Redetermination of clinobaryl­ite, BaBe2Si2O7

Domizio, A.J.D.; Downs, R.T.; Yang, H.

doi:10.1107/S1600536812040457

inorganic compounds

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Volume 68| Part 10| October 2012| Pages i78-i79

https://doi.org/10.1107/S1600536812040457

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Redetermination of clinobarylite, BaBe₂Si₂O₇

Adrien J. Di Domizio,^a ^* Robert T. Downs ^a and Hexiong Yang ^a

^aDepartment of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721-0077, USA
^*Correspondence e-mail: ajdidomizio727@email.arizona.edu

(Received 31 August 2012; accepted 25 September 2012; online 29 September 2012)

Clinobarylite, ideally BaBe₂Si₂O₇ (chemical name barium diberyllium disilicate), is a sorosilicate mineral and dimorphic with barylite. It belongs to a group of compounds characterized by the general formula BaM²⁺₂Si₂O₇, with M²⁺ = Be, Mg, Fe, Mn, Zn, Co, or Cu, among which the Be-, Fe-, and Cu-members have been found in nature. The crystal structure of clinobarylite has been re-examined in this study based on single-crystal X-ray diffraction data collected from a natural sample from the type locality (Khibiny Massif, Kola Peninsula, Russia). The structure of clinobarylite can be considered as a framework of BeO₄ and SiO₄ tetrahedra, with one of the O atoms coordinated to two Be and one Si, one coordinated to two Si, and two O atoms coordinated to one Si and one Be atom. The BeO₄ tetrahedra share corners, forming chains parallel to the c axis, which are interlinked by the Si₂O₇ units oriented parallel to the a axis. The Ba²⁺ cations (site symmetry m..) are in the framework channels and are coordinated by eleven O atoms in form of an irregular polyhedron. The Si—O_br (bridging O atom, at site symmetry m..) bond length, the Si—O_nbr (non-bridging O atoms) bond lengths, and the Si—O—Si angle within the Si₂O₇ unit are in marked contrast to the corresponding values determined in the previous study [Krivovichev et al. (2004 ). N. Jb. Miner. Mh. pp. 373–384].

Related literature

For clinobarylite, see: Chukanov et al. (2003 ); Rastsvetaeva & Chukanov (2003 ); Krivovichev et al. (2004). For clinobarylite-related minerals and compounds, see: Lin et al. (1999 ); Fleet & Liu (2001 ); Kolitsch et al. (2009 ); Yang et al. (2012 ). For general information on applications of clinobarylite-related materials, see: Barry (1970 ); Robinson & Fang (1977 ); Adams & Layland (1996 ); Yao et al. (1998 ); Lu et al. (2000 ); Yamada et al. (2001 ); Ohta et al. (2004 ); Bertaina & Hayn (2006 ); Zvyagin (2006 ); Zheludev et al. (2007 ); Yang et al. (2012).

Experimental

Crystal data

BaBe₂O₇Si₂
M_r = 323.54
Orthorhombic, P m n 2₁
a = 11.6491 (5) Å
b = 4.9175 (2) Å
c = 4.6746 (2) Å
V = 267.78 (2) Å³
Z = 2
Mo Kα radiation
μ = 7.85 mm⁻¹
T = 293 K
0.05 × 0.05 × 0.04 mm

Data collection

Bruker APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2005 ) T_min = 0.695, T_max = 0.744
3929 measured reflections
965 independent reflections
947 reflections with I > 2σ(I)
R_int = 0.020

Refinement

R[F² > 2σ(F²)] = 0.011
wR(F²) = 0.026
S = 1.08
965 reflections
60 parameters
1 restraint
Δρ_max = 0.47 e Å⁻³
Δρ_min = −0.42 e Å⁻³
Absolute structure: Flack (1983 ), 399 Friedel pairs
Flack parameter: 0.502 (12)

Table 1
Selected geometric parameters (Å, °)

Si—O1	1.6065 (13)
Si—O4	1.616 (2)
Si—O2ⁱ	1.6315 (14)
Si—O3	1.6566 (10)

Siⁱⁱ—O3—Si	128.82 (13)
Symmetry codes: (i) $[-x+{\script{3\over 2}}, -y+1, z+{\script{1\over 2}}]$ ; (ii) -x+1, y, z.

Data collection: APEX2 (Bruker, 2004 ); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks I, New_Global_Publ_Block. DOI: https://doi.org/10.1107/S1600536812040457/wm2678sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536812040457/wm2678Isup2.hkl

checkCIF report

Comment top

Clinobarylite, ideally BaBe₂Si₂O₇, is a sorosilicate mineral and dimorphic with the mineral barylite (Chukanov et al., 2003). It belongs to a group of compounds characterized by the general formula BaM²⁺₂Si₂O₇, with M²⁺ = Be, Mg, Fe, Mn, Zn, Co, or Cu (Yang et al., 2012). In addition to the Be-member, the Fe- and Cu-members of this group have also been found in nature, and are known as andrémeyerite and scottyite, respectively. The BaM₂Si₂O₇ compounds have been the subject of numerous investigations for scientific and industrial interests. For example, the materials with M = Be, Mg, and Zn are suitable hosts for luminescent activating ions. In particular, Pb²⁺-doped BaBe₂Si₂O₇ is used commercially as an UV-emitting material in moth-killing lamps and (Eu²⁺/Mn²⁺)-doped BaMg₂Si₂O₇ is a deep-red luminescent emitter through effective energy transfers from Eu²⁺ to Mn²⁺ (Barry, 1970; Yao et al., 1998). Moreover, the compounds with M = Cu, Co, and Mn are ideal prototypical quasi-one-dimensional quantum spin (S = 1/2, 3/2, and 5/2, respectively) Heisenberg antiferromagnets with adjustable superexchange interactions, vital for our understanding of high-Tc superconductivity (e.g., Adams & Layland, 1996; Lu et al., 2000; Yamada et al., 2001; Ohta et al., 2004; Bertaina & Hayn, 2006; Zvyagin, 2006; Zheludev et al., 2007).

Clinobarylite was first described by Chukanov et al. (2003) as monoclinic with space group Pm and unit-cell parameters a = 11.618 (3), b = 4.904 (1), c = 4.655 (1) Å, β = 89.92 (2)°. Its structure was subsequently determined by Rastsvetaeva & Chukanov (2003), yielding a reliability factor R = 0.052 with isotropic displacement parameters for all atoms. However, Krivovichev et al. (2004) examined the monoclinic structure reported by Rastsvetaeva & Chukanov (2003) and noted that a shift of 0.0088 Å along b in all the atomic positions would result in a change of symmetry from monoclinic Pm to orthorhombic Pmn2₁. They subsequently collected single-crystal X-ray diffraction data from a new sample, and found that systematic intensity absences were consistent with space group Pmn2₁ and a racemic twinning model (R1 = 0.030). Yet, they were unable to obtain positive definite anisotropic displacement parameters for Be and O atoms, and attributed that to the effect of the dominant Ba scattering factor. The resulting geometric parameters, such as bond lengths and angles, matched those obtained from the Pm structural model determined by Rastsvetaeva & Chukanov (2003). An examination of the clinobarylite structure reported by Krivovichev et al. (2004), nevertheless, reveals a rather peculiar feature: The Si—O_br (bridging O atom) distance (1.597 Å) is significantly shorter than the Si—O_nbr (non-bridging O atoms) distances (1.619–1.631 Å). This contradicts the previous observations specifically for disilicate compounds (e.g., Lin et al., 1999; Fleet & Liu, 2001; Kolitsch et al., 2009), including all other compounds in the BaM²⁺₂Si₂O₇ group (Yang et al., 2012). The present study was conducted to clarify this controversy.

The crystal structure of clinobarylite is based on a framework of SiO₄ and BeO₄ tetrahedra, with one of the O atoms (O2) coordinated to two Be and one Si, one (O3) coordinated to two Si, and two O atoms (O1, O4) coordinated to one Si and one Be. The BeO₄ tetrahedra share corners to form chains parallel to the c axis, which are interlinked by the Si₂O₇ units oriented parallel to the a axis. The Ba²⁺ cations are situated in the framework channels and are coordinated in form of irregular polyhedra by eleven O atoms if Ba—O distances < 3.4 Å are considered as relevant (Figs. 1, 2). The average Si—O, Be—O, and Ba—O bond lengths in clinobarylite are 1.630, 1.941, and 2.825 Å, respectively. Our study confirmed the space group Pmn2₁ for clinobarylite, as determined by Krivovichev et al. (2004), but revealed different bond length from those given by Krivovichev et al. (2004): The Si—O_br bond length [1.6566 (10) Å] is, in fact, substantially longer than the Si—O_nbr bond lengths [1.6065 (13) - 1.6315 (14) Å], in marked contrast to the corresponding values of 1.597 (4) Å, 1.619 (6)–1.631 (7) Å as reported by Krivovichev et al. (2004). Moreover, the Si—O_br—Si angle within the Si₂O₇ disilicate unit from our study is 128.82 (13)°, in contrast to 138.5° (Krivovichev et al., 2004).

The Raman spectrum of clinobarylite is plotted in Fig. 3, along with that of barylite (R060620 from the RRUFF Project) for comparison. Evidently, the two Raman spectra are quite similar. In general, they can be divided into four regions. Region 1, between 800 and 1100 cm^-1, contains bands attributable to the Si—O symmetric and anti-symmetric stretching vibrations (ν₁ and ν₃ modes) within the SiO₄ tetrahedra. Region 2, between 660 and 700 cm^-1, includes bands resulting from the Si—O_br—Si bending vibrations within the Si₂O₇ tetrahedral dimers. Major bands in region 3, ranging from 420 to 660 cm^-1, are ascribed to the O—Si—O symmetric and anti-symmetric bending vibrations (ν₂ and ν₄ modes) within the SiO₄ tetrahedra. The bands in region 4, below 420 cm^-1, are mainly associated with the rotational and translational modes of SiO₄ tetrahedra, as well as the Be—O interactions and lattice vibrational modes.

One of the noticeable features in Fig. 3 is that the wavenumbers of the bands due to the Si—O_br—Si bending mode for barylite and clinobarylite are nearly identical (~685 cm^-1), indicating that the Si—O_br bond lengths and the Si—O_br—Si angles in these two minerals are rather comparable. This is indeed the case. The Si—O_br distance and the Si—O_br—Si angle are 1.657 Å and 128.59°, respectively, in barylite (Robinson & Fang, 1977), and 1.6566 (10) Å and 128.82 (13)° in clinobarylite.

Related literature top

For clinobarylite, see: Chukanov et al. (2003); Rastsvetaeva & Chukanov (2003); Krivovichev et al. (2004). For clinobarylite-related minerals and compounds, see: Lin et al. (1999); Fleet & Liu (2001); Kolitsch et al. (2009); Yang et al. (2012). For general information on applications of clinobarylite-related materials, see: Barry (1970); Robinson & Fang (1977); Adams & Layland (1996); Yao et al. (1998); Lu et al. (2000); Yamada et al. (2001); Ohta et al. (2004); Bertaina & Hayn (2006); Zvyagin (2006); Zheludev et al. (2007); Yang et al. (2012).

Experimental top

The clinobarylite sample used in this study is from the type locality Yukspor Mountain, Khibiny Massif, Kola Peninsula, Russia, and is in the collection of the RRUFF project (deposition, http://rruff.info/ R060606). The chemical composition of the sample was analyzed with a CAMECA SX50 electron microprobe. The average composition (12 analysis points) is (%_wt) BaO 47.5 (2), SiO₂ 37.0 (2), TiO₂ 0.19 (2), and BeO 15.3 (estimated by the difference from 100%). The empirical chemical formula, calculated on the basis of 7 O atoms, is Ba_1.0Be_2.0Si_2.0O₇.

The Raman spectrum of clinobarylite was collected from a randomly oriented crystal at 100% power on a Thermo Almega microRaman system, using a solid-state laser with a wavelength of 532 nm, and a thermoelectrically cooled CCD detector. The laser is partially polarized with 4 cm^-1 resolution and a spot size of 1 µm.

Structure description top

For clinobarylite, see: Chukanov et al. (2003); Rastsvetaeva & Chukanov (2003); Krivovichev et al. (2004). For clinobarylite-related minerals and compounds, see: Lin et al. (1999); Fleet & Liu (2001); Kolitsch et al. (2009); Yang et al. (2012). For general information on applications of clinobarylite-related materials, see: Barry (1970); Robinson & Fang (1977); Adams & Layland (1996); Yao et al. (1998); Lu et al. (2000); Yamada et al. (2001); Ohta et al. (2004); Bertaina & Hayn (2006); Zvyagin (2006); Zheludev et al. (2007); Yang et al. (2012).

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. Crystal structure of clinobarylite. The gray spheres represent Ba atoms. The yellow and purple tetrahedra represent BeO₄ and SiO₄ groups, respectively.
	Fig. 2. Atoms in clinobarylite with corresponding ellipsoids at the 99.9% probability level. The gray, yellow, green, and red ellipsoids represent Ba, Be, Si, and O atoms, respectively.
	Fig. 3. Raman Spectrum of clinobarylite, along with that of barylite for comparison. The spectra are shown with vertical offset for more clarity.

Barium diberyllium disilicate top

Crystal data top

BaBe₂O₇Si₂	F(000) = 296
M_r = 323.54	D_x = 4.013 Mg m⁻³
Orthorhombic, Pmn2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac -2	Cell parameters from 3074 reflections
a = 11.6491 (5) Å	θ = 3.5–32.6°
b = 4.9175 (2) Å	µ = 7.85 mm⁻¹
c = 4.6746 (2) Å	T = 293 K
V = 267.78 (2) Å³	Cuboid, colourless
Z = 2	0.05 × 0.05 × 0.04 mm

Data collection top

Bruker APEXII CCD area-detector diffractometer	965 independent reflections
Radiation source: fine-focus sealed tube	947 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.020
φ and ω scan	θ_max = 32.6°, θ_min = 3.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 2005)	h = −17→16
T_min = 0.695, T_max = 0.744	k = −7→7
3929 measured reflections	l = −6→7

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0139P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.011	(Δ/σ)_max < 0.001
wR(F²) = 0.026	Δρ_max = 0.47 e Å⁻³
S = 1.08	Δρ_min = −0.42 e Å⁻³
965 reflections	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
60 parameters	Extinction coefficient: 0.0160 (9)
1 restraint	Absolute structure: Flack (1983), 399 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.502 (12)

Crystal data top

BaBe₂O₇Si₂	V = 267.78 (2) Å³
M_r = 323.54	Z = 2
Orthorhombic, Pmn2₁	Mo Kα radiation
a = 11.6491 (5) Å	µ = 7.85 mm⁻¹
b = 4.9175 (2) Å	T = 293 K
c = 4.6746 (2) Å	0.05 × 0.05 × 0.04 mm

Data collection top

Bruker APEXII CCD area-detector diffractometer	965 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2005)	947 reflections with I > 2σ(I)
T_min = 0.695, T_max = 0.744	R_int = 0.020
3929 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.011	1 restraint
wR(F²) = 0.026	Δρ_max = 0.47 e Å⁻³
S = 1.08	Δρ_min = −0.42 e Å⁻³
965 reflections	Absolute structure: Flack (1983), 399 Friedel pairs
60 parameters	Absolute structure parameter: 0.502 (12)

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

	x	y	z	U_iso*/U_eq
Ba	0.5000	0.20316 (2)	0.5905	0.00932 (5)
Be	0.75108 (15)	0.1693 (4)	0.0849 (14)	0.0070 (4)
Si	0.62826 (4)	0.67528 (8)	0.0692 (2)	0.00526 (12)
O1	0.63895 (10)	0.3560 (2)	0.1367 (3)	0.0073 (3)
O2	0.77699 (10)	0.1340 (2)	−0.2702 (3)	0.0066 (2)
O3	0.5000	0.7764 (3)	0.1793 (5)	0.0077 (3)
O4	0.63272 (12)	0.7295 (2)	−0.2716 (3)	0.0082 (2)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ba	0.01102 (6)	0.00872 (6)	0.00823 (7)	0.000	0.000	0.00004 (8)
Be	0.0052 (7)	0.0071 (7)	0.0087 (10)	−0.0001 (5)	−0.0020 (17)	0.0017 (18)
Si	0.00460 (16)	0.00420 (14)	0.0070 (3)	−0.00035 (10)	0.0000 (3)	−0.0001 (2)
O1	0.0077 (4)	0.0055 (4)	0.0088 (10)	0.0007 (3)	0.0022 (4)	0.0011 (4)
O2	0.0079 (5)	0.0051 (4)	0.0067 (6)	−0.0008 (4)	0.0007 (4)	0.0003 (4)
O3	0.0045 (7)	0.0082 (7)	0.0103 (9)	0.000	0.000	−0.0024 (6)
O4	0.0075 (6)	0.0109 (5)	0.0064 (7)	−0.0016 (4)	−0.0007 (5)	0.0000 (4)

Geometric parameters (Å, º) top

Ba—O1ⁱ	2.7721 (13)	Ba—O2^vi	3.3093 (12)
Ba—O1	2.7721 (13)	Be—O4^vii	1.591 (3)
Ba—O3ⁱⁱ	2.8459 (18)	Be—O1	1.615 (2)
Ba—O4ⁱⁱⁱ	2.8689 (13)	Be—O2^viii	1.670 (4)
Ba—O4^iv	2.8689 (13)	Be—O2	1.696 (7)
Ba—O4^v	3.0831 (12)	Si—O1	1.6065 (13)
Ba—O4^vi	3.0831 (12)	Si—O4	1.616 (2)
Ba—O1^v	3.1151 (14)	Si—O2^vii	1.6315 (14)
Ba—O1^vi	3.1151 (14)	Si—O3	1.6566 (10)
Ba—O2^v	3.3093 (12)

O4^vii—Be—O1	116.6 (2)	O1—Si—O2^vii	114.78 (8)
O4^vii—Be—O2^viii	106.0 (3)	O4—Si—O2^vii	109.70 (8)
O1—Be—O2^viii	106.8 (2)	O1—Si—O3	107.59 (8)
O4^vii—Be—O2	107.1 (2)	O4—Si—O3	106.60 (10)
O1—Be—O2	110.4 (3)	O2^vii—Si—O3	107.14 (8)
O2^viii—Be—O2	109.90 (19)	Siⁱ—O3—Si	128.82 (13)
O1—Si—O4	110.64 (8)

Symmetry codes: (i) −x+1, y, z; (ii) x, y−1, z; (iii) −x+1, y−1, z+1; (iv) x, y−1, z+1; (v) x, y, z+1; (vi) −x+1, y, z+1; (vii) −x+3/2, −y+1, z+1/2; (viii) −x+3/2, −y, z+1/2.

Experimental details

Crystal data
Chemical formula	BaBe₂O₇Si₂
M_r	323.54
Crystal system, space group	Orthorhombic, Pmn2₁
Temperature (K)	293
a, b, c (Å)	11.6491 (5), 4.9175 (2), 4.6746 (2)
V (Å³)	267.78 (2)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	7.85
Crystal size (mm)	0.05 × 0.05 × 0.04

Data collection
Diffractometer	Bruker APEXII CCD area-detector
Absorption correction	Multi-scan (SADABS; Sheldrick, 2005)
T_min, T_max	0.695, 0.744
No. of measured, independent and observed [I > 2σ(I)] reflections	3929, 965, 947
R_int	0.020
(sin θ/λ)_max (Å⁻¹)	0.758

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.011, 0.026, 1.08
No. of reflections	965
No. of parameters	60
No. of restraints	1
Δρ_max, Δρ_min (e Å⁻³)	0.47, −0.42
Absolute structure	Flack (1983), 399 Friedel pairs
Absolute structure parameter	0.502 (12)

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XtalDraw (Downs & Hall-Wallace, 2003), publCIF (Westrip, 2010).

Selected geometric parameters (Å, º) top

Si—O1	1.6065 (13)	Si—O2ⁱ	1.6315 (14)
Si—O4	1.616 (2)	Si—O3	1.6566 (10)

Siⁱⁱ—O3—Si	128.82 (13)

Symmetry codes: (i) −x+3/2, −y+1, z+1/2; (ii) −x+1, y, z.

Acknowledgements

We gratefully acknowledge support of this study by the Arizona Science Foundation.

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