A new monoclinic structure type for ternary gallide MgCoGa₂

The crystal structure of MgCoGa₂ (magnesium cobalt digallide) was solved by direct methods and refined in two space groups as P2₁/c (standard choice) and P2₁/n (non-standard choice). The refined lattice parameters for the standard choice are a = 5.1505 (2), b = 7.2571 (2), c = 8.0264 (3) Å and β = 125.571 (3)°, and for the non-standard choice are a = 5.1505 (2), b = 7.2571 (2), c = 6.5464 (2) Å and β = 94.217 (3)°. All parameters for MgCoGa₂ refined to R₁ = 0.027 and wR₂ = 0.042 using 594 reflections. The crystal structure peculiarities of this com­pound are discussed. Particular attention has been given to relationships with other similar structures, such as YPd₂Si and Fe₃C. Crystallographic analysis, together with linear muffin-tin orbital electronic structure calculations, reveals the presence of three-dimensional polyatomic nets with partial covalent bonding between the Ga atoms.

Computing details

Data collection: CrysAlis PRO (Rigaku OD, 2015); cell refinement: CrysAlis PRO (Rigaku OD, 2015); data reduction: CrysAlis PRO (Rigaku OD, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015b).

Magnesium cobalt digallide

Crystal data

MgCoGa2	F(000) = 404
Mr = 222.68	Dx = 6.061 Mg m^−3 Dm = 6.08 (2) Mg m^−3 Dm measured by volumetric
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 5.1505 (2) Å	Cell parameters from 594 reflections
b = 7.2571 (2) Å	θ = 4.2–28.5°
c = 8.0264 (3) Å	µ = 28.48 mm^−1
β = 125.571 (3)°	T = 293 K
V = 244.03 (2) Å^3	Prism, metallic dark grey
Z = 4	0.06 × 0.04 × 0.03 mm

Data collection

Agilent SuperNova Dual Source diffractometer with an Atlas detector	594 independent reflections
Radiation source: fine-focus sealed tube	524 reflections with I > 2σ(I)
Mirror monochromator	Rint = 0.035
ω scans	θmax = 28.5°, θmin = 4.2°
Absorption correction: empirical (using intensity measurements) ABSPACK in CrysAlis PRO (Rigaku OD, 2015)	h = −6→6
Tmin = 0.284, Tmax = 0.409	k = −9→9
3025 measured reflections	l = −10→10

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.021	Secondary atom site location: difference Fourier map
wR(F^2) = 0.042	w = 1/[σ^2(Fo^2) + (0.0169P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.08	(Δ/σ)max = 0.001
594 reflections	Δρmax = 1.05 e Å^−3
37 parameters	Δρmin = −0.89 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

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

	x	y	z	Uiso*/Ueq
Mg	0.1827 (3)	0.04414 (19)	0.2985 (2)	0.0049 (3)
Co	0.28699 (13)	0.39736 (8)	0.19208 (8)	0.00378 (14)
Ga1	0.21859 (10)	0.72437 (6)	0.08003 (7)	0.00448 (13)
Ga2	0.38498 (11)	0.14078 (6)	0.03372 (7)	0.00476 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mg	0.0046 (7)	0.0055 (7)	0.0039 (7)	0.0008 (6)	0.0021 (6)	0.0007 (6)
Co	0.0033 (3)	0.0038 (3)	0.0029 (3)	−0.0004 (2)	0.0011 (2)	−0.0005 (2)
Ga1	0.0035 (2)	0.0042 (2)	0.0036 (2)	−0.00024 (18)	0.00081 (19)	−0.00008 (18)
Ga2	0.0054 (2)	0.0049 (3)	0.0033 (2)	0.00067 (18)	0.0021 (2)	−0.00014 (18)

Geometric parameters (Å, º)

Mg—Co^i	2.6843 (14)	Co—Mg^x	2.9112 (14)
Mg—Ga2^ii	2.7550 (14)	Ga1—Co^vi	2.3905 (7)
Mg—Co	2.8500 (14)	Ga1—Co^viii	2.4469 (7)
Mg—Co^iii	2.8915 (14)	Ga1—Ga2^viii	2.6046 (7)
Mg—Ga2^iv	2.8963 (15)	Ga1—Ga2^xi	2.8511 (6)
Mg—Ga1^ii	2.9072 (14)	Ga1—Ga2^vi	2.8554 (6)
Mg—Co^ii	2.9111 (14)	Ga1—Mg^x	2.9072 (14)
Mg—Ga2	2.9445 (13)	Ga1—Mg^viii	2.9449 (14)
Mg—Ga1^iii	2.9450 (14)	Ga1—Mg^xii	2.9784 (14)
Mg—Ga1^v	2.9785 (14)	Ga1—Mg^vi	3.0030 (14)
Mg—Ga1^vi	3.0031 (14)	Ga1—Mg^ix	3.0459 (13)
Mg—Mg^vii	3.043 (3)	Ga2—Co^x	2.4981 (7)
Co—Ga1^vi	2.3905 (7)	Ga2—Co^iii	2.5481 (7)
Co—Ga1^iii	2.4469 (7)	Ga2—Ga2^xiii	2.5726 (8)
Co—Ga2	2.4665 (7)	Ga2—Ga1^iii	2.6046 (7)
Co—Ga1	2.4892 (7)	Ga2—Mg^x	2.7550 (14)
Co—Ga2^ii	2.4981 (7)	Ga2—Ga1^xi	2.8511 (6)
Co—Ga2^viii	2.5481 (7)	Ga2—Ga1^vi	2.8554 (6)
Co—Mg^ix	2.6843 (14)	Ga2—Mg^iv	2.8963 (15)
Co—Mg^viii	2.8915 (14)
Co^i—Mg—Ga2^ii	107.33 (5)	Ga2^ii—Co—Mg^x	177.83 (4)
Co^i—Mg—Co	134.06 (5)	Ga2^viii—Co—Mg^x	116.57 (3)
Ga2^ii—Mg—Co	52.90 (3)	Mg^ix—Co—Mg^x	111.86 (3)
Co^i—Mg—Co^iii	134.92 (5)	Mg—Co—Mg^x	120.56 (4)
Ga2^ii—Mg—Co^iii	108.23 (5)	Mg^viii—Co—Mg^x	63.25 (5)
Co—Mg—Co^iii	89.96 (4)	Co^vi—Ga1—Co^viii	168.36 (3)
Co^i—Mg—Ga2^iv	53.02 (3)	Co^vi—Ga1—Co	80.08 (2)
Ga2^ii—Mg—Ga2^iv	142.40 (5)	Co^viii—Ga1—Co	110.61 (2)
Co—Mg—Ga2^iv	113.97 (5)	Co^vi—Ga1—Ga2^viii	133.20 (2)
Co^iii—Mg—Ga2^iv	106.60 (4)	Co^viii—Ga1—Ga2^viii	58.355 (18)
Co^i—Mg—Ga1^ii	50.43 (3)	Co—Ga1—Ga2^viii	59.982 (19)
Ga2^ii—Mg—Ga1^ii	101.30 (4)	Co^vi—Ga1—Ga2^xi	115.89 (2)
Co—Mg—Ga1^ii	153.89 (6)	Co^viii—Ga1—Ga2^xi	55.636 (17)
Co^iii—Mg—Ga1^ii	95.78 (4)	Co—Ga1—Ga2^xi	117.76 (2)
Ga2^iv—Mg—Ga1^ii	88.78 (4)	Ga2^viii—Ga1—Ga2^xi	104.45 (2)
Co^i—Mg—Co^ii	68.14 (3)	Co^vi—Ga1—Ga2^vi	55.235 (18)
Ga2^ii—Mg—Co^ii	51.52 (3)	Co^viii—Ga1—Ga2^vi	121.95 (2)
Co—Mg—Co^ii	104.24 (4)	Co—Ga1—Ga2^vi	109.95 (2)
Co^iii—Mg—Co^ii	116.75 (5)	Ga2^viii—Ga1—Ga2^vi	114.47 (2)
Ga2^iv—Mg—Co^ii	121.12 (4)	Ga2^xi—Ga1—Ga2^vi	128.99 (2)
Ga1^ii—Mg—Co^ii	50.66 (3)	Co^vi—Ga1—Mg^x	59.95 (3)
Co^i—Mg—Ga2	144.88 (6)	Co^viii—Ga1—Mg^x	119.53 (3)
Ga2^ii—Mg—Ga2	98.36 (4)	Co—Ga1—Mg^x	64.75 (3)
Co—Mg—Ga2	50.35 (3)	Ga2^viii—Ga1—Mg^x	114.87 (3)
Co^iii—Mg—Ga2	51.77 (3)	Ga2^xi—Ga1—Mg^x	73.43 (3)
Ga2^iv—Mg—Ga2	92.15 (4)	Ga2^vi—Ga1—Mg^x	114.58 (3)
Ga1^ii—Mg—Ga2	146.25 (5)	Co^vi—Ga1—Mg^viii	120.85 (3)
Co^ii—Mg—Ga2	146.00 (5)	Co^viii—Ga1—Mg^viii	63.02 (3)
Co^i—Mg—Ga1^iii	162.59 (6)	Co—Ga1—Mg^viii	63.65 (3)
Ga2^ii—Mg—Ga1^iii	59.92 (3)	Ga2^viii—Ga1—Mg^viii	63.74 (3)
Co—Mg—Ga1^iii	49.92 (3)	Ga2^xi—Ga1—Mg^viii	56.73 (3)
Co^iii—Mg—Ga1^iii	50.48 (3)	Ga2^vi—Ga1—Mg^viii	173.54 (3)
Ga2^iv—Mg—Ga1^iii	144.34 (5)	Mg^x—Ga1—Mg^viii	62.65 (5)
Ga1^ii—Mg—Ga1^iii	117.35 (5)	Co^vi—Ga1—Mg^xii	114.71 (3)
Co^ii—Mg—Ga1^iii	94.54 (4)	Co^viii—Ga1—Mg^xii	63.53 (3)
Ga2—Mg—Ga1^iii	52.49 (3)	Co—Ga1—Mg^xii	125.05 (3)
Co^i—Mg—Ga1^v	94.19 (4)	Ga2^viii—Ga1—Mg^xii	75.81 (3)
Ga2^ii—Mg—Ga1^v	157.20 (5)	Ga2^xi—Ga1—Mg^xii	102.85 (3)
Co—Mg—Ga1^v	115.93 (4)	Ga2^vi—Ga1—Mg^xii	59.49 (3)
Co^iii—Mg—Ga1^v	49.24 (2)	Mg^x—Ga1—Mg^xii	169.16 (5)
Ga2^iv—Mg—Ga1^v	58.14 (3)	Mg^viii—Ga1—Mg^xii	124.25 (3)
Ga1^ii—Mg—Ga1^v	86.43 (4)	Co^vi—Ga1—Mg^vi	62.59 (3)
Co^ii—Mg—Ga1^v	135.81 (5)	Co^viii—Ga1—Mg^vi	105.89 (3)
Ga2—Mg—Ga1^v	65.89 (3)	Co—Ga1—Mg^vi	140.20 (4)
Ga1^iii—Mg—Ga1^v	97.43 (4)	Ga2^viii—Ga1—Mg^vi	159.41 (3)
Co^i—Mg—Ga1^vi	98.59 (4)	Ga2^xi—Ga1—Mg^vi	71.56 (3)
Ga2^ii—Mg—Ga1^vi	89.56 (4)	Ga2^vi—Ga1—Mg^vi	60.28 (3)
Co—Mg—Ga1^vi	48.12 (3)	Mg^x—Ga1—Mg^vi	83.88 (2)
Co^iii—Mg—Ga1^vi	108.44 (4)	Mg^viii—Ga1—Mg^vi	123.73 (5)
Ga2^iv—Mg—Ga1^vi	66.16 (3)	Mg^xii—Ga1—Mg^vi	85.28 (4)
Ga1^ii—Mg—Ga1^vi	148.93 (5)	Co^vi—Ga1—Mg^ix	63.41 (3)
Co^ii—Mg—Ga1^vi	126.89 (5)	Co^viii—Ga1—Mg^ix	125.86 (3)
Ga2—Mg—Ga1^vi	57.37 (3)	Co—Ga1—Mg^ix	56.96 (3)
Ga1^iii—Mg—Ga1^vi	93.35 (4)	Ga2^viii—Ga1—Mg^ix	74.16 (3)
Ga1^v—Mg—Ga1^vi	94.72 (4)	Ga2^xi—Ga1—Mg^ix	174.61 (3)
Co^i—Mg—Mg^vii	108.35 (6)	Ga2^vi—Ga1—Mg^ix	55.55 (3)
Ga2^ii—Mg—Mg^vii	72.66 (5)	Mg^x—Ga1—Mg^ix	102.29 (3)
Co—Mg—Mg^vii	103.58 (6)	Mg^viii—Ga1—Mg^ix	118.56 (5)
Co^iii—Mg—Mg^vii	58.69 (4)	Mg^xii—Ga1—Mg^ix	81.95 (2)
Ga2^iv—Mg—Mg^vii	140.00 (7)	Mg^vi—Ga1—Mg^ix	111.61 (5)
Ga1^ii—Mg—Mg^vii	59.28 (4)	Co—Ga2—Co^x	132.69 (2)
Co^ii—Mg—Mg^vii	58.06 (4)	Co—Ga2—Co^iii	108.051 (18)
Ga2—Mg—Mg^vii	101.84 (6)	Co^x—Ga2—Co^iii	118.71 (2)
Ga1^iii—Mg—Mg^vii	58.07 (4)	Co—Ga2—Ga2^xiii	164.88 (3)
Ga1^v—Mg—Mg^vii	93.76 (6)	Co^x—Ga2—Ga2^xiii	60.31 (2)
Ga1^vi—Mg—Mg^vii	151.03 (7)	Co^iii—Ga2—Ga2^xiii	58.40 (2)
Ga1^vi—Co—Ga1^iii	126.89 (2)	Co—Ga2—Ga1^iii	57.623 (18)
Ga1^vi—Co—Ga2	72.00 (2)	Co^x—Ga2—Ga1^iii	148.24 (2)
Ga1^iii—Co—Ga2	64.02 (2)	Co^iii—Ga2—Ga1^iii	57.762 (19)
Ga1^vi—Co—Ga1	99.91 (2)	Ga2^xiii—Ga2—Ga1^iii	107.30 (3)
Ga1^iii—Co—Ga1	128.77 (3)	Co—Ga2—Mg^x	67.51 (3)
Ga2—Co—Ga1	124.19 (3)	Co^x—Ga2—Mg^x	65.50 (3)
Ga1^vi—Co—Ga2^ii	112.28 (2)	Co^iii—Ga2—Mg^x	164.53 (4)
Ga1^iii—Co—Ga2^ii	70.41 (2)	Ga2^xiii—Ga2—Mg^x	123.50 (4)
Ga2—Co—Ga2^ii	120.72 (2)	Ga1^iii—Ga2—Mg^x	110.16 (3)
Ga1—Co—Ga2^ii	113.45 (3)	Co—Ga2—Ga1^xi	107.77 (2)
Ga1^vi—Co—Ga2^viii	150.21 (3)	Co^x—Ga2—Ga1^xi	53.954 (17)
Ga1^iii—Co—Ga2^viii	80.28 (2)	Co^iii—Ga2—Ga1^xi	106.02 (2)
Ga2—Co—Ga2^viii	137.46 (2)	Ga2^xiii—Ga2—Ga1^xi	72.66 (2)
Ga1—Co—Ga2^viii	62.26 (2)	Ga1^iii—Ga2—Ga1^xi	95.144 (19)
Ga2^ii—Co—Ga2^viii	61.29 (2)	Mg^x—Ga2—Ga1^xi	63.35 (3)
Ga1^vi—Co—Mg^ix	69.63 (3)	Co—Ga2—Ga1^vi	52.768 (17)
Ga1^iii—Co—Mg^ix	138.21 (4)	Co^x—Ga2—Ga1^vi	101.53 (2)
Ga2—Co—Mg^ix	140.54 (4)	Co^iii—Ga2—Ga1^vi	124.42 (2)
Ga1—Co—Mg^ix	72.03 (3)	Ga2^xiii—Ga2—Ga1^vi	138.93 (3)
Ga2^ii—Co—Mg^ix	67.85 (3)	Ga1^iii—Ga2—Ga1^vi	104.750 (19)
Ga2^viii—Co—Mg^ix	81.73 (3)	Mg^x—Ga2—Ga1^vi	65.73 (3)
Ga1^vi—Co—Mg	69.29 (3)	Ga1^xi—Ga2—Ga1^vi	128.99 (2)
Ga1^iii—Co—Mg	67.06 (3)	Co—Ga2—Mg^iv	115.13 (3)
Ga2—Co—Mg	66.81 (3)	Co^x—Ga2—Mg^iv	59.14 (3)
Ga1—Co—Mg	162.56 (4)	Co^iii—Ga2—Mg^iv	106.32 (3)
Ga2^ii—Co—Mg	61.60 (3)	Ga2^xiii—Ga2—Mg^iv	77.30 (3)
Ga2^viii—Co—Mg	120.70 (4)	Ga1^iii—Ga2—Mg^iv	151.19 (3)
Mg^ix—Co—Mg	91.05 (3)	Mg^x—Ga2—Mg^iv	88.67 (2)
Ga1^vi—Co—Mg^viii	132.10 (4)	Ga1^xi—Ga2—Mg^iv	113.06 (3)
Ga1^iii—Co—Mg^viii	67.23 (3)	Ga1^vi—Ga2—Mg^iv	62.37 (3)
Ga2—Co—Mg^viii	79.53 (3)	Co—Ga2—Mg	62.84 (3)
Ga1—Co—Mg^viii	65.87 (3)	Co^x—Ga2—Mg	146.67 (4)
Ga2^ii—Co—Mg^viii	115.31 (4)	Co^iii—Ga2—Mg	63.04 (3)
Ga2^viii—Co—Mg^viii	65.19 (3)	Ga2^xiii—Ga2—Mg	111.24 (4)
Mg^ix—Co—Mg^viii	134.92 (5)	Ga1^iii—Ga2—Mg	63.76 (3)
Mg—Co—Mg^viii	131.56 (4)	Mg^x—Ga2—Mg	122.74 (4)
Ga1^vi—Co—Mg^x	69.33 (3)	Ga1^xi—Ga2—Mg	158.89 (3)
Ga1^iii—Co—Mg^x	109.93 (3)	Ga1^vi—Ga2—Mg	62.34 (3)
Ga2—Co—Mg^x	60.97 (3)	Mg^iv—Ga2—Mg	87.85 (4)
Ga1—Co—Mg^x	64.59 (3)

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