The use of a high resolution NMR spectrometer for recording solid state 31P spectra

Spectmchimics Acta,Vol. 27A,pp. 1381to 138% Pergamonm,

The use

1971.PrintedIn NorthernIrelsnd

of a high resolution NMR spectrometer for recording solid state a1Pspectra K. B. DILLON and T. C. WADDINCITON Department of Chemistry, Uuiverslty of Durham (Received 18 August 1970)

determmatlon of slP NMR spectra of sobds usmg a high resolution NMR spectrometer and a computer of average transients is reported. It appears that chemical smfts can be measured qmte accurately by thle method and structural information about the solid oompound obtamed. Results for solid compounds wmch contam phosphorus tiectly bonded to fluorme, cblorme, bromme, oxygen, nitrogen, carbon and hydrogen are reported.

Abstract-The

Hra~ resolution NMR spectroscopy is usually limited to the study of liquids and gases, since most solid samples give rise to broad signals, due to the direct dipolar interaction of nuclear spins [l]. Some compounds have very limited solubility, however. Others may change their structure either on dissolution or with a change of solvent, so that more direct information on solid structures is desirable. Solid state NMR spectra for various nuclei may be recorded using broad line spec-

trometers which give an increased signal-to-noise ratio but correspondingly lower resolution. The precision of the chemical shift values obtained is not high [2], and there are few commercial instruments available. ANDREW et al. [3-51 have obtained well-resolved spectra from poly-crystalline solids by rotating the sample at high speed about an axis making an angle of 54”44’ with the applied magnetic field, which minimises the dipolar interactions. By this method, they showed that solid phosphorus pentachloride gives two distinct slP signals corresponding to the PCl,+ and PC&- ions [3, 41. Because of the magnet inhomogeneity, chemical shifts could only be measured to 10 ppm, even for samples with good signal-to-noise ratios [5]. We have recorded the solid state 31Pspectra of a number of compounds containing phosphorus directly bonded to various different nuclei, including phosphorus pentachloride, using a conventional high resolution instrument in conjunction with a spectrum accumulator. The chemical shifts are reproducible in all cases to f 1 ppm, and for narrower resonances to -&O-5ppm. EXPERIMENTAL

,

All chemicals purchased were of the highest available commercial grade, and were used without further purification. The phosphorus oxychloride-antimony (V) chloride adduct was prepared by mixing stoichiometric quantities of the reagents [l] [2] [3] [4] [5]

J. A. POPLE, W. G. SCHNEIDER and H. J. BIIZNSTEIN, High Resolution Nuclem Magnetic Resmame. McGraw-Htil (1969). W. WIEKER Bnd A. R. Gm, 2. i%&U9$9.8C~. Zlb,1103 (1966). E. R. ANDREW, A. BRADBURY, R. G. EADES aud G. J. JENKS, Nutwe 188, 1096 (1900). E. R. ANDREW and R. G. EADES, Discussiolu, Pam&y Sot. M, 38 (1962). E. R. ANDREW and V. T. WYNN, Proc. Roy. Sot. A. 991, 257 (1966). 1381

K.

1382

B. DILLON

and T. C.

WADDING~N

in fluorotrichloromethane under nitrogen and separating the pale yellow precipitate in the drybox. Tetrachlorophosphorus (V) hexachloroantimonate was prepared by adding a slight excess of antimony (V) chloride to a solution of phosphorus (V) chloride in dichloromethane [6]. The white precipitate was separated under nitrogen and washed with pentane to remove solvent and excess antimony pentachloride. Tetrabutylphosphonium iodide was prepared by adding 1-iodobutane (l-05 mole) to tributylphosphine (1 mole). The mixture was left for a short time at room temperature, until white crystals of the salt separated out. The solid was filtered off and washed well with pentane to remove the excess iodobutane. The compounds were finely powdered in a drybox before transfer to 8.5 mm o.d. glass tubes with neoprene bungs. NMIR spectra were recorded on a Per&in-Elmer RlO spectrometer operating at 24.29 Mc/sec, with a N&544signal averaging accessory, using stationary samples. The two resonances of phosphorus (V) chloride, the single resonance of phosphorus (V) bromide and the signal of tetrabutylphosphonium iodide could be seen in a single sweep, but spectrum accumulation was required to establish clearly the chemical shift position in the other compounds used. For most samples, both absorption and dispersion mode spectra were recorded. Good agreement was obtained between the two methods. Chemical shifts were measured relative to P,O, as external reference [7], but have been expressed relative to 85% phosphoric acid to facilitate comparison with literature data. RESULTS The chemical shifts obtained are given in Table 1, and include results for compounds with phosphorus directly bonded to fluorine, chlorine, bromine, oxygen, nitrogen, carbon and hydrogen. The values will be considered separately, and compared with the available solution and broad line solid state data. Table 1. Chemical shifts of some sohd phosphorus compounds d31P (ppm) from 85%

Compound KPF, PC& [PCl,]+[SbCl,]PBrs POCl,

-

PH,I (C,H,),PI K3P0,

[PNW,

SbC1,

*

H,PO,

+148 f 1 -88 3 (PCla), +299*7 -88.3 +104 f 1 (PBra+) -55 3 +77*5 f 1 -35 1 -120 -4.5 f 1

(P&-)

All chemlcsl shafts reproduolble to rtO.5 ppm unless stated otherwrse. (a)

Fig.

[6] [7]

Potassium hexaj&wrophoephate KPF, The compound gives a very broad 31P resonance (AY c-’ 2600 Hz) as shown in 1. The chemical shift of +148 f 1 ppm is in good agreement with literature I. R. BEATTIE and M. WEBSTER, J. Cbn. Sot. 38 (1963). A. C. CRAPE~AN,J. HOMER, D. J. MOWTHORPE ctnd R. T. JONES, Chem. Comm. 121

(1966).

The use of 8 high resolution NMR spectrometer

for recordmg sohd at&e *lP ape&s

200

150

100

1383

83’p,ppm Fig. 1. The solid “P

NMR

spectrum of KPF,.

values for the PF,- ion in solution [ELlo], and with broad line measurements on solid KPF,, which gave a value of +145 ppm [2]. The published data do not include a solution value for potassium hexafluorophosphate, for which we tid dslP = 142.5 f 0.5 ppm, J PF = 716 f 1 Hz (saturated aqueous solution). (b) Phosphorus (V) chloride, [PCl,]+[PCl,]- and tetruchZorophosphon;honium hexac7doroantimonate,[PCl,]+[SbCl& Solid phosphorus (V) chloride shows two distinct well separated peaks in a 1: 1 intensity ratio, as shown in Fig. 2a (absorption mode) and Fig. 2b (dispersion mode), with chemical shifts of -88.3 and +299*7 ppm. These are assigned to the [PCl4]+ and [PCI,]- ions respectively. ANDREW et al, using the rotating sample method, obtained values of -91 and +282 ppm for these resonances, [3-61. WIEKER and GRIMMERdetermined @P values of -92 and +289 ppm using a broad line spectrometer [2]. Our values are in better agreement with solution data on compounds containing these ions, however [ll-151. SCHMIDPETER and BRECHT determined values of -87.9 and -87.1 ppm for the PC&+ ion in [PCl]4+[SbCl,]- and [PCl,+]ClO,- respectively, dissolved in nitromethane [ll], and both LATSCHA[12] and PLUCK[U-15] report @lP values between +295 and +305 ppm for the hexachlorophosphate ion in various solvents. A big change in shift between solid and solution is not expected for six-co-ordinate phosphorus compounds, so that our solid state value for [PCl,]- appears reliable. The discrepancy with the published results may be due to the inherent imprecision of the methods used previously [2, 51. R. A. Y. JONES and A. R. [Q] J. W. E~LEY, J. FEENEY [S]

[lo] [ll] [12] [13] [14] [16] 11

KATRITZKY, Amgew. Chern. 74, 60 (1962). and L. H. SUTCLIFYFE, Hagh Reeok&m Nuclear Magnetic Resonance &mtroscopy, vol. 2. Pergmnon (1966). V. MARK, C. H. DUNGAN, M. M. CRUTCHYIELD and J. R. VANWAZER, IIITop~.8 in Boaphoru~ C?m&t~ (E&ted by M. GRAYSON and E. J. GRIFFITH), Vol. 6. Intersclence (1967). A. SCHIXIDPETERand H. BRECHT, Angew. Chem. 79,635 (1967). H. P. LATSCEA, 2. Natuvjomch. 23b, 139 (1968). E. FLUCK, 2. Anorg. A&em. Chem. 316, 181 (1962). E. FLUCK, 2. Alawg. Allgem. Chem. 315, 191 (1962). E. FLUCK, 2. Amrg. AUgem. Chem. 820, 64 (1963).

1384

K.

B. DILLON and T. C. WADDINGTON

Fig. 2. The sohd “P NMB of PCl,. (a) m absorption mode. (b) m dispersion mode.

-80

S3’p. Fig. 3. The sohd slP NMR

ppm spectrum of PCl,+SbC16-.

The I,IS~of 8 lvgh resolution NMR spectrometer for recordmg solid state 31Pspectra

1386

The 1: 1 ctdduct of phosphorus(V) chloride and antimony(V) chloride has a single s1P signal at -88.3 ppm (Fig. 3), thus confirming its formulation as a tetrachlorophoaphonium salt, [PClJ+[SbCJ]-.

Phosp~rw (V) brmiae The compound has a single, comparatively sharp slP resonance (Av ‘v 120 HZ) at, +104 f 1 ppm (Fig. 4). WIEKER and GRIMMERfound chemical shifts between (c)

83’P. wm Fig. 4. The solid slP NMR spectrum of PBr,.

+6S and +SO p.p.m. for phosphorus (V) bromide end some of its adducts [2, 161, but quote a solution value for the [pBr4’J+cation, (determined by FLUCK)of +lOl ppm [2]. We have obtained similar values for solutions of phosphorus (V) bromide in various solvents [17], and ascribe the peak in the solid spectrum to the [PBrJ+ ion, in agreement with the known crystal structure [US]. The shift is very much higher than that of the [PC&]+ ion, probably showing the greater effectiveness of bromine in diamagnetic shielding. A similar effect is observed in POBr, (6”P + 102.9 ppm) [9] and POCl, (@lP - 3 ppm [lo]. (d) P7m.spharous ozycirloride-antimony

(V) chloride adduct, POCl,-SbCl,

The spectrum consists of a, single, rather asymmetric peak at -553 aa shown in Fig. 5. The downGeld shift of approximately phosphorus oxychloride is much smaller than the shift between phosphorus (V) chloride and the PCl,+ ion. We co-ordination to antimony (V) chloride take place via the

ppm, 52 ppm with respect to difference of 167 ppm therefore conclude that oxygen atom of POCl,,

[16] W. WIEKER and A. R. GRIMMER,2. Naturforsch. 22b, 257 (1967). [17] K. B. DILLON and T. C. WADDINUTON,uupubhshed results. [18] H. M. POWELL and D. CLARK, Nature 145, 971 (1940)

1380

K. B. DILLON and T. C. WADDIN~TON

in agreement with the crystal structure [19], and that the hypothetical POCl,+ ion is not formed. The downfield shift is thus caused by the lowering of the P-O bond order and reduction of electron density a,round phosphorus. A similaz effect is observed in other complexes, and on proton&ion of phosphorus oxychloride, which is also expected to take place at the oxygen atom [17, 201. POCI, - SCCI,

d’ P. Fig. 6. The sohd SIP NMR

wm

spectrumof the POCl,, SbCl, adduct.

Pkqhmium iodide, PHJ The “P NiKR spectrum of phosphonium iodide comprises a very broad single peak at +77-5 f 1 ppm (Fig. 6). SHELDRICK recorded the solution spectrum of the phosphonium ion by dissolving phosphine in aqueous or methanolic solutions (e)

s3’P.

porn

Fig. 6. The solid slP NMR spectrum of PH,I. [lS] I. LINDQUIST and C.-I. BRANDEN, Acta Cry&. 12, 642 (1969). [20] R. C. PAUL, V. P. KAPILA and K. C. MALHOTRA,Chem. Comm. 644 (1968).

The use of a high resolution NMR spectrometer for reoordmg sohd state aP

speotra 1387

of boron trifIuoride [2 13, and measured the shift ss +217 & 1 ppm relative to phosphorus (III) oxide. This gives a value of f1046 f 1 ppm on the phosphoric acid scsle, as compared with the value of +238 ppm for phosphine [9]. Chemical shifts of phosphorus (III) compounds are expected to be very dependent on environment in both solid state and solution, so that the difference between the values for PH,+ is not surprising. tc,l-q,

-5q

-35

S3'p.

PI

-20

ppm

Fig. 7. The sohd =P NMR spectrum of (C,H,),PI.

(f) Tetra-n-butylpmsphonium iodide, (C,H&,PI The compound gives a sharp *lP resonance (AY N 40 Hz) at -351 ppm (Fig. 7), in excellent agreement with solution data on (C,H,),PBr (-34 ppm) and (C,H,),PI ( -32 ppm) [lo]. The phosphorus atom is thus less effected by change of state than in phosphonium iodide, perhaps showing the effect of the bulky1 butyl groups. (g) Tripotisizlln orthophosphute,K,POI The slP resonance of the solid salt occurs at -12 ppm, (Fig. 8) close to the solution shift of -6 ppm [9]. The small downfield shift caused by successive replacement of hydrogen by potassium in the series H,PO,, KH,PO,, K&PO,, K,PO, may thus be slightly larger in the solid state. (h) Phosphonitrilic chloride tetrumer, [PNCl& The very broad signal of this compound has a maximum at -4.6 f 1 ppm, (Fig. 9), which is close to the solution value of +7*4 ppm end upfield from phosphonitrilic chloride trimer [9]. DISCUSSION In conclusion, we have succeeded in recording the solid stake 81P spectra of cornpounds with phosphorus directly bonded to various elements. The spectra, are very [21] G. M. SHELDRICK, Tram. Fwu&y Sot. 63, 1077 (1967).

K. B. DILLON and T. C. WADDINQTON

1388

I

.,

,

53

0

-50

S3’p,

ppm

Wg. 8. The sohd 31P NMR spectrum of K,PO,.

reproducible, and the shifts are in general in good agreement with literature data and with the expected molecular structures. The method does not give satisfactory results in all cases, however. We were unable to obtain spectra from solid tetra-npropylammonium tetrabromophosphite, (C,H,),N+PBr,-, even though the compound dissolved in nitrobenzene showed the expected peaks of phosphorus (III) bromide at -229 ppm [22]; or from tetraphenylphosphonium chloride.* With the former,

S3’p.

ppm

Fig. 9. The solid 31P NMB spectrum of (PNCI,),.

this may be due to the asymmetry of the cation [22], which could make the chemical shift dependent on its orientation with respect to the applied magnetic field [23], but the reason for the failure of the latter to give signals is not clear. A further limitation on the use of the method is that for compounds with more than one * Note addedin woof. We have recently succeeded m recordmg the slP spectrum of tetrsphenylphosphonmm chloride, usmg 8 wider sweep (370 ppm). The resonance 1s very broad (Av = 4600 Hz), thus accountmg for our fadure to obtam 8 satisfactory spectrum using a 200 ppm sweep mdth. [22] K. B. DILLONand T. C. WADDINGTON, J. Chem. Sot. (D) 1317 (1969). [23] J. A. S. SMITE,pnvate communication.

The use of a resolutionNMR speotometer for recording solid state s1P spectra

1389

resonance, the sign& must be well-separated. The spectrum of hexaguanidinium tetrapolyphosphate [24], which should give two signals separated by about 13 ppm [25], was recorded, and showed indications of two peaks, but reliable shift measurements could not be made because they overlapped too much. Despite these drawbacks, the technique is of considerable potential use in determining or con6rming the structures of solid phosphorus-containing compounds. [24] 0. T. QUINBY and F. P. KRAUSE, Inorg. Sp. 5, 97 (1967). [26] K. B. DILLON and T. C. WADDINGTON, J. Chem. Sot. (A) 1146 (1970).