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Ca2N adopts the anti-CdCl2 structure in which two sheets of calcium ions enclose a sheet of N3- ions, with each calcium bonded to three N3- at 2.4500 (3) Å and each nitro­gen octahedrally coordinated by six calciums. Within one calcium sheet, each metal has three others at 3.2944 (8) Å and a further six at 3.6271 (3) Å. The distance between two calcium layers with no intervening nitro­gen layer is 4.3221 (6) Å, and this intervening region contains no observable electron density. Neutron and X-ray powder diffraction studies have shown that the c-axis dimension changes with the synthetic method employed. In the single-crystal, c is significantly lower, reflecting the higher temperature employed in its formation.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801000472/br6000sup1.cif
Contains datablocks BR6000, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536801000472/br6000Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 298 K
  • Mean [sigma](Ca-N) = 0.0003 Å
  • R factor = 0.017
  • wR factor = 0.038
  • Data-to-parameter ratio = 14.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

General Notes

ABSTM_02 When printed, the submitted absorption T values will be replaced by the scaled T values. Since the ratio of scaled T's is identical to the ratio of reported T values, the scaling does not imply a change to the absorption corrections used in the study. Ratio of Tmax expected/reported 0.861 Tmax scaled 0.561 Tmin scaled 0.494

Comment top

There is considerable interest in the A2N nitrides of the Group 2 elements due to their unusual formal oxidation state and electrical properties. A previous crystal structure determination (Keve & Skapski, 1968) showed the major features of the Ca2N structure but could not be completed as the crystals were lost. We have repeated the determination on high quality crystals obtained from an unusual preparative route. Single crystals of Ca2N were prepared by firstly reacting calcium metal dissolved in an excess of liquid sodium with a positive pressure of nitrogen gas at 723 K for 3 d. The excess sodium was removed by vacuum distillation at 973 K and 10 -5 Torr leaving a polycrystalline product. The product was then heated at 1393 K for 5 d in a stainless steel crucible lined with cobalt foil and welded shut in an argon atmosphere. Single crystals of the air-sensitive Ca2N were removed from the crucible in a high-integrity, nitrogen-filled glove-box (O2 content <2 p.p.m., H2O content <5 p.p.m.) and placed in RS3000 perfluoropolyether for mounting on the diffractometer.

Ca2N has the anti-CdCl2 structure in which two sheets of calcium ions enclose a sheet of N3- ions and each calcium is bonded to three N3- ions at 2.4500 (3) Å. Each nitrogen is octahedrally coordinated by calciums. Within the layer each calcium has three calcium ions at 3.2944 (8) Å and a further six at 3.6271 (3) Å. The distance between two calcium layers with no intervening nitrogen layers is 4.3221 (6) Å, and this intervening region contains no observable electron density. Neutron and X-ray powder diffraction studies (Gregory et al., 2000) have shown that the c axis dimension changes according to the synthetic method used: the c dimension of the single-crystal was significantly lower than those of the powders, reflecting the higher temperature employed in the formation of the single crystals.

Experimental top

Synthetic details are given in the Comment section.

Refinement top

There were no unusual aspects to the structure analysis.

Computing details top

Data collection: STADI4 (Stoe & Cie, 1997); cell refinement: STADI4; data reduction: X-RED (Stoe & Cie, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2000).

Figures top
[Figure 1] Fig. 1. A view of the crystal structure of Ca2N showing the layer lattice (Ca blue spheres; N pink spheres). The figure was produced using ATOMS (Dowty, 1998).
[Figure 2] Fig. 2. A view showing the atom labelling and the immediate coordination around Ca and N. Displacement ellipsoids are drawn at 50% the probability level.
(I) top
Crystal data top
Ca2NDx = 2.170 Mg m3
Mr = 94.17Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3mCell parameters from 49 reflections
a = 3.6271 (3) Åθ = 12.5–16.5°
c = 18.972 (2) ŵ = 3.61 mm1
V = 216.15 (3) Å3T = 298 K
Z = 3Sphenoid, dark red
F(000) = 1410.24 × 0.16 × 0.16 mm
Data collection top
Stoe Stadi-4 four-circle
diffractometer
99 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.055
Graphite monochromatorθmax = 29.9°, θmin = 3.2°
ω/θ scansh = 55
Absorption correction: ψ scan
(X-RED; Stoe & Cie, 1997)
k = 55
Tmin = 0.574, Tmax = 0.652l = 2525
864 measured reflections3 standard reflections every 60 min
104 independent reflections intensity decay: random variation +1.6%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.017 w = 1/[σ2(Fo2) + 0.28P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.038(Δ/σ)max = 0.001
S = 1.28Δρmax = 0.23 e Å3
104 reflectionsΔρmin = 0.30 e Å3
7 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.063 (8)
Crystal data top
Ca2NZ = 3
Mr = 94.17Mo Kα radiation
Trigonal, R3mµ = 3.61 mm1
a = 3.6271 (3) ÅT = 298 K
c = 18.972 (2) Å0.24 × 0.16 × 0.16 mm
V = 216.15 (3) Å3
Data collection top
Stoe Stadi-4 four-circle
diffractometer
99 reflections with I > 2σ(I)
Absorption correction: ψ scan
(X-RED; Stoe & Cie, 1997)
Rint = 0.055
Tmin = 0.574, Tmax = 0.6523 standard reflections every 60 min
864 measured reflections intensity decay: random variation +1.6%
104 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0177 parameters
wR(F2) = 0.0380 restraints
S = 1.28Δρmax = 0.23 e Å3
104 reflectionsΔρmin = 0.30 e Å3
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
xyzUiso*/Ueq
Ca1.00001.00000.26631 (3)0.0136 (2)
N0.66670.33330.33330.0134 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ca0.0125 (3)0.0125 (3)0.0157 (3)0.00624 (13)0.0000.000
N0.0114 (8)0.0114 (8)0.0175 (13)0.0057 (4)0.0000.000
Geometric parameters (Å, º) top
Ca—N2.4500 (3)Ca—Caii3.6271 (3)
Ca—Cai3.2944 (8)Ca—Caiii4.3221 (6)
Caii—N—Caiv95.503 (14)Cav—Ca—Caix90.0
Caii—N—Ca95.503 (14)Caiv—Ca—Caix180
Caiv—N—Ca95.503 (14)Nviii—Ca—Cax137.752 (7)
Caii—N—Cav84.496 (14)Nix—Ca—Cax42.248 (7)
Caiv—N—Cav180N—Ca—Cax90.0
Ca—N—Cav84.496 (14)Cai—Ca—Cax90.0
Caii—N—Cavi84.496 (14)Cavii—Ca—Cax123.401 (9)
Caiv—N—Cavi84.496 (14)Cav—Ca—Cax56.599 (9)
Ca—N—Cavi180Caiv—Ca—Cax120
Cav—N—Cavi95.504 (14)Caix—Ca—Cax60
Caii—N—Cavii180Nviii—Ca—Caviii42.248 (7)
Caiv—N—Cavii84.496 (14)Nix—Ca—Caviii90.0
Ca—N—Cavii84.496 (14)N—Ca—Caviii137.752 (7)
Cav—N—Cavii95.505 (14)Cai—Ca—Caviii56.599 (9)
Cavi—N—Cavii95.505 (14)Cavii—Ca—Caviii90.0
Nviii—Ca—Nix95.503 (14)Cav—Ca—Caviii123.401 (9)
Nviii—Ca—N95.503 (14)Caiv—Ca—Caviii120
Nix—Ca—N95.503 (14)Caix—Ca—Caviii60
Nviii—Ca—Cai47.752 (7)Cax—Ca—Caviii120
Nix—Ca—Cai47.751 (7)Nviii—Ca—Caxi42.248 (7)
N—Ca—Cai98.20 (2)Nix—Ca—Caxi137.752 (7)
Nviii—Ca—Cavii47.752 (7)N—Ca—Caxi90.0
Nix—Ca—Cavii98.20 (2)Cai—Ca—Caxi90.0
N—Ca—Cavii47.751 (7)Cavii—Ca—Caxi56.599 (9)
Cai—Ca—Cavii66.802 (18)Cav—Ca—Caxi123.401 (9)
Nviii—Ca—Cav98.20 (2)Caiv—Ca—Caxi60
Nix—Ca—Cav47.752 (7)Caix—Ca—Caxi120
N—Ca—Cav47.752 (7)Cax—Ca—Caxi180
Cai—Ca—Cav66.802 (18)Caviii—Ca—Caxi60
Cavii—Ca—Cav66.802 (18)Nviii—Ca—Caii137.752 (7)
Nviii—Ca—Caiv90.0Nix—Ca—Caii90.0
Nix—Ca—Caiv137.752 (7)N—Ca—Caii42.248 (7)
N—Ca—Caiv42.248 (7)Cai—Ca—Caii123.401 (9)
Cai—Ca—Caiv123.401 (9)Cavii—Ca—Caii90.0
Cavii—Ca—Caiv56.599 (9)Cav—Ca—Caii56.599 (9)
Cav—Ca—Caiv90.0Caiv—Ca—Caii60
Nviii—Ca—Caix90.0Caix—Ca—Caii120
Nix—Ca—Caix42.248 (7)Cax—Ca—Caii60
N—Ca—Caix137.752 (7)Caviii—Ca—Caii180
Cai—Ca—Caix56.599 (9)Caxi—Ca—Caii120
Cavii—Ca—Caix123.401 (9)
Symmetry codes: (i) x+7/3, y+8/3, z+2/3; (ii) x, y1, z; (iii) x+5/3, y+4/3, z+1/3; (iv) x1, y1, z; (v) x+7/3, y+5/3, z+2/3; (vi) x+4/3, y+2/3, z+2/3; (vii) x+4/3, y+5/3, z+2/3; (viii) x, y+1, z; (ix) x+1, y+1, z; (x) x+1, y, z; (xi) x1, y, z.

Experimental details

Crystal data
Chemical formulaCa2N
Mr94.17
Crystal system, space groupTrigonal, R3m
Temperature (K)298
a, c (Å)3.6271 (3), 18.972 (2)
V3)216.15 (3)
Z3
Radiation typeMo Kα
µ (mm1)3.61
Crystal size (mm)0.24 × 0.16 × 0.16
Data collection
DiffractometerStoe Stadi-4 four-circle
diffractometer
Absorption correctionψ scan
(X-RED; Stoe & Cie, 1997)
Tmin, Tmax0.574, 0.652
No. of measured, independent and
observed [I > 2σ(I)] reflections
864, 104, 99
Rint0.055
(sin θ/λ)max1)0.701
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.017, 0.038, 1.28
No. of reflections104
No. of parameters7
Δρmax, Δρmin (e Å3)0.23, 0.30

Computer programs: STADI4 (Stoe & Cie, 1997), STADI4, X-RED (Stoe & Cie, 1997), SIR97 (Altomare et al., 1994), SHELXL97 (Sheldrick, 1997), SHELXL97 and PLATON (Spek, 2000).

Selected bond lengths (Å) top
Ca—N2.4500 (3)Ca—Caii3.6271 (3)
Ca—Cai3.2944 (8)Ca—Caiii4.3221 (6)
Symmetry codes: (i) x+7/3, y+8/3, z+2/3; (ii) x, y1, z; (iii) x+5/3, y+4/3, z+1/3.
 

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