3d Metal perchlorate complexes with quinoxaline 1-oxide[1]

J. inorg, nucl. Chem., 1977, Vol. 39, pp, 585-590. Pergamon Press. Printed in Great Britain

3d METAL PERCHLORATE COMPLEXES WITH QUINOXALINE 1-OXIDE[I] D. E. CHASAN and L. L. PYTLEWSKI Departments of Chemistry, Drexel University, Philadelphia, PA 19104, U.S.A. and C. OWENS and N. M. KARAYANNISt Rutgers University, Camden, NJ 08102, U.S.A. (Received 7 July 1976)

Abstract--Hexacoordinated 3d metal perchlorate complexes with quinoxaline l-oxide(N-QxO) were prepared and characterized by means of spectral and magnetic studies. Several of the new complexes involve exclusively oxygen-bonded unidentate N-QxO ligands and are probably of the types: [Cr(N--QxOh(OH2)(OCIO3)](C104)2'5H20; [Fe(N--QxO)~(OH2)(OCIO3)2](CIO,);and [M(N--QxO)4(OH2)2](CIO4)2.xH20(M = Fe, Co, Ni; x = 1 for Co; x = 6 for Fe or Ni). The rest of the new complexes contain some N- and some O-bonded N-QxO groups; likely formulations for these compounds are: [Mn(ONCsHtN). (NCsHtNO)5_, (OC103)](C10,).4H20; [Zn(ONCsHtN), (NCsHtNO)3, (OH2)3](C104)2; [Cu(ONCd-I,N)(NCsH,NO)(OH2)2(O2CIO2)](C104).H~O; and [(NCsHtNO), (ONCsI4~N)3_,(O3CIO)Cu(N--QxO)2Cu(OCIO3)(NC.H,NOh_,(ONCsHtN),](CIO,)2.4H~O. The latter complex is apparently the only binuclear compound of the series, involving two O-bonded bridging N--QxO ligands, as suggested by its subnormal magnetic moment (0.99/zB). The Fe(III) compound also shows a subnormal/zo~ (2.61 #B), which was attributed to spin-state equilibria, while the rest of the new complexes with paramagnetic metal ions are magnetically normal high-spin compounds. INTRODUCTION

Earlier work by these laboratories involved 3d metal complexes with pyrazine 1-oxide(N-pyzO)[2--4], which can function either as a unidentate O- or N-bonding ligand, or as a bidentate(O,N-bonding) bridging group [27]. Information available in the literature on metal complexes with the N-oxides and N,N-dioxides of quinoxaline and phenazine is rather scattered and restricted to only a few metal ions, i.e. Cu(II) halide complexes with quinoxaline 1-oxide(N--QxO) and 1,4dioxide(N,N-QxO2)[8], Cu(II) chelates with hydroxyderivatives of phenazine 5-oxide(N-phzO) and 5,10dioxide(N,N-phzO2)[9, 10] and with 2-quinoxaline carboxylic acid 1A-dioxide [ 11], Mn(II) and Zn(II) derivatives of 2-mercaptoquinoxaline 1-oxide and the corresponding disulfide[12] and an intercalation product of TiS2 with N,N--QxO2 [13]. It was felt that extention of our previous studies with N-pyzO metal complexes, to include 3d metal chloride and perchlorate complexes with quinoxaline and phenazine N-oxides was in order. Accordingly, work in this direction was undertaken[I, 14-17] and we have already reported on synthetic and characterization studies of N-QxO-3d metal chloride complexes [15]. The present paper deals with the corresponding 3d metal perchlorate complexes. EXPERIMENTAL Chemicals. Reagent grade chemicals were used throughout this work. N-QxO was prepared by the method of Landquist[18] and purified as recommended by Emerson and Rees [19], as described elsewhere[15]. The authenticity of the ligand was confirmed by elemental analysis, melting point determination (122-123"C)[18], IR[8, 20, 21] and electronic[22, 23] spectra. tAmoco Chemicals Corp., Naperville, IL 60540, U.S.A. JINC Vol. 39, No. 4--C

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Synthetic procedure. As all the new metal complexes are very hygroscopic, the preparation and filtration of these compounds were performed in a dry-box (dry N2 atmosphere). The hydrated metal perchlorate (1 mmole)was dissolved in 8-10 ml ethyl acetate and stirred for 30 rain with ca. 3 g molecular sieve 4A (Davison's, grade 515)[14], at room temperature. The ligand (3.5 mmole) was separately dissolved in 8 ml chloroform and treated in the same manner with 3 g molecular sieve 4A. Subsequently, the ligand solution was filtered through a medium sintered glass funnel into a filtering flask containing a magnetic stirring bar, and the metal perchlorate solution was then filtered through a similar funnel into the stirred ligand solution. In all cases investigated, solid precipitates formed immediately. The reaction mixtures were allowed to stir for 2 minutes and then the solids were quickly filtered, washed with hexane and stored in an evacuated desiccator over phosphorus pentoxide. A second Cu(CIO4)2 complex, involving a 2:1 ligand to Cu ratio, was precipitated by allowing ligand and salt to interact at a 1: 1 molar ratio, under the same synthetic conditions as above. In the rest of the cases examined (Cr(III), Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Zn(II) perchlorates), variations of the ligand to metal ratio during the preparative procedure did not lead to the precipitation of complexes with different stoicheiometries than those prepared at the 3.5 : 1 molar ratio. Table 1 shows analytical results (C,H,N by Schwarzkopf Microanalytical Laboratory, Woodside, New York; metals by atomic absorption spectroscopy). The new complexes dissolve readily in water and several organic solvents (methanol, acetone, nitromethane, dimethyl sulfoxide,N,N-dimethylformamide), yielding either colorless or light yellow solutions. As was also the case with the corresponding metal chloride complexes [15], the new complexes apparently dissociate in contact with the above solvents, as suggested by the dramatic color changes observed upon dissolution. Characterization studies. IR spectra (Table 2) of the new metal complexes were obtained on hexachlorobutadiene (40001200 cm-') and Nujol (1650-350cm-~) mulls between NaCI and KBr windows, respectively, by using a Perkin-Elmer 621 spectrophotometer. Far-IR spectra (525-33 cm-1) (Table 3) were obtained on Nujol mulls between high-density polyethylene

586

D. E. CHASAN a aL T~lel. AnalyficfldataforN-QxO(L)complexeswithme~perchlora~s

Complex

Color

C (%) Calc. Found

Cr(CIO,)3L'6H20 Mn(C104)2Ls'4H20 Fe(CIO4)2L4-8H20 Fe(CIO4)3L3"H20 Co(CIO4)2L,'3H20 Ni(CIO4)2L'8 H 2 0 Cu(C10,)2L'2H20 Cu(CIO,)2L2'3H20 Zn(C104)2L3.3H20

Light blue-green Red-orange Brown Beige Pink Ivory-yellowish Tan Olive--green White

36.85 45.46 39.24 35.55 42.87 38.% 43.51 31.57 38.08

36.54 45.70 39.09 35.55 42.76 39.12 43.16 31.10 37.99

Analyses H N (%) (%) C a l c . Found C a l c . Found

Metal (%) C a l c . Found

3.49 3.62 4.12 2.49 3.37 4.10 3.20 2.99 3.20

5.0 5.2 5.7 6.9 6.6 6.0 7.2 10.4 8.6

3.14 3.31 3.88 2.55 3.47 3.93 3.00 2.71 3.58

10.75 13.26 11.44 10.38 12.50 11.36 12.69 9.21 11.10

10.76 13.19 11.21 10.65 12.16 11.14 12.23 8.74 11.50

4.6 4.8 5.9 6.4 6.1 6.2 6.7 10.0 8.1

Table 2. IR spectra of N-QxO-metal perchlorate complexes (4000-525cm-~ region) Compound

IR maxima,cm-~

N-QxO=L

3015m, 2976m, 1800w, 1571m, 1531w, 1492m,sh, 1450m, 1420m, 1370m,1364m, 1325s, 1260m,1245m, 1213w, 1168w, 1129w, ll01w, 1049w, 1012w, %0w, 890m, 825m, b, 810m, 752s, 637m, 579m, 546m 34t0m, b,* 3117m, 3050w, 3014w, 1830w, 1730w, 1630w, 1611w, 1579m, 1538w, 1497w, 1457w, 1422m, 1380m, 1367m, 1319m, 1313m, 1307m, 1260m, 1252m, 1242m, 1214m, 1169s, l147s,t, ll02s,t 1072s,t 1048m, sh, 972w, 945w, 930w,t 892m, 869m, 851m,760s, 732m, 639m,t 632m, sh,t 624s,t 600w, 582w, 547w 3650-3200m-w, vvb, 3070m, 3010m, 1830w, 1724w, 1645w, sh, 1571m, 1540m, sh, 1510w, sh, 1496m, 1462m, 1420m, 1381m, 1365ra,b, 1300s, 1245s, 1214m, 1164m, l150m, sh,t 1137m,sh, ll00s,t" 1066s,t 1042s, 976m, sh, 933m,t 878m, 839m, 813m, 761m, 747s, 728s, 666w, 635w-m,t 620m,t 576m, 545m 3380m, b,* 3110m, 3014m, sh, 1920w, 1730w, 1654w, 1613w, sh, 1579m, 1545w, 1500s, 1462w, 1426m, 1388m, 1370m, 1303s, 1247m, 1217m, 1203w, sh, 1166m,sh, l105s, b,l" 1047s,sh, 972w, 933w,t 890s, 852m, 819m, 770s, 732m, 654w, sh, 625m,~"581m, 555m 3400m,b, 3117m,3100m,sh, 3050w,3010w, 1829w, 1729w, 1610w, 1577m,1540m,1499s, 1452w, 1421m, 1379m, 1366m, 1318m, 1312m, 1305m, 1259m, 1251m, 1243m, 1214m, 1167m, l142s,t ll01s,t 1080s,t 1045m, sh, %0w, 944w, 929w,I 895m, 866m, 850m, 815m, 758s, 731m, 653w, 639m,t 631m3 623m,t 580m, 545m 3400m, vvb,* 3100m, 1738w, 1652w, 1620w, 1574s, 1542m, sh, 1498s, 1459w, 1422m, 1383m, 1365m, 1303m, 1248m, 1212m, 1163m, 1136s, sh, l103s, b,~ 1045s, sh, 970w, 930w,t 911w, 889w, 843m, 814m, 767m, 729m, 663w, 620m,t 578m, 549w 3420s, vb,* 3104s, 2958m, 2924m, 1740w, 1640m,b, 1620w, 1578m, 1538w, sh, 1500m, 1458w, 1424m, 1383m, 1367m, 1303s, 1250m, 1212m, 1162m,sh, 1138m,sh, 1104s,b,t 1045m,sh, 979w, 928w,t 914w, 895m, 889m, 844w, 814m, 769m, 729m, 620m,t 578w, 550w, sh 3650--3280m-w,vb, 3090m, 3012m, 1728w, 1650w, 1585m,1540m,sh, 1511m,sh, 1497s, 1460w, 1424m, 1388s, 1368s, 1335w, 1320w, 1298m, 1255m, 1237m, 1208m, 1163m, 1137m,sh,t ll01s,t 1068s,t 1040s, 975m, sh, 933m,t 884s, 849m, 820m, 762s, 731s, 668w, 645w,t 620m,t 599m,'~583m, 549m 3500m,* 3220m, 3190m, 3160m, 3124m, 3084m, 3054m, 3012m,2980w, 1731m, 1623m, 1609m, 1591m, 1579m, 1559w, 1540w, 1510m, 1472m, 1464w, 1452m, 1437w, 1421s, 1386m, 1341m, 1320w,sh, 1301m, 1259w, sh, 1236m, 1218m, 1167m, l157m,t ll20s,t 1095s, b,t 1040m, sh, 1016m, sh,t 983w, 922m,t 914m, 895w, 843m, 818m, 781m, 732m, 653w, 644w,t 631m,t 621m,t 586m, 575w, 564w, 553w 3400m, b, 3110m, 1650w, 1623w, 1610w, 1580m, 1542w, 1511m, sh, 1502m, 1455w, 1424m, 1387m, 1370m, 1343m, 1305s, 1253m, 1215m, 1166m, ll01s,t 1045s, sh, 985w, 973w, 924m,t 898m, sh, 891m, 843w, 816m, 770m, 732m, 620m3 583m, 569w, 556w

Cr(CIO,)3L'6H20

Mn(CIO4)2L~.4H20 Fe(C104)2L,.8H20 Fe(C10,)3L3.H20

Co(CIO,)2L4.3H20 Ni(C10,)2L4.SH20 Cu(C104)2L,.2H20 Cu(C104)2L2.3H20

Zn(C10,)2L~.3H20

Abbreviations: s, strong; m, medium; w, weak; b, broad; v, very; sh, shoulder. *Weak absorption covers the 3650-3200cm-t region, apparently including several maxima; the most intense peak is indicated. *Fundamental vibrations of the perchlorate group: v3 at 1200-1000; vl at 933-922; and v4 at 645-600cm-1 [29-33]. Note: vNm band assignments are shown in italics. windows, by using a Perkin-Elmer 181 spectrophotometer. Solid-state (Nujol mull)electronic spectral and magneticsusceptibility measurements (Table 4) were performed by methods described elsewhere[2]. The dissociationof the new complexes in organic solvents, hampered any attempts at obtaining solution electronic spectra or molar conductivity measurements. DISCUSSION Stoichiometries of the new metal complexes. As indicated in Table 1, the new compounds prepared by using a 3.5:1 ligand to salt molar ratio involve, in most cases, three or four N-QxO molecules per metal ion. Only Mn(C104)~ produced a 5:1 complex, while Cu(C10,)2

formed also a 2: 1 complex, when a lower metal to salt (1:1) ratio was used during the preparation. All the complexes contain a number of water molecules. It has been already pointed out that molecular sieve 4A is a poorer dehydrating agent than the conventionally used triethyl orthoformate or 2,2-dimethoxypropane[15]. Nevertheless, the use of the latter compounds during attempts at the syntheses of N--QxO 3d metal complexes does not lead to the precipitation of solid compounds, apparently owing to the decomposition of the complexes formed by the ethanol or methanol liberated by hydrolysis of triethyl orthoformate [24] or 22dimethoxypropane[25], respectively. The utilization of

3d metalperchloratecomplexeswith quinoxaline 1-oxide

587

Table 3. Far-IR spectra of N-QxO-metalperchloratecomplexes(525-33cm-' region) Compound N-QxO=L Cr(CIO,)3L4"6H20 Mn(CIOO~L~.4H20 Fe(CIO4)2L4'8H20 Fe(CIO4)3L3"H20 Co(CIO4)2L'3H20 Ni(CIO,)2L'8H20 Cu(CIO4)2L'2H20 Cu(CIO,)2I-~'3H20 Zn(CIO4)2L3"3H20

Far-IR maxima,cm-~ 503m, 491s, 467m, 426s, 349w, 317s, 261m, 188m, 164m, 159m 510w, 496w, 461w, 428w, 423w, 389w, b, 324w, 322w, 275w, 194m, 148w, 67vw 509m, 491m, 464w, 428m, 332m, 325m, b, 321m, 297w, 279m, 222m, sh, 193s, 188s, 143w, 122w, 106w, 63vw 516w, 510w, 495m, 465w, b, 426w, 377m, 366w, b, 328m, 325m, 325m, 279w, 194w, b, 63vw 510w, 496m, 463w, b, 428m, 329w, sh, 323m, 278m, 195m, b, 152m, sh, 68w 511m, 496m, 463w, 424w, 382m, sh, 367m, b, 320w, 278w, 194m, b, 68vw 512w, 495w, 480w, 465w, b, 424w, 393w, 371w, b, 324w, b, 276w, 194m, b, 70w 516m, 494m, 453w, 446w, sh, 396m, b, 319m, 314m, 278w, 261w, 194m, 94w, b, 67w, b 520w, 511w, 505w, 490m, 466w, 450w, 442w, 427w, 405m, 394m, sh, 380w, 372w, 331m, 320m, 308w, 280w, 221m, 208m, 178w, 88w, 66w 516w, 511w, 495m, 465w, 426m, 368w, 358w, 329w, 320w, 285w, 280w, 203w, 194w, b, 62w

Abbreviations: s, strong; m, medium; w, weak; b, broad; v, very; sh, shoulder. Table 4. Electronicspectra (Nujolmull)and magneticproperties(297°K)of N--QxO-metalperchloratecomplexes Compound

a .... nm

N-QxO=L Cr(CIO4)~L-6H20

238vs, 252sh, 325s, 332s, 340sh, 348s 236vs, 253sh, 325sh, 331s, 340sh, 348s, 437s, sh, 480s, sh, 545m-s, sh, 578m-s, 622m, 825w-m, b, 860w-m, b 239s, 253sh, 325sh, 331m, 339sh, 348m 238vs, 252sh, 325sh, 332s, 340s, 340sh, 348s, 480m-s, sh, 840m, sh, 955m, 1200m-w, b, 1340m-w, b, sh 240s, 252sh, 325sh, 331s, 340sh, 349s, 547w 239vs, 252sh, 324sh, 332s, 340sh, 348s, 440m-s, 460m-s, b, 480m-s, sh, 525m, sh, 610w, b, 800w, b, 930w, b, ll00w, vb 239vs, 253sh, 280sh, 325sh, 332s, 340sh, 347s, 375s, sh, 475m, b, 540m, b, 1060w, vvb 239vs, 325s, 330s, 339sh, 349s, 483s, sh, 682m-s, sh, 695m-s, b, 780m, sh, 840m, sh, 1155w, b, 1380w, b 239vs, 253sh, 331s, 340m, 348s, 430s, sh, 470s, sh, 624m-s, 647m-s, 675m-s, 690m-s, 710m, sh, 790m-w, 1085w, l190w, 140(O, b 240vs, 252sh, 325sh, 332s, 340sh, 348s

Mn(CIO4)2L~.4H20

Fe(C104)2Lc8H20 F¢(CIO4)3L3'H20 Co(CIO4)2L,'3H20 Ni(C104)2L-SH20 Cu(C10,)2L,'2H:O Cu(CIO~)2L2"3H20 Zn(CIO,)~L3'3H~O

10"~W, cgsu

~ t~B

--

--

5303 13,147

3.53 5.60

11,733 2838 8397

5.3l 2.61 4.49

3255

2.79

415

0.99

1330 1.78 Diamagnetic

Abbreviations:s, strong; m, medium; w, weak; b, broad; v, very; sh, shoulder. molecular sieve 4A, at least prevents the precipitation of than 1325 cm-l. This demonstrates the presence of both heavily hydrated products, as reported elsewhere[14]. O- and N-bonded N-QxO in these complexes. ExaminaIR evidence. As previously discussed, N-QxO exhibits tion of the At + B~(vcc + VcN)IR region [27] (four bands at IR absorptions attributable to vN-o in two regions of the 1571-1450 cm-l in free N--QxO) leads to similar concluspectrum, namely at 1380-1364 and 1325- sions as above, regarding the bonding site or sites of the 1319 cm-t [8, 15,20]. During the characterization of N- ligand. Thus, the Mn(II), Cu(II) and Zn(II) complexes QxO-3d metal chloride complexes, it became apparent show larger shifts as well as splittings of these bands (five that the 1325 cm -l band is considerably more sensitive to to nine maxima at 1591-1437cm-1), indicative of the metal complex formation, (and has primarily vN-o presence of N-bonded N-QxO [5]. Whereas, the rest of character) than the doublet at 1370, 1364 cm-1 [15]. This the complexes show only small shifts and no splittings of was further confirmed during the present work (Table 2). these bands; this is suggestive of exclusive O-bonding of On the basis of the shifts of the 1325 cm-~ absorption in the ligand. The 8N-o mode in N-QxO is probably the spectra of the new metal complexes, N-QxO appears associated with the 825 and 810cm -t bands[15]. In the to be exclusively O-bonded in the Cr(III), Fe(II), Fe(III), spectra of the metal complexes, the absorptions at Co(II) and Ni(II) compounds, as suggested by negative 820-813 cm-L are due to 8N-o,while those at 855-840 cm-t frequency shifts of this band [2-5, 15, 26]. The Cr(III) and are associated with the vibration XIX of Fe(III) complexes show also splittings of the vN-o band, quinoxaline[27, 28], probably overlapping with a second with all components appearing below 1325 cm-L In the 8N-o band. case of the Mn(II) complex, in addition to a negative vN-o The new complexes are also characterized by the frequency shift (1300 cm-~), the relatively broad character presence of two additional potential iigands (perchlorato of the band at 1365 cm -~ might be taken as suggestive of and aquo). Although N--QxO shows a rich spectrum in the the presence of a second component of the vN-o mode regions of the four fundamental vibrational modes of the (positive frequency shift), overlapping with the ligand CIO4 group[29], it is generally possible to distinguish band in this region. If this is indeed so, the Mn(I1) between exclusively ionic or both coordinated and ionic complex would involve both O- and N-bonded ligand perchlorate in the spectra of the complexes. Thus, the groups[2-5]. The two Cu(II) complexes and the Zn(II) Cr(III), Mn(II), Fe(III) and Cu(II) compounds show compound exhibit clearly split vN-o bands, the compo- splittings of the v4(CIO4) mode (650-599cm-1)[29-33] nents of which lie at both higher and lower frequencies (Table 2). The rest of the new complexes exhibit single v4

588

D. E. CHASAN et al.

bands at 625--620cm-t. In the v3(C104) region, N--QxO shows the following bands (cm-~): 1213w, 1168w, 1129w, ll01w, 1049w, 1012w. Transition metal complex formation results in the intensification, small shifting and occasional splitting of these bands; thus, the IR spectra of 3d metal chloride complexes with N-QxO show the following absorptions in this region (cm-l): 1219-1206m (one or two bands), l167-1161m-w, l145-1131m-s, 1118-1104m (one or two bands), 1068-1042m or w (with an additional weak band at 1075 cm-1 in Zn(N--QxO)CI2), 1023-1010w[15]. From these data it becomes obvious that it would be rather difficult to detect any v3 splittings. The v3 mode of ionic (Ta) perchlorate is present in the spectra of all new complexes at 1105-1095 cm-1. In addition, the Cr(III), Mn(II), Fe(III) and Cu(II) complexes, which exhibit a split v4 mode, show five or six bands at 1200-1000 cm-t, as compared to only three or four for the rest of the new complexes. Hence, the v3 evidence seems to also favor the presence of both ionic and coordinated perchlorate in the former complexes[29-33]; tentative assignments for the components of the split v3 mode in the spectra of these complexes are given in Table 2. In the v1(CIO4) region, weak to medium absorption at 933914 cm-~ is observed in all the spectra obtained; nevertheless, IR-activation of ~ might be caused either by the presence of coordinated perchlorate[29--33] or by site symmetry lowering of ionic C104- in the crystal lattice [34]. Finally, it is not possible to reach conclusions regarding the presence or absence of IR-active v2(C104)(500--450 cm-~ region), in view of the presence of medium to strong ligand absorption in this region (Table 3). The water present in the complexes may be of two types, i.e. coordinated or lattice[2-4, 15]. The IR evidence favors the presence of coordinated aquo ligands in the Cr(III), Fe(II), Fe(III), Co(II), Ni(II), Zn(II) and 2:1 Cu(II) complexes, which exhibit a medium intensity Vo. band at 3500-3380 cm-t [35]. On the other hand, the new complexes show, with some exceptions (Fe(III), Zn(II)), a weaker very broad absorption at 3650-3200cm -', indicative of the presence of several VoH maxima, and attributable to lattice water[36]. Metal-ligand bands in the lower frequency IR-region (Table 3) were tentatively assigned, on the basis of previous work with N--QxO and N-pyzO [2-4, 15], as well as far-IR studies of aromatic diazine[37, 38], aromatic amine N-oxide[39-41], perchlorato[42] and aquo[43] transition metal complexes, as follows (cm-~): vM-o (aquo): M = Cr3÷, Fe a÷ 496; Fe 2÷ 377; Co2* 382; Niz÷ 393; Cu 2÷(2:1 complex) 405,394; Zn2÷ 388. vu-o (perchlorato): M = C r 3+ 324, 322; Mn2. 297; Fe 3+ 329, 323; Cu2÷: 2:1 complex 331, 308; 4:1 complex 314. vM, (N-QxO): M = Cr3÷423,389; Mn2÷ 332; Fe 2+325; Fe 3÷428; Co2÷367; Ni2+ 371; Cu2+: 2:1 380, 372; 4:1 396, 319; Zn 2÷329. vu_~: M = Mn 2÷ 222; Cu2÷ 2:1 221,208, 4:1 194; Zn2÷ 203. The various vM_o band assignments are suggestive of hexacoordinated configurations for the central metal ions; the ~M, (N-QxO) assignments, although at somewhat higher wavenumbers than those in hexacoordinated pyridine N-oxide complexes with these metal ions [39], are within the range of values reported for analogous 4-substituted quinoline N-oxide metal complexes [41] and in agreement with the Irving-Williams series for the M(II) compounds, as expected[39]. The location of the VM-N modes is suggestive of exclusively terminally N-bonded N-QxO in the Mn(II), Cu(II) and Zn(II) complexes[38]. The relatively wide vc~-o (N-QxO) splitting in the 4:1 complex

may be attributed to the presence of both terminal and briding O-bonded N--QxO[44] (vide in[ra). As discussed elsewhere[15], a number of metal-sensitive ligand bands are observed at 317, 261 and at 164,159 cm-t; these bands are most probably due to the/3s-o and ys-o modes of the ligand [45], respectively. No attempt is made at assigning these ligand bands in the spectra of the complexes, as they overlap with several metal-ligand modes (such as 8o-M,, 80-M-N, etc.)[39]. Finally, the weak absorption at 700 60cm -l is due to translatory lattice modes of the perchlorate ion[39, 46]. Electronic spectra and magnetic moments. The magnetic moments of the Cr(III), Mn(II), Fe(II), Co(II), Ni(II) and the 2:1 Cu(II) complexes (Table 4) are within the range of values corresponding to high-spin compounds of these metal ions[47]. In some ~ s e s (Cr3+, Mn 2÷, Co2÷, Ni2÷), the txo~values are somewhat low for magnetically normal octahedral complexes. Nevertheless, low symmetry hexacoordinated Co(II) and Cr(III) complexes with amine N-oxides, reportedly exhibit low magnetic moments relative to those corresponding to purely octahedral compounds of these cations [48], whereas several magnetically normal, high-spin, monomeric Cr(III), Mn(II) and Ni(II) complexes have been found to show/*on values in the same range as those shown in Table 4[47-49]. The Fe(III) and 4:1 Cu(II) complexes are magnetically subnormal. In the case of Fe(III), the presence of spin-free (S=5/2)-spin-paired ( S = 1/2) equilibria (rAt-2T2 crossover situation) appears to be a quite common phenomenon for aromatic amine N-oxide complexes[50, 51]. The same type of magnetic behavior was observed for the FeC13-N-QxO complex[15] and it is considered as most probable that the new ferric complex (/zoo= 2.61 I~B) also involves spin-state equilibria. The 4:1 Cu(II) complex (ge~ = 0.99t~B) shows a subnormal moment, which is presumably due to the presence of O\ / C u ( ~/Cu bridges, as is commonly the case with bi- or \ / O poly-nuclear aromatic amine N-oxide-bridged cupric complexes[26,52,53]. In these complexes, spin-spin coupling occurs by a magnetic superexchange mechanism, operating through the orbitals of the bridging oxygen atoms[26, 52, 53]. In contrast, bi- or polynuclear Cu(II) complexes, involving bidentate (N,N- or N,O-bonded) bridging pyrazine[37], quinoxaline[54] or N-pyzO[3] ligands, exhibit usually normal room temperature t~on values (above 1.70/zB). The diazine complexes of this type were found to show substantial t~o~decreases at low temperatures (below 100°K.) and an antiferromagnetic behavior[55]. It follows from the above discussion that the magnetic evidence favors an oxygen-bridged structure for the new 4:1 Cu2+ complex. N-QxO is characterized by a rich spectrum in the 200-350nm region ( ~ r ~ r * and no~r* transitions) [22, 23,561. As was also the case with the corresponding metal chloride complexes[15], the electronic spectra of the new complexes are characterized by small shifts and splittings of the ligand bands and intense metal-to-ligand charge-transfer bands, originating in the UV and trailing off into the visible. Metal-to-ligand charge-transfer bands are common in aromatic diazine [57] and aromatic amine N-oxide [58, 59], including N-pyzO [2-4], complexes with 3d metal ions. The (d-d) transition spectra of the new complexes are generally characteristic of low symmetry hexacoordinated structures, as suggested by splittings of the (d-d) bands, which appear as single absorptions in the

3d metalperchloratecomplexeswith quinoxaline1-oxide spectra of purely Oh 3d metal complexes[48, 54, 60]. viz. (band maxima in rim): Cr(III) complex: ~A2s(F) ~ 4T~ (F) 437, 480; --,4T2n(F) 545, 578, 622; Fe(II) complex: 5T2g--, 5E~ 840, 955, 1200, 1340; Co(II) complex: 4T,g(F)~ 4T~g(P), 4A2g(F) 440, 460, 480, 525; ~4T2~(F) 930, 1100; Ni(II) complex: 3A2~(F)--,3TIg(P) 375 (overlapping with charge-transfer band); --,3Try(F) 475, 540; ~3T2g(F) 1060. In the spectra of the two Cu(II) complexes, the 2Es--,2T2~ transition is split into several maxima at 620-1400 rim. The (d-d) bands of the Mn(II) and Fe(III) complexes are apparently completely masked by the ligand and charge-transfer absorptions. N-QxO can be expected to be a stronger O-ligand than N-pyzO, just as quinoline N-oxide is a somewhat stronger ligand than pyridine N-oxide[26,41,61]; whereas, when functioning as a N-ligand, N-QxO would be a somewhat weaker ligand than N-pyzO, as is the case with the parent bases [57, 62]. The new complexes are generally characterized by the presence of O-bonded N-QxO; an approximate Dq value for the Ni(II) complex is 943 cm -1, while the corresponding N-pyzO complex exhibits a D~ of about 930 cm -t [2]. Although this tends to confirm the above statement, no conclusions can be drawn from such

589

Co; x = 6 for Fe and Ni), as suggested by the overall evidence. However, the rest of the new complexes appear to contain both O- and N-bonded N--QxO. The Mn(II) complex can be tentatively formulated as [Mn(ONCsI-IrN)n (NCsHrNO)5-, ((OC103)](CIO4)'4H20 (n =integer<5) and the Zn(II) compound as [Zn(ONCsH6N),, (NCsHrNO)3-,, (OH2)3](C104)2 (m = integer < 3). The 2:1 Cu(II) complex might involve a bidentate (C2o symmetry) instead of a unidentate (C3o symmetry) perchlorato ligand. In fact, the ~3(C104) mode in this compound seems to be split into four components (three for bidentate -O2CIO2 and one for ionic perchlorate[29-33]), in contrast to the other new complexes, which involve C104 coordination (Table 2). Hence, [Cu(ONCsHrN)(NCsHrNO)(OH2)z(O2CIO2)](C104).H20 is considered as a likely structure for this compound. Finally, the magnetically subnormal 4:1 Cu(II) complex is probably the only bi- or poly-nuclear compound of the series, characterized by c u / O \ c u

bridges. Structure

\o / (I) for this compound (y =integer<3) is the most compatible with the available evidence.

0 ~ [(NCsH~NO), (O'NCsHrN)3_y(O,C10)Cu f~o/CU(OC103)(NCsH, NO)3_, (ONCsHrN), ](C104)2-4H 20

(I)

I

comparisons, since N-pyzO-3d metal perchlorate complexes involve either both terminal O-bonded and bridging bidentate ligand groups (Cr3÷, Co2+, Ni2÷) or exclusively N-bonded N-pyzO(Cu2+)[2]. Regarding N-bonded NQxO and N-pyzO, a similar tentative comparison can be made from the spectra of their NiC12complexes [3, 15], for which approximate Dq values of 862 and 873cm -1, respectively, are calculated. These values are again in agreement with the trends predicted above. Formulation of the new complexes. As discussed elsewhere[15], when N-pyzO or N-QxO function as unidentate ligands, there seems to be no definite preference for O- or N-bonding, and the bonding site is determined by combination of electronic and steric effects (the former favoring N-[63] and the latter 0-[64] bonding), as well as the nature of the additional potential ligands, competing for the first coordination sphere of the metal ion. In the case under study, the coordination of N--QxO through oxygen seems to be generally favored in the presence of water molecules and perchlorate anions. An environment comprising these potential ligands apparently introduces more severe hindrance to the coordination of N-QxO through nitrogen, relative to the environment of chloride ions and water, previously studied[15]. Thus, the Cr(III), Fe(II), Fe(III), Co(II) and Ni(II) perchlorate complexes involve exclusively Obonded N--QxO, and are, most probably, monomeric of the types [Cr(ONCsHrN),(OH2)(OC103)](CIO,)2.5H20, [Fe(ONCsH6N)3(OH2)(OC103)2](CIO4), and [M(ONCsHrN)4(OH2)2](C104)2"xH20 (M = Fe, Co, Ni; x = 1 for

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