THE AMERIC.\N MINERALOGIST. VOL. 56. SI]PTI'MBER_OCTOBER, 1971

A NOVEL FACE-SHARING OCTAHEDRAL TRIMERIN THE CRYSTAL STRUCTURE OF SEAMANITE

Paur B. Moonn, Department of the Geophysical Sciences, The Uniaersitltof Chicago, Chicago, Illi.nois 60637

AND

Susnare Guosr, Planetologlt Branch, Goddard Space

Fl,ight Center, G'reenbelt, Maryland 2077 1.

Assrnacr

The atomic arrangement of seamanire, Mnl+(oI{)dB(oH)4][Po{1, a 7.811 (5). 615.114 (10), r 6 691 (5) L, Z:+, space group Pbnm,was deciphered b1. vector set tech-niques. Utilizing 1217 independent reflections, full-matrix refinement converged to Rau:0.062.

The structure is based on a novel face-sharing Mn-O octahedral trimer which links bvedge-sharing with symmetry equivalent trimers to form infinite chains running parallelto the c-axis Each chain is weakly linked to an equivalent chain through common hy-droxyl groups to form a band. The ligands include (OH)- anions, and tetrahedral [B(OH){land [POa] groups The tetrahedral groups bridge octahedral bands to form a fairly rigidthree-dimensional edifice. One oxygen atom associated rvith P does not bond to the octa-hedral cations but accepts four possible hydrogen bonds which, with the P5+ cation, definea distorted trigonal bipyramid.

The peculiar trimer is apparently stabilized by the short O-O'edge associated rvith theborate tetrahedron. Of the three trimeric face-sharing octahedral isomers, two are no$known to exist in natural crystals

ItTrnooucrror.I

Seamanite, a rare hydrated borate-phosphate of manganese, was f irst

described by Kraus, Seaman, and Slawson (1930). I t occurred in frac-

tures cutt ing si l iceous rock at the Chicagon Mine, Iron River, Michigan,

as pale pink to yellow acicular crystals associated with sussexite, man-

ganic oxyhydroxides, and calcite. Few specimens were preserved, most

of which appear in the A. E. Seaman Mineralogical Museum at Michigan

Technological University. McConnell and Pondrom (1941), by X-ray

s tudy and e tch tes ts , es tab l i shed a 7 .83 (2 ) , b 15 . I4 (2 ) , c 6 .71 (2 ) , space

group Pbnrn On the basis of powder photographs, they further con-

cluded that seamanite, bel ieved to be Mq(BOB) (POD.3H2O, was prob-

ably not isostructural with reddingite, Mq(PO4)2'3H2O.

As part of a general program concerning octahedral clustering in

manganese anisodesmic oxysalts, we report a detai led study of the

seamanite atomic arrangement. We wish to remind readers that the

rari ty of a species has l i t t le bearing on the signif icance of formal crystal

structure analysis directed toward furthering our knowledge of crvstal

chemistry. As a point of fact, some of the most unexpected clusters have

t527

ls28 MOORE AND GEOSE

been revealed only through the study of more exotic species. Seamaniteproved no exception; not only have we found a novel octahedral face-sharing cluster hitherto believed impossible on geometrical grounds, butwe are also committed to interpret the seamanite crystal-chemical for-mula as a basic compound with composirion Mry2+(OH)r[B(OH).][POI].

ExprnnmNur-A nearly perfectly symmetrical rectangular prism (U.S. National Museum No. 96282)

of 0.005 mmt volume was selected for study. 3000 reflections with c as the rotation axiswere collected on a PATLRED automated difiractometer using a graphite monochromatorand Mo radiation to 20:650. The cell parameters in Table 1 were obtained from con-ventional least-squares refinement of the indexed powder data in Table 2. These powderdata were obtained from a spherical powder mount utilizing a 114.6 mm diameter Buergercamera and Mn-filtered Fe radiation, and the corresponding Miller indices were un-ambiguously selected by comparison with the strong intensities of the single crystal study.Individual single crystal integrated intensities were obtained using a 1.8o half-angle scan,with background counting time on each side of the peak of.20 seconds.

Reflection pairs of the kind I (hkl) , I (ilkl) were averaged since o-scans about the basalreflections revealed that absorption anisotropy correction amounted to only 6 percent ofthe mean peak value. A total of 1217 s)'nmetry independent non-zero reflections wereprocessed and were the only ones used in the ensuing study. Among the remaining 515zero-reflections were the space group absences as well as weak data which were within theerror of the background difierences and these data were excluded from further considera-tion.

TABI,E 1. SEAIANITE: CRYSTAI, CELL DATA

ed )!. (8)

s. (8)v 63)

6pace group

fomula

z

specific gravityl

I calc

7.8r r (s )

Is.1r4 (10)

6 .6er (s )

7e0.0 (7 )

B!lg,. t r 1

le'3 (olD z [B (o]D nl Lnou J4

3 .128

3.L32 gry'cn3

I-Kraus, Seaman and SLawson (1930).

STRUCTURE OF SEAMANITE

TABLE 2. SEAI'AMTE: PO{DER DATAa

r_/r_o

6

10

5

5

6

5

6

5

3

3

5

8

2

3

?

2

6

I

2

3

2

4

I

2

I

2

I

I

5

I

2

d(obs)

7 . 5 5 1

6 . 9 1 7

5 .420

4 . 8 0 7

4 . 2 0 4

3 . 8 9 9

3 . 7 7 7

3.467

3 . 3 9 4

3 . 3 1 3

3 . 2 8 6

3 . 0 5 7

2 . 8 4 3

2 . 7 L 3

2.6L7

2 . 5 8 r

2 . 5 5 5

2.502

2 . 3 9 3

2 .3s l

2 . 3 0 9

2.263

2 . 1 8 4

2.II I

2 . 0 7 3

2 . 0 6 1

2.O25

2.0r5

L . 9 7 4

r . 9 4 5

1 . 9 0 1

I . 8 1 8

1 . 7 6 9

d (calc)

7 .557

6 : 9 3 9

5 .43r

4 . 8 1 7

4.2L7

3 . 9 0 6

3 . 7 8 1

3 .469

3 .401

3 .345

3 .290

3 . 0 5 9

2 . 8 4 8

2 . 7 L 5

2.625

2 . 5 6 6

2 . 5 r 9

2 . 5 0 6

2.397

2.357

2 . 3 1 0

2.269

2 .186

2.LI7

2 . 1 0 8

2 . 0 8 I

2 . 0 6 3

2 . 0 3 6

2.018

2.OL?

I . 9 8 7

1 . 9 4 5

1 . 9 0 3

1.8 I8

L . 7 7 L

lEl

020ll0

120u1l2r200210220140oo204ro22L222401323r00602L216006I32L232331260242L70L233L226I062t7r25233227L181

1530 MOORL:, AND GHOSIi

TABLE 2. (contintled)'

T, /T- - o

Itl+

$(obs)

t _ . 7 3 6

I . 6 8 7

L . 6 7 2

r . 6 4 3

r . 6 3 6

1 . 6 1 0

1 . 5 9 4

r . 5 r + 2

r . 5 2 8

I . 5 0 2

1 . 4 8 8

I . 4 I 9

1 . 4 0 2

L " 3 7 2

r . 3 3 0

1 . 3 2 5

1 " 3 0 4

L"262

r .25r+

ILl440

402

4L2

004

082

450

182

362

290

380

520

144

3 7 2

183

311+

292

164

254

472

542

193

600

630

0 8 4

g (cale)

L . 7 3 5

1 . 6 8 7

r . 6 7 6

r . 6 7 3

I . 6 4 5

1 . 6 4 0

1 . 6 r 0

1 . 5 9 2

1 . 5 4 3

r . 5 2 9

I . 5 2 9

1 . 5 0 1

r . 4 8 8

I . 4 I 8

1 . 4 0 1

1 . 4 0 1

I . 3 7 2

I . 3 7 1

r . 3 2 9

L.326

L.322

1 . 3 0 2

1 . 2 6 0

L.252

a

3

z

3

I

I

z

I

2

l_

t F"K* ; 114.6 mrn camera dianeter. Filrn conrected fon

shrinkage. When morb than one reflection contributes

to d(obs), al l are l isted in decreasing value of

spacing.

ST'RUCTU RE OF S I.:.A M A N IT li 1531

Sor,urron ol tun Srnucrunp

Patterson projections, P(ua) and P(z'ru), combined with polyhedral packing modelsassisted in the structure determination. The only hindrance in the experiment was theprejudice on the part of the investigators that the clusters revealed by vector set analysiswere crystallochemically impossible and were rejected in the initial trial parameter refine-ments, thus rendering the problem more costly in time than justified.

The correct model, consisting of two s)zmmetry independent Mn atoms and one P atom,yielded a heavy atorn least-squares refinement of

R _ I i i r*,"1 - la"," l loo, : =:2

p_ :0.28

Difierence synthesis of the phases thus produced unambiguousiy revealed all oxygen atomsin the asymmetric unit of the crystal structure. Inclusion of the anions in the refinementfollowed by further difference synthesis revealed the position of the boron atom.

RerrntlmN:r

The study by McConnell and Pondrom (1941) indicated a centrosynmetric crystal andwe did not find it necessary to consider lower s],'rnmetry throughout this study. AII atomicfree parameters in the asymmetric unit were refined according to full-matrix least-squaresprocedures using a local version of the familiar program of Busing, Martin, and Levy(1962). Scattering curves for Mnl+, P3+, B2+, and Or- r,r'ere obtained from MacGillavryand Rieck (1962). The reliability index, R7,47, converged to 0.O62 Ior alI 1277 non-zeroreflections which were each ascribed unit weight. The atomic coordinates and isotropicthermal vibration parameters are listed in Table 3 and the lF.o"l -f'",r" data appear inTable 4.1 A ratio of independent data to variable parameters of 30:1, Iow estimated stan-dard errors for the atomic parameters and thermal vibration parameters typical for theirionic species add confidence to the interatomic distances discussed further on.

DnscnrprroN oF THE Srnucrune

Seamanite is certainly a candidate for one of the most exotic of min-eral structures. The Mn-O octahedral arrangement is one of the mostpeculiar and unexpected on record, and we shall discuss it in detail.

Figure 1 features a polyhedral diagram of the octahedral backboneand its surrounding tetrahedral [B(OH)4] and [PO4] l igands, projecteddown the ,r-axis. We isolate the octahedral backbone and show it inFigure 2. It consists of an octahedral face-sharing trimer which jcins toidentical trimers by reflection across shared edges. The resulting chainruns parallel to the prismatic c-axis of the crystal. The face-sharingtrimer is the most peculiar feature of the structure since its arrangementon geometrical grounds utilizing regular octahedra with oxygen atoms

I To obtain a copy of Table 4, order NAPS Documdnt 101519 from National AuxiliaryPublications Service of the A.S.I.S., c/o CCM Information Corporation, 909 ThirdAvenue, New York, New York 10022; remitting $2.00 for microfiche or $5.00 for photo-copies payable to CCMIC-NAPS.

1532 MOORE AND GIIOSE

TABLE 3. SEAIANITE: ATOMIC CO0RDINATES AND ISOtROPIC TEMPERATURE FACTORS.

Gstimlgg g@da4 errors in parentheses refer to the last dieit.)

l4n(I)

},fu'(2)

P

B

o(1) = 6s-

o (2) = oH-

0(3) = oH- (B)

o(a) = sg1s ;

o(s) = 611-131

0(6) = oz- (P)2 -

o(7) = 0- (P)

o (8 ) = 62 -qP ;

x

o . ?7 83 (2 )

.3s07 (r )

. 69 3 r ( 2 )

.o07 2 (r2)

. r+6ls (8)

. 1862 (8 )

. 03ee (e )

- .r-8+6 (8)

" 08r-0 (6)

.7246 (6)

. s042 (8)

.8 l tz(8)

0 .47s8 (1 )

.6406 (r_)

.ssr l2 ( I )

.3146 (6)

.3688 (r+)

.6165 (r+)

trnaa rtr\

. 3027 (4 )

. 27 3e (3 )

. r+9 61 (3)

qRtrq r tr f

.6340 (r+)

z

0 . 2 5 0 0

.s016 (r )

. 25 00

.2500

.25 00

. 2 5 0 0

.2500

.2500

.07r+2 (81

.0648 (7 )

. 2500

.2 500

qt82l

o .s3 (2 )

. s8 (r)

.30 (2 )

.63 (1r)

.e1 (8)

. 80 ( 8 )

1 .01 (e )

. 6e (8 )

L . r 2 ( 7 )

. e1 (6)

. e0 (e)

.e6 (e)

at the vertices would be impossible. The Mn(1)-O octahedron, situatedon a mirror plane, shares two adjacent faces with the Mn(2) -O octahedra'

Closer inspection of octahedral clusters in general reveals that onlythree kinds of topologically and geometrically distinct f ace-sharingtrimers can exist and all three possess the stoichiometry Magrz, where

M is the octahedral center and Q a vertex. Figure 3 features the threetrimers projected down the octahedral edge and arranged to most effec-tively show their point symmetries. One arrangement has point sym-metry 2f m and the other two possess mm2 _sYmnretry. The centro-symmetric arrangement persists in the ('5.1A" fibrous basic ferrous-ferric phosphates, as discussed in detail by Moore (1970). In the seamanitearrangement, the trimer is the least favored geometrically since the gap

between the two free vertices across the mirror plane is only 1.5 A,

referring to a regular octahedral edge of 3.0 A. The third arrangement'which so far has not been found in crystals, is favorable on geometricalgrounds.

This peculiar trimer is apparently stabil ized by the B(OH)4 ligandgroup, since the O(5)-O(5)' tetrahedral ed^ge which bridges the free ver'

t ices is 2.35A. The dilation of cc. *0.8A away from the undistortedoctahedral model is indicative of forced ligancl' ' In seamanite' the

STRUCTURE OF SEAMANITE 1533

OH

t-I

b = l l t

c=0

Ib=Vq

Ott c:0

Lb= lc=0

Frc. 1. Polyhedral diagram of the seamanite atomic arrangement. The octahedralLackbone is stippled and the surrounding P-O and B-O tetrahedra are featured.TheO(1)hydroxyl anion connects to two octahedral backbones related by the inversion operation.

The O(1) position is shown on a black disk. The O(2) hydroxyl anion is situated under the

stippled backbone and is bonded to 2 Mn(2) f Mn(1). Its position is near the symbol "OH."

r^I

b . hIu- t4

Ib = lc = l

F'rc. 2. The octahedral backbone in seamanite. Note the edge-sharing of the octahedralface-sharing trimers which results in the chain running parallel to the c-axis.

b= lc= l

Lb = lc = 0

IJ. '4 MOORE AND GHOSE

mm2 mm2Ftc. 3. The three possible topologically distinct octahedral face-sharing trimers. They areprojected parallel to octahedral edges and oriented to fully show their point symmetry

tr imers share their terminal edges with each other by reflection. Here,the bridging O(6)-0(6)' :2.48 L atoms belong to the [POo] tetrahedraledge. The size difference between the two different tetrahedra must beaccepted as a stabil izins feature for the octahedral chains and, for thisreason, the B and P atoms are ordered in the non-equivalent oxygentetrahedra. The crystal structure analysis suggests that the deviationfrom the 1: 1 B: P ratio found in the seamanite chemical analysis ofKtaus, Seaman,.and Slawson (1930) is largely an analytical error.

Figure 1 reveals that the octahedral backbone is not strictly insularwith respect to other octahedra but is weakly condensed with the sym-metry equivalent chain related by the inversion operation. As shown inFigure 1, the two chains l ink by the O(1) hydroxyl ions toforma band.Individual bands are further joined by the tetrahedral l igand groupswhich also link to similar bands generated by the glide operations toform a three-dimensional array of corner-l inked polyhedra.

Cnvsrar CnBursrnv

Table 5 presents electrostatic valence balances of the cationic chargecontributions to the anions. It is readily apparent that O(1), O(2), O(3),

ST RUCT U R]J OF S EA M A N I'I' E. 1535

O(4), and O(5) are hvdroxyl groups, and O(6) and O(7) are oxide anions.Despite the fact that it is considerably oversaturated with respect tocations, O(4), with 2:1.42, has to be accepted as an hydroxyl anion.Thus, the l igand groups are (OH)-, [B(OH)4], and [POr] and the seaman-ite crystal formula is Mn32+(OH)r[B(OH)4][PO+]. No water moleculesare present either as l igands or as water of hydration and the stoichio-metrically similar formula Mne[BOa][PO4].3HrO is crystallochemicallymeaningless. Seamanite is an interesting example of a coordination com-plex where a neutral acid-[POrl-and a basic fraction-(OH)--arepresent in the same crystal which includes the amphoteric [B(OH)a]group. This would suggest that the compound forms under rather re-stricted pH conditions which, in combination with the mr.rtual presenceof boron, phosphorus, and manganese, may be a contributing factor inthe restricted occunence of the soecies.

INrBnn torrrc DrsrANcES

The relativelv low errors in atomic positions and the unusual octa-hedral clustering in seamanite warrant a detailed discussion of theinteratomic distances. Table 6 l ists Me-O and O-O' distances in order ofincreasing values for each polyhedron. Most interesting are the distancesassociated with O(7) since this anion is considerably over-saturatedelectrostatically with respect to cations and since the anion occurs atthe vertex common to the two Mn(1)-O shared faces. The Mn(1)-O(7):2.11 h is unusually long-in excess of +O.20 A for typical Mn2+-Ooctahedral averages. In addition to its cation oversaturation, theMn(2)=+Mn( 1)e-Mn(2) cation-cation repulsions across the shared face

TABLE 5. SEAIANITE: ELECTROSTATIC VALENCE BAIANCES 0F CATIONS AB0llT ANIONS

o(1) = s6

o(2) = 6Y-

0 (3 ) = 66

o (a) = 611-

0(s) = oH-

0 (6 ) = e2 -

o (7 ) = 62 -

o (8 ) = 62 -

Ifrt(1) +ltr(2) +lftt(2)

lftt (1) +t'ln (2) {+h (2)

r.tl(1)+B

}&r (2) +I,ln (2) +B

r.h(2) +B

ltr (I) +l'h (2) +P

l'h(1) +D'ln(2) +l"tr(2) +P

P

U6+U6+U6

U6+U6+UE

U6+3/4

U6+U6+3/4

z/6+3/4

U6+2/6+s/+

U6+U6+U6+5/4

5/+

xr .00

r .00

r n o

r . 42

l_.09

L . 9 2

1 . 2 5

Ax'+0 .00

+0 .00

+0 .09

+0 .42

+0 .09

-0 .08

+0 . 25

- 0 . 7 5 4

aExclutles the plesence of four BossibLe hydrogen bonds.

1s36 MOORD AND GHOSD

TAIU 6 . SLASNITE: POLYI [ iDmI ]NTt l0 lOMrC DISTANC|So,

( i s t i f ra ted s tandard er ro rs : Mn-o , P-O +o.006 I , B 'o +0 .0r3 8 , o -o +0 .00S 8)

ll

I P - o ( 8 )

? - 0 ( 6 )

r - o ( 7 )

r 0 ( 6 ) - 0 ( 6 ) "

2 0 ( 6 ) - o ( 7 )

r o ( 8 ) - o ( 7 )

2 0 ( 6 ) - o ( 8 )

B

2 B - o ( s )

r - o ( 3 )

r - o ( q )

h ( l )

I n r ( I ) - o ( 3 )

2 - 0 ( 6 ) '

| - 0 ( r )

r - o ( 2 )

r - o ( 7 )

average

u r o l z y - o q ; 1b z o 1 z 1 - o q e l '" 2 o ( 7 ) - 0 ( 6 )

z o 1 : 1 - o 1 o 1 '

2 o ( r ) - 0 ( 6 ) '

I o ( r ) - o ( 7 )

r o ( 2 ) - o ( 3 )

r o ( r ) - 0 ( 3 )

average

h ( r ) - b ( 2 )

m ( 2 ) - u n ( 2 ) " "

h ( 2 ) - h ( 2 ) "

M n ( 2 )

r h ( 2 ) - o ( s ) " '- o ( 2 )- 0 ( 6 )

'

- 0 ( r )- o ( 7 )- o ( c )

'

a v e r a g c

ur o lzy " ' ,o121" r 0 (6) - o (2)' r o q r l ' - o 1 + 1 '" r 0 (7) - 0 (6)r o 1 u 1

' - o 1 s ; " 'r 0 ( r ) ' - 0 ( 6 ) 'r ogs l " ' -o1r1r o ( r ) ' - o ( 5 ) " 'r o ( 2 ) - o ( s ) " 'r o1r ; ' - o loy '

r o ( 1 ) ' - o ( 7 )

r 0(2) - o(4)

1 o ( s )

t o( ' r)

2 O ( 3 )

2 o ( 4 )

- o (s )- o (3)- o(s)- o (s )

1 . 5 1 7 A

r . 5 3 8

r . 5 q 5

r . s : l I

2 . \ 7 9

2 . 5 0 7

2 . 5 L 2

2 . 5 t 7

2 . 5 0 6

l . q q 7

l . q 6 l

1 . 5 0 9

t . q 6 6

2 . 3 5 1

2 . 3 4 7

2 . 3 8 9

2 -qzq

2 . 3 9 4

2 . f f f

2 . 1 5 0

2 . r 5 9

2 . 2 \ q

2 . q 1 1

2 . 2 0 q

2 . 5 3 0

2 . 7 9 6

3 . 0 2 0

3 . L 3 7

3 . 2 7 q

3 . 2 7 6

3 . 3 2 q

3 . 3 s 2

3 . 0 7 8

3 . 0 5 8

3 . 1 2 6

3 . 3 6 9

2 . 1 ' r r l

2 . 1 5 0

2 , 1 8 8

2 . 2 2 2

2 - 2 3 \

2 . 2 7 7

2 . 2 0 3

2 . 5 3 0

2 . 7 9 6

2 . 9 3 9

3 . 0 2 0

3 . C 6 6

3 . O 7 6

3 . 1 6 5

3 . 1 9 9

3 . 2 r 7

3 -252

3 . 4 3 2

3 . 5 6 q

3 . I 0 5

uun(l) - m(z) *a"ed face and h(2) - Mn(Z) " shared edse.

om(r) - m(z) shared face onfy.

"m(z) - w(z) " " $u""a edse onf y.

dSuperscripts reresent swetry equivalent positions of Table 3:

' = - x , - Y , V 2 + z i

' , = x , y , 1 / 2 - " ;

t t t = V 2 - x , V 2 + y , V 2 - z i

t t , , = x , y , 3 / 2 - 2 .

are so profound that the Mn(1)-O(7) distance is affected along with theforeshortening of the octahedral edges associated with the shared faces.The O(2)-O(7) :2.534 edge is common to the two Mn( l ) -O sharedfaces and a shared edge between the Mn(2)-O octahedra. This edge isforeshortened by co. -0.55 A with respect to O-O' averages associatedwith Mn-O octahedra, indicative of particularly violent cation-cationrepulsion effects. As shown in Table 6, all O-O' distances associated withshared edges are among the shortest for their polyhedra. Thus, the un-usual face-sharing trimer cannot be explained solely on the presence ofMn-Mn metallic bonds since the edge distance relationships follow theelectrostatic model. Although a weak metallic bond may be present,distortion of the octahedral clusters conform to a model with predomi-

nant ionic character.As interpreted, the O(4):(OH)- anion is considerably oversaturated

with respect to cations since it coordinates to two Mn-O octahedra and

STRUCTURE AF SEAMANITE

one B atom. Consequently, the Mn(2)-O(a) and B-O(4) distances are

the longest for their polyhedra. This correlation between charge balance

and interatomic distances adds support to the interpretation that O(4)is an hydroxyl group.

But this means that O(S) mav be severely undersaturated with respect

to cations since it coordinates only to the P atom. The P-O(8) distanceis the shortest for the tetrahedron but in addition O(8) potentially re-

ceives four hydrogen bonds. These bonds incl,ude 2 O(8) ' ' 'O(5) 2.7 1,

O(8 ) . . .O (+ ) 2 .73 , and O(8 ) ' ' 'O (2 ) 2 .944 . They may be desc r i bedas two lateral bonds from hydroxyl groups associated with boron atomsrelated by the mirror plane, one bond in the *a direction to an hydroxylgroup and one in the -a direction to a boron hydroxyl group. This net-

work of bonds through the unit cell is shown in Figure 4. Such an

arrangement adds further confidence to the interpretation that O(8) is

an oxide anion whereas O(4) is an hydroxyl anion. Indeed, Baur andRama Rao (1968) have found a similar example in metavauxite,Fe(HzO)e 'Alr(OH)r(HrO)z(POr)2, where one phosphorus oxvgen doesnot coordinate to octahedral cations but receives three hydrogen bondsinstead. In the crystal structure of Nar(HrO)i(PO3OH), Baur and Khan(1970) have found that each of the three tetrahedral oxYgen atoms

receives four hydrogen bonds which, including the P5+ cation, d,efine a

tetragonal pyramid. The range of these bonds are 2.72-3.06A. The

L-lb= | b= |c : o c = l

Frc. 4. The possible O-H' ' ' O(8) bonds in seamanite. The tails of the arrows are

located at the hydroxyl donor and the heads point toward the O(8) acceptol. Heights are

siven in fractional coordinates.

r.).t /

1538 MOORI':, AND GHOSE

polyhedron in seamanite is a highly distorted trigonal bipyramid includ-ing the P5+ cation in the coordination sphere. We have performed athree-dimensional difference synthesis as an attempt to locate hvdrogenatom positions, but the peak heights proved to have litt le physicalmeaning, doubtless arising from the presence of the heavy atoms in thestructure and the feeble contribution of hydrogen atoms to the struc-ture factors.

Acxxowr,nocrlmltls

We thank Dr. George Switzer of the U.S. National Museum for the donation of theseamanite crystals used in this study. one of us (P.B.M.) acknowledges the NSF GA10g32research grant and a Dreyfus Foundation grant for financial support.

Rnlnnrncns

Baun, W. H., Arrt B. Reua Reo (1967) The crystal structure of metavauxite. Notur-wissenschaJtm 21, 561'562.

eNo A. A. Ku,u (1970) On the crystal chemistry of salt hydrates. VI. The crystalstructures of disodium hydrogen orthoarsenate heptahydrate and disodium hydrogenorthophosphate heptahydrate. ,4 cta Crystdlogr. 826, 1584-1596.

BusrNc, W. R., K. O. ManrrN, lNo H. A. Lrw (1962) ORFLS, a Fortran crystallographicleast-squares program. U .5. Oak Riilge Nat,. Lab. (U .5. Cleari.nghouse Fd. Sci. Tech.InJo.) Rep. ORNLTM-30S.

Kneus, E. H., W. A. Snaunx, eNp C. B. Sr,awsor (1930) Seamanite, a new manganesephospho-borate from fron County, Michigan. Amu. MineraJ. lSr 220-225.

MncGrrr,avnv, C. H., axo G. D. Rmcr, EDS. (1962) International Tables Jor X-ro-t.Crystallography, VoL 3,TheKynoch Press, Birmingham, England.

McCoxNnrr., D., exo W L. Poxonou, Jr. (1941) X-ray crystailography of seamanite.Amer. Mineral. 26, MGM7.

Moonr, P. B (1970) Crystal chemistry of the basic iron phosphates. Amer. Mineral. SS,135-169.

M anu,seripl recehed., f anuary 12, 197 I ; accepted for publicolion, M arch 23, 197 1 .