A new topological semimetal candidate: SmMnBi₂

The new compound SmMnBi₂ has been synthesized by the self-flux method and shown to crystallize in space group I4/mmm with a = 4.5054 (4) Å, c = 20.5914 (19) Å and Z = 4. Its structure comprises two-dimensional square Mn-nets layers, puckered rock-salt-like SmBi slabs and two-dimensional square Bi-nets layers, alternating along the c axis in an …Mn-net–SmBi slab–Bi-net–SmBi slab–Mn-net… sequence. Surprisingly, the atomic arrangement differs from its neighboring compound EuMnBi₂ which has similar layers but with a different stacking arrangement. This gives rise to edge-shared square planar MnBi₄ polyhedral layers in SmMnBi₂ while EuMnBi₂ has edge-shared MnBi₄ tetrahedral layers. The MMnX₂ (M = alkaline earth/rare earth metals, X = Sb/Bi) family has emerged as topological Dirac or Weyl semimetal candidates, all of them sharing similar structural features. Although SmMnBi₂ has a different stacking arrangement to EuMnBi₂, its layer structure still makes it a topological Dirac or Weyl semimetal candidate.

Computing details

Data collection: APEX3 (Bruker, 2018); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: Superflip (Palatinus & Chapuis, 2007); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS (Betteridge et al., 2003).

(I)

Crystal data

Bi2MnSm	Dx = 9.904 Mg m^−3
Mr = 623.29	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4/mmm	Cell parameters from 292 reflections
Hall symbol: -I 4 2	θ = 4.0–33.7°
a = 4.5054 (4) Å	µ = 100.50 mm^−1
c = 20.5914 (19) Å	T = 100 K
V = 417.98 (8) Å^3	Plate, metallic black
Z = 4	0.06 × 0.05 × 0.02 mm
F(000) = 1012

Data collection

Bruker Photon II CMOS diffractometer	292 independent reflections
Radiation source: microfocus sealed tube, Incoatec IµS 3.0	247 reflections with I > 2.0σ(I)
Multilayer mirror monochromator	Rint = 0.078
ω and φ scans	θmax = 33.7°, θmin = 4.0°
Absorption correction: numerical SADABS 2016/2: Krause, L., Herbst-Irmer, R., Sheldrick G.M. & Stalke D., J. Appl. Cryst. 48 (2015) 3-10	h = −7→7
Tmin = 0.046, Tmax = 0.677	k = −6→7
5072 measured reflections	l = −32→32

Refinement

Refinement on F^2	Primary atom site location: other
Least-squares matrix: full	Method, part 1, Chebychev polynomial, (Watkin, 1994, Prince, 1982) [weight] = 1.0/[A0*T0(x) + A1*T1(x) ··· + An-1]*Tn-1(x)] where Ai are the Chebychev coefficients listed below and x = F /Fmax Method = Robust Weighting (Prince, 1982) W = [weight] * [1-(deltaF/6*sigmaF)^2]^2 Ai are: 28.7 36.0 11.9
R[F^2 > 2σ(F^2)] = 0.037	(Δ/σ)max = 0.0003
wR(F^2) = 0.074	Δρmax = 10.73 e Å^−3
S = 1.10	Δρmin = −5.16 e Å^−3
292 reflections	Extinction correction: Larson (1970), Equation 22
13 parameters	Extinction coefficient: 0.91 (9)
0 restraints

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

	x	y	z	Uiso*/Ueq
Sm1	0.5000	0.5000	0.62275 (10)	0.0149
Mn1	0.0000	0.5000	0.5000	0.0170
Bi1	0.0000	0.5000	0.7500	0.0153
Bi2	0.0000	0.0000	0.59612 (7)	0.0138

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sm1	0.0130 (6)	0.0130 (6)	0.0188 (8)	0.0000	0.0000	0.0000
Mn1	0.030 (4)	0.011 (3)	0.0100 (19)	0.0000	0.0000	0.0000
Bi1	0.0145 (4)	0.0145 (4)	0.0168 (6)	0.0000	0.0000	0.0000
Bi2	0.0128 (4)	0.0128 (4)	0.0159 (6)	0.0000	0.0000	0.0000

Geometric parameters (Å, º)

Sm1—Mn1^i	3.3857 (16)	Sm1—Mn1^iii	3.3857 (16)
Sm1—Mn1^ii	3.3857 (16)	Mn1—Bi2	2.9987 (10)
Mn1^i—Sm1—Mn1^ii	56.13 (3)	Mn1^vii—Bi2—Mn1	64.17 (2)
Mn1^i—Sm1—Mn1^iii	56.13 (3)	Mn1^vii—Bi2—Mn1^viii	97.39 (4)
Mn1^ii—Sm1—Mn1^iii	83.42 (5)	Mn1—Bi2—Mn1^viii	64.17 (2)
Sm1^iv—Mn1—Sm1^v	96.58 (5)	Mn1^vii—Bi2—Mn1^ix	64.17 (2)
Sm1^iv—Mn1—Bi2	60.48 (2)	Mn1—Bi2—Mn1^ix	97.39 (4)
Sm1^v—Mn1—Bi2	119.52 (2)	Mn1^viii—Bi2—Mn1^ix	64.17 (2)
Sm1^iv—Bi1—Sm1^vi	125.10 (3)

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