Crystal structures and comparisons of huntite aluminum borates REAl₃(BO₃)₄ (RE = Tb, Dy and Ho)

Three huntite-type aluminoborates of stoichiometry REAl₃(BO₃)₄ (RE = Tb, Dy and Ho), namely, terbium/dysprosium/holmium trialuminium tetrakis(borate), were synthesized by slow cooling within a K₂Mo₃O₁₀ flux with spontaneous crystallization. The crystal structures were determined using single-crystal X-ray diffraction (SC-XRD) data. The synthesized borates are isostructural to the huntite [CaMg₃(CO₃)₄] structure and crystallized within the trigonal R32 space group. The structural parameters were compared to literature data of other huntite REAl₃(BO₃)₄ crystals within the R32 space group. All three borates fit well into the trends calculated from the literature data. The unit-cell parameters and volumes increase linearly with larger RE cations whereas the densities decrease. All of the crystals studied were refined as inversion twins.

1. Chemical context

Rare-earth aluminum borates (REAB) with the general chemical formula REAl₃(BO₃)₄ (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) have been studied extensively for applications in lasers, nonlinear optics, sensors, and phosphors because of their optical and magnetoelectric properties as well as the capacity to be doped with other rare-earth metals (Koporulina et al., 2000; Leonyuk & Leonyuk, 1995; Leonyuk et al., 1998; Mills, 1962; Belokoneva & Timchenko, 1983; Belokoneva, 1994). The REAB crystals are promising materials for self-frequency-doubling lasers as their nonlinear optical properties can be changed by doping with different rare-earth elements including Nd, Dy, Er, Yb, Tm, or Y (Leonyuk et al., 1998, 2007; Földvári et al., 2003; Chen et al., 2012). The REAB compounds with RE = Tb, Ho, Er, or Tm exhibit the magnetoelectric properties useful for sensor applications (Liang et al., 2011, 2012), and REAB with the RE = Pr, Sm, Eu, Gd, Tb, or Ho can be used as phosphors (Li & Wang, 2007; He et al., 2015).

The REAB compounds are generally synthesized by a flux-assisted growth method with or without seeds at 800–1150°C (Leonyuk & Leonyuk, 1995; Koporulina et al., 2000; Wang, 2012; Leonyuk, 2017). The K₂Mo₃O₁₀ (Tu et al., 1994; Wang et al., 1995; Leonyuk & Leonyuk, 1995; Teshima et al., 2006) compound is the most commonly used flux for the crystallization of REAB, although other fluxes such as Bi₂O₃–B₂O₃ (Chani et al., 1994) and BaO–B₂O₃ (Jung et al., 1995) have been used. Two major drawbacks of using the K₂Mo₃O₁₀ flux are the potential incorporation of Mo into the REAB structure and co-crystallization of other phases (Wang, 2012; Leonyuk, 2017; Kuz'micheva et al., 2019). In the current study, K₂Mo₃O₁₀ flux was used to synthesize REAl₃(BO₃)₄ (RE = Tb, Dy, Ho) crystals, and the structural parameters of the synthesized REAB crystals were compared to literature data.

2. Structural commentary

The crystal structures of the synthesized REAB crystals are isostructural to the huntite structure (Mills, 1962) with the R32 space group (Fig. 1). The huntite aluminoborates generally crystallize within the R32 space group; however, REAB compounds with RE = Pr, Nd, Sm, Eu, Tb, Ho, or Gd showed the transition in space group from R32 to lower symmetry monoclinic C2/c and C2 space groups in the disordered structures caused by variations in the growth temperature, cooling rate, and composition (Belokoneva & Timchenko, 1983; Belokoneva et al., 1988, 1994; Leonyuk & Leonyuk, 1995; Plachinda & Belokoneva, 2008; Leonyuk, 2017). The structures of the REAB crystals are composed of rare-earth cations with a distorted trigonal–prismatic coordination (REO₆), aluminum cations with a distorted octa­hedral coord­ination (AlO₆), and boron cations with a trigonal–planar coordination (BO₃) as shown in Fig. 2. The AlO₆ octa­hedra form helical chains along the c-axis direction by sharing edges, and these chains are connected by BO₃ units (see Fig. 3).

Figure 1 Crystal structure of REAl3(BO3)4.

Figure 2 Coordination of oxygen atoms around (a) rare-earth, (b) aluminum, and (c) boron atoms shown as polyhedra.

Figure 3 Structure showing the helical chains composed of edge sharing AlO6 units along the c axis connected by BO3 in REAl3(BO3)4.

The structural parameters of the synthesized REAB compounds were added to literature data for comparison (see Fig. 4), and they were in good agreement when plotted versus the average ionic crystal radius of the six-coordinated RE element according to Shannon (1976). The trendlines show that the unit-cell parameters and volumes increase linearly whereas the densities decrease with the larger rare-earth cations in the structures. The data included in Fig. 4 include literature data for REAl₃(BO₃)₄ where RE = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu, as well as mixtures of Y/Er and Y/Nd (Belokoneva et al., 1981; Hong & Dwight, 1974; Xu et al., 2002; Jia et al., 2006; Kuroda et al., 1981; Leonyuk & Leonyuk, 1995; Malakhovskii et al., 2014; Mészáros et al., 2000; Mills, 1962; Plachinda & Belokoneva, 2008; Prokhorov et al., 2013, 2014; Sváb et al., 2012; Wang et al., 1991).

Figure 4 Summary of (a) unit-cell parameter a, (b) unit-cell parameter c, (c) unit-cell volume (V), and (d) density (ρ) as a function of the average ionic crystal radii of the RE in the crystal structures (coordination number = 6) from Shannon (1976).

3. Synthesis and crystallization

The REAB single crystals were synthesized using Tb₂O₃ (Alfa Aesar, 99.9%), Dy₂O₃ (Alfa Aesar, 99.9%), Ho₂O₃ (Alfa Aesar, 99.9%), Al(OH)₃ (Almatis, 99.5%), B₂O₃ (Alfa Aesar, 99.98%), and K₂Mo₃O₁₀ flux. All the rare-earth oxides, Al(OH)₃, and B₂O₃ were used as received; the B₂O₃ was stored and handled in a nitro­gen glovebox to prevent hydration (M-Braun, Inc., < 0.1 ppm of O₂ and H₂O). The K₂Mo₃O₁₀ flux was synthesized using K₂CO₃ (Alfa Aesar, 99%) and MoO₃ (Alfa Aesar, 99.5%). For the flux, appropriate amounts of K₂CO₃ and MoO₃ were mixed in a mortar and pestle and placed into a Pt/10%Rh crucible. The crucible was heated to 520°C at 5°C min⁻¹, maintained at that temperature for 8 h, and then cooled down to room temperature at 5°C min⁻¹. For the synthesis of the REAB crystals, the rare-earth oxide was mixed with Al(OH)₃ and B₂O₃ in a 1:6:5 molar ratio, and then K₂Mo₃O₁₀ was added at 40 mass% of the total precursor mass. The mixed powder of each rare-earth element was put into a Pt/10%Rh crucible, tightly covered with a Pt/10%Rh lid, and placed in a Thermolyne box furnace. The furnace was heated to 900°C at 5°C min⁻¹, maintained at that temperature for 4 h, cooled to 400°C at 5°C h⁻¹, and then shut off to cool naturally. The synthesized products were washed with deionized water in a sonic bath, and the crystals were recovered with vacuum filtration using a Büchner funnel. The REAB crystals along with KRE(MoO₄)₂ were synthesized by this process as expected from previous studies (Leonyuk et al., 1998; Teshima et al., 2006; Leonyuk, 2017; Kuz'micheva et al., 2019).

The REAB crystals generally have hexa­gonal prismatic shapes, and they were often agglomerated (Fig. 5), as observed with scanning electron microscopy (JSM-7001F field emission gun SEM; JEOL USA, Inc.). Crystals of SmAl₃(BO₃)₄ and LuAl₃(BO₃)₄ were also grown using the same procedure as described above and these are shown in Fig. 5 for comparison; however, the crystal structures are not reported due to the poor diffraction of SmAl₃(BO₃)₄ and unresolvable displacement parameters during structural refinement for LuAl₃(BO₃)₄. Finally, for the crystal growth conditions used here, the average crystallite sizes for the different REAl₃(BO₃)₄ crystals herein (RE = Sm, Tb, Dy, Ho, Lu) are shown in Fig. 6 with standard deviations based on measurements of ≥ 7 crystals from each sample.

Figure 5 Back-scattered electron SEM micrographs of REAl3(BO3)4 crystals including (a) and(b) SmAl3(BO3)4, (c) TbAl3(BO3)4, (d) DyAl3(BO3)4, (e) HoAl3(BO3)4, and (f) LuAl3(BO3)4. Note that some KLu(MoO4)2 crystals are seen in (a) and (d) as the smaller and brighter crystallites.

Figure 6 Summary of crystal size in terms of average length and width as a function of the average ionic crystal radii of the RE in the crystal structures (coordination number = 6) from Shannon (1976).

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. Suitable crystals were selected for SC-XRD and were placed on cryoloops in oil (Parabar 10312, Hampton Research). Data were collected with a scan width of 0.5° in φ and ω with a 10 sec dwell time per frame at 100 K. All the REAB crystals had chiral structures and were refined with inversion twinning. The final refinements for TbAl₃(BO₃)₄, DyAl₃(BO₃)₄, and HoAl₃(BO₃)₄ converged at R₁ = 1.97% with goodness-of-fit of 1.08, R₁ = 0.80% with goodness-of-fit of 1.14, and R₁ = 1.15% with goodness-of-fit of 1.08, respectively.

Table 1
Experimental details

	Tb-borate	Dy-borate	Ho-borate
Crystal data
Chemical formula	TbAl3(BO3)4	DyAl3(BO3)4	HoAl3(BO3)4
Mr	475.1	478.7	481.1
Crystal system, space group	Trigonal, R32	Trigonal, R32	Trigonal, R32
Temperature (K)	100	100	100
a, c (Å)	9.2992 (8), 7.2588 (7)	9.2938 (5), 7.2348 (4)	9.2832 (3), 7.2345 (3)
V (Å^3)	543.61 (8)	541.18 (5)	539.93 (3)
Z	3	3	3
Radiation type	Mo Kα	Mo Kα	Mo Kα
μ (mm^−1)	10.21	10.81	11.45
Crystal size (mm)	0.03 × 0.03 × 0.02	0.05 × 0.05 × 0.03	0.05 × 0.05 × 0.03
Data collection
Diffractometer	Bruker D8 QUEST CMOS area detector	Bruker D8 QUEST CMOS area detector	Bruker D8 QUEST CMOS area detector
Absorption correction	Multi-scan (SADABS; Krause et al., 2015)	Multi-scan (SADABS; Krause et al., 2015)	Multi-scan (SADABS; Krause et al., 2015)
Tmin, Tmax	0.530, 0.747	0.588, 0.723	0.570, 0.709
No. of measured, independent and observed [I > 2σ(I)] reflections	6957, 270, 270	7295, 420, 420	5662, 381, 381
Rint	0.113	0.044	0.047
Refinement
R[F > 3σ(F)], wR(F), S	0.020, 0.021, 1.08	0.010, 0.010, 1.14	0.012, 0.015, 1.08
No. of reflections	270	420	381
No. of parameters	32	35	35
Δρmax, Δρmin (e Å^−3)	0.59, −0.88	0.29, −0.39	0.54, −0.65
Absolute structure	Refined as an inversion twin with a twin ratio of 0.51 (2):0.49 (2)	Refined as an inversion twin with a twin ratio of 0.509 (8):0.491 (8)	Refined as an inversion twin with a twin ratio of 0.558 (12):0.442 (12)
Absolute structure parameter	0.49 (2)	0.491 (8)	0.442 (12)
Computer programs: APEX3 and SAINT (Bruker, 2012), JANA2006 (Petříček et al., 2014), SUPERFLIP (Palatinus & Chapuis, 2007), VESTA (Momma & Izumi, 2011) and publCIF (Westrip, 2010).

Supporting information

Computing details

For all structures, data collection: APEX3 (Bruker, 2012); cell refinement: JANA2006 (Petříček et al., 2014); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SUPERFLIP (Palatinus & Chapuis, 2007); program(s) used to refine structure: JANA2006 (Petříček et al., 2014); molecular graphics: VESTA (Momma & Izumi, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).

Terbium trialuminium tetrakis(borate) (Tb-borate)

Crystal data

TbAl3(BO3)4	Dx = 4.354 Mg m^−3
Mr = 475.1	Mo Kα radiation, λ = 0.71075 Å
Trigonal, R32	Cell parameters from 6957 reflections
Hall symbol: R 3 2"	θ = 3.8–33.2°
a = 9.2992 (8) Å	µ = 10.21 mm^−1
c = 7.2588 (7) Å	T = 100 K
V = 543.61 (8) Å^3	Hexagonal prism, light white
Z = 3	0.03 × 0.03 × 0.02 mm
F(000) = 660

Data collection

Bruker D8 QUEST CMOS area detector diffractometer	270 reflections with I > 2σ(I)
Radiation source: X-ray tube	Rint = 0.113
φ and ω scans	θmax = 33.2°, θmin = 3.8°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −13→14
Tmin = 0.530, Tmax = 0.747	k = −14→13
6957 measured reflections	l = −11→11
270 independent reflections

Refinement

Refinement on F	Primary atom site location: iterative
R[F > 3σ(F)] = 0.020	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
wR(F) = 0.021	(Δ/σ)max = 0.041
S = 1.08	Δρmax = 0.59 e Å^−3
270 reflections	Δρmin = −0.88 e Å^−3
32 parameters	Absolute structure: Data was refined with inversion twinning in JANA2006, and the twin ratio was 0.51(2):0.49(2).
0 restraints	Absolute structure parameter: 0.49 (2)
0 constraints

Special details

Refinement. Data was refined with inversion twinning, and the twin ratio was 0.51 (2):0.49 (2).

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

	x	y	z	Uiso*/Ueq
Tb1	0	0	0	0.01126 (13)
Al1	0.5557 (2)	0	0	0.0052 (6)
B1	0.666667	0.333333	−0.166667	0.0054 (19)
O1	0.7418 (7)	0.0752 (7)	0.166667	0.012 (2)
O2	0.3668 (5)	−0.1151 (5)	−0.1448 (5)	0.0098 (12)
O3	0.8151 (5)	0.4818 (5)	−0.166667	0.0091 (14)
B2	0.8912 (11)	0.2245 (11)	0.166667	0.0066 (12)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Tb1	0.01027 (16)	0.01027 (16)	0.0133 (2)	0.00513 (8)	0	0
Al1	0.0040 (6)	0.0036 (8)	0.0078 (9)	0.0018 (4)	0.0005 (3)	0.0010 (6)
B1	0.004 (2)	0.004 (2)	0.008 (3)	0.0021 (12)	0	0
O1	0.007 (2)	0.007 (2)	0.017 (3)	0.000 (2)	0.0008 (9)	−0.0008 (9)
O2	0.0082 (16)	0.0086 (15)	0.0123 (15)	0.0039 (13)	0.0003 (12)	−0.0013 (12)
O3	0.0075 (15)	0.0075 (15)	0.011 (2)	0.0031 (18)	−0.0010 (8)	0.0010 (8)

Geometric parameters (Å, º)

Tb1—O2^i	2.336 (4)	B1—O3	1.381 (4)
Tb1—O2^ii	2.336 (4)	B1—O3^vii	1.381 (6)
Tb1—O2^iii	2.336 (6)	B1—O3^viii	1.381 (6)
Tb1—O2^iv	2.336 (4)	O1—B2	1.389 (8)
Tb1—O2^v	2.336 (4)	O2—B2^ix	1.362 (12)
Tb1—O2^vi	2.336 (6)
O2^i—Tb1—O2^ii	89.15 (16)	O2^iii—Tb1—O2^vi	144.93 (12)
O2^i—Tb1—O2^iii	89.15 (16)	O2^iv—Tb1—O2^v	89.15 (16)
O2^i—Tb1—O2^iv	119.88 (12)	O2^iv—Tb1—O2^vi	89.15 (16)
O2^i—Tb1—O2^v	144.93 (19)	O2^v—Tb1—O2^vi	89.15 (16)
O2^i—Tb1—O2^vi	73.32 (15)	O3—B1—O3^vii	120.0 (4)
O2^ii—Tb1—O2^iii	89.15 (16)	O3—B1—O3^viii	120.0 (4)
O2^ii—Tb1—O2^iv	144.93 (19)	O3^vii—B1—O3^viii	120.0 (4)
O2^ii—Tb1—O2^v	73.32 (14)	Tb1^x—O2—B2^ix	105.0 (3)
O2^ii—Tb1—O2^vi	119.88 (18)	O1—B2—O2^xi	117.7 (9)
O2^iii—Tb1—O2^iv	73.32 (15)	O1—B2—O2^xii	117.7 (9)
O2^iii—Tb1—O2^v	119.88 (18)	O2^xi—B2—O2^xii	124.7 (6)

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

Dysprosium trialuminium tetrakis(borate) (Dy-borate)

Crystal data

DyAl3(BO3)4	Dx = 4.406 Mg m^−3
Mr = 478.7	Mo Kα radiation, λ = 0.71075 Å
Trigonal, R32	Cell parameters from 7295 reflections
Hall symbol: R 3 2"	θ = 3.8–31.5°
a = 9.2938 (5) Å	µ = 10.81 mm^−1
c = 7.2348 (4) Å	T = 100 K
V = 541.18 (5) Å^3	Hexagonal prism, light white
Z = 3	0.05 × 0.05 × 0.03 mm
F(000) = 663

Data collection

Bruker D8 QUEST CMOS area detector diffractometer	420 reflections with I > 2σ(I)
Radiation source: X-ray tube	Rint = 0.044
φ and ω scans	θmax = 31.5°, θmin = 3.8°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −12→13
Tmin = 0.588, Tmax = 0.723	k = −13→13
7295 measured reflections	l = −10→10
420 independent reflections

Refinement

Refinement on F	Primary atom site location: iterative
R[F > 3σ(F)] = 0.010	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
wR(F) = 0.010	(Δ/σ)max = 0.017
S = 1.14	Δρmax = 0.29 e Å^−3
420 reflections	Δρmin = −0.39 e Å^−3
35 parameters	Absolute structure: The crystal had chiral structure. Data was refined with inversion twinning in JANA2006, and the twin ratio was 0.509(8):0.491(8).
0 restraints	Absolute structure parameter: 0.491 (8)
0 constraints

Special details

Refinement. Data was refined with inversion twinning, and the twin ratio was 0.509 (8):0.491 (8).

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

	x	y	z	Uiso*/Ueq
Dy1	0	0	0	0.00585 (4)
Al1	0.55590 (10)	0	0	0.0031 (2)
O1	0.7422 (3)	0.0755 (3)	0.166667	0.0084 (9)
B1	0.666667	0.333333	−0.166667	0.0062 (7)
O3	0.36691 (18)	−0.11579 (17)	−0.14502 (18)	0.0065 (4)
O2	0.8159 (2)	0.4825 (2)	−0.166667	0.0067 (5)
B2	0.8916 (5)	0.2249 (5)	0.166667	0.0063 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Dy1	0.00546 (6)	0.00546 (6)	0.00665 (6)	0.00273 (3)	0	0
Al1	0.0027 (2)	0.0023 (3)	0.0042 (3)	0.00114 (15)	−0.00007 (10)	−0.0001 (2)
O1	0.0075 (11)	0.0075 (11)	0.0082 (10)	0.0022 (11)	−0.0006 (4)	0.0006 (4)
B1	0.0068 (9)	0.0068 (9)	0.0051 (13)	0.0034 (4)	0	0
O3	0.0058 (6)	0.0063 (5)	0.0072 (5)	0.0029 (4)	−0.0011 (4)	−0.0013 (4)
O2	0.0060 (6)	0.0060 (6)	0.0071 (7)	0.0022 (7)	−0.0004 (3)	0.0004 (3)
B2	0.0083 (11)	0.0083 (11)	0.0058 (9)	0.0068 (15)	−0.0001 (5)	0.0001 (5)

Geometric parameters (Å, º)

Dy1—O3^i	2.3260 (16)	Al1—Al1^viii	2.9992 (7)
Dy1—O3^ii	2.3260 (13)	O1—B2	1.388 (4)
Dy1—O3^iii	2.326 (2)	B1—O2	1.3866 (13)
Dy1—O3^iv	2.3260 (16)	B1—O2^ix	1.387 (2)
Dy1—O3^v	2.3260 (13)	B1—O2^x	1.387 (2)
Dy1—O3^vi	2.326 (2)	O3—B2^xi	1.364 (6)
Al1—Al1^vii	2.9992 (7)
O3^i—Dy1—O3^ii	89.16 (6)	O3^iv—Dy1—O3^v	89.16 (6)
O3^i—Dy1—O3^iii	89.16 (6)	O3^iv—Dy1—O3^vi	89.16 (6)
O3^i—Dy1—O3^iv	119.78 (5)	O3^v—Dy1—O3^vi	89.16 (6)
O3^i—Dy1—O3^v	145.03 (7)	Al1^vii—Al1—Al1^viii	118.02 (3)
O3^i—Dy1—O3^vi	73.33 (6)	O2—B1—O2^ix	120.00 (13)
O3^ii—Dy1—O3^iii	89.16 (6)	O2—B1—O2^x	120.00 (13)
O3^ii—Dy1—O3^iv	145.03 (7)	O2^ix—B1—O2^x	120.00 (13)
O3^ii—Dy1—O3^v	73.33 (5)	Dy1^xii—O3—B2^xi	105.29 (15)
O3^ii—Dy1—O3^vi	119.78 (7)	O1—B2—O3^xiii	117.3 (4)
O3^iii—Dy1—O3^iv	73.33 (6)	O1—B2—O3^xiv	117.3 (4)
O3^iii—Dy1—O3^v	119.78 (7)	O3^xiii—B2—O3^xiv	125.4 (3)
O3^iii—Dy1—O3^vi	145.03 (5)

Symmetry codes: (i) x−1/3, y+1/3, z+1/3; (ii) −y−1/3, x−y−2/3, z+1/3; (iii) −x+y+2/3, −x+1/3, z+1/3; (iv) y+1/3, x−1/3, −z−1/3; (v) x−y−2/3, −y−1/3, −z−1/3; (vi) −x+1/3, −x+y+2/3, −z−1/3; (vii) −y+2/3, x−y−2/3, z+1/3; (viii) −x+y+4/3, −x+2/3, z−1/3; (ix) −y+1, x−y, z; (x) −x+y+1, −x+1, z; (xi) x−2/3, y−1/3, z−1/3; (xii) x+1/3, y−1/3, z−1/3; (xiii) x+2/3, y+1/3, z+1/3; (xiv) y+1, x, −z.

Holmium trialuminium tetrakis(borate) (Ho-borate)

Crystal data

HoAl3(BO3)4	Dx = 4.439 Mg m^−3
Mr = 481.1	Mo Kα radiation, λ = 0.71075 Å
Trigonal, R32	Cell parameters from 5662 reflections
Hall symbol: R 3 2"	θ = 3.8–30.5°
a = 9.2832 (3) Å	µ = 11.45 mm^−1
c = 7.2345 (3) Å	T = 100 K
V = 539.93 (3) Å^3	Hexagonal prism, light pink
Z = 3	0.05 × 0.05 × 0.03 mm
F(000) = 666

Data collection

Bruker D8 QUEST CMOS area detector diffractometer	381 reflections with I > 2σ(I)
Radiation source: X-ray tube	Rint = 0.047
φ and ω scans	θmax = 30.5°, θmin = 3.8°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −13→13
Tmin = 0.570, Tmax = 0.709	k = −13→12
5662 measured reflections	l = −10→10
381 independent reflections

Refinement

Refinement on F	Primary atom site location: iterative
R[F > 3σ(F)] = 0.012	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
wR(F) = 0.015	(Δ/σ)max = 0.036
S = 1.08	Δρmax = 0.54 e Å^−3
381 reflections	Δρmin = −0.65 e Å^−3
35 parameters	Absolute structure: The crystal had chiral structure. Data was refined with inversion twinning in JANA2006, and the twin ratio was 0.558(12):0.442(12).
0 restraints	Absolute structure parameter: 0.442 (12)
0 constraints

Special details

Refinement. Data was refined with inversion twinning, and the twin ratio was 0.558 (12):0.442 (12).

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

	x	y	z	Uiso*/Ueq
Ho1	0	0	0	0.01041 (7)
Al1	0.55519 (15)	0	0	0.0062 (3)
B1	0.666667	0.333333	−0.166667	0.0090 (12)
O1	0.7428 (5)	0.0762 (5)	0.166667	0.0123 (14)
O3	0.3668 (3)	−0.1161 (3)	−0.1461 (3)	0.0101 (7)
O2	0.8155 (3)	0.4822 (3)	−0.166667	0.0094 (8)
B2	0.8911 (8)	0.2245 (8)	0.166667	0.0105 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ho1	0.00996 (9)	0.00996 (9)	0.01130 (10)	0.00498 (4)	0	0
Al1	0.0058 (4)	0.0056 (5)	0.0071 (5)	0.0028 (2)	−0.00023 (15)	−0.0005 (3)
B1	0.0105 (15)	0.0105 (15)	0.0060 (18)	0.0053 (8)	0	0
O1	0.0107 (17)	0.0107 (17)	0.0140 (16)	0.0044 (17)	−0.0021 (7)	0.0021 (7)
O3	0.0100 (10)	0.0098 (9)	0.0106 (7)	0.0050 (7)	−0.0004 (6)	−0.0009 (7)
O2	0.0078 (9)	0.0078 (9)	0.0119 (10)	0.0033 (11)	0.0000 (5)	0.0000 (5)
B2	0.0131 (18)	0.0131 (18)	0.0090 (15)	0.009 (2)	0.0006 (9)	−0.0006 (9)

Geometric parameters (Å, º)

Ho1—O3^i	2.318 (3)	B1—O2	1.382 (2)
Ho1—O3^ii	2.318 (2)	B1—O2^vii	1.382 (4)
Ho1—O3^iii	2.318 (3)	B1—O2^viii	1.382 (4)
Ho1—O3^iv	2.318 (3)	O1—B2	1.377 (6)
Ho1—O3^v	2.318 (2)	O3—B2^ix	1.364 (9)
Ho1—O3^vi	2.318 (3)
O3^i—Ho1—O3^ii	89.28 (9)	O3^iii—Ho1—O3^vi	144.97 (7)
O3^i—Ho1—O3^iii	89.28 (9)	O3^iv—Ho1—O3^v	89.28 (9)
O3^i—Ho1—O3^iv	119.73 (7)	O3^iv—Ho1—O3^vi	89.28 (9)
O3^i—Ho1—O3^v	144.97 (12)	O3^v—Ho1—O3^vi	89.28 (9)
O3^i—Ho1—O3^vi	73.16 (9)	O2—B1—O2^vii	120.0 (2)
O3^ii—Ho1—O3^iii	89.28 (9)	O2—B1—O2^viii	120.0 (2)
O3^ii—Ho1—O3^iv	144.97 (12)	O2^vii—B1—O2^viii	120.0 (2)
O3^ii—Ho1—O3^v	73.16 (8)	Ho1^x—O3—B2^ix	105.5 (2)
O3^ii—Ho1—O3^vi	119.73 (11)	O1—B2—O3^xi	117.4 (7)
O3^iii—Ho1—O3^iv	73.16 (9)	O1—B2—O3^xii	117.4 (7)
O3^iii—Ho1—O3^v	119.73 (11)	O3^xi—B2—O3^xii	125.3 (4)

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