The Ternary Uranium Transition Metal Phosphides ...

The Ternary Uranium Transition Metal Phosphides UV5P3, UCr5P3, and UMn5P 3 W olfgang Jeitschko*, R einhold B rink, and Peter G. Pollmeier A norganisch-C hem isches In stitu t der U niversität M ünster, W ilhelm -K lem m -Straße 8, D -W -4400 M ünster Z. N aturforsch . 48b, 5 2 -5 7 (1993); received Septem ber 1, 1992 C rystal S tructure, M agnetic Susceptibility, Tin Flux, S tructural R elationships The title co m p o u n d s were p rep ared from prereacted sam ples o f the elem ental co m p o n en ts by arc-m elting. U C r5P 3 was also o b tain ed from a tin flux. U V 5P 3 and U C r5P 3 crystallize w ith a new structu re type, w hich w as determ ined from X -ray d ata o f a tw inned crystal o f U C r5P3: P 2 1/m , a = 959.1(2), b = 370.95(6), c = 696.7(1) pm , ß = 100.05(3)°, Z = 2, R = 0.030 for 827 stru ctu re factors and 29 variable param eters. U M n ,P , is isotypic w ith Y C o 5P 3. The structure was refined to a residual o f R = 0.054 for 455 structure factors and 28 variables. U C r5P3 has a relatively high, alm ost tem p eratu re independent param ag n etic susceptibility as is frequently observed for m etallic u ran iu m com pounds. The crystal stru ctu res o f these p h o s phides are discussed to g eth er w ith those o f oth er phosphides and silicides o f sim ilar co m p o si tion.

Introduction Only few tern ary actinoid tran sitio n m etal phos phides are know n. M o st o f them have a m etal to p h o sp h o ru s ratio close to 2 : 1 and can be classified by the various kinds o f linkages o f the trigonal prism s o f m etal ato m s su rro u n d in g the p h o sp h o rus atom s. T h 6C o 20P i 3 is an early exam ple for this stru ctu ral fam ily [1], It is m ost likely isotypic with U 6R h 20P 13 [2] and Z r 6N i 20P 13 [3]. O ther examples are U 2M n 12P v [4], U 2F e 12P 7 [5], and U 2N i 12P 7 [6 ] with Z r 2F e 12P 7 type stru ctu re [7], U M n 4P 2 [8 ], the two m odifications o f U C r 6P 4 [9], as well as the recently characterized phosphides T h 5F e 19P 12 an d T h F e 4P 2 [10], O f the co m p o u n d s reported here U V 5P 3 and U C r 5P 3 crystallize w ith a new stru ctu re type. U M n 5P 3 is isotypic w ith Y C o 5P 3 [11]. Prelim inary accounts a b o u t the crystal stru ctu res o f these phosphides were given earlier [4, 12], Sample Preparation and Properties S tarting m aterials were platelets o f uranium (M erck: “ n u k learrein ”), pow ders o f vanadium (> 9 9 .7 % ), chrom ium (99.99% ), an d m anganese (99.9% ), red p h o sp h o ru s in the form o f small pieces (H oechst-K napsack: “u ltra p u re ”), and granules o f tin (M erck, 99.9% ). A p p ro p riate mix* R eprint requests to Prof. W. Jeitschko. V erlag der Z eitschrift für N a tu rfo rsch u n g , D -W -7400 T übingen 0 9 3 2 -0 7 7 6 /9 3 /0 1 0 0 -0 0 5 2 /$ 01.00/0

tures o f the elem ents were sealed in evacuated sili ca tubes and annealed betw een 700 C and 900 °C for about one week. The reaction pro d u cts were cold-pressed to pellets and arc-m elted u nder an a t m osphere o f purified argon. All three com pounds were present already in the “as ca st” b u tto n s w ith out further annealing. They are black w ith m etallic lustre and stable in air for long periods o f time. Energy dispersive X -ray fluorescence analyses in a scanning electron m icroscope did n o t reveal any foreign elem ents heavier th a n sodium . A well crystallized sam ple o f U C r 5P 3 was o b tained by the tin flux technique. The elem ents in the atom ic ratio U :C r :P :S n = 5 :1 7 :8 :7 0 were sealed in a silica tube, slowly heated ( 2 0 °/h) to 900 C, held at this tem perature for tw o days and cooled to 700 °C w ithin a few days. The tin-rich m atrix was then dissolved in cold hydrochloric acid, which leaves the needle-form ed crystals o f U C r 5P 3 essentially u n attacked. T hey are slowly dissolved, how ever, in hot hydrochloric acid. The products were characterized by the G uinier pow der technique using « -q u a rtz (a = 491.30 pm, c = 540.46 pm ) as a stan d ard . Indices could be as signed on the basis o f the cells o btained from the single-crystals investigations. This was facilitated by com paring the experim ental p attern s w ith the ones calculated [13] using the positional p aram e ters o f the structure determ inations. T he following lattice constants were o btained by the leastsquares fits for U V 5P 3: m onoclinic, a = 1018.0(3), b = 341.0(1), c = 748.8(2) pm ,/? = 100.36(3)°, V =

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W. Jeitschko et al. • U V 5P3, U C r5P 3, and U M n^P,

F o rm u la w eight Space group a [pm] b [pm] c [pm] ß[°] V [nm 3] C alculated density [g/cm 3] C rystal size [//m3] 0 2 0 scans up to R ange in h k l H ighest/low est transm ission T o tal no. o f reflections U nique reflections In n er residual, R ] Reflections w ith I0> n e r(I0) N u m b er o f variables C o n ventional residual, R W eighted residual, R w

53

U C r5P 3

U M n 5P3

590.9 P 2 ,/m 959.1(2) 370.95(6) 696.7(1) 100.05(3) 0.2441 8.04 8 x 8 x 100 2 0 = 80° ± 1 7 ± 6 ± 12 1.49 6028 1679 0.038 827 (n = 3)* 29 0.030 0.032

605.6 Pnm a 1225.0(3) 369.3(1) 1072.6(2) 0.4850 8.29 11x11x100 20 = 95° ± 2 2 ± 7 ± 18 1.31 8794 2344 0.082 455(«=2) 29 0.054 0.044

0.2557 n m \ F o r U C r 5P 3 and U M n 5P 3 the lattice constants are listed in Table I. The m agnetic susceptibility o f U C r 5P 3 was de term ined w ith a F arad ay balance between liquid nitrogen an d ro o m tem perature as described ear lier [14]. T he com pound show s alm ost tem perature-indepen d en t param agnetism . A t 78 K the sus ceptibility is / = 0.00443(2) cm 3/m ol. It decreases gradually to a value o f % = 0.00372(2) cm 3/m ol at 291 K. These susceptibility d a ta are sim ilar to those o f the tw o m odifications o f U C r 6P 4 [9], They are m uch higher th an the Pauli param agnetism o f norm al m etals. Sim ilar alm ost tem perature-inde pendent, high param agnetic susceptibilities were observed by us for m any phosphides and carbides o f cerium and u ranium [14-16], They m ost likely are related to the mixed o r interm ediate valence o f these elem ents in such com pounds.

Structure Determinations N eedle-shaped crystals o f U C r 5P 3 were taken from the sam ple prepared in the tin flux. The crys tal o f U M n 5P 3 was isolated from the surface o f an arc-m elted sam ple. In b o th cases the needle axes turned o ut to correspond to the short axes. The crystals were investigated w ith W eissenberg cam eras to establish their sym m etry and suitability for the intensity d a ta collections. The crystals o f U C r 5P 3 tu rn ed o u t to have a strong tendency for tw inning. Intensity d ata were collected on a four-

T able I. C rystal d a ta fo r U C r5P 3 and U M n 5P,

* T his n u m b er already excludes the reflec tions w ith h + / = 8 n , w hich had to be om itted because o f the overlap w ith the twin.

circle diffractom eter w ith graphite m onochrom ated M o K a rad iation, a scintillation counter w ith pulse-height discrim ination, using 0 / 2 0 scans w ith background counts at b oth ends o f each scan. A b so rption corrections were m ade from y/ scan data. The positions o f m ost atom s were obtained from P atterso n syntheses; those o f the other atom s were found on difference F o u rier m aps. The stru c ture o f U C r 5P 3 is o f a new type with space group P 2 ,/m (N o. 11) and Z = 2 form ula units per cell. U M n 5P 3 tu rned o u t to be isotypic w ith Y C o 5P 3 [11], space group Pnm a (N o. 62), Z = 4. O ther d a ta are listed in T able I. B oth structures were re fined by full-m atrix least-squares cycles using atom ic scattering factors [17], corrected for a n o m alous dispersion [18]. The w eights consisted o f a c o n stan t and a term accounting for the counting statistics. P aram eters correcting for isotropic sec o n d ary extinction were refined and applied to the calculated structure factors. F o r the U C r 5P 3 struc ture, the W eissenberg d a ta h ad show n previously th a t reflections w ith h + I = 8 n were superim posed w ith the corresponding ones o f the o th er twin d o m ain (Fig. 1); they were therefore excluded in the final refinem ent. T he reflections w ith h + 1 = 8 « ± 3 were also close to each other, b u t the resid uals for these were low and therefore the c o rre sponding structure factors could be included in the last refinem ent cycles. R efinem ents w ith ellipsoi dal therm al p aram eters show ed no great im prove m ents o f the residuals and the displacem ent pa-


54

W. Jeitschko et al. • U V 5P3, U C rsP 3, an d UMn^P^

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Fig. 1. R eciprocal lattice h k l o f a crystal o f U C r5P 3 (dots) superim osed by the reciprocal lattice h ' k T o f the twin (circles). The tw o lattices m atch fo r the lattice points h + I = 8«.

ram eters were close to the isotropic ones. T o check for the correct com position we also refined occu pancy param eters togeth er w ith the therm al p a ram eters using fixed scale factors. A s the highest and lowest values we o b tain ed 102.1(5)% for C r2 and 97.7(5)% for C r3 in U C r 5P 3; fo r U M n 5P 3 the occupancies covered the range betw een 108(5)% for P 3 an d 98(2)% for P I . T hus, w ithin five sta n d ard deviations all occupancies were at the ideal values, an d in the final least-squares cycles they were again fixed at the ideal values. D ifference F o u rier syntheses show ed as highest residual elec tro n densities the values o f 3.3 and 5.8 e/Ä 3 for the chrom ium and m anganese co m p o u n d , respective ly, a t locations to o close to occupied m etal posi tions to be suitable for ad d itio n al atom ic sites. The final residuals for the refinem ent w ith isotropic therm al param eters, the atom ic param eters, and in teratom ic distances are given in T ables I —III. The structure factor tables are available [19, 20]*.

T able II. A tom ic param eters for U C r5P 3 and U M n 5P 3. The last colum n lists the isotropic therm al p aram eter B (x 100 in units o f n m 5). S tan d ard deviations in the p o si tions o f the last listed digits are given in p arentheses th ro u g h o u t the paper. A tom

X

y

z

B

U Cr 1 C r2 Cr 3 C r4 C r5 PI P2 P3

0.21929(5) 0.2772(2) 0.5059(2) 0.9174(2) 0.9110(2) 0.4898(2) 0.6722(3) 0.0159(3) 0.6636(3)

1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4

0.80794(7) 0.3169(3) 0.1314(3) 0.5395(3) 0.9178(3) 0.6194(3) 0.4354(5) 0.2512(5) 0.9009(4)

0.300(4) 0.51(2) 0.66(3) 0.48(2) 0.53(2) 0.49(2) 0.45(4) 0.49(4) 0.42(4)

U Mn 1 M n2 M n3 M n4 Mn 5 PI P2 P3

0.2060(1) 0.4844(5) 0.9907(4) 0.6779(4) 0.1969(5) 0.4349(5) 0.6194(7) 0.3722(8) 0.8878(7)

1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4

0.9164(1) 0.7931(5) 0.0906(7) 0.2832(5) 0.6200(5) 0.0373(5) 0.081(1) 0.238(1) 0.905(1)

0.31(1) 0.34(8) 0.47(7) 0.29(7) 0.36(7) 0.31(7) 0.5(1) 0.4(1) 0.5(1)

T able III. Interatom ic distances in U C r5P 3 an d U M n 5P 3. All distances shorter than 340 pm (for the U , C r, and M n atom s) and 300 pm (P atom s) are listed. S tan d ard deviations are all equal or less th an 0.3 pm fo r the chrom ium and 1.4 pm for the m anganese co m pound. U C r5P 3 U:

C r 1:

C r2: They m ay be ob tained from the F achin fo rm atio n szen trum K arlsruhe, G esellschaft für w issenschaftliche Inform ation m bH , D -W -7514 E ggenstein-L eopoldshafen 2, by quoting the R egistry N o. C SD 56781, the nam es o f the au th o rs and the jo u rn a l citation.

U M n 5P3 2P1 2P3 2P2 2 C r4 1C r 5 2 C r3 1C r 3 1 C r4 2 C r2 1 C r2 1 P2 2P1 2P3 1C r 5 1 C r2 2C r 5 2 C r4 2C r 3 1 P3 1P I 2P3 2C r 5 2 C r2 1C r 1 2U 1U


283.1 283.2 289.4 308.0 310.6 314.8 316.1 318.0 319.0 323.6 246.8 252.2 252.3 266.5 273.3 287.8 288.8 292.8 239.1 241.9 245.1 253.6 259.5 273.3 319.0 323.6

2P1 2P2 2P3 2M n2 1 M n5 2 M n4 2M n3 1M n4 1M n2 1 M n3 M n 1: 1 P3 2P2 2P1 1M n 5 1M n4 2M n5 2M n3 2M n2 M n2: 1 P2 1 P3 2P3 1 M n3 2M n2 2M n 1 2U 1U

U:

282.5 282.6 289.5 303.7 309.0 309.7 316.5 318.2 323.2 324.0 243.6 257.0 261.7 268.8 276.5 277.4 283.4 286.8 234.1 235.3 237.2 266.3 269.0 286.8 303.7 323.2

55

W. Jeitschko et al. • U V SP3, U C rsP3, an d U M n ?P T able III. (continued).

UCnP, C r3:

C r4:

C r5:

P I:

P2:

P3:

U M n ,P 5l 3 1P1 1 P2 2P2 2C r 3 1 C r4 2C r 1 2U 1U 1P3 1P2 2P2 2 C r4 1C r 3 2C r 1 2U 1U 1P3 1P1 2P1 2C r 5 2 C r2 1C r 1 2C r 1 1U 1C r 3 1C r 5 2C r 5 1 C r2 2Cr 1 2U 1 C r3 1 C r4 2 C r4 2Cr 3 1C r 1 2U 1C r 5 1 C r4 1 C r2 2 C r2 2C r 1 2U

233.7 236.4 237.7 256.1 264.7 292.8 314.8 316.1 235.6 236.5 236.8 264.3 264.7 288.8 308.0 318.0 234.1 234.2 240.7 252.2 253.6 266.5 287.8 310.6 233.7 234.2 240.7 241.9 252.2 283.1 236.4 236.5 236.8 237.7 246.8 289.4 234.1 235.6 239.1 245.1 252.3 283.2

1P1 1P 2 2P3 2M n4 1M n2 2M n 1 2U 1U M n4: 1P3 1P1 2P2 2M n5 2M n3 1M n 1 2U 1U M n 5: 1P2 1P1 2P1 2M n5 2M n4 1M n 1 2 Mn 1 1U 1M n3 P I: 1M n 5 2M n5 1M n 4 2M n 1 2U P2: 1M n5 1M n2 1 M n3 2M n4 2M n 1 2U 1M n2 P3: 1M n 4 2M n2 2M n3 1M n 1 2U

M n3:

228.3 239.2 240.3 261.5 266.3 283.4 316.5 324.0 235.4 235.7 239.5 260.9 261.5 276.5 309.7 318.2 228.7 230.9 233.8 256.7 260.9 268.8 277.4 309.0 228.3 230.9 233.8 235.7 261.7 282.5 228.7 234.1 239.2 239.5 257.0 282.6 235.3 235.4 237.2 240.3 243.6 289.5

tio nal m etal atom s outside the rectangular faces of the prism s. The m etal atom s have c o o rd in atio n polyhedra which fit their size with coo rd in atio n n um bers (C N ) varying m ostly betw een 12 and 23. O f these neighbors usually between 4 and 6 are m etalloid atom s. The orthorhom bic TiN iSi [21] an d the hexagonal T iC oG e [22] structures are ea r ly an d the m ost simple examples. H ere we will co n sider m ainly the structure types w ith the com posi tio n 1 :5 :3 , o f which the structure o f U C r 5P 3 is a new example. O f these the Y C o 5P 3 type structure has the larg est num ber o f representatives w ith the series R F e 5P 3 (R = Y, G d - L u ) [23] and R C o 5P 3 (R = Y, C e - N d , Sm, G d - L u ) [11, 24], as well as the pres-

y

u

1/4

0

0

Cr P

•

314 O

O

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O o

Discussion The phosphides described here belong to a very large family o f co m pounds w ith a m etal to m etal loid ratio o f o r near 2:1 [1 -1 1 ]. In these structures m ost or all atom s are situated on tw o m irro r planes, which are p erpendicular to the sh o rt tra n s lation period, w hich is best suited for the projec tion direction (Figs 2 and 3). In these stru ctu res the m etalloid atom s (mostly silicon o r p hosphorus and their hom ologues) have trigonal p rism atic m etal coordination, w hich is augm ented by three a d d i

Fig. 2. C rystal structures an d co o rd in atio n po ly h ed ra o f U C r5P 3 and U M n 5P 3. A tom s connected by thin and thick lines are separated from each o th er by h a lf a tra n s latio n p eriod o f the p rojection direction.


W. Jeitschko et al. • U V 5P3, U C rsP 3, and U M n sP,

56

UCr5P3

UMn5P3 (YCO5P3 type)

UCo 5Si3

Fig. 3. L inkages o f th e trigonal prism s o f m etal atom s in the structures o f U C r5P 3, U M n 5P 3 (Y C o 5P3 type), U N i5Si3, L aC o 5P 3, a n d U C o 5Si3. T he lan th an u m and uranium ato m s are show n as large circles, the tran sitio n m etal atom s as sm all circles, and the m etalloid atom s as dots. A tom s connected by thick and thin lines are sep ar ated from each o th e r by h a lf a tran slatio n period.

ently characterized new com pound U M n 5P 3. The stru ctu re o f U N i 5Si 3 [25] occurs also for the silicides R N i 5Si 3 (R = Y, Tb, H o, Er, and Y b) [25], The U C o 5Si3 type structure is also know n for Z rC o 5Si3 [26], while the L aC o 5P 3 type structure [27] was also found for S rN i 5P 3 [6 ], L aN i 5P 3 [28], E u N i 5P 3 [29], S rN i 5A 3 [6 ], and E u N i 5A s 3 [6 ]. O f these five stru ctu re types the structures of U C r 5P 3, Y C o 5P 3 (U M n 5P 3), and U N i 5Si3 are m ost closely related if we consider the coordination p olyhedra and the m etal-m etalloid interactions as the m ost im p o rta n t criteria for such relationships.

The uranium (yttrium ) atom s o f these three struc ture types have C N 20 w ith six neighbors at the sam e m irro r plane as the central atom , six neigh bors each on the tw o m irro r planes above and be low, and the tw o identical uranium atom s o f the adjacent cells along the short axis (coordination 6 + 6 + 6 + 2; these neighbors are show n in the Figs 1 an d 2 ; they m ay n o t be listed as neighbors in T able III if they exceed the indicated interatom ic distances). O f these 20 neighbors six are m etalloid (Si, P) atom s form ing a trigonal prism. The transi tion m etal atom s in these three structures occupy five equipoints. In one o f these the transition metal ato m (C r 1 in U C r 5P 3, M n 1 in U M n 5P 3, and N i4 in U N i 5Si3) has C N 17 w ith five neighbors each above and below , five at the “belt” o f the coordi n atio n polyhedron, and the tw o identical tran si tion m etal atom s above and below (coordination 5 +5 + 5 + 2). O f these 17 neighbors five are m etal loid atom s in square pyram idal arrangem ent. T hus, this site o f the central tran sitio n m etal atom is som etim es called the “ pyram idal site” . This em phasizes the strength o f the transition m etal-m etal loid bond, although the m etal-m etal bonding should n o t be neglected [21, 30, 31]. T he other four tran sitio n m etal sites o f these three structure tpyes have C N 14 (co o rd in atio n 4 + 4 + 4 + 2 ) or CN 12 (co o rd in atio n 4 + 4 + 4 ) depending on w hether one counts the identical tran sitio n m etal atom s one tran slatio n period above and below as neighbors o r not. F o u r o f these neighbors are m etalloid atom s in tetrah ed ral arrangem ent (“tetrahedral site”). T he m etalloid atom s o f the three structure types U C r 5P 3, Y C o 5P 3 (U M n 5P 3), and U N i 5Si3 oc cupy three different sites in each o f these three structures. They all have nine m etal neighbors: seven tran sitio n m etal atom s and two uranium (yttrium ) neighbors. Six o f these form a trigonal prism , the o th er three neighbors are situated o u t side the rectangular faces o f the prisms. The m ost im p o rta n t difference o f the L aC o 5P 3 structure to the structure o f the other 1 :5 :3 com p ounds lies in the c o o rd in atio n o f the lanthanum atom . As a consequence o f its large size it has a higher c o o rd in atio n num ber: CN 23 vs. C N 20 for the uranium atom s in the o th er 1 :5 :3 com pounds. Its 7 + 7 +7 + 2 coo rd in atio n contains seven phos phorus neighbours. A n o th er significant difference o f this structure is the absence o f a pyram idal co b alt site. Instead this structure contains a cobalt


W. Jeitschko et al. • UV^Pj, UCr^P^, and U M n 5P,

57

site with four p h o sp h o ru s neighbors form ing a rec tangle. The m ajo r difference o f the U C o 5Si3 stru c ture to the o th e r 1 :5 :3 structures can be seen in one cobalt site w ith only three silicon neighbors and one silicon site w ith eight m etal neighbors. In the c o o rd in atio n polyhedron o f this site one m etal atom outside the rectangular faces o f the trigonal prism is m issing. Instead there are two silicon a t om s som ew hat fu rth er aw ay w ith a S i-S i distance o f 267 pm , w hich m ight still be considered as weakly bonding. In this large structural family o f transition m etalm etalloid co m p o u n d s w ith a m etal to m etalloid ra tio o f 2 : 1 the differences in the architecture be com e m ost a p p a re n t if one em phasizes the trigonal prism s o f m etal atom s surrounding the m etalloid atom s. This is show n in Fig. 3. It is im m ediately obvious th a t the atom ic arrangem ent o f U C r 5P 3 and U N i 5Si3 is very similar. H ow ever, the m o n o clinic structure o f U C r 5P 3 (P 2 ,/m ) is n o t simply a distorted version o f the orth o rh o m b ic structure o f U N i 5Si3 (Pnm a) even though the space group P 2j/

m is a translationengleiche subgroup o f Pnm a. Both structures actually m ay be considered as de rived from a structure w ith the subcell o f space group Pnm a. The structure o f U N i 5Si3 derives from th at subcell by doubling o f the translation period a, (a klassengleiche tran sform ation), while the structure o f U C r 5P 3 derives from th a t o rth o r hom bic subcell by a m onoclinic d istortion (a trans lationengleiche tran sfo rm atio n ) [32,33].

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We are indebted to D ipl.-Chem . G . Schrick for prelim inary w ork on the system uranium -vanadium -phosphorus. D ipl.-Ing. U . R odew ald and D r. M. H. M öller kindly collected the diffractom e ter data. W e also appreciate D r. M. Reehuis, w ho determ ined the m agnetic susceptibility o f U C r 5P 3 and M rs. U. G öcke, w ho helped w ith the d raw ings. We are grateful for gifts o f u ltrap u re red pho sp h o ru s (H oechst A G , W erk K napsack) and silica tubes (D r. G . H öfer, H eraeus Q uarzschmelze). This w ork was su p p o rted by the D eutsche Forschungsgem einschaft and the Fonds der C hem ischen Industrie.
