Neptunium(III) copper(I) diselenide

Abstract

The title compound, NpCuSe₂, is the first ternary neptunium transition-metal chalcogenide. It was synthesized from the elements at 873 K in an evacuated fused-silica tube. Single crystals were grown by vapor transport with I₂. NpCuSe₂ crystallizes in the LaCuS₂ structure type and can be viewed as a stacking of layers of CuSe₄ tetra­hedra and of double layers of NpSe₇ monocapped trigonal prisms along [100]. Because there are no Se—Se bonds in the structure, the formal oxidation states of Np/Cu/Se may be assigned as +III/+I/−II, respectively.

Related literature

For discussion of the LaCuS₂ structure type, see: Julien-Pouzol et al. (1981 ▶); Ijjaali et al. (2004 ▶). For other compounds with Cu—Se bonds, see: Daoudi et al. (1996 ▶); Strobel & Schleid (2004 ▶); Ijjaali et al. (2004 ▶). For other neptunium selenides, see: Wastin et al. (1995 ▶); Wojakowski (1985 ▶). For computational details, see Gelato & Parthé (1987 ▶).

Experimental

Crystal data

• NpCuSe₂

• M _r = 458.46

• Monoclinic,

• a = 6.6796 (5) Å

• b = 7.4384 (6) Å

• c = 7.1066 (5) Å

• β = 97.156 (1)°

• V = 350.34 (5) ų

• Z = 4

• Mo Kα radiation

• μ = 56.06 mm⁻¹

• T = 100 (2) K

• 0.08 × 0.05 × 0.04 mm

Data collection

• Bruker APEXII CCD diffractometer

• Absorption correction: numerical (face indexed; SADABS; Sheldrick, 2006 ▶) T _min = 0.045, T _max = 0.212

• 6189 measured reflections

• 1376 independent reflections

• 1309 reflections with I > 2σ(I)

• R _int = 0.036

Refinement

• R[F ² > 2σ(F ²)] = 0.028

• wR(F ²) = 0.068

• S = 1.35

• 1376 reflections

• 37 parameters

• Δρ_max = 2.43 e Å⁻³

• Δρ_min = −4.48 e Å⁻³

Data collection: APEX2 (Bruker, 2006 ▶); cell refinement: SAINT (Bruker, 2006 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: CrystalMaker (Palmer, 2008 ▶); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶).

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected geometric parameters (Å, °).

Cu1—Se2i	2.4409 (9)
Cu1—Se1ii	2.4490 (9)
Cu1—Se1iii	2.5066 (9)
Cu1—Se1	2.5899 (9)
Np1—Se2iv	2.9330 (6)
Np1—Se2v	2.9540 (6)
Np1—Se2	2.9743 (6)
Np1—Se1vi	2.9784 (6)
Np1—Se2vii	2.9785 (6)
Np1—Se1	2.9950 (6)
Np1—Se1viii	3.1419 (6)

Se2i—Cu1—Se1ii	116.52 (4)
Se2i—Cu1—Se1iii	102.85 (3)
Se1ii—Cu1—Se1iii	112.76 (4)
Se2i—Cu1—Se1	103.94 (3)
Se1ii—Cu1—Se1	103.44 (3)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) ; (viii) .

supplementary crystallographic information

Comment

In keeping with earlier descriptions of the LaCuS₂ structure type (Julien-Pouzol et al., 1981; Ijjaali et al., 2004) the structure of NpCuSe₂ can be viewed as a stacking of layers of CuSe₄ tetrahedra and double layers of NpSe₇ monocapped trigonal prisms along [100]. Figure 1 provides a view nearly down [010] of the unit cell. It displays the stacking of layers along [100] where atom Se1 is contained within the Cu layer and atom Se2 is contained within the Np double layer. The Cu—Se bond distances are reasonable for a Cu(I) compound; they range from 2.4409 (9) to 2.5899 (9) Å compared to 2.458 (2) to 2.490 (4) Å in SrCuCeSe₃ (Strobel & Schleid, 2004) and 2.450 (1) to 2.607 (1) Å in the Ce analogue CeCuSe₂ (Ijjaali et al., 2004). The Np—Se bond distances range from 2.9330 (6) to 3.1419 (6) Å. Comparisons are limited but can be made with the Np—Se distance of 2.903 (1) Å in NpSe (Wastin et al., 1995) and those of 2.932 and 3.086 Å in NpAsSe (Wojakowski, 1985). There are no Se—Se bonds in NpCuSe₂, so formal oxidation states may be assigned for Np/Cu/Se of +III/+I/-II.

The chemistry of Np is transitional between that of U and Pu. All three elements exhibit multiple oxidation states in their compounds. NpCuSe₂ is the first example of a neptunium chalcogenide compound analogous to a lanthanide(III) structure rather than to a transition-metal or uranium(IV) structure. The Pu analogue is unknown, although arguments based on the stability of various Pu oxidation states suggest it should be stable.

Experimental

NpCuSe₂was formed in an attempted synthesis of the Np analogue of U₃Cu₂Se₇ (Daoudi et al., 1996). Caution! ²³⁷Np is an α-emitting radioisotope and as such is considered a health risk. Its use requires appropriate infrastructure and personnel trained in the handling of radioactive materials. The following reagents were used as obtained from the manufacturer: Cu (Aldrich, 99.5%) and Se (Aldrich, 99%). Resublimed I₂ was utilized as a transport reagent. ²³⁷Np chunks were crushed and used as provided from Oak Ridge National Laboratory. A reaction mixture of 20.2 mg Np (0.085 mmol), 3.58 mg Cu (0.056 mmol), and 15.55 mg Se (0.197 mmol) was loaded into a fused-silica ampoule in an Ar-filled dry box that was then evacuated to 10 ^-4 Torr and sealed. The sample was placed in a computer controlled furnace, heated to 873 K in 8 h, kept at 873 K for 72 h, cooled at 5 K/h to 373 K, and finally air cooled in the oven to 298 K. The resultant black powder was reloaded into a fused-silica ampoule with 4 mg I₂. The ampoule was evacuated to 10 ^-4 Torr and sealed. The sample was placed in a computer controlled furnace, heated to 873 K in 8 h, kept at 873 K for 336 h, cooled at 6.94 K/h to 373 K, before finally being air cooled to 298 K. Black rectangular plates and blocks of NpCuSe₂ were obtained in low yield. The crystals used in characterization were manually extracted from the product mixture.

Refinement

The program STRUCTURE TIDY (Gelato & Parthé, 1987) was employed to standardize the atomic coordinates of the structure. The highest peak is 1.71 Å and the deepest hole is 0.08 Å from atom Np1.

Figures

Fig. 1.

A view nearly down [010] of the unit cell of NpCuSe2, with displacement ellipsoids at the 99% probability level.

Crystal data

NpCuSe2	F(000) = 760
Mr = 458.46	Dx = 8.692 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 4110 reflections
a = 6.6796 (5) Å	θ = 4.0–33.7°
b = 7.4384 (6) Å	µ = 56.06 mm−1
c = 7.1066 (5) Å	T = 100 K
β = 97.156 (1)°	Block, black
V = 350.34 (5) Å3	0.08 × 0.05 × 0.04 mm
Z = 4

Data collection

Bruker APEXII CCD diffractometer	1376 independent reflections
Radiation source: fine-focus sealed tube	1309 reflections with I > 2σ(I)
graphite	Rint = 0.036
φ and ω scans	θmax = 33.9°, θmin = 3.1°
Absorption correction: numerical (face indexed; SADABS; Sheldrick, 2006)	h = −10→10
Tmin = 0.045, Tmax = 0.212	k = −11→11
6189 measured reflections	l = −11→11

Refinement

Refinement on F2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.028	Secondary atom site location: difference Fourier map
wR(F2) = 0.068	w = [1/[σ2(Fo2) + (0.0312)Fo2]2
S = 1.35	(Δ/σ)max < 0.001
1376 reflections	Δρmax = 2.43 e Å−3
37 parameters	Δρmin = −4.48 e Å−3

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

	x	y	z	Uiso*/Ueq
Cu1	0.07000 (11)	0.66155 (10)	0.04945 (11)	0.00850 (14)
Np1	0.30684 (3)	0.04823 (3)	0.19759 (3)	0.00478 (8)
Se1	0.09977 (8)	0.39107 (7)	0.28075 (8)	0.00539 (11)
Se2	0.58173 (9)	0.27585 (7)	0.00026 (8)	0.00520 (11)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Cu1	0.0082 (3)	0.0081 (3)	0.0091 (3)	−0.0008 (2)	0.0009 (2)	−0.0017 (2)
Np1	0.00560 (11)	0.00354 (11)	0.00509 (11)	−0.00032 (6)	0.00021 (8)	−0.00020 (6)
Se1	0.0063 (2)	0.0041 (2)	0.0056 (2)	0.00028 (16)	−0.00019 (18)	−0.00004 (17)
Se2	0.0058 (2)	0.0044 (2)	0.0051 (2)	0.00028 (17)	−0.00027 (18)	0.00013 (17)

Geometric parameters (Å, °)

Cu1—Se2i	2.4409 (9)	Np1—Se1	2.9950 (6)
Cu1—Se1ii	2.4490 (9)	Np1—Se1v	3.1419 (6)
Cu1—Se1iii	2.5066 (9)	Np1—Cu1viii	3.3772 (8)
Cu1—Se1	2.5899 (9)	Np1—Cu1x	3.3866 (8)
Cu1—Cu1iii	2.6421 (15)	Np1—Cu1vii	3.4894 (8)
Cu1—Np1ii	3.3772 (8)	Se1—Cu1viii	2.4490 (9)
Cu1—Np1iv	3.3866 (8)	Se1—Cu1iii	2.5066 (9)
Cu1—Np1v	3.4894 (8)	Se1—Np1ii	2.9784 (6)
Np1—Se2vi	2.9330 (6)	Se1—Np1vii	3.1419 (6)
Np1—Se2vii	2.9540 (6)	Se2—Cu1i	2.4409 (9)
Np1—Se2	2.9743 (6)	Se2—Np1vi	2.9330 (6)
Np1—Se1viii	2.9784 (6)	Se2—Np1v	2.9540 (6)
Np1—Se2ix	2.9785 (6)	Se2—Np1xi	2.9785 (6)
Se2i—Cu1—Se1ii	116.52 (4)	Se2vi—Np1—Cu1viii	135.297 (18)
Se2i—Cu1—Se1iii	102.85 (3)	Se2vii—Np1—Cu1viii	86.489 (18)
Se1ii—Cu1—Se1iii	112.76 (4)	Se2—Np1—Cu1viii	130.824 (18)
Se2i—Cu1—Se1	103.94 (3)	Se1viii—Np1—Cu1viii	47.587 (17)
Se1ii—Cu1—Se1	103.44 (3)	Se2ix—Np1—Cu1viii	85.522 (17)
Se1iii—Cu1—Se1	117.57 (3)	Se1—Np1—Cu1viii	44.705 (16)
Se2i—Cu1—Cu1iii	116.56 (4)	Se1v—Np1—Cu1viii	101.316 (18)
Se1ii—Cu1—Cu1iii	126.51 (5)	Se2vi—Np1—Cu1x	44.728 (17)
Se1iii—Cu1—Cu1iii	60.33 (3)	Se2vii—Np1—Cu1x	145.739 (18)
Se1—Cu1—Cu1iii	57.24 (3)	Se2—Np1—Cu1x	128.963 (18)
Se2i—Cu1—Np1ii	155.73 (3)	Se1viii—Np1—Cu1x	44.687 (17)
Se1ii—Cu1—Np1ii	59.35 (2)	Se2ix—Np1—Cu1x	73.231 (18)
Se1iii—Cu1—Np1ii	100.32 (3)	Se1—Np1—Cu1x	125.113 (18)
Se1—Cu1—Np1ii	58.107 (19)	Se1v—Np1—Cu1x	72.255 (17)
Cu1iii—Cu1—Np1ii	69.64 (3)	Cu1viii—Np1—Cu1x	91.556 (15)
Se2i—Cu1—Np1iv	57.74 (2)	Se2vi—Np1—Cu1vii	98.092 (18)
Se1ii—Cu1—Np1iv	58.79 (2)	Se2vii—Np1—Cu1vii	88.423 (18)
Se1iii—Cu1—Np1iv	124.26 (3)	Se2—Np1—Cu1vii	162.568 (18)
Se1—Cu1—Np1iv	117.81 (3)	Se1viii—Np1—Cu1vii	44.741 (17)
Cu1iii—Cu1—Np1iv	172.48 (5)	Se2ix—Np1—Cu1vii	43.454 (17)
Np1ii—Cu1—Np1iv	113.38 (2)	Se1—Np1—Cu1vii	88.717 (17)
Se2i—Cu1—Np1v	57.06 (2)	Se1v—Np1—Cu1vii	123.660 (17)
Se1ii—Cu1—Np1v	160.72 (3)	Cu1viii—Np1—Cu1vii	45.22 (2)
Se1iii—Cu1—Np1v	56.76 (2)	Cu1x—Np1—Cu1vii	66.861 (13)
Se1—Cu1—Np1v	95.83 (3)	Cu1viii—Se1—Cu1iii	99.74 (3)
Cu1iii—Cu1—Np1v	65.14 (3)	Cu1viii—Se1—Cu1	148.28 (3)
Np1ii—Cu1—Np1v	134.78 (2)	Cu1iii—Se1—Cu1	62.43 (3)
Np1iv—Cu1—Np1v	111.51 (2)	Cu1viii—Se1—Np1ii	76.53 (2)
Se2vi—Np1—Se2vii	122.772 (13)	Cu1iii—Se1—Np1ii	78.50 (2)
Se2vi—Np1—Se2	91.915 (16)	Cu1—Se1—Np1ii	74.31 (2)
Se2vii—Np1—Se2	74.152 (12)	Cu1viii—Se1—Np1	75.95 (2)
Se2vi—Np1—Se1viii	89.408 (17)	Cu1iii—Se1—Np1	81.29 (2)
Se2vii—Np1—Se1viii	128.634 (17)	Cu1—Se1—Np1	122.48 (3)
Se2—Np1—Se1viii	150.258 (17)	Np1ii—Se1—Np1	142.27 (2)
Se2vi—Np1—Se2ix	74.394 (9)	Cu1viii—Se1—Np1vii	79.17 (2)
Se2vii—Np1—Se2ix	72.516 (18)	Cu1iii—Se1—Np1vii	178.90 (3)
Se2—Np1—Se2ix	127.853 (11)	Cu1—Se1—Np1vii	118.47 (3)
Se1viii—Np1—Se2ix	80.988 (16)	Np1ii—Se1—Np1vii	101.074 (17)
Se2vi—Np1—Se1	160.988 (17)	Np1—Se1—Np1vii	98.541 (17)
Se2vii—Np1—Se1	74.905 (16)	Cu1i—Se2—Np1vi	77.53 (2)
Se2—Np1—Se1	86.315 (17)	Cu1i—Se2—Np1v	109.10 (3)
Se1viii—Np1—Se1	82.962 (10)	Np1vi—Se2—Np1v	100.770 (17)
Se2ix—Np1—Se1	121.133 (17)	Cu1i—Se2—Np1	146.34 (3)
Se2vi—Np1—Se1v	76.958 (16)	Np1vi—Se2—Np1	88.085 (16)
Se2vii—Np1—Se1v	141.588 (16)	Np1v—Se2—Np1	103.371 (19)
Se2—Np1—Se1v	72.469 (16)	Cu1i—Se2—Np1xi	79.48 (2)
Se1viii—Np1—Se1v	78.926 (17)	Np1vi—Se2—Np1xi	148.12 (2)
Se2ix—Np1—Se1v	144.944 (16)	Np1v—Se2—Np1xi	107.484 (18)
Se1—Np1—Se1v	84.479 (14)	Np1—Se2—Np1xi	99.254 (17)

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