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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 24–30
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Review Article
Structural, spectroscopic and voltammetric studies of bis(acetazolamido)bis(aquo)bis(nicotinamide)copper(II) _ Filiz Öztürk a,⇑, Ahmet Bulut a, Hümeyra Pasßaog˘lu a, Iclal Bulut b, Orhan Büyükgüngör a a b
Ondokuz Mayıs University, Faculty of Arts and Sciences, Department of Physics, Samsun, Turkey Ondokuz Mayıs University, Faculty of Arts and Sciences, Department of Chemistry, Samsun, Turkey
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" One of very few EPR studies on
acetazolamide. " One of very few structural studies
emphasizing the role of acetazolamide in supramolecular structure formation. " Of importance in understanding the tautomerism in acetazolamide.
a r t i c l e
i n f o
Article history: Received 9 December 2011 Received in revised form 22 March 2012 Accepted 2 May 2012 Available online 24 May 2012 Keywords: Cu(II) Acetazolamide X-ray crystal structure EPR IR Cyclic voltammetry
a b s t r a c t Polymeric copper(II) complex, [Cu(Hacm)2(na)2(H2O)2] [H2acm; acetazolamide, na; nicotinamide] was synthesized and characterized by spectroscopic (IR; infrared spectroscopy, EPR; electron paramagnetic resonance), structural (XRD) and voltammetric structural (CV) methods. The copper(II) compound Z = 1, with the unit-cell dimensions: a = 7.672 (5) Å, crystallizes in the triclinic space group P1, b = 8.681 (5) Å, c = 11.938 (5) Å, a = 90.807 (7)°, b = 98.616 (5)° and c = 110.647 (5)°. The Cu(II) ion has a distorted octahedral coordination geometry. The crystal packing of the complex is stabilized by intermolecular O–H. . .O and N–H. . .O hydrogen bonds. The powder EPR spectrum of copper(II) complex have indicate that the paramagnetic center is in a tetragonal symmetry with the Cu2+ ion having a distorted octahedral geometry. The vibrational investigation has been carried out on the basis of some characteristic IR bands of acetazolamide and nicotinamide molecules. Ó 2012 Elsevier B.V. All rights reserved.
Contents Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X-ray crystallography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Synthesis of [Cu(Hacm)2(na)2(H2O)2]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
⇑ Corresponding author. Fax: +90 3624576081. E-mail address: fi
[email protected] (F. Öztürk). 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.05.036
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Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molecular structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EPR investigation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IR investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrochemical investigation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix. Supplementary data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction Aromatic sulfonamides and their derivative compounds with the 1,3,4-thiadiazole ring are well-known as inhibitors of the carbonic anhydrase enzyme [1] (Fig. 1). The acetazolamide (5-acetamido-1,3,4-thiadiazole-2-sulfonamide) (H2acm) has been extensively used clinically (under the trademark Diamox) as a diuretic drug, and is still used to treat glaucoma, epilepsy and other neuromuscular diseases and as a diagnostic tool [2–4]. Several works based on complexes which were synthesized in laboratories confirmed this fact [5–7]. The coordination behavior of acetazolamide [8–15], in particular towards the Cu(II) ion, has been investigated for its synthetic analogs that can be used for elucidating the versatility of the ligand. On the other hand, nicotinamide (pyridine-3-carboxamide, 3-pyridinecarboxamide, vitamin B3) as a pyridine derivative is an important bioligand occurring in the metabolic processes of human organism (Fig. 1). It also dominates in plants and human tissues [16–18] showing the significant biological activity with a coenzyme called NAD (nicotinamide adenine dinucleotide) [19]. Nicotinamide as the amide form of na has the anti-flammatory properties and reveals pharmacological importance as a vital compound in drug industry [20–22]. In the present study we have synthesized mixed-ligand copper complex of acetazolamide with nicotinamide. Although a number of structural studies have been reported for other metal complexes in the solid state, this is the first investigation on the structure of [Cu(Hacm)2(na)2(H2O)2] complex. The structural, spectroscopic properties of the complexes have been characterized by X-ray diffraction, IR and EPR techniques, respectively. Experimental General method All chemical reagents used were analytical grade commercial products. Solvents were purified by conventional methods. The EPR spectrum was 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 g values were obtained by comparison with a diphenylpicrylhydrazyl sample of g = 2.0036. The IR spectrum was recorded in the 4000– 400 cm1 region with a Bruker Vertex 80 V FT-IR spectrometer using KBr pellets. An EcoChemie Autolab-30 potentiostat with the electrochemical software package GPES 4.9 (Utrecht, Nether-
Fig. 1. (a) Acetazolamide (H2acm), (b) Nicotinamide (na).
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lands) was used for voltammetric measurements. A three electrode system was used: a Pt counter electrode, an Ag/AgCl reference electrode and a Pt wire electrode as working electrode. The potentiostat/galvonastat have an IR-compensation option. Therefore, the resistance due to the electrode surface was compensated throughout the measurements. Oxygen-free nitrogen was bubbled through the solution before each experiment. All experiments were carried out at room temperature. X-ray crystallography A suitable single crystal was mounted on a glass fiber and data collection was performed on a STOE IPDS(II) image plate detector using Mo Ka radiation (k = 0.71069 Å) at 293 K. Details of the crystal structure are given in Table 1. Data collection was carried out using Stoe X-AREA [23], cell refinement was carried out using Stoe X-AREA [23] and data reduction was carried out using Stoe X-RED [23]. The structure was solved by direct methods using SIR–97 [24] and anisotropic displacement parameters were applied to nonhydrogen atoms in a full-matrix least squares refinement based on F2 using SHELXL-97 [25]. All carbon hydrogens were positioned geometrically and refined by a riding model with Uiso 1.2 times that of attached atoms and remaining hydrogen atoms were found by Fourier difference. Molecular drawings were obtained using ORTEP-III [26].
Table 1 Crystal data and structure refinement parameters for Cu(Hacm)2(na)2(H2O)2. Formula
C20H24CuN12O10S4
Formula weight Temperature(K) Radiation,k(MOKa) Crystal system Space group
784.29 293 0.71073 Triclinic P1
Unit cell dimensions a, b, c (Å) a, b, c (°) Volume (Å3) Z Calculated density (g cm3) l(mm1) F(000) Crystal size (mm) h range (°) Index ranges
Measured reflections Independent reflections Reflections observed [I P 2r(I)] Absorption correction Refinement method Data/restrains/parameters Goodness-of-fit on F2 Final R indices [I P 2r(I)] R indices (all data) Largest diff. peak and hole (e Å3)
7.672(5), 8.681(5), 11.938(5) 90.807(7), 98.616(5), 110.647(5) 733.7(7) 1 1.776 1.11 401 0.580 0.367 0.150 2.51–27.38 9 6 h 6 9 –11 6 k 6 11 –15 6 l 6 14 13869 3148 2965 Integration Full matrix least-squares on F2 3148/0/262 1.07 R1 = 0.028; wR2 = 0.080 0.030 0.76; 0.46
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Fig. 2. The molecular structure of [Cu(Hacm)2(na)2(H2O)2] with atom-labeling scheme [Symmetry code: (i) x + 1, y, z].
Table 2 Bond lengths (Å) for Cu(Hacm)2(na)2(H2O)2. Cu1—N4 Cu1—N4i Cu1—N5 Cu1—N5i Cu1—O5 S2—O2 S2—O3 S2—N4 N3—C3 N3—C2
2.0147(16) 2.0147(16) 2.0490(16) 2.0490(16) 2.5021(19) 1.4390(13) 1.4443(15) 1.5430(16) 1.364(2) 1.376(2)
N6—C10 N6—H6 N6—H7 O5—H13 O5—H12 C1—N1 N1—N2 C2—N2 N3—H1
1.325(2) 0.81(2) 0.82(2) 0.87(2) 0.861(18) 1.290(2) 1.372(2) 1.297(2) 0.77(2)
Table 3 Bond langles (°) for Cu(Hacm)2(na)2(H2O)2. N4—Cu1—N4i N4—Cu1—N5 N4i—Cu1—N5 N4—Cu1—N5i N4i—Cu1—N5i
180.00(14) 91.27(6) 88.73(6) 88.73(6) 91.27(6)
N5—Cu1—N5i N4—Cu1—O5 N4i—Cu1—O5 N5—Cu1—O5 N5i—Cu1—O5
180.00(8) 93.31(7) 86.69(7) 90.64(7) 89.36(7)
Symmetry code: (i) x + 1, y, z.
Synthesis of [Cu(Hacm)2(na)2(H2O)2] An aqueous solution (20 ml) of acetazolamide (0.444 g, 2.0 mmol) was added to an aqueous (2:2) solution (20 ml) of nicotinamide (0.244 g, 2.0 mmol) and CuCl2H2O (0.170 g, 1.0 mmol) with stirring. The mixture was neutralized with NaOH and then
cooled to room temperature. Two weeks later, well formed blue crystals were selected for X-ray study. Anal.Calc. for C20H26CuN12O10S4: C, 30.54; H, 3.33; N, 21.37%. Found: C, 30.43; H, 3.22; N,21.27%. Results and discussion Molecular structure The structure of [Cu(Hacm)2(na)2(H2O)2] consists of a neutral unit. The Cu(II) ions sits a crystallographic inversion center and the coordination geometry around it is an elongated octahedral coordination geometry as shown in Fig. 2. The equatorial plane of the octahedron is occupied by four nitrogen atoms (two acetazolamide and two nicotinamide) and apical sites are taken by oxygen atoms (O5, O5i) of aqua ligands. The Cu–N distances are close to each other, and the average value of Cu–N distance (2.0178 (17)–2.0494 (17) Å) is slightly shorter than average Cu–Oaqua distances (2.502 Å). These values are comparable to those reported for mononuclear Cu(II) complexes of acetazolamide [11]. Axial elongation is caused by Jahn–Teller distortion as observed in most octahedral Cu(II) complexes. The selected bond lengths and angles are given in Tables 2 and 3. The N1–N2 [1.372 Å(2)] bond lengths in the title complex (Table 2) are slightly different from the corresponding lengths reported for acetazolamide [N1–N2 = 1.372 (3) Å] [27], [Ni(Acm)2(NH3)4] [N1–N2 = 1.376 (6) Å] [9], [Cu(Acm)(NH3)2(OH2)]22H2O [N1–N2 = 1.374 (6) Å] [10], [Cu(Hacm)2(en)2]
Fig. 3. The molecular packing of [Cu(Hacm)2(na)2(H2O)2].
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F. Öztürk et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 24–30 Table 4 Hydrogen bond geometry for Cu(Hacm)2(na)2(H2O)2 (Å, °). D—HA ii
N6—H6N2 N3—H1O4ii N6—H7O3iii O5—H12O3iv O5—H13O2iv O5—H13O2 O5—H13S2
D—H
HA
DA
D—HA
0.81(2) 0.77(2) 0.82(2) 0.861(18) 0.87(2) 0.87(2) 0.87(2)
2.11(2) 2.21(2) 2.27(3) 2.53(3) 2.59(6) 1.99(4) 2.91(4)
2.911(2) 2.972(2) 3.074(3) 3.299(3) 3.123(3) 2.725(3) 3.573(2)
171(2) 172(2) 167(2) 149(4) 121(5) 142(6) 134(5)
Symmetry codes: (ii)x + 2, y + 1, z + 1; (iii) x + 1, y + 1, z; (iv) x, y, z.
Fig. 4. EPR spectrum of copper(II) complex (polycrystalline at 298 K).
Table 5 Principal g values of copper(II) complexes. Complexes
g ==
g?
Ref.
Cu(acm)2(na)2(H2O)2 [Cu(Acm)(NH3)2(OH2)]2 2H2O [Cu(Acm)(NH3)3 [Cu(Acm)(NH3) H2O
2.54 2.25 2.06 2.22
2.08 2.06 2.13 2.11
a [10] [10] [10]
a: Present work
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and [Cu(Hacm)2(tn)2] [N1–N2 = 1.379 (2) Å and N1–N2 = 1.371 (2) Å] [11]. The N2–C2 bond length in the present complex is shorter [1.297 (2) Å] than in acetazolamide [1.311 (3) Å] and even that in the Ni(II) complex [1.330 (7) Å], Cu(II) complexes [ 1.339 (6), 1.318 (2), 1.323 (4) Å,], whereas the N1–C1 distance is shorter [1.290 (2) Å] than those reported in the related compounds [1.294 (6) Å for the Cu(II) complex; 1.302 (8) Å for the Ni(II) complex; 1.294 (3) Å for acetazolamide]. The reduction of the N2–C2 bond order is consistent with the decrease of electronic density owing to the coordination and with the important increase of the C2–N3 bond order. The S2–O2 [1.4390 (13) Å] bond lengths in the title complex is shorter than in acetazolamide -metal complexes. Furthermore, the S2–N4 bond length is slightly longer than the corresponding distances of acetazolamide and other metal complexes [9–11,27]. The modifications observed in this group come from the deprotonation and the following delocalization of the negative charge through the O3–S2–N4 bonds. The crystal packing of the complex is achieved via intra-and inter-molecular hydrogen bonds (Fig. 3). The hydrogen bond geometry is given in Table 4. Analysis of the crystal packing indicates that the intermolecular O–H. . .O and N–H. . .O hydrogen bonds in complex occur between oxygen atoms of the water molecules, the nitrogen atoms of acetazolamide and nicotinamide (Fig. 3). In the extended structure (Fig. 3), the nicotinamide ligands are mutually connected by O–H. . .O hydrogen bonds, resulting in a centrosymmetric R22 ð4Þ motif [28]. As is seen from Fig. 3, the O5 of aqua ligand acts as a donor atom, via H12, to O3 atom of acetazolamide ligand, producing a chain C(6) running through the a axis and a centrosymmetric R22 ð4Þ ring centered at (n, n, n) (n = zero or integer). It is also seen that N6—H6N2ii and N3—H1O4ii hydrogen bonds constitute R22 ð4Þ rings in the bc plane. These inter-molecular hydrogen bonds play an important role in the formation of 3D supramolecular network of [Cu(Hacm)2(na)2(H2O)2] complex. EPR investigation The powder EPR spectra of Cu(II) complex at room temperature were recorded (Fig. 4). As can be seen from Table 5, the g values are in the order of g == i g ? i g e (free electron g value, g = 2.0023). Considering these values together with the observed characteristic g == and g ? values for Cu2+ ions, it can be concluded that the paramagnetic center is axially symmetric, the ground state of unpaired
Fig. 5. The FT-IR spectra of [Cu(Hacm)2(na)2(H2O)2].
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electron is dx2–y2 (2B1g state) and the Cu2+ ions are located in distorted octahedral sites (D4h) elongated along the z-axis [29,30]. The exchange parameter, G ¼ ðg == 2Þ= ðg ? 2Þ, reflects the exchange interaction between the copper(II) centers in polycrystalline solids [31]. According to Hathaway [31], if G > 4 the exchange interaction is negligible and the observed g-values are considered to reflect approximately the local copper(II) ion g-values. A value of G < 4 indicates considerable exchange interaction in the solid complex. The G value of 6,75 for the title complex indicates that there is no exchange interaction between the adjacent Cu(II) centers with the separations of 9,341, 8681 and 7672 Å in between. Hence, the observed g-values can be considered to reflect the local Cu(II) molecular geometry.
IR investigation FT-IR spectrum of the title compound is given in Fig. 5. The absorption bands between 3600 and 3400 cm1 are characteristic of v(H2O) vibrations of aqua and crystal water molecules [32]. The existence of v(H2O) bands at 3612 cm1 indicates the participation of aqua OH groups in hydrogen bonding. In the complex, the v(NH2) vibrational modes appear as four absorption bands which are shifted to higher values when compared to uncoordinated na (Table 6 and Fig. 5). These positive shifts obviously originate from hydrogen bonding effect [17]. It is known from crystallographic studies that acetazolamide ligand is deprotanated from NH2 group of sulfonamide moiety and coordinated to Cu(II) ion acting as monodentate anionic ligand.
Table 6 The infrared wave numbers (cm1) of acm, na and copper(II) complex. Assignments
H2acm
na
[Cu(Hacm)2(na)2(H2O)2]
v(H2O) vas(NH2) vs(NH2) vas(NH2) vs(NH2) v(N–H)acm v(N–H)acm(RCONH) v(C–H)na vas(CH3) vs(CH3) v(N–H)ring(imin tautomer) v(C@O)na v(C@O)acm
– 3300s 3180s – – – 3090w – 2990sh 2935sh 2900m 2770m – 1680 – – – 1540s –
– – – 3368vs 3161s – – 3060sh – – – 1697sh, 1679vs – 1618vs 1592vs 1573s – 1484vs
3612m – – 3419ws, 3375sh, 3297vw 3217m 3139m 3110sh 3070w 3009w 2934w 2844sh 2768m 1695vs 1681s 1622m 1601m 1575m 1539vs 1482w
1425w 1415sh – 1370sh 1355s 1315s 1275m 1240m – – 1175s – 1110m – 1040m 1005m – 975m 910s – – – – – – 705sh – 675s – – – 585m – – 510s – –
– – 1395vs – – – –
1439sh 1422sh 1391m 1376s 1304vs – 1279m 1243m 1219w 1205m 1142vs 1155w 1093s 1056w 1034vw 1014vw 984s 968vw 948w – 939w 831w 806w 795m 766m 722sh 697s 677m 641m 626s 610m 580m 557m 528m 506m 446m 422w
d(N–H)ip yada NH2 def Ring str(py) Ring str(py) vas(C@N)ring(acm) Ring str(py)
vs(C@N)ring(acm) das(CH3) CN str(am) ds(CH3) vas(SO2) vas(C–N–C) v(C–N)ring v(C–C) Ring str(py) C–C str(py) vs(SO2) NH2 rock v(C–N)ring Ring breat (py) v(C–N)ring v(C–N)ring Ring breat(py) v(N–N) v(SN) o.p. C–H (py) o.p. C–H (py) o.p. C–H (py) N–O def o.p. C–H (py) o.p. C–H (py) vas(CS) o.p. ring def vs(CS) NH2 wag i.p. ring def O@CN bend d(SO2)sci d(HO2)wag/twi o.p. C–H (py) d(SO2)wag o.p. ring def o.p. ring def
1231w 1204m 1154w – 1029s – – 1028ms – – 970w 936vw 829m 805m 778m – 702s – 644vw 622s 602s – – 510m – 433sh 411m
(py, pyridine; am, amide; asy, asymmetric; sym, symmetric; rock, rocking; str, stretching; i.p., in plane; breath, breathing; o.p., out of plane; def, deformation; vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder.)
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Scheme 1. The two tautomeric forms of acetazolamide.
Electrochemical investigation Cyclic voltammetric studies of the complexes were performed in dimethylformamide (DMF) using a three electrode system with platin as a working electrode. Pt is an auxiliary electrode and Ag/ AgCl as reference electrode. Tetrabutyl ammonium perchlorate (TBAP) 0.05 M as the supporting electrolyte. The cyclic voltammogram exhibits only one metal centered quasi-reversible redox couple. CV obtained at a scan rate 100 mV s1 in the 0.75 to +1.5 V potential range. Fig. 6 shows that for the complex a reduction peak (Ic) at 0.705 V is appeared. During the reverse scan a well defined anodic peak (Ia) at 0.125 V is observed. For this system the DEðmVÞ ¼ E1pa E1pc value 580 mV and the ratio of peak current
Fig. 6. The cyclic voltammogram of 5 10–3 M copper complex at a Pt wire electrode in 0.05 M DMF–Bu4NClO4, potential scan rate 100 mV s1.
The bands of v(N–H) vibrations in the IR spectrum of complex showed absorption band at 3139 cm1. It has been demonstrated from structural data that these ligands exhibit amine-imine tautomerism in the solid state (Scheme 1). We also report the correlation between this tautomerism and the vibrational spectra. The band at about 3110 cm1 is due to the stretching vibration of the N–H group of carbonamide moiety of acetazolamide which corresponds to amine form of the ligand. Interestingly, the band about 2768 cm1 is the characteristic of v(N–H) ring vibration, showing the imine tautomer of the ligand [33]. The shoulders at 3009–2934 cm1 and the broad band at 2844 cm1 were identified as asymmetrical and symmetrical stretching modes of the CH3 group [33]. The acm and na ligands in the complexes give rise to strong stretching bands of C@O groups. Conjugation between the carbonyl group and the amide nitrogen causes small frequency shifts. The v(C@O) stretching vibrations of na and acm were observed at 1965 and 1681 cm–1, respectively. A medium-intensity band can be observed at about 1622 cm1: this band is NH2 in plane deformation [34,35]. The bands of pyridine ring vibrations in the IR spectrum of the complex (1601–1575 and 1482 cm1) are shifted to higher values with respect to free state values of the ligand (Table 6), suggesting that the coordination of nicotinamide to Cu(II) ion through the pyridine ring nitrogen atom [17,21,36]. As is seen in Table 6, the C@N vibration values show no shift in the complex since acetazolamide ligand is not coordinated through the ring nitrogen atom [33,34]. On the other hand, there is a slight shift in the CN stretching vibrations of the amide group of na complexes. This indicates that the na ligand is not coordinated to Cu(II) ion through its amine group as also confirmed by X-ray results (Fig. 3). The shifts in v(SO2) and v(S–N) respectively towards lower and higher values are due to the fact that the delocalization of the negative charge between O–S–N bonds causes a reduction of S@O bond order [33], as also confirmed by the structural data (Table 2).
(Ipc/Ipa) is not equal to 1. This phenomena show that this process has an irreversible character. In the complex, the occurrence of a relatively slow electron transfer, quasi-reversible in electrochemical terms can be indicative of important chemical reorganizations or structural modification. Conclusions As being a potential agent in pharmacology, the mixed ligand copper complex of acetazolamide with nicotinamide has been synthesized and its structural, spectroscopic and voltammetric properties have been determined. X-ray diffraction analysis of the complex have shown that copper(II) compound consists of a neutral [Cu(Hacm)2(na)2(H2O)2] unit. The Cu(II) ion has a distorted octahedral coordination geometry. The equatorial plane of the octahedron is occupied by four nitrogen atoms (two acetazolamide and two nicotinamide) and apical sites are taken by oxygen atoms (O5, O5i) of aqua ligands. Considering these values together with the observed g == and g ? values for Cu2+ ions, the ground state of unpaired electron is dx2–y2 (2B1g state) and the Cu2+ ions are located in distorted octahedral sites (D4h) elongated along the z-axis. We also report the correlation between amine-imine tautomerism and the vibrational spectra. Finally, for the complex the DEðmVÞ ¼ E1pa E1pc value 580 mV and the ratio of peak current (Ipc/Ipa) is not equal to 1. Appendix. Supplementary data Crystallographic data for the structure in this paper have been deposited with the Cambridge Crystallographic Data Centre as the supplementary publication No. CCDC 737749. 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:
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