Spectral and magnetic properties of mono-, di- and tetranuclear copper(II) carboxylates with nicotine

inorg, had Chem. Vol. 41, pp. 779--783 Pergamon Press Ltd., 1979. Printed in Great Britain

SPECTRAL AND MAGNETIC PROPERTIESOF MONO-, DIAND TETRANUCLEAR COPPER(II) CARBOXYLATES WITH NICOTINE MILAN MELN|K Department of Inorganic Chemistry, Slovak Technical University, 880 37 Bratislava, Czechoslovakia (Received 29 March 1978; receivedfor publication 8 August 1978) Abstract--New nicotine adducts of copper(II) acetate, propionate, benzoate, 2-fluoro, 2-chloro-,2-bromo-, 2-iodoand 3-fluoro-benzoate,were prepared. The magnetic and spectroscopic properties of these adducts indicate the presence of copperOI) dimers structurally similar to those in copper(II) acetate monohydrate. Besides these a di(nicotine)adduct of copper(II) 4-chlorbenzoate as well as two isomers of Cu(4-FCtH4COOhnic2were obtained. All the compounds sum to possess octahedral stereochemistry with different tetrngonal distortions around the Cu(II). On the basis of spectral and magnetic behaviour of the green Cu(4-FCtH4COOhnic and Cul4CICtH4COO)2nic,prepared from their di(nicotine)adducts, tetranuclear structures were proposed. INTRODUCTION Nicotine (3-(1-methyl-3-pyrrolidinyl)pyridine) and its derivatives possess very interesting pharmacological properties and are very important from a biological point of view. The nicotine shows marked activity as a ganglion-blocking drug[l]. Nicotine is one of the oldest insecticides[2, 3] and Dezelic and Nikolin[4] have been studied the insecticidal activity of some copper(II) compounds with nicotine. The inhibiting action of nicotine compounds on the corrosion of Cu in K2S2Os solution has been investigated [5]. The order of efficiency was nicotinic acid > nicotine > nicotinamide. Muratami and Hatano[6] have studied the absorption and circular dichroism spectra of some copper(II) /]-diketonates in nicotine. The nicotine coordinates in axial positions on the copper(II) compounds. Tetrachloro-cuprate(II) salts with protonated nicotine has been prepared and characterized spectroscopically [7]. But Copper(II) compounds with nicotine as ligand have not been studied in the solid state.

in a vacuum pistol. On exposure to the atmosphere, the anhydrous salt did not regain its water of crystallization.The green Cu(4-FCtH4COOhnic was obtained by drying the di-nicotine adduct of Cu(4-FCtH4COO)2 at about 105°C. A weight loss of 24% was recorded and the resultant mononicotinesalt showed no further loss in weight on prolonged drying at that temperatnre. The elemental analyses are given in Table 1. Spectral studies. Electronic spectra in the region 10-28kK were measured with a Perkin-Elmer 450 spectrofotometer and IR spectra in the region 400-3600¢m-t with the UR 10 spectrophotometer. In both cases the Nujol suspension technique was used. EPR spectra of the powdered samples were run on a Varian Model E 4 spectrometer at room temperature. Magnetic susceptibility measurements. The magnetic susceptibilities of powdered samples were determined at different temperatures on a Gouy balance (Newport Instruments Ltd), standardized with mercury tetrathiocyanatocobaltate(II)[8].The molar susceptibilities were corrected for diamagnetism using Pascal's constants[9]. The effective magnetic moments were calctilated using the expression/t ca = 2.83 (XM x T)~12,

RESULTS AND DISCUSSION The syntheses of compounds composition CuX2nic, where X is 4-FCsH~COO- or 4-CIC6H,COO-, by direct EXPERIMENTAL Preparative. The copper(II) carboxylate compounds of reaction between the Cu(II) salt and nicotine were uncomposition CuX2nic, where X=CH3COO-, CH3CH2COO-, successful. As was noted in the experimental part, two CtHsCOO-, 2-FCtH4COO-, 2-CICd-I4COO-,2-BrCd-I4COO-,2- isomeric forms of Cu(4-FCffI4COO)2nic2 as well as ICd/4COO-, or 3-FC~COO-; and nic=nicotine; were pre- green Cu(4-FC6H4COO)2nic were observed (Scheme 1). pared by treating nicotine (in a small excess) with a copper(II) The IR spectrum of Cu(4-FCd-I4COO)2nic2.H20 shows carboxylate and a small amount of the corresponding free acid in a broad absorption band at--3450 cm-L This frequency hot methanol solution. The solutions were left to stand at room corresponds to the antisymmetric and symmetric OH temperature. The fine light green microcrystals that precipitated stretch[10]. This band clearly confirm the presence of were filtered off, washed with cold methanol, and dried in an evacuated desiccator over phosphorus pentoxide. The water of crystallization in the compound. This band was absent in the spectra of the other compounds. Each compounds are stable in air. Cu(4-CICd-I4COO)znicz,was prepared by adding nicotine (in compound showed the carboxylate stretching, frequenexcess) to a methanol suspension of Cu(4-CICd-I4COO)2.H20. cies, Vcoo-(sym) and Vcoo-(asym), the data are given in After digestinga solution was obtained, this was left to stand in a Table 1. The position of the bands are characteristic of refrigerator. The fine pale blue crystals that precipitated were filtered, washed with cold methanol and dried at room temperaCuX2"H20 + 2.5 n i c a , ot-CuX2nic2 ~ CuX2nic ture. The green Cu(4-CICsH4COOhnic,was obtained by drying Cu(4-CICd-I4COO)2nic2at 105°Cand found to be stable in air. The violet-blue a-Cu(4-FCcj/4COOhniczwas prepared in a similar way. When the mother liquid, after separation of the } violet-blue precipitate, was concentrated one obtained a blue solid Cu(4-FCd-l,COOhnic2.H20,which was filtered, washed CuX2nic2.H~O c ,~-CuX2nic2 with cold methanol and dried ha the air. The blue B-Cu(4FC6H4COOhnic2 was obtained by drying Cu(4- Scheme 1. (a) In hot methanol; (b) from mother liquid; (c) over FC6H4COOhnic2.H20over phosphorus pentoxide at about 70°C P20~ at about 70°12;(d) at 105°C.

1

779

'

780

MILAN MELN[K Table 1. Elemental analyses and IR spectral data (cm-j) Compound

Cu

Cu(CH3COO)2nic Cu(CH3CH2COO)2nic Cu(C6HsCOO)znic

Cu(2-FC6H4COOhnic Cu(2-C1C6H4COO)2nic Cu(2-BrC6H4COO)2nic Cu(2-IC6H~COOhnic Cu(3-FC6H4COO)2nic Cu(4-FC6H4COOhnic Cu(4-C1C6H4COOhnic a-Cu(4-FC6H4COOhnic2 fl-Cu(4-FC6H4COOhnic2 Cu(4-FC6H4COOhnic2"H20 Cu(4-CIC6H4COOhnic2

Calc. (Found) (%) C H

N

ucoo-(asym)

18.47 (18.60) 17.08

48.90 (48.65) 51.67

5.86 (5.85) 6.50

8.15 (8.25) 7.53

1630s

(17.20)

(51.70)

(6.52)

(7.55)

1635 s

13.57

61.59

5.17

5.98

(13.63) 12.61 (12.78) 11.83 (11.95) 10.15 (9.97) 8.82 (8.84) 12.61 (12.71) 12.61 (12.64) 11.83 (11.70) 9.54 (9.57) 9.54 (9.50)

(60.78) 57.19 (56.73) 53.69 (54.00) 46.06 (46.32) 40.09 (39.75) 57.19 (57.06) 57.19 (57.00) 53.69 (54.00) 61.29 (61.00) 61.29 (60.54)

(5.17) 4.40 (4.31) 3,90 (3.75) (3.59) 3.08 (3.08) 4.40 (4.41) 4.40 (4.42) 3,90 (3.97) 5.45 (5.42) 5.45 (5.39)

9.28 (9.25) 9.09 (9.33)

59.68 (59.62) 58.41 (58.00)

5.59 (5.68) 5.19 (5.00)

3.54

Ucoo-(sym)

1410m

(5.89) 1640s 1405m 5.56 (5.38) 1650s 1405s 5.22 (5.30) 1635 s 1410m 4.47 (4.57) 1640s 1435w 3.89 (3.94) 1635s 1430w, 1395s 5.56 (5.51) 1640s 1400s 5.56 (5.63) 1635s 1410m 5.22 (5.37) 1630s 1400m 8.41 (8,30) 1620s, 1630sh 1410s 8.41 (8,25) 1620s, 1635sh 1410m 8.19 (8.18) 8.01 (7.82)

1625 s

1410 m

1605 s 1700w

1410 m

1620sh Note: s, strong; m, medium; w, weak; sh, shoulder. copper(II) carboxylate compounds [ l 1]. The strectching vibration of the C=N in the pyridine ring of nicotine appeared at 1590 cm -~ [12]. Upon complex formation the peak shifts to higher frequencies[13]. The shifts (to about 1605 cm -~) may suggest bond formation by the metal with the nitrogen of pyridine ring, for the dipolar contribution of C=N + in the heterocyclic ring increases[D]. Magnetic susceptibility measurements of polycrystalline samples od CuX2nic2 between 93 and 293 K obey the Curie-Weiss law

x~ =

C/(T-

Table 2. Magnetic data a-Cu(4-FC6H4COOhnic2 (-A x 106= 3 7 1 )

T(K) XMx 106 93 113 133 153 173

193 213 233 253

8)

where

273 C -- Ng2~2S(S+

1)/3 k

with S = 1/2. The values of #c~, are slightly dependent on temperature (Table 2). Since all di-nicotine adducts posses small negative Weiss constant (Table 3) a weak anti-ferromagnetic interaction may occur especially in the case of the ~-isomer and Cu(4-CICffI4COO)2nic2. The solid state electronic spectrum of the a-isomer exhibits a broad ligand field band with a maximum at 17.0kK and a shoulder at ~-13.6kK, the //-ismoer has only a band with a maximum at about 14.8 kK. Similar spectra were also observed for Cu(4-FCdt4COO)2nic2 and Cu(4-FCffI4COO)2nic2.H20 with a maximum at 15.0kK for the first and at 15.4kK for the second and a shoulder at ~-13.6kK in both cases. This type of d*-d spectra are typical for a tetragonal arrangement around

4443 3656 3104 2738 2444 2189

Iz.~,B.,. 1.82 1.82 1.82 1.83 1.84

1989 1813 1671

1.84 1.84 1.84 i.84

1553

1.84

0-Cu(4-FC6H4COO)2nic2 ,v~ x

106

~.c~,B.M.

4555 3730 3180 2827 2418 2263

1.84 1.84 1.84 1.86 1.83 1.87

2060 1892 1760

1.87 1.88 1.89

293 1448 1.84 Cu(4-FCc,H4COOhnic2.H20 ( - A x 106 = 384)

1638 1.89 1537 1.90 Cu(4-CIC6H4COOhnic2 ( - ~ x 106=401)

T(K)

XMx 106

~,f,B.M.

, ~ x 106

~.~,B.M,

93 113 133 153 173

4433 3654 3075 2730 2411

1.82 1,82 1,81 1.83 1,83

4246 3578 3042 2726 2345

1.78 1.80 1.80 1.83 1.80

193 213

2190 1984

!.84 1.84

2147 1950

1.82 1.82

233 253 273 293

1820 1672 1553 1452

1.84 1.84 1.84 1.85

1802 1638 1520 1432

1.83 1.82 1.82 1.83

Spectral and magnetic proterties of mono-, di- and tetranuclear copper(ll) carboxylates with nicotine

781

Table 3. The values of Weiss (O) and Curie (C) constant and EPR data of di(nicotine)adducts Compound

O(K)

a-Cu(4-FC6H4COOhnic2 /3-Cu(4-FCrH4COO)2nic2 Cu(4-FCrH4COOhnic2"H20 Cu(4-CICrH4COO)2nic2

-4.4 - 13 -0.6 -11.5

C

g~

gll

g~

0.431 2.072 2.264 2.138 0.467 2.069 2 . 2 % 2.126 0.419 2.08o 0.429 2.066 2.236 2.123

Cu(II). The lower value of magnetic moment (Table 2) of Table 4. Magnetic data the a-isomer indicating a somewhat greater tetragonal Cu(4-FC6H4COO)2nic Cu(4-CIC6H4COO)2nic distortion about the Cu(II) atom for the a- than the (-A x 106= 261) (-A x 106= 289) 3-isomer. Greater tetragonal distortion leads to a lower T(K) ;(~ X 106 tt~tr,B.M. XM× 106 getr,B.M. magnetic moment. This is in a good agreement with the ligand field band position as well as its splitting. This 93 1713 1.13 1410 !.025 splitting suggests somewhat greater tetragonal distortion. 113 1510 1.17 1362 11 These may be distortion isomers of the type described 133 1394 1.22 1312 .18 for some copper(II) compounds[14]. 153 1378 1.30 1354 .29 EPR spectra of the powdered isomers are of axial .34 173 1325 1,35 1294 type[15] with values of the g factor (Table 3) which are 193 1310 1.42 1336 ,43 213 1234 1.45 1287 .48 typical for compounds with tetragonal distortion around 233 1222 1.51 1226 .51 the Cu(lI) atom. A similar axial spectrum was observed 253 1170 1.54 1195 .55 for Cu(4-CIC6H4COO)znic2 and pseudo-isotropic for 273 1141 1.58 1098 .55 Cu(4-FC6H4COO)2nic2H20(Table 3). 293 1076 1.59 1126 .62 As was noted in the experimental part, green Cu(4FC6H4COO)2nic and Cu(4-CIC6H4COO)2nic were obtained by heating their di-nicotine adducts. These two where S = 1 and the other symbols have their usual compounds show subnormal magnetic moments at room meaning. It should be noticed that no splitting of the temperature as can be seen in Table 4. This drastic perpendicular components were observed thus supportchange in magnetic behaviour is accompanied by ing our neglect of an E parameter. The spin Hamiltonian concurrent structural changes in the first coordination parameters can be calculated in a relatively straight sphere of the paramagnetic unit. These values are high forward manner from the observed spectrum[18]. The even when compared with other binuclear copper(II) calculated parameters are presented in Table 5. The carboxylates. It is clear from the temperature variation adducts also displays a line at ~3200G which can be of # ~n that there is antiferromagnetic interaction in these attributed to a mono-nuclear impurity. compounds. This interaction cannot be satisfactrily Each of the compounds show in this electronic spectra represented by a simple Curie-Weiss law. The magnetic a band at ~13.5 kK (band I) which was identified with behaviour of these two compounds is almost the same as d - d transitions of the Cu(II), and a shoulder at ~26 kK that observed by Little et al.[16] for the tetranuclear (band II) (Table 8). The shoulder should be the charac[Cu2OH(O2CCF3h(quinoline)2]2 and by Haase[17] for teristic of the bridging system with antiferromagnetic the chloro(2-diethylaminocthanolato)copper(II). Little et interaction [ 19]. al.[16] reported that the EPR spectrum of From the foregoing it may reasonably be supposed [Cu2OH(O2CCF3)3(quinoline)2h is weak and ill-defined. that Cu(4-FCrH4COOhnic and Cu(4-CICrH4COO)2aic We find that a polycrystalline sample of our green Cu(4- possess tetranuclear structures with a distorted square C1C6H4COO)2nic exhibits a well-resolved absorption pyramidal configuration around each copper(II) atom. typical of a triplet in which D > h~,. The spectrum can be Each of the Cu(II) atoms is coordinated to four oxygen adequately described by the axial spin Hamiltonian. atoms and a nicotine nitrogen atom. The molar susceptibilities corrected for diamagnetism H = grillS+ D(S~ 2 - 1/3S(S+ 1)) and magnetic moments for CuX2nic (X=CH3COO-, Table 5. EPR data of mono-nicotineadducts

Compound

g~-

gl

gay

IDl,cm-'

g~ g±

Cu(CH3COO)2nic Cu(CH3CH2COO)2nic Cu(CrHsCOOhnic Cu(2-FCsH4COO)2nic Cu(2-CICrH4COOhnic Cu(2-BrCrH4COOhnic Cu(2-ICrH4COOhnic Cu(3-FCrH4COOhnic Cu(4-FCrH4COOhnic Cu(4-CICnH4COO)2nic tMononuclear impurity.

2.10o 2.088 2.092 2.093 2.103 2.087 2.094 2.085 2.080 2.091

2.355 2.330 2.354 2.362 2.358 2.362 2.366 2.346 2.350 2.354

2.187

2.172 2.183 2.186

2.191 2.183 2.188 2.175 2.174 2.182

0.333 0.348 0.362 0.375 0.375 0.376 0.379 0.366 0.349 0.357

gll

2.05 2.39 2.05 2.39 2.07 2.16 2.12 2.05 2.24 2.09 2.10 2.09 2.05 2.23 2.07 2.17

782

MILAN MELN~K

CH3CH2COO-, C61-15COO-, 2-FCd-I,COO-, 2CIC~I-I4COO-, 2-BrCsI-I4COO-, 2-IC6H4COO -, or 3FCrI-14COO-) are reported at various temperature in Table 6. The temperature-susceptibility data for all these mono-nicotine adducts can be described by the equation:

g2N~2

t

X u = 3kT

1

1 1 + ~ exp - 2 J/kT

+~

+N~

Table 6. Magneticdata Cu(CH3COOhnic (-A x los = 180) T(K)

Xu x los

#+~,B.M.

93

335

056

360 0.57 470 0.71 572 0.84 639 0.94 710 1.05 760 1.14 779 1.20 792 1.26 810 1.33 797 1.37 CufC~HsCOOhnic (-A × lip = 254)

113 133 153 173 193 213 233 253 273 293 T(K)

93 I 13 133 153 173 193 213 233 253 273 293

Xu x IOS

/z+s,B.M.

503 0.61 566 0.72 644 0.83 779 0.98 853 1.09 892 1.17 896 1.23 913 1.31 946 1.38 974 1.46 935 1.48 Cu(2-CICsH4COOhnic (-A x los = 289)

T(K) ,~ 93 I13 133 153 173 193 213 233 253 273 293

x los

~ef,B.M.

740 0.74 765 0.83 843 0.95 935 1.07 1043 1.20 1083 1.29 1136 1.39 1143 1.46 1150 1.52 1144 1.58 1095 1.60 Cn(2-ICrH4COO)2nic (-A x los = 338)

Cu(CH3CH2COOhnic (-A x IOS = 204) ~,~ x IOS p,s,B.M.

369 0.52 411 0.61 478 0.71 604 0.86 658 0.95 722 1.06 802 1.17 811 i.23 832 1.30 858 1.37 847 1.41 Cu(2-FCrl-14COOhnic (-A x los = 261) X~ x los #+~,B.M. 339 0.50 426 0.62 542 0.76 702 0.93 789 1.045 815 1.12 840 1.20 828 1.24 940 1.38 953 1.44 890 1.45 Cn(2-BrCrH4COOhnic (-A × los = 310) t

~u x

IOS

~,,e,B.M.

365 0.52 500 0.67 631 0.82 768 0.9"/ 873 !.10 948 1.21 976 1.29 1016 1.37 1009 1.43 1044 1.51 1012 1.54 Ce(3-FCrH4COO)2nic (-A x l0s = 261)

T(K)

A'~ux los

tt=f,B.M.

Xu x 106

93 113 133 153 173 193 213 233 253 273 293

242 508 551 732 793 871 914 923 985 976 952

0.425 0.68 0.77 0.95 1.05 1.16 1.25 1.31 1.41 1.46 1.49

248 333 448 618 724 774 825 842 862 869 841

/t~,B.M.

0.43 0~ 5 0.69 0.87 1.00 1.09 1.19 1.24 1.32 138 1.405

where - 2 J is the exchange coupfing constant, Y the mole fraction of the mononuclear impurity, and the other symbols have the usual meaning. The susceptibility-temperature data were fitted to a three parameter (g, 2 J and Y) equation by use of a non-linear least-squares method using a Fortran V program on an Univac 1108 computer. The results are shown in Table 7. The energy separation (-2 J) between the triplet and singiet states as well as the spin-Hamiltonian parameters are similar to those of copper(II) acetate monohydrate and other related copper(II) carboxylates[20, 21]. The value of the exchange energy for Cu(2-CIGJ-I4COO)2nic is the lowest in the series. The compound contains a noticable amount of mononuclear impurity. The mole fractions of singlet and triplet States for the compounds were calculated from the observed susceptibilities by the method of Hatfield et al.[22].The singlet~triplet equilibrium constants obtained from the mole fractions were used to calculate AH and AS. The values are given in Table 7. The values found for the enthalpy are in good agreement with the values of - 2 J, The values for the entropy change are in agreement with the value 2.2 e.u. expected for a singlet-triplet equilibrium, that is R In 3, where 3 is the degeneracy ratio assuming that the only contribution is that from the electronic entropy. At room temperature the EPR spectra of the poly-" crystalline CuX2nic (X=CH3COO-, CH3CH2COO-, C6HsCOO-, 2-FCcJ-I4COO-, 2-CICffI4CO0-, 2BrC6H4COO-, 2-IC6H4C00-, 3-FCd-14COO-) contained the absorption bands of axially-symmetric binuclear species, the parameters are summarized in Table 5. The electronic spectra of these adducts are similar to those reported for binuclear copper(II) acetate monohydrate [23] (Table 8). The magnetic and spectroscopic properties of these compounds indicate the presence of binuclear units structurally similar to those in copper(II) acetate monohydrate[24]. Copper(II) atoms in the structural units Cu2X4nica are bridged in pairs by the carboxylic, X, while the molecules of nicotine are bonded through nitrogen atoms in apical positions. As we can see in Table 9 the value of - 2 J for the compounds of copper(II) acetate and propionate tends increase according to the series of terminal ligands: hydrate < anhydrous < pyridine < nicotine < dioxan. No such tendency exist in the case of copper(II) arylcarboxylates. The singiet-triplet separation - 2 J for Cu(2XCrH4COO)2.H20 ( X = F , Cl, Br and J) was found[25, 26] to be ~-254 cm -I, but for anhydrous Cu(2XC~I4COO)2 (X = CI, Br) only ~165 cm-t[25, 26], the value of 286cm -I was observed for Cu(2ICrH4COOh[26], and for the nicotine adducts ~-280 cm -t. These values are lower than the values of -2 J found for dimethylformamide adducts (,~310cm-~)[27], as well as for pyridine adduct of copper(II) 2-chlorobenzoate (312 cm -~) 25 and copper(II) 2-bromobenzoate (309 cm-t)[28].

Acknowledgements--Magneticmeasurements were done in the laboratory of Prof. P. Lumme, University of Helsinki by H. Sandstrrm. The author is also indebted to Mr. M. Viisinen, Ph.M., for the least-squares program. The calculations were made on an Univac 1108computer at the Helsinki-Espoo.

Spectral and magnetic properties of mono-, di- and tetranuclear copper(ll) carboxylates with nicotine

783

Table 7. Exchange parameters of the copper(II) carboxylate dimers Compound

g (-+0.01)

Cu(CH3COOhnic Cu(CH3CH2COO)2nic Cu(Cd-isCOOhnic Cu(2-FC~,H4COO)2nic Cu(2-ClC6H4COOhnic Cu(2-BrC~-I4COOhnic Cu(2-1C6H4COOhnic Cu(3-FC6H4COOhnic

2.13 2.22 2.05 2.20 2.17 2.26 2.24 2.18

-2J, cm i AH, cm i AS, e.u. (-+10) (-+0.01) (-+0.1) 339 354 253 314 229 280 292 312

320 335 240 298 240 273 296 301

2.1 2.2 2.3 2.0 2.3 2.2 2.2 2.1

M.I.t 0.15 0.05 1.0 0.11 5.2 0.1 0.05 0.14

tMononuclear impurity. Table 8. Absorption bands (u,B~ (kK)) of mononicotine adducts of copper(II) carboxylates Compound

BandI.

Band II

14.2 14.1 13.5 13.0 13.2 13.3 12.9 13.6 13.5 13.3

26.2 sh 26.0 sh 26.0 sh 25.5 sh 25.8 sh 25.5 sh 27.0 sh 26.0 sh 26.0 sh 26.0 sh

Cu(CH3COO)2nic Cu(CH3CH2COOhnic Cu(C6HsCOO)2nic Cu(2-FC6H4COO)2nic Cu(2-CIC6H4COO)2nic Cu(2-BrCd-I4COOhnic Cu(2dCd-I4COOhnic Cu(3-FC6H4COO)2nic Cu(4-FC6H4COO)2nic Cu(4-CIC6H4COOhnic sh, shoulder.

Table 9. The values of -2J, for some copper(II) acetate and copper(II) propionate compounds Compound

-2J, cm -~

Cu(CHjCOOh'H20 Cu(CH3COO)2 Cu(CH3COOhpy Cu(CH3COOhnic Cu(CH~COOhCoqsO2 Cu(CH3CH2COOh'H20 Cu(CH3CH2COO)2 Cu(CH3CH2COO)2py Cu(CH3CHzCOO)2nic Cu(CH3CH2COO):,0.5(C4HsO2)

286 3{)0 325 339 358 300 322 350 354 386

Ref. [29] [29] [30] This work [3I] [32] [32] [33] This work [34]

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