Uranium cobalt tetraaluminide, UCoAl4

Stêpieň-Damm, J.; Tougait, O.; Zaremba, V.I.; Noël, H.; Troc˘, R.

doi:10.1107/S0108270103027252

Uranium cobalt tetraaluminide, UCoAl₄

J. Stêpien-Damm, O. Tougait, V. I. Zaremba, H. Noël and R. Troc

The structure of UCoAl₄ can be viewed as a succession of atomic layers, with the compositions UCoAl and Al₃, that alternate along the c axis. The packing within the pure Al layer at z = ${1 \over 2}$ results from edge-sharing of triangles, squares and pentagons of Al atoms. Two successive Al₃ layers thus define pentagonal, square-based and trigonal prisms which are centred at z = 0 by the U, Co and remaining Al atoms. UCoAl₄ is a high-temperature phase that is only observed in as-cast samples.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103027252/bc1029sup1.cif Contains datablocks global, I
	Structure factor file (CIF format) https://doi.org/10.1107/S0108270103027252/bc1029Isup2.hkl Contains datablock I

Comment top

Investigations of rare earth or actinide (R) intermetallic compounds which combine a transition metal (T) with an element of the p block (X) have led to the synthesis and characterization of numerous compounds with a wide variety of anomalous physical properties. For a given formula, compounds form between most f-block elements and various transition metals, as well as some p-block elements of the same column. In the ternary R—Co—Al systems, where R is a 4f or 5f element, the compounds RCoAl₄ are reported to exist with R = La, Ce or Pr (Rykhal' et al., 1977). They adopt the orthorhombic LaCoAl₄ structure type (Pmma, oP12; Rykhal' et al., 1977). During a study of the ternary U—Co—Al phase diagram, the title novel compound UCoAl₄ was found in as-cast samples and its crystal structure has been determined by single-crystal X-ray diffraction.

UCoAl₄ adopts a new type of structure which can be described as a succession of two layers that alternate along the hexagonal c axis. Their compositions of UCoAl and Al₃ correspond to the basal planes lying at z= 0 and z = 1/2, respectively. The pure Al layer (z = 1/2) is formed by triangles, squares and pentagons of Al atoms assembled by edge-sharing (Fig. 1a). According to the Schläfli notation (Reference?), the tesselation of this slab can be described as 3454 and 3545 nets of the Al1 and Al2 sites, respectively. A double layer thus defines pentagonal, square-based and trigonal prisms, within which the U, Co and Al3 atoms are located at z = 0. Neighbouring atoms within the slab additionally cap all the rectangular faces of the various prisms.

The interatomic distances in UCoAl₄ compare well those reported for other ternary U—Co—Al compounds, such as U₂Co₂Al (Sampaio et al., 1968) and U₂Co₆Al₁₉ (Tougait et al., 2003). The structure of hexagonal UCoAl₄ is closely related to that of orthorhombic LaCoAl₄ (Fig. 1 b). The latter structure can also be viewed as a stacking of two kinds of layers, having the compositions LaCoAl and Al₃, alternating along the short b axis. The main difference between the UCoAl₄ and LaCoAl₄ structures arises from a different arrangement of the building motifs within the pure Al slab which defines a 345² net in the rare-earth compound.

UCoAl₄ is a high-temperature phase. Complete chemical and structural analyses of as-cast and heat-treated samples have confirmed the presence of this compound in the as-cast samples only. Electron microprobe analysis and powder X-ray diffraction have shown the occurrence of three phases in the as-cast samples, viz. hexagonal UCoAl₄ (P −62m, hP18) as the major component, cubic UAl_{2 − x}Co_x (ternary extension of UAl₂, MgCu₂-type, Fd-3 m, cF24; Petzow et al., 1964) and monoclinic U₂Co₆Al₁₉ (C2/m, mC108; Tougait et al., 2003). Annealing the samples at temperatures up to 1873 K yields a three-phase mixture of cubic UAl_{2 − x}Co_x, cubic UAl_{3 − x}Co_x (ternary extension of UAl₃, AuCu₃, Pm-3 m, cP4; Lupşa et al., 1994) and orthorhombic U₂Co₃Al₉ (Y₂Co₃Ga₉-type, Cmcm, oC56; Grin' et al., 1984). Thus, UCoAl₄ decomposes according to the peritectic reaction UCoAl₄ → UAl_{3 − x}Co_x + U₂Co₃Al₉. Due to the absence of single-phase samples, the complete investigation and interpretation of the magnetic properties of UCoAl₄ has not yet been carried out.

Experimental top

Samples with U:Co:Al atomic ratios of 1:1:4 were prepared by standard arc-melting techniques. Ingots were placed in alumina crucibles and sealed in fused silica tubes under a residual atmosphere of argon for a heat-treatment at 1173 K for 500 h, or annealed at 1873 K for 10 h using a high-frequency furnace. Single crystals of UCoAl₄ could be extracted from crushed as-cast samples. X-ray diffraction powder patterns were collected using monochromatic Cu Kα₁ radiation and Co Kα radiation. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) were performed on samples embedded in resin and polished using SiC paper and diamond paste down to 1 µm. A thin layer of gold was deposited on their surfaces before metallographic analyses.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2003); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Bergerhoff, 1996); software used to prepare material for publication: SHELXL97.

Figures top

Fig. 1. (a) UCoAl₄ viewed down the c axis. (b) LaCoAl₄ viewed down the b axis. Open and filled circles represent atoms at z = 0, and hatched circles represent atoms at z = 1/2.

uranium cobalt tetraaluminide top

Crystal data top

UCoAl₄	D_x = 6.746 Mg m⁻³
M_r = 404.88	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P62m	Cell parameters from 2952 reflections
Hall symbol: P -6 -2	θ = 4.5–46.0°
a = 9.161 (1) Å	µ = 45.38 mm⁻¹
c = 4.114 (1) Å	T = 293 K
V = 299.01 (9) Å³	Prism, black
Z = 3	0.11 × 0.02 × 0.02 mm
F(000) = 513

Data collection top

Kuma KM4 CCD area-detector diffractometer	1001 independent reflections
Radiation source: fine-focus sealed tube	949 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.041
ω scans	θ_max = 46.1°, θ_min = 4.5°
Absorption correction: analytical SHELXL70 in CrysAlis; Oxford Diffraction, 2003)	h = −18→14
T_min = 0.038, T_max = 0.468	k = −17→17
5480 measured reflections	l = −8→5

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0168P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.022	(Δ/σ)_max < 0.001
wR(F²) = 0.037	Δρ_max = 2.42 e Å⁻³
S = 1.01	Δρ_min = −1.91 e Å⁻³
1001 reflections	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
25 parameters	Extinction coefficient: 0.0154 (5)
0 restraints	Absolute structure: Flack (1983), 561 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.046 (7)

Crystal data top

UCoAl₄	Z = 3
M_r = 404.88	Mo Kα radiation
Hexagonal, P62m	µ = 45.38 mm⁻¹
a = 9.161 (1) Å	T = 293 K
c = 4.114 (1) Å	0.11 × 0.02 × 0.02 mm
V = 299.01 (9) Å³

Data collection top

Kuma KM4 CCD area-detector diffractometer	1001 independent reflections
Absorption correction: analytical SHELXL70 in CrysAlis; Oxford Diffraction, 2003)	949 reflections with I > 2σ(I)
T_min = 0.038, T_max = 0.468	R_int = 0.041
5480 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.022	0 restraints
wR(F²) = 0.037	Δρ_max = 2.42 e Å⁻³
S = 1.01	Δρ_min = −1.91 e Å⁻³
1001 reflections	Absolute structure: Flack (1983), 561 Friedel pairs
25 parameters	Absolute structure parameter: 0.046 (7)

Special details top

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
U	0.40522 (2)	0.0000	0.0000	0.00660 (4)
Co1	0.0000	0.0000	0.0000	0.0088 (2)
Co2	0.3333	0.6667	0.0000	0.01168 (19)
Al1	0.29637 (16)	0.47944 (17)	0.5000	0.0078 (2)
Al2	0.16977 (19)	0.0000	0.5000	0.0075 (3)
Al3	0.7420 (3)	0.0000	0.0000	0.0116 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
U	0.00699 (6)	0.00747 (8)	0.00550 (7)	0.00373 (4)	0.000	0.000
Co1	0.0086 (3)	0.0086 (3)	0.0092 (6)	0.00429 (16)	0.000	0.000
Co2	0.0151 (3)	0.0151 (3)	0.0049 (4)	0.00753 (15)	0.000	0.000
Al1	0.0085 (5)	0.0077 (5)	0.0070 (5)	0.0040 (5)	0.000	0.000
Al2	0.0102 (5)	0.0083 (7)	0.0035 (6)	0.0042 (4)	0.000	0.000
Al3	0.0110 (5)	0.0148 (9)	0.0102 (8)	0.0074 (4)	0.000	0.000

Geometric parameters (Å, º) top

U—Co2ⁱ	2.7834 (3)	Al1—Al1^xviii	2.725 (2)
U—Co2ⁱⁱ	2.7834 (3)	Al1—Al1^xvii	2.725 (2)
U—Al2ⁱⁱⁱ	2.9806 (13)	Al1—Al2^xiv	2.7780 (17)
U—Al2	2.9806 (13)	Al1—Al3^xi	2.7851 (14)
U—Al3	3.085 (2)	Al1—Al3^xxii	2.7851 (14)
U—Al1^iv	3.1516 (10)	Al1—Al1^ix	2.905 (2)
U—Al1^v	3.1516 (10)	Al1—U^xxii	3.1516 (10)
U—Al1^vi	3.1516 (10)	Al1—U^xi	3.1516 (10)
U—Al1^vii	3.1516 (10)	Al1—U^xiv	3.1967 (10)
U—Al1^viii	3.1967 (10)	Al1—U^xxiii	3.1967 (10)
U—Al1^ix	3.1967 (10)	Al2—Co1^xxi	2.5788 (11)
U—Al1^x	3.1967 (10)	Al2—Al2^x	2.694 (3)
Co1—Al3^xi	2.364 (2)	Al2—Al2^xiv	2.694 (3)
Co1—Al3^xii	2.364 (2)	Al2—Al1^ix	2.7780 (17)
Co1—Al3^xiii	2.364 (2)	Al2—Al1^x	2.7780 (16)
Co1—Al2^viii	2.5788 (11)	Al2—Al3^xii	2.9259 (13)
Co1—Al2^xiv	2.5788 (11)	Al2—Al3^xxii	2.9259 (13)
Co1—Al2	2.5788 (11)	Al2—Al3^xi	2.9259 (13)
Co1—Al2ⁱⁱⁱ	2.5788 (11)	Al2—Al3^xxiv	2.9259 (13)
Co1—Al2^xv	2.5788 (11)	Al2—U^xxi	2.9806 (13)
Co1—Al2^x	2.5788 (11)	Al3—Co1^xxv	2.364 (2)
Co2—Al1^xvi	2.5898 (9)	Al3—Al1^v	2.7851 (14)
Co2—Al1^xvii	2.5898 (9)	Al3—Al1^iv	2.7851 (14)
Co2—Al1^xviii	2.5898 (9)	Al3—Al1^vii	2.7851 (14)
Co2—Al1ⁱⁱⁱ	2.5898 (9)	Al3—Al1^vi	2.7851 (14)
Co2—Al1^xix	2.5898 (9)	Al3—Al2^vi	2.9259 (13)
Co2—Al1	2.5898 (9)	Al3—Al2^xxvi	2.9259 (13)
Co2—U^xx	2.7834 (3)	Al3—Al2^xxvii	2.9259 (13)
Co2—U^xiv	2.7834 (3)	Al3—Al2^v	2.9259 (13)
Co2—U^xi	2.7834 (3)	Al3—U^vi	3.2547 (5)
Al1—Co2^xxi	2.5898 (9)	Al3—U^xxvii	3.2547 (5)

Co2ⁱ—U—Co2ⁱⁱ	143.649 (7)	Al1^xviii—Al1—U^xxii	65.44 (5)
Co2ⁱ—U—Al2ⁱⁱⁱ	103.046 (6)	Al1^xvii—Al1—U^xxii	109.92 (4)
Co2ⁱⁱ—U—Al2ⁱⁱⁱ	103.046 (6)	Al2^xiv—Al1—U^xxii	125.69 (4)
Co2ⁱ—U—Al2	103.046 (6)	Al3^xi—Al1—U^xxii	119.91 (5)
Co2ⁱⁱ—U—Al2	103.046 (6)	Al3^xxii—Al1—U^xxii	62.26 (5)
Al2ⁱⁱⁱ—U—Al2	87.28 (5)	Al1^ix—Al1—U^xxii	62.56 (2)
Co2ⁱ—U—Al3	71.824 (4)	Co2^xxi—Al1—U^xi	119.48 (5)
Co2ⁱⁱ—U—Al3	71.824 (4)	Co2—Al1—U^xi	56.994 (18)
Al2ⁱⁱⁱ—U—Al3	136.36 (2)	Al1^xviii—Al1—U^xi	65.44 (5)
Al2—U—Al3	136.36 (2)	Al1^xvii—Al1—U^xi	109.92 (4)
Co2ⁱ—U—Al1^iv	104.49 (2)	Al2^xiv—Al1—U^xi	125.69 (4)
Co2ⁱⁱ—U—Al1^iv	51.286 (19)	Al3^xi—Al1—U^xi	62.26 (5)
Al2ⁱⁱⁱ—U—Al1^iv	152.33 (2)	Al3^xxii—Al1—U^xi	119.91 (5)
Al2—U—Al1^iv	89.13 (3)	Al1^ix—Al1—U^xi	62.56 (2)
Al3—U—Al1^iv	53.03 (2)	U^xxii—Al1—U^xi	81.49 (3)
Co2ⁱ—U—Al1^v	51.286 (19)	Co2^xxi—Al1—U^xiv	117.90 (4)
Co2ⁱⁱ—U—Al1^v	104.49 (2)	Co2—Al1—U^xiv	56.335 (17)
Al2ⁱⁱⁱ—U—Al1^v	89.13 (3)	Al1^xviii—Al1—U^xiv	108.63 (3)
Al2—U—Al1^v	152.33 (2)	Al1^xvii—Al1—U^xiv	63.72 (4)
Al3—U—Al1^v	53.03 (2)	Al2^xiv—Al1—U^xiv	59.36 (3)
Al1^iv—U—Al1^v	106.07 (4)	Al3^xi—Al1—U^xiv	65.51 (3)
Co2ⁱ—U—Al1^vi	51.286 (19)	Al3^xxii—Al1—U^xiv	122.41 (6)
Co2ⁱⁱ—U—Al1^vi	104.49 (2)	Al1^ix—Al1—U^xiv	123.46 (2)
Al2ⁱⁱⁱ—U—Al1^vi	152.33 (2)	U^xxii—Al1—U^xiv	173.41 (5)
Al2—U—Al1^vi	89.13 (3)	U^xi—Al1—U^xiv	98.825 (15)
Al3—U—Al1^vi	53.03 (2)	Co2^xxi—Al1—U^xxiii	56.335 (17)
Al1^iv—U—Al1^vi	54.88 (4)	Co2—Al1—U^xxiii	117.90 (4)
Al1^v—U—Al1^vi	81.49 (3)	Al1^xviii—Al1—U^xxiii	108.63 (3)
Co2ⁱ—U—Al1^vii	104.49 (2)	Al1^xvii—Al1—U^xxiii	63.72 (4)
Co2ⁱⁱ—U—Al1^vii	51.286 (19)	Al2^xiv—Al1—U^xxiii	59.36 (3)
Al2ⁱⁱⁱ—U—Al1^vii	89.13 (3)	Al3^xi—Al1—U^xxiii	122.41 (6)
Al2—U—Al1^vii	152.33 (2)	Al3^xxii—Al1—U^xxiii	65.51 (3)
Al3—U—Al1^vii	53.03 (2)	Al1^ix—Al1—U^xxiii	123.46 (2)
Al1^iv—U—Al1^vii	81.49 (3)	U^xxii—Al1—U^xxiii	98.825 (15)
Al1^v—U—Al1^vii	54.88 (4)	U^xi—Al1—U^xxiii	173.41 (5)
Al1^vi—U—Al1^vii	106.07 (4)	U^xiv—Al1—U^xxiii	80.10 (3)
Co2ⁱ—U—Al1^viii	50.75 (2)	Co1—Al2—Co1^xxi	105.82 (6)
Co2ⁱⁱ—U—Al1^viii	139.903 (16)	Co1—Al2—Al2^x	58.51 (3)
Al2ⁱⁱⁱ—U—Al1^viii	53.31 (3)	Co1^xxi—Al2—Al2^x	58.51 (3)
Al2—U—Al1^viii	106.90 (2)	Co1—Al2—Al2^xiv	58.51 (3)
Al3—U—Al1^viii	102.24 (2)	Co1^xxi—Al2—Al2^xiv	58.51 (3)
Al1^iv—U—Al1^viii	152.429 (8)	Al2^x—Al2—Al2^xiv	60.0
Al1^v—U—Al1^viii	50.84 (4)	Co1—Al2—Al1^ix	108.734 (14)
Al1^vi—U—Al1^viii	102.03 (3)	Co1^xxi—Al2—Al1^ix	108.734 (14)
Al1^vii—U—Al1^viii	92.663 (14)	Al2^x—Al2—Al1^ix	152.18 (4)
Co2ⁱ—U—Al1^ix	139.903 (16)	Al2^xiv—Al2—Al1^ix	92.18 (4)
Co2ⁱⁱ—U—Al1^ix	50.75 (2)	Co1—Al2—Al1^x	108.734 (14)
Al2ⁱⁱⁱ—U—Al1^ix	106.90 (2)	Co1^xxi—Al2—Al1^x	108.734 (14)
Al2—U—Al1^ix	53.31 (3)	Al2^x—Al2—Al1^x	92.18 (4)
Al3—U—Al1^ix	102.24 (2)	Al2^xiv—Al2—Al1^x	152.18 (4)
Al1^iv—U—Al1^ix	50.84 (4)	Al1^ix—Al2—Al1^x	115.64 (8)
Al1^v—U—Al1^ix	152.429 (8)	Co1—Al2—Al3^xii	50.38 (4)
Al1^vi—U—Al1^ix	92.663 (14)	Co1^xxi—Al2—Al3^xii	118.94 (5)
Al1^vii—U—Al1^ix	102.03 (3)	Al2^x—Al2—Al3^xii	62.59 (3)
Al1^viii—U—Al1^ix	155.52 (5)	Al2^xiv—Al2—Al3^xii	103.85 (4)
Co2ⁱ—U—Al1^x	50.75 (2)	Al1^ix—Al2—Al3^xii	131.31 (4)
Co2ⁱⁱ—U—Al1^x	139.903 (16)	Al1^x—Al2—Al3^xii	58.39 (4)
Al2ⁱⁱⁱ—U—Al1^x	106.90 (2)	Co1—Al2—Al3^xxii	118.94 (5)
Al2—U—Al1^x	53.31 (3)	Co1^xxi—Al2—Al3^xxii	50.38 (4)
Al3—U—Al1^x	102.24 (2)	Al2^x—Al2—Al3^xxii	103.85 (4)
Al1^iv—U—Al1^x	92.663 (14)	Al2^xiv—Al2—Al3^xxii	62.59 (3)
Al1^v—U—Al1^x	102.03 (3)	Al1^ix—Al2—Al3^xxii	58.39 (4)
Al1^vi—U—Al1^x	50.84 (4)	Al1^x—Al2—Al3^xxii	131.31 (4)
Al1^vii—U—Al1^x	152.429 (8)	Al3^xii—Al2—Al3^xxii	165.34 (8)
Al1^viii—U—Al1^x	80.10 (3)	Co1—Al2—Al3^xi	50.38 (4)
Al1^ix—U—Al1^x	94.70 (4)	Co1^xxi—Al2—Al3^xi	118.94 (5)
Al3^xi—Co1—Al3^xii	120.0	Al2^x—Al2—Al3^xi	103.85 (4)
Al3^xi—Co1—Al3^xiii	120.0	Al2^xiv—Al2—Al3^xi	62.59 (3)
Al3^xii—Co1—Al3^xiii	120.0	Al1^ix—Al2—Al3^xi	58.39 (4)
Al3^xi—Co1—Al2^viii	127.09 (3)	Al1^x—Al2—Al3^xi	131.31 (4)
Al3^xii—Co1—Al2^viii	72.450 (13)	Al3^xii—Al2—Al3^xi	88.79 (6)
Al3^xiii—Co1—Al2^viii	72.450 (13)	Al3^xxii—Al2—Al3^xi	89.34 (5)
Al3^xi—Co1—Al2^xiv	72.450 (13)	Co1—Al2—Al3^xxiv	118.94 (5)
Al3^xii—Co1—Al2^xiv	127.09 (3)	Co1^xxi—Al2—Al3^xxiv	50.38 (4)
Al3^xiii—Co1—Al2^xiv	72.450 (13)	Al2^x—Al2—Al3^xxiv	62.59 (3)
Al2^viii—Co1—Al2^xiv	144.90 (3)	Al2^xiv—Al2—Al3^xxiv	103.85 (4)
Al3^xi—Co1—Al2	72.450 (13)	Al1^ix—Al2—Al3^xxiv	131.31 (4)
Al3^xii—Co1—Al2	72.450 (13)	Al1^x—Al2—Al3^xxiv	58.39 (4)
Al3^xiii—Co1—Al2	127.09 (3)	Al3^xii—Al2—Al3^xxiv	89.34 (5)
Al2^viii—Co1—Al2	144.90 (3)	Al3^xxii—Al2—Al3^xxiv	88.79 (6)
Al2^xiv—Co1—Al2	62.97 (5)	Al3^xi—Al2—Al3^xxiv	165.34 (8)
Al3^xi—Co1—Al2ⁱⁱⁱ	72.450 (13)	Co1—Al2—U^xxi	170.73 (5)
Al3^xii—Co1—Al2ⁱⁱⁱ	72.450 (13)	Co1^xxi—Al2—U^xxi	83.451 (17)
Al3^xiii—Co1—Al2ⁱⁱⁱ	127.09 (3)	Al2^x—Al2—U^xxi	128.810 (19)
Al2^viii—Co1—Al2ⁱⁱⁱ	62.97 (5)	Al2^xiv—Al2—U^xxi	128.810 (19)
Al2^xiv—Co1—Al2ⁱⁱⁱ	144.90 (3)	Al1^ix—Al2—U^xxi	67.33 (4)
Al2—Co1—Al2ⁱⁱⁱ	105.82 (6)	Al1^x—Al2—U^xxi	67.33 (4)
Al3^xi—Co1—Al2^xv	72.450 (13)	Al3^xii—Al2—U^xxi	125.28 (5)
Al3^xii—Co1—Al2^xv	127.09 (3)	Al3^xxii—Al2—U^xxi	66.869 (18)
Al3^xiii—Co1—Al2^xv	72.450 (13)	Al3^xi—Al2—U^xxi	125.28 (5)
Al2^viii—Co1—Al2^xv	62.97 (5)	Al3^xxiv—Al2—U^xxi	66.869 (18)
Al2^xiv—Co1—Al2^xv	105.82 (6)	Co1—Al2—U	83.451 (17)
Al2—Co1—Al2^xv	144.90 (3)	Co1^xxi—Al2—U	170.73 (5)
Al2ⁱⁱⁱ—Co1—Al2^xv	62.97 (5)	Al2^x—Al2—U	128.809 (19)
Al3^xi—Co1—Al2^x	127.09 (3)	Al2^xiv—Al2—U	128.810 (19)
Al3^xii—Co1—Al2^x	72.450 (13)	Al1^ix—Al2—U	67.33 (4)
Al3^xiii—Co1—Al2^x	72.450 (13)	Al1^x—Al2—U	67.33 (4)
Al2^viii—Co1—Al2^x	105.82 (6)	Al3^xii—Al2—U	66.869 (18)
Al2^xiv—Co1—Al2^x	62.97 (5)	Al3^xxii—Al2—U	125.28 (5)
Al2—Co1—Al2^x	62.97 (5)	Al3^xi—Al2—U	66.869 (18)
Al2ⁱⁱⁱ—Co1—Al2^x	144.90 (3)	Al3^xxiv—Al2—U	125.28 (5)
Al2^xv—Co1—Al2^x	144.90 (3)	U^xxi—Al2—U	87.28 (5)
Al1^xvi—Co2—Al1^xvii	105.17 (5)	Co1^xxv—Al3—Al1^v	115.29 (5)
Al1^xvi—Co2—Al1^xviii	144.63 (2)	Co1^xxv—Al3—Al1^iv	115.29 (5)
Al1^xvii—Co2—Al1^xviii	63.49 (4)	Al1^v—Al3—Al1^iv	129.42 (10)
Al1^xvi—Co2—Al1ⁱⁱⁱ	63.49 (4)	Co1^xxv—Al3—Al1^vii	115.29 (5)
Al1^xvii—Co2—Al1ⁱⁱⁱ	144.63 (2)	Al1^v—Al3—Al1^vii	62.87 (5)
Al1^xviii—Co2—Al1ⁱⁱⁱ	144.63 (2)	Al1^iv—Al3—Al1^vii	95.22 (6)
Al1^xvi—Co2—Al1^xix	63.49 (4)	Co1^xxv—Al3—Al1^vi	115.29 (5)
Al1^xvii—Co2—Al1^xix	144.63 (2)	Al1^v—Al3—Al1^vi	95.22 (6)
Al1^xviii—Co2—Al1^xix	105.17 (5)	Al1^iv—Al3—Al1^vi	62.87 (5)
Al1ⁱⁱⁱ—Co2—Al1^xix	63.49 (4)	Al1^vii—Al3—Al1^vi	129.42 (10)
Al1^xvi—Co2—Al1	144.63 (2)	Co1^xxv—Al3—Al2^vi	57.17 (4)
Al1^xvii—Co2—Al1	63.49 (4)	Al1^v—Al3—Al2^vi	172.26 (9)
Al1^xviii—Co2—Al1	63.49 (4)	Al1^iv—Al3—Al2^vi	58.15 (4)
Al1ⁱⁱⁱ—Co2—Al1	105.17 (5)	Al1^vii—Al3—Al2^vi	120.72 (4)
Al1^xix—Co2—Al1	144.63 (2)	Al1^vi—Al3—Al2^vi	87.27 (3)
Al1^xvi—Co2—U^xx	72.91 (3)	Co1^xxv—Al3—Al2^xxvi	57.17 (4)
Al1^xvii—Co2—U^xx	72.91 (3)	Al1^v—Al3—Al2^xxvi	58.15 (4)
Al1^xviii—Co2—U^xx	71.72 (3)	Al1^iv—Al3—Al2^xxvi	172.26 (9)
Al1ⁱⁱⁱ—Co2—U^xx	127.41 (2)	Al1^vii—Al3—Al2^xxvi	87.27 (3)
Al1^xix—Co2—U^xx	71.72 (3)	Al1^vi—Al3—Al2^xxvi	120.72 (4)
Al1—Co2—U^xx	127.41 (2)	Al2^vi—Al3—Al2^xxvi	114.35 (9)
Al1^xvi—Co2—U^xiv	71.72 (3)	Co1^xxv—Al3—Al2^xxvii	57.17 (4)
Al1^xvii—Co2—U^xiv	71.72 (3)	Al1^v—Al3—Al2^xxvii	120.72 (4)
Al1^xviii—Co2—U^xiv	127.41 (2)	Al1^iv—Al3—Al2^xxvii	87.27 (3)
Al1ⁱⁱⁱ—Co2—U^xiv	72.91 (3)	Al1^vii—Al3—Al2^xxvii	172.26 (9)
Al1^xix—Co2—U^xiv	127.41 (2)	Al1^vi—Al3—Al2^xxvii	58.15 (4)
Al1—Co2—U^xiv	72.91 (3)	Al2^vi—Al3—Al2^xxvii	54.82 (7)
U^xx—Co2—U^xiv	120.0	Al2^xxvi—Al3—Al2^xxvii	89.34 (5)
Al1^xvi—Co2—U^xi	127.41 (2)	Co1^xxv—Al3—Al2^v	57.17 (4)
Al1^xvii—Co2—U^xi	127.41 (2)	Al1^v—Al3—Al2^v	87.27 (3)
Al1^xviii—Co2—U^xi	72.91 (3)	Al1^iv—Al3—Al2^v	120.72 (4)
Al1ⁱⁱⁱ—Co2—U^xi	71.72 (3)	Al1^vii—Al3—Al2^v	58.15 (4)
Al1^xix—Co2—U^xi	72.91 (3)	Al1^vi—Al3—Al2^v	172.26 (9)
Al1—Co2—U^xi	71.72 (3)	Al2^vi—Al3—Al2^v	89.34 (5)
U^xx—Co2—U^xi	120.0	Al2^xxvi—Al3—Al2^v	54.82 (7)
U^xiv—Co2—U^xi	120.0	Al2^xxvii—Al3—Al2^v	114.35 (9)
Co2^xxi—Al1—Co2	105.17 (5)	Co1^xxv—Al3—U	180.0
Co2^xxi—Al1—Al1^xviii	58.253 (19)	Al1^v—Al3—U	64.71 (5)
Co2—Al1—Al1^xviii	58.253 (19)	Al1^iv—Al3—U	64.71 (5)
Co2^xxi—Al1—Al1^xvii	58.253 (19)	Al1^vii—Al3—U	64.71 (5)
Co2—Al1—Al1^xvii	58.253 (19)	Al1^vi—Al3—U	64.71 (5)
Al1^xviii—Al1—Al1^xvii	60.0	Al2^vi—Al3—U	122.83 (4)
Co2^xxi—Al1—Al2^xiv	114.44 (4)	Al2^xxvi—Al3—U	122.83 (4)
Co2—Al1—Al2^xiv	114.44 (4)	Al2^xxvii—Al3—U	122.83 (4)
Al1^xviii—Al1—Al2^xiv	162.92 (7)	Al2^v—Al3—U	122.83 (4)
Al1^xvii—Al1—Al2^xiv	102.92 (7)	Co1^xxv—Al3—U^vi	81.03 (4)
Co2^xxi—Al1—Al3^xi	174.94 (4)	Al1^v—Al3—U^vi	125.57 (3)
Co2—Al1—Al3^xi	79.80 (3)	Al1^iv—Al3—U^vi	63.35 (2)
Al1^xviii—Al1—Al3^xi	125.12 (6)	Al1^vii—Al3—U^vi	63.35 (2)
Al1^xvii—Al1—Al3^xi	126.30 (4)	Al1^vi—Al3—U^vi	125.57 (3)
Al2^xiv—Al1—Al3^xi	63.47 (5)	Al2^vi—Al3—U^vi	57.37 (3)
Co2^xxi—Al1—Al3^xxii	79.80 (3)	Al2^xxvi—Al3—U^vi	111.73 (5)
Co2—Al1—Al3^xxii	174.94 (4)	Al2^xxvii—Al3—U^vi	111.73 (5)
Al1^xviii—Al1—Al3^xxii	125.12 (6)	Al2^v—Al3—U^vi	57.37 (3)
Al1^xvii—Al1—Al3^xxii	126.30 (4)	U—Al3—U^vi	98.97 (4)
Al2^xiv—Al1—Al3^xxii	63.47 (5)	Co1^xxv—Al3—U^xxvii	81.03 (4)
Al3^xi—Al1—Al3^xxii	95.22 (6)	Al1^v—Al3—U^xxvii	63.35 (2)
Co2^xxi—Al1—Al1^ix	117.41 (2)	Al1^iv—Al3—U^xxvii	125.57 (3)
Co2—Al1—Al1^ix	117.41 (2)	Al1^vii—Al3—U^xxvii	125.57 (3)
Al1^xviii—Al1—Al1^ix	109.26 (5)	Al1^vi—Al3—U^xxvii	63.35 (2)
Al1^xvii—Al1—Al1^ix	169.26 (5)	Al2^vi—Al3—U^xxvii	111.73 (5)
Al2^xiv—Al1—Al1^ix	87.82 (4)	Al2^xxvi—Al3—U^xxvii	57.37 (3)
Al3^xi—Al1—Al1^ix	58.57 (3)	Al2^xxvii—Al3—U^xxvii	57.37 (3)
Al3^xxii—Al1—Al1^ix	58.57 (3)	Al2^v—Al3—U^xxvii	111.73 (5)
Co2^xxi—Al1—U^xxii	56.994 (18)	U—Al3—U^xxvii	98.97 (4)
Co2—Al1—U^xxii	119.48 (5)	U^vi—Al3—U^xxvii	162.06 (8)

Symmetry codes: (i) x, y−1, z; (ii) y, x, −z; (iii) x, y, z−1; (iv) −x+1, −x+y, −z+1; (v) −y+1, x−y, z−1; (vi) −y+1, x−y, z; (vii) −x+1, −x+y, −z; (viii) −x+y, −x, z−1; (ix) y, x, −z+1; (x) −x+y, −x, z; (xi) −x+y+1, −x+1, z; (xii) −y, x−y−1, z; (xiii) x−1, y, z; (xiv) −y, x−y, z; (xv) −y, x−y, z−1; (xvi) −x+y, −x+1, z−1; (xvii) −x+y, −x+1, z; (xviii) −y+1, x−y+1, z; (xix) −y+1, x−y+1, z−1; (xx) x, y+1, z; (xxi) x, y, z+1; (xxii) −x+y+1, −x+1, z+1; (xxiii) −y, x−y, z+1; (xxiv) −y, x−y−1, z+1; (xxv) x+1, y, z; (xxvi) −x+y+1, −x, z−1; (xxvii) −x+y+1, −x, z.

Experimental details

Crystal data
Chemical formula	UCoAl₄
M_r	404.88
Crystal system, space group	Hexagonal, P62m
Temperature (K)	293
a, c (Å)	9.161 (1), 4.114 (1)
V (Å³)	299.01 (9)
Z	3
Radiation type	Mo Kα
µ (mm⁻¹)	45.38
Crystal size (mm)	0.11 × 0.02 × 0.02

Data collection
Diffractometer	Kuma KM4 CCD area-detector diffractometer
Absorption correction	Analytical SHELXL70 in CrysAlis; Oxford Diffraction, 2003)
T_min, T_max	0.038, 0.468
No. of measured, independent and observed [I > 2σ(I)] reflections	5480, 1001, 949
R_int	0.041
(sin θ/λ)_max (Å⁻¹)	1.014

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.022, 0.037, 1.01
No. of reflections	1001
No. of parameters	25
Δρ_max, Δρ_min (e Å⁻³)	2.42, −1.91
Absolute structure	Flack (1983), 561 Friedel pairs
Absolute structure parameter	0.046 (7)

Computer programs: CrysAlis CCD (Oxford Diffraction, 2003), CrysAlis CCD, CrysAlis RED (Oxford Diffraction, 2003), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), DIAMOND (Bergerhoff, 1996), SHELXL97.

Selected bond lengths (Å) top

U—Co2ⁱ	2.7834 (3)	Al1—Al1^viii	2.905 (2)
U—Al2	2.9806 (13)	Al1—U^ix	3.1516 (10)
U—Al3	3.085 (2)	Al1—U^iv	3.1516 (10)
U—Al1ⁱⁱ	3.1516 (10)	Al1—U^v	3.1967 (10)
U—Al1ⁱⁱⁱ	3.1967 (10)	Al2—Co1^vi	2.5788 (11)
Co1—Al3^iv	2.364 (2)	Al2—Al2^x	2.694 (3)
Co1—Al2	2.5788 (11)	Al2—Al1^x	2.7780 (16)
Co2—Al1	2.5898 (9)	Al2—Al3^xi	2.9259 (13)
Co2—U^v	2.7834 (3)	Al2—U^vi	2.9806 (13)
Al1—Co2^vi	2.5898 (9)	Al3—Co1^xii	2.364 (2)
Al1—Al1^vii	2.725 (2)	Al3—Al1^xiii	2.7851 (14)
Al1—Al2^v	2.7780 (17)	Al3—Al2^xiv	2.9259 (13)
Al1—Al3^iv	2.7851 (14)	Al3—U^xiv	3.2547 (5)

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

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