Synthesis and Characterization of Cu(1) Complex Compounds With Methyl Isonicotinate MOHAMED A. S. GOHER

Transcription

1 Synthesis and Characterization of Cu(1) Complex Compounds With Methyl Isonicotinate MOHAMED A. S. GOHER Department of Inorganic Chemistry, Charles Universiv, Prague 2, Czechoslovakia1 Received January 31,1975 MOHAMED A. S. GOHER. Can. J. Chem. 53,2657 (1975). The preparation of Cu(1) complexes of methyl isonicotinate, MeIN, of the formula (MeIN).- CuX, in which n = 1, 2, 3, and 4 and X is C1, Br, I, CN, SCN, and C104, has been described. The isolated complexes are characterized by their analytical data, diamagnetism, and conductivity measurements. The M + L charge transfer bands in the visible spectra and the i.r. spectra of these complexes are discussed. MOHAMED A. S. GOHER. Can. J. Chem. 53,2657 (1975). On dkrit la preparation de complexes du Cu(I), avec I'isonicotinate de methyle (MeIN), de formule (MeIN).CuX dans lesquels n = 1, 2, 3 et 4 et X = C1, Br, I, CN, SCN et C104. On a caracterise les complexes par leurs donnees analytiques et des mesures de conductivitc et de diamagnetisme. On discute des spectres i.r. ainsi que des bandes de transfert de charge M + L dans les spectres visibles de ces complexes. [Traduit par le journal] Introduction In a series of publications (1-3) we have reported the preparation and characterization of some Cu(1) complex compounds with pyridine monocarboxylic acids and their derivatives. As Cu(I1) complexes of methyl isonicotinate have been studied from different points of view (4, 5), and as Cu(1) complexes of this ligand have not yet been mentioned, we tried to prepare these latter complex compounds. With methyl isonicotinate ligand we isolated Cu(1) complexes of Cu/L ratio I : 1, 1 : 2, 1 : 3, and 1 : 4 depending on the anion present. Experimental Chemicals and Apparatus Methyl isonicotinate was g.1.c. purified. The other chemicals were analytical grade and commercially available. Magnetic measurements were made by the Faraday method at room temperature. X-Ray powder patterns were taken on a Mikrometa 2 (Chirana, Prague) instrument, + = 53.3 mm, with LCuK, radiation. Conductivity measurements were carried out at 25 "C on F solutions in chloroform, nitrobenzene, and acetone under dry nitrogen with a Radiometer conductivity bridge model CDM 2e. Electronic spectra were recorded on a Unicam spectrophotometer SP 800. Refledtance spectra of the solids were measured over the nm range on a VSU-1 (Zeiss, Jena) instrument with MgO as a standard and diluent. Infrared spectra in the region cm-' were measured on a UR-20 (Zeiss, Jena) spectrophotometer. The solid samples were measured as Permanent address: Department of Chemistry, Faculty of Science, Alexandria University, Egypt. Nujol mulls or KBr pellets, and the liquid ligand as a capillary film. Far i.r. spectra have been measured on a Perkin-Elmer 325 spectrophotometer. Analysis Microanalysis of C, H, N were carried out on the Perkin-Elmer 240 elemental analyzer. Halogens were determined gravimetrically as AgX. Copper was determined either by titration against disodium EDTA or gravimetrically as CuSCN after degradation and oxidation of the complexes with boiling mixtures of concentrated and 30% H202. Preparation of the Complexes The complexes were prepared according to the procedure described previously (1, 3). Table 1 summarizes the elemental analysis and some properties of the prepared complexes. The separation of pure Cu(1) perchlorate complexes caused some difficulties. However, the preparation of these complexes in such form was effected as follows. The 1 : 4 complex was prepared by mixing the ligand (six- to eightfold) with Cu(I1) salt in aqueous medium, followed by addition of ascorbic acid and then sodium perchlorate pentahydrate. The final product was recrystallized from ethanol in presence of excess ligand and ascorbic acid to prevent air oxidation. The 1:3 complex was prepared from aqueous solutions of the ligand and copper in the exact molar ratio followed by slow addition of the perchlorate ion in the least amount of water. Care must be taken otherwise the complex will change immediately to one of the other two complexes. The white microcrystalline powder was prepared by mixing the ligand and copper ion in aqueous solution (Cu/L = 1 : 2). The faint yellow sheets were isolated by addition of an ethanolic solution of the ligand and an aqueous solution of CuS04.5H20 (Cu/L = 1:2) and after addition of ascorbic acid and the perchlorate ion the mixture was stirred about 15 min until faint yellow sheets isolated. This product was then recrystallized from ethanol.

2 Complex Appearance Yellow needles turned green Yellow needles Yellow powder Pale yellow powder Yellow powder Red-brown needles Brown needles Red-orange needles White microcrystalline Melting point ("C) dec. 178 dec. 183 dec ' 145 dec. TABLE 1. Analytical data Calcd. Cu Found powder (MeIN),CuC104* Very faint yellow sheets (MeIN)3CuC104 Yellow microcrystalline powder (MeIN)4CuC104 Red-orange crystals "Unstable form. bsufficiently stable form. CAt this temperature the complex changes to yellow 1 : 1. Calcd. X Found Analysis (%) C Calcd. Found H Id Calcd. Found Calcd. Found n b

3 GOHER: Cu(I) COMPLEXES OF METHYL ISONICOTINATE 2659 TABLE 2. Reflectance spectra and conductivitiesa Molar conductivitiesb I i (n-i cm2 m01-i) 1 Compound n-n* M+L Nitrobenzene Acetone :. :...i MeIN 275' (Me1N)CuBr (Me1N)CuI (Me1N)CuCN (Me1N)CuSCN (MeIN)2CuCl 270 d 490 vb (MeIN),CuBr 280 d 470 vb 1.4 Yellow precipitate... (MeIN)2CuI 280 d 510 vb Turbid Yellow precipitate.. (MeIN)2CuC d d O d.... (MeIN),CuC (MeIN),CuC vb Ol. is given in nm. vb is very broad bthe conductivities given are based on the formula weights , 'From the electronic spectra of M in chloroform 'Strong absorption without definite maxima. ethe filtrate solutions are conducting. 1 Results and Discussion The complexes were prepared simply by mixing ligand and CuS04.5H20 in the appropriate stoichiometric ratio in aqueous or ethanolic media followed by addition of ascorbic acid as the reducing agent and then the desired anion. By such a procedure Cu(1) nitrate com- I plexes of MeIN have been prepared as yellow or red compounds, but they are too easily oxidized to permit their isolation and analysis. Alternatively, the halide complexes can be prepared by direct interaction between the components in suitable molar ratios. Because reactions leading to different stoichiometries are often competitive, pure samples are difficult to obtain. However, recrystallization could effect their purification. Only in one case we isolated two isomers of the formula (MeIN),CuClO,. One is white microcrystalline powder and not sufficiently stable and the other is faint yellow sheets and stable enough. All the complexes isolated are colored, except the 1 : 2 perchlorate, diamagnetic compounds and are fairly stable in air except the 1 : 1 chloride and the white 1 :2 perchlorate complexes. As was observed (2, 6) for Cu(1) halide complexes of other ligands, the stability with respect to air oxidation of the isolated Cu(1) complexes depends critically on the identity of the halogen and increases from chloride to iodide. The X-ray powder patterns showed that the 1 : 1 bromide and iodide and the 1 : 2 halide complexes are isomorphous. The Cu(1) perchlorate complexes behave in nitrobenzene (7) and acetone (8) as 1 : 1 electrolytes (see Table 2). The Cu(1) halide complexes, on the other hand, gave nonconducting solutions in chloroform and nitrobenzene. In acetone the measured conductivities are very small compared to those of 1 : 1 electrolytes (8). However, the results are reproducible for different samples and hence they are not due to impurities. The Cu(1) halide complexes dissociate in solvents like chloroform, acetone, or alcohols to free ligand and complexes of lower ligand content or simple CuX. In general the intense red color of solutions of the 1 :2 complexes obtained at higher concentrations changes very rapidly upon dilution. The faint yellow solutions obtained did not show the M + L charge transfer bands which are observed in the spectra of the solid samples. Electronic Spectra Table 2 summarizes the reflectance spectra data. In the U.V. region of the spectra of solutions of free ligand and complexes as well as in the spectra of the solid samples, an absorption band is observed around nm. This band is attributed to a n-n* transition in comparison with the assignment given for similar transition in the parent acid (9). Around nm other absorption bands are observed in the reflectance spectra of some complexes,

4 TABLE 3. Infrared spectral data" 1:l 1:l 1:l 1:l 1:2 1:2 1:2 1:2O 1:3 1:4 MeIN bromide iodide cyanide thiocyanide chloride bromide iodide. perchlorate perchlorate perchlorate Assignments 1740 vs 1740 vs,sp 1735 vs,sp 1740 vs,sp 1738 vs,sp 1735 vs,sp 1738 vs,sp 1735 vs 1738 vs,sp 1744 vs,sp 1740 vs,sp vc=o st. 0 > 1602 m,sp 1612 vw 1612 w 1615 ms 1612 vw 1608 vw 1608 wm 1610 w 1625 w 1618 w 1618 w V,., ~(c-c) 2: 1568 s,sp 1565 w 1568 w 1570 ms 1568 w 1562 w 1565 wm 1565 m,sp 1565 w,sp 1565 w 1568 wm vab, v(gc)? 1497 vs,sp 1505 sh 1500 sh 1500 sh 1500 sh 1500 sh 1500 sh 1510sh 1510 w 1510sh 1510sh v,,.,v(gc,c-n) 1440 vs S,SP 1440 vs 1440 vs,sp 1400 vs 1445 sh 1440 vs 1450 sh 1440 sh 1445 sh 1445 sh vr-sens. z 1430 s m 1412 vs,sp 1418 ms 1415 s 1420 vs 1420 vs,sp 1415 s,sp 1420 s,sp 1412 vs,sp 1412 s 1420 s 1425 vs v15.b~ ~((3-C, GN), P(C-H) 1328 vs 1330 s 1325 vs 1335vs 1330s 1322 m,sp 1328 vs 1324 vs 1340 s,sp 1332 s,sp 1330 s,sp v14, v(c-c, GN) < 1220 s 1230wm 1232wm 1236ms 1230w 1230 wm 1228 ms 1225 s 1225 m 1225 wm 1228 m vs., P(CH) 0 r 1155 w 1150sh 1150sh 1150sh 1150 sh 1154 wm 1160m 1140 vs 1140 sh 1135 vs vls, P(C-R, C--H) VI 1125 vs 113Os,sp 1124vs 1132s,sp 1125s 1122s,sp 1125vs 1128 vs 1120 vs 1130s 1125 vs vs, P(C-H) w 1068 s,sp 1080 sh 1080 m 1085sh 1085sh 1082w 1085 sh 1085 m (++) (+ +) (+ +) V18b. P(CH) 1028 sh 1065 w 1062 ms 1068 ms,sp 1062 ms,sp 1056 w 1058 s 1058ms 1062s 1070 s 1060 s VIZ. ring 995 ms 1020 w 1018wm 1018ms,sp 1020~ 1020 vw 1020 w 1016 w 1005 w 1020 w 1015 w VI, ring, KC-M) 668 w 668 w 668 w 668 w 668 w 668 w 668 w 665 w 668 w 668 w V6b, ring 485 w 490 w 492 w 498 wm 495 w 485 wm 486 w 484 w 495 w 507 vw 485 vw v6,,, ring, R-sens. 402 vw 400 vw 408 w 400 vw 400 vw 400 vw 405 w 400 w 400 vw 400 vw vl,, R-sens. -w = weak, m = medium, s = strong, v = very, b = broad, sh = shoulder, sp = sharp, st = stretching, (+ +) = masked by the strong absorption of C104 group. G 2

5 GOHER: Cu(1) COMPLEXES OF METHYL ISONICOTINATE 2661 TABLE 4. Vibration frequencies (cm-l) of the perchlorates, cyanide, and thiocyanate anions C104 Compound VI v3 v4 v(cn) G(NCS) 'White compound. bfaint yellow compound. but not in the spectra of their solutions. These bands cannot be assigned as X + M charge transfer bands since the perchlorate compounds also showed strong absorption in this region. Intense absorption bands are observed in the visible region of the reflectance spectra of Cu(1)-MeIN complexes, except for the 1 : 2 perchlorates. These bands are assigned as M + L charge transfer from the completely filled dl0 orbitals of the Cu(1) ion to an empty IT* orbital on the ligand. Similar M + L charge transfer bands are observed in the visible spectra of Cu(1) complexes of bipyridine and phenanthroline (10, 11). The electron attracting carbomethoxy group causes the electron density to migrate from the delocalized system on the pyridine ring to the substituent and thus lowers the electron density on the nitrogen atom. Therefore, increasing the number of ligands per Cu(1) ion increases the reducing power, that is, its tendency to accept electrons, of the acceptor part in the complex molecule, and hence M + L charge transfer band shifts to longer h,,, as the number of ligands increased (12), as seen from Table 2. The cation [(MeIN),Cu]+ is white and does not exhibit an M + L charge transfer band. Therefore the structure [(MeIN),CuIf [CuX,]- is not probable for (Me1N)CuX (X = halide, CN, or SCN) complexes. Since these latter complexes exhibit M + L bands similar to the trigonal cation [(MeIN),Cu]+, structures involving trigonally coordinated Cu(1) ion are, therefore, proposed for these 1 : 1 complexes. Similarly, the reflectance spectra of the halides of 1 : 2 complexes are very similar to that of the cation [(MeIN),Cu]+ in the U.V. and visible regions. Tetrahedral geometries are, therefore, postulated for the 1 : 2 complexes. Infrared Spectra Wong and Brewer (5, 13) have carried out the coordinate analysis calculations on 1 : 1 complex models between Cu(I1) or Zn(I1) ions and MeIN among other Csubstituted pyridines. Following them, we assign the in-plane vibrations as given in Table 3. In Table 4 the vibrational frequencies of the anions are tabulated. At 668 cm-' a new band appears in the spectra of the Cu(1) complexes. It may be attributed to v,, vibration since a similar band given the same assignment was observed in the spectrum of Cu(I1)-MeIN complex (5). The v,, vibration mode has been calculated to be at 516 cm-' and at 488 cm-' for the 1 : 1 complex model of Cu(I1) and Zn(1I) with MeIN, respectively. No bands have been observed in the spectra of both compounds to be assigned for this vibration mode. However, a band of weak to medium intensity is observed at cm-i in the spectra of all Cu(1)-MeIN complexes. It may be attributed to v,, ring vibration mode. The positions of most frequencies observed in the spectra of Cu(1) complexes are in good agreement with those observed for Cu(I1) and Zn(I1) complexes of MeIN (5,13). The position of the C=O stretching vibration frequency, as seen from Table 3, is essentially constant in free and coordinated MeIN. On the other hand, the ring C-C, C-N stretching, ring C-H in-plane, and ring breathing v, and v,, vibration frequencies all are blue shifted upon coordination of MeIN. These shifts are in line with those observed for coordinated

6 CAN. J. CHEM. VOL. 53, 1975 TABLE 5. Copper(1)-nitrogen stretching vibration frequencies (cm-') Complex Cu(1)-N Complex Cu(1)-N pyridine (14, 19, indicating the coordination of MeIN via the nitrogen atom. Taking the shifts of the v,, vibration mode as a measure of the relative n-contribution to the coordination bond (4), we observe that the n-contribution in the case of Cu(1)-MeIN complexes is slightly higher than in the case of Cu(I1) or Zn(I1) complexes with MeIN (5, 13). Examination of Table 4 shows that the perchlorates of 1 : 4, 1 : 3, and the white 1 : 2 MeIN complexes are ionic, since the vibrations of the perchlorate groups are consistent only with noncoordinated groups (ref. 16 and references cited therein). Therefore, these complexes are formulated as [(MeIN),Cu] + C10,-, [(MeIN),Cu] + C10,-, and [(MeIN),Cu] + C10,- with tetrahedral, trigonal, and linear geometries respectively. In the spectrum of the faint yellow 1 :2 Cu(1) perchlorate complex, v,, the antisymmetrical stretching, and v,, the antisymmetrical bending, vibration modes split into three 'components for each. The splitting of these modes in this manner is consistent only with a bidentate perchlorate group. This compound is, therefore, formulated as [(MeIN),- CuClO,] in which Cu(1) ion is tetrahedrally coordinated in the solid state. For the 1 : 1 cyanide complex, the appearance of a single v(cn) at 2140 cm-' which is higher than those of the terminal cyanide groups in the complex K,Cu(CN),, cm-' (17), strongly suggests a bridging cyanide group (18, 19). The 1 : 1 thiocyanate complex showed two cyanide stretching frequencies. The higher frequency indicates an S-bonded, and the lower an N-bonded, thiocyanate group (20, 21). Therefore this compound is postulated to exhibit a bridging thiocyanate group. In an attempt to obtain further information concerning the structures of the complexes, the low frequency (20&400 cm-') i.r. spectra of some of them were measured (Table 5). Wong and Brewer (13) have assigned the two bands observed at 230 and 203 cm-' in the spectrum of Zn(I1)-MeIN complex as Zn(I1)- N stretching vibrations in accordance with the calculated values. Similarly we have assigned the bands in the region cm-' and around 200 cm-' in the spectra of Cu(1)-MeIN complexes as Cu(1)-N stretching vibrations. As expected the 1 : 2 halide complexes showed two Cu(1)-N stretching frequencies. However, there are no bands attributable to Cu(1)-Cl frequencies above 200 cm-' in the spectrum of the 1 :2 chloride. For the 1 :2 halides a structure of the type may account for these observations, with each metal atom having approximately tetrahedral geometry through halide bridges. In the spectrum of the faint yellow Cu(1) perchlorate 1 :2 compound, two bands have been observed at 251 and 264cm-I. Since these bands are absent from the spectra of all the measured complexes we attributed them to Cu(1)-0 stretching vibrations. This observation confirms our conclusion that the perchlorate group acts as a bidentate ligand in this complex. The author expresses his gratitude to Dr. M. Dritovskf for valuable discussion and Dr. M. Ferles, Department of Organic Chemistry, Institute of Chemical Technology, Prague, who very kindly suppged methyl isonicotinate. His thanks are also due to Dr. Silha and Mrs. Zemanovi for their help with some measurements. I. M. A. S. GOHER and M. DLTOVSKL, Coll. Czech. Chem. Commun. 40,26 (1975). 2. M. A. S. GOHER and M. DLTOVSKL. Naturwissenschaften, 62,96 (1975). 3. M. A. S. Go~~~and M. DLTOVSKL. J. Inorg. Nucl. Chem. In press. 4. P. T. T. WONG and D. G. BREWER. Can. J. Chem. 46, 131 (1968). 5. P. T. T. WONG and D. G. BREWER. Can. J. Chem. 46, 139 (1968). 6. N. MARSICH, A. CAMUS, and E. CEBULEC. J. Inorg. Nucl. Chem. 34,933 (1972).

7 GOHER: Cu(1) COMPLEXES OF METHYL ISONICOTINATE E. W. A~NSCHOUGH and R. A. PLOWMAN. Austr. J. Chem. 23,699(1970). 8. J. E. FERGUSSON and J. HICKFORD. Austr. J. Chem. 23,453 (1970). 9. H. P. STEPHENSON and H. SPONER. J. Am. Chem. SOC. 79,2050 (1957). 10. R. J. P. WILLIAMS. J. Chem. Soc. 137 (1955). 11. B. R. JAMES, M. PARRIES, and R. J. P. WILLIAMS. J. Chem. Soc (1961). 12. A. B. P. LEVER. Inorganic electronic spectroscopy. Elsevier Publishing Company, Amsterdam Chapt P. T. T. WONG and D. G. BREWER. Can. J. Chem. 47, 4590 (1969). N. S.GILL,R.H.NU~ALL,D.E.SCAIFE,~~~R. W. A. SHARP. J. Inorg. Nucl. Chem. 18,79 (1961). N. N. GREENWOOD and K. WADE. J. Chem. Soc (1960). K. NAKAMOTO. Infrared spectra of inorganic and coordination compounds, 2nd ed. Wiley Interscience, New York p L. H. JONES, J. Chem. Phys. 29,463 (1958). R. D. GILLARD. J. Inorg. Nucl. Chem.27,1321(1965). I. S. AHUJA and A. GARG. J. Inorg. Nucl. Chem. 34, 2681 (1972). A. TRAMER. J. Chim. Phys. 59,232 (1962). G. CONTRERAS and R. SCHMIDTH. J. Inorg. Nucl. Chem. 32,127 (1970).