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The structure of Ba2CoSi2O7 consists of layers made from corner-sharing of [SiO4] and [CoO4] polyhedra. These layers, lying parallel to (001), are linked by Ba...O interactions. Co2+ forms flattened CoO4 tetrahedra (point symmetry \overline 4), which are isolated in the structure. The blue color of the solid might be explained by the coordination mode of the Co atoms.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803006329/br6091sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536803006329/br6091Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](Si-O) = 0.006 Å
  • R factor = 0.025
  • wR factor = 0.064
  • Data-to-parameter ratio = 16.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Amber Alert Alert Level B:
PLAT_213 Alert B Atom O1 has ADP max/min Ratio ........... 4.40 prolate General Notes
REFLT_03 From the CIF: _diffrn_reflns_theta_max 30.48 From the CIF: _reflns_number_total 575 Count of symmetry unique reflns 359 Completeness (_total/calc) 160.17% TEST3: Check Friedels for noncentro structure Estimate of Friedel pairs measured 216 Fraction of Friedel pairs measured 0.602 Are heavy atom types Z>Si present yes Please check that the estimate of the number of Friedel pairs is correct. If it is not, please give the correct count in the _publ_section_exptl_refinement section of the submitted CIF.
0 Alert Level A = Potentially serious problem
1 Alert Level B = Potential problem
0 Alert Level C = Please check

Comment top

In the mixed-silicate system MO–TO–SiO2, where M is an alkaline earth metal and T is a divalent 3 d metal atom, many compounds of type (M,T)3Si2O7 have been reported in the literature: Ca2CoSi2O7 (Kimata, 1982, 1983; Hagiya et al.. 1993), Ca2.33Mn0.67Si2O7 (Kimata, 1989), Ca2ZnSi2O7 (Warren et al., 1930; Louisnathan 1969), Sr2CuSi2O7 (Tovar et al., 1998), BaCo2Si2O7 (Adams et al., 1993), Ba2CoSi2O7 (Adams et al., 1996), Ba2CuSi2O7 (Malinovskii, 1984), BaCu2Si2O7 (Janczak et al., 1990), BaZn2Si2O7 (Lin et al., 1999). Adams et al. (1996) did not mention any structure transformation when they reported the monoclinic form Ba2CoSi2O7. The present paper deals with a new tetragonal form of this mixed silicate, which is isostructutral with Ca2MSi2O7 (M = Co and Zn). Crystals of the new phase were obtained quite by chance during the melting of a phosphate powder in a crucible made of quartz. The structure of Ba2CoSi2O7 can de described as a two-dimensional framework of [SiO4] and [CoO4] tetrahedra sharing corners. These layers, lying parallel to the (001) plane at around x = 1/2, are interconnected by barium ions, as shown in Fig. 1. Alternatively, the structure can be described as being composed of BaO8 polyhedra sharing edges and faces to form a sheet. These Ba sheets share corners with Si2O7 moieties to delimit tunnels, parallel to [001], which contain Co2+ cations. Fig. 2 depicts the projection of the structure on to the ab plane.

Co2+ forms flattened CoO4 tetrahedra (point symmetry 4), the four apices of the tetrahedron belonging to four Si2O7-4 groups, as shown on Fig. 3. The average Co—O distance of 1.964 Å which can be compared with the value of 1.926 Å in Ca2CoSi2O7. Co2+ polyhedra are isolated in the structure, the shortest Co···Co distance is 5.778 Å, larger than that reported in Ca2CoSi2O7 (5.015 Å; Kimata, 1982). The blue colour is a consequence of the geometry of Co2+. In general, for many compounds containing this metal in the 2+ oxidation state, the rose color points to an octahedral conformation, while a blue color indicates tetrahedral geometry.

Ba+2 occupies an eight-coordinated site. The average Ba···O distance is 2.763 Å, a value close to the value of 2.814 Å reported for Ba2CuSi2O7, but it is shorter than the value of 2.927 Å in monoclinic Ba2CoSi2O7. Such a value is also reported for phosphates like Ba2Ni(PO4)2 (2.765 Å; El Bali et al., 1994).

Tetrahedral Si4+ in two neighbouring SiO4 units share O1 to form the pyrosilicate [Si2O7]4- group. Si—O distances range from 1.592 to 1.664 Å, with an average of 1.633 Å, similar to other mixed pyrosilicates; e.g. 1.636 Å in Ca2ZnSi2O7 and 1.628 Å in Ba2CuSi2O7. Si2O7 can be also characterized by its almost eclipsed conformation and the bridging angle ϕ(Si,O,Si) of 142.8 (5)°, a value close to those reported in the homologous phases; e.g. 142.2° in monoclinic Ba2CoSi2O7, 142° in Ba2CuSi2O7 and 141.5° in Ba2ZnSi2O7. Fig. 4 shows a fragment of Ba2CoSi2O7 with the atomic connectivity.

Experimental top

A mixture of BaCO3, CoCO3 and (NH4)2HPO4, in a 2:1:2 molar ratio, was ground and heated progressively to 1173 K. The resulting powder was then melted at 1423 K in a crucible made of quartz. Two materials were obtained, viz. blue crystals of the title compound and an unknown amorphous substance.

Computing details top

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty,1999); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Perspective view of the crystal structure of Ba2CoSi2O7. Dashed yellow polyhedra [Si2O7], dashed blue polyhedra [CoO4] and grey balls Ba+2.
[Figure 2] Fig. 2. Projection of the structure on to the ab plane. Blue polyhedra [BaO8], yellow polyhedra [Si2O7] and pink ball Co2+.
[Figure 3] Fig. 3. Coordination of Co2+ in Ba2CoSi2O7. Colors as in Fig. 2.
[Figure 4] Fig. 4. Perspective view of a fragment of Ba2CoSi2O7, showing the atomic connectivity, with the atom labeling. Displacement ellipsoids are drawn at 50% probability levels. Symmetry codes for equivalent atoms: (i) x - 1, y, z; (ii) x, y, z - 1; (iii) 1 - x, -y, z; (iv) 1 - x, -y, z - 1; (v) y, 1 - x, -z; (vi) y, 1 - x, 1 - z; (vii) -y, x - 1, 1 - z; (viii) x - 0.5, -y + 0.5, 1 - z; (ix) y + 0.5, x - 0.5, z; (x) y + 0.5, x - 0.5, z - 1.
Barium cobalt disilicate top
Crystal data top
Ba2CoSi2O7Dx = 4.677 Mg m3
Mr = 501.79Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P421mCell parameters from 922 reflections
Hall symbol: P -4 2abθ = 3.6–30.3°
a = 8.1709 (7) ŵ = 13.56 mm1
c = 5.3374 (7) ÅT = 293 K
V = 356.34 (6) Å3Prism, intense blue
Z = 20.13 × 0.05 × 0.05 mm
F(000) = 446
Data collection top
Bruker SMART CCD area-detector
diffractometer
575 independent reflections
Radiation source: fine-focus sealed tube536 reflections with I > \2s(I)
Graphite monochromatorRint = 0.026
ω scansθmax = 30.5°, θmin = 3.5°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 116
Tmin = 0.392, Tmax = 0.522k = 811
1383 measured reflectionsl = 77
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)] = 0.025 w = 1/[σ2(Fo2) + (0.0223P)2 + 0.683P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.064(Δ/σ)max < 0.001
S = 1.18Δρmax = 1.04 e Å3
575 reflectionsΔρmin = 0.87 e Å3
34 parametersAbsolute structure: Flack (1983), 0000 Friedel pairs
0 restraintsAbsolute structure parameter: 0.12 (7)
Crystal data top
Ba2CoSi2O7Z = 2
Mr = 501.79Mo Kα radiation
Tetragonal, P421mµ = 13.56 mm1
a = 8.1709 (7) ÅT = 293 K
c = 5.3374 (7) Å0.13 × 0.05 × 0.05 mm
V = 356.34 (6) Å3
Data collection top
Bruker SMART CCD area-detector
diffractometer
575 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
536 reflections with I > \2s(I)
Tmin = 0.392, Tmax = 0.522Rint = 0.026
1383 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0250 restraints
wR(F2) = 0.064Δρmax = 1.04 e Å3
S = 1.18Δρmin = 0.87 e Å3
575 reflectionsAbsolute structure: Flack (1983), 0000 Friedel pairs
34 parametersAbsolute structure parameter: 0.12 (7)
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
Ba10.33427 (4)0.16573 (4)0.00875 (10)0.01252 (14)
Co10.00000.00000.50000.0087 (3)
Si10.63650 (18)0.13650 (18)0.5426 (4)0.0060 (4)
O10.50000.00000.6421 (15)0.0090 (16)
O20.8056 (5)0.0780 (5)0.6806 (8)0.0094 (9)
O30.6393 (6)0.1393 (6)0.2445 (11)0.0130 (13)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ba10.01256 (16)0.01256 (16)0.0124 (2)0.00251 (16)0.00097 (16)0.00097 (16)
Co10.0068 (4)0.0068 (4)0.0126 (7)0.0000.0000.000
Si10.0060 (5)0.0060 (5)0.0060 (11)0.0012 (7)0.0006 (5)0.0006 (5)
O10.013 (3)0.013 (3)0.001 (4)0.006 (4)0.0000.000
O20.006 (2)0.011 (2)0.011 (2)0.0016 (17)0.0021 (17)0.0017 (16)
O30.017 (2)0.017 (2)0.006 (3)0.006 (3)0.0017 (16)0.0017 (16)
Geometric parameters (Å, º) top
Ba1—O3i2.628 (6)Si1—O31.592 (6)
Ba1—O2ii2.681 (4)Si1—O2x1.637 (5)
Ba1—O2iii2.681 (4)Si1—O21.637 (5)
Ba1—O1iv2.738 (6)Si1—O11.664 (3)
Ba1—O32.800 (5)O1—Si1v1.664 (3)
Ba1—O3v2.800 (5)O1—Ba1xi2.738 (6)
Ba1—O2vi2.888 (4)O1—Ba1xii2.738 (6)
Ba1—O2vii2.888 (4)O2—Co1xiii1.964 (4)
Co1—O2viii1.964 (4)O2—Ba1xiv2.681 (4)
Co1—O2v1.964 (4)O2—Ba1xi2.888 (4)
Co1—O2iii1.964 (4)O3—Ba1xv2.628 (6)
Co1—O2ix1.964 (4)O3—Ba1v2.800 (5)
O3i—Ba1—O2ii77.97 (15)O2viii—Co1—O2iii121.2 (3)
O3i—Ba1—O2iii77.97 (15)O2v—Co1—O2iii103.93 (12)
O2ii—Ba1—O2iii58.74 (19)O2viii—Co1—O2ix103.93 (12)
O3i—Ba1—O1iv103.42 (17)O2v—Co1—O2ix121.2 (3)
O2ii—Ba1—O1iv150.63 (10)O2iii—Co1—O2ix103.93 (12)
O2iii—Ba1—O1iv150.63 (10)O3—Si1—O2x116.2 (2)
O3i—Ba1—O3144.85 (11)O3—Si1—O2116.2 (2)
O2ii—Ba1—O381.96 (13)O2x—Si1—O2106.9 (3)
O2iii—Ba1—O3115.08 (14)O3—Si1—O1109.7 (4)
O1iv—Ba1—O380.96 (13)O2x—Si1—O1103.1 (2)
O3i—Ba1—O3v144.85 (11)O2—Si1—O1103.1 (2)
O2ii—Ba1—O3v115.08 (14)Si1v—O1—Si1142.8 (5)
O2iii—Ba1—O3v81.96 (13)Si1v—O1—Ba1xi103.17 (16)
O1iv—Ba1—O3v80.96 (13)Si1—O1—Ba1xi103.17 (16)
O3—Ba1—O3v70.2 (2)Si1v—O1—Ba1xii103.17 (16)
O3i—Ba1—O2vi82.31 (12)Si1—O1—Ba1xii103.17 (16)
O2ii—Ba1—O2vi151.53 (5)Ba1xi—O1—Ba1xii88.8 (2)
O2iii—Ba1—O2vi97.26 (18)Si1—O2—Co1xiii123.8 (3)
O1iv—Ba1—O2vi54.63 (10)Si1—O2—Ba1xiv97.1 (2)
O3—Ba1—O2vi124.86 (13)Co1xiii—O2—Ba1xiv119.09 (19)
O3v—Ba1—O2vi71.90 (14)Si1—O2—Ba1xi98.0 (2)
O3i—Ba1—O2vii82.31 (12)Co1xiii—O2—Ba1xi113.19 (18)
O2ii—Ba1—O2vii97.26 (18)Ba1xiv—O2—Ba1xi101.42 (14)
O2iii—Ba1—O2vii151.53 (5)Si1—O3—Ba1xv122.1 (3)
O1iv—Ba1—O2vii54.63 (10)Si1—O3—Ba1116.0 (2)
O3—Ba1—O2vii71.90 (14)Ba1xv—O3—Ba1105.18 (15)
O3v—Ba1—O2vii124.86 (13)Si1—O3—Ba1v116.0 (2)
O2vi—Ba1—O2vii100.25 (17)Ba1xv—O3—Ba1v105.18 (15)
O2viii—Co1—O2v103.93 (12)Ba1—O3—Ba1v86.30 (18)
O3—Si1—O1—Si1v0.0O2x—Si1—O1—Si1v124.43 (18)
O2—Si1—O1—Si1v124.43 (18)
Symmetry codes: (i) y, x+1, z; (ii) x1/2, y+1/2, z+1; (iii) y, x+1, z+1; (iv) x, y, z1; (v) x+1, y, z; (vi) x+1, y, z1; (vii) y+1/2, x1/2, z1; (viii) y, x1, z+1; (ix) x1, y, z; (x) y+1/2, x1/2, z; (xi) x+1, y, z+1; (xii) x, y, z+1; (xiii) x+1, y, z; (xiv) y+1, x, z+1; (xv) y+1, x, z.

Experimental details

Crystal data
Chemical formulaBa2CoSi2O7
Mr501.79
Crystal system, space groupTetragonal, P421m
Temperature (K)293
a, c (Å)8.1709 (7), 5.3374 (7)
V3)356.34 (6)
Z2
Radiation typeMo Kα
µ (mm1)13.56
Crystal size (mm)0.13 × 0.05 × 0.05
Data collection
DiffractometerBruker SMART CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.392, 0.522
No. of measured, independent and
observed [I > \2s(I)] reflections
1383, 575, 536
Rint0.026
(sin θ/λ)max1)0.714
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.025, 0.064, 1.18
No. of reflections575
No. of parameters34
Δρmax, Δρmin (e Å3)1.04, 0.87
Absolute structureFlack (1983), 0000 Friedel pairs
Absolute structure parameter0.12 (7)

Computer programs: SMART (Bruker, 1999), SAINT (Bruker, 1999), SAINT, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ATOMS (Dowty,1999), SHELXL97.

Selected bond lengths (Å) top
Ba1—O3i2.628 (6)Co1—O2v1.964 (4)
Ba1—O2ii2.681 (4)Si1—O31.592 (6)
Ba1—O1iii2.738 (6)Si1—O21.637 (5)
Ba1—O32.800 (5)Si1—O11.664 (3)
Ba1—O2iv2.888 (4)
Symmetry codes: (i) y, x+1, z; (ii) x1/2, y+1/2, z+1; (iii) x, y, z1; (iv) x+1, y, z1; (v) y, x1, z+1.
 

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