Structure determination of Mg₃(OH)₅Cl·4H₂O (F5 phase) from laboratory powder diffraction data and its impact on the analysis of problematic magnesia floors

The crystal structure with the idealized formula Mg₃(OH)₅Cl·4H₂O, the so-called F5 phase according to 5Mg(OH)₂·MgCl₂·8H₂O in the system MgCl₂-MgO-H₂O, has been solved ab initio from high-quality laboratory powder diffraction data at room temperature. The F5 phase is structurally related to 3Mg(OH)₂·MgCl₂·8H₂O (F3 form). The F5 phase consists of infinite triple chains with one Mg(OH)₆ and two Mg(OH)₄(OH₂)₂ octahedra as building units intercalated by chlorides, which are partly substituted by disordered hydroxides in the real structure. The F5 phase is of technological importance as the most important binder phase in Sorel cements. Knowledge of the crystal structure enables the full quantitative phase analysis of magnesia cements for the first time, which turns out to be very helpful in the search for possible causes of broken or bleached magnesia floors. Two real-life examples are given.

Computing details

Figures

Trimagnesium pentahydroxide triaqua chloride monohydrate

Crystal data

ClH13Mg3O9	V = 230.44 (3) Å^3
Mr = 265.46	Z = 1
Monoclinic, p2/m	Dx = 1.913 Mg m^−3
a = 9.6412 (5) Å	Cu Kα1 radiation, λ = 1.54059 Å
b = 3.1506 (2) Å	T = 295 K
c = 8.3035 (5) Å	white
β = 113.986 (6)°	?, ? × ? × ? mm

Data collection

Bruker D8 advance diffractmeter diffractometer	Data collection mode: transmission
Specimen mounting: glass capillary	Scan method: continuous

Refinement

Rp = 0.042	Profile function: fundamental parameters convolution-based
Rwp = 0.060	16 parameters
Rexp = 0.019	H-atom parameters not defined
χ^2 = NOT FOUND
? data points

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Mg1	0.8063 (16)	0	0.694 (2)	0.0623 (4)*
Mg2	0.5	0.5	0.5	0.0623 (4)*
Cl1	0.6826 (19)	0.5	0.114 (2)	0.0623 (4)*	0.5
O1	0.715 (3)	0.5	0.523 (3)	0.0623 (4)*
O2	0.600 (4)	0	0.683 (3)	0.0623 (4)*
O3	1.023 (3)	0	0.685 (3)	0.0623 (4)*
O4	0.861 (2)	0.5	0.884 (3)	0.0623 (4)*
O5	0.6826 (19)	0.5	0.114 (2)	0.0623 (4)*	0.5
H1	0.7324	0.5	0.412	0.0623 (4)*
H2	0.5862	0	0.7936	0.0623 (4)*
H3	1.1057	−0.1875	0.7587	0.0623 (4)*	0.5
H4	1.0496	0.1875	0.6078	0.0623 (4)*	0.5
H5	0.8	0.5	0.9534	0.0623 (4)*	0.75
H6	0.9659	0.5	0.9688	0.0623 (4)*	0.75
H7	0.7679	0.5	0.0865	0.0623 (4)*	0.5
H8	0.582	0.5	0.0186	0.0623 (4)*	0.5

Geometric parameters (Å, º)

Mg1—O1	2.066 (15)	Mg2—O1	2.00 (3)
Mg2—O2	2.127 (13)	O1—H1	1.002
Mg1—O2	1.96 (3)	O2—H2	0.980
Mg2—O2^i	2.127 (13)	O3—H3	0.980
Mg1—O4	2.14 (2)	O3—H4	0.975
Mg2—O1^ii	2.00 (3)	O4—H5	0.973
Mg1—O1^iii	2.066 (15)	O4—H6	0.971
Mg2—O2^ii	2.127 (13)	O5—H7	0.939
Mg1—O4^iii	2.14 (2)	O5—H8	0.972
Mg2—O2^iv	2.127 (13)
O1^iii—Mg1—O1	99.3 (8)	O2—Mg2—O2^i	95.6 (5)
O1^iii—Mg1—O2	79.9 (10)	O2—Mg2—O2^ii	84.4 (5)
O1^iii—Mg1—O3	97.3 (11)	O2—Mg2—O2^iv	180.0
O1^iii—Mg1—O4^iii	81.6 (6)	O2^i—Mg2—O2^ii	180.0
O1^iii—Mg1—O4	168.0 (14)	O2^i—Mg2—O2^iv	84.4 (5)
O1—Mg1—O2	79.9 (10)	O2^ii—Mg2—O2^iv	95.6 (5)
O1—Mg1—O3	97.3 (11)	Mg1—O1—Mg1^i	99.3 (9)
O1—Mg1—O4^iii	168.0 (14)	Mg1—O1—Mg2	101.6 (12)
O1—Mg1—O4	81.6 (6)	Mg1^i—O1—Mg2	101.6 (12)
O2—Mg1—O3	175.7 (12)	Mg1—O2—Mg2^iii	101.0 (12)
O2—Mg1—O4^iii	88.6 (9)	Mg1—O2—Mg2	101.0 (12)
O2—Mg1—O4	88.6 (9)	Mg2^iii—O2—Mg2	95.6 (8)
O3—Mg1—O4^iii	94.5 (8)	Mg1—O4—Mg1^i	94.9 (11)
O3—Mg1—O4	94.5 (8)	Mg1—O1—H1	116.6
O4^iii—Mg1—O4	94.9 (9)	Mg2—O1—H1	118.1
O1—Mg2—O1^ii	180.0	Mg1—O2—H2	118.4
O1—Mg2—O2	77.4 (10)	Mg2—O2—H2	118.4
O1—Mg2—O2^i	77.4 (10)	Mg1—O3—H3	122.3
O1—Mg2—O2^ii	102.6 (10)	Mg1—O3—H4	123.1
O1—Mg2—O2^iv	102.6 (10)	H3—O3—H4	114.6
O1^ii—Mg2—O2	102.6 (10)	Mg1—O4—H5	114.2
O1^ii—Mg2—O2^i	102.6 (10)	Mg1—O4—H6	113.9
O1^ii—Mg2—O2^ii	77.4 (10)	H5—O4—H6	106.0
O1^ii—Mg2—O2^iv	77.4 (10)	H7—O5—H8	118.9

Symmetry codes: (i) x, y+1, z; (ii) −x+1, y, −z+1; (iii) x, y−1, z; (iv) −x+1, y+1, −z+1.