Reinvestigation of the structure of BaCuSi₂O₆ - evidence for a phase transition at high temperature

Superstructure reflections have been observed in the room-temperature X-ray diffraction pattern of BaCuSi₂O₆, barium copper disilicate. The tetragonal structure has a fourfold unit-cell volume compared with the original structure determined by Finger et al. [(1989), Am. Mineral. 74, 952-955]. At T_s = 610 K BaCuSi₂O₆ undergoes a structural phase transition upon which the superstructure reflections disappear. The description of the structure in the larger cell removes the crystal-chemical inconsistencies observed for the original structure.

Computing details

For both compounds, data reduction: STOE X-RED; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS v5.1; software used to prepare material for publication: WinGX v1.64.05 (Farrugia, 1999).

Figures

(bcso293) Barium copper cyclosilicate

Crystal data

CuO6Si2·Ba	Dx = 4.167 Mg m^−3
Mr = 353.06	Mo Kα radiation, λ = 0.71069 Å
Tetragonal, I41/acd	Cell parameters from 1214 reflections
Hall symbol: -I 4bd 2c	θ = 3.6–32.8°
a = 10.0091 (16) Å	µ = 11.12 mm^−1
c = 22.467 (6) Å	T = 293 K
V = 2250.8 (8) Å^3	Cuboid, purple
Z = 16	0.17 × 0.16 × 0.11 mm
F(000) = 2575

Data collection

STOE IPDS diffractometer	1056 independent reflections
Radiation source: fine-focus sealed tube	523 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.000
rotation method scans	θmax = 32.8°, θmin = 3.6°
Absorption correction: numerical via equivalents using STOE X-SHAPE and X-RED (Stoe & Cie, 1996)	h = 0→15
Tmin = 0.179, Tmax = 0.288	k = 0→15
1056 measured reflections	l = 0→34

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.028	w = 1/[σ^2(Fo^2) + (0.P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.042	(Δ/σ)max = 0.001
S = 1.26	Δρmax = 1.12 e Å^−3
1056 reflections	Δρmin = −2.04 e Å^−3
48 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.000065 (7)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Ba1	0.2500	0.98870 (9)	0.5000	0.01258 (12)
Cu1	0.0000	0.2500	0.06374 (3)	0.01012 (16)
Si1	0.27554 (11)	0.7511 (2)	0.8760 (4)	0.0096 (3)
O1	0.1916 (9)	0.7218 (11)	0.8166 (4)	0.0139 (17)
O2	0.3725 (8)	0.8786 (8)	0.85939 (16)	0.0226 (10)
O3	0.3075 (9)	0.7813 (11)	0.0639 (5)	0.0139 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ba1	0.0132 (5)	0.0120 (4)	0.01251 (15)	0.000	−0.0018 (3)	0.000
Cu1	0.0089 (15)	0.0092 (16)	0.0123 (3)	0.0000 (6)	0.000	0.000
Si1	0.0078 (6)	0.0069 (5)	0.0140 (6)	0.0002 (10)	−0.007 (3)	−0.0008 (10)
O1	0.010 (4)	0.016 (3)	0.017 (4)	0.005 (4)	0.003 (3)	0.002 (4)
O2	0.016 (4)	0.015 (4)	0.037 (3)	−0.0024 (14)	−0.003 (4)	0.002 (4)
O3	0.008 (3)	0.015 (3)	0.019 (4)	−0.004 (4)	0.002 (3)	0.012 (4)

Geometric parameters (Å, º)

Ba1—O1^i	2.719 (10)	Si1—O1^xxxi	3.813 (11)
Ba1—O1^ii	2.719 (10)	O1—Cu1^xxxii	1.939 (9)
Ba1—O3^iii	2.773 (10)	O1—O2	2.582 (14)
Ba1—O3^iv	2.773 (10)	O1—O2^xxiii	2.644 (13)
Ba1—O2^v	2.959 (4)	O1—Ba1^xxx	2.719 (10)
Ba1—O2^vi	2.959 (4)	O1—O3^xxv	2.731 (15)
Ba1—O3^vii	3.114 (12)	O1—O3^xxii	2.750 (5)
Ba1—O3^viii	3.114 (12)	O1—O3^xxxiii	2.772 (16)
Ba1—O1^v	3.237 (11)	O1—Ba1^xxix	3.237 (11)
Ba1—O1^vi	3.237 (11)	O1—O1^xxvi	3.26 (2)
Ba1—O2^ix	3.640 (4)	O1—Cu1^xvi	3.314 (10)
Ba1—O2^x	3.640 (4)	O1—Si1^xxiv	3.392 (11)
Cu1—O1^xi	1.939 (9)	O2—Si1^xxvii	1.638 (11)
Cu1—O1^xii	1.939 (9)	O2—O3^xxxii	2.604 (13)
Cu1—O3^xiii	1.952 (9)	O2—O1^xxvii	2.644 (13)
Cu1—O3^xiv	1.952 (9)	O2—O2^xxvii	2.657 (6)
Cu1—O1^xv	3.314 (10)	O2—O2^xxiii	2.657 (6)
Cu1—O1^xvi	3.314 (10)	O2—O3^xxii	2.677 (13)
Cu1—O3^xvii	3.372 (10)	O2—Ba1^xxix	2.959 (4)
Cu1—O3^xviii	3.372 (10)	O2—O2^xxxi	3.523 (9)
Cu1—Ba1^xix	3.7444 (8)	O2—O3^xxv	3.622 (13)
Cu1—Ba1^xx	3.7444 (8)	O2—O1^xxxiv	3.624 (13)
Cu1—Ba1^xxi	3.8926 (9)	O3—Si1^xxii	1.614 (13)
Cu1—Ba1^vii	3.8926 (9)	O3—Cu1^xxxiv	1.952 (9)
Si1—O1	1.605 (13)	O3—O2^xi	2.604 (13)
Si1—O3^xxii	1.614 (13)	O3—O2^xxii	2.677 (13)
Si1—O2^xxiii	1.638 (11)	O3—O1^xxxv	2.731 (15)
Si1—O2	1.646 (11)	O3—O1^xxii	2.750 (5)
Si1—O1^xxiv	3.392 (11)	O3—O1^xxxvi	2.772 (16)
Si1—O3^xxv	3.405 (11)	O3—Ba1^ix	2.773 (10)
Si1—Ba1^xxvi	3.685 (7)	O3—O3^xxxvii	3.09 (2)
Si1—O2^xxvii	3.767 (6)	O3—Ba1^vii	3.114 (12)
Si1—O2^xxviii	3.773 (6)	O3—Cu1^xxxviii	3.372 (10)
Si1—Ba1^xxix	3.774 (7)	O3—Si1^xxxv	3.405 (11)
Si1—Ba1^xxx	3.804 (7)
O1^i—Ba1—O1^ii	160.0 (4)	O3^xvii—Cu1—Ba1^xxi	138.04 (19)
O1^i—Ba1—O3^iii	105.0 (3)	O3^xviii—Cu1—Ba1^xxi	81.74 (19)
O1^ii—Ba1—O3^iii	91.63 (11)	Ba1^xix—Cu1—Ba1^xxi	81.962 (8)
O1^i—Ba1—O3^iv	91.64 (11)	Ba1^xx—Cu1—Ba1^xxi	81.861 (8)
O1^ii—Ba1—O3^iv	105.0 (3)	O1^xi—Cu1—Ba1^vii	56.0 (3)
O3^iii—Ba1—O3^iv	67.8 (5)	O1^xii—Cu1—Ba1^vii	125.7 (3)
O1^i—Ba1—O2^v	79.2 (3)	O3^xiii—Cu1—Ba1^vii	138.0 (3)
O1^ii—Ba1—O2^v	93.2 (3)	O3^xiv—Cu1—Ba1^vii	42.1 (3)
O3^iii—Ba1—O2^v	145.8 (3)	O1^xv—Cu1—Ba1^vii	89.07 (17)
O3^iv—Ba1—O2^v	78.3 (3)	O1^xvi—Cu1—Ba1^vii	127.82 (19)
O1^i—Ba1—O2^vi	93.2 (3)	O3^xvii—Cu1—Ba1^vii	81.74 (19)
O1^ii—Ba1—O2^vi	79.2 (3)	O3^xviii—Cu1—Ba1^vii	138.04 (19)
O3^iii—Ba1—O2^vi	78.3 (3)	Ba1^xix—Cu1—Ba1^vii	81.861 (8)
O3^iv—Ba1—O2^vi	145.8 (3)	Ba1^xx—Cu1—Ba1^vii	81.962 (8)
O2^v—Ba1—O2^vi	135.8 (3)	Ba1^xxi—Cu1—Ba1^vii	136.83 (2)
O1^i—Ba1—O3^vii	56.27 (19)	O1—Si1—O3^xxii	117.4 (2)
O1^ii—Ba1—O3^vii	104.7 (3)	O1—Si1—O2^xxiii	109.2 (5)
O3^iii—Ba1—O3^vii	157.0 (3)	O3^xxii—Si1—O2^xxiii	106.4 (6)
O3^iv—Ba1—O3^vii	121.3 (4)	O1—Si1—O2	105.2 (6)
O2^v—Ba1—O3^vii	50.7 (3)	O3^xxii—Si1—O2	110.4 (5)
O2^vi—Ba1—O3^vii	88.9 (2)	O2^xxiii—Si1—O2	108.0 (3)
O1^i—Ba1—O3^viii	104.7 (3)	O1—Si1—O1^xxiv	80.2 (4)
O1^ii—Ba1—O3^viii	56.27 (19)	O3^xxii—Si1—O1^xxiv	54.1 (4)
O3^iii—Ba1—O3^viii	121.3 (4)	O2^xxiii—Si1—O1^xxiv	84.6 (3)
O3^iv—Ba1—O3^viii	157.0 (3)	O2—Si1—O1^xxiv	163.2 (3)
O2^v—Ba1—O3^viii	88.9 (2)	O1—Si1—O3^xxv	52.1 (4)
O2^vi—Ba1—O3^viii	50.7 (3)	O3^xxii—Si1—O3^xxv	82.4 (5)
O3^vii—Ba1—O3^viii	59.6 (4)	O2^xxiii—Si1—O3^xxv	160.8 (4)
O1^i—Ba1—O1^v	119.0 (3)	O2—Si1—O3^xxv	83.9 (3)
O1^ii—Ba1—O1^v	65.8 (3)	O1^xxiv—Si1—O3^xxv	87.23 (9)
O3^iii—Ba1—O1^v	103.8 (3)	O1—Si1—Ba1^xxvi	118.3 (4)
O3^iv—Ba1—O1^v	53.36 (17)	O3^xxii—Si1—Ba1^xxvi	56.9 (5)
O2^v—Ba1—O1^v	49.0 (3)	O2^xxiii—Si1—Ba1^xxvi	51.5 (3)
O2^vi—Ba1—O1^v	144.9 (2)	O2—Si1—Ba1^xxvi	135.8 (3)
O3^vii—Ba1—O1^v	97.64 (10)	O1^xxiv—Si1—Ba1^xxvi	44.94 (18)
O3^viii—Ba1—O1^v	104.0 (3)	O3^xxv—Si1—Ba1^xxvi	128.8 (2)
O1^i—Ba1—O1^vi	65.8 (3)	O1—Si1—O2^xxvii	128.7 (5)
O1^ii—Ba1—O1^vi	119.0 (3)	O3^xxii—Si1—O2^xxvii	110.3 (4)
O3^iii—Ba1—O1^vi	53.36 (17)	O2^xxiii—Si1—O2^xxvii	72.4 (2)
O3^iv—Ba1—O1^vi	103.8 (3)	O2—Si1—O2^xxvii	37.48 (16)
O2^v—Ba1—O1^vi	144.9 (2)	O1^xxiv—Si1—O2^xxvii	147.4 (3)
O2^vi—Ba1—O1^vi	49.0 (3)	O3^xxv—Si1—O2^xxvii	121.3 (2)
O3^vii—Ba1—O1^vi	104.0 (3)	Ba1^xxvi—Si1—O2^xxvii	102.60 (17)
O3^viii—Ba1—O1^vi	97.64 (10)	O1—Si1—O2^xxviii	110.1 (4)
O1^v—Ba1—O1^vi	155.1 (3)	O3^xxii—Si1—O2^xxviii	128.9 (5)
O1^i—Ba1—O2^ix	46.4 (3)	O2^xxiii—Si1—O2^xxviii	37.12 (16)
O1^ii—Ba1—O2^ix	144.7 (3)	O2—Si1—O2^xxviii	72.2 (2)
O3^iii—Ba1—O2^ix	94.4 (2)	O1^xxiv—Si1—O2^xxviii	121.6 (2)
O3^iv—Ba1—O2^ix	47.0 (3)	O3^xxv—Si1—O2^xxviii	145.4 (3)
O2^v—Ba1—O2^ix	63.56 (13)	Ba1^xxvi—Si1—O2^xxviii	85.16 (13)
O2^vi—Ba1—O2^ix	136.04 (9)	O2^xxvii—Si1—O2^xxviii	41.27 (6)
O3^vii—Ba1—O2^ix	81.6 (2)	O1—Si1—Ba1^xxix	58.4 (5)
O3^viii—Ba1—O2^ix	141.2 (2)	O3^xxii—Si1—Ba1^xxix	119.0 (4)
O1^v—Ba1—O2^ix	79.0 (2)	O2^xxiii—Si1—Ba1^xxix	133.7 (4)
O1^vi—Ba1—O2^ix	91.9 (2)	O2—Si1—Ba1^xxix	48.7 (3)
O1^i—Ba1—O2^x	144.7 (3)	O1^xxiv—Si1—Ba1^xxix	129.24 (19)
O1^ii—Ba1—O2^x	46.4 (3)	O3^xxv—Si1—Ba1^xxix	45.08 (18)
O3^iii—Ba1—O2^x	47.0 (3)	Ba1^xxvi—Si1—Ba1^xxix	173.83 (4)
O3^iv—Ba1—O2^x	94.4 (3)	O2^xxvii—Si1—Ba1^xxix	83.05 (14)
O2^v—Ba1—O2^x	136.04 (9)	O2^xxviii—Si1—Ba1^xxix	100.83 (17)
O2^vi—Ba1—O2^x	63.56 (13)	O1—Si1—Ba1^xxx	37.7 (4)
O3^vii—Ba1—O2^x	141.2 (2)	O3^xxii—Si1—Ba1^xxx	134.2 (4)
O3^viii—Ba1—O2^x	81.6 (2)	O2^xxiii—Si1—Ba1^xxx	71.7 (2)
O1^v—Ba1—O2^x	91.9 (2)	O2—Si1—Ba1^xxx	113.6 (4)
O1^vi—Ba1—O2^x	79.0 (2)	O1^xxiv—Si1—Ba1^xxx	80.59 (17)
O2^ix—Ba1—O2^x	137.2 (3)	O3^xxv—Si1—Ba1^xxx	89.8 (2)
O1^xi—Cu1—O1^xii	176.2 (6)	Ba1^xxvi—Si1—Ba1^xxx	97.21 (6)
O1^xi—Cu1—O3^xiii	90.9 (6)	O2^xxvii—Si1—Ba1^xxx	112.18 (17)
O1^xii—Cu1—O3^xiii	89.1 (6)	O2^xxviii—Si1—Ba1^xxx	77.85 (15)
O1^xi—Cu1—O3^xiv	89.1 (6)	Ba1^xxix—Si1—Ba1^xxx	82.76 (17)
O1^xii—Cu1—O3^xiv	90.9 (6)	O1—Si1—O1^xxxi	87.4 (4)
O3^xiii—Cu1—O3^xiv	179.8 (6)	O3^xxii—Si1—O1^xxxi	38.1 (5)
O1^xi—Cu1—O1^xv	98.1 (4)	O2^xxiii—Si1—O1^xxxi	142.4 (4)
O1^xii—Cu1—O1^xv	78.7 (5)	O2—Si1—O1^xxxi	99.2 (2)
O3^xiii—Cu1—O1^xv	123.8 (4)	O1^xxiv—Si1—O1^xxxi	64.8 (3)
O3^xiv—Cu1—O1^xv	56.0 (3)	O3^xxv—Si1—O1^xxxi	44.34 (14)
O1^xi—Cu1—O1^xvi	78.7 (5)	Ba1^xxvi—Si1—O1^xxxi	90.9 (2)
O1^xii—Cu1—O1^xvi	98.1 (4)	O2^xxvii—Si1—O1^xxxi	123.4 (2)
O3^xiii—Cu1—O1^xvi	56.0 (3)	O2^xxviii—Si1—O1^xxxi	161.8 (3)
O3^xiv—Cu1—O1^xvi	123.8 (4)	Ba1^xxix—Si1—O1^xxxi	83.88 (15)
O1^xv—Cu1—O1^xvi	71.6 (3)	Ba1^xxx—Si1—O1^xxxi	120.31 (18)
O1^xi—Cu1—O3^xvii	54.6 (3)	Si1—O1—Cu1^xxxii	121.3 (6)
O1^xii—Cu1—O3^xvii	121.6 (4)	Si1—O1—Ba1^xxx	121.1 (5)
O3^xiii—Cu1—O3^xvii	100.5 (4)	Cu1^xxxii—O1—Ba1^xxx	105.8 (4)
O3^xiv—Cu1—O3^xvii	79.3 (5)	Si1—O1—Ba1^xxix	96.6 (5)
O1^xv—Cu1—O3^xvii	48.2 (3)	Cu1^xxxii—O1—Ba1^xxix	94.2 (4)
O1^xvi—Cu1—O3^xvii	49.0 (3)	Ba1^xxx—O1—Ba1^xxix	114.2 (3)
O1^xi—Cu1—O3^xviii	121.6 (4)	Ba1^xxix—O1—O1^xxvi	49.4 (3)
O1^xii—Cu1—O3^xviii	54.6 (3)	Si1—O1—Cu1^xvi	67.2 (4)
O3^xiii—Cu1—O3^xviii	79.3 (5)	Cu1^xxxii—O1—Cu1^xvi	56.1 (2)
O3^xiv—Cu1—O3^xviii	100.5 (4)	Ba1^xxx—O1—Cu1^xvi	128.1 (4)
O1^xv—Cu1—O3^xviii	49.0 (3)	Ba1^xxix—O1—Cu1^xvi	115.2 (3)
O1^xvi—Cu1—O3^xviii	48.2 (3)	Si1—O1—Si1^xxiv	96.6 (5)
O3^xvii—Cu1—O3^xviii	70.8 (3)	Cu1^xxxii—O1—Si1^xxiv	63.7 (3)
O1^xi—Cu1—Ba1^xix	137.8 (3)	Ba1^xxx—O1—Si1^xxiv	73.3 (3)
O1^xii—Cu1—Ba1^xix	44.3 (3)	Ba1^xxix—O1—Si1^xxiv	157.8 (3)
O3^xiii—Cu1—Ba1^xix	123.9 (3)	Cu1^xvi—O1—Si1^xxiv	54.91 (18)
O3^xiv—Cu1—Ba1^xix	56.2 (3)	Si1^xxvii—O2—Si1	150.7 (3)
O1^xv—Cu1—Ba1^xix	82.49 (18)	Si1^xxvii—O2—Ba1^xxix	102.8 (4)
O1^xvi—Cu1—Ba1^xix	138.70 (19)	Si1—O2—Ba1^xxix	106.6 (4)
O3^xvii—Cu1—Ba1^xix	127.90 (17)	Si1^xxii—O3—Cu1^xxxiv	118.7 (6)
O3^xviii—Cu1—Ba1^xix	90.53 (15)	Si1^xxii—O3—Ba1^ix	118.8 (5)
O1^xi—Cu1—Ba1^xx	44.3 (3)	Cu1^xxxiv—O3—Ba1^ix	109.7 (4)
O1^xii—Cu1—Ba1^xx	137.8 (3)	Ba1^ix—O3—O3^xxxvii	56.1 (2)
O3^xiii—Cu1—Ba1^xx	56.2 (3)	Si1^xxii—O3—Ba1^vii	97.3 (5)
O3^xiv—Cu1—Ba1^xx	123.9 (3)	Cu1^xxxiv—O3—Ba1^vii	92.4 (4)
O1^xv—Cu1—Ba1^xx	138.70 (19)	Ba1^ix—O3—Ba1^vii	116.3 (3)
O1^xvi—Cu1—Ba1^xx	82.49 (18)	Si1^xxii—O3—Cu1^xxxviii	66.1 (4)
O3^xvii—Cu1—Ba1^xx	90.53 (15)	Cu1^xxxiv—O3—Cu1^xxxviii	54.7 (2)
O3^xviii—Cu1—Ba1^xx	127.90 (17)	Ba1^ix—O3—Cu1^xxxviii	128.2 (4)
Ba1^xix—Cu1—Ba1^xx	135.03 (2)	Ba1^vii—O3—Cu1^xxxviii	113.6 (3)
O1^xi—Cu1—Ba1^xxi	125.7 (3)	Si1^xxii—O3—Si1^xxxv	94.7 (5)
O1^xii—Cu1—Ba1^xxi	56.0 (3)	Cu1^xxxiv—O3—Si1^xxxv	63.9 (3)
O3^xiii—Cu1—Ba1^xxi	42.1 (3)	Ba1^ix—O3—Si1^xxxv	74.5 (3)
O3^xiv—Cu1—Ba1^xxi	138.0 (3)	Ba1^vii—O3—Si1^xxxv	156.4 (3)
O1^xv—Cu1—Ba1^xxi	127.82 (19)	Cu1^xxxviii—O3—Si1^xxxv	53.91 (18)
O1^xvi—Cu1—Ba1^xxi	89.07 (17)

Symmetry codes: (i) −y+3/4, x+3/4, −z+5/4; (ii) y−1/4, x+3/4, z−1/4; (iii) −x+1/2, −y+2, z+1/2; (iv) x, −y+2, −z+1/2; (v) −y+5/4, −x+5/4, −z+5/4; (vi) y−3/4, −x+5/4, z−1/4; (vii) −x+1/2, −y+3/2, −z+1/2; (viii) x, −y+3/2, z+1/2; (ix) −x+1/2, −y+2, z−1/2; (x) x, −y+2, −z+3/2; (xi) y−3/4, x+1/4, z−3/4; (xii) −y+3/4, −x+1/4, z−3/4; (xiii) x−1/2, −y+1, z; (xiv) −x+1/2, y−1/2, z; (xv) x, y−1/2, −z+1; (xvi) −x, −y+1, −z+1; (xvii) y−3/4, −x+3/4, −z+1/4; (xviii) −y+3/4, x−1/4, −z+1/4; (xix) −x+1/2, −y+1, z−1/2; (xx) x−1/2, y−1/2, z−1/2; (xxi) x−1/2, y−1, −z+1/2; (xxii) −x+1/2, y, −z+1; (xxiii) −y+5/4, x+1/4, −z+7/4; (xxiv) −y+3/4, −x+3/4, −z+7/4; (xxv) y−3/4, −x+5/4, z+3/4; (xxvi) −x+1/2, −y+3/2, −z+3/2; (xxvii) y−1/4, −x+5/4, −z+7/4; (xxviii) −x+1, −y+3/2, z; (xxix) −y+5/4, x+3/4, z+1/4; (xxx) y−3/4, −x+3/4, −z+5/4; (xxxi) y−3/4, x+3/4, −z+7/4; (xxxii) y−1/4, x+3/4, z+3/4; (xxxiii) −y+3/4, x+1/4, z+3/4; (xxxiv) −x+1/2, y+1/2, z; (xxxv) −y+5/4, x+3/4, z−3/4; (xxxvi) y−1/4, −x+3/4, z−3/4; (xxxvii) −x+1/2, y, −z; (xxxviii) y+1/4, −x+3/4, −z+1/4.

(bcso640) Barium copper cyclosilicate

Crystal data

CuO6Si2·Ba	Dx = 4.151 Mg m^−3
Mr = 353.06	Mo Kα radiation, λ = 0.71069 Å
Tetragonal, I4/mmm	Cell parameters from 988 reflections
Hall symbol: -I 4 2	θ = 3.4–24.8°
a = 7.1104 (13) Å	µ = 11.08 mm^−1
c = 11.175 (3) Å	T = 640 K
V = 565.0 (2) Å^3	Cuboid, purple
Z = 4	0.27 × 0.24 × 0.17 mm
F(000) = 644

Data collection

STOE IPDS diffractometer	170 independent reflections
Radiation source: fine-focus sealed tube	135 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.000
rotation method scans	θmax = 24.8°, θmin = 3.4°
Absorption correction: numerical via equivalents using STOE X-SHAPE and X-RED (Stoe & Cie, 1996)	h = 0→8
Tmin = 0.050, Tmax = 0.144	k = 0→8
170 measured reflections	l = 0→13

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.015	w = 1/[σ^2(Fo^2) + (0.P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.025	(Δ/σ)max < 0.001
S = 1.02	Δρmax = 0.53 e Å^−3
170 reflections	Δρmin = −0.51 e Å^−3
23 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0021 (2)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ba	0.0000	0.5000	0.2500	0.0242 (3)
Cu	0.0000	0.0000	0.12341 (16)	0.0200 (5)
Si	0.2756 (2)	0.2756 (2)	0.0000	0.0157 (7)
O1	0.2415 (14)	0.5000	0.0239 (18)	0.034 (6)	0.50
O2	0.1916 (5)	0.1916 (5)	0.1209 (4)	0.0392 (14)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ba	0.0238 (4)	0.0238 (4)	0.0250 (5)	0.000	0.000	0.000
Cu	0.0190 (7)	0.0190 (7)	0.0220 (11)	0.000	0.000	0.000
Si	0.0101 (9)	0.0101 (9)	0.0269 (14)	−0.0010 (14)	0.000	0.000
O1	0.049 (5)	0.010 (3)	0.043 (19)	0.000	0.022 (8)	0.000
O2	0.0478 (19)	0.0478 (19)	0.022 (2)	−0.021 (2)	0.0004 (17)	0.0004 (17)

Geometric parameters (Å, º)

Ba—O2^i	2.958 (2)	Si—O1^x	1.636 (4)
Ba—O2^ii	2.958 (2)	Si—O1^xii	1.636 (4)
Ba—O2	2.958 (2)	O1—O1^x	0.53 (4)
Ba—O2^iii	2.958 (2)	O1—Si^xiii	1.636 (4)
Ba—O2^iv	2.958 (2)	O1—O2^iv	2.472 (10)
Ba—O2^v	2.958 (2)	O1—O2	2.472 (10)
Ba—O2^vi	2.958 (2)	O1—O1^iv	2.599 (14)
Ba—O2^vii	2.958 (2)	O1—O1^xi	2.599 (14)
Ba—O1^vii	3.056 (18)	O1—O1^xiii	2.653 (17)
Ba—O1^i	3.056 (18)	O1—O1^xii	2.653 (17)
Ba—O1^v	3.056 (18)	O1—O2^x	2.748 (13)
Ba—O1	3.056 (18)	O1—O2^xiii	2.748 (13)
Cu—O2^viii	1.927 (5)	O2—O1^xi	2.472 (10)
Cu—O2	1.927 (5)	O2—O2^x	2.701 (9)
Cu—O2^ix	1.927 (5)	O2—O2^ix	2.725 (7)
Cu—O2^ii	1.927 (5)	O2—O2^ii	2.725 (7)
Si—O2^x	1.593 (5)	O2—O1^x	2.748 (13)
Si—O2	1.593 (5)	O2—O1^xii	2.748 (13)
Si—O1	1.636 (4)	O2—Ba^iii	2.958 (2)
Si—O1^xi	1.636 (4)	O2—O2^iii	3.116 (9)
O2^i—Ba—O2^ii	157.09 (18)	O2^iii—Ba—O1^v	48.51 (10)
O2^i—Ba—O2	103.77 (7)	O2^iv—Ba—O1^v	145.12 (17)
O2^ii—Ba—O2	54.85 (17)	O2^v—Ba—O1^v	48.51 (10)
O2^i—Ba—O2^iii	54.85 (17)	O2^vi—Ba—O1^v	81.68 (18)
O2^ii—Ba—O2^iii	103.77 (7)	O2^vii—Ba—O1^v	145.12 (17)
O2—Ba—O2^iii	63.58 (15)	O1^vii—Ba—O1^v	133.2 (3)
O2^i—Ba—O2^iv	63.58 (15)	O1^i—Ba—O1^v	68.4 (5)
O2^ii—Ba—O2^iv	121.59 (16)	O2^i—Ba—O1	89.2 (2)
O2—Ba—O2^iv	95.71 (18)	O2^ii—Ba—O1	81.68 (18)
O2^iii—Ba—O2^iv	103.77 (7)	O2—Ba—O1	48.51 (10)
O2^i—Ba—O2^v	121.59 (16)	O2^iii—Ba—O1	89.2 (2)
O2^ii—Ba—O2^v	63.58 (15)	O2^iv—Ba—O1	48.51 (10)
O2—Ba—O2^v	103.77 (7)	O2^v—Ba—O1	145.12 (17)
O2^iii—Ba—O2^v	95.71 (18)	O2^vi—Ba—O1	145.12 (17)
O2^iv—Ba—O2^v	157.09 (18)	O2^vii—Ba—O1	81.68 (18)
O2^i—Ba—O2^vi	95.71 (18)	O1^vii—Ba—O1	68.4 (5)
O2^ii—Ba—O2^vi	103.77 (7)	O1^i—Ba—O1	133.2 (3)
O2—Ba—O2^vi	157.09 (18)	O1^v—Ba—O1	133.2 (3)
O2^iii—Ba—O2^vi	121.59 (16)	O2^viii—Cu—O2	178.3 (3)
O2^iv—Ba—O2^vi	103.77 (7)	O2^viii—Cu—O2^ix	89.988 (5)
O2^v—Ba—O2^vi	54.85 (17)	O2—Cu—O2^ix	89.988 (5)
O2^i—Ba—O2^vii	103.77 (7)	O2^viii—Cu—O2^ii	89.988 (5)
O2^ii—Ba—O2^vii	95.71 (18)	O2—Cu—O2^ii	89.988 (5)
O2—Ba—O2^vii	121.59 (16)	O2^ix—Cu—O2^ii	178.3 (3)
O2^iii—Ba—O2^vii	157.09 (18)	O2^x—Si—O2	116.0 (3)
O2^iv—Ba—O2^vii	54.85 (17)	O2^x—Si—O1	116.6 (6)
O2^v—Ba—O2^vii	103.77 (7)	O2—Si—O1	99.9 (7)
O2^vi—Ba—O2^vii	63.58 (15)	O2^x—Si—O1^xi	116.6 (6)
O2^i—Ba—O1^vii	145.12 (17)	O2—Si—O1^xi	99.9 (7)
O2^ii—Ba—O1^vii	48.51 (10)	O1—Si—O1^xi	105.2 (7)
O2—Ba—O1^vii	81.68 (18)	O2^x—Si—O1^x	99.9 (7)
O2^iii—Ba—O1^vii	145.12 (17)	O2—Si—O1^x	116.6 (6)
O2^iv—Ba—O1^vii	81.68 (18)	O1—Si—O1^x	18.8 (14)
O2^v—Ba—O1^vii	89.2 (2)	O1^xi—Si—O1^x	108.4 (7)
O2^vi—Ba—O1^vii	89.2 (2)	O2^x—Si—O1^xii	99.9 (7)
O2^vii—Ba—O1^vii	48.51 (10)	O2—Si—O1^xii	116.6 (6)
O2^i—Ba—O1^i	48.51 (10)	O1—Si—O1^xii	108.4 (7)
O2^ii—Ba—O1^i	145.12 (17)	O1^xi—Si—O1^xii	18.8 (14)
O2—Ba—O1^i	145.12 (17)	O1^x—Si—O1^xii	105.2 (7)
O2^iii—Ba—O1^i	81.68 (18)	Si^xiii—O1—Si	154.6 (12)
O2^iv—Ba—O1^i	89.2 (2)	Si^xiii—O1—Ba	102.6 (6)
O2^v—Ba—O1^i	81.68 (18)	Si—O1—Ba	102.6 (6)
O2^vi—Ba—O1^i	48.51 (10)	Si—O2—Cu	122.9 (3)
O2^vii—Ba—O1^i	89.2 (2)	Si—O2—Ba	107.96 (13)
O1^vii—Ba—O1^i	133.2 (3)	Cu—O2—Ba	101.03 (13)
O2^i—Ba—O1^v	81.68 (18)	Si—O2—Ba^iii	107.96 (13)
O2^ii—Ba—O1^v	89.2 (2)	Cu—O2—Ba^iii	101.03 (13)
O2—Ba—O1^v	89.2 (2)	Ba—O2—Ba^iii	116.42 (15)

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