Incommensurately modulated phase of Rb₂CoBr₄ at 295 and 200 K

The crystal structure of RbCoBr at 295 and 200 K has been determined. At these temperatures RbCoBr exhibits an incommensurately modulated structure with wavevector . At room temperature only the average structure was refined. Lattice parameters are a = 9.732 (3), b = 13.328 (4), c = 7.654 (3) Å, space group Pnam. The R(F) value was 0.0414 for 286 observed reflections (0.0778 for all 477 reflections). At 200 K the lattice parameters are a = 9.691 (4), b = 13.278 (5), c = 7.630 (6) Å, superspace group P:Pnam:ss. Main reflections and satellite reflections of first order were measured. The refinement converged at R(F) = 0.052 for 309 observed reflections (255 main reflections and 54 satellites) and 0.2971 for all reflections (1849; 695 main reflections and 1154 satellites). Amplitudes and phases of the modulation function as well as bond distances show close relationships to those observed in the incommensurately modulated phase of RbZnBr.

Computing details

For both compounds, data collection: STOE IPDS; cell refinement: STOE IPDS. Data reduction: X-RED (STOE & CIE, GmbH 1998) for rcb110. Program(s) used to solve structure: SHELXS97 (Sheldrick, 1990) for rcb110. Program(s) used to refine structure: JANA98 (Petricek & Dusek,1998) for rbcobr; SHELXL97 (Sheldrick, 1997) for rcb110.

(rbcobr)

Crystal data

Rb2CoBr4	F(000) = 964
Mr = 549.5	Dx = 3.717 Mg m^−3
Orthorhombic, Pnam	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2c -2n	Cell parameters from 707 reflections
a = 9.691 (4) Å	θ = 2.5–45°
b = 13.278 (5) Å	µ = 27.79 mm^−1
c = 7.630 (6) Å	T = 200 K
V = 981.8 (16) Å^3	Irregular, blue-green
Z = 4	0.12 × 0.08 × 0.02 mm

Data collection

IPDS Stoe diffractometer	309 reflections with I > 2σ(I)
θ–dependant scans	Rint = 0.485
Absorption correction: gaussian XRED (STOE & CIE GmbH, 1998)	θmax = 23.8°, θmin = 2.6°
Tmin = 0.024, Tmax = 0.069	h = −10→10
15154 measured reflections	k = −14→13
1849 independent reflections	l = −8→8

Refinement

Refinement on F	56 parameters
R[F > 3σ(F)] = 0.297	Weighting scheme based on measured s.u.'s w = 1/σ^2(F)
wR(F) = 0.038	(Δ/σ)max = 0.0001
S = 1.77	Δρmax = 5.43 e Å^−3
1849 reflections	Δρmin = −6.05 e Å^−3

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

	x	y	z	Uiso*/Ueq
Rb	0.0132 (4)	0.6755 (3)	0.25	0.038 (2)
Rb2	0.3736 (5)	0.4025 (4)	0.25	0.063 (2)
Co	0.7760 (4)	0.4232 (4)	0.25	0.035 (2)
Br1	1.0196 (4)	0.4160 (4)	0.25	0.056 (3)
Br2	0.6771 (4)	0.5864 (4)	0.25	0.050 (3)
Br3	0.6870 (4)	0.3395 (3)	0.5003 (6)	0.062 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Rb	0.033 (2)	0.036 (2)	0.043 (3)	−0.002 (2)	0	0
Rb2	0.045 (3)	0.098 (5)	0.044 (4)	0.007 (3)	0	0
Co	0.037 (3)	0.046 (4)	0.020 (3)	0.003 (3)	0	0
Br1	0.035 (3)	0.066 (4)	0.068 (6)	0.003 (3)	0	0
Br2	0.033 (3)	0.045 (3)	0.071 (8)	0.005 (3)	0	0
Br3	0.063 (3)	0.090 (5)	0.033 (2)	−0.030 (4)	−0.005 (3)	0.028 (3)

(rcb110) Rubidium Tetra Bromo Cobaltate

Crystal data

Rb2CoBr4	Dx = 3.676 Mg m^−3
Mr = 274.76	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pnam	Cell parameters from 1204 reflections
Hall symbol: -P 2c -2n	θ = 2–40°
a = 9.732 (3) Å	µ = 27.48 mm^−1
b = 13.328 (4) Å	T = 293 K
c = 7.654 (3) Å	Irregular, blue-green
V = 992.8 (6) Å^3	0.12 × 0.08 × 0.02 mm
F(000) = 964

Data collection

STOE IPDS diffractometer	477 independent reflections
Radiation source: fine-focus sealed tube	286 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.124
Imaging plate scans	θmax = 19.5°, θmin = 2.6°
Absorption correction: gaussian XRED (STOE & CIE GmbH, 1998)	h = −9→9
Tmin = 0.024, Tmax = 0.069	k = −12→11
2800 measured reflections	l = −7→7

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: model
R[F^2 > 2σ(F^2)] = 0.041	Secondary atom site location: difference Fourier map
wR(F^2) = 0.100	Calculated w = 1/[σ^2(Fo^2) + (0.0518P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.81	(Δ/σ)max < 0.001
477 reflections	Δρmax = 0.66 e Å^−3
40 parameters	Δρmin = −0.83 e Å^−3

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
Rb	0.0149 (3)	0.6764 (3)	0.25	0.0570 (9)
Rb2	0.3712 (3)	0.4028 (3)	0.25	0.081 (1)
Co	0.7742 (4)	0.4231 (3)	0.25	0.039 (1)
Br1	0.0183 (3)	0.4149 (3)	0.25	0.087 (1)
Br2	0.6802 (4)	0.5881 (3)	0.25	0.101 (2)
Br3	0.6840 (3)	0.3414 (2)	0.5013 (3)	0.102 (1)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Rb1	0.043 (2)	0.052 (2)	0.076 (2)	−0.0016 (18)	0.000	0.000
Rb2	0.046 (2)	0.127 (3)	0.087 (2)	−0.001 (3)	0.000	0.000
Co1	0.034 (2)	0.041 (3)	0.0400 (19)	−0.002 (2)	0.000	0.000
Br1	0.036 (2)	0.074 (3)	0.151 (3)	0.011 (2)	0.000	0.000
Br2	0.052 (2)	0.048 (2)	0.202 (4)	0.011 (2)	0.000	0.000
Br3	0.0781 (18)	0.165 (3)	0.0627 (14)	−0.042 (2)	−0.0134 (13)	0.0546 (17)

Geometric parameters (Å, º)

Rb1—Br2^i	3.464 (5)	Rb2—Br3^iv	3.941 (5)
Rb1—Br1	3.486 (5)	Rb2—Br3^v	3.941 (5)
Rb1—Br3^ii	3.494 (4)	Rb2—Rb1^xii	4.998 (4)
Rb1—Br3^iii	3.494 (4)	Rb2—Rb1^xiii	4.998 (4)
Rb1—Br3^iv	3.502 (4)	Co1—Br2	2.381 (5)
Rb1—Br3^v	3.502 (4)	Co1—Br3^x	2.378 (3)
Rb1—Br2^vi	3.527 (5)	Co1—Br3	2.378 (3)
Rb1—Br1^vii	4.029 (2)	Co1—Br1^xiv	2.378 (5)
Rb1—Br1^viii	4.029 (2)	Co1—Rb1^xiv	4.109 (5)
Rb1—Co1^i	4.109 (5)	Br1—Co1^i	2.378 (5)
Rb1—Rb2^ix	4.998 (4)	Br1—Rb1^vii	4.029 (2)
Rb1—Rb2^iii	4.998 (4)	Br1—Rb1^viii	4.029 (2)
Rb2—Br1	3.439 (5)	Br2—Rb1^xiv	3.464 (5)
Rb2—Br3	3.693 (4)	Br2—Rb1^xv	3.527 (5)
Rb2—Br3^x	3.693 (4)	Br2—Rb2^xi	3.8615 (16)
Rb2—Br2^xi	3.8615 (16)	Br2—Rb2^iv	3.8615 (16)
Rb2—Br2^iv	3.8615 (16)	Br3—Rb1^xiii	3.494 (4)
Rb2—Br2	3.891 (5)	Br3—Rb1^iv	3.502 (4)
Rb2—Co1	3.931 (5)	Br3—Rb2^iv	3.941 (5)
Br2^i—Rb1—Br1	70.66 (10)	Br2^iv—Rb2—Br3^iv	58.43 (7)
Br2^i—Rb1—Br3^ii	72.11 (9)	Br2—Rb2—Br3^iv	63.68 (8)
Br1—Rb1—Br3^ii	129.39 (10)	Co1—Rb2—Br3^iv	94.39 (10)
Br2^i—Rb1—Br3^iii	72.11 (9)	Br1—Rb2—Br3^v	79.82 (10)
Br1—Rb1—Br3^iii	129.39 (10)	Br3—Rb2—Br3^v	123.77 (11)
Br3^ii—Rb1—Br3^iii	66.03 (11)	Br3^x—Rb2—Br3^v	93.02 (9)
Br2^i—Rb1—Br3^iv	139.79 (7)	Br2^xi—Rb2—Br3^v	58.43 (7)
Br1—Rb1—Br3^iv	85.65 (9)	Br2^iv—Rb2—Br3^v	115.72 (12)
Br3^ii—Rb1—Br3^iv	102.13 (8)	Br2—Rb2—Br3^v	63.68 (8)
Br3^iii—Rb1—Br3^iv	143.37 (10)	Co1—Rb2—Br3^v	94.39 (10)
Br2^i—Rb1—Br3^v	139.79 (7)	Br3^iv—Rb2—Br3^v	57.77 (9)
Br1—Rb1—Br3^v	85.65 (9)	Br1—Rb2—Rb1^xii	104.46 (8)
Br3^ii—Rb1—Br3^v	143.37 (10)	Br3—Rb2—Rb1^xii	94.71 (9)
Br3^iii—Rb1—Br3^v	102.13 (8)	Br3^x—Rb2—Rb1^xii	44.33 (6)
Br3^iv—Rb1—Br3^v	65.86 (10)	Br2^xi—Rb2—Rb1^xii	44.67 (7)
Br2^i—Rb1—Br2^vi	137.01 (12)	Br2^iv—Rb2—Rb1^xii	143.76 (12)
Br1—Rb1—Br2^vi	152.33 (13)	Br2—Rb2—Rb1^xii	102.23 (7)
Br3^ii—Rb1—Br2^vi	72.10 (9)	Co1—Rb2—Rb1^xii	79.65 (7)
Br3^iii—Rb1—Br2^vi	72.10 (9)	Br3^iv—Rb2—Rb1^xii	157.27 (9)
Br3^iv—Rb1—Br2^vi	71.27 (9)	Br3^v—Rb2—Rb1^xii	100.52 (5)
Br3^v—Rb1—Br2^vi	71.27 (9)	Br1—Rb2—Rb1^xiii	104.46 (8)
Br2^i—Rb1—Br1^vii	79.74 (6)	Br3—Rb2—Rb1^xiii	44.33 (6)
Br1—Rb1—Br1^vii	72.47 (7)	Br3^x—Rb2—Rb1^xiii	94.71 (9)
Br3^ii—Rb1—Br1^vii	131.55 (9)	Br2^xi—Rb2—Rb1^xiii	143.76 (12)
Br3^iii—Rb1—Br1^vii	68.17 (7)	Br2^iv—Rb2—Rb1^xiii	44.67 (7)
Br3^iv—Rb1—Br1^vii	124.26 (10)	Br2—Rb2—Rb1^xiii	102.23 (7)
Br3^v—Rb1—Br1^vii	61.97 (6)	Co1—Rb2—Rb1^xiii	79.65 (7)
Br2^vi—Rb1—Br1^vii	107.78 (6)	Br3^iv—Rb2—Rb1^xiii	100.52 (5)
Br2^i—Rb1—Br1^viii	79.74 (6)	Br3^v—Rb2—Rb1^xiii	157.27 (9)
Br1—Rb1—Br1^viii	72.47 (7)	Rb1^xii—Rb2—Rb1^xiii	99.94 (10)
Br3^ii—Rb1—Br1^viii	68.17 (7)	Br1—Rb2—Rb1	43.76 (9)
Br3^iii—Rb1—Br1^viii	131.55 (9)	Br3—Rb2—Rb1	136.78 (10)
Br3^iv—Rb1—Br1^viii	61.97 (6)	Br3^x—Rb2—Rb1	136.78 (10)
Br3^v—Rb1—Br1^viii	124.26 (10)	Br2^xi—Rb2—Rb1	83.57 (8)
Br2^vi—Rb1—Br1^viii	107.78 (6)	Br2^iv—Rb2—Rb1	83.57 (8)
Br1^vii—Rb1—Br1^viii	143.58 (13)	Br2—Rb2—Rb1	94.17 (11)
Br2^i—Rb1—Co1^i	35.36 (8)	Co1—Rb2—Rb1	129.61 (12)
Br1—Rb1—Co1^i	35.30 (8)	Br3^iv—Rb2—Rb1	43.88 (6)
Br3^ii—Rb1—Co1^i	101.60 (9)	Br3^v—Rb2—Rb1	43.88 (6)
Br3^iii—Rb1—Co1^i	101.60 (9)	Rb1^xii—Rb2—Rb1	126.18 (4)
Br3^iv—Rb1—Co1^i	114.91 (9)	Rb1^xiii—Rb2—Rb1	126.18 (4)
Br3^v—Rb1—Co1^i	114.91 (9)	Br2—Co1—Br3^x	106.33 (14)
Br2^vi—Rb1—Co1^i	172.37 (12)	bR2—Co1—Br3	106.33 (14)
Br1^vii—Rb1—Co1^i	72.91 (6)	Br3^x—Co1—Br3	108.0 (2)
Br1^viii—Rb1—Co1^i	72.91 (6)	Br2—Co1—Br1^xiv	115.25 (19)
Br2^i—Rb1—Rb2^ix	114.44 (6)	Br3^x—Co1—Br1^xiv	110.32 (13)
Br1—Rb1—Rb2^ix	126.99 (6)	Br3—Co1—Br1^xiv	110.32 (13)
Br3^ii—Rb1—Rb2^ix	47.60 (6)	Br2—Co1—Rb2	71.36 (13)
Br3^iii—Rb1—Rb2^ix	99.21 (10)	Br3^x—Co1—Rb2	66.45 (10)
Br3^iv—Rb1—Rb2^ix	55.89 (7)	Br3—Co1—Rb2	66.45 (10)
Br3^v—Rb1—Rb2^ix	105.77 (8)	Br1^xiv—Co1—Rb2	173.40 (17)
Br2^vi—Rb1—Rb2^ix	50.32 (5)	Br2—Co1—Rb1^xiv	57.35 (12)
Br1^vii—Rb1—Rb2^ix	158.05 (9)	Br3^x—Co1—Rb1^xiv	125.91 (10)
Br1^viii—Rb1—Rb2^ix	58.18 (6)	Br3—Co1—Rb1^xiv	125.92 (10)
Co1^i—Rb1—Rb2^ix	128.49 (5)	Br1^xiv—Co1—Rb1^xiv	57.89 (12)
Br2^i—Rb1—Rb2^iii	114.44 (6)	Rb2—Co1—Rb1^xiv	128.71 (12)
Br1—Rb1—Rb2^iii	126.99 (6)	Co1^i—Br1—Rb2	179.98 (15)
Br3^ii—Rb1—Rb2^iii	99.21 (10)	Co1^i—Br1—Rb1	86.81 (14)
Br3^iii—Rb1—Rb2^iii	47.60 (6)	Rb2—Br1—Rb1	93.22 (13)
Br3^iv—Rb1—Rb2^iii	105.77 (8)	Co1^i—Br1—Rb1^vii	86.21 (7)
Br3^v—Rb1—Rb2^iii	55.89 (7)	Rb2—Br1—Rb1^vii	93.78 (7)
Br2^vi—Rb1—Rb2^iii	50.32 (5)	Rb1—Br1—Rb1^vii	107.54 (7)
Br1^vii—Rb1—Rb2^iii	58.18 (6)	Co1^i—Br1—Rb1^viii	86.21 (7)
Br1^viii—Rb1—Rb2^iii	158.05 (9)	Rb2—Br1—Rb1^viii	93.78 (7)
Co1^i—Rb1—Rb2^iii	128.49 (5)	Rb1—Br1—Rb1^viii	107.54 (7)
Rb2^ix—Rb1—Rb2^iii	99.94 (10)	Rb1^vii—Br1—Rb1^viii	143.58 (13)
Br1—Rb2—Br3	146.50 (7)	Co1—Br2—Rb1^xiv	87.28 (14)
Br1—Rb2—Br3^x	146.50 (7)	Co1—Br2—Rb1^xv	175.46 (17)
Br3—Rb2—Br3^x	62.77 (10)	Rb1^xiv—Br2—Rb1^xv	97.26 (10)
Br1—Rb2—Br2^xi	82.48 (7)	Co1—Br2—Rb2^xi	94.52 (9)
Br3—Rb2—Br2^xi	129.04 (10)	Rb1^xiv—Br2—Rb2^xi	96.38 (7)
Br3^x—Rb2—Br2^xi	66.28 (7)	Rb1^xv—Br2—Rb2^xi	85.01 (8)
Br1—Rb2—Br2^iv	82.48 (7)	Co1—Br2—Rb2^iv	94.52 (9)
Br3—Rb2—Br2^iv	66.27 (7)	Rb1^xiv—Br2—Rb2^iv	96.38 (7)
Br3^x—Rb2—Br2^iv	129.04 (10)	Rb1^xv—Br2—Rb2^iv	85.01 (8)
Br2^xi—Rb2—Br2^iv	164.68 (14)	Rb2^xi—Br2—Rb2^iv	164.67 (14)
Br1—Rb2—Br2	137.93 (16)	Co1—Br2—Rb2	73.20 (13)
Br3—Rb2—Br2	60.23 (8)	Rb1^xiv—Br2—Rb2	160.49 (13)
Br3^x—Rb2—Br2	60.23 (8)	Rb1^xv—Br2—Rb2	102.25 (11)
Br2^xi—Rb2—Br2	94.60 (8)	Rb2^xi—Br2—Rb2	85.40 (8)
Br2^iv—Rb2—Br2	94.60 (8)	Rb2^iv—Br2—Rb2	85.40 (8)
Br1—Rb2—Co1	173.37 (16)	Co1—Br3—Rb1^xiii	158.96 (14)
Br3—Rb2—Co1	36.18 (5)	Co1—Br3—Rb1^iv	99.34 (11)
Br3^x—Rb2—Co1	36.18 (5)	Rb1^xiii—Br3—Rb1^iv	97.16 (7)
Br2^xi—Rb2—Co1	97.30 (7)	Co1—Br3—Rb2	77.37 (11)
Br2^iv—Rb2—Co1	97.30 (7)	Rb1^xiii—Br3—Rb2	88.08 (9)
Br2—Rb2—Co1	35.44 (8)	Rb1^iv—Br3—Rb2	171.06 (13)
Br1—Rb2—Br3^iv	79.82 (10)	Co1—Br3—Rb2^iv	92.58 (13)
Br3—Rb2—Br3^iv	93.02 (9)	Rb1^xiii—Br3—Rb2^iv	101.86 (9)
Br3^x—Rb2—Br3^iv	123.76 (11)	Rb1^iv—Br3—Rb2^iv	84.86 (9)
Br2^xi—Rb2—Br3^iv	115.72 (12)	Rb2—Br3—Rb2^iv	86.98 (9)

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