Crystal structure refinement, low- and high-temperature X-ray diffraction and Mössbauer spectroscopy study of the oxoborate ludwigite from the Iten'yurginskoe deposit

This paper reports an investigation of the chemistry, crystal structure refinement and thermal behavior (80–1650 K) of ludwigite from the Iten'yurginskoe deposit (Eastern Chukotka, Russia). Its chemical composition was determined by electron microprobe analysis, giving an empirical formula (Mg_1.70Fe²⁺_0.29Mn_0.01)_Σ2.00(Fe³⁺_0.90Al_0.08Mg_0.02)_Σ1.00O₂(BO₃). A refinement of the crystal structure from single-crystal X-ray diffraction data (SCXRD) was provided for the first time for ludwigite from this deposit (R = 0.047). The structure can be described as a framework composed of [MO₆]ⁿ⁻ octahedra and isolated [BO₃]³⁻ triangles located in triangular interstices of the framework. Based on a comprehensive analysis of SCXRD and Mössbauer spectroscopy data, the M1 site is occupied by Mg, M2 and M3 by Mg and Fe²⁺, M4 by Fe³⁺, Mg and Al. There are also oxo-centered [O4M₄]ⁿ⁺ and [O2M₅]ⁿ⁺ polyhedra building up a framework with the [BO₃]³⁻ triangles located in its hexagonal interstices. No indications of magnetic ordering are found in the temperature range investigated. The Fe²⁺ → Fe³⁺ oxidation occurs above 600 K, and is accompanied by a decrease of the unit-cell parameters and subsequent incomplete solid-phase decomposition with the formation of hematite, warwickite and magnetite. The mineral melts at temperatures above 1582 K. The thermal expansion of ludwigite is slightly anisotropic, which is explained by a dense packing of the [MO₆]ⁿ⁻ octahedra as well as a virtually perpendicular orientation of the oxo-centered double chains to each other. At room temperature, maximum expansion is along the c axis (α_c = 9.1 × 10⁻⁶ K⁻¹) and minimum expansion is in the ab plane (α_a = 8.6 × 10⁻⁶, α_b = 7.6 × 10⁻⁶ K⁻¹), which is due to the preferred orientation of the [BO₃]³⁻ triangles. A comparison of the thermal behavior of three oxoborates of the ludwigite group, namely azoproite (Mg,Fe²⁺)₂(Fe³⁺,Ti,Mg,Al)O₂(BO₃), vonsenite (Fe²⁺,Mg)₂(Fe³⁺,Mn²⁺,Sn,Al)O₂(BO₃) and ludwigite (Mg_,Fe²⁺_,Mn)₂(Fe³⁺_,Al_,Mg)O₂(BO₃), is provided.

Computing details

Data collection: CrysAlis PRO 1.171.41.104a (Rigaku OD, 2021); cell refinement: CrysAlis PRO 1.171.41.104a (Rigaku OD, 2021); data reduction: CrysAlis PRO 1.171.41.104a (Rigaku OD, 2021).

(I)

Crystal data

Al0.08BFe1.183Mg1.737O5	F(000) = 389
Mr = 201.26	Dx = 3.881 Mg m^−3
Orthorhombic, Pbam	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P -2xab;-2yab;-2z	Cell parameters from 436 reflections
a = 9.2532 (14) Å	θ = 4.0–32.7°
b = 12.3025 (18) Å	µ = 5.35 mm^−1
c = 3.0256 (5) Å	T = 293 K
V = 344.43 (9) Å^3	Prism, black
Z = 4	0.2 × 0.05 × 0.05 mm

Data collection

XtaLAB Synergy, Single source at home/near, HyPix diffractometer	380 independent reflections
Radiation source: X-ray tube	272 reflections with I > 3σ(I)
Mirror monochromator	Rint = 0.100
Detector resolution: 10.0000 pixels mm^-1	θmax = 33.0°, θmin = 4.0°
ω scans	h = −10→13
Absorption correction: multi-scan CrysAlisPro 1.171.41.104a (Rigaku Oxford Diffraction, 2021) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	k = −18→16
Tmin = 0.582, Tmax = 1	l = −4→4
2325 measured reflections

Refinement

Refinement on F	0 restraints
R[F^2 > 2σ(F^2)] = 0.047	10 constraints
wR(F^2) = 0.043	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
S = 1.53	(Δ/σ)max = 0.045
380 reflections	Δρmax = 1.40 e Å^−3
60 parameters	Δρmin = −1.64 e Å^−3

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Fe4	0.73942 (19)	0.38552 (11)	0.5	0.0065 (5)	0.90
Mg4	0.73942 (19)	0.38552 (11)	0.5	0.0065 (5)	0.02
Al4	0.73942 (19)	0.38552 (11)	0.5	0.0065 (5)	0.08
Mg2	0.5	0	0.5	0.0089 (9)	0.477 (18)
Fe2'	0.5	0	0.5	0.0089 (9)	0.523 (18)
Mg3	0.0021 (4)	0.2796 (2)	0	0.0101 (11)	0.978 (12)
Fe3'	0.0021 (4)	0.2796 (2)	0	0.0101 (11)	0.022 (12)
Mg1	0	0	0	0.0077 (14)
O5	0.3498 (8)	0.2624 (5)	0.5	0.008 (2)
O3	0.6253 (7)	0.1418 (5)	0.5	0.011 (2)
O1	0.8499 (8)	0.0442 (5)	0.5	0.010 (2)
O4	0.1104 (7)	0.1419 (5)	0	0.011 (2)
O2	0.3843 (7)	0.0769 (5)	0	0.012 (2)
B1	0.2733 (14)	0.3588 (8)	0.5	0.010 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe4	0.0051 (9)	0.0075 (8)	0.0071 (8)	0.0021 (7)	0	0
Mg4	0.0051 (9)	0.0075 (8)	0.0071 (8)	0.0021 (7)	0	0
Al4	0.0051 (9)	0.0075 (8)	0.0071 (8)	0.0021 (7)	0	0
Mg2	0.0134 (19)	0.0055 (14)	0.0077 (16)	−0.0005 (12)	0	0
Fe2'	0.0134 (19)	0.0055 (14)	0.0077 (16)	−0.0005 (12)	0	0
Mg3	0.012 (2)	0.0090 (17)	0.0094 (19)	0.0011 (16)	0	0
Fe3'	0.012 (2)	0.0090 (17)	0.0094 (19)	0.0011 (16)	0	0
Mg1	0.010 (3)	0.008 (2)	0.005 (2)	−0.001 (2)	0	0
O5	0.011 (4)	0.009 (3)	0.006 (4)	−0.003 (3)	0	0
O3	0.008 (4)	0.015 (3)	0.010 (3)	−0.004 (3)	0	0
O1	0.006 (4)	0.012 (3)	0.012 (4)	0.002 (3)	0	0
O4	0.016 (4)	0.007 (3)	0.009 (4)	0.000 (3)	0	0
O2	0.014 (4)	0.007 (3)	0.016 (4)	0.003 (3)	0	0
B1	0.024 (8)	0.006 (4)	0.001 (5)	−0.004 (5)	0	0

Geometric parameters (Å, º)

Fe4—O5^i	2.087 (7)	Fe2'—O2	2.081 (4)
Fe4—O1^ii	2.120 (7)	Fe2'—O2^v	2.081 (4)
Fe4—O4^iii	1.956 (4)	Fe2'—O2^iv	2.081 (4)
Fe4—O4^i	1.956 (4)	Fe2'—O2^vi	2.081 (4)
Fe4—O2^iii	2.074 (5)	Mg3—O5^vii	2.131 (6)
Fe4—O2^i	2.074 (5)	Mg3—O5^viii	2.131 (6)
Mg4—O5^i	2.087 (7)	Mg3—O3^vii	2.127 (5)
Mg4—O1^ii	2.120 (7)	Mg3—O3^viii	2.127 (5)
Mg4—O4^iii	1.956 (4)	Mg3—O4	1.968 (7)
Mg4—O4^i	1.956 (4)	Mg3—O2^vii	2.075 (7)
Mg4—O2^iii	2.074 (5)	Fe3'—O5^vii	2.131 (6)
Mg4—O2^i	2.074 (5)	Fe3'—O5^viii	2.131 (6)
Al4—O5^i	2.087 (7)	Fe3'—O3^vii	2.127 (5)
Al4—O1^ii	2.120 (7)	Fe3'—O3^viii	2.127 (5)
Al4—O4^iii	1.956 (4)	Fe3'—O4	1.968 (7)
Al4—O4^i	1.956 (4)	Fe3'—O2^vii	2.075 (7)
Al4—O2^iii	2.074 (5)	Mg1—O1^ix	2.124 (5)
Al4—O2^i	2.074 (5)	Mg1—O1^x	2.124 (5)
Mg2—O3	2.095 (6)	Mg1—O1^xi	2.124 (5)
Mg2—O3^iv	2.095 (6)	Mg1—O1^iv	2.124 (5)
Mg2—O2	2.081 (4)	Mg1—O4	2.023 (6)
Mg2—O2^v	2.081 (4)	Mg1—O4^xii	2.023 (6)
Mg2—O2^iv	2.081 (4)	O5—B1	1.381 (13)
Mg2—O2^vi	2.081 (4)	O3—B1^i	1.369 (14)
Fe2'—O3	2.095 (6)	O1—B1^i	1.388 (13)
Fe2'—O3^iv	2.095 (6)
O5^i—Mg4—O4^iii	98.5 (2)	O3^iv—Fe2'—O2	95.4 (2)
O5^i—Mg4—O4^i	98.5 (2)	O3^iv—Fe2'—O2^v	95.4 (2)
O5^i—Mg4—O2^iii	83.0 (2)	O3^iv—Fe2'—O2^iv	84.6 (2)
O5^i—Mg4—O2^i	83.0 (2)	O3^iv—Fe2'—O2^vi	84.6 (2)
O4^iii—Mg4—O4^i	101.3 (2)	O2—Fe2'—O2^v	93.29 (18)
O4^iii—Mg4—O2^iii	82.5 (2)	O2—Fe2'—O2^iv	86.71 (18)
O4^iii—Mg4—O2^i	175.6 (2)	O2—Fe2'—O2^vi	180
O4^i—Mg4—O2^iii	175.6 (2)	O2^v—Fe2'—O2^iv	180
O4^i—Mg4—O2^i	82.5 (2)	O2^v—Fe2'—O2^vi	86.71 (18)
O2^iii—Mg4—O2^i	93.7 (2)	O2^iv—Fe2'—O2^vi	93.29 (18)
O3—Mg2—O3^iv	180	O4—Mg3—O2^vii	178.9 (3)
O3—Mg2—O2	84.6 (2)	O5^vii—Fe3'—O5^viii	90.4 (2)
O3—Mg2—O2^v	84.6 (2)	O5^vii—Fe3'—O3^vii	87.70 (19)
O3—Mg2—O2^iv	95.4 (2)	O5^vii—Fe3'—O3^viii	165.8 (3)
O3—Mg2—O2^vi	95.4 (2)	O5^vii—Fe3'—O4	97.4 (2)
O3^iv—Mg2—O2	95.4 (2)	O5^vii—Fe3'—O2^vii	81.9 (2)
O3^iv—Mg2—O2^v	95.4 (2)	O5^viii—Fe3'—O3^vii	165.8 (3)
O3^iv—Mg2—O2^iv	84.6 (2)	O5^viii—Fe3'—O3^viii	87.70 (19)
O3^iv—Mg2—O2^vi	84.6 (2)	O5^viii—Fe3'—O4	97.4 (2)
O2—Mg2—O2^v	93.29 (18)	O5^viii—Fe3'—O2^vii	81.9 (2)
O2—Mg2—O2^iv	86.71 (18)	O3^vii—Fe3'—O3^viii	90.7 (2)
O2—Mg2—O2^vi	180	O3^vii—Fe3'—O4	96.8 (3)
O2^v—Mg2—O2^iv	180	O3^vii—Fe3'—O2^vii	83.9 (2)
O2^v—Mg2—O2^vi	86.71 (18)	O3^viii—Fe3'—O4	96.8 (3)
O2^iv—Mg2—O2^vi	93.29 (18)	O3^viii—Fe3'—O2^vii	83.9 (2)
O3—Fe2'—O3^iv	180	O4—Fe3'—O2^vii	178.9 (3)
O3—Fe2'—O2	84.6 (2)	O4—Mg1—O4^xii	180
O3—Fe2'—O2^v	84.6 (2)	O5—B1—O3^viii	120.6 (9)
O3—Fe2'—O2^iv	95.4 (2)	O5—B1—O1^viii	118.5 (10)
O3—Fe2'—O2^vi	95.4 (2)	O3^viii—B1—O1^viii	121.0 (9)

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