Tris-(isopropoxy methylphosphonato) complexes of trivalent rare-earth metal ions

Journal of the Less-Common Elsevier

Sequoia

S.A.,

Metals

Lausanne

- Printed

TRIS-(ISOPROPOXY METHYLPHOSPHONATO) TRIVALENT RARE-EARTH METAL IONS

N. M. KARAYANNIS, 1.1. M. LABES

C. M. MIKULSKI,

Department of Chemistry, (Received

September

29

in The Netherlands

J. 1’.

COMPLEXES

MINKIEWICZ,

L.

L.

OF

PYTLEWSKI

AND

Drexel Institute of Technology, Philadelphia, Pa. 191oq (U.S.A.)

~zth, 1969)

SUMMARY

Tris-(isopropoxy methylphosphonato) rare earth complexes were obtained by interaction of diisopropyl methylphosphonate with trivalent rare-earth chlorides at 5o”-~oooC. The complexes were characterized by means of infrared, magnetic and X-ray powder diffraction studies. A distorted Oh symmetry is assigned to the metal ions. Far infrared evidence indicates the presence of strong lanthanide(III)-oxygen bonds, possibly having partially covalent character. Possible structures of the new complexes, including monomeric chelates and oligomers or polymers, involving eightmembered phosphonate bridges and four-membered chelate rings, are discussed.

INTRODUCTION

Diisopropyl methylphosphonate (DIMP) reacts with trivalent metal halides at temperatures between 40 and 2ooT with precipitation of the corresponding tris-(isopropoxy methylphosphonato) metal complexes (M(IMP)a) and evolution of a mixture of isopropyl chloride, hydrogen chloride and propenei. The M(IMP)a complexes have, most probably, a polymeric structure 1. Similar complexes are formed by reaction of various neutral phosphate or phosphonate esters with trivalent transition metal halides (Ti(III), V(III), Cr(III), Fe(III))z-4. Organophosphoryl compounds have been extensively utilized as extractants for the rare-earth metalionss. Complexes of the types Ln[H(DBP)a]8 and Ln(DBP)a798 have been isolated from the interaction of dibutyl phosphate (DBP) with trivalent lanthanide salts. A polymeric structure has been suggested for the Ln(DBP)s complexesa. Moreover, a number of complexes of the general type LnLK13 (L = triphenylphosphine oxides, hexamethylphosphoramideio) have been reported recentlyS*iO. In view of the relative dearth of information on tris-(phosphate)-, (phosphonato)-or (phosphinato)-Ln(II1) complexes we have extended our studies’ to include the tris(IMP) complexes of the rare-earth elements. The present paper deals with synthetic and characterization studies of SC(IMP)a, Y(IMP)3 and Ln(IMP)s. J. Less-Common

Metals, 20 (1970) 29-36

N. M. KARAYANNIS

30

et al.

EXPERIMENTAL

Chemicals Water-free DIMP was provided by Edgewood without further purification. The purest commercially and solvents were used.

Arsenal, Maryland, available rare-earth

and used chlorides

Synthetic jvocedure

The salt (anhydrous or hydrated) was dissolved in excess DIMP and the resulting mixture heated at 5o”-~oo0C until the M(IMP)3 complex was precipitated. The Sc(II1) complex was obtained at 50°C and those of Y(II1) and the trivalent lanthanides at 7o”-~oooC. Precipitation at these temperatures occurred after 3 h. for Sc(II1) and 30 min-3 h for the other metal ions. The precipitation was immediate at higher temperatures (150”~zoo”C). The precipitates were filtered, washed thoroughly with acetone and anhydrous ether and dried over magnesium perchlorate in an evacuated desiccator. The new complexes were stable in the atmosphere and did not melt or decompose at temperatures up to 350°C. They are insoluble in all common organic solvents (e.g., ketones, alcohols, halogenated hydrocarbons, nitromethane, acetonitrile, decahydronaphthalene, piperidine), DIMP, and water, and dissolve with decomposition in mineral acids. The volatile products of the reaction were isopropyl chloride, hydrogen chloride and propene. They were collected and identified as described elsewhere’. The reproducibility of the syntheses was excellent and the yields of the M(IMP)3 complexes were almost quantitative (g5-Ioo% theoretical). Analyses were performed by Schwarzkopf Microanalytical Laboratory, Woodside, New York and are given in Table I. Qectral,

magnetic and X-ray studies

Infrared TABLE

DATA

C(%) Calc.

SC

31.59

Y

28.82

La Ce Pr Nd Sm EU Gd Tb

26.20 26.14

DY Ho Er Tm Yb LU

in Nujol mulls between

IRTRAN

z (zinc sulfide)

I

ANALYTICAL

M

spectra were obtained

26.11 25.96 25.66

25.59 25.35 25.28 25.14 25.01 24.91 24.84 24.67 24.59

ON

M(IMP)s COMPLEXES*

Metal (%)

P(%)

H(%) FOl.Wd

Calc.

Found

Calc.

Found

31.45 29.12

6.63 6.05

6.58 6.20

19.80

26.37 26.37 26.32 26.21

5.50 5.48 5.48 5.44 5.38 5.37 5.32 5.30 5.27 5.25 5.23 5.2I

5.85 5.73 5.73 5.68

20.37 18.58 16.89 16.85 16.83

5.30 5.15 5.12

16.34 16.30 16.21 16.13 16.06 16.01

5.17 5.16

5.50 5.13

15.90 15.85

25.39 25.71 25.17 25.26 24.84 24.72 25.10 24.4’ 24.92 24.49

5.52 5.59 5.32 5.33 5.28

16.73 16.54 16.50

18.49

17.02

16.73 17.02 16.62 16.50 16.45 16.74 16.56 16.45 16.44 15.84 15.86 15.85 IS.74

Calc.

9.85 17.77 25.25 25.4’ 25.52 25.96 26.77 26.98 27.66 27.87 28.35 28.62 28.91 29.II 29.61 29.85

Found 9.92 17.72 24.94 25.20 Z:48 26.89 27.06 27.36 28.14 28.62 28.29 29.11 29.34 29.74 29.80

* With the exception of the Pr (pale green), Nd (lilac) and Er (pale pink) compounds, the M(IMP)a complexes are white. Elemental analyses established that all the above complexes are chlorine-free. J. Less-Common

Metals,

20

(1970)

29-36

TRIS-(ISOPROPOXY

MET~YLPHOS~HO~ATO)

COMPLEXES

3r

windows in the dooo-7oo cm-l region, and high-density polyethylene windows in the 700-200 cm-l region, by using a Perkin-Elmer 621 spectrophotometer. Magnetic moments were obtained as described elsewhere 11. For X-ray powder diffraction patterns a North American Phillips Company Diffractometer was utilized. RESULTS AND DISCUSSION

General The magnetic moments of the Ln(IMP)3 complexes are given in Table II, and IR data are given in Table III and Fig. I and 2. The X-ray powder diffraction patterns of the ~~(I~P)~ complexes (M=Sc, Y, Ln, Al, Ga, In, Cr, etc.) are generally similar, TABLE

11

MAGNETICMOMENTSOF M(IMP)z COMPLEXESAT --M pp?l! IO6 kff (Bhfl

297’K

_~

CC?

1.835

2.11

Pr Nd Sm

5,318 5.404 874

3.59 3.60 1.46

Eu Gd

5,160 28,158

3.50 8.17

Tb =Y HO

36,246 49,450

9.35 10.83 10.86

Er Tm

49,705 39,268 22,605

Yb

6,980

TABLE

9.65 7~32 4.10

III

PO0 VIBRATIONAL PLEXES ---_-.--.._-

MODES

M vpOO(cm-l) __-.. .___ I725m, 116om-s, SC Y La Ce l?r Nd

Sm EU Gd Tb DY Ho Er Tm Yb LU Ga In

Cr

(1800-1000 cm-l) AND

ro7zm-s* 1732m, 1141s, 1073s* r73om, rzzos, 1065s 1733m, 1ri8s, 1059s 17&m, rr&, 1059s 1732m, 1121s, 1066s

FAR IR BANDS (600-300

cm-l)

OF M(IMP)s

COM-

_Far

IR bands (cm-l)

58om, 57ow, 57ow, 569w, 566w, 54gw,

gIovs, b, 475s, sh, 41om, sh, 38om, 36om,345sh,33ow,sh 51os, 469s, 4r6s, 392s‘ 365~s 34&h, 329~1 sb 513~8 472~2 42os,381s, 36% 34Qshs 333W, sh 511s~ 470s~ 41% 380s~ 361s~ 34gsh. 333w, sb !joQs, 467% 4165,38os, 361% 349sb, 33IW, sh sros, 461% 412% 384% 361s, 34gsb, 32QW, sh 1733rn, 11zzs, xo66s 572W, 514s, 469~2 419% 384s, 36% 35osh, 333~. sh 1732m, 1121s, 1067s* 56zw, 508s, 461s, 41os, 384s, 36os, 346sh, 323~. sh 1735m, 1126s,1068s 565~~ 504s. 463s. 410% 384% 358% 34gsh, 32%~~ sh 173zm, 11zgs, 1068s 565w, 509s~ 465~~ 416s~ 386s, 361~~ 34Qsh, 328~~ sh r73zm, I 135-IIZOS, b, 1069s 567w, 511s, 466s. 417% 389s, 364~~ 3gosh, 33ow, sh r731m, 1135-11225, b, 1070s 566w, go6s, 464s, 413s, 38Qs, 36os, 344sh, pgw, sh r73om, II~OS, 11zosh, 1067s 57ow, 508s, 467s, 419% 391s. 362s, 342% 318~ 1731m, 1144S, IIZZS, 1065s 57OW, 514S, 469s, 422% 416sh, 394s, 359% 342S, 318W 1734m, 1147s, 1120% 1067s 57ow, 512% 469s, 422% 395% 360s~ 345S, 320~ 1734m, 1155% 1120% 1070s 57Iw, 513% 469~~ 423% 395% 360s~ 3465,32ow 172gm,II65~S,1073s, sh* 57gsh, 538% 5o4m, 468~~ 436% 419% sh, 378sh, 37=n, 349sh I 734m, *146s, 107os* 575sh, 53osh, 502s, 466s, b, 41osh, 398s, 362s, gsosh, 327w, sh r730m, 1122vs, 1064x& 564% 505% 467~~ 41os, 320% sh, 3o6s, b

* vpoo data from Ref. I. medium; w, Weak,; b, broad: sh, shoulder; v, very.

s, strong: m,

J. I.ess-Common

Metals, 20 (1970) 29-36

N. M. KARAYANNISet al.

32

and these complexes have almost the same structure. Complexes obtained at relatively low temperatures (Al, Ga, SC at 50°C Y Ln, Cr at 70n-~~~oC) gave patterns characterized by various X-ray bands in the 2t3= 5”-30” region and are, therefore, crystalline. The analogs obtained at higher temperatures (x50”--~00°C) exhibited only one strong band at 20 =7--g”, which was also present in the low-temperature products. This may be indicative of lower degree of crystallinity due to formation of higher polymeric species. Both low-and high-temperature products gave analyses corresponding to the

Fig. I. Infrared spectra (1800-700 cm-l) of Nd(IMP)s, Gd(IMP)s and Ho(IMP)3. The asterisks indicate maxima of Nujol absorptions. Fig. 2. Far infrared spectra (600-300 cm-l) of Nd(IMP)s, Gd(IMl+, Ho(IMP)3, Ga(lMI% and

Cr(IMP)3.

formula M(I~P)~, and had identical magnetic properties and IR spectra. The hightemperature products were isolated in many cases in the form of membranes or rubberlike materials. A distorted Oh octahedral symmetry is assigned to the central metal ions on the basis of the electronic spectrum of Cr(IMP)$ and the similarity of the X-ray powder diffraction patterns of the M(IMP)r complexes. The evolution of isopropyl chloride during the reaction is in agreement with the mechanism proposed by GUTMANNAND BEERS. The presence of Hclandpropeneinthe volatile products has been attributed1 to dehydrochlorination of isopropyl chloride, catalyzed by the complex metal halide residuei”?ra. I?zfrared sj&ra (4000-700 cm-l] and magnetic morne~~s The magnetic moments of the lanthanide complexes (Table II) are within the range of values predicted and observed in compounds of the Ln3f ion+*-1s. J. Less-Common

Metals, 20 (1970) 29-36

TRIS-(ISOPROPOXYMETHYLPHOSPHONATO) COMPLEXES

33

The IR spectrum of isopropyl methylphosphonate has been reportedr7>18. The main bands {cm-i) in the 2700-700 cm-i region Were assigned as followsi7-20: z65ob (-OH vibration), zzgob (VP-o_(n)+ aon), r68o-r675b (combination of POO- vibrations), 1312s (YP-cnJ, XZIOS~~or 1205siS (VP-O), 1x80s 1139s IOggs (Y>CH-O-(P)), IOOOVS,g88sh (Yp-O-(H)+YP-O-(C)), $Ioos(vP-CHB), 777s (VP-O-(C)), 720s (VP-C). The infrared spectra (4000-700 cm-l) of the M(IMP) 3 complexes (Table III, Fig. I) do not exhibit absorptions in the 2700-2000 cm-i region, Where vibrational modes of the P-O-H and OH groups occuri7. They are also characterized by the complete absence of water bands. The absorptions of the free ligand at 1312, rooo, goo, 777, and 720 cm-1 do not show any appreciable shifts upon complex formation. A positive shift is observed for the 1680-1675 cm-1 band, which occurs at 173551725 cm-r in the complexes. This band has been attributed to a combination of POO- vibrations’9 and the shifts observed during this work substantiate this assignment. Absorptions at 11601118 and 1075-1065 cm-i are also assigned to YPOO modes7,“i. The bands at 1160--1118 cm-i overlap with the strong r>CH-O-(P) absorptions in this region and, in some cases, the determination of the maxima is not possible (Table III, Fig. I). Finally, the strong band at cu. 1000 cm-l is assigned to pure VP-~(C). Far infrared spectra The far infrared spectra of alkyl alky~phopshonates are generally characterized by two medium broad bands at 570-540 and 500-450 cm-r and a weak absorption at 320-300 cm-l (ref. 22). The spectrum of DIMP in this region is as follows (cm-i): 56ow, 5o5m-s, 42om,vb, 325W. The far JR spectra of the M(IMP)a complexes are characterized by several strong bands (Table III, Fig. 2). The spectra of the new rareearth~~)mplexesaregenerally very similar, andthoseof the GajIII), In(II1) and CrfIII) analogs, which Were reported elseWherei, were also obtained (Table III, Fig. z) Bands at 575~560,515-502,472-460,422-410 and 330-320 cm-larecommonin all the complexes of Table III and are, thus, attributed primarily to ligand vibrations. Absorptions in the 600-400 cm-i region in the spectra of metal complexes of acidic phosphoryl compounds have been assigned to O-P-O and C-P-O vibrational modes With participation of v~~-ovibrations 23324.On the other hand, in metal complexes of bidentate oxygen ligands, several far IR bands are associated with ‘nf-o vibrational modes (e.g., bidentate carbonato complexes 25 and rare-earth acetylacetonato complexes2”-2R). In tris-(acetylacetonato)Ln(III) complexes, bands at 432-412, 333-304 and below 250 cm-i have been attributed to modes involving VL~-Oparticipation”6,“s. On the basis of the above discussion, the two strong bands at 395-380 and 366358cm-1, whicllo~cl~rinvariablyin theY(II1) and Ln(II1) complexes, are assigned to primarily vh~~ovibrations. The former band occurs at higher frequency with increasing lanthanide contraction (Table III). A similar trend has been observed in tris(acetylacetonato) Ln(II1) complexes 28. Bands in the same region are also observed for In(IMP)z and are, presumably, due to VI~-O. The spectra of the Sc(III), Ga(II1) and Cr(II1) complexes differ from those of the rare-earth analogs in the positions of the YDI-omodes, Which are tentatively assigned as follows: ysc-o: 510 (overlapping with the Iigand vibration), 430, 3%0, 360 cm-l; vGa-0: 538, 436, 371 cm-i; YC~-O:564, 306 cm-l. The similarities in the far IRspectraof theY(III),Ln(III) andIn(II1) complexes are attributed to the small differences in the ionic radii of these metal ions (Y3+ 0.9 A, Ln3+ 0.848-1.061 A, Ina+ o.81 A). The spectra of Sc(IMP)a and Ga(IMP)s exhibit J. Less-commoa?&tazs, 20 (1970) 29.-36

34

N.

M. KARAYANNISet

al.

similar patterns to those of the In(III), Y(II1) and Ln(II1) analogs. In fact, the band at 430-436 cm-i in the Sc(II1) and Ga(II1) complexes may be assigned to the same vibrational mode (v&r-o) to that of the 398-380 cm-i band in the In(III), Y(II1) and Ln(II1) complexes. In addition, the vos-o band at 538 cm-i occurs as a shoulder at 530 cm-i in In(IMP)s and, presumably, overlaps with the 515-502 cm-i band in the rare-earth compounds (Table III, Fig. z). Cr(IMP) 3 exhibits a different far IR spectrum, in particular in the 400-300 cm-i region, probably due to d,-9, back-bonding from Cr to oxygenzs, which is absent in the other complexes discussed. It is noteworthy that in trivalent lanthanide complexes, characterized by P-0-LnSO

or H&,, /P-o\Ln3i groups, no definitive evidence for the presence of
The monomeric structure (I) has been proposed by GUTMANN AND BEER for the tris(dimethoxyphosphato)M(III) complexes (M =Ti, V, Cr)3. Structure II has been assigned to a number of (phosphinato) complexes of trivalent metal ions34. The complexes obtained at higher temperatures may be higher polymers containing exclusively eightmembered phosphonate bridges2233”. Although considerable steric strain in four-membered chelate rings of the type makes

J. Less-Common

their

Metals,

formation

20 (1970)

29-36

improbable

24935,

the

synthetic

method

followed

TRIS-(ISOPROPOXY

METHYLPHOSPHONATO)

COMPLEXES

35

during this work suggests that the monomer is formed, at least, initially. In fact, in DIMP solutions of trivalent lanthanides, the adduct Ln(DIMP)& is, presumably, formedg. When the temperature is increased, coordination of one alkoxy oxygen and subsequent elimination of isopropyl chloride occurs according to the GUTMANN-BEER mechanisms:

1

7’

DIMP

CH3\p/o\M(, C3H70’

%of

\*

DIMP

The new complex is stabilized by the chelate effects. The evidence available is not sufficient for the definitive assignment of a monomeric or polymeric structure to the rare-earth complexes reported here. Further studies, involving the preparation of analogous compounds, by direct interaction of isopropyl methylphosphonate with trivalent rare-earth salts33, and thiophosphonate-rareearth chelates32 would add valuable information. Unfortunately, characterization studies involving molecular weight determinations or crystal growth and subsequent X-ray analysis are impossible, due to the general insolubility of the new complexes. ACKNOWLEDGEMENT

The support of U. S. Army Edgewood is gratefully acknowledged.

Arsenal under contract

No. DAAA 15-67-C-0644

REFERENCES

I C. M. MIKULSKI,

6 7 8 9 IO II

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