Infrared sprctea (4000-60 cm−) of the antimony(III) and bismuth(III) trihalide complexes with piperidine and piperidine

Journal

of Molecular

QElsevier Scientific

Structure, 30 (1976) Publishing Company,

85-94 Amsterdam

-

Printed in

The Netherlands

INFRARED SPECTRA (4000-60 cm-’ ) OF THE ANTIMONY(II1) AND BISMUTH(II1) TRIHALIDE COMPLEXES WITH PIPERIDINE AND PIPERAZINE

GIUSEPPE

MARCOTRIGIANO

Cat tedra di Chinzica, LEDI MENABUE

Istituto

di Chimica

(Received

Facolth and GIAN

Generale

S February

di MedicinaCARLO

Vctcrinaria,

University

of Bari, 70126

Bari (Italy)

PELLACANI

ed Inorgarzica.

University

of hlodena,

41100

Modena

(Italy)

1975)

ABSTRACT Antimony(Ii1) and bismuth(II1) halides react with piperidine (pipd) and piperazine (pipz) to form compounds of the types MX, .3L and MX, - L. the product depending upon the esperimental conditions and the amount of ligand used. The IR spectra (4000-60 cm-‘) of these compounds, which are insoluble in the common solvents, have been measured and structural considerations are presented for the solid state species. In the MX i - 3pipz complexes piperazine seems to act as chelated ligand and in the MX, - pipz as bridging ligand.

INTRODUCTION

Piperidine (pipd) and piperazine (pipz) are of great importance for, not only are they of interest as biologically active materials, but also their ring occurs as a constituent in many complex organic compounds which are of practical use. These secondary heterocyclic amines can exist in at least two conformations of the “boat-chair” type, and the piperazine, containing two donor nitrogen atoms, may act as bidentate ligand, forming both “rings” and “bridged” compounds. Many transition piperidino- and piperazino-metal complexes [l-11] have already been synthesized and investigated. All of these studies, however, have been confined to the transition metal complexes and only a few deal with other types of complexes, such as the complexes of boron trichloride with piperidine [12], the piperazinobisdiborane [13] and the complexes of I2 and IBr with piperidine and piperazine [ 141. The antimony(II1) and bismuth(III) halide adducts, which are the subject of the present work, have not yet been reported on. An aim of the investigation is to determine the mode of coordination of

86

the piperazine molecule by comparing its spectroscopic behaviour on coordination to group VB trihalides with that of the piperidine molecule,

ahout the mode of coordination

of which there can be no doubt.

EXPERIMENTAL

Preparation

of the complexes

All MX3 - L complexes were prepared by adding the ligand solut ion to the metal halide solution, with a metal to ligand molar ratio of l:l, using as solvent, dichloromethane for MC13 - pipz (M=Sb, Bi) and SbX3 - pipd (X=Cl, Br), benzene for SbXJ - pipz (X=Br, I) and BiBrJ - pipd, dichloromethane and acetone for Bi13 - L (L=pipd, pipz) and BiC13 - pipd, dichloromethane and acetone for BiBr3 and dichloromethane and ethyl ether for pipd in the preparation of BiBr, - pipd. All MX3 - 3L complexes were prepared by adding the metal halide solution to the ligand solution, with a metal to ligand molar ratio of 1:5, using as solvent, dichloromethane for MC13 - 3pipz (M=Sb, Bi) and SbX3 - 3pipd

(X=Cl, Br), benzene for SbX3 - Spipz (X=Br, I) and BiBr, - Spipz, dichloromethane+acetone for Bi13- 3pipz and dichloromethane and acetone (in which the metal salt was dissolved) and dichloromethane and ethyl ether (in which the ligand was dissolved) for the preparation of Sb13 - 3pipd and BiXs - 3pipd (X=Cl, Br). In all cases the compounds precipitated instantaneously and were washed with ethyl ether and dried in vacua at room temperature. Analyses Bismuth was determined by complexometric titration with EDTA (ethylenediamenetetraacetic acid), hydrogen and carbon by the standard combustion method and the halides directly on the complexes, without disgregation, by the Volhard method. Physical

measurements

IR spectra were recorded with a Perkin-Elmer 521 spectrophotometer in the solids in KBr pellets (4000-250 cm-‘) and in Nujol mulls on polythene (600-250 cm-‘) and with Perkin-Elmer FIS3 spectrophotometer in Nujol mulls on polythene (400-60 cm-‘). RESULTS

AND

DISCUSSION

The analytical data and melting points are available from BLL*. *Data deposited T :I-.-..-. T ,....3:,r

Elemen-

as Supplementary Publication No. 26009 (2 pages) with the British lx..:,:,,. ,mr T \ ~-,4.,, c!-.. ur-Lx..,.-L.. v--1.-l-:-T c-n.3 vmr\ _L n-L_:-

87

tal analysis of the compounds

used was found to be within experimental

error. All the prepared compounds are new except SbC13- pipd [ 151 and SbCl, - 3pipd [16], the preparations of which are known. All the complexes are stable in air at room temperature and are non-hygroscopic. Attempts to determine molar conductivities and molecular weights were frustrated as they are very sparingly soluble in alI the solvents. The SbX3 - 3L and all the bismuth--halide complexes hydrolyze in water, methanol, ethanol or N,N’dimethylformamide. Structural information is therefore derived from the IR spectra examined on the solids. The absence of IR absorption over the range 4000-3200 cm-’ excludes the presence of water or hydroxyl groups. In the spectra of the pipd and pipz compounds, the nature of the central atom, Sb or Bi, does not alter greatly the position of the various bands, while some spectral differences are observed when the MX, - L complexes are compared with the MX3 - 3L complexes. Piperidino complexes In Fig. 1 we have reported the IR absorption spectra of MX,

- 3pipd (M=Sb

and Bi; X=Cl, Br and I) (full line) and MX, - pipd (M=Sb and Bi; X=Ci, Br and I) (dotted line). The IR spectra of MX3 - 3pipd complexes are similar to one another, the only difference being the strong band at 725-740 cm-‘, which appears only in the antimony (III) complexes, while there are some spectral differences with MX3 - pipd complexes in the region in question. These differences are very marked in the 3000-1600 cm-’ region, where in the case of &is-piperidino compounds, some sharp bands appear which are not observed in the spectra of mono-piperidino compounds. In the 1600-600 cm-’ region the spectral differences result in the shift or intensity of some bands. It is possible that the slightly more complex nature of the spectra of the tris-pipd

” I

I

, I,

I

1500

I

I,

I

I, 1000

.

I

cm-l

I,

I,, 500

88

complexes is due either to a combination of ligand coupling and crystal symmetry effects or to the formation of isomers involving axial and equatorial positions of the hydrogen atoms and metal ions about the nitrogen atoms [Z, 17,181. The effects of complexation on the principal bands of piperidine are similar in aI1 the compounds. The frequencies of the NH stretching and NH deformation bands in piperidine [12,19,20] (Table 1) are shifted to lower frequencies in the tris- and mono-pipd complexes, indicating that the nonbonding pairs of electrons on the nitrogen are involved in donor-acceptor interaction with the metal ions. The shift of the NH stretching vibration, similar to that observed in the boron trichloride-piperidino complex [12], is greater than that observed when the piperidine coordinates to Pt”, Pd” and Rhl [ 121, in accordance with the relative electron-acceptor strength of the metals. Also, the shifts of the ring vibrations of piperidine upon complexation agree with those observed in boron trichloride-piperidino complex [12] (Table 1). The NH deformation [12,19, 201 apparently moves from 1500 to 1552-86 and from 822 to 852-8 cm-’ ; these and the NH stretching vibration are the largest frequency shifts of any of the piperidine modes on complex formation. Low-frequency IR (600-60 cm-‘) spectra of piperidino complexes are reported in Table 2. The IR spectra of MX3 - 3pipd complexes are very similar, suggesting that these compounds are isomorphous. In the far IR spectra they show two clearly distinguished bands in the region 320-251 cm-‘, for which no abrupt frequency shift is noted when comparing chloride, bromide and iodide complexes and which can be assigned to the metalligand (M-N) stretching vibrations. In addition, a strong broad band, the position of which is halogen dependent, is observed in the 170-120 cm-’

TABLE

1

More relevant IR bands of piperidino

pipda SbCI, - pipd SbBr, - pipd SbI, - pipd SbCI, - 3pipd SbBr, - 3pipd SbI, - 3pipd BiCI, - pipd BiBr, - pipd BiCI, - 3pipd BiBr, - 3pipd aRefs.

complexes

(cm-‘)

I! (NH)

5 (NH)

Ring vibrations

3210 3150sh 3124m 3150m 3178~ 3157m 3148m 3135m 3150ms 3176~ 3150w

1500 157ovs 1558~s 1552vs 1586~s 1575vs 157ovs 1568~s 1555vs 1582~s 1574vs

1117 1152~ 1153w 1148m 1158m 1155m 1151m 1150wb 1150vw 1558m 1155m

19 and 20.

1080 1045sh 104ow 1045w 1051w 1048~ 1048~ 1040sh 1038~ 105ow 1045w

6 (NH) 1035 1018ms 1015ms 1008m 1026ms 1023ms 1020m 1016ms 1005m 1027ms 1022m.s

942 938ms 935ms 935m 943m 942m 940m 936m 932ms 944m 940m

860 908ms 906ms 903m 938m 928m 927m 908ms 900m 938m 927m.s

836 856ms 852m 854ms 856m 853m 853m 854m 850m 858m 850m

l

SbCl, - pipd SbBr, 0pipd Sbf, spipd BiCI, 0pipd BiBr, apipd SbCI, s3pipd SbBr, v3pipd SbI, r dpipd BiCI, * 3pipd BiBr, B3pipd SbCl, * pipz SbBr, * pipz SbI, epipz BiCl i pipz BiBr, * pipz BiI, 5pipz

305s 288~s 261s 204m 178sb 168sh 150~ 154m 147vs 140~11 247m 226m 162sb 162ms 118m 170vsb 145vs 127s 170vsb 143s 250mw 180vs.b 232m 180sh 144~s 144m 130vsb 234m 164vsb 150sh 136~s 1lOvsb

v(M-X)

290sb 290sb 283~s 276~s 299m 320sh 305sh 304m 302m 280~ 325sb 312sh 278~

v( M-N)

278mb 250wb

251s 252m 274s 283s 276~s 280~ 292sh 266sh

cm-‘)

545s 524sh 429s 385m 15&b 133m 540s 517mb 424s 310sh 249m 120wb 543s 474mb 425s 374mb 238~ 95m 552s 493vs 430s 392m 544s 427s 377m 104m 561~s 439vs 386vsb 347~ 103~s 67m 553~s 435~s 384vsb 346~ 119m 85m 78m 550m 429m 385vsb 346~ 250~ 158m 86w 60m 559vs 440~s 395m 103s 553~s 525sh 435m 394w 370~ 258sh 1118m 80sb 587s 578sh 560s 464~ 575~s 428mb 573ms 430~ 380wb 576~s 534mb 458~ 590ms 530mb 425ms 560~ 462,442mb

Other far IR bands

Far-infrared spectra of MX, - pipd, MX, * 3pipd and MX, - pgu complexes (600-60

TABLE 2

90

region. The range and the broadness of these (M-X) bands from individual complexes, together with the insolubility of the complexes, may suggest that these compounds are polymer with bridging halogen [ 211, but recently it was suggested that compounds formally containing a lone pair of electrons in the valence shell might exhibit abnormally broad bands in the IR spectrum in the metal-halogen stretching region [22, 231. Only two bands are IR active in MXh3-

(M=Se Iv, Teiv, Pb’v, BiIII, Sb III, In”’ octahedral environment (point group 0,)

and Tl”‘)

compounds

with regular [24,25] and of these two bands only the fundamental vj (t,,) is clearly recognized in MXh3- compounds and found at 178 [23] and 172 [26] cm-’ in SbClb3-, at 141 cm-’ in SbBr, 3- [26], at 121 cm-’ in SbI, 3- [26], at 175 [23] and 171 1251 cm- ’ in BiC& 3- and at 126 cm-’ in BiBrb 3- [25], while for the deformation band 21~(t,, ) there are no certain assignments. If the IR fundamentals of MX6 3- are compared with the M-X bands found for the tris-piperidino complexes, we may conclude that the MX, 3species are also present in these complexes and tentatively propose for them ionic configurations of the types ML6 3+- MX6 3- - The easy hydrolysis of these compounds may support this hypothesis. In the far IR spectra of SbX, -pipd complexes, bands assignable to the metal ligand vibrations are not clearly distinguished, while a group of three bands, the positions of which are halogen dependent, can be assigned to M-X vibrations. On the basis of the number and position of the M-X bands, a pyramidal arrangement with C, symmetry can be assigned to these complexes [ 271. The far IR spectra of BiXJ - pipd complexes show a broad band around 290 cm-‘, which can be assigned to a metal-ligand (M-N) stretching vibration, and some bands which are halogen-dependent at 247, 226 and 162 cni’ in chloride and at 162 and 118 cm-’ in bromide. The low frequency values of the M-X bands suggest a polymeric six-coordinate configuration with bridging halogen for these compounds.

Piperazino

complexes

The spectra between 3000-400 cm-’ of the piperazino complexes are fairly complicated and cannot as yet be assigned with any certainty. The observed NH stretching frequencies for solid complexes are more greatly reduced in frequency, with respect to free piperazine at 3350 cm-’ [18], in the mono-piperazino complexes (Table 3) than in the tris-piperazino complexes (Table 4), which show more than one band assignable to v(NH) stretching. Hendra and Powell have studied the IR spectra of pipz and its metal complexes [ 2] and have shown that a 1:2 complex with C2H4 - PtC12 contains a pipz molecule in a “chair” configuration, bridging two acceptor molecules. The same authors have also reported the IR spectra for 1 :l complexes of pipz with HgClz and CdC12 [2]. They are more complicated

91 TABLE

3

infrared spectra for 1: 1 complexes

of piperazine

(cm-’

pipz - HgCI,=

pipz - I:b

MX,

3123s

3274 3050

31 ZO-3070sh 3020-3000m 2960-30mb 2760-40m 2735-l 5sh 1620-OOsh 1585-60~s 1450-4ovs 1420-oow 1380-7Oms 1345-40sh 13 15-OOmb 121ow 1 ZOO-1 190m 1142-30m

2932w 2830~ 167%~ 1447m 1418ms 1377m 1347w 1314w 1256~ 1174vw 113ovw 1llOm 1072~s 104ovw 1017m 1OOOm 966vw 890w 879ms 858~s 690wm 673m 656vw aRef.

2; bref. 14

1434m 1429m 1380m 1351m 1312m 1212m 1181m 1128s 1109w 1081s 1058m 1029s

)

- pipz

llOO-1075ms 1057-4oms lOOO-978m

922m 89Ow 866s 850~s 720~

935-25m

626s

650sb

867-45ms 720-700sh

The bands in the 3050-2000

cm-’

region are not reported.

than those of pipz-2(C2 H, - PtC12 ). They have proposed a polymer chain structure for these HgClz and CdClz complexes. The IR spectra of MX3 -pipz complexes in many respects resemble that of the HgClz complex (Table 3), so it seems probable that the MX3 -pipz also have a polymer chain structure. For the sake of comparison, Table 3 also reports the IR spectrum of the pipz’. I2 complex, for which a polymer chain structure was conciuded [ 141. The far IR spectra of MX3 - pipd complexes (Table 2) are very poor, but the bands found around 250 cm-’ may be assigned to M-N stretching bands, while the bands, which are halogen-dependent, as reported in Table 2, suggest the presence of bridging halogen. We may therefore conclude, particularly in view of the striking similarity between their IR spectra, that these compounds are isomorphous and presumably isostructural with a polymeric chain structure with piperazine molecules and halogen atoms bridging metal ions. The IR spectra of MX3 - 3pipz complexes are reported in Table 4. They

92 TABLE

4

Infrared spectra of tris-piperazino

complexes

(cm-‘)

SbCI, - 3pipz

SbBr, - 3pipz

SbI, - 3pipz

BiCl, .3pipz

BiBr, - 3pipz

BIT, - 3pipz

3230~s

3170vs

3220~s

3212~s 3178m

3177vs

3218~s

309ovs 2970s 2935sh 2918s 2855s 2740m 27 1 Osh 2650m 2570wb 2500wb 1580~s

2978vs

309ovs 2960w 2918w 2850~

2965vsb

1524~ 1458 143gvs

1508~

3196m 3105m 2975sh 2925mb 2875~ 2795w 2720~ 2620~

1645~s 1598w 1535w 1482~ 1465~

2855~ 2800~ 2705~ 2600wb

2925wb 2855~~ 2770wb 2705m 2600wb

1620~s

1624~s

1458~s

1463 1443vs

1415vw 1382~s 1342vs 1320~ 1237m 1215s 1198s 1139vs 1lOOv.s 1088m 107Om 1060~ 1032~ 1003ms 968m.s 920m 898m 889m 876~s 868w 839s 746vsb 621s 509s 468m 443sh 436~s

1366 1360’ 1322m 1290m

137ovs

1360m

1322s

1320ms 1300w

2720wb 2645~

1620m 157 5vs 1515w 1443 1432vs 1417sh 1370 1355mS 1318m 1290m

2845~ 2790w 2700~ 2600wb

1617~s

1458~s 1405vw 1366s 1320s 1209sh

1240sh 1221vs 1198m 1166m llllvs 1083~s

1195m 1170m 1116~s 1080s 1060m

1215~ 1195m 1172m 1117vs 1079s 1065s 1049 103gm

1217~s 1192m

1052s

1038m

1012m

900m 868vs

1013sh 982vw 960 952ms 918m 874m

1109vs 1078s

1196m 1168ms 1112vs 1075s 1065m

1058~s

1042ms

1018rn.5 988vs

1020sh 982w 956m

904s 873~s

878m

1012vw 980sh 970m 946m 902sh 878m

852~

851~s

855~s

848~s

848~s

818s 730vsb 618s 526m 474vs

815111s 7 30vsb 598ms 508m 489s 454vs

818ms 710wb 6OOms 507ms 467~

813s 700vwb 612ms 534m 475vs

818ms 7oovw 593ms 508m 488ms

434ms

457m

454s

457m

982vs

93 TABLE

4 (continued)

SbCl, - 3pipz

390m.5 277sh 263sh 246m 205ms 162ms

SbBr, - 3pipz 400sh 39oms 333s 277~s 264sh 248ms

BiCI, - 3pipz

BiBr, - 3pipz

BiI, - 3pipz 424sh

388ms

400m

281m 264sh 250m

302~ 290w 240~ 205m.s 161ms

333m

186ms

104s 74rns

SbI, - 3pipz

188rn.s

147w 116s 84m 66ms

113vs

275m

302~ 282m 250~

185m

190s

144w 114vs 81m 68rns

104m 74ms

66m.s

114vs 69s

are very similar and show a greater number of bands with respect to the

spectra of 1: 1 complexes. For purposes of comparison, Fig. 2 shows the IR spectra of SbC13 3pipz (full line) and that of SbC13 pipz (dotted line). We would suggest that these differences are not due to a combination of ligand coupling and crystal symmetry or to the formation of equatorial and axial isomers as in the case of piperidino complexes, but rather to the chelated ligand, which in the tris complexes has a “boat” structure. It should be noted that if the ligands have a “boat” rather than a “chair” structure the spectra would be expected to contain more absorption peaks, owing to the increased number of IR active fundamental vibrations. The presence of two NH stretching vibrations, both at lower frequencies than the (NH) in free piperazine, seems to indicate that the two NH groups of the pipz molecule are both, but differently, involved in the metal coordination. For these complexes we may assume a six-coordinate environment around the central metal ion of three chelated piperazines. The absence of halogen-dependent bands in the l

3000

2500

l

2000

1500

1000

Fig. 2. IR spectra of SbCl, - 3pipz (full line) and SbCl, - pipz (dotted

line).

94

far-IR spectra of these complexes strongly supports this hypothesis. As free pipz shows two bands at 368 and 275 cm-’ we may tentatively assign the bands at 263-264sh and 240-250 cm-’ to M-N stretching vibrations. ACKNOWLEDGEMENTS

The authors thank Mr. A. Benassi of the C.N.R. Centre of Ozzano (Bologna) for technical assistance.

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