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Terbium triborate, TbB3O6, is confirmed to adopt at least two different structural modifications. Its monoclinic modification represents the terminal member of the isostructural series of REB3O6 with RE = La-Tb, and crystallizes in space group I2/a. The structure consists of chains of [B6O12]n6- building units, that run parallel to the c axis, and tenfold coordinated Tb3+ which link the borate chains to give a three-dimensional framework.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803009553/br6096sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536803009553/br6096Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](O-B) = 0.005 Å
  • R factor = 0.036
  • wR factor = 0.082
  • Data-to-parameter ratio = 33.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

PLATON alerts of the form PLAT_7?? have been detected for an inorganic
structure. These tests are under development  for inorganics and
comments are welcomed. It is not necessary to supply a data
validation response form for these alerts at this time.


Red Alert Alert Level A:
PLAT_702 Alert A Angle Calc 149.01(8), Rep 137.26(16), Dev. 146.88 Sigma O3 -TB1 -O3 3.555 1.555 4.555 PLAT_702 Alert A Angle Calc 82.79(8), Rep 76.68(11), Dev. 76.38 Sigma O3 -TB1 -O2 4.555 1.555 1.555 PLAT_702 Alert A Angle Calc 34.19(8), Rep 54.95(10), Dev. 259.50 Sigma O3 -TB1 -O1 4.555 1.555 5.666 PLAT_702 Alert A Angle Calc 76.24(6), Rep 88.12(10), Dev. 198.00 Sigma O3 -TB1 -O1 4.555 1.555 1.555
4 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
0 Alert Level C = Please check

Comment top

Among the binary rare earth oxoborates of the general composition REB3O6 only the compounds LaB3O6 (Ysker & Hoffmann, 1970; Abdullaev et al., 1981), NdB3O6 (Pakhomov et al., 1972), SmB3O6 and GdB3O6 (Abdullaev et al., 1975) are fully structurally characterized. They form an isostructural series and crystallize in monoclinic space group I2/a. For REB3O6 with RE = Dy—Lu only a somewhat doubtful indication of their existence can be found in the literature (Tananaev et al., 1975). In earlier works on cell parameters of TbB3O6 (Bambauer et al., 1969, Weidelt, 1970), the compound is described as crystallizing with monoclinic symmetry, similar to REB3O6 with RE = La—Gd, while a later structural analysis on single crystals of TbB3O6 reveals an orthorhombic symmetry Pbnm or Pbn21 of the compound (Pakhomov et al., 1971). Very recently the crystal structure of orthorhombic TbB3O6 has been solved by Nikelski & Schleid (2003), the results of our own structure determination of the orthorhombic structure of TbB3O6 are in good agreement with the data of these authors. Orthorhombic TbB3O6 crystallizes with symmetry Pnma (No. 62) and a = 15.9770 (7) Å, b = 7.4136 (3) Å, c = 12.2905 (6) Å and Z = 16.

During our systematic investigations of the crystal chemistry and crystal-growth conditions of binary rare earth borates, methods of synthesis from ternary systems were established that led to single crystals of REB3O6 with RE= La—Tb. Depending on the composition of the ternary system used, orthorhombic as well as monoclinic crystals of TbB3O6 were grown. The crystal structure of the monoclinic modification of TbB3O6 is presented here for the first time. Monoclinic TbB3O6 is isostructural with REB3O6 with RE = La, Nd, Sm and Gd, and crystallizes in space group I2/a (No. 15). The structure consists of infinite chains of [B6O12]n6− running along the c axis. Tenfold coordinated Tb atoms link the borate chains to a three-dimensional framework. The complex borate polyanion (4D2T:D<DTDT>D; Becker, 2001) is composed of [BO4] tetrahedra that are linked via two [BO3] triangles at a time to the adjacent [BO4] tetrahedra on both sides. Each [BO3] is connected to two [BO4], the bridging O atoms belong also to the coordination polyhedron of one Tb. The nonbridging O atoms of the [BO3] groups coordinate two Tb simultaneously, each. The irregular [TbO10] coordination polyhedra are connected via edges to infinite chains along the c axis.

The mean B—O distances of 1.370 Å for [BO3] and of 1.465 Å for [BO4] fit well into the range of B—O distances found for many other borate structures [see, for comparison, Zobetz (1982) and Zobetz (1990)]. However, the [BO3] triangles are substantially distorted with a B—O distance of non-bridging atoms O2 that is significantly shorter than the B—O distances of bridging atoms O1 and O3 (see Table 1).

According to the results of the structure work on TbB3O6, the compound seems to play the role of a transient point within the series of REB3O6 with RE = La—Lu. TbB3O6 shows a structural flexibility that allows to be on one hand the terminal member of the isostructural monoclinic series of REB3O6 with RE = La—Tb, but as well to be probably the starting point of an assumed orthorhombic series for the smaller lanthanides Dy—Lu, that still has to be synthesized.

The found structural variability of TbB3O6 is further corroborated by a structural phase transition at about 143 K that was recently discovered in our group.

Experimental top

Crystals of monoclinic TbB3O6 were grown in the ternary system Tb2O3–B2O3–PbO. A homogenized powder mixture of Tb4O7 (99.9%, Alfa Aesar), H3BO3 (99.8%, Merck) and PbO (99%, Riedel de Haën), in a mol% ratio of 1.1:87.9:11.0, was heated in a covered platinum crucible to 1213 K and subsequently cooled at a rate of about 3.4 K h−1 to 943 K. Transparent single crystals of the title compound were separated from the lead borate flux using hot diluted HCl.

Computing details top

Data collection: MACH3 (Enraf-Nonius, 1993); cell refinement: MACH3; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 2002) and ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Projection of the structure of the title compound along [100]. Tb atoms are shown as red spheres, O atoms as small blue spheres, [BO4] groups (olive) and [BO3] (green) are represented as polyhedra.
[Figure 2] Fig. 2. ORTEPIII projection (Burnett & Johnson, 1996) of the tenfold Tb coordination and the main features of the borate chains of title compound with atom-numbering scheme (projection along [100]). Atoms are shown as 50% probability ellipsoids.
Terbium(III) trioxoborate top
Crystal data top
TbB3O6F(000) = 512
Mr = 287.35Dx = 4.910 Mg m3
Monoclinic, I2/aMo Kα radiation, λ = 0.71073 Å
Hall symbol: -I 2yaCell parameters from 25 reflections
a = 6.2147 (4) Åθ = 12.3–19.1°
b = 8.0225 (5) ŵ = 18.13 mm1
c = 7.8111 (7) ÅT = 293 K
β = 93.44 (1)°Parallelepiped, colourless
V = 388.74 (5) Å30.15 × 0.13 × 0.11 mm
Z = 4
Data collection top
Nonius MACH3
diffractometer
1321 reflections with I > 2σ(I)
Radiation source: fine-focus sealed X-ray tubeRint = 0.094
Graphite monochromatorθmax = 44.9°, θmin = 3.6°
ω/2θ scansh = 1212
Absorption correction: ψ scan
MolEN (Fair, 1990)
k = 1515
Tmin = 0.082, Tmax = 0.136l = 1515
5729 measured reflections3 standard reflections every 60 min
1602 independent reflections intensity decay: 4.5%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.036 w = 1/[σ2(Fo2) + (0.0215P)2 + 2.4096P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.082(Δ/σ)max < 0.001
S = 1.07Δρmax = 2.91 e Å3
1602 reflectionsΔρmin = 2.45 e Å3
48 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0023 (4)
Crystal data top
TbB3O6V = 388.74 (5) Å3
Mr = 287.35Z = 4
Monoclinic, I2/aMo Kα radiation
a = 6.2147 (4) ŵ = 18.13 mm1
b = 8.0225 (5) ÅT = 293 K
c = 7.8111 (7) Å0.15 × 0.13 × 0.11 mm
β = 93.44 (1)°
Data collection top
Nonius MACH3
diffractometer
1321 reflections with I > 2σ(I)
Absorption correction: ψ scan
MolEN (Fair, 1990)
Rint = 0.094
Tmin = 0.082, Tmax = 0.1363 standard reflections every 60 min
5729 measured reflections intensity decay: 4.5%
1602 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.03648 parameters
wR(F2) = 0.0820 restraints
S = 1.07Δρmax = 2.91 e Å3
1602 reflectionsΔρmin = 2.45 e Å3
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Tb10.75000.70532 (4)0.50000.00547 (7)
O10.6011 (4)0.3864 (5)0.3960 (3)0.0095 (4)
O20.6961 (5)0.5921 (4)0.2056 (4)0.0108 (5)
O30.6040 (4)0.3171 (4)0.1002 (4)0.0083 (4)
B10.6367 (6)0.4370 (6)0.2267 (5)0.0060 (5)
B20.75000.2756 (10)0.50000.0093 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Tb10.00585 (8)0.00450 (11)0.00611 (9)0.0000.00080 (5)0.000
O10.0120 (8)0.0101 (13)0.0064 (8)0.0032 (10)0.0008 (7)0.0025 (10)
O20.0148 (9)0.0049 (13)0.0128 (10)0.0034 (9)0.0009 (8)0.0002 (10)
O30.0059 (6)0.0091 (12)0.0102 (9)0.0016 (8)0.0019 (7)0.0060 (9)
B10.0062 (9)0.0051 (15)0.0064 (11)0.0012 (10)0.0009 (9)0.0000 (11)
B20.0065 (14)0.015 (3)0.0069 (17)0.0000.0022 (13)0.000
Geometric parameters (Å, º) top
Tb1—O2i2.323 (3)B1—O21.311 (6)
Tb1—O3ii2.460 (3)B1—O31.385 (5)
Tb1—O22.477 (3)B2—O3iv1.440 (5)
Tb1—O1iii2.485 (3)B2—O3v1.440 (5)
Tb1—O12.823 (4)B2—O1vi1.489 (6)
B1—O11.414 (5)B2—O11.489 (6)
O1iii—Tb1—O1vii145.55 (18)O2—Tb1—O1vii70.14 (9)
O1—Tb1—O1vi50.04 (11)O2i—Tb1—O1140.75 (10)
O2i—Tb1—O2viii91.21 (17)O2viii—Tb1—O1119.57 (10)
O2—Tb1—O2vi136.98 (17)O3ii—Tb1—O1133.89 (10)
O3ii—Tb1—O3ix137.26 (16)O3ix—Tb1—O188.12 (10)
O2i—Tb1—O3ii71.84 (10)O2—Tb1—O151.46 (10)
O2viii—Tb1—O3ii78.57 (11)O2vi—Tb1—O187.63 (10)
O2i—Tb1—O2151.81 (11)O1iii—Tb1—O163.03 (12)
O2viii—Tb1—O268.38 (14)O1vii—Tb1—O185.23 (8)
O3ii—Tb1—O2119.84 (9)O2—B1—O3126.8 (4)
O3ix—Tb1—O276.68 (11)O2—B1—O1116.8 (4)
O2viii—Tb1—O1vii79.36 (11)O3—B1—O1116.3 (4)
O2viii—Tb1—O1iii126.79 (10)O3iv—B2—O3v117.9 (6)
O3ii—Tb1—O1iii142.20 (9)O3iv—B2—O1102.33 (16)
O3ix—Tb1—O1iii54.95 (10)O3v—B2—O1113.77 (17)
O2—Tb1—O1iii97.04 (10)O1vi—B2—O1106.7 (6)
Symmetry codes: (i) x, y+3/2, z+1/2; (ii) x+1/2, y+1/2, z+1/2; (iii) x+1, y+1, z+1; (iv) x, y+1/2, z+1/2; (v) x+3/2, y+1/2, z+1/2; (vi) x+3/2, y, z+1; (vii) x+1/2, y+1, z; (viii) x+3/2, y+3/2, z+1/2; (ix) x, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaTbB3O6
Mr287.35
Crystal system, space groupMonoclinic, I2/a
Temperature (K)293
a, b, c (Å)6.2147 (4), 8.0225 (5), 7.8111 (7)
β (°) 93.44 (1)
V3)388.74 (5)
Z4
Radiation typeMo Kα
µ (mm1)18.13
Crystal size (mm)0.15 × 0.13 × 0.11
Data collection
DiffractometerNonius MACH3
diffractometer
Absorption correctionψ scan
MolEN (Fair, 1990)
Tmin, Tmax0.082, 0.136
No. of measured, independent and
observed [I > 2σ(I)] reflections
5729, 1602, 1321
Rint0.094
(sin θ/λ)max1)0.994
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.036, 0.082, 1.07
No. of reflections1602
No. of parameters48
Δρmax, Δρmin (e Å3)2.91, 2.45

Computer programs: MACH3 (Enraf-Nonius, 1993), MACH3, MolEN (Fair, 1990), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ATOMS (Dowty, 2002) and ORTEPIII (Burnett & Johnson, 1996), SHELXL97.

Selected bond lengths (Å) top
Tb1—O2i2.323 (3)B1—O11.414 (5)
Tb1—O3ii2.460 (3)B1—O21.311 (6)
Tb1—O22.477 (3)B1—O31.385 (5)
Tb1—O1iii2.485 (3)B2—O3iv1.440 (5)
Tb1—O12.823 (4)B2—O11.489 (6)
Symmetry codes: (i) x, y+3/2, z+1/2; (ii) x+1/2, y+1/2, z+1/2; (iii) x+1, y+1, z+1; (iv) x, y+1/2, z+1/2.
 

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