Crystal growth and redetermination of strontium nitride iodide, Sr₂NI

Single crystals of Sr₂NI have been grown for the first time. Redetermination from single-crystal X-ray diffraction data confirms the anti-α-NaFeO₂ structure, previously found from powder diffraction data [Bowman, Smith & Gregory (2006). J. Solid State Chem. 179, 130–139]. Iodide ions occupy octa­hedral voids between layers of edge-sharing NSr₆ octa­hedra.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma]() = 0.000 Å
• R factor = 0.061
• wR factor = 0.192
• Data-to-parameter ratio = 18.3

checkCIF/PLATON results

No syntax errors found



Alert level A
REFLT03_ALERT_3_A  Reflection count > 15% excess reflns - sys abs data present?
           From the CIF: _diffrn_reflns_theta_max           24.85
           From the CIF: _diffrn_reflns_theta_full          24.85
           From the CIF: _reflns_number_total                165
           TEST2: Reflns within _diffrn_reflns_theta_max
           Count of symmetry unique reflns           96
           Completeness (_total/calc)            171.88%

Author Response: ... The data are from two twin components, hence the apparent excess of reflections. Further details of the twinning and how it was dealt with are given in the experimental details. ( _exptl_special_details )

PLAT027_ALERT_3_A _diffrn_reflns_theta_full (too) Low ............      24.85 Deg.

Author Response: ... A 2-theta cut-off of 50 degrees was applied so the limit should be 25 degrees.

PLAT029_ALERT_3_A _diffrn_measured_fraction_theta_full Low .......       0.85

Author Response: ... Output from platon is given below. The calculated value is perhaps due to confusion due to the data coming from two twin components?

 ===============================================================================
 Summary of Reflection Data in FCF
 ===============================================================================
 Total  (in FCF) ..............    338  (Hmax =  4, Kmax =  5, Lmax = 29) Obs
 Actual Theta(Max) (Deg.) .....  27.35  (Hmax =  5, Kmax =  5, Lmax = 29) Exp
 Actual Theta(Min) (Deg.) .....   5.31

 Unique (Expected) ............    121  (HKL   121, -H-K-L     0)
 Unique (in FCF) ..............    118  (HKL   118, -H-K-L     0)
 Observed [I .gt. 2 Sig(I)] ...    117  (HKL   117, -H-K-L     0)
 Less-Thans ...................      1  (HKL     1, -H-K-L     0)
 Missing (Total) ..............      3  (HKL     3, -H-K-L     0)

 Missing Below Th(Min) ........      1
 Missing Th(Min) to STh/L=0.600      2
 Missing STh/L=0.600 to Th(Max)      0
 Missing Very Strong Refl. ....      0

 Space Group Extinctions ......      0


Alert level B
PLAT021_ALERT_1_B Ratio Unique / Expected Reflections too High ...       1.72

Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?

   3 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   1 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

S1. Comment

Sr₂NI belongs to the A₂NX (A = Ca—Ba, X = F—I) family of compounds which were originally synthesized several decades ago (Ehrlich & Deissmann, 1958; Ehrlich et al., 1964; Emons et al., 1964; Emons et al., 1968; Andersson, 1970; Ehrlich et al., 1971). It has only been recently that the structures and properties of these compounds have been revealed (Hadenfeldt & Herdejürgen, 1987; Hadenfeldt & Herdejürgen, 1988; Bowman et al., 2001; Nicklow et al., 2001; Reckeweg & DiSalvo, 2002; Wagner, 2002; Sebel & Wagner, 2004; Bowman et al., 2005; Jack et al., 2005; Bowman et al., 2006). With the exception of Ca₂NX (X = Cl, Br, I) (Hadenfeldt & Herdejürgen, 1987; Hadenfeldt & Herdejürgen, 1988), single-crystal determinations have been restricted to the lighter halide (X = F) members. These single-crystal determinations have often shown the structures to exhibit important differences to those refined from powder data. We recently investigated the structure of Sr₂NI using powder X-ray diffraction (Bowman et al., 2006). Now the successful and unprecedented growth of single crystals of a strontium nitride halide (Sr₂NX) phase has allowed the single-crystal structure of Sr₂NI to be determined precisely for the first time. Importantly, this study has allowed an accurate determination of the Sr position within the rhombohedral cell and describes well defined thermal parameters which are elongated only slightly along the c direction for Sr and I and very close to isotropic for N.

The data (obtained at 150 K) show that Sr₂NI crystallizes in space group R-3 m (No. 166). The structure consists of [NSr₂]⁺ slabs in which N is coordinated octahedrally to six Sr atoms. The layers of the edge-sharing NSr₆ octahedra lie parallel to the ab plane stacked along the c-direction. The iodide ion occupies the octahedral voids between these positively charged N—Sr layers. This creates alternating edge-sharing layers of NSr₆ and ISr₆ octahedra in a cubic close packed (CCP) arrangement (Fig. 1, Fig. 2).

The Sr—N distance is in excellent agreement with that found in the binary subnitride Sr₂N (2.6118 (3) Å) (Brese & O'Keeffe, 1990). Further, the Sr—I bond length is also in close agreement with data for SrI₂ (3.3382–3.4142 Å) (Rietschel & Baernighausen, 1969).

Related literature

For related literature, see: Andersson (1970); Brese & O'Keeffe (1990); Bowman et al. (2001, 2005, 2006); Ehrlich & Deissmann (1958); Ehrlich et al. (1964, 1971); Hadenfeldt & Herdejürgen (1987, 1988); Emons et al. (1964, 1968); Jack et al. (2005); Nicklow et al. (2001); Reckeweg & DiSalvo (2002); Rietschel & Baernighausen (1969); Sebel & Wagner (2004); Wagner (2002).

For related literature, see:.

S2. Experimental

The title Sr₂NI crystals were prepared by reaction of SrI₂ (Aldrich, 99.99+%) with distrontium subnitride, Sr₂N. Sr₂N powder was prepared by the reaction of cleaned Sr metal (Alfa, 99%) with dried nitrogen at 793 K. Due to the air sensitivity of the reactants and products involved, all manipulations were carried out in glove boxes (either recirculating nitrogen-filled or evacuable argon-filled). Stoichiometric ratios of the reactants were thoroughly mixed and ground together, then pressed to form a pellet (ca 1 g). The pellet was placed in a molybdenum foil liner and transferred to a stainless steel crucible, which was subsequently welded shut under an argon atmosphere. The sealed crucibles were heated in a tube furnace (1023 K, 5 d) under flowing argon to prevent oxidation of the steel crucibles. The furnace was cooled slowly (20 K h^-1). The crucibles were opened in an N₂-filled glove-box. Orange irregular crystals were observed on the pellet surface. Crystals were selected in a recirculating N₂-filled glove-box under an optical microscope and placed under RS3000 perfluoropolyether (Riedel de Haën) on a microscope slide prior to mounting on the diffractometer. The moisture-free viscous perfluoropolyether protects the crystals from atmospheric oxygen and moisture without interfering with the diffraction experiment.

S3. Refinement

Due to twinning present in the crystal the data were integrated using 2 orientation matrices, related by the twin law (-1 0 0, 1 1 0, 0 0 - 1), giving 682 reflections, 388 have contributions from only one component - 197 only belong to the first component, 186 only to second and 303 have contributions from both components. The fraction of the twin component was refined to 0.183 (6).

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002) and SHELXTL (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 1998); software used to prepare material for publication: enCIFer (Allen et al., 2004) and PLATON (Spek, 2003).

Figures

	Fig. 1. Polyhedral representation of the structure of Sr2NI, showing [Sr2N]^+ layers of edge-sharing NSr6 octahedra alternating with layers of I^-.
	Fig. 2. ORTEP-type plot of the local coordination of Sr to N and I. Both anions are coordinated in a distorted octahedral geometry. (Ellipsoids are drawn at the 90% probability level).

Distrontium nitride iodide

Crystal data

INSr2	Dx = 4.918 Mg m^−3
Mr = 316.15	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3m	Cell parameters from 340 reflections
Hall symbol: -R 3 2"	θ = 5.3–27.2°
a = 4.0049 (6) Å	µ = 31.99 mm^−1
c = 23.055 (7) Å	T = 150 K
V = 320.24 (12) Å^3	Needle, orange
Z = 3	0.14 × 0.04 × 0.04 mm
F(000) = 408

Data collection

Bruker SMART1000 CCD area-detector diffractometer	165 independent reflections
Radiation source: sealed tube	163 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
ω scans	θmax = 24.9°, θmin = 5.3°
Absorption correction: multi-scan (TWINABS; Bruker, 2007)	h = −4→4
Tmin = 0.175, Tmax = 0.278	k = −4→4
682 measured reflections	l = −26→26

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)] = 0.061	Secondary atom site location: difference Fourier map
wR(F^2) = 0.192	w = 1/[σ^2(Fo^2) + (0.1578P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.21	(Δ/σ)max < 0.001
165 reflections	Δρmax = 1.77 e Å^−3
9 parameters	Δρmin = −1.76 e Å^−3

Special details

Experimental. Data were integrated using 2 orientation matrices, related by the twin law (-1 0 0, 1 1 0, 0 0 - 1). This gave a total of 682 reflections; 379 of these have contributions from only one component, 197 only belong to component 1, 186 only to 2 and 294 have contributions from both components.

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.

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

	x	y	z	Uiso*/Ueq
I1	0.0000	0.0000	0.0000	0.0134 (11)
Sr1	0.0000	0.0000	0.22397 (11)	0.0095 (10)
N1	0.0000	0.0000	0.5000	0.019 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.0117 (11)	0.0117 (11)	0.017 (2)	0.0059 (5)	0.000	0.000
Sr1	0.0085 (11)	0.0085 (11)	0.0117 (17)	0.0042 (5)	0.000	0.000
N1	0.019 (7)	0.019 (7)	0.019 (18)	0.009 (4)	0.000	0.000

Geometric parameters (Å, º)

I1—Sr1^i	3.421 (2)	Sr1—Sr1^iii	3.511 (4)
I1—Sr1^ii	3.421 (2)	Sr1—Sr1^i	3.511 (4)
I1—Sr1^iii	3.421 (2)	Sr1—Sr1^vi	3.511 (4)
I1—Sr1^iv	3.421 (2)	Sr1—Sr1^x	4.0049 (6)
I1—Sr1^v	3.421 (2)	Sr1—Sr1^xi	4.0049 (6)
I1—Sr1^vi	3.421 (2)	Sr1—Sr1^xii	4.0049 (6)
Sr1—N1^ii	2.6631 (13)	N1—Sr1^xiii	2.6631 (13)
Sr1—N1^iv	2.6631 (13)	N1—Sr1^vii	2.6631 (13)
Sr1—N1^v	2.6631 (13)	N1—Sr1^xiv	2.6631 (13)
Sr1—I1^vii	3.421 (2)	N1—Sr1^viii	2.6631 (13)
Sr1—I1^viii	3.421 (2)	N1—Sr1^ix	2.6631 (13)
Sr1—I1^ix	3.421 (2)	N1—Sr1^xv	2.6631 (13)
Sr1^i—I1—Sr1^ii	180.00 (6)	I1^ix—Sr1—Sr1^vi	96.29 (3)
Sr1^i—I1—Sr1^iii	71.65 (5)	Sr1^iii—Sr1—Sr1^vi	69.54 (9)
Sr1^ii—I1—Sr1^iii	108.35 (5)	Sr1^i—Sr1—Sr1^vi	69.54 (9)
Sr1^i—I1—Sr1^iv	108.35 (5)	N1^ii—Sr1—Sr1^x	41.24 (3)
Sr1^ii—I1—Sr1^iv	71.65 (5)	N1^iv—Sr1—Sr1^x	138.76 (3)
Sr1^iii—I1—Sr1^iv	180.00 (6)	N1^v—Sr1—Sr1^x	90.0
Sr1^i—I1—Sr1^v	108.35 (5)	I1^vii—Sr1—Sr1^x	125.83 (2)
Sr1^ii—I1—Sr1^v	71.65 (5)	I1^viii—Sr1—Sr1^x	54.17 (2)
Sr1^iii—I1—Sr1^v	108.35 (5)	I1^ix—Sr1—Sr1^x	90.0
Sr1^iv—I1—Sr1^v	71.65 (5)	Sr1^iii—Sr1—Sr1^x	55.23 (4)
Sr1^i—I1—Sr1^vi	71.65 (5)	Sr1^i—Sr1—Sr1^x	124.77 (4)
Sr1^ii—I1—Sr1^vi	108.35 (5)	Sr1^vi—Sr1—Sr1^x	90.0
Sr1^iii—I1—Sr1^vi	71.65 (5)	N1^ii—Sr1—Sr1^xi	138.76 (3)
Sr1^iv—I1—Sr1^vi	108.35 (5)	N1^iv—Sr1—Sr1^xi	41.24 (3)
Sr1^v—I1—Sr1^vi	180.00 (6)	N1^v—Sr1—Sr1^xi	90.0
N1^ii—Sr1—N1^iv	97.52 (6)	I1^vii—Sr1—Sr1^xi	54.17 (2)
N1^ii—Sr1—N1^v	97.52 (6)	I1^viii—Sr1—Sr1^xi	125.83 (2)
N1^iv—Sr1—N1^v	97.52 (6)	I1^ix—Sr1—Sr1^xi	90.0
N1^ii—Sr1—I1^vii	162.27 (8)	Sr1^iii—Sr1—Sr1^xi	124.77 (4)
N1^iv—Sr1—I1^vii	94.14 (2)	Sr1^i—Sr1—Sr1^xi	55.23 (4)
N1^v—Sr1—I1^vii	94.14 (2)	Sr1^vi—Sr1—Sr1^xi	90.0
N1^ii—Sr1—I1^viii	94.14 (2)	Sr1^x—Sr1—Sr1^xi	180.00 (15)
N1^iv—Sr1—I1^viii	162.27 (8)	N1^ii—Sr1—Sr1^xii	41.24 (3)
N1^v—Sr1—I1^viii	94.14 (2)	N1^iv—Sr1—Sr1^xii	90.0
I1^vii—Sr1—I1^viii	71.65 (5)	N1^v—Sr1—Sr1^xii	138.76 (3)
N1^ii—Sr1—I1^ix	94.14 (2)	I1^vii—Sr1—Sr1^xii	125.83 (2)
N1^iv—Sr1—I1^ix	94.14 (2)	I1^viii—Sr1—Sr1^xii	90.0
N1^v—Sr1—I1^ix	162.27 (8)	I1^ix—Sr1—Sr1^xii	54.17 (2)
I1^vii—Sr1—I1^ix	71.65 (5)	Sr1^iii—Sr1—Sr1^xii	90.0
I1^viii—Sr1—I1^ix	71.65 (5)	Sr1^i—Sr1—Sr1^xii	124.77 (4)
N1^ii—Sr1—Sr1^iii	48.76 (3)	Sr1^vi—Sr1—Sr1^xii	55.23 (4)
N1^iv—Sr1—Sr1^iii	101.45 (10)	Sr1^x—Sr1—Sr1^xii	60.0
N1^v—Sr1—Sr1^iii	48.76 (3)	Sr1^xi—Sr1—Sr1^xii	120.0
I1^vii—Sr1—Sr1^iii	141.004 (11)	Sr1^xiii—N1—Sr1^vii	180.0
I1^viii—Sr1—Sr1^iii	96.29 (3)	Sr1^xiii—N1—Sr1^xiv	97.52 (6)
I1^ix—Sr1—Sr1^iii	141.003 (11)	Sr1^vii—N1—Sr1^xiv	82.48 (6)
N1^ii—Sr1—Sr1^i	101.45 (10)	Sr1^xiii—N1—Sr1^viii	82.48 (6)
N1^iv—Sr1—Sr1^i	48.76 (3)	Sr1^vii—N1—Sr1^viii	97.52 (6)
N1^v—Sr1—Sr1^i	48.76 (3)	Sr1^xiv—N1—Sr1^viii	180.0
I1^vii—Sr1—Sr1^i	96.29 (3)	Sr1^xiii—N1—Sr1^ix	82.48 (6)
I1^viii—Sr1—Sr1^i	141.004 (11)	Sr1^vii—N1—Sr1^ix	97.52 (6)
I1^ix—Sr1—Sr1^i	141.003 (11)	Sr1^xiv—N1—Sr1^ix	82.48 (6)
Sr1^iii—Sr1—Sr1^i	69.54 (9)	Sr1^viii—N1—Sr1^ix	97.52 (6)
N1^ii—Sr1—Sr1^vi	48.76 (3)	Sr1^xiii—N1—Sr1^xv	97.52 (6)
N1^iv—Sr1—Sr1^vi	48.76 (3)	Sr1^vii—N1—Sr1^xv	82.48 (6)
N1^v—Sr1—Sr1^vi	101.45 (10)	Sr1^xiv—N1—Sr1^xv	97.52 (6)
I1^vii—Sr1—Sr1^vi	141.003 (11)	Sr1^viii—N1—Sr1^xv	82.48 (6)
I1^viii—Sr1—Sr1^vi	141.003 (11)	Sr1^ix—N1—Sr1^xv	180.00 (10)

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