885
The CanadianM bu ral ogi st
Vol.32,pp. 885-894(1994)
KALIBORITE:
BOND
HYDROGEN
SYMMETRICAL
AN EXAMPLEOFA CRYSTALLOGRAPHICALLV
PETER C. BURNS* ANDFRANKC.
HAWTHORNE
Departmentof GeolagicalSciences,Universityof Manitoba Winttipeg,ManitobaRiT 2N2
ABSTRACT
monoclinic,a 18.572(6),b 5.466(3),c 14.639(0 A,
The crystal structue of kaliborite, KMg2H[B6Os(O]Dslz(HzO)e,
B 100.02(3)', V 2274(l) 43, Z = 4, spacegroup AJc,has been refined by full-matrix least-squaresmethodsto an R index
of.4.4Eoand a wR index of 4.7Vofor 2403 unique observedtF > 5o(41 reflections measuredwith MoKcr X-radiation. The
kaliborite structurecontainsa 6iQ + 3Q + A fundamentalbuilding block (FBB).Each FBB containsa pentaborate(24 + 3I)
unit composedof two three-membered(lL + 2T) rings and an additionaltriangle that is attachedto the pentaboraleunit. The
borateFBBspolymerize,forming zigzagchainsalongb. The Mg cation is in octahedralcoordination,andlinked to an adjacent
boratechain.The heteropolyhedralchainsarejoined throughthe K atoms,wtich are in a distortedcubic coordination,and via
hydrogenbonds.Nine of the ten hydrogenatomsprovide bonding betweenthe heteropolyhedralchains,fhe other hydrogen
6le6 iinks anionsof the sameheteropolyhedralchain. Kaliborite is one of two borate mineralsthat axeknowr to contain a
crystallographicallysymmenicalhydrogenbond.
Keywords:hydrogenbonding,kaliborite, bora.te,crystal structue.
Solfttens
monoclinique,a 18.572(6),b3.466(3),c 14.689(5)A,
Ia sfucture cristalline de la kaliborite, KMg2HfB6Os(OII)slz@zO)a,
p 1m.02(3)", V 2274(1) 43,Z = 4, groupe spatial AJc, a 6tAaffin6 pm moindrescarr6sI matrice entibrejusqu'l un rdsidu
R de 4.4Vo(wR = 4.7/o) en utilisant 2403 r6flexions uniquesobserv6es[F > 56(F^)]et mesur6esavec rayonnementMo/(ct.
La structurecontientun bloc structuralfondamental6:QA + 37) + A. Chacunde cesblocs contientune unitd d cinq atomesde
bore (2A + 37) composdede deux anneauxI trois membres(\L + 2I) et un triangle additionnelrattach6i I'unit€ pentaborat6e.
Ces blocs structuralrxfondarnentauxsont polym6risdsen chalnesen ngzag le long de &. l,e cation Mg a une coordinence
octaddrique,et est li6 i une chalnede borate adjacente.ks chaineshdtdropoly6driquessotrt articul6espar les atomesde I(,
qui possddentune coordinencecubiquedifforme, et par desliaisonshydrogbne.Neuf desdix atomesd'hydrogbnecontribuent
et l'autre atome d'hydrogbnelie les anions au sein d'une mOmecha?ne
e h hison entre chalnesh6t6ropoly6driques,
h6t6ropoly6drique.La kaliborite eit un de deux boratescotrnusayant une liaison hydrogdnecristallographiquement
symdhique.
(Iraduit par la R6daction)
Mots-cl6s:liaison hydrogbne,kaliborite, borate,structurecristalline.
using X-ray datarecordedon photogaphic plales,and
they refined the structureto an R index of9.5vo.
Clark & Christ (1977) noted that ttrere are appaoccursin
Kaliborite, KMg2H[B6O3(OH)5]2(H2O)4,
a number of localities, including the salt depositsat rently unusual(i.e., crystallographicallysymmetrical)
Leopoldshall,at Neusflassfurt,and nearAschersleben, hydrogenbonds in the structuresof prepbrazhenskite
Saxony, Germany;in the salt depositsat Mte. andkaliborite, althoughthe precisionof the X-ray data
Sambuco,CalascibettaSicily; at Sallent,Spain;andin collected for these minerals by Rumanovaet al.
the Inder Lake deposits,Kazakhstan.Cotazza& (1972) and Corazza& Sabelli (1966) precludedthe
Sabelli (1966) determinedthe structureof kaliborite location of thesehydrogen atoms. We have recently
verified that there is a crystallographically symmerical hydrogen bond in preobrazhenskite(Burns &
Hawthorne 1994a),and here we report a refinement
* Presentaddress:Deparfinentof Earth Sciences,University of the structureof kaliborite, including a discussionof
the hydrogenbonds.
of Cambridge,Downing Street"CambridgeCB2 3EQ, U.K.
Ir.nnooucnou
886
TTIECANADIAN MINERALOGIST
E;ennnllEvrer,
Srnusrurs REI.NHVIENT
CoilecrtonofX-ray data
Scattering curves for neutral atomsotogether
with anomalous-dispersioncorrections, were
A sample of kaliborite from Kazakhstanwas taken from Cromer & Mann (1968) and Cromer &
obtained from the CanadianMuseum of Nature Liberman (1970), respectively. The Siemens
(samplenumber 53372). A small cleavagefragment SHELXTL PLUS (PC version) system of programs
was mountedon a Nicolet R3m automatedfour-circle was usedthroughoutthis study. The R indices are of
diffractometer.Twenty-two reflectionsover the range the form given in Table 1 and are expressedas
11' < 2e 327o werc centeredusing graphite-mono- percentages.
chromatedMoKo X-radiation. The unit-cell dimenRefinementof the structurewas done in the space
sions(Iable l) were derivedfrom the settinganglesof groupC2/c using the atomic parametersof Corazza&
the twenty-two automatically aligned reflections by Sabelli (1966)asthe startingmodel.Refinementof the
least-squares
lsqhniques.Data were collectedusing atomic positional parametersand isotropic displacethe 0-20 scanmethodwitha2.2o 20 scanrangeanda ment parametersgtve an R rndexof 8.2Vo.Conversion
variable scan-rateranging from 4 to 29.3" 2olmin. A to an anisotropicdisplacementmodel, togetherwith
total of 3642 reflections was measured;the index refinementof all parameters,gavean .Rndex of 5.3Vo.
ranges0 < h < 26, 0 < ft < 11,,-20 S / S 20 were At this stage of the refinement, a three-dimensional
covered,and reflectionsforbidden by the C-centering difference-Fouriermap was calculated,and the posiwere omitted.Two standardreflectionsweremeasured tion of ten hydrogen atoms was determined.Subseevery fifty reflections; no significant changein their quent cycles ofrefinement showedthat the hydrogen
intensitiesoccurredduring datacollection. An empiri- positions were not well-behaved,as indicatedby
cal absorption-correction
basedon 36 psi-scansfor anomalouslyshort O-H bond lengths,a common
eachof 10 reflectionsover the range11o< 20 < 56
featureof hydrogenpositionsrefined usingX-ray data.
was applied, reducing.R(azimuthal)from 2.55 to The "soft" constraintthat O-H distancesshouldbe
2.04Vo.T\e datawere correctedfor Lorentz, polariza- -0.96 A was imposedby adding extra weighted
tion, and backgroundeffects; of tJle3&2 reflections observationalequationsto the least-squares
matrix.
measured,there were 2403 classedas observed Only the O-H distanceis constrained,and each H
tF> so(Dl.
position is free to refine around the oxygen atom.
Neutron-diffractionstudies(i.e., Hamilton & Ibers
Infrared spectroscopy
1968)of structurescontaininghydrogenbondshave
shown that donor-hydrogen bond lengths do vary
A powderedsamplewas preparedby grinding somewhatwith the hydrogen-acceptorbond length.
about 20 mg of kaliborite in an alumina mortar until However, the donor-hydrogenbond lengths obtained
the grain size was generally less than 2 pm. About yia unconstrainedrefinement of X-ray data normally
2 mg of. samplewas mixed with 150 mg of KBr by fall well outsidethe range found using neutron data,
grinding in an alumina mortar. The resulting mixture and this makesthe hydrogenbonding in the structure
was pressedin an evacuateddie into a ll-mm pellet. diffrcult or impossibleto interpret.Neutron-diffraction
A high-resolutioninfrared spectrumwas recordedon a studies of borate minerals are limited owing to
Bomen Michelson 100 Fourier-transforminterfero- extremeabsorptioneffects.Therefore,the most apprometric infrared spectrometer.Frequencymeasure- priate way to obtaininformation on hydrogenbonding
mentswere calibratedintemally againsta He-Ne laser is yic constrainedrefinement of X-ray data, and we
and are accurateto 0.01 cm-l, accordingto the manu- havefound @urns& Hawthorne1993a,b, 1,994b)thtut
facturer.
this approachgives realistic hydrogen-bonding
schemesfor variousborateminerals.Refinementof all
parametersgave a final R index of 4.4Voarld a wR
TABI.E 1. MISCELLANEOUSINFOFMATION FOR KAUBORITE
tndex of.4.7Vo.Models including a refinableweighting
Spacsgrap
C2lc
CrystalShe (mml O.t2x0.16xO.24
schemeof sffucturefactorsand an isotropic extinction
s d!
18.672(6t
Totsl ret.
3842
correctionwere tried, but did not improve the results.
, {A
8.4e6(3)
tF > 6r{Rl
2403
Final atomic positional and equivalentisotropic disc tA
14,68s(6)
FinatR
4.4
placementparametersaregiven in'Iablez, anisotropic
p l"l
100.02(3)
FinetuB
4.7
displacementparametersin Table 3, selectedinterv(4")
2274111
coF.
2.6
atomic distancesand anglesin Table 4, and a bondyalenceanalysisis given in Table 5. Observedand
urdt€ll mntonts 4{KMg2H1B6o6(oHu.{H2ot1}
calculated structure-factorsare available from the
a-t(lr.l -lalrnlr.1
Depository of UnpublishedData, CISTI, National
wR E tEwtlF:l - lF.ll2';wFjlb,
w - ltdllFl
ResearchCouncil of Canada,Ottawa,Ontario K1A
' GOF - Goodness of ft
0s2.
887
TIIE STRUCTURBOF KALIBORITE
TABLE 2. ATOMIC GOOFDINATEAAND EOUIVATENTISOTROPTC
DISPLACEMENTPARAMETERSF(IR KAUBORITE
tu^
K
Mg
Bfil
Bl2t
a3l
B(4)
8(6)
8(6!
o(11
oH(21
o(3)
o(4)
o(5)
0(6)
o(71
o(81
oH(91
oH(10)
oH(l11
oH(12)
oH(13)
ow(14)
ow(l5)
H(1)
H(2)
H(31
H(4)
H(5)
H(6)
H(7)
H(81
l{(9}
H(10)
O
0.13784{5}
0.6005(1)
0.0891(21
o.r'log(lt
O,2A2A|'ll
0.3&t7(1)
0,2399(2)
0.o1341r)
0.0361(11
0.1171(1)
0.37643(9!
0.1658(1)
0.2046(1)
o.2466t1t
0.2991(1)
0.4214(11
o.4278(1t
0.0321(rl
0.2657{1}
0,1710(1)
o.o988(1)
0.3892(11
O
0.,108(31
0.383(11
O.OO3(21
O.207(1t
o.146t2t
O.120t2t
O,O?712t
0.404(3)
0.341(1)
0,1187(1)
0.4234111
0.1473(4)
0.8378(41
0.7s56(3t
0.2025(3)
O.459r(3)
0.4974(41
0.7310(21
O.7340t2t
O.e722l2l
0.3994(21
O,6612(2t
0.6096(2)
0.3461(2)
0.4463(3)
0.1362{2)
0.5920(91
0.488(21
0.9680(4)
0.4836(3)
O.20rr8(3)
0.8767(3)
0.257(8)
0.236(31
0.540(61
O,422Et
0.939(01
0.439(6)
0.101(3)
0.196(6)
0.964(4}
0.861(6)
114
o.16721(6)
o,1077t2t
0.0265(2)
0.1964(2!
o.254612t
o,1s2aQl
0.0236(21
o.o241(1)
o.1889(1)
0.1054(1)
o.22eg(1)
0.2086(1)
0.2380(1)
o.2104(1)
o,o914(11
0.1073(1)
0.0508(1)
o.1126(1)
0.0647(11
o.o41r(11
o.12O4(21
0.2046(1'
314
0.130(3)
0.067(3)
0.008(2)
0.076(3)
-0.0200)
0.123(3)
o.o57(1)
o.172(31
o,'t73(3)
2A2Bl
97(3)
107|7t
t/t|l(8)
S4l7',t
107l7l
8s(7)
173(8)
r63(5)
11J(6)
130(5)
112(5)
116(5'
176(6)
ti7(51
176(6)
146(5)
270t71
152(6)
327|8l
200(6t
230(61
204(0)
564(4S)..
664(48)
664(481
604(4Sl
664(48)
564(48)
564(,18)
564(48)
664(48)
664(48)
' U- = uq x 1d
'i A singleUb was rgfinedtor all H.
TABLE3, ANtsoTRoptc uspr.AcEME\rT pARA[tETEns FoR KAuBoRm 'Ut
U6
us
ub
urz
Uo
K
Ms
B(11
Bt2t
B(3)
B(4)
B(5)
8(6)
o(1)
oH(zt
o(3)
o(4)
o(5t
o(01
ool
o(81
oH(g)
oH(l0)
oH(11)
oH(l2)
oH(l31
own4,
ow(15)
241{5t
87(41
89fi1)
1271121
100(12)
116(13)
79(1tl
150(131
167(9)
so(81
123(8)
87(8!
91(81
116(8,
97(8)
119(81
84(81
261(111
132(9)
162(1O)
123(9t
244(111
228116)
'Ul'Utx ld
252rct
254(61
90(4)
104(4)
13O(13t
93(1tl
181(14) 130(13)
a7|J.2t
94(11)
s9(131 103(12t
g2l12t
97(1r)
263t171 1o0fi31
17719t
103(8t
151(sl
88(8t
151(9)
r10(8'
107(8)
130(81
82(S'
159(91
114(9)
2S1t11l
9r(8)
157(9)
274(11't 114(81
159(9)
182(l0'
403(14!
137(91
r14(91
188(91
676(191 131fiO)
348(13) 117(9)
'| 19(10) 2744.J1!
203(11) 18r(10)
o
-2(31
-r9(rol
-6(11)
-s(10t
-4(rol
7(S!
6021
7r7t
-2AQl
19(7t
36(71
-18(7)
-69(Sl
2A0t
o3(8t
-28(8)
50(41
-8(31
-6(9t
-3(10)
o
-7(3'
-s(lol
-20(11t
14(9l
13(10)
-0(S'
-8(1 1!
-e(7)
o(1ol
12(10)
-16(S)
-14112'
-58(8)
-32(71
-38(7)
4,(6!
5c,1
-1 (6)
-21(71
-18(8)
4{6}
-23(71
-SC7t
s8(10) -19(8)
-30(8t
-30(71
12O(11) -6(8)
11(9) -16{71
-17(9) -96(9t
-16(8)
33(8)
11(0)
12(71
2t7l
3(6)
-30(s)
-20171
-146(rOl
10(7l
-431121
-46(8)
r7(8)
-46(91
TABLS4. S4ECIED INTERATOMTCDIS|TANCE6(AI AND ANGIES (O} FORKAUEilTE
K-ot4la.b
K-OH(I ole,!
K-oW(141p
K-oW(15lr.b
<K-O>
2.e25lA 2,
2.O22et e.
2,SOS(:D x2
2.gA9lA ,a
?-449
B{3I-oH(2}
Ms-Ot6)
Ms-oH(l I I
Mg-OH(1 3l
Mg-OW(141
Mg-OW(18)b
<Mg-o>
2.141(21
2,113,t21
2.OA4Q\
2,O7eel
2,OO2|.21
2.071(31
2.@S
a4l-ol6lb
Bt4l-otob
El4|-or1
<Bl4l-o>
B(1FOfi )d
B(1)-OH€)d
B(ll-oH(9)
Bl1)-oH(l 1l€
<B(1)-O>
1.479141
1.488131
1.472131
1.461(41
1.486
BI2FO(1 '
B(2t-O(3t
B(2)-OHt 10)t
<Be){>
1.372t4'
1.376t3'
't.358t41
e&-ool
6{3t-O{31
B(3)-ol4)s
E43)-0(6)
<B(31-O>
q6)-o(4t
8{81-t)(6t
Bl6Forr)
Bt5'-O{8}
<B|6FO>
1.470€)
1.508(31
t,4t8l3l
r.61 6t3l
1.474
13A8(3t
1.343(4)
L.3s9!3L
1.372
1.r+31(3)
1.46414)
1.49SG)
L192(3L
1.471
B(6)-Ot8)
B{€FOH(I2tt
q6l-oH03)
<qal-o>
1.38213)
1,38fll4l
1.370141
1,308
1.389
Hydrogon bording
oH{2th-H(1}
oH(2)-oH(2)r
1.212Q1
2.421t41
H!l,-OH(2ll
oHelh-Hlil-oHel
1.21217't
173P)
oH(9'-H(21
oHtgl-o(4)
0.95(3)
3.O:+9(3)
H(2)-€(4)
oH(s'-H(2)-o{4t
2.14141
I 6a(41
oH(10t-H(3)
oH(10t-o€)
0.96(3)
[email protected]
H(3)-O(S)
oH{10)-H(3t-OGt
1.73(3)
173(6)
oH(1 1t-Hl4l
oHtl 1t-o(1)j
o.s6(4)
2.7@tsl
H(4)-O(1ti
oH(111-H(4t-Otlt
oHtl2t-H(61
oH(121-O(31
o.s5(31
2.836(31
H(61-O{3)
ofl(12FHt8l-O(3)
1.80(41
166(41
,t.SS(3)
oH(131-Ht8)
oH( t 3FOH(gtk
0.05t3)
2.6€3t3)
H(o)-oH(g)k
oH(13)-Ht6)-OHl9tk
ow(1At-H(7)
ow{14,-o(3}i
owr4)-Hl8l
ow(141-ot1)l
HOt-H(St
o.86(3t
2.849(3)
0.s6e)
2.75713t
1.3S(6)
HO)-Jo(3lr
ow(14)-HO)-O(3I
H(81-O{1tl
ow(141-H(8)-O(1)j
HP)-OW(141-H(SI
1.eel2:l
166(4)
1.98(41
1S7t4l
94Kt
ow(rgl{(s}
owI6,-oH{strn
ow(18)-H(10)
owl1.6l-otlll2l
H(gt-H(lot
o.0B(4t
2.743131
o.s8(3t
3.O14€l
1.81tel
H(91-oH(9lm
OW(l5FHlgl-OH€1fr
Hfol-oH(l2)
orv(l8FHl1oFoHfi 21
H(9FOWrEFHrOI
r .79(41
17414,
z23t3l
13S(4)
104{4)
3.261t.|1 d
3,&2l3l rQ
4.058fi|rc
3.291tal ra
33S7(A ,A
2.g24lgt ,e
4.Oss(3l
3.4{.:l
Of4la.F.K-oHllo,a,b
o(4f€,b.-K-ow(141F
o(4la,b--K-ow(1518.b
OH(i0}€$-K-OW(141,
oH(lob,b-K-ow(1E)a,b
Ow(t4lr-K-ow(l6la,b
Ow(t6l€-K-Ow(161b
<o-K-o>
67.7111 P,
7o.7l1l f,.
86.6(1) 12
6e.O(1),4
7o.1(1) :€
88,0(11 12
86.4(ll
71.e
3.O5e(9)
3.Ol r(3)
2.9S1(3)
2.SS4tgt
2.Sr0(3)
3.074(31
3.Ol 3(3)
2,967131
2.698{3)
2.ga43l
2.916(3)
2.924t31
2.943
Olsl-Ms-of,'
o(51-$4s-OH(11)
o(5)-Ms-oH(131
O(5)-Mg-ow(14)b
Oo)-Mg-OH(l3l
Oo)-Ms-ow(l4|
oo-Mg-ow(l5lb
OH(l1l-Mg-OH(l3)
OH(l1|-MgiOW(l41
oH{l1FMs-ow(i5}b
oH{13t-M€-OW(14)
OW(14)-Mg-ow(l6)b
<o-Mg-O>
g2.o(lI
2.3e4(3)
2.407tst
2.421|31
2.406(3t
2.sill3l
2.389(sl
2.393
oil)d-E(1rcH(2ld'
o(1ld-80)-oH(st
O(1ld-Bl1t-OH(l1le
oH(2ld-B(11-oHl9)
OH(2)d-B(11-oH(1116
OH(S)-B(l)-OH(l1ls
<o-Bll,-o>
[email protected](2)
10s.7t21
112.211
r1o.3(2'
1O7.6121
1O9.1€)
109.0
171t41
'1.76(31
18gt3l
K polyharlrd
o(4la,b--oH(l 0)a.b
o(4F,b..ow04tt
O(4la,b--ow(1618J
OH(1ote"b-Ow(141tr
OHtlo)a,Fow(16F,b
ow(l41&OW(16b.b
ow(1 5la-OW(l 6'b
<o-o>
Mg @tah€dro
o(6)-oot
o(6)-oHll 1)
0(6)-oH(13)
o(6)-ow0 Blb
ol7,-oH(131
oot-owtr4)
oo)-ow(151b
oH(1 'l-OH(13'
oHfltl-owfi4)
oHIl 1t-ow{l6)b
oH(13t-OWt14)
owtl4l-ow{15}b
<o-o>
91.5(1,
go3(1t
90.8(1)
44.4(11
44.8(ll
02,1(ll
31.1lr)
8'1.7(11
e2.3(1}
89.8(11
8o.1(11
0O.O
B(l) @hodro
onld-oHad
o(1)d-oH(91
O(1FOH(11'6
oH(2)d-oH(g)
OH(2ld-oH(11)e
OH(9)-oH(1l|e
<o-o>
888
TI{E CANADIAN MINERAI-OGIST
TABLE4 - (Continued)
DESCRIPTIoN oF TT{ESIRUcTURE
Fundamentalbuilding block
B{a t'laegl€
otl)-o(3)
o(l,-oH(1ott
o(3)-oH(10)t
<o-o>
2.4o213't
2.302t9t
2.403(3)
2.36€
o(1t-B(2)-O(S)
ofi)-Bt2)-oH(10)t
ol3)-g2t-oH(101r
<o-B(21-o>
12r.8Bl
1.t5.0(2)
123.1(3)
t20.0
2.4p4$l
2.txlr (3t
z4a6(3|
2.458t3)
2414t3't
2417t?t
2.413
olf (2FB(3)tl3)
oll(21-AsFo{41€
oH(2FBA)-O{8)
q3FBf3l-o(4lg
o(3)-Bt3l-o(51
ol4h-q3Fo(51
<GB{31-O>
107.qA
107.8121
1ro,8(2t
114.2i'21
105.0(21
110.s(21
109.4
2.3S0(31
2.4r 813)
2,31713)
2.376
o€fb-R4t-ot6lb
o{8}b-q4Fool
o(6lb-B&)-ool
<o-Bt4l-o>
122.ata
121.212t
116,2(21
120.0
2.305€l
2.424131
2.389{S)
2.410t3)
2.407(3)
2.45r(3)
2.&3
o{41-El6t-ot0)
o(41-BI6FOO)
o{41-Bl5)-o(sl
o(01-B{51-ool
0(8)-8(61-O{8)
o0-Bt5)-o(a)
<0-8{61-o>
10s.5(2)
111.7t21
107.ee,
108.9(2)
10s.012)
'|10.1Q)
[email protected]
2.38813)
2.373(3)
2.338(3)
2.3@
o(81-B{6)-OH(12tt
o(81-Bt6)-oHt13t
oHfi2lt-B{6)-OHl13)
<o-Bt0-o>
122.019!.
120.6(31
110.6(21
120-0
The tundamentalbuilding block (FBB) in kaliborite
contains six boron atoms (Fig. l). There are three
IB(O,OH)41teftahedraand thrce [B(O,OII):] hiangles
in the FBB. The B(l)O(OH)3, B(3)O3(OH),and
B(5)O4 tetrahedrahave <B-O> distancesof 1.466,
L.478,and1.471"
A, respectively,
andthe B(2)O2(OI!,
B(4)03, and B(6)0(OH), triangles^have
<B-O>
distancesof 1.369,1.372,and 1.366A, respectively.
These distancesare within the rangestypical of
<t4lB-O>and<t3lB-O>observedin minerals.
T\e FBB contaihs two tlree-memberedrings that
contain two tetrahedraand one triangle (Fig. 1). The
(lA + 2D rings form a pentaborateunit by sharingthe
B(3)O3(OH)tetrahedron.Using the notation of Christ
& Clark (1977), this pentaborateunit may be written
as (2A + 3I). The kaliborite FBB has an additional
[B(O,OH)3]ftiangle that is attachedto the pentaborate
unit via corner-sharing(Frg. 1); thus the FBB may be
written as 6:(2L + 37) + A. Such a FBB has not been
observedin other borate minerals,but the (24, + 3T)
pentaborateunit is quite common. It occurs as an
isolated cluster in the structuresof garrelsite and
ulexite, and it polymerizesto form chainsin the structures of larderellite and probertite, sheetsin the
structureof heidornite. and frameworks in the structuresof the polymorphsof hilgardite.
B€l ffirEdrm
OHEFOBI
OHl2rc(4ls
oHt2Ftsl
o€)-o(4,€
o(31-ot6)
o(4ls-OFl
<o-o>
Bl4) trloigl€
o€)b-ol6,b
o(8)b-oo,
o(8tH)t )
<GO>
B16)tehditd
o(41-0(8)
o(41-ofr)
o{4FOl8)
o{8)-orr)
oi0,-o(8,
oot-ot8l
<GO>
B(8) tddrqlo
o(8!-oH(1at
o(8}-oH(13)
oH(l 2tt-oH( 131
<GO>
6 - r-1A, t-k, zt b - y-x, y-1A, U-zt c - 4, y, y,-zt d e x+ tt, y + y., 4 a rtk, y-'A, 2i | - U-x,1 +1 tA,Vt g - k-x, y + k, :a-z; h - i,i+t,
?tt; I - i.
t-,A-x,y':,7t
l -\,y-1,2t m o x,y+'t,2.
l+1,2+1At l -A,i+1,7:
TABLE6. BON}VALENCE' ANALYSISFORKAUBORM
Ms
Btll
B(21 Bl3)
o(11
0.759 0.997
oH(2)
0.790
o(31
o(41
B(4)
Blsl
8{6}
H(11
H(zt H(3t Ht4l H(5) H(0t H(71 H(8t H(0) Hllol r
0.117*[
0.676
o(61
o(7t
0.321
1.929
1.079 0,779
1.867
1.989
0.721 1.053
oH(91
oH(11)
0.850
0.965
0.960 0.708
o(8)
0.761
oH(10)0.116,1
0.16
o.17
0.881
0.298
2.055
2.@7
't.908
0.60{l
0.987 0.690
o(6t
2,080
0.15
0 . 1I
0.766
0.20
1.974
2.0a!
0.19
0.88
1.036
0.80
1.962
0.3670.784
0H(12)
1.971
0.10 1.941
1.011
oH(131
0.362
owll41 0.108'l
0.369
0.979
0w(15)0.099,1 03@
2.067 3.094 3.020 3.012 2,994 3.067 3,043 1.00
' pa6mEtors from Brown & Alt€matt (1986)
0.80
2.131
0.84 0.86
2.147
0.81 0.90 2.r09
r.00 1.00 1.oo r.00 1.@ 1.00 1.00 1.00 1.@
889
TIIE STRUCTT]REOF KALIBORITE
oH(11)
o(6)
B(4)
/
O(7)
o(1)
It,
OH(1g)
B(6
Be)
o(3)
oH(10)
oH(12)
Flc. 1. The fundamentalbuildins block in kaliborite.
two hydroxyl groupsand four (H2O)groupslocatedat
the cornersof a distortedcube.The <K-O> distanceis
The kaliborite structurecontainsone Mg position. 2.949 L, and individual bond-lengthsrange from
The Mg cation is coordinatedby two oxygen anions, 2.925to2.989A.
two hydroxyl groups, and two (H2O) groups in an
octahedralarrangement.The <Mg-O> distanceis Strucnral connectivity
2.088 A, aad in.iividual Mg-O distancesrangefrom
The borateFBBs polymerizeto form chainsrun2.062to 2.141A. The singlepositionoccupiedby K
in the kaliborite structureis located on a center of ning alongb (Fig.2). The FBBs polymerizeby sharing
symmeu'y.It is coordinatedby two oxygen anions, the 0(6) anion, which links the B(5) tetrahedronof
Mg and K coordinations
Flc. 2. The heteropolyhedralchainsofkaliborite projectedonto (001). Borate tetrahedra
are shadedwith crosses,boratetrianglesare given as solid triangles,and magnesium
octahedraare cross-hatched.
890
THE CANADIAN MINERALOGIST
Flc. 3. The structureof kaliborite projectedonto (010). Boratetetrahedraare shadedwith
crosses,boratetrianglesare given as opentriangles,magnesiumoctahedraare crosshatche4 and potassiumatoms are representedby circles shadedwith a random-dot
pattern.
ore FBB and the B(4) triangle of the next FBB in
the chain. The B(5) tetrahedraand B(4) triangles
alternatealong b, and the rest of the FBB is oriented
such that its long direction is subperpendicularto the
chain. This FBB linkage results in a zigzag chain
(Fte.2).
The MgQu(Q: unspecifiedligand) octahedraattach
to the borale chains,forming heteropolyhedralchains
(Fig. 2). The Mg cation bondsto four anionsthat are
part of the boratechain and to two (HrO) groups.In a
given Mg octahedron,there are two bondsto each of
the adjacentborats FBBs,both of which are members
of the sameborate chain; Mg thus does not provide
any interchainlinkage.
The heteropolyhedralchainsare linked through the
K cation and,via a network of hydrogen bonds (see
below). The K cation bondsto four different adjacent
chains (Fig. 3). The tlilo heteropolyhedral chains
closest to the K position attach through three bonds
each;two involve (II'O) groupsof the Mg octahedron,
the third involves the O(4) anion, which bridges
betweenthe B(3) and B(5) tetrahedraof the same
botate FBB. The K atom also has a bond to two more
distant chains uia the OH(10) anion, which bonds to
the B(2) cation.
Hvpnocmt Bor.nnqc
The hydrogenpositions obtainedyia constrained
least-squares
refinementof the X-ray dataarerealistic
in terms of bond lengthsand angles(Iable 4), as well
as in the bond-valencerequirementsof the donor and
acceptoranions (Table 5). There are ten hydrogen
positionsin kaliborite(table2, Fig.4), nine of which
provide linkagesbetweenthe heteropolyhedralchains.
Of these,six positionsprovide linkagesalong [001],
and three do so along [101]. The other hydrogenatom
links anionsof the sameheteropolyhedralchain along
t010t.
Hydrogenbond*along [00 I ]
Six hydrogen atoms provide linkages along [001]
betweenadjacentheteropolyhedra"l
chains (Fig. 4).
The OH(2) position is sharedbetweenthe B(1) and
B(3) tetrahedra,which contribute 1.55 v.u. toward
the bond-valencerequirementsof the oxygen atom;
thus the donor-hydrogenbond must be considerably
weaker tlan is normally the case(i.e., <<0.8 v.u.).
This requirementis mel as tle H(l) position is on a
2-fold rotation axis, and it bondsto two symmetrically
891
TIIE STRUCTI,]REOF KALIBORITE
ow(14)
t
I
I ql)
3O'
t
I
t
a
ti
).)
Frc. 4. The structue of kaliborite pojected onto (010). Boron atomsare opencircles with shadingin the lower-left comers,
magnesiumatoms are shadedwith parallel lines, potassiumatoms are cross-hatched,oxygen atoms with a regular-dot
patiern,andhydrogenatomsaregiven as small opencircles.Hydrogenbondsareshownasheavysolid anddashedlines.
equivalent OH(2) positions, which occur in adjacent
FBBs. The OH(2)-^H(1)and H(l)-OH(2)i bondlengths areL.2L2Q)A, indicating a very snonghydrogen bond. This crystallographicallysymmetrical
hydrogenbond is consideredfurtherbelow.
The OH(10)andOH(12)anionsarebondedto B(2)
and B(6), respectively.The OH(10)-H(3)...O(8)and
O H ( 1 2 ) - H ( 5 ) . . . O ( 3b
) o n d sb r i d g e a l o n g [ 0 0 i ]
betweenadjacentheteropolyhedralchains (Fig. ).
The O(8) and O(3) anions are bondedto 8(6) and
B(2), respectively,and thus these hydrogenbonds
completean eight-memberedring of B, O and H. The
oH( 10)-H(3)...O(8)and oH( I 2)-H(5)...O(3)bonds
are quite strong,as indicatedby thp faidy short accepL.73(3)and 1.89(3)A, respectively.
tor distances,
The OH(9)-H(2)...O(4)bond is of intermediate
strength,-as indicated by an acceptordistanceof
2.1414)A. ttre bond bridgesadjacentheteropolyhedral chains along [001]; the OH(9) anion bonds to
B(1), and the O(4) anionis sharedbetweenB(3) and
B(5).
The OW(15) anion is the donor of two hydrogen
bonds,eachof which bridgesbet\ileenadjacentheteropolyhedralchainsalong t0011(Fig. 4). The OW(15)
anion bondsto the K and Mg cations.The hydrogenbond acceptoranions belong to different heteropolyhedral chains; OH(9) bonds to B(l), and OH(12)
bondsto 8(6). The OW(15)-H(9)...OH(9)bond is
quite strong,asindicatedby an acceptoranionat a disbond
tanceof 1.79(4)L. The OW(15)-H(10)...OH(12)
is significantly weaker, with an acceptor anion at a
distanceof 2.23(3)L.
892
THE CANADIAN MINERATOGIST
Hydrogm bondingalong [101]
The OH(13)-H(6)...OH(9)
bond bridgesbetween
adjacentheteropolyhedral
chainsalong t10ll (Fig. ).
The OH(13)anionbondsro B(6) and Mg. The OH(9)
anionbondsto B(1), and actsas a donorfor the H(2)
atom and an acceptorfor the H(9) atom. The
OH(13FH(6)...OH(9)bond is slrong,as indicatedby
an acceptordistanceof 1.75(3)A.
The oW( 14)-H(8)...o(1) and oH( 11)-H(4)...o(1)
bondsare orientedalong [101], and bridge between
anions of adjacentheteropolyhedralchains. The
OW(14) anion bondsto Mg and K, and the OH(11)
anionbondsto B(1) and Mg. The O(l) anionis an
acceptorfor both of thesehydrogenbonds.The O(l)
anion bondsto B(1) and B(2), which provide 1.756
v.u. toward its anion bond-valencerequirements,and
the remaining bond-valencerequirementat O(l) is
satisfied by acceptingthe hydrogen bonds. The
ow( I I )-H(4)...o(1) and ow( 14)-H(8)...o(t) bonds
are of intennediatestrength,as indicatedby acceptor
anionsat distancesof 1.86(4)and 1.98(4)A, respectively.
Hydrogenbondingalong [0 I 0]
The OW(14)-H(7)...O(3)bond linls anionsof the
sameheteropolyhedralchain (Fig. 4). The OW(14)
anionbondsto Mg and K, and O(3) bondsto B(2) anct
B(3). The OW(14)-H(7)...O(3)
bondis of intermediate
strength,as indicated by an acceptoranion at a distanceof 1..96(2)
A.
Crystall ographically sym.rne
tri cal hydrogen bond
A tlree-dimensionaldifference-Fouriermap calculated around the vacant H(1) position in kaliborite
showsthe presenceof the H(1) atom(Fig. 5), asthere
is a significant amountof electrondensitybetweenthe
symmetrically equivalent OH(2) positions. However,
the electron density showstwo well-developedmaxima, locaredslighrly off-the oH(2)-oH(2) join, and
separatedby about 0.7 A. This feature indicatesthat
the H(1) positionmay be disorderedoff the trvo-fold
axis.
Severalcycles of refinementwere done with the
H(l) atom displacedoff the two-fold axis to account
for the observedanisotropyof the electrondensity
aroundthe H(1) position.The refinementconverged,
but it did not lower the,it valuesrelative to the refinementsdonewith the H(1) positionfixed on the fwofold axis.The sptt H(1)'and H(l)" positionsrefined
to a separationof 0.7(2) A. Only one of theseH(1)
positionswill be locally occupied.The resulting local
configurationhas a donorat a distanceof Q.8S(12)
A
and an acceptorat a distanceof 1.56(12)A, and the
refinedOH(2)h-H(1)...OH(2)iangleis 165(9)'.
There are two possible explanationsfor the
observedanisotropyin electrondensityat the H(1) site
in kaliborite:(1) the H(1) atom is dynamicallydisorderedbetweenthe H(1)'and H(1)" positions;(2) there
is a local staticorderingof the H(l) atomat the H(1)'
or the H(1)" positions.In the latter case,the refined
OH(2)-H(1) donordistanceof 0.88(12)A hasa bondvalenceof -0.8 v.u. The OH(2) anionalsoreceivesa
total of 1.55v.u. from theB(1) andB(3) posirions,and
sucha local configurationwould result in an excessof
bond valenceat the donor OH(2) anion.In addition, a
significant bond-valencedeficiency will occur at the
acceptorOH(2) anion of the samelocal configuration.
Thesebonding argumentssuggestthat the anisotropy
Crystallographicallysymmslricalhydrogenbonds
are very rare in borate minerals;only two are known
to date. Clark & Christ (1977) reportedthat such
hydrogenbondsmight occur in the structuresofpreobrazhenskiteand kaliborite. Burns & Hawthorne
(1994a)recently verified that a crystallographically
symmetricalhydrogenbond doesoccur in the structure of preobrazhenskite.
The situation in the preobrazhenskitestructureis very similar to that reported
herein the kaliborite structure;the hydrogenatom lies
on a two-fold axis, and it bridgesbetweensymmetrically equivalentanions,eachof which bondsto two
tetrahedrallycoordinatedB atoms. The two B atoms
contribute-1.5 v.u. towmd the bond-valencerequirements of the anion; the rest is provided by the
crystalo$aphically symmetricalhydrogenbond.
The electrondensity associatedwith the symmetrical hydrogen bond in preobrazhenskitewas
examinedin difference-Fouriermaps calculatedwith
the H position vacant.The peakin the electrondensity
ocqurson the two-fold axis, andthereis only onepeak
in that vicinity, althoughthe electrondensityis cleariy Ftc. 5. Difference-Fouriermap of the H(l) position calculatedwith the H(l) positionvacant.Contorr intervalis
anisotropic(seeFig. 4, Burns & Hawthorne1,994a}
0.1elA3.
893
TIIE STRUCTTIREOF KALIBORITE
nr)
v.L
nlq
nl
nntr'
n
-\J.A 1
I
JOUU
3204
3400
(cm')
Frequency
3000
Flc. 6. The infrared spectrumofkaliborite in the principal OH-strerchingregion.
in electron density associatedwith the H(l) site is
attributable to a dynamic disorder of the H atom,
ratler thanlocal static orderingof the H(1) atom at the
H(1)' or H(1)" positions.
relationship of band intensities and band frequencies
reportedby Burns& Hawthorne(1994a).
Infrared spectrum
This work was supported by the Natural Sciences
and Engineering Research Council of Canada via
Operating, Equipment and Infrastructure grants to
FCH. The University of Manitoba supported this
work with a Postgraduate Fellowship to PCB. Reviews
by two anonymous referees, and editorial work by
Drs. R.F. Martin and R.C. Rouse improved the quality
and clarity of the manuscript.
ACKNOWLEDGEMEI{TS
The powderinfrarcd spectrumof kaliborite (Frg. 6)
in the principal OH-stretchingregion shows one
prominentpeak at -3200 cm-r and a broad,poorly
resolvedseriesof peakscenteredat -3400 cm-l, with
severalprominentshouldersto the high-frequencyside
of the envelope.There are ten distinct hydrogenpositions in kaliborite (Table 2), and the spectrumis too
RffunnIcEs
complex to lead to unambiguousidentification of the
positionsof individual bands.
The powder infrared spectrumof preobrazhenskite Bnowrv,I.D. & At-mruarr, D. (1985):Bond-valenceparameters obtained frorn a systematicanalysisof the inor@urns & Hawthorne 1994a)is considerablysimpler
ganic crystal structue database.Acta Crystallogr, B4l,
positions
and
than that of kaliborite, and the band
14+247.
intensitieswere obtained.The lowest-frequencybaud
in the principal OH-stretchingregion in preobrazhen- Buru{s, P.C. & IlewnronrB, F.C. (1993a):Hydrogenbondskite occursat -3200 cm-l, and this was attributedto
ing in colemanite:an X-ray and structure-energystudy.
a crystallographicallysymmetricalhydrogenbond.
Can.Mineral. 31. 297-304.
The kaliborite spectrum also has an intense band
(1993b):Hydrogenbonding in meyer&at -3200 cm-l 1Fig. 6), and this band also may be
hofferite: an X-ray and structure energy study. Cdr.
attributed to the crystallographically symmetrical
Mineral.3l.305-312.
hydrogenbond. The broad envelopein the kaliborite
spectrumpresumably contains contributions from (1994a);Structureandhydrogenbond&the other nine H positions, and thus the band at
ing in preobrazhenskite,a complex heteropolyhedral
-3200 cm-l is relativelv verv intense.in line with the
botate, Can. M ineral. 32. 387-396.
894
T}IE CANADIAN MINERALOGIST
(1994b): Srructureand hydrogen
& boudingin inderborite,a heteropolyhedralsheetsffucture.
Can.M incral. 32. 533-539.
& MANN,J.B. (1968): X-ray scatteringfactors
computedfrom numericalHartree-Fockwave functions.
Acta Crystallogr. LA, 321-324.
Cnnrsr, C.L. & Cr,{R& J.R. (1977): A crystal-chemicalclassification of boratestructureswith emphasison hy&ated
borates.P&ys.Chem.Minerals 2, 59-87.
HawroN, W.C, & IBERS,
J.A. (1968):HydrogenBonding in
Solids.W.A. Benjamin,Inc.,New York
CLAR&J.R. & Crnrsr, C,L. (1,977):Unusualhydrogenbonding in somehydratedboratestructures.Acta Crystallogr.
Rr,:rr4ANovA,
I.M., ReanaNova,Z.P.& Bnov, N.V. (1972):
Crystal structureof preobrazhenskite3MgO.5.582O3.
4.5H2O= Mg3[B11O1a(O]DrHOrl.
Sov.Phys.Dokl. 16,
518-521.
B$.3n2-3n3.
Conez.e,,E. & Segmrr, C. (1966):The crystalstructureof
kalibodte.AttiAccad. Naz Lincei, RC' Cl. Sci. Fis.Mat
Nat.4l.5n-552.
CRoNGR,
D.T. & LnrRMAN,D. (1970): Relativistic calculation of anomalousscatteringfactorsfor X nys. J. Chen.
Phys.53,1891-1898.
ReceivedJanuary 12, 1994, revisedmanuscriptaccepted
April 5, 1994.