Crystal structure and EPR studies of doped Cu2+ ion in [Zn(sac)2(en)2] single crystal

Spectrochimica Acta Part A 75 (2010) 1195–1199

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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

Crystal structure and EPR studies of doped Cu2+ ion in [Zn(sac)2 (en)2 ] single crystal Bünyamin Karabulut a,∗ , I˙ brahim Uc¸ar a , Fevzi Köksal a , Yusuf Yerli b a b

Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139, Samsun, Turkey Department of Physics, Faculty of Science, Gebze Institute of Technology, 41400, Gebze, Turkey

a r t i c l e

i n f o

Article history: Received 29 January 2009 Received in revised form 13 October 2009 Accepted 26 October 2009 Keywords: X-ray diffraction Crystal structure Electron paramagnetic resonance (EPR) Magnetic properties

a b s t r a c t The tran-bis(ethylenediamine)bis(saccharinato)Zinc(II), [Zn(sac)2 (en)2 ] (ZSED), (en: ethylenediamine and sac: saccharinate) complex has been synthesized and its crystal structure has been determined by X-ray diffraction analysis. The compound crystallizes in space group P21 /c. The Zn(II) ion is hexacoordinated by four nitrogens of two bidentate en ligands composing the basal plane and two nitrogen atoms from the monodentate two sac ligands (N-bonded) occuping the axial sites, adopting an elongated octahedral sphere. Both en and sac ligands occupy the trans positions of the coordination octahedron. The Zn(II) ion in title compound sits on a inversion centre and is octahedrally coordinated two bidentate en (ethylenediamine) and two sac (saccharinate) (N-bonded) ligands. The magnetic environments of Cu2+ doped [Zn(sac)2 (en)2 ] complex have been identified by electron paramagnetic resonance (EPR) technique. Cu2+ doped ZSED single crystals have been studied at room temperature in three mutually perpendicular planes. The calculated results of the Cu2+ doped ZSED indicate that Cu2+ ion contains two magnetically inequivalent Cu2+ sites in distinct orientations occupying substitutional positions in the host lattice and show very high angular dependence. © 2009 Elsevier B.V. All rights reserved.

1. Introduction Saccharin (C7 H5 NO3 S, also known o-sulphobenzimide, 1,2benzothiazole-3(2H)-one 1,1-dioxide) is one of the best known and most widely used artificial sweetening agents [1,2]. The chemical properties and biochemical activity of saccharin and its compounds have been intensively investigated mainly due to its suspected cancerogenic nature [3]. But it is now thought that saccharin is safe at human levels of consumption. On the other hand the saccharin molecule contains imino hydrogen which is acidic in nature and can easily be lost producing the anion (C7 H4 NO3 S)− . This anion has several potential donor atoms such as imino nitrogen, one carbonyl and two sulphonyl oxygen atoms, which make the saccharinate anion very interesting and versatile polyfunctional ligand in coordination chemistry. For transition metal cations M–N are the preferred interactions while M–O predominates in the case of alkaline and alkaline-earth saccharinates [4,5]. Additionally, saccharinate anion acts as a bridging ligand in certain cases, through its N and O (carbonyl) atoms [6,7].

∗ Corresponding author. Tel.: +90 362 3121919; fax: +90 362 4576081. E-mail address: [email protected] (B. Karabulut). 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.10.038

Recently, we have initiated the crystallographic and spectroscopic characterization of mixed ligand metal saccharinate complexes in which the saccharinate acts as a counter anion [8]. As a continuation of these studies, we have now prepared and thoroughly characterized a new Zn(II) complex containing two saccharinate anions together with ethylenediamine ligand. Owing to possible use in pharmacology and evaluate it as a pharmacological agent, the detailed knowledge of its physical properties should be known. In this context, we have determined both structural and magnetic properties of ZSED. In order to obtain EPR data, transition metal ions should be doped in the host lattice of ZSED as an impurity. It is now well known that the transition metal ions as a probe can be used to determine the symmetry environments of the complexes in host lattices by EPR technique [9–12]. When these ions form paramagnetic centres then one can get information about the local symmetry. Since Cu2+ ions are generally used as probes to enter the lattice substitutionally in place of the divalent cation in the lattices containing divalent cations in the literature, we have used Cu2+ ions in ZSED [13–15] and a numerical technique together with a trial and error procedure is used to resolve the spectra. The complexes are identified and structural deformations were discussed using the spin Hamiltonian parameters obtained from the spectra obtained the EPR data [16].

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2. Experimental 2.1. General method All chemical reagents were analytical grade commercial products. Solvents were purified by conventional methods. The EPR spectra were recorded using a Varian E-109C model X-band spectrometer. The magnetic field modulation frequency was 100 kHz and the microwave power was around 10 mW. The single crystals were mounted on a goniometry and the spectra were recorded in three mutually perpendicular planes at 10◦ intervals at 298 K. The g values were obtained by comparison with a diphenylpicrylhydrazyl sample of g = 2.0036. 2.2. Synthesis of [Zn(sac)2 (en)2 ] Into aqueous solution of the corresponding Zn(II) acetate, [Zn2+ (OAc)2 ] (2 mmol, 20 mL) was added to an aqueous solution of sodium saccharinate (4 mmol, 20 mL). After stirring for 30 min, precipitates were filtered and washed with acetone to yield the compounds [Zn2+ (saccharinato)2 (H2 O)4 ]·2H2 O. An aqueous solution of ethylenediamin (en) (4 mmol, 20 mL) were added into aqueous solutions of these compounds (2 mmol, 20 mL), under stirring, and the mixtures were allowed to stand at 333 K temperature. After a few days, well formed crystals were selected for X-ray studies. The single crystals of Cu2+ doped ZSED were also grown by slow evaporation of the saturated aqueous solutions admixtured in stochiometric ratios with about 0.05% CuCl2 ·6H2 O salt. The well developed single crystals of suitable sizes were selected for EPR investigation after about a week.

Table 1 Crystal data and structure refinement for [Zn(sac)2 (en)2 ]. Formula Formula weight Temperature (K) Radiation, , (MoK␣) Crystal system Space group

C18 H24 N6 O6 S2 Zn 549.96 297(2) 0.7107 Monoclinic P21 /c

Unit cell dimensions a, b, c (Å) ˇ (◦ ) Volume (Å3 ) Z Calculated density (g cm−3 )  (mm−1 ) F(0 0 0) Crystal size (mm)  range (◦ )

11.3585(17), 7.0749(13), 14.939(3) 111.706(13) 1115.4(3) 2 1.638 1.337 568.0 0.42 × 0.31 × 0.26 2.35–27.25

Index ranges

−14 ≤ h ≤ 12 −9 ≤ k ≤ 4 −19 ≤ l ≤ 15

Reflections collected Independent reflections Reflections observed [I ≥ 2(I)] Absorption correction Refinement method Data/restrains/parameters Goodness-of-fit on F2 Final R indices [I ≥ 2(I)] R indices (all data) Largest diff. peak and hole (eÅ−3 )

2188 1842 [R(int) = 0.029] 1363 Integration Full-matrix least-squares on F2 1842/4/167 1.036 0.040 0.059 0.31, −0.33

Fourier difference map. Molecular drawings were obtained using ORTEP-III [19].

2.3. X-ray crystallography 3. Results and discussion Suitable single crystals were mounted on a glass fiber and data collection were performed on a STOE IPDSII image plate detector using Mo K␣ radiation ( = 0.71019 Å). Details of the crystal structure are given in Table 1. Data collection: Stoe X-AREA [17]. Cell refinement: Stoe X-AREA [17]. Data reduction: Stoe X-RED [17]. The structure was solved by direct-methods using SHELXS-97 [18] and anisotropic displacement parameters were applied to nonhydrogen atoms in a full-matrix least-squares refinement based on F2 using SHELXL-97 [18]. All carbon hydrogens were positioned geometrically and refined by a riding model with Uiso 1.2 times that of attached atoms and remaining H atoms were located from the

3.1. Crystal structure of ZSED An ORTEP III [19] view of trans-[Zn(sac)2 (en)2 ] with the atom labelling is shown in Fig. 1. The selected bond lengths and angles together with the hydrogen bonding geometry are listed in Table 2. Single crystal X-ray structural analysis shows that the structure consists of a neutral molecules of trans-[Zn(sac)2 (en)2 ], in which the zinc(II) ion located on a inversion centre. The Zn(II) ion is hexa-coordinated by four nitrogens of two bidentate en ligands composing the basal plane and two nitrogen atoms from the mon-

Fig. 1. The molecular structure of zinc(II) complex, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level and H atoms are shown as small spheres of arbitrary radii. Symmetry code (i) = 1 − x, 1 − y, 1 − z.

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Table 2 Interatomic bond distances (Å) and angles (◦ ). (a) Bond lengths, bond angles Bond lengths (Å) N1–Zn1: 2.125(3)

N2–Zn1: 2.116(3)

N3–Zn1: 2.360(3)

N1–Zn1–N3: 91.29(12) N2–Zn1–N3i : 90.63(13)

N2–Zn1–N1: 82.47(12) N1–Zn1–N3i : 88.71(12)

◦

Bond angles ( ) N2–Zn1–N3: 89.37(13) N2–Zn1–N1i : 97.53(12)

(b) Hydrogen-bonding interactions (Å,◦ ) D–H· · ·A N1–H1A· · ·O1 N1–H1B· · ·O3i N1–H1B· · ·O2ii N2–H2A· · ·O2

D–A 0.88(2) 0.89(2) 0.89(2) 0.87(2)

H· · ·A 2.49(3) 2.21(3) 2.55(4) 2.28(3)

D· · ·A 3.266(5) 2.958(5) 3.069(4) 3.105(5)

∠ D–H· · ·A 148(3) 142(4) 118(3) 157(5)

Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii) 1 − x, 2 − y, 1 − z.

odentate two sac ligands (N-bonded) occupying the axial sites, adopting an elongated octahedral sphere. Both en and sac ligands occupy the trans positions of the coordination octahedron. The Zn1–Nsac bond length [2.360(3) Å] is significantly longer than the equivalent distances found in the following complexes: [Zn(sac)2 (H2 O)4 ]·2H2 O [2.200(4) Å] [20], [Zn(sac)2 (py)2 ] [1.977(2) Å] [21], [Zn(sac)2 (im)2 ] [1.971(3) and 2.033(3) Å] [22], [Zn(sac)2 (bzim)2 ]2 ·2Et-OH·H2 O [2.043(4) Å and 2.014(4) Å] [6], [Zn(sac)(bpy)2 (H2 O)]·sac [2.159(3) Å] [23], [Zn(sac)3 (H2 O)·ApyH [1.990(2), 1.965(2) and 1.980(2) Å] [24]; this may be indicative of a stronger metal–ligand interaction in the compound (py: pyridine, im: imidazole, bzim: benzimidaole, Et–OH: ethanol, bpy: 2,2 dipyridyl, ApyH: 2-Aminopyridinium). The Zn1–Nen bond lengths ranging from 2.116(3) Å to 2.125(3) Å are found to be almost same as in Zn(II) complexes with en ligand [25–28]. The crystal packing analyses indicate that the structure of [Zn(sac)2 (en)2 ] exhibits an interesting hydrogen bonding interactions. The amino hydrogen atoms of the en ligands form mono-and bifurcated intra and intermolecular hydrogen bonds of the N–H· · ·O type with the carbonyl and sulfonyl oxygen atoms of the adjacent sac ligands along the a-axis. This results in a one-dimensional hydrogen bonded chain. The hydrogen bonded chains running along the c axis are further connected by weak C–H· · ·␲ interactions [C8–H8B· · ·Cg* : Cg is centroid of atoms S1, N3, C1, C2, C7; *: x, −y + 0.5, z + 0.5; d(H8B· · ·Cg* ) = 3.017 Å, the angle of C8–H8B· · ·Cg* is 165.51◦ , the perpendicular distance from the H8B to Cg* is 2.867 Å], forming a three-dimensional network. 3.2. EPR investigation Cu2+ ion doped ZSED single crystal is in d9 state. The recorded EPR spectra of Cu2+ doped ZSED single crystal show two sets of four

Fig. 2. EPR spectrum of Cu2+ doped ZSED single crystal for the magnetic field is in the (bc) plane 170◦ away from the b-axis.

hyperfine lines in all the three mutually perpendicular axes b, a*, and c for every 10◦ interval. EPR spectra of the Cu2+ doped ZSED single crystal are shown in Fig. 2 when the magnetic field is in the (b c) plane 170◦ away from the b-axis. These spectra obviously belong to Cu2+ , for which S = 1/2 and I = 3/2. Since the line width is broad, the 63 Cu2+ and 65 Cu2+ hyperfine lines are not clearly resolved at all orientations. The angular variations of the EPR spectra of Cu2+ doped ZSED single crystals are shown in Fig. 3. From the figure, the g2 values of all detected single lines are plotted against the rotation angle in mutually three perpendicular planes. When the magnetic field is along the crystallographic b-axis or in the a*c plane the spectrum consists of a single set of four hyperfine lines, but when the magnetic field is in the ba* and cb planes, the spectra consist of two sets of four hyperfine lines of the Cu2+ ions. This is consistent with the monoclinic symmetry of the crystals and indicates the presence of two magnetically different sites for Cu2+ ion. Therefore, we concluded that Cu2+ substitutes Zn2+ ions. The g2 () and a2 () (hyperfine) values are calculated in three planes from the variations of all lines as described in [29]. They are fitted to Eq. (1) to obtain g2 and A2 tensor elements. Both parameters change with the functions. gk2 () = gii2 cos2 i + gjj2 sin2 j + 2gij2 sin i cos j a2k () = a2ii cos2 i + a2jj sin2 j + 2a2ij sin i cos j

(1)

where i, j, k = x, y, z. The spectrum can be described in terms of a spin Hamiltonian of the form H = ˇ[gxx Hx Sx + gyy Hy Sy + gzz Hz Sz ] + Azz Izz Sz + Ay Iy Sy + Ax Ix Sx (2)

Fig. 3. Angular variations of the g2 values of all lines in three mutually perpendicular planes of Cu2+ doped ZSED single crystal.

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Table 3 Principal g and A values of Cu2+ doped in ZSED single crystals at room temperature (g = ±0.002, A = ±3G). Complex

g

Hyperfine A (G)

I

gxx = 2.064 gyy = 2.056 gzz = 2.229

0.906 −0.048 0.418

0.067 0.972 −0.029

−0.416 0.057 0.907

Axx = 42.2 Ayy = 46.0 Azz = 183.5

0.711 0.580 0.397

II

gxx = 2.065 gyy = 2.026 gzz = 2.229

0.912 0.028 −0.407

−0.039 0.998 −0.029

0.406 0.043 0.912

Axx = 53.0 Ayy = 38.3 Azz = 182.8

0.797 0.452 −0.398

Powder

g|| = 2.226

Direction cosines a*

b

Direction cosines

c

g⊥ = 2.052

a*

A|| = 180G

b

c

−0.619 0.783 −0.0353

−0.331 −0.221 0.917

−0.504 0.862 −0.029

0.33 0.224 0.916

A⊥ = 48G

Table 4 Ground state wave function parameters of Cu2+ ions observed in different environments.  is the Fermi contact term. Environment

T (K)

Site

␬

˛ 2

˛

ˇ

Ref.

[Zn(sac)2 (en)2 ] [Zn(sac)2 (en)2 ] [Co(ina)2 (H2 O)4 ](sac)2 ·1.5H2 O [Co(ina)2 (H2 O)4 ](sac)2 ·1.5H2 O Laps Laps Lap Laps [Zn(sac)2 (H2 O)4 ]·2H2 O [Zn(sac)2 (H2 O)4 ]·2H2 O CdK2 (SO4 )2 ·6H2 O [Zn(sac)2 (py)2 ]

300

I II I II I II I II I II

0.301 0.339 0.720 0.657 0.975 0.960 0.705 0.713 0.317 0.322 0.315 0.322

0.887 0.870 0.531 0.580 0.563 0.590 0.429 0.460 0.900 0.892 0.769 0.895

0.991 0.993 0.981 0.969 0.926 0.909 0.994 0.958 0.987 0.986 0.996 0.985

0.127 0.116 0.195 0.247 0.377 0.418 0.113 0.288 0.163 0.169 0.077 0.175

a a [8] [8] [10] [10] [11] [11] [31] [31] [33] [35]

300 300 300 300 77 300

a: this work.

which includes only electronic Zeeman and hyperfine interactions. Nuclear Zeeman and quadrupole interactions are neglected. In order to find the g and A values, we have used an iterative numerical technique [29]. After the calculation, g and A tensors were constructed and diagonalized to find principal g and A values. The results are given in Table 3. The direction cosines in Table 3 indicate that the principal axes of the g and hyperfine values coincide, since they have nearly the same direction cosines. The Cu2+ ion substitutes with the divalent Zn2+ ion and coordinates with two ethylenediamine molecule in the equatorial plane and two saccarinato molecule in the axial position of the octahedron. From these results it is inferred that there is magnetically inequivalent but chemically equivalent two Cu2+ ions in the unit cells of the ZSED single crystals. These results are consistent with the monoclinic symmetry properties. Hence, taking also consideration that ionic radius of Zn2+ (75 pm) is enough for substitution of Cu2+ (72 pm), we conclude that the Cu2+ ion has entered the Zn2+ ion in this complex. The powder EPR spectrum was resolved into two components (g⊥ , g|| ). The calculated values of g⊥ , g|| and the hyperfine values of A⊥ , A|| are given in Table 3. These parameters are in good agreement with those obtained from the single crystal EPR data. We deduce that Cu2+ ions have an distorted octahedral sites (D4h ) elongated along the z-axis and ground state of the unpaired electron is dx2 −y2 (2 B1g state). Moreover, it can be seen from Table 3 that gzz > gxx > gyy . When the ratio R = (gxx − gyy )/(gzz − gxx ) less than unity, the unpaired electron is dominantly in the dx2 −y2 state and when R is greater than unity, the unpaired electron is in the d3z2 −r 2 state. The calculated R values for two sites are RI = 0.05 and RII = 0.21. The R values for two chemically different Cu2+ complexes are found to be less than unity, so the ground state of the unpaired electron in both complexes is dx2 −y2 . The ground state wave function of Cu2+ ion with

d9 configuration in octahedral symmetry has been determined by several authors [30–34], and the same method is applied in this work. The hyperfine and the g value variations show that the octahedron is slightly distorted to tetragonal symmetry via degenerate

dx2 −y2 orbital. The 2 D state of the Cu2+ ion in an octahedral crystal field splits into a triplet T2g and a doublet Eg states. Depending on the slight a distorted octahedron, the Eg state changes to dz2 or to dx2 −y2 . But when the symmetry gets lower, the ground state becomes a mixture of dz2 and dx2 −y2 . Therefore, the ground state wave function of Cu2+ ion should be a linear combination of dx2 −y2 and dz2 orbitals and it can be written as 2 1/2

 = (˛ )

[˛dx2 −y2 + ˇd3z2 −r 2 ]

(3)

where square of ˛ 2 is the probability of finding the electron in the metal d orbitals [34,35]. The normalization condition for the mixing coefficients ˛ and ˇ is ˛2 + ˇ2 = 1.

(4)

Using the experimental values for ZSED, the ground state wave functions can be constructed for two complex sites as I = (0.887)1/2 [0.991|dx2 −y2  + 0.127|dz2 ]

(5a)

I = (0.870)1/2 [0.993|dx2 −y2  + 0.116|dz2 ]

(5b)

The covalency parameter ˛ 2 = 0.934 obviously explains that the unpaired electron spends 6.6% of its life time on ligand orbitals, whereas the rest is spent on the Cu d orbital, 98% of which is spent over dx2 −y2 orbital for site I and II. The ground state wave function

parameters of Cu2+ ions observed in different lattices are listed in Table 4. 4. Conclusions

The trans-bis(ethylenediamine)bis(saccharinato)Zinc(II) disaccharinate, [Zn(sac)2 (en)2 ] complex has been synthesized and its crystal structure and EPR parameters have been determined at room temperature. The Zn(II) ion in title compound sits on a inversion centre and is octahedrally coordinated two bidentate ethylenediamine and two saccharinate (N-bonded) ligands.

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The crystal packing analyses indicate that the structure of [Zn(sac)2 (en)2 ] exhibits an interesting hydrogen bonding interactions. EPR studies of Cu2+ doped in [Zn(sac)2 (en)2 ] single crystal reveal that the Cu2+ ions enter the lattice in substitutional position in the host lattice with nearly axial symmetry of the electrostatic field around the ion. The Cu2+ spectra and the angular variation show the presence of two magnetically distinct sites for the Cu2+ ion. The Cu2+ ion enters for the divalent Zn2+ and the Cu2+ ion has an octahedral complex coordination through four nitrogen atoms of two ethylenediamine ligands in the equatorial plane and two nitrogen atoms of saccarinato molecules in the axial position. The site symmetry of Cu2+ ion in ZSED have a distorted octahedral sites (D4h ) elongated along the z-axis, and ground state of the unpaired electron is dx2 −y2 . Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.saa.2009.10.038. References [1] E.J. Baran, Quim. Nova 28 (2005) 326. [2] L.O. Nabors, Alternative Sweeteners, Marcel Dekker, New York, 2001. [3] M.E. Gerland, T. Sakata, M.J. Fisher, T. Masui, M.S. Cohen, Cancer Res. 49 (1989) 225. [4] E.J. Baran, V.T. Yilmaz, Coord. Chem. Rev. 250 (2006) 1980. [5] F.A. Cotton, L.R. Falvello, R. Llusar, E. Libby, C.A. Murillo, W. Schwotzer, Inorg. Chem. 5 (1986) 3423. [6] F.A. Cotton, L.R. Falvello, W. Schwotzer, C.A. Murillo, G. Valle-Bourret, Inorg. Chim. Acta 89 (1991) 190.

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