Cerium(III) dihydroxidohexa­oxidotetra­borate chloride

The crystal structure of the title compound, Ce[B₄O₆(OH)₂]Cl, is built from polyborate sheets parallel to the (001) plane. These sheets stack along the [001] direction and are linked by Ce atoms exhibiting an CeO₈Cl₂ coordination sphere. O—H...O and O—H...Cl hydrogen bonds additionally stabilize the structural set-up. The polyborate sheet is made up of zigzag borate chains running along the [10] direction. These zigzag chains are inter­connected by shared O-vertices, resulting in a two-dimensional layer with nine-membered rings. All B and O atoms (except for the terminal OH atoms) lie in the nearly planar sheets of polyborates, leading to their isotropic atomic displacement parameters being significantly smaller than usual. This may be attributed to the fact that the atomic displacement parameters correlate not only with their atomic masses but with their coordination environments also.

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](O-B) = 0.007 Å
• R factor = 0.020
• wR factor = 0.051
• Data-to-parameter ratio = 11.4

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT976_ALERT_2_B Negative Residual Density at 1.03A from O6     .      -1.60 eA-3

Alert level C
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600         26
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          1
PLAT915_ALERT_3_C Low Friedel Pair Coverage ......................         86 Perc.
PLAT972_ALERT_2_C Large Calcd. Non-Metal Negative Residual Density      -1.60 eA-3
PLAT975_ALERT_2_C Positive Residual Density at 0.84A from O3     .       0.42 eA-3
PLAT975_ALERT_2_C Positive Residual Density at 0.94A from O7     .       0.41 eA-3

Alert level G
REFLT03_ALERT_4_G 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.
           From the CIF: _diffrn_reflns_theta_max           28.01
           From the CIF: _reflns_number_total               1532
           Count of symmetry unique reflns          843
           Completeness (_total/calc)            181.73%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       689
           Fraction of Friedel pairs measured     0.817
           Are heavy atom types Z>Si present        yes
PLAT002_ALERT_2_G Number of Distance or Angle Restraints on AtSite          4
PLAT003_ALERT_2_G Number of Uiso or Uij Restrained Atom Sites ....          1
PLAT004_ALERT_5_G Info: Polymeric Structure Found with Dimension .          3
PLAT005_ALERT_5_G No _iucr_refine_instructions_details in CIF ....          ?
PLAT232_ALERT_2_G Hirshfeld Test Diff (M-X)  Ce1    --  Cl1     ..        5.3 su
PLAT232_ALERT_2_G Hirshfeld Test Diff (M-X)  Ce1    --  Cl1_l   ..        5.7 su
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......         10
PLAT961_ALERT_5_G Dataset Contains no Negative Intensities .......          !

   0 ALERT level A = Most likely a serious problem - resolve or explain
   1 ALERT level B = A potentially serious problem, consider carefully
   6 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   9 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   8 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   3 ALERT type 5 Informative message, check

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S1. Comment

Borate compounds have been extensively studied due to their variety of fundamental building blocks and crystal structure types (Burns et al., 1995), as well as their successful industry applications as nonlinear optical materials, e.g. β-Ba(B₂O₄) (BBO) (Chen et al., 1985) and LiB₃O₅ (LBO) (Zhao et al., 1990). Besides alkali metals and alkaline-earth metals (Sun, Sun et al., 2010), rare-earth elements become highlighted with being introduced into the borate system in order to obtain multifunctional materials with the distinctive luminescence properties of rare-earth elements. Belokoneva et al. (2002) claimed that Ln(B₄O₆(OH)₂)Cl (Ln = Pr, Nd) exhibits excellent nonlinear optical properties. But the atomic coordinates of its cerium analogue have not been reported until now. Herein, we report the crystal structure of Ce(B₄O₆(OH)₂)Cl determined from single-crystal X-ray diffraction data, including the sites of hydrogen atoms.

The crystal structure of Ce(B₄O₆(OH)₂)Cl is characterized as a layered strcuture of polyborate sheets parallel to (001)(Fig. 1 & 2). In the structure boron atoms have two types of polyhedral coordinations. One is 3-coordinated by oxygen atoms, forming a triangular planar [BO₃] group. The other is 4-coordinated to three O-atoms and one hydroxyl group to form a [BO₃(OH)] tetrahedron (Fig. 3). Both [BO₃] group and [BO₃(OH)] polyhedron link to three neighbouring borate groups via their common O-corners except for OH terminals. Two [BO₃(OH)] tetrahedra and two triangular planar [BO₃] groups compose a borate tetramer as a fundamental building block (FBB) (Fig. 2) (Burns et al., 1995). The FBBs share their common oxygen vertices to form a zigzag borate chain running along the [110] direction. The zigzag chains are further interconnected with each other by sharing their common O-corners, resulting in a two-dimensional layer with 9-membered rings within the layer. The 9-membered ring has a nearly equilateral (about 7.00 Å) triangular motif (Fig. 2). The Ce atoms just reside at the center of 9-membered rings and adopt a 10-coordination with the surrounding eight oxygen and two chlorine atoms, forming a 1-6-3 crown-shaped polyhedron (Fig. 2). The two-dimensional layers stack along the [001] direction and are linked by Ce and Cl atoms as well as hydrogen bonds to form the three-dimensional crystal structure (Fig. 1). It is interesting that all boron and oxygen atoms (except for OH terminals) lying in the nearly planar sheets of polyborates lead to their isotropic atomic parameters significantly smaller than as-expected usually. For example, the isotropic atomic parameters of boron atoms are distributed in the range of 0.0062 (10) to 0.0085 (10) Ų, significantly smaller than that of chlorine atom (0.0130 (2) Ų). This may give a hint that the atomic displacement parameters correlate not only with their atomic masses but with their coordination environments also. However the standard uncertainties of atomic displacement parameters do have close correlation with their atomic masses of individual elements. As-observed in the title compound, standard uncertainties of atomic displacement parameters of all atoms distribute as-expected in the sequence of Ce, Cl, O, B and H, increasing while their atomic masses decrease.

Related literature

For background to borate compounds and their applications, see: Burns et al. (1995); Chen et al. (1985); Zhao et al. (1990); Sun, Sun et al. (2010); Sun, Zhou et al. (2010). For related structures, see: Belokoneva et al. (2002) for Ln(B₄O₆(OH)₂)Cl (Ln = Pr, Nd).

S2. Experimental

The title compound, Ce(B₄O₆(OH)₂)Cl was synthesized by using a hydrothermal method during our systematically exploiting rare earth borates (Sun, Zhou et al., 2010). Typically, a mixture of Ce₂O₃ (0.33 g), CrCl₃.6H₂O (0.80 g), H₃BO₃ (2.00 g) and 2 ml distilled water with molar ratio of Ce: Cl: B = 1: 9: 32 was prepared, and transferred into a Teflon-lined stainless-steel autoclave (30 ml in volume), then heated to and kept at 468 K for three days. Transparent, colorless crystals of the title compound were obtained by filtration, rinsed with distilled water several times, and dried in desiccators. Optical examination and powder X-ray diffraction (PXRD) analyses were used to identify the phases of the solid products.

S3. Refinement

The hydrogen positions were obtained from the difference Fourier map and refined via fixing the bond distance of d(OH) = 0.82 (2)Å with the donator of coordinated oxygen atoms. Moreover a common variable was set for the isotropic atomic displacement parameters of all hydrogen atoms during the refinement.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2011) and ATOMS (Dowty, 2004); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. Crystal structure of Ce(B4O6(OH)2)Cl. ([BO4] drawn in red tetrahedra; [BO3] in blue triangular groups; Ce in black spheres; Cl in green spheres; H in small black balls).
	Fig. 2. Left: a two-dimensional sheet with 9-membered rings, the fundamental building block (FBB) marked by a dash-line ellipse; Right upper: a 9-membered ring with a nearly equilateral triangular motif; Right down: coordination environment of Ce in a 1-6-3 crown-shaped polyhedron.
	Fig. 3. Coordination environment of metal atoms, with displacement ellipsoids drawn at the 50% probability level (symmetry codes: (vi) x–1/2, y–1/2, z; (vii) x–1, y, z; (viii) x + 1/2, y–1/2, z)

Cerium(III) dihydroxidohexaoxidotetraborate chloride

Crystal data

Ce[B4O6(OH)2]Cl	F(000) = 644
Mr = 348.83	Dx = 3.359 Mg m^−3
Monoclinic, Cc	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C -2yc	Cell parameters from 2825 reflections
a = 6.5169 (11) Å	θ = 3.6–28.0°
b = 11.245 (2) Å	µ = 7.00 mm^−1
c = 9.7575 (17) Å	T = 295 K
β = 105.284 (3)°	Prism, colorless
V = 689.8 (2) Å^3	0.16 × 0.07 × 0.03 mm
Z = 4

Data collection

Bruker SMART APEX CCD area-detector diffractometer	1532 independent reflections
Radiation source: fine-focus sealed tube	1523 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.022
1800 images,ϕ = 0, 90, 180°, χ = 54.74°, Δω=0.3°, Exp time: 15 s. scans	θmax = 28.0°, θmin = 3.6°
Absorption correction: multi-scan (SADABS; Bruker, 2001)	h = −8→8
Tmin = 0.401, Tmax = 0.818	k = −14→14
2825 measured reflections	l = −12→12

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.020	All H-atom parameters refined
wR(F^2) = 0.051	w = 1/[σ^2(Fo^2) + (0.0285P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max = 0.001
1532 reflections	Δρmax = 0.53 e Å^−3
134 parameters	Δρmin = −1.64 e Å^−3
10 restraints	Absolute structure: Flack (1983), 716 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.034 (19)

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
Ce1	0.98063 (4)	0.706775 (17)	0.56430 (4)	0.00585 (8)
Cl1	0.6202 (2)	0.82445 (12)	0.37031 (14)	0.0130 (2)
B1	0.1685 (9)	0.4466 (5)	0.6439 (6)	0.0073 (10)
B2	0.8287 (9)	0.4064 (5)	0.6939 (6)	0.0085 (10)
B3	0.5112 (9)	0.5338 (5)	0.6256 (6)	0.0068 (10)
B4	0.5809 (9)	0.7447 (5)	0.7169 (6)	0.0062 (10)
O1	0.9639 (5)	0.4852 (3)	0.6324 (3)	0.0076 (7)
O2	0.7362 (6)	0.8358 (3)	0.6858 (4)	0.0086 (7)
O3	0.6294 (6)	0.6361 (3)	0.6426 (4)	0.0093 (7)
O4	0.3652 (6)	0.7819 (3)	0.6635 (4)	0.0068 (7)
O5	0.2933 (6)	0.5383 (3)	0.6124 (4)	0.0087 (7)
O6	0.6027 (6)	0.4259 (3)	0.6207 (4)	0.0086 (7)
O7	0.6335 (7)	0.7247 (3)	0.8706 (4)	0.0116 (7)
O8	0.8688 (6)	0.4269 (3)	0.8477 (4)	0.0101 (7)
H1	0.894 (13)	0.495 (3)	0.876 (7)	0.04 (2)*
H2	0.731 (13)	0.706 (6)	0.940 (7)	0.04 (2)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ce1	0.00577 (12)	0.00558 (12)	0.00601 (12)	0.00003 (13)	0.00121 (8)	0.00002 (14)
Cl1	0.0132 (6)	0.0155 (6)	0.0094 (6)	0.0047 (5)	0.0012 (5)	−0.0001 (5)
B1	0.004 (2)	0.009 (2)	0.009 (3)	−0.0008 (19)	0.001 (2)	−0.002 (2)
B2	0.009 (3)	0.006 (2)	0.009 (3)	0.001 (2)	0.002 (2)	−0.001 (2)
B3	0.011 (3)	0.005 (2)	0.005 (2)	0.001 (2)	0.0029 (19)	0.0021 (19)
B4	0.009 (3)	0.003 (2)	0.006 (2)	0.003 (2)	0.002 (2)	−0.0001 (19)
O1	0.0040 (16)	0.0072 (16)	0.0124 (17)	0.0020 (13)	0.0036 (14)	0.0006 (13)
O2	0.0079 (18)	0.0045 (16)	0.0131 (19)	0.0007 (14)	0.0025 (14)	−0.0005 (14)
O3	0.0083 (18)	0.0063 (15)	0.0145 (18)	0.0011 (14)	0.0055 (14)	−0.0014 (14)
O4	0.0061 (17)	0.0036 (16)	0.0105 (19)	0.0009 (12)	0.0015 (14)	−0.0010 (12)
O5	0.0046 (16)	0.0042 (15)	0.0180 (18)	−0.0009 (13)	0.0041 (14)	0.0023 (14)
O6	0.0027 (15)	0.0077 (14)	0.0138 (17)	−0.0020 (13)	−0.0004 (13)	−0.0019 (13)
O7	0.0091 (19)	0.0155 (17)	0.0097 (19)	0.0059 (15)	0.0017 (15)	0.0023 (15)
O8	0.0161 (18)	0.0084 (17)	0.0048 (17)	−0.0029 (14)	0.0007 (14)	−0.0010 (13)

Geometric parameters (Å, º)

Ce1—O7^i	2.480 (4)	B1—O5	1.396 (6)
Ce1—O8^ii	2.539 (4)	B2—O4^viii	1.464 (6)
Ce1—O4^iii	2.579 (4)	B2—O8	1.472 (6)
Ce1—O1	2.589 (3)	B2—O6	1.474 (6)
Ce1—O6^iv	2.603 (3)	B2—O1	1.483 (7)
Ce1—O2	2.654 (4)	B3—O6	1.359 (6)
Ce1—O3	2.716 (4)	B3—O3	1.370 (6)
Ce1—O5^iii	2.731 (3)	B3—O5	1.392 (7)
Ce1—Cl1^v	2.9041 (14)	B4—O4	1.427 (6)
Ce1—Cl1	2.9168 (14)	B4—O7	1.465 (6)
B1—O2^vi	1.349 (6)	B4—O3	1.496 (6)
B1—O1^vii	1.378 (6)	B4—O2	1.526 (7)
O7^i—Ce1—O8^ii	68.55 (12)	O8^ii—Ce1—Cl1	73.91 (9)
O7^i—Ce1—O4^iii	68.81 (13)	O4^iii—Ce1—Cl1	129.17 (8)
O8^ii—Ce1—O4^iii	122.93 (12)	O1—Ce1—Cl1	121.47 (8)
O7^i—Ce1—O1	123.18 (11)	O6^iv—Ce1—Cl1	81.76 (8)
O8^ii—Ce1—O1	67.76 (11)	O2—Ce1—Cl1	64.30 (8)
O4^iii—Ce1—O1	108.75 (10)	O3—Ce1—Cl1	73.81 (8)
O7^i—Ce1—O6^iv	72.87 (12)	O5^iii—Ce1—Cl1	149.66 (8)
O8^ii—Ce1—O6^iv	137.83 (11)	Cl1^v—Ce1—Cl1	134.62 (5)
O4^iii—Ce1—O6^iv	53.00 (10)	Ce1^ix—Cl1—Ce1	126.35 (5)
O1—Ce1—O6^iv	152.63 (11)	O2^vi—B1—O1^vii	123.2 (5)
O7^i—Ce1—O2	125.41 (12)	O2^vi—B1—O5	125.8 (5)
O8^ii—Ce1—O2	128.40 (12)	O1^vii—B1—O5	110.9 (4)
O4^iii—Ce1—O2	106.95 (11)	O4^viii—B2—O8	111.2 (4)
O1—Ce1—O2	109.92 (11)	O4^viii—B2—O6	103.8 (4)
O6^iv—Ce1—O2	64.77 (11)	O8—B2—O6	110.9 (4)
O7^i—Ce1—O3	147.45 (13)	O4^viii—B2—O1	110.1 (4)
O8^ii—Ce1—O3	89.01 (12)	O8—B2—O1	110.8 (4)
O4^iii—Ce1—O3	142.92 (12)	O6—B2—O1	109.9 (4)
O1—Ce1—O3	63.28 (10)	O6—B3—O3	121.1 (5)
O6^iv—Ce1—O3	116.78 (11)	O6—B3—O5	118.4 (5)
O2—Ce1—O3	52.04 (11)	O3—B3—O5	120.6 (4)
O7^i—Ce1—O5^iii	85.14 (13)	O4—B4—O7	111.1 (4)
O8^ii—Ce1—O5^iii	76.69 (11)	O4—B4—O3	112.1 (4)
O4^iii—Ce1—O5^iii	63.61 (10)	O7—B4—O3	110.4 (4)
O1—Ce1—O5^iii	50.80 (10)	O4—B4—O2	111.9 (4)
O6^iv—Ce1—O5^iii	116.61 (11)	O7—B4—O2	108.6 (4)
O2—Ce1—O5^iii	144.19 (12)	O3—B4—O2	102.5 (4)
O3—Ce1—O5^iii	113.23 (11)	B1^iii—O1—B2	116.4 (4)
O7^i—Ce1—Cl1^v	137.84 (10)	B1^iv—O2—B4	119.9 (4)
O8^ii—Ce1—Cl1^v	136.70 (9)	B3—O3—B4	124.1 (4)
O4^iii—Ce1—Cl1^v	69.13 (9)	B4—O4—B2^x	113.8 (4)
O1—Ce1—Cl1^v	69.06 (8)	B3—O5—B1	126.3 (4)
O6^iv—Ce1—Cl1^v	84.35 (8)	B3—O6—B2	120.5 (4)
O2—Ce1—Cl1^v	70.67 (8)	B4—O7—H2	143 (8)
O3—Ce1—Cl1^v	74.57 (8)	Ce1^xi—O7—H2	80 (8)
O5^iii—Ce1—Cl1^v	73.87 (8)	B2—O8—H1	117 (5)
O7^i—Ce1—Cl1	77.35 (10)	Ce1^xii—O8—H1	107 (5)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O8—H1···O1^xii	0.82 (2)	2.43 (7)	2.859 (5)	114 (6)
O8—H1···Cl1^v	0.82 (2)	2.52 (5)	3.219 (4)	145 (7)
O7—H2···O4^v	0.83 (2)	2.13 (6)	2.860 (6)	148 (10)
O7—H2···Cl1^v	0.83 (2)	2.81 (11)	3.220 (4)	112 (9)

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