Structure and complex twinning of dysprosium disilicate (Dy₂Si₂O₇), Type B

Dysprosium disilicate (Dy₂Si₂O₇) is triclinic with a = 6.6158 (2), b = 6.6604 (2), c = 12.0551 (4) Å, α = 94.373 (2), β = 90.836 (2), γ = 91.512 (2)°, V = 529.4 (1) ų, space group P, Z = 4 and D_x = 6.156 g cm⁻³. The structure (single-crystal X-ray, R = 0.033, wR = 0.041) is built from a linear triple tetrahedral group [Si₃O₁₀] and isolated [SiO₄] tetrahedron cross-linked by Dy³⁺ in one sixfold and three eightfold coordinated positions, and corresponds to the presently revised type B structure of Ho₂Si₂O₇. The formation of the unusual linear triple tetrahedral group in the type B structure allows for a more continuous transition in the mean size of REE³⁺O_n (REE = rare earth element) polyhedra in REE disilicates through the 4f transition metal series. The crystal of Dy₂Si₂O₇ investigated was complexly twinned such that the diffraction pattern was also consistent with a larger dimensionally monoclinic unit cell (a = 22.5354, b = 14.2102, c = 6.6158 Å, β = 91.788°), which resulted in an apparent superstructure of the type B structure in space group C1. Lattice coincidence with the type B unit cell appears to have been maintained during crystal synthesis and quenching by the complex sector-zoned growth twin.

Computing details

Data collection: COLLECT (Nonius, 1997); cell refinement: COLLECT (Nonius, 1997); data reduction: SUNY Buffalo DATAP77; program(s) used to solve structure: SHELXTL PC Siemens; program(s) used to refine structure: SUNY Buffalo LINEX77; molecular graphics: Shape Software ATOMS, ORTEP-3 for Windows.

dysprosium disilicate

Crystal data

Dy2Si2O7	Z = 4
Mr = 493.17	Dx = 6.156 Mg m^−3
Triclinic, P1	Mo Kα radiation, λ = 0.70926 Å
a = 6.6158 (2) Å	Cell parameters from 32768 reflections
b = 6.6604 (2) Å	θ = 2–35°
c = 12.0551 (4) Å	µ = 28.45 mm^−1
α = 94.373 (2)°	T = 293 K
β = 90.836 (2)°	Prism, colorless
γ = 91.512 (2)°	0.11 × 0.10 × 0.05 mm
V = 529.39 Å^3

Data collection

Nonius KappaCCD diffractometer	4470 independent reflections
Radiation source: fine-focus sealed tube	3220 reflections with I ≥ 3σ(I)
Graphite monochromator	Rint = 0.107
area detector and scans	θmax = 35°, θmin = 2°
Absorption correction: gaussian (Coppens, Leiserowitz & Rabinovich, 1965)	h = −10→10
Tmin = 0.144, Tmax = 0.380	k = −5→9
32768 measured reflections	l = 0→19

Refinement

Refinement on F	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)] = 0.033	w = 1/[σ(F)^2 + (0.025F)^2], except w = 0 if I < 3σ(I)
wR(F^2) = 0.041	(Δ/σ)max = 0.001
S = 0.98	Δρmax = 4.65 e Å^−3
4470 reflections	Δρmin = −4.70 e Å^−3
204 parameters	Extinction correction: B-C type 1 Lorentzian isotropic, Coppens & Hamilton (1970)
0 restraints	Extinction coefficient: 0.31 (2)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Dy(1)	0.94853 (4)	0.33132 (4)	0.11643 (2)	0.00588 (9)
Dy(2)	0.88556 (4)	0.09387 (4)	0.35971 (2)	0.00579 (9)
Dy(3)	0.37254 (4)	0.78116 (4)	0.36895 (2)	0.00749 (9)
Dy(4)	0.66787 (4)	0.82973 (4)	0.10747 (2)	0.00742 (9)
Si(1)	0.1553 (2)	0.8528 (2)	0.1164 (1)	0.0048 (3)
Si(2)	0.4873 (3)	0.3370 (2)	0.1759 (1)	0.0061 (3)
Si(3)	0.3777 (3)	0.2743 (2)	0.4048 (1)	0.0064 (3)
Si(4)	0.1433 (3)	0.3702 (2)	0.6180 (1)	0.0056 (3)
O(1)	0.6418 (6)	0.4938 (6)	0.1256 (3)	0.0076 (7)
O(2)	0.6179 (7)	0.1419 (6)	0.2095 (4)	0.0120 (8)
O(3)	0.2978 (7)	0.2990 (7)	0.0947 (3)	0.0097 (8)
O(4)	0.4055 (6)	0.4283 (6)	0.3065 (3)	0.0072 (7)
O(5)	0.5836 (7)	0.1702 (6)	0.4454 (4)	0.0090 (8)
O(6)	0.2276 (6)	0.0965 (6)	0.3755 (4)	0.0100 (8)
O(7)	0.2885 (7)	0.4229 (6)	0.5118 (3)	0.0093 (8)
O(8)	0.2841 (7)	0.2167 (7)	0.6875 (4)	0.0118 (8)
O(9)	0.9629 (7)	0.2255 (6)	0.5700 (4)	0.0113 (8)
O(10)	0.0732 (7)	0.5777 (6)	0.6854 (4)	0.0109 (8)
O(11)	0.2411 (7)	0.9129 (7)	0.9994 (3)	0.0111 (8)
O(12)	0.3462 (6)	0.7886 (7)	0.1888 (4)	0.0095 (8)
O(13)	0.9982 (6)	0.6683 (6)	0.0809 (3)	0.0077 (8)
O(14)	0.0029 (6)	0.0165 (6)	0.1830 (3)	0.0075 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Dy(1)	0.0081 (1)	0.0071 (1)	0.0026 (1)	−0.00055 (9)	0.00044 (9)	0.00098 (9)
Dy(2)	0.0061 (1)	0.0076 (1)	0.0037 (1)	−0.00091 (9)	0.00145 (9)	0.00084 (9)
Dy(3)	0.0078 (1)	0.0126 (1)	0.0020 (1)	0.0012 (1)	0.00071 (9)	−0.00059 (9)
Dy(4)	0.0100 (1)	0.0072 (1)	0.0054 (1)	0.00030 (9)	0.00416 (9)	0.00193 (9)
Si(1)	0.0049 (7)	0.0072 (7)	0.0024 (6)	−0.0016 (5)	0.0017 (5)	0.0014 (5)
Si(2)	0.0075 (7)	0.0070 (7)	0.0039 (7)	−0.0010 (5)	0.0007 (5)	0.0026 (5)
Si(3)	0.0073 (7)	0.0070 (7)	0.0050 (7)	−0.0016 (5)	0.0001 (5)	0.0016 (5)
Si(4)	0.0060 (7)	0.0044 (6)	0.0063 (7)	−0.0014 (5)	0.0001 (5)	0.0005 (5)
O(1)	0.006 (2)	0.011 (2)	0.005 (2)	0.003 (1)	0.001 (1)	0.001 (1)
O(2)	0.019 (2)	0.007 (2)	0.010 (2)	0.003 (2)	−0.002 (2)	0.002 (1)
O(3)	0.009 (2)	0.019 (2)	0.002 (2)	−0.002 (2)	−0.001 (1)	0.002 (1)
O(4)	0.011 (2)	0.010 (2)	0.001 (2)	−0.004 (1)	0.000 (1)	0.003 (1)
O(5)	0.008 (2)	0.014 (2)	0.005 (2)	−0.004 (1)	0.001 (1)	0.004 (1)
O(6)	0.005 (2)	0.010 (2)	0.014 (2)	0.002 (1)	−0.002 (2)	−0.006 (2)
O(7)	0.013 (2)	0.010 (2)	0.005 (2)	−0.002 (2)	0.006 (1)	−0.004 (1)
O(8)	0.006 (2)	0.016 (2)	0.015 (2)	0.003 (2)	0.000 (2)	0.004 (2)
O(9)	0.014 (2)	0.011 (2)	0.008 (2)	−0.006 (2)	−0.004 (2)	0.001 (1)
O(10)	0.017 (2)	0.010 (2)	0.006 (2)	0.005 (2)	−0.001 (2)	0.000 (1)
O(11)	0.019 (2)	0.010 (2)	0.003 (2)	−0.008 (2)	0.006 (2)	−0.003 (1)
O(12)	0.006 (2)	0.016 (2)	0.007 (2)	−0.004 (2)	0.000 (1)	0.000 (1)
O(13)	0.006 (2)	0.008 (2)	0.008 (2)	−0.006 (1)	0.001 (1)	−0.003 (1)
O(14)	0.008 (2)	0.006 (2)	0.008 (2)	−0.002 (1)	−0.001 (1)	0.001 (1)

Geometric parameters (Å, º)

Dy(1)—O(1)	2.325 (2)	Dy(4)—O(2)^vi	2.367 (4)
Dy(1)—O(2)	2.789 (3)	Dy(4)—O(3)^vii	2.537 (4)
Dy(1)—O(3)^i	2.343 (1)	Dy(4)—O(8)^ii	2.531 (5)
Dy(1)—O(10)^ii	2.427 (4)	Dy(4)—O(11)^viii	2.295 (4)
Dy(1)—O(11)^ii	2.380 (3)	Dy(4)—O(12)	2.374 (2)
Dy(1)—O(13)	2.333 (4)	Dy(4)—O(13)	2.475 (2)
Dy(1)—O(13)^iii	2.410 (4)	Dy(4)—O(14)^ix	2.629 (2)
Dy(1)—O(14)^i	2.336 (4)	Si(1)—O(11)^x	1.602 (4)
Dy(2)—O(2)	2.558 (3)	Si(1)—O(12)	1.610 (3)
Dy(2)—O(5)	2.313 (2)	Si(1)—O(13)^xi	1.616 (3)
Dy(2)—O(6)^i	2.267 (4)	Si(1)—O(14)^vi	1.673 (3)
Dy(2)—O(8)^iv	2.354 (4)	Si(2)—O(1)	1.600 (4)
Dy(2)—O(9)	2.656 (4)	Si(2)—O(2)	1.652 (4)
Dy(2)—O(9)^v	2.571 (4)	Si(2)—O(3)	1.582 (3)
Dy(2)—O(10)^ii	2.304 (4)	Si(2)—O(4)	1.744 (4)
Dy(2)—O(14)^i	2.304 (4)	Si(3)—O(4)	1.635 (4)
Dy(3)—O(4)	2.429 (4)	Si(3)—O(5)	1.630 (3)
Dy(3)—O(5)^ii	2.250 (4)	Si(3)—O(6)	1.542 (3)
Dy(3)—O(6)^vi	2.328 (4)	Si(3)—O(7)	1.688 (4)
Dy(3)—O(8)^ii	2.381 (1)	Si(4)—O(7)	1.665 (4)
Dy(3)—O(9)^ii	2.348 (1)	Si(4)—O(8)	1.665 (4)
Dy(3)—O(12)	2.181 (4)	Si(4)—O(9)^xi	1.588 (3)
Dy(4)—O(1)	2.267 (4)	Si(4)—O(10)	1.630 (4)
O(11)^x—Si(1)—O(12)	106.8 (3)	O(4)—Si(3)—O(6)	114.4 (2)
O(11)^x—Si(1)—O(13)^xi	103.1 (2)	O(4)—Si(3)—O(7)	103.3 (2)
O(11)^x—Si(1)—O(14)^vi	116.8 (2)	O(5)—Si(3)—O(6)	104.8 (2)
O(12)—Si(1)—O(13)^xi	113.6 (2)	O(5)—Si(3)—O(7)	109.0 (2)
O(12)—Si(1)—O(14)^vi	114.9 (2)	O(6)—Si(3)—O(7)	109.7 (2)
O(13)^xi—Si(1)—O(14)^vi	101.1 (2)	O(7)—Si(4)—O(8)	103.2 (2)
O(1)—Si(2)—O(2)	107.6 (2)	O(7)—Si(4)—O(9)^xi	107.6 (2)
O(1)—Si(2)—O(3)	109.4 (2)	O(7)—Si(4)—O(10)	110.2 (2)
O(1)—Si(2)—O(4)	111.0 (2)	O(8)—Si(4)—O(9)^xi	102.7 (2)
O(2)—Si(2)—O(3)	118.8 (3)	O(8)—Si(4)—O(10)	117.2 (2)
O(2)—Si(2)—O(4)	100.6 (2)	O(9)^xi—Si(4)—O(10)	114.8 (3)
O(3)—Si(2)—O(4)	109.1 (2)	Si(2)—O(4)—Si(3)	119.7 (3)
O(4)—Si(3)—O(5)	115.7 (2)	Si(3)—O(7)—Si(4)	131.4 (3)

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