Low-tem­per­ature investigation of natural iron-rich oxoborates vonsenite and hulsite: thermal deformations of crystal structure, strong negative thermal expansion and cascades of magnetic transitions

This work is devoted to an investigation of the magnetic properties and thermal behaviour of the natural oxoborates vonsenite and hulsite in the tem­per­ature range 5–500 K. The local environment, the oxidation states of the Fe and Sn atoms, and the charge distribution were determined using Mössbauer spectroscopy and are in accordance with a refinement of the crystal structure of hulsite from single-crystal X-ray diffraction data (SCXRD) in anisotropic approximation for the first time. The magnetic properties were studied by vibrating sample magnetometry (VSM) (5 ≤ T ≤ 400 K) and are reported for the first time for iron-rich hulsite. Both oxoborates show a very complex magnetic behaviour. Cascades of magnetic transitions are revealed and the critical tem­per­atures were determined. The sequences of magnetic transitions in both vonsenite and hulsite with increasing tem­per­ature were found to be as follows: magnetically ordered state → partial magnetic ordering → paramagnetic state. According to X-ray diffraction data (93 ≤ T ≤ 500 K), these processes are accompanied by anomalies in the unit-cell parameters and thermal expansion of the oxoborates at critical tem­per­atures. A strong negative volume thermal expansion is observed for both oxoborates at tem­per­atures below ∼120 K.

Computing details

Data collection: CrysAlis PRO 1.171.39.46 (Rigaku OD, 2018) for (I). Cell refinement: CrysAlis PRO 1.171.39.46 (Rigaku OD, 2018) for (I). Data reduction: CrysAlis PRO 1.171.39.46 (Rigaku OD, 2018) for (I).

(I)

Crystal data

B1Fe2.654Mg0.346O5	F(000) = 505
Mr = 247.4	Dx = 4.716 Mg m^−3
Orthorhombic, Pbam	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P -2xab;-2yab;-2z	Cell parameters from 1018 reflections
a = 9.3166 (9) Å	θ = 4.0–32.1°
b = 12.2751 (11) Å	µ = 10.86 mm^−1
c = 3.0518 (3) Å	T = 100 K
V = 349.01 (6) Å^3	Prism, black
Z = 4	0.4 × 0.1 × 0.1 mm

Data collection

Xcalibur, Eos diffractometer	633 independent reflections
Radiation source: X-ray tube	547 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.038
Detector resolution: 16.2096 pixels mm^-1	θmax = 32.4°, θmin = 2.7°
ω scans	h = −13→8
Absorption correction: multi-scan CrysAlisPro 1.171.39.46 (Rigaku Oxford Diffraction, 2018) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	k = −17→14
Tmin = 0.765, Tmax = 1	l = −4→2
1752 measured reflections

Refinement

Refinement on F	4 constraints
R[F^2 > 2σ(F^2)] = 0.057	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
wR(F^2) = 0.069	(Δ/σ)max = 0.020
S = 2.48	Δρmax = 1.84 e Å^−3
633 reflections	Δρmin = −1.65 e Å^−3
34 parameters	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
0 restraints	Extinction coefficient: 930 (130)

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Fe1	0	0	0	0.0011 (4)*	0.76
Mg1'	0	0	0	0.0011 (4)*	0.24
Fe2	0.5	0	0.5	0.0168 (5)
Fe3	0.00119 (12)	0.27600 (12)	0	0.0106 (4)*	0.77
Mg3'	0.00119 (12)	0.27600 (12)	0	0.0106 (4)*	0.25
Fe4	0.74311 (10)	0.39731 (8)	0.5	0.0036 (3)
O1	0.8465 (6)	0.0439 (4)	0.5	0.0059 (10)*
O2	0.3871 (6)	0.0777 (4)	0	0.0067 (10)*
O3	0.6233 (6)	0.1410 (4)	0.5	0.0057 (10)*
O4	0.1122 (5)	0.1410 (4)	0	0.0026 (9)*
O5	0.3460 (5)	0.2622 (4)	0.5	0.0042 (9)*
B1	0.2714 (8)	0.3606 (6)	0.5	0.0014 (13)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe4	0.0041 (5)	0.0037 (5)	0.0028 (5)	−0.0008 (4)	0	0
Fe2	0.0174 (9)	0.0146 (9)	0.0184 (9)	−0.0007 (7)	0	0

Geometric parameters (Å, º)

Fe1—O1	2.077 (5)	Fe4—O3	2.075 (5)
Fe1—O1^i	2.077 (5)	Fe4—O4^iii	2.076 (4)
Fe1—O4^ii	2.084 (4)	Fe4—O4^i	2.076 (4)
Fe1—O4	2.084 (4)	Fe4—O5	2.091 (5)
Fe1—O4^iii	2.084 (4)	Fe2—O2	2.022 (5)
Fe1—O4^i	2.084 (4)	Fe2—O2^v	2.022 (5)
Mg1'—O1	2.077 (5)	Fe3—O2	1.950 (5)
Mg1'—O1^i	2.077 (5)	Fe3—O4^vi	2.091 (5)
Mg1'—O4^ii	2.084 (4)	Mg3'—O2	1.950 (5)
Mg1'—O4	2.084 (4)	Mg3'—O4^vi	2.091 (5)
Mg1'—O4^iii	2.084 (4)	B1—O1^vii	1.381 (9)
Mg1'—O4^i	2.084 (4)	B1—O3	1.393 (9)
Fe4—O2	1.985 (3)	B1—O5^vi	1.365 (9)
Fe4—O2^iv	1.985 (3)
O1—Fe1—O1^i	180.0 (5)	O4^ii—Mg1'—O4^i	180.0 (5)
O1—Fe1—O4^ii	95.86 (17)	O4—Mg1'—O4^iii	180.0 (5)
O1—Fe1—O4	95.86 (17)	O4—Mg1'—O4^i	85.88 (15)
O1—Fe1—O4^iii	84.14 (17)	O4^iii—Mg1'—O4^i	94.12 (15)
O1—Fe1—O4^i	84.14 (17)	O2—Fe4—O2^iv	100.49 (16)
O1^i—Fe1—O4^ii	84.14 (17)	O2—Fe4—O3	97.27 (16)
O1^i—Fe1—O4	84.14 (17)	O2—Fe4—O4^iii	82.42 (15)
O1^i—Fe1—O4^iii	95.86 (17)	O2—Fe4—O4^i	176.92 (16)
O1^i—Fe1—O4^i	95.86 (17)	O2—Fe4—O5	85.25 (16)
O4^ii—Fe1—O4	94.12 (15)	O2^iv—Fe4—O3	97.27 (16)
O4^ii—Fe1—O4^iii	85.88 (15)	O2^iv—Fe4—O4^iii	176.92 (16)
O4^ii—Fe1—O4^i	180.0 (5)	O2^iv—Fe4—O4^i	82.42 (15)
O4—Fe1—O4^iii	180.0 (5)	O2^iv—Fe4—O5	85.25 (16)
O4—Fe1—O4^i	85.88 (15)	O3—Fe4—O4^iii	83.28 (17)
O4^iii—Fe1—O4^i	94.12 (15)	O3—Fe4—O4^i	83.28 (17)
O1—Mg1'—O1^i	180.0 (5)	O3—Fe4—O5	176.0 (2)
O1—Mg1'—O4^ii	95.86 (17)	O4^iii—Fe4—O4^i	94.64 (16)
O1—Mg1'—O4	95.86 (17)	O4^iii—Fe4—O5	94.03 (18)
O1—Mg1'—O4^iii	84.14 (17)	O4^i—Fe4—O5	94.03 (18)
O1—Mg1'—O4^i	84.14 (17)	O2—Fe2—O2^v	180.0 (5)
O1^i—Mg1'—O4^ii	84.14 (17)	O2—Fe3—O4^vi	179.0 (2)
O1^i—Mg1'—O4	84.14 (17)	O2—Mg3'—O4^vi	179.0 (2)
O1^i—Mg1'—O4^iii	95.86 (17)	O1^vii—B1—O3	119.1 (6)
O1^i—Mg1'—O4^i	95.86 (17)	O1^vii—B1—O5^vi	121.6 (6)
O4^ii—Mg1'—O4	94.12 (15)	O3—B1—O5^vi	119.3 (6)
O4^ii—Mg1'—O4^iii	85.88 (15)

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

(II)

Crystal data

BFe2.796Mg0.181O5Sn0.017	F(000) = 245
Mr = 253.4	Dx = 4.75 Mg m^−3
Monoclinic, P2/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2y	Cell parameters from 1449 reflections
a = 10.638 (3) Å	θ = 1.9–29.2°
b = 3.063 (2) Å	µ = 11.36 mm^−1
c = 5.445 (5) Å	T = 293 K
β = 93.38 (4)°	Tablet, black
V = 177.1 (2) Å^3	0.06 × 0.03 × 0.01 mm
Z = 2

Data collection

Bruker CCD diffractometer	218 reflections with I > 3σ(I)
Radiation source: X-ray tube	Rint = 0.081
Graphite monochromator	θmax = 29.2°, θmin = 1.9°
Absorption correction: multi-scan (Krause et al., 2015)	h = −14→14
Tmin = 0.800, Tmax = 0.860	k = −4→4
1449 measured reflections	l = −7→7
346 independent reflections

Refinement

Refinement on F	3 restraints
R[F^2 > 2σ(F^2)] = 0.063	25 constraints
wR(F^2) = 0.065	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
S = 1.74	(Δ/σ)max = 0.046
346 reflections	Δρmax = 1.28 e Å^−3
51 parameters	Δρmin = −1.14 e Å^−3

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Fe1	0	0	0	0.019 (2)	0.97 (2)
Sn1'	0	0	0	0.019 (2)	0.03 (2)
Fe2	0	0.5	0.5	0.030 (4)	0.6 (2)
Mg2'	0	0.5	0.5	0.030 (4)	0.4 (2)
Fe3	0.5	0	0	0.024 (2)
Fe4	0.5	0	0.5	0.021 (2)
Fe5	0.2726 (4)	0.5	0.2210 (6)	0.0202 (17)
O1	−0.6908 (16)	−1	−0.499 (2)	0.019 (4)
O2	0.4659 (14)	0.5	0.242 (3)	0.019 (4)
O3	−0.6969 (16)	−1	−0.059 (2)	0.019 (4)
O4	−0.8872 (13)	−1	−0.291 (3)	0.019 (4)
O5	0.0922 (17)	0.5	0.183 (3)	0.019 (4)
B1	−0.7586 (14)	−1	−0.295 (2)	0.018 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe1	0.037 (5)	0.015 (3)	0.003 (3)	0	−0.001 (2)	0
Sn1'	0.037 (5)	0.015 (3)	0.003 (3)	0	−0.001 (2)	0
Fe2	0.045 (7)	0.026 (6)	0.019 (5)	0	−0.005 (3)	0
Mg2'	0.045 (7)	0.026 (6)	0.019 (5)	0	−0.005 (3)	0
Fe3	0.042 (4)	0.010 (3)	0.020 (3)	0	0.004 (3)	0
Fe4	0.024 (4)	0.024 (3)	0.015 (3)	0	0.000 (2)	0
Fe5	0.038 (3)	0.016 (2)	0.007 (3)	0	0.0010 (18)	0
O1	0.031 (7)	0.018 (6)	0.006 (6)	0	−0.001 (3)	0
O2	0.031 (7)	0.018 (6)	0.006 (6)	0	−0.001 (3)	0
O3	0.031 (7)	0.018 (6)	0.006 (6)	0	−0.001 (3)	0
O4	0.031 (7)	0.018 (6)	0.006 (6)	0	−0.001 (3)	0
O5	0.031 (7)	0.018 (6)	0.006 (6)	0	−0.001 (3)	0
B1	0.022 (11)	0.016 (9)	0.013 (8)	0	−0.008 (6)	0

Geometric parameters (Å, º)

Fe1—O4^i	2.042 (16)	Fe3—O3^xii	2.101 (17)
Fe1—O4^ii	2.042 (16)	Fe4—O1^vi	2.030 (17)
Fe1—O5^iii	2.046 (11)	Fe4—O1^xii	2.030 (17)
Fe1—O5	2.046 (11)	Fe4—O2^iii	2.096 (10)
Fe1—O5^iv	2.046 (11)	Fe4—O2	2.096 (10)
Fe1—O5^v	2.046 (11)	Fe4—O2^xiii	2.096 (10)
Fe2—O4^vi	2.219 (11)	Fe4—O2^xiv	2.096 (10)
Fe2—O4^vii	2.219 (11)	Fe5—O1^vi	2.180 (10)
Fe2—O4^ii	2.219 (11)	Fe5—O1^vii	2.180 (10)
Fe2—O4^viii	2.219 (11)	Fe5—O2	2.054 (16)
Fe2—O5	2.035 (16)	Fe5—O3^i	2.199 (10)
Fe2—O5^ix	2.035 (16)	Fe5—O3^xv	2.199 (10)
Fe3—O2^iii	2.066 (10)	Fe5—O5	1.918 (18)
Fe3—O2	2.066 (10)	B1—O1	1.36 (2)
Fe3—O2^x	2.066 (10)	B1—O3	1.408 (18)
Fe3—O2^xi	2.066 (10)	B1—O4	1.37 (2)
Fe3—O3^i	2.101 (17)
O4^i—Fe1—O4^ii	180.0 (5)	O2^x—Fe3—O2^xi	95.7 (4)
O4^i—Fe1—O5^iii	95.2 (5)	O2^x—Fe3—O3^i	96.5 (5)
O4^i—Fe1—O5	95.2 (5)	O2^x—Fe3—O3^xii	83.5 (5)
O4^i—Fe1—O5^iv	84.8 (5)	O2^xi—Fe3—O3^i	96.5 (5)
O4^i—Fe1—O5^v	84.8 (5)	O2^xi—Fe3—O3^xii	83.5 (5)
O4^ii—Fe1—O5^iii	84.8 (5)	O3^i—Fe3—O3^xii	180.0 (5)
O4^ii—Fe1—O5	84.8 (5)	O1^vi—Fe4—O1^xii	180.0 (5)
O4^ii—Fe1—O5^iv	95.2 (5)	O1^vi—Fe4—O2^iii	82.4 (5)
O4^ii—Fe1—O5^v	95.2 (5)	O1^vi—Fe4—O2	82.4 (5)
O5^iii—Fe1—O5	96.9 (5)	O1^vi—Fe4—O2^xiii	97.6 (5)
O5^iii—Fe1—O5^iv	83.1 (5)	O1^vi—Fe4—O2^xiv	97.6 (5)
O5^iii—Fe1—O5^v	180.0 (5)	O1^xii—Fe4—O2^iii	97.6 (5)
O5—Fe1—O5^iv	180.0 (5)	O1^xii—Fe4—O2	97.6 (5)
O5—Fe1—O5^v	83.1 (5)	O1^xii—Fe4—O2^xiii	82.4 (5)
O5^iv—Fe1—O5^v	96.9 (5)	O1^xii—Fe4—O2^xiv	82.4 (5)
O4^vi—Fe2—O4^vii	87.3 (4)	O2^iii—Fe4—O2	93.9 (4)
O4^vi—Fe2—O4^ii	92.7 (4)	O2^iii—Fe4—O2^xiii	86.1 (4)
O4^vi—Fe2—O4^viii	180.0 (5)	O2^iii—Fe4—O2^xiv	180.0 (5)
O4^vi—Fe2—O5	99.4 (5)	O2—Fe4—O2^xiii	180.0 (5)
O4^vi—Fe2—O5^ix	80.6 (5)	O2—Fe4—O2^xiv	86.1 (4)
O4^vii—Fe2—O4^ii	180.0 (5)	O2^xiii—Fe4—O2^xiv	93.9 (4)
O4^vii—Fe2—O4^viii	92.7 (4)	O1^vi—Fe5—O1^vii	89.3 (4)
O4^vii—Fe2—O5	99.4 (5)	O1^vi—Fe5—O2	79.9 (5)
O4^vii—Fe2—O5^ix	80.6 (5)	O1^vi—Fe5—O3^i	88.2 (4)
O4^ii—Fe2—O4^viii	87.3 (4)	O1^vi—Fe5—O3^xv	161.2 (6)
O4^ii—Fe2—O5	80.6 (5)	O1^vi—Fe5—O5	102.2 (5)
O4^ii—Fe2—O5^ix	99.4 (5)	O1^vii—Fe5—O2	79.9 (5)
O4^viii—Fe2—O5	80.6 (5)	O1^vii—Fe5—O3^i	161.2 (6)
O4^viii—Fe2—O5^ix	99.4 (5)	O1^vii—Fe5—O3^xv	88.2 (4)
O5—Fe2—O5^ix	180.0 (5)	O1^vii—Fe5—O5	102.2 (5)
O2^iii—Fe3—O2	95.7 (4)	O2—Fe5—O3^i	81.4 (5)
O2^iii—Fe3—O2^x	84.3 (4)	O2—Fe5—O3^xv	81.4 (5)
O2^iii—Fe3—O2^xi	180.0 (5)	O2—Fe5—O5	177.0 (6)
O2^iii—Fe3—O3^i	83.5 (5)	O3^i—Fe5—O3^xv	88.3 (4)
O2^iii—Fe3—O3^xii	96.5 (5)	O3^i—Fe5—O5	96.5 (5)
O2—Fe3—O2^x	180.0 (5)	O3^xv—Fe5—O5	96.5 (5)
O2—Fe3—O2^xi	84.3 (4)	O1—B1—O3	120.3 (14)
O2—Fe3—O3^i	83.5 (5)	O1—B1—O4	126.4 (13)
O2—Fe3—O3^xii	96.5 (5)	O3—B1—O4	113.3 (13)

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