Synthesis, crystal structure, EPR spectra of Cu2+ doped [Zn(methylisonicotinate)2(H2O)4]·(sac)2 single crystal

Spectrochimica Acta Part A 79 (2011) 1829–1836

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Synthesis, crystal structure, EPR spectra of Cu2+ doped [Zn(methylisonicotinate)2 (H2 O)4 ]·(sac)2 single crystal Esat Bozkurt ∗ , Ahmet Döner, I˙ brahim Uc¸ar, Bünyamin Karabulut Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayis University, Kurupelit, 55139 Samsun, Turkey

a r t i c l e

i n f o

Article history: Received 27 December 2010 Received in revised form 15 May 2011 Accepted 24 May 2011 Keywords: X-ray diffraction IR Crystal structure EPR Cu2+ ion Spin-Hamiltonian

a b s t r a c t The tetraaquabis(methylisonicotinate)zinc(II) disaccharinate [hereafter, [Zn(mein)2 (H2 O)4 ]·(sac)2 ], complex has been synthesized and characterized by spectroscopic IR, EPR and X-ray diffraction technique. The octahedral Zn(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate mein ligands through the ring nitrogen and four aqua ligands to form discrete [Zn(mein)2 (H2 O)4 ] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bonds. The magnetic environments of Cu2+ doped [Zn(mein)2 (H2 O)4 ]·(sac)2 complex have been identified by electron paramagnetic resonance (EPR) technique. EPR spectra of Cu2+ doped [Zn(mein)2 (H2 O)4 ]·(sac)2 single crystals have been studied between 113 and 300 K in three mutually perpendicular planes. The calculated results of the Cu2+ doped [Zn(mein)2 (H2 O)4 ]·(sac)2 indicate that Cu2+ ion contains two different complexes and each complexes are located in different chemical environments and each environment contains two magnetically inequivalent Cu2+ sites in distinct orientations occupying substitutional positions in the lattice. The vibrational spectra of this compound were discussed in relation to other compounds containing methyl isonicotinate and saccharinate complexes. The assignments of the observed bands were discussed. © 2011 Elsevier B.V. All rights reserved.

1. Introduction The electron paramagnetic resonance (EPR) technique plays an important role in the study of diamagnetic host lattices. The EPR study of this kind shows the behavior of paramagnetic ions enabling one to estimate the site symmetry of the ion in the lattice [1]. Cu2+ ion with 3d9 electron configuration is of interest in transition metal complexes because it represents a relatively simple magnetic hole system, giving information about the ground state and local symmetry of the ion [2]. Cu2+ ions have been used as a main dopant in many systems. In the lattices containing divalent cations in the majority of cases the Cu2+ ions, as being probes were used by many workers as given in the literatures [1–6]. Saccharin (C7 H5 NO3 S, also known O-sulphobenzimide) has been commonly used as non-caloric artificial sweetener, being the principal sweetening component of diabetic diets. The chemical and biochemical properties of saccharin and its compounds have been investigated mainly due to their carcinogenicity, but it is now believed that saccharin is safe at human level of consumption [7–10]. A number of saccharinato complexes and salts are thus, both structurally and spectroscopically, well investigated

∗ Corresponding author. Tel.: +90 3623121919; fax: +90 3624576081. E-mail address: [email protected] (E. Bozkurt). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.05.067

[11–16]. As a continuation of these studies, we have now prepared and thoroughly characterized a new Zn(II) complex containing two saccharinate anions together with methylisonicotinate 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 study, we have determined both structural and magnetic properties of [Zn(mein)2 (H2 O)4 ]·(sac)2 complex. In order to obtain electron paramagnetic resonance (EPR) data, transition metal ions should be doped in the host lattice of [Zn(mein)2 (H2 O)4 ]·(sac)2 as an impurity. Cu2+ ion is generally used probes to enter the lattice substitutionally in place of the divalent cations [1,2,17,18]. When this ion form paramagnetic centres then one can get information about the local symmetry. It is therefore, we have used Cu2+ ions in [Zn(mein)2 (H2 O)4 ]·(sac)2 and obtained the EPR data

2. Experimental 2.1. General method All chemical reagents were analytical grade commercial products. Solvents were purified by conventional methods. The IR spectra were recorded on a Vertex 80v Bruker FTIR spectrophotometer in the 4000–400 cm−1 using KBr discs. The EPR spectra were recorded by using a Varian E-109C model X-band

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Table 1 Crystal data and structure refinement for title complex. Formula Formula weight Temperature (K) Wavelength (MoK␣) Crystal system Space group 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 (◦ ) Index ranges

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 (Å−3 )

C28 H30 N4 O14 S2 Zn 776.09 297(2) 0.71073 Monoclinic P 21 /c 7.0564(5), 16.6051(9), 13.8688(9) 97.298(5) 1611.87(18) 2 1.5991(2) 0.968 800.0 0.30 × 0.25 × 0.20 1.66–26.50 −7 ≤ h ≤ 7 −20 ≤ k ≤ 20 −17 ≤ l ≤ 17 26,842 1613 [Rint = 0.047] 1466 Integration Full-matrix least-squares on F2 1613/9/235 1.068 0.0259 0.0306 0.154, −0.144

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 between 113 and 300 K. The g values were obtained by comparison with a diphenylpicrylhydrazyl (dpph) sample of g = 2.0036. Reported values involve errors within ±0.0005 for g values and ±0.5 G for hyperfine coupling constants (hfcc), respectively. 2.2. Syntheses of tetraaquabis(methylisonicotinate)zinc(II) disaccharinate Into aqueous solution of the corresponding Zn(II) acetate, [Zn(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 [Zn(saccharinato)2 (H2 O)4 ]·2H2 O. Aqueous solution of methylisonicotinate (mein) (4 mmol, 20 mL) were added into aqueous solutions of these compounds under stirring, and the mixtures were allowed to stand at the room temperature. After about a week, colorless well-shaped single crystals of the compound were obtained. The well-developed single crystals of suitable size were selected for the X-ray diffraction. The single crystals of Cu2+ doped [Zn(mein)2 (H2 O)4 ]·(sac)2 were also grown by slow evaporation of the saturated aqueous solutions admixtured in stochiometric ratios with about 0.05% CuCl2 ·6H2 O salts. The well-developed single crystals of suitable sizes were selected for EPR investigation after about a week. 2.3. X-ray crystallography Suitable single crystals were mounted on a glass fiber and data collection were performed on a STOE IPDSII image plate detector ˚ Details of the crystal strucusing Mo K␣ radiation ( = 0.71019 A). ture are given in Table 1. Data collection: Stoe X-AREA [19]. Cell refinement: Stoe X-AREA [19]. Data reduction: Stoe X-RED [19]. The structure was solved by direct-methods using SHELXS-97 [20] and anisotropic displacement parameters were applied to non-

hydrogen atoms in a full-matrix least-squares refinement based on F2 using SHELXL-97 [20]. All carbon hydrogen atoms 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 Fourier difference map. The crystal was a non-morehedral twin crystal with two reciprocal lattice differently oriented giving rise to double diffraction spot sets. Reflection data were measured for the two twin domains, scaled and combined together, but overlapping reflections could not be satisfactorily measured and were discarded, leading to a data completeness of only about 50%. Molecular drawings were obtained using DIAMOND 3.0 (demonstrated version) [21].

3. Results and discussion 3.1. Crystal structure of [Zn(mein)2 (H2 O)4 ]·(sac)2 A view of the Zn(II) compound with the labeling scheme are shown in Fig. 1. Selected bond distances and angles are listed in Table 2. The structure of the title compound consists of [Zn(mein)2 (H2 O)4 ]2+ (mein: methylisonicotinate) cation and non-coordinated two saccharinate anions. The Zinc(II) ion is located on a crystallographic inversion centre in a slightly distorted octahedral environment. The four aqua oxygens ˚ [Zn–Oaqua = 2.113(3)–2.125(3) A] form the equatorial plane ˚ are sited perpendicwhile mein molecules [Zn–Nmein = 2.140(4) A] ularly above and below the equatorial plane, occupying the axial positions. The Zn–Oaqua distances are similar to those found in [Zn(ina)2 (H2 O)4 ]·(sac)2 (ina: isonicotinamide) [22] [Zn–O: ˚ and [Zn(eina)2 (H2 O)4 ]·(sac)2 ein: ethylison2.102(1)–2.095(1) A] ˚ while those distances icotinate) [11] [Zn–O: 2.112(1)–2.104(1) A] are slightly shorter than those found in [Zn(pyet)2 (H2 O)2 ]·(sac)2 ˚ (pyet: 2-pyridylethanole) [23] [Zn–O: 2.1417(8) A] and ˚ [Zn(tea)2 ]·(sac)2 (tea: triethanolamine) [24] [Zn–O: 2.156(1) A] due most probably to the hydrogen bonding interactions between the aqua and acceptor groups. The Zn1–Nein lengths in title complex are in good agreement with the corresponding distances reported for [Zn(na)2 (H2 O)4 ]·(sac)2 (na: nicotinamide) [25] ˚ ˚ [Zn–N: 2.153(1) A], [Zn(ina)2 (H2 O)4 ]·(sac)2 [Zn–N: 2.169(1) A], ˚ [Zn(pyet)2 (H2 O)2 ]·(sac)2 [Zn(tea)2 ]·(sac)2 [Zn–N: 2.104(1) A], ˚ [Zn–N: 2.1417(8) A], [Zn(bpy)2 (sac)(H2 O)]·sac [26] [Zn–N: ˚ 2.169(3) A] (bpy: 2,2-bipyridine) but slightly longer than those found in [Zn(mpy)2 (sac)2 ] (mpy: 2-pyridylmthanol) [27] ˚ [Zn(sac)2 (im)2 ] (im: imidazole) [28] [Zn–N: [Zn–N: 2.0887(17) A], ˚ and [Zn(sac)2 (bzim)2 ]·2EtOH·H2 O (bzim: benzimida2.010(3) A] ˚ The bond angles of the zole, EtOH: ethanol) [28] [Zn–N: 2.032(3) A]. metal-free saccharinate ions in which the ring nitrogen is deprotonated as in the title complex are in good agreement with those of the metal bonded saccharinato ligands such as [Cu(H2 O)(py)2 (sac)2 ] (A) [29] (py: pyridine) and [Cu(na)2 (sac)2 (H2 O)]·H2 O (B) [30], showing that the metal bonding to the ring nitrogen exerts little effect on the molecular dimensions; for instance, the bond angle S–N–C = 110.2(3)◦ in the title complex (Table 2) and the corresponding angles of 111.8(2)◦ and 112.1(2)◦ in (A) and (B). The crystal packing is formed by intermolecular hydrogen bonding and ␲–␲ interactions (Fig. 2). The aqua ligands link the complex cation to sac ion through hydrogen bonding interactions (see Table 2 for details). The aqua ligands, saccharinate carbonyl oxygen and nitrogen atoms form R22 (8) motifs. Apart from these, there is also symmetry-unrelated weak slipping face to face ␲–␲ stacking interaction between the saccharinate (S1–N2–C8–C13–C14, ring A) and pyridine ring of mein (ring B) (Fig. 1). The centroidto-centroid and centroid-to-plane distances between the rings A

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Fig. 1. The molecular structure of Zn(II) complex, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii [dashed lines indicate the hydrogen bonding and ␲–␲ interactions, symmetry code (i) 1 − x, 1 − y, 1 − z)]. Table 2 Interatomic bond distances (Å) and angles (◦ ) around the Zn(II) ion and hydrogen bonding interactions in title complex. (a) Bond lengths, bond angles Bond lengths (Å) O1–Zn1: 2.113(3) O6–S1: 1.436(2) Bond angles (◦ ) O1–Zn1–O2: 91.54(12) O1–Zn1–O2i : 88.46(12) C14–N2–S1: 110.2(3)

O2–Zn1: 2.125(3) O7–S1: 1.433(2)

N1–Zn1: 2.140(4) C14–O5: 1.249(5)

O1–Zn1–N1: 91.14(14) O1–Zn1–N1i : 88.86(14) O7–S1–O6: 115.14(14)

O2–Zn1–N1: 88.54(11) O2–Zn1–N1i : 91.46(11) O5–C14–N2: 123.0(4)

(b) Hydrogen-bonding interactions (Å,◦ ) D–H· · ·A

D–A

H· · ·A

D· · ·A

D–H· · ·A

O1–H1A· · ·O3iii O1–H1B· · ·N2i O2–H2A· · ·O5 O2–H2B· · ·N2iii

0.822(10) 0.82(3) 0.83(3) 0.83(3)

1.94(3) 2.15(3) 1.87(3) 2.154(16)

2.742(8) 2.969(4) 2.688(4) 2.952(4)

167(3) 176(4) 173(3) 161(3)

Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii) x, 2.5 − y, 1.5 + z; (iii) 2 − x, 1 − y, 1 − z.

Fig. 2. Three dimensional structure of Zn(II) compound. Dashed lines indicate the hydrogen bonding interactions.

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Fig. 3. The infrared spectrum of [Zn(mein)2 (H2 O)4 ]·(sac)2 ]complex.

˚ dihedral angle between these ring planes and B are 3.698(2) A, is 6.43(13)◦ . The closest interatomic distance between these ring ˚ planes is [C3· · ·C13] 3.519(4) A. 3.2. FT-IR investigation The infrared spectrum of [Zn(mein)2 (H2 O)4 ]·(sac)2 complex is given in Fig. 3, which was recorded on a Vertex 80v Bruker FT-IR Spectrophotometer in the 4000–400 cm−1 range. The assignment of bands observed in the infrared spectra of [Zn(mein)2 (H2 O)4 ]·(sac)2 complex is listed in Table 3. The results obtained are also compared with those previously obtained on other some saccharinate and methylisonicotinate complexes. A very strong absorption band was observed at 1734 cm−1 which was assigned to mode ␯(C O). This band corresponding to methylisonicotinate ligand

and it was observed in characteristic ␯(CO) at 1730 cm−1 [31] and 1740 cm−1 [32] in literature. A band with medium intensity was observed at 1456 cm−1 and 1564 cm−1 which was assigned to ␯(C–C). This band was observed in 1602 cm−1 and 1568 cm−1 at methylisonicotinate complex [32]. A medium absorption band was observed at 1438 cm−1 which was assigned to the asymmetric methyl deformation mode ␦a (CH3 ). A sharp band assigned to the symmetrical methyl deformation mode ␦sym (CH3 ), appears at 1418 cm−1 . The prepared complexes exhibit a medium to strong intensity IR band at ∼3350 cm−1 , assignable to ␯(OH) vibrations of the coordinated (in both complexes) and lattice H2 O (in 2H2 O). The broadness and relatively low frequency of this band are both indicative of hydrogen bonding [33]. In this study, the band of ␯(OH) was observed in 3453 cm−1 . The broad and strong absorption (Fig. 3)

Table 3 Characteristic FT-IR bands of some methylisonicotinate and saccharinate complexes at room temperature (cm−1 ). MeIN [40]

Methylisonicotinate [41]

Na(sac)· H2 O [42]

[Zn(ein)2 (H2 O)4 ]·(sac)2 [11]

[Zn(mein)2 (H2 O)4 ]·(sac)2 ]

Assignment

–

–

3507s,br

–

3453s, br; 3350 s,br 3086 vw

␯(OH)

–

1740vs –

1759vs –

1602m,sp; 1568s, sp

1601w; 1571w

1497vs,sp – 1412vs,sp – – – – –

1495vw 1446m 1413m – – – – –

– – – – – – –

– – 993w – – – –

3333s,br; 3264 s 3080vw; 3050w; 3012vw – 1642vs; 1629 sh – 1590s; 1555vw; 1460m – – – 1336m 1258vs 1150vs –– 1165sh; 1118s; 1051m 950m 794w – 677m 610m 543w 530m

3087vw

␯(CH)

␯(CO)meIN ␯(CO)sac

1590s; 1482w 1455s

1734vs 1649vs; 1620 sh 1586s 1456 m; 1564w

– – – 1330s 1284vs; 1245vs 1168vs; 1153vs 1122m 1054m

1503vw 1438m 1418vs,sp 1332m 1289vs; 1257vs 1195vs; 1153vs 1123m 1055vs

␯(C–C, C–N) ␦asym (CH3 ) ␦sym (CH3 ), ␯(C–C, C–N) ␯sym (CNS) ␯asym (SO2 ) ␯sym (SO2 ) ␦(CH)py ␦(CH)

966vs 748s 990vw 678s 601s 555s 532s

965vs 747m 990w 677s 610m 544m 530s

␯asym (CNS) ␦(CO) ␯(C–N) and ring deformation ␦(CCC) ␦(SO2 ) ␦ (CNS) ␥(CCC)

– 1631 vs

␯(CC)py ␯(CC)

asym: asymmetric, sym: symmetric, m: medium, s: strong, w: weak, vs: very strong, ␯: stretching, ␦: bending, ␥: out-of-plane bending, ␳: rocking, vw: very weak, sp: sharp.

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bands centered at 3350 cm−1 characterize ␯(OH) vibrations of the aqua ligands. The existence of ␯(OH) bands close to 3500 cm−1 might be taken as an indication of that some of the aqua OH groups are very weakly hydrogen bonded. The most characteristic bands of metal–saccharinate complexes are those of the carbonyl and sulfonyl groups. The sharp split bands at 1649 and 1620 cm−1 are assigned to the carbonyl group of the saccharinate ligand. Usually the pair of most prominent, appreciably broad bands in the 1350–1150 cm−1 region for the spectra of various saccharinates are assigned to the stretching modes of the sulfonyl groups [34]. Thus, the bands at 1289, 1257 cm−1 in the FT-IR spectra of the [Zn(mein)2 (H2 O)4 ]·(sac)2 ] compound, can be assigned to the ␯asym (SO2 ) mode while those at 1195, 1153 cm−1 can be attributed to the ␯sym (SO2 ) mode (Fig. 3). The relatively weak absorption band at 3086 cm−1 is assigned to the ␯(CH) vibrations of this compound. The strong absorption bands between 1586 and 1456 cm−1 correspond to the ␯(C–C) vibrations of the aromatic rings and methyl groups. The absorption bands of the ␯sym (CNS) and ␯asym (CNS) modes of saccharinate were observed at 1332 and 965 cm−1 .

3.3. EPR investigation The EPR spectra of Cu2+ -doped [Zn(mein)2 (H2 O)4 ]·(sac)2 single crystals were recorded at ambient temperature for all rotations in three perpendicular planes (bc, a*c and ba*) at 10◦ steps between 0◦ and 180◦ . Here the a*-axis is perpendicular to the crystallographic b and c axes. No significant change in either single crystal or powder spectra of Cu2+ ion was observed from room temperature down to liquid nitrogen temperature, so all the measurements were studied at room temperature. The EPR spectra of Cu2+ doped [Zn(mein)2 (H2 O)4 ]·(sac)2 single crystal when the magnetic field in a*c plane 120◦ away from the b-axis as shown in Fig. 4. The spectra consist of two sets of four hyperfine lines and each have merge into two sites due to the interaction of the unpaired electron (S = 1/2) with copper nucleus (I = 3/2). The number position and spacings of lines are highly dependent on orientations. The lines appearing at one orientation disappear almost completely at some other orientation, so it is too difficult to trace all of the lines in all orientations. We therefore used a simple technique to resolve and identify the lines as given in previous papers [35]. The g2 values of all detected single lines are ploted against the rotation angle in mutually three perpendicular planes, as shown in

Fig. 4. The EPR spectra of Cu2+ doped [Zn(mein)2 (H2 O)4 ]·(sac)2 ] single crystal when the magnetic field in a*c plane at 120◦ away from the b-axis.

Fig. 5. Angular variations of the EPR spectra of Cu2+ doped [Zn(mein)2 (H2 O)4 ]·(sac)2 ] single crystals.

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Table 4 The principal values and their direction cosines of g and A tensors of Cu2+ doped [Zn(mein)2 (H2 O)4 ] (sac)2 ]single crystal (g = ±0.05 and A = ±5 G). Complex no.

Site

g

Direction cosines a*

I

II

b

Hyperfine

Direction cosines

c

A(G)

a*

b

c

I

gx = 2.212 gy = 2.096 gz = 2.261

0.862 −0.459 −0.216

0.506 0.808 0.302

0.036 −0.369 0.928

Ax = 18.3 Ay = 79.7 Az = 89.6

0.784 −0.019 −0.621

0.231 0.937 0.262

0.576 −0.349 0.739

II

gx = 2.203 gy = 2.018 gz = 2.344

0.976 0.049 0.215

0.047 0.905 −0.423

−0.215 0.423 0.880

Ax = 36.4 Ay = 67.4 Az = 89.8

0.646 −0.586 0.489

0.719 0.682 −0.133

0.256 0.438 0.862

I

gx = 2.174 gy = 2.020 gz = 2.338

0.850 −0.050 0.524

0.357 0.787 −0.504

−0.386 0.615 0.687

Ax = 40.5 Ay = 71.9 Az = 85.9

0.826 −0.447 −0.344

0.502 0.860 0.089

0.256 −0.246 0.935

II

gx = 2.175 gy = 2.024 gz = 2.323

0.869 0.047 −0.492

−0.346 0.769 −0.538

0.353 0.638 0.685

Ax = 49.9 Ay = 66.7 Az = 101.2

0.832 −0.466 −0.302

0.552 0.749 0.364

0.057 −0.469 0.881

Fig. 5. The g2 variation of a line with respect to the rotation angle in each plane must fit to the expression, g 2 () = gii2 cos2 ii + gjj2 sin2 jj + 2gij2 cos i sin j

(1)

where i, j, k = x, y, z are coordinates cyclically and  is the rotation angle. gii2 , gjj2 and gij2 are the g tensor elements which will be found after least squares fitting [36]. Four set of quartet are clearly resolved in the bc and ba* planes as shown in Fig. 5. When the magnetic field is in the a*c plane, however, they merge into two quartet. Referring to the spectral behavior, the complexes can be collected into two groups, each having two complex sites. In other words, there are two different Cu2+ complex groups located in different chemical environments, and each environment contains two magnetically distinct sites as shown in Fig. 5. 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 ] + Axx Ix Sx + Ayy Iy Sy + Azz Iz Sz

(2)

g and A values are calculated by means of an iterative numerical technique [37] which includes only electronic Zeeman and hyperfine interactions. The nuclear Zeeman and quadrupole interactions are neglected. The spin-Hamiltonian, Eq. (2), the principal values of the g and A values were found by diagonalization. The results are given in Table 4. The direction cosines in Table 4 indicate that the principal axes of the g and hyperfine values almost coincide, since they have nearly the same direction cosines. The intensities of all complexes seem to be almost equal when traced in all orientations, which means that the formations of complexes are equally probable. When the Cu2+ ions substitute with the Zn2+ ions in crystal lattice, probably two distinct axial bond (N–Cu–N and N –Cu –N ) distances are formed, comparing to axial bond in coordination sphere of Zn2+ ions. Due to these two distinct axial bonds, two Cu2+ complexes are formed as complex 1 and complex 2 in crystal lattice. In this case, each complex group shows two sites in EPR spectra as is clearly seen in Fig. 5 for bc, a*c and ba* planes. Additionally, the

Fig. 6. The X-band EPR powder spectrum of Cu2+ doped [Zn(mein)2 (H2 O)4 ]·(sac)2 ].

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Table 5 Ground state wave function parameters of Cu2+ ions observed in different environments.  is the Fermi contact term. Enviroment

Site

˛ 2

˛

ˇ



Ref

I-[Zn(mein)2 (H2 O)4 ]·(sac)2 ]

I II I II

0.759 0.869 0.861 0.889 0.782 0.895 0.624 0.628 0.899 0.904 0.531 0.580 0.900 0.892 0.956

0.981 0.985 0.988 0.992 0.992 0.985 0.994 0.993 0.987 0.982 0.981 0.969 0.987 0.986 0.988

0.196 0.175 0.155 0.125 0.126 0.175 0.109 0.114 0.185 0.189 0.195 0.247 0.163 0.169 0.050

0.244 0.211 0.187 0.188 0.193 0.322 0.625 0.621 0.306 0.300 0.720 0.657 0.317 0.322 0.227

This work This work This work This work This work [1] [11] [11] [12] [12] [22] [22] [38] [38] [39]

II-[Zn(mein)2 (H2 O)4 ]·(sac)2 ] Powder-[Zn(mein)2 (H2 O)4 ]·(sac)2 ] [Zn(sac)2 (py)2 ] [Zn(ein)2 (H2 O)4 ]·(sac)2 [Co(ein)2 (H2 O)4 ]·(sac)2 [Co(ina)2 (H2 O)4 ](sac)2 ·1.5H2 O [Zn(sac)2 (H2 O)4 ]·2H2 O

I II I II I II I II

[Co(nic)2 (H2 O)4 ]·(sac)2

nic: nicotinamide; ina: isonicotinamide, ein:ethyl isonicotinate, sac: saccharinate.

deviation of g value of Cu2+ complex from the free electron g indicates that the Cu2+ ion has distorted octahedral geometry as shown in crystallographic data. From these results it is inferred that there is magnetically inequivalent but chemically equivalent two Cu2+ ions in the unit cells of the [Zn(mein)2 (H2 O)4 ]·(sac)2 single crystals. These results are consistent with monoclinic symmetry properties. Hence, we conclude that the Cu2+ ion has entered the Zn2+ ions in this complex taking also consideration that ionic radius of Zn2+ ˚ is approximately enough for substitution of Cu2+ (0.72 A). ˚ (0.74 A) From the EPR parameters (Table 4) we deduce that Cu2+ ions have an octahedral environment with a rhombic distortion. The X-band EPR powder spectrum of Cu2+ ion in the [Zn(mein)2 (H2 O)4 ]·(sac)2 complex were recorded at room temperature is shown in Fig. 6. The principal values of g and A tensor obtained from Fig. 6 were the following: gxx = 2.167, gyy = 2.049, gzz = 2.284, Axx = 44 G, Ayy = 67 G, Azz = 88 G. In this study, the average value of hyperfine values is nearly 60 G. This value is consistent with the results for the single crystals data given in Table 4 and other lattices [11,38,39]. In Table 4, it can be clearly seen that the symmetry of paramagnetic centre is rhombic. The d orbitals of an ion split into a doublet (Eg ) and a triplet (T2g ) symmetry states in an octahedral crystal field. The base functions of Eg , are dx2 −y2 and d3z2 −r 2 orbitals, and the degeneracy of the energy levels are removed in a distorted crystal field. When the site symmetry is tetragonal, the ground state is either d3z2 −r 2 or dx2 −y2 , depending on whether the distortion is compressional or elongational [5]. When the site symmetry is rhombic or lower, then the ground state is an admixture of these d orbitals. So, the ground state wave function of Cu2+ ion can be written as,  = ˛ [˛ |x2 − y2  + ˇ |3z 2 − r 2 ]

(3)

where the square of ˛ is the probability of finding the electron in the d orbitals of Cu2+ ion [38]. The normalization condition for the mixing coefficients ˛ and ˇ is ˛

2

+ˇ

2

=1

(4)

with the experimental values for [Zn(mein)2 (H2 O)4 ]·(sac)2 ] single crystal, one can construct the ground-state wave function for the Cu2+ complexes, 1 = (0.871)1/2 [0.981 |x2 − y2  + 0.196 |3z 2 − r 2 ] 2 = (0.932)1/2 [0.985 |x2 − y2  + 0.175 |3z 2 − r 2 

(5)

The ground state wave function parameters of Cu2+ ions observed in different environments are listed in Table 5. From these

results, the covalency parameter ˛ 2 = 0.932 obviously explains that the unpaired electron spends approximately 6.8% of its time on ligand orbitals, where as the remaining time is spent on the Cu2+ d orbitals for the site II. Similar results are also found for site I as given in Table 4. Since the coefficient of dx2 −y2 is significantly grater than that of d3z2 −r 2 , one can conclude that the rhombic distortion results dominantly from the d3z2 −r 2 orbital of the Cu2+ ion. 4. Conclusions The tetraaquabis(methylisonicotinate)zinc(II) disaccharinate, [Zn(mein)2 (H2 O)4 ]·(sac)2 , complex has been synthesized and its crystal structure and EPR parameters have been determined at room temperature. The crystallographic results indicates that the octahedral Zn(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate mein ligands through the ring nitrogen and four aqua ligands to form discrete [Zn(mein)2 (H2 O)4 ] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bonds. Moreover, two distinct axial bond (N–Cu–N and N –Cu –N ) distances are formed, comparing to axial bond in coordination sphere of Zn2+ ions. Due to these two distinct axial bonds, two Cu2+ complexes are formed as complex 1 and complex 2 in crystal lattice. EPR studies of Cu2+ doped in [Zn(mein)2 (H2 O)4 ]·(sac)2 ] single crystal reveal that the Cu2+ ions enter the lattice in substitutional position in the host lattice with rhombic symmetry of the electrostatic field around the ion. The Cu2+ spectra and the angular variation show the presence of two complex groups and each group two magnetically distinct sites for the Cu2+ ion. The Cu2+ ion enters for the divalent Zn2+ . It was observed that temperature independent anisotropic EPR spectra of Cu2+ doped in [Zn(mein)2 (H2 O)4 ]·(sac)2 ] single crystal. The site symmetry of Cu2+ ion [Zn(mein)2 (H2 O)4 ]·(sac)2 have an distorted octahedral sites (D4h ) elongated along the z-axis, and ground state of the unpaired electron is dx2 −y2 so that the dominating orbital is dx2 −y2 . Supplementary data Crystallographic data (excluding structure factors) for the structure in this paper have been deposited with the Cambridge Crystallographic Data Centre as the supplementary publication no. CCDC 788541 Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge, CB12 1EZ, UK, fax: +44 1223 366 033, e mail: deposit@ccdc cam ac uk or on the web www: http://www ccdc cam ac uk.

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