid state electronic spectral data (cm1) for the copper(II) complexes Compound
d–d
CT
n ! p*
p ! p*
HL [CuLCl] (1) [CuLBr] (2) [CuL(NO3)] (3) [CuLN3] Æ 1/2H2O (4) [CuL(NCS)] (5) [Cu2LCl3] (6) [Cu2L2SO4]2 Æ 3H2O (7)
17857, 13947 sh 17094 w, 14534 sh 17793, 13263 sh 18050 sh, 14471 sh 16000 sh 17730, 14347 16025 sh
27473, 23475 sh, 22573 sh 25445 sh, 23310 s,b 25445 sh, 23584 s,b 25641sh, 22883 s,b, 25380 sh, 23041 s,b, 26246 s, 22624 s,b 25125 sh, 23809 s,b
30864, 29154 sh 32154 s, 32573 s, 31152 sh 32467 s,b, 31446 sh 32573 s,b 31446 s,b 31250 s, 31645 sh, 31152 sh
36231 sh, 35087 sh 32679 sh 34634 sh 38167 m 33112 sh
V. Philip et al. / Polyhedron 25 (2006) 1931–1938
1937
Table 8 Tentative assignments of the selected IR bands (cm1) of the copper(II) complexes Compound
m(N–H)
m(C@N) + m(N@C)
m(C@S)
d(C@S)
m(Cu–N)
m(Cu–S)
m(Cu–Xa)
HL [CuLCl] (1) [CuLBr] (2) [CuL(NO3)] (3) [CuLN3] Æ 1/2H2O (4) [CuL(NCS)] (5) [Cu2LCl3] (6) [Cu2L2SO4]2 Æ 3H2O (7)
3049 m
1582 1593 1594 1599 1592 1593 1599 1593
1330 1289 1285 1278 1278 1295 1278 1296
808 784 780 789 784 787 789 784
409 412 411 410 419 411 406
336 325 328 334 325 328 332
320 250 445 312 318 310 303
a
s s s m s s m s
s w m m w m m m
m m w m w w m w
s s s m m s s
w m m w m m w
sh w m sh sh m m
X represents the anion Cl, Br, etc.
from the loss of the thioamide hydrogen from the thiosemicarbazone moiety [29–33]. The band at 808 cm1 shifts to lower wavenumbers in all complexes and this can be assigned to the d(C@S) vibration suggesting the change of bond order and strong electron-delocalization upon chelation [34]. Coordination of the pyridine nitrogen causes the out-of-the plane bending vibrational bands to shift from 600 cm1 to higher frequencies by 12–20 cm1 [20]. Compounds 1 and 6 showed sharp bands at 320 and 310 cm1, respectively, indicating terminally bonded rather than bridging chlorine ligands. A sharp band at 250 cm1 due to m(Cu–Br) vibrations is suggestive of terminally bonded bromine in 2. The ratio of m(Cu–Br)/m(Cu–Cl) is 0.77, which is consistent with the usual values obtained for the first row transition metals. For the nitrato complex (3), medium bands are observed at 1384, 1285 and 1013 cm1 corresponding to m4, m2 and m1, respectively, with a separation of 102 cm1, suggestive of terminally bonded monodentate nitrato groups [35]. The bands due to m3, m5 and m6 could not be assigned due to the richness of the spectrum. The m(Cu–N) of the complex is found at 445 cm1. The spectrum of complex 4 showed a strong band at 2042 cm1 due to the asymmetric m(N3) mode. The band
associated with the symmetric m(N3) mode is located at 1369 cm1. The band at 312 cm1 is assigned to the m(Cu–Nazide) mode. We have obtained three bands for compound 5, a strong sharp band at 2081 cm1, medium band at 787 cm1 and a weak band at 480 cm1 corresponding to m(CN), m(CS) and d(NCS), respectively. The intensity and band position indicates the unidentate coordination of the thiocyanate through the nitrogen atom. The sulfato complex 7 exhibits four fundamental vibrations: 970 cm1 due to m1, a medium band at 459 cm1 due to m2, medium and weak bands at 1243, 1181 and 1112 cm1 corresponding to m3, and medium and weak bands at 650, 615 and 575 cm1 due to m4, which are assigned to the bidentately coordinated sulfato group [35]. 3.4. EPR spectral investigations EPR parameters found for the complexes in the polycrystalline state (293 K) and in DMF at 293 and 77 K are presented in Table 9. The spectra in the polycrystalline state gave much information about the coordination geometry around the copper(II) ion. The complexes 1 and 3 revealed rhombic features. The compounds 2, 4, 5 and 7
Table 9 EPR spectral assignments of the copper(II) complexes Compound
State
Temperature (K)
[CuLCl] (1)
polycrystalline DMF DMF
298 298 77
[CuLBr] (2)
polycrystalline DMF
298 77
[CuL(NO3)] (3)
polycrystalline DMF DMF
298 298 77
polycrystalline DMF DMF
298 298 77
2.084
2.036
2.162
2.116
[CuL(NCS)] (5)
polycrystalline DMF
298 77
2.171 2.169
2.050 2.045
Cu2LCl3 (6)
DMF DMF
298 77
polycrystalline DMF DMF
298 298 77
[CuLN3] Æ 1/2H2O (4)
[Cu2L2SO4]2 Æ 3H2O (7)
gi
g1
g^
g2
g3
2.006
2.060
2.145
2.176
2.058
1.980
2.040
2.070
2.180
1.990
2.060
2.211
giso 2.101
2.124 2.093
2.063 2.066 2.110
2.076
2.090 2.020
2.061
2.151
2.060
2.180
2.051
2.789 2.080
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showed an axial spectrum with well defined gi and g^ features. The variation in the g values indicates that the geometry of the compound is affected by the nature of the coordinating anions. The solution state EPR measurements in DMF at 298 K give isotropic spectra with well resolved hyperfine lines. The isotropic nature of the spectra is due to the tumbling motion of the molecules in DMF. The spectra of complexes showed clearly four well resolved hyperfine lines, which are due to the interaction of the electron spin with the copper nuclear spin (65Cu, I = 3/2). The A0 and g0 values show variations indicating dissimilar bonding character of the complexes. The EPR spectra of compounds 1, 3 and 6 in DMF at 77 K showed rhombic features with three g values g1, g2 and g3. However the azido complex (4) shows an axial spectrum. The g values for complexes in the solid state at 298 K and in DMF at 77 K are close to each other, which perceives that the geometry around the copper(II) ion is unaffected on cooling the solution to liquid nitrogen temperature. Acknowledgements The authors are thankful to the Regional Sophisticated Instrumentation Centre, CDRI, Lucknow, India, for the elemental analysis. M.R.P. Kurup is thankful to the Department of Science and Technology, Government of India, New Delhi for financial assistance. The authors also acknowledge DST IRPHA for X-ray data collection. Appendix A. Supplementary data Crystallographic data for 7 has been deposited at the Cambridge Crystallographic Centre with CCDC No. 272580. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 0 1223 336033; e-mail: [email protected]). Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2005.12.023. References [1] [2] [3] [4]
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