Selective oxidation of sulfide catalysed by Cu complex of a triazamacrocyclic ligand with carbamoyl pendant arms

Inorganica Chimica Acta 360 (2007) 656–662 www.elsevier.com/locate/ica

Selective oxidation of sulfide catalysed by Cu complex of a triazamacrocyclic ligand with carbamoyl pendant arms Rui Liu, Li-zhen Wu, Xi-mei Feng, Zhong Zhang, Yi-zhi Li, Zhi-lin Wang

*

School of Chemistry and Chemical Engineering, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China Received 13 June 2006; received in revised form 5 August 2006; accepted 5 August 2006 Available online 18 August 2006

Abstract Copper(II) complex with a new ligand 1,4,7-tris(carbamoylethyl)-1,4,7-triazacyclononane (L) has been synthesized and characterized by elemental analysis, FT-IR, ES-MS, UV–Vis and cyclic voltammetry. Determined by X-ray analysis, the crystal structure shows the metal center is six-coordinated. The compound can catalyze the oxygenation of ethyl phenyl sulfide (EPS) utilizing H2O2 under ambient conditions. EPS was converted to the corresponding sulfoxide and sulfone step by step which was confirmed by 1H NMR spectra. The existence of sulfoxide and sulfone was identified by GC–MS. The gradually disappearance of EPS’s ultraviolet absorption at 290 nm was significantly correlated with the rates of sulfide consumption. The initial reaction rate during the first 3 h is consistent with the first-order law in substrate concentration. The averaged pseudo-first-order rate constant is calculated to be (2.25 ± 0.42) · 103 min1 at 25 C and (4.44 ± 0.17) · 103 min1 at 30 C. The oxidation product is almost sulfoxide by choosing the molar concentrations of Cu complex (2% of substrate) and H2O2 (seven times as much as substrate).  2006 Elsevier B.V. All rights reserved. Keywords: Copper complex; Triazacyclononane; Catalyze; Oxygenation of ethyl phenyl sulfide

1. Introduction Transition metal compounds with 1,4,7-triazacyclononane (TACN) and its derivatives were largely researched due to their ascendant properties [1]. Recent years, Barker and Ren [2] reported the oxygenation of organic sulfides with H2O2 catalyzed by Mn–Me3TACN compounds caused the basic products mostly sulfones. Oxygenation of organic sulfides occur stepwise (Scheme 1). The capability of obtaining sulfoxide products is interesting in both organic synthesis and mustard gas decontamination [3]. Moreover, organic sulfoxides play important roles in biomedicine because of the similarity sulfinyl center in most active bio-molecules [4]. As a main method to get sulfoxide products, how to oxidize sulfides selectively excite scientists to find better *

Corresponding author. Tel.: +86 25 83686082; fax: +86 25 83317761. E-mail address: [email protected] (Z.-l. Wang).

0020-1693/$ - see front matter  2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.08.008

catalysts. Catalysts capable of accelerating sulfide oxygenation with simple oxidants such as H2O2, tBuOOH and O2 under ambient conditions remain highly desired [5]. Methyl phenyl sulfide as a substrate was widely studied while ethyl phenyl sulfide (EPS) was scarcely explored. Here in this paper, EPS was selected as a substrate. In order to compare the catalyzing properties with Mn– Me3TACN compounds, a ligand with CH2CONH2 pendant arms based on TACN was designed (Scheme 2) and its Cu(II) complex was synthesized as a catalyst. The six donor atoms of the ligand can encapsulate metal ions to form stable structure complex and the metal– carbamoyl bonding mode behave some activity in catalyzing. The complex [CuL](ClO4)2 with the ligand 1,4,7-tris(carbamoylethyl)-1,4,7-triazacyclononane (L) is characterized by elemental analyses, FT-IR, ES-MS, UV–Vis, X-ray diffraction and cyclic voltammetry. 1H NMR, UV–Vis and GC–MS studies were carried out to explore its catalyzing properties.

R. Liu et al. / Inorganica Chimica Acta 360 (2007) 656–662

O S

657

O

S

Catalyze

S

+

H 2 O2

O

Scheme 1. EPS oxidation reaction. O H2N N

O NH

HN H N

NH2

CH2=CHCONH2

N N

MeOH

O

Ligand(L)

H2N

Scheme 2. Synthetic route of the ligand (L).

2. Results and discussion 2.1. Synthesis and characterization of the new ligand The new ligand 1,4,7-tris(carbamoylethyl)-1,4,7-triazacyclononane (L) is synthesized from 1,4,7-triazacyclononane (TACN) and acrylamide by Michael addition [6]. The ligand was purified by recrystallizing in methanol–ether. ES-MS and 1H NMR results help to confirm the structure of the ligand. In the electrospray mass spectra (ES-MS), the ligand catches a proton in the solution to give protonated species [L+H+]+ of high abundance, m/z = 343.3 (100) (shown in S.Fig. 4 of supplementary materials). The small peak at m/z = 685.0(6) is assigned to [2L+H+]+. The IR spectrum of L exhibit characteristic bands as [3406 cm1 (s, m(N–H)), 1672 cm1 (s, m(C@O)) and 1590 cm1 (s, d(N–H))]. 1 H NMR spectrum of the ligand is shown in S.Fig. 5 of supplementary materials. The chemical shifts of the protons at 2.81–2.89 ppm are designated to methylenes in the TACN ring. The triplet peaks at 2.26 ppm are due to the protons of methylene linked to TACN ring. The triplet peaks at about 2.12 ppm are designated to the methylene adjacent to carbamoyl group. The area ratios of the peaks are consistent with the supposed structure of L. 2.2. Description of the structure Crystal structure of complex [CuL](ClO4)2 consists of the dication [CuL]2+ and well-separated perchlorate anions. It crystallizes in the space group P21/c. Fig. 1 displays perspective views of the dication structure in complexes and gives the corresponding atom-labeling schemes. Table 1 summarizes important bond distances and angles. The ligand provides six donor atoms, with three nitrogen donors of the macrocyclic backbone and three carbonyl oxygen atoms of the pendant amide groups

Fig. 1. ORTEP diagrams of the dications [CuL]2+ (30% thermal ellipsoids), H atoms were omitted for clarity. Table 1 ˚ ) and angles () of complex Selected coordination bond lengths (A [CuL](ClO4)2 Cu(1)–O(1) Cu(1)–O(2) Cu(1)–O(3) O(1)–Cu(1)–O(2) O(1)–Cu(1)–O(3) O(2)–Cu(1)–O(3)

2.093(3) 2.157(3) 2.171(2) 96.16(10) 88.48(10) 93.52(10)

Cu(1)–N(2) Cu(1)–N(1) Cu(1)–N(3) N(2)–Cu(1)–N(3) N(2)–Cu(1)–N(1) N(1)–Cu(1)–N(3)

2.255(3) 2.275(3) 2.300(3) 77.41(11) 79.13(11) 77.74(12)

completing the coordination sphere, which are coordinated to the metal ion Cu(II). The resulting CuN3O3 polyhedron is best described as pseudo-octahedron. The twist angle

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R. Liu et al. / Inorganica Chimica Acta 360 (2007) 656–662

defined as reported [7] is 35.5. The angle # is 0 in a regular trigonal prism and 60 in an octahedron. Facial coordination of the 1,4,7-triazacyclononane (TACN) moiety results in similar bond angles and distances, within this portion of the ligand, to those found in other copper(II) complexes of TACN derivatives with different pendant arms [8]. Thus, Cu–N bond distances, ˚ , and the N–Cu–N bite 2.255(3), 2.275(3) and 2.300(3) A angles (average 78.09 (10)) to the TACN nitrogens match those in [Cu(TACN)2]2+ [9]. Cu–O bond distances, ˚ , are about 0.1 A ˚ shorter 2.093(3), 2.157(3) and 2.171(2) A than Cu–N bond distances. O–Cu–O bite angles (average 92.72 (10)) are larger than N–Cu–N angles. These differences lead to a trigonal elongation of the octahedron towards the triangular face formed by the macrocyclic N-donors [10]. A number of hydrogen bonds that construct the 3D network of the complex mainly occur between carbonyl oxygen atom and the amino nitrogen or between carbonyl oxygen atom and carbon atoms of the pendant arms provided by neighboring molecules. Clearly seen, down through a-axis, among the adjacent cations, there are ˚ , [i]x, 0.5  y, 0.5 + z) and N4–H4E  O3[i] (3.079(6) A [ii] ˚ , [ii]x, 0.5  y, 0.5 + z) C10–H10B  O1 (3.359(6) A hydrogen bonds. These hydrogen bonding interactions help to form a cationic 1D zigzag chain (Fig. 2). The surrounding ClO4  anions link these chains to a threedimensional supramolecular network through other N– H  O(ClO4  ) and C–H  OðClO4  Þ hydrogen bonds (shown in S.Table 1 of supplementary materials).

Fig. 3. UV–Vis spectra of [CuL](ClO4)2 in aqueous solution (1 · 103 mol L1).

2.4. Electrochemical study The redox behavior of complex [CuL](ClO4)2 in aqueous solution has been studied by cyclic voltammetry. Cycling between 0.00 and 1.00 V, a pair of anodic and cathodic peaks with peak potential of Epa = 0.35 V, Epc = 0.57 V (E1/2 = 0.46 V (Ag/AgCl), ipa/ipc  1) appear in the CV diagram of Cu complex (Fig. 4). The electrode process of the complex can be characterized as a quasi-reversible process of Cu(II)/Cu(I) [13,14].

2.3. UV–Vis spectrum 2.5. Catalytic oxidation of sulfide with Cu complex The UV–Vis spectrum of complex [CuL](ClO4)2, pseudo-octahedral environment (N3O3 donor unit) is illustrated as following. Judged on the basis of absorption coefficients, the single d–d transition band around 685 nm as well as a more intense N(r)–Cu(II) ligand to metal charge transfer (LMCT) band around 303 nm [11,12] exist as shown in Fig. 3.

The disappearance of ethyl phenyl sulfide’s ultraviolet absorption 290 nm (S.Fig. 1 of supplementary materials) can be used to monitor the consumption of ethyl phenyl sulfide (EPS) without the influence of Cu complex (LMCT absorption of the Cu complex is 303 nm). UV–Vis spectra of sulfoxide and sulfone show no distinct absorption at

Fig. 2. A cationic 1D zigzag chain along the a-axis hydrogen-bonding in complex [CuL](ClO4)2. Intermolecular hydrogen bonds indicated by dashed lines. Symmetry code: i = x, 2/3  y, 1/2 + z; ii = x, 2/3  y, 1/2 + z.

R. Liu et al. / Inorganica Chimica Acta 360 (2007) 656–662

659

1.0

3 1 4 2

0.9 0.8 0.7

Abs.

0.6 0.5 0.4 0.3 0.2 0.1 0.0 0

1

2

3

4

5

6

7

8

Time (hour)

Fig. 4. The cyclic voltammograms of [CuL](ClO4)2 (5 · 103 mol L1, scan rate, 0.20 V Æ s1) in NaClO4 0.1 mol L1aqueous solutions. Potentials in V vs. Ag/AgCl.

Fig. 7. Oxidation of EPS by Cu complex, monitored at 290 nm when substrate concentration and temperature are varied (substrate 1–4: 0.14 mol L1, 0.15 mol L1, 0.16 mol L1, 0.20 mol L1; temperature 1– 3: 25 C, 4: 30 C; 6H2O2). 1.5

290 nm (sulfoxide and sulfone were extracted with ethyl ether from the mixture of reaction system for purification). This is a convenient and efficient way to track the reaction.

1 2 3 4

ln[1/S]

1.2 0.9 0.6

0.7 0.3

Abs.

0.6

2% 1% 3% 0%

0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Time (hour) 0.4

Fig. 8. Application of the integrated first-order rate law for EPS oxidation by [CuL](ClO4)2 when substrate concentration and temperature are varied (Substrate 1–4: 0.14 mol L1, 0.15 mol L1, 0.16 mol L1, 0.20 mol L1; temperature 1–3: 25 C, 4: 30 C; 6H2O2).

0.3 0

2

4

6

8

Time (hour) Fig. 5. Oxidation of EPS by Cu complex, monitored at 290 nm when complex concentration is varied (substrate: 0.15 mol L1; 6H2O2).

0.8

5 H2O2

Table 2 Pseudo-first-order rate constant calculated by varying substrate concentrations and temperatures Substrate concentration (mol L1)

kpseudo (initial 3 h)

Std. deviation

Temperature (C)

0.14 · 103

2.18 · 103 min1 (2.180 · 103 min1) (2.226 · 103 min1) (2.170 · 103 min1)

1.853 · 105

25

0.15 · 103

2.29 · 103 min1 (2.290 · 103 min1) (2.300 · 103 min1) (2.284 · 103 min1)

8.038 · 106

25

0.16 · 103

2.29 · 103 min1 (2.290 · 103 min1) (2.269 · 103 min1) (2.305 · 103 min1)

1.795 · 105

25

0.20 · 103

4.44 · 103 min1 (4.361 · 103 min1) (4.579 · 103 min1) (4.240 · 103 min1)

1.724 · 104

30

8 H2O2

0.7

7 H2O2 6 H2O2

0.6

Abs.

0.0

0.5 0.4 0.3 0.2 0

1

2

3

4

5

6

7

8

9

Time (hour) Fig. 6. Oxidation of EPS by Cu complex, monitored at 290 nm when H2O2 concentration is varied (substrate: 0.15 mol L1; 2% Cu complex).

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Monitored by UV–Vis spectroscopy upon variations in peroxide and catalyst concentrations relative to substrate concentrations, the oxidation reactions provide differing insights into the mechanism of EPS. Varying catalyst (Cu complex) concentration from 1% to 3% (contrast to substrate molar concentration: 0.15 mol L1) results in an increase in the rate of sulfide consumption (Fig. 5). Similarly, varying H2O2 concentration from 5 to 8 times than substrate molar concentration (0.15 mol L1) also help the rate increase (Fig. 6). These increases in rates show the rate dependence both on Cu complex and H2O2. In order to find the correlation between the rates and the substrate concentrations, the concentra-

tions of Cu complex (2%) and H2O2 (six times) were fixed and the substrate concentrations were varied: 0.14 mol L1, 0.15 mol L1, 0.16 mol L1. The rate law can be expressed in the following way: rate ¼ k½oxidizing speciesn ½substratem m

or rate ¼ k pseudo ½substrate ; k pseudo ½oxidizing species

n

Then, the relationship between reaction rates and substrate concentrations could   be examined. According to the ploting methods, ln S1 was used to be X-axis and T (time) was used to be Y-axis. The UV–Vis data (Fig. 7) from the initial 3 h of the reaction at   25 C was fit to the integrated first-order rate law, ln S1 ¼ kt þ ln S 0 , which gives the straight lines (1–3 in Fig. 8) with slopes equal to pseudo-first-order rate constants. The forth line which has a greater slope attributes to the reaction carried under 30 C (substrate concentration: 0.20 mol L1). A summary of all pseudo rate constants (kpseudo) can be found in Table 2. The observed pseudo-first-order rate constants averaged from the integrated rate law calculations are about (2.25 ± 0.42) · 103 min1 at 25 C and (4.44 ± 0.17) · 103 min1 at 30 C. Obviously, the oxidation rate increases once temperature increases. In order to identify the oxidation products, 1H NMR (Fig. 9), FT-IR (S.Fig. 2) and GC–MS data (Table 3) were collected. Substrate concentration was diluted to 0.015 mol L1 (one tenth of the other substrate concentrations) to slow the reaction rate so the stepwise oxidation process can be clearly seen from 1H NMR spectra. The aromatic protons shifted from 7.16–7.30 ppm (sulfide) to 7.58–7.68 ppm (sulfoxide) and then to approximate 8.0 ppm account for the stepwise reaction [15]. FT-IR spectrum peaks primarily approve the separated products of the reaction after 30 h, 1086 cm1 (s, m(Ph–S)) [14], 1045 cm1 (s, m(S@O)) [16]. From GC–MS data (original data shown in S.Fig. 3), the condition with 2% complex and seven times H2O2 as much as substrate concentration gives not only better reaction rate (shown in half-life, estimated from UV–Vis data), but also the highest ratio of sulfoxide and sulfone. 2.6. Comparison to existing systems Compared to other sulfide catalysts as Mn–Me3TACN (shown in Table 4), acid buffer as co-catalyst (oxidation

Fig. 9. Oxidation reaction monitored by 1H NMR (substrate concentration: 0.015 mol L1).

Table 3 Oxidation products of EPS with varied H2O2 concentrations in the presence of different Cu complex concentrations Entry

Substrate (mol L1)

Catalyst (%)

H2O2

Reaction time (h)

Sulfide

Sulfoxide

Sulfone

t1/2 (h)

1 2 3 4

0.15 0.15 0.15 0.15

2 2 2 3

6 7 8 6

0.015

2

6

4.89 0 0 4.24 9.33 0 0

91.77 91.74 72.55 92.33 91.14 96.21 79.19

3.33 5.63 27.45 3.44 0 1.66 20.30

6.98 5.87 4.82 5.68

5

12 12 12 12 24 30 48

Note: t1/2 were estimated from UV–Vis data.

R. Liu et al. / Inorganica Chimica Acta 360 (2007) 656–662

661

Table 4 Comparison of Cu complex and Mn–Me3TACN catalysts Entry

Substrate (mol L1)

Catalyst

Reaction time (h)

Sulfide

Sulfoxide

Sulfone

1 2 3

EPS EPS EPS

Cu complex Mn–Me3TACN [2] Mn–Me3TACN and co-catalyst [2]

12 4h 30 min

4.89 32 0

91.77 25 0

3.33 23 100

Note: Co-catalyst is oxalic acid–oxalate [2].

product almost sulfone), Cu complex, no other co-catalyst (reported in this paper, oxidation product almost sulfoxide) has its advantage in stability and product selectivity. However, every coin has two sides, the oxidation rate of reaction catalyzed by Cu complex (average half-life 5.83 h at 25 C) is no faster than Mn–Me3TACN catalysts. 3. Conclusions Cu complex with ligand 1,4,7-tris(carbamoylethyl)1,4,7-triazacyclononane (L) shows catalytic property in oxygenation of ethyl phenyl sulfide. Monitored by UV– Vis spectra, varied complex and H2O2 concentrations cause different reaction rates. The initial 3 h of the reaction is fit to the integrated first-order law toward substrate concentration. The averaged calculated pseudo-first-order rate constant is about (2.25 ± 0.42) · 103 min1 at 25 C and (4.44 ± 0.17) · 103 min1 at 30 C which imply the oxidation rate increases with increasing temperature. GC–MS data reported which catalytic condition (2% complex, seven times H2O2, concentrations relative to substrate) lead to the highest ratio of sulfoxide and sulfone. From 1H NMR spectrum, the stepwise oxidation process is clearly seen. That’s a good evidence to show the selectivity of the products. Unlike the other catalysts as Mn–Me3TACN (sulfone as main product), the oxidation product is almost sulfoxide by choosing the molar concentrations of Cu complex and H2O2. 4. Experimental 4.1. Materials All starting materials were of reagent grade. 1,4,7-triazacyclononane (TACN) was prepared according to the literature method [17,18]. Cu(II) perchlorates were prepared by adding perchloric acid to the solution of Cu(II) carbonate. Caution: Although we encountered no problems, perchlorate salts of organic ligands are potentially explosive and should be handled with care and only in small quantities. 4.2. Physical measurements Elemental analysis was performed using a Perkin– Elmer 240c analytical instrument. IR spectra was mea-

sured as KBr discs using a Nicolet 5DX FT-IR spectrophotometer. Electronic spectra were recorded on a UV-3100 spectrophotometer. 1H NMR measurement was performed on a Bruker AM-500 spectrometer (TMS as the internal reference). The ES-MS was determined on a Finnigan LCQ mass spectrograph. The concentration of the samples was about 0.1 mmol L1, their MeOH solutions were electrosprayed at a flow-rate of 5 · 106 mol min1 with a needle voltage of +4.5 kV. The temperature of the heated capillary in the interface is 200 C and a fused-silica sprayer was used. The mobile phase was an aqueous solution of methanol (1:1, v/v). The samples were run in the positive ion mode. The cyclic voltammogram experiments were carried out on a PAR Model 273 potentiostat coupled to a PAR Model 175 universal programmer in highly pure nitrogen atmosphere at 25 ± 0.1 C. A glassy carbon electrode was employed as working electrode, a silver/silver chloride electrode (Ag/ AgCl) as reference electrode and a platinum wire as auxiliary electrode. The supporting electrolyte was 0.1 mol L1 NaClO4. The complex concentrations were 5.0 · 103mol L1 in aqueous solutions. Unless otherwise stated all the potentials reported are referenced to the Ag/AgCl. GCMS-QP2010 SHIMADZU collected the product data, chromatogram column is DB5-ms, highly pure He gas as fluid phase, 100–250 C, rate 20 C/min, the column pressure is 4 · 104 Pa. 4.3. Crystallographic data collection and refinement Slow diffusion of diethyl ether vapor into the methanol solution of [CuL](ClO4)2 gave crystals suitable for X-ray diffraction. The details of the X-ray crystal data, and the structure solution and refinement for all complexes are given in Table 5. The X-ray intensity data for the complexes were collected on a SMART-CCD area-detector diffractometer. Data reduction and cell refinement were performed by SMART and SAINT Program [19]. The absorption corrections were carried out by empirical method. The structure was solved by direct methods (Bruker Shelxtl) and refined on F2 by full-matrix least-squares (Bruker Shelxtl) using all unique data [20]. The non-H atoms in the structure were subjected to anisotropic refinement. All hydrogen atoms were located geometrically and treated with the constraint mode. The free perchlorate ions present in complex was refined with no disorder, giving bond distanced and angles typical for those ions.

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Table 5 Crystallographic data for [CuL](ClO4)2 Formula Formula weight Crystal size (mm) Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z Dcalc (Mg m3) Absorption coefficient (mm1) F(0 0 0) Temperature (K) hMinimum–maximum () Reflections collected (Rint) Data/parameters R1/wR2/S ˚ 3] Largest difference in peak/hole [e A

Acknowledgement C15H30N6O11CuCl2 604.89 0.16 · 0.34 · 0.36 monoclinic P21/c 18.6480(14) 12.0891(9) 11.2671(9) 90 104.9280(10) 90 2454.3(3) 4 1.637 1.174 1252 293 2.0–26.0 13 265(0.038) 4795/316 0.0536/0.1335/1.02 0.41/0.68

4.4. Synthesis of 1,4,7-tris(carbamoylethyl)-1,4,7triazacyclononane (L)

This work was supported by the Natural Science Foundation of China (No. 20475026). Appendix A. Supplementary data Crystallographic data for this paper can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK, fax: +44 1223 336 033; or e-mail: [email protected]). CCDC 600540 for complex [CuL](ClO4)2. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2006.08.008. References [1] [2] [3] [4] [5] [6] [7]

TACN (10 mmol, 1.3 g) and acrylamide (40 mmol, 3 g) were dissolved in MeOH (30 ml). Then the mixture reacted under nitrogen atmosphere at 60 C for 12 h. The white solid (L) was obtained by evaporating the solvent and then recrystallized from methanol–ether solution for purification. Yield: 2.6 g (76%). IR (KBr, cm1): 3406 (s, m(N–H)); 1672 (s, m(C@O)); 1590 (s, d(N–H)). 1H NMR (500 MHz, CD3CN): d = 2.8–2.9 (m, 12H, N–CH2–CH2–N), 2.26 (t, 6H, N–CH2), 2.12 (t, 6H, CH2–CONH2) ppm. ES-MS (m/z): 343 [L+H+]+. Anal. Calc. for [C15H30N6O3]: C, 52.61; H, 8.83; N, 24.54. Found: C, 52.86; H, 8.53; N, 24.34%. 4.5. Synthesis of the Cu complex The appropriate metal salt Cu(ClO4)2 Æ 6H2O (0.4 mmol) was dissolved in MeOH (20 ml) and added to a stirred solution of the ligand L (0.3 mmol, 103 mg) in MeOH (10 ml). The solution was stirred at boiling point for about 2 h. Precipitate formed quickly. After filtration, the solid was washed with acetic ether and dried in vacuum. Yield: 93 mg (51%). IR (KBr pellet): 3416 (s, m(N–H)); 1649 (s, m(C@O)); 1589 (s, d(N–H)); 1088 vs, mClO4  . ES-MS (m/z): 202 [L+Cu2+]2+, 504 [L+Cu2++ClO4  ]+. Anal. Calc. for [C15H30N6O11CuCl2]: C, 29.78; H, 5.00; N, 13.89. Found: C, 29.72; H, 4.84; N, 13.84%. UV–Vis in aqueous solution (kmaxnm) (e; M1 cm1): 685 (119), 303 (2424). Color: blue. The single crystals suitable for X-ray diffraction studies were grown by diffusion of diethyl ether vapor into a MeOH solution.

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