Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270109035987/fa3198sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270109035987/fa3198CaIn2P2sup2.hkl | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270109035987/fa3198SrIn2P2sup3.hkl | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270109035987/fa3198BaIn2P2sup4.hkl |
For related literature, see: Alemany et al. (2008); Brock et al. (1994); Carrillo-Cabrera, Somer, Peters & von Schnering (1996); Condron et al. (2007); Grytsiv et al. (2002); Hellmann et al. (2007); Jiang & Kauzlarich (2006); Kauzlarich (1996); Kim & Kanatzidis (2001); Kim et al. (2008); Leoni et al. (2003); Mathieu et al. (2008); Nesper (1990); Park et al. (2003); Pfuner et al. (2008); Shannon (1976); Somer et al. (1998); Xia & Bobev (2007, 2008).
AIn2P2 crystals were grown by reaction of the pure elements in an alumina crucible with the molar ratio A:In:P = 3:110:6, where A = Ca, Sr, Ba. The metals Ca (Aldrich, 99.99% purity), Sr (Aldrich, 99% purity), Ba (Aldrich, 99% purity) and In (Cerac, 99.99% purity) were cut into small pieces and layered in a 5 ml crucible with indium on top and bottom, and sealed under vacuum in quartz tubes. All materials were handled in an inert atmosphere or under vacuum. The reaction contents were heated in a programmable furnace at 60 K h-1 to 1373 K, maintained at that temperature for 16 h, cooled at 2 K h-1 to 1146 K, maintained at that temperature for 24 h and centrifuged to remove molten In flux. The crystals were then removed after breaking the quartz jacket in air. In the cases of Ca and Sr, the reactions yielded a few highly reflective black plate-like crystals on the sides and bottom of the crucible. In the Ba reactions, larger yields of black needle crystals were found within the crucible. All the crystals were found to be air stable. Attempts were made to increase the yield by decreasing the flux ratio, but this had the opposite effect of lowering the yield. In the case of Ba, some crystals of Ba2In5P5 (Mathieu et al., 2008) were also present. The Ba2In5P5 phase is reported to be air sensitive and decomposed upon exposure to air, whereas the BaIn2P2 crystals remained stable in air. The best formed crystals and highest yields of the 1–2–2 phases were for Ba.
The chemical composition of the Ba crystals was verified with an SEM (scanning electron microscopy) microprobe on a single crystal using a Camera SX-100 Electron Probe Microanalyzer equipped with a wavelength-dispersive spectrometer and calibrated standards. The samples were prepared by embedding the crystals in epoxy and polishing to ensure smooth surfaces. Each sample was scanned with a spot size of 1 µm and data collected at five to eight points along its surface. Composition totals for all points summed to 100%. The compositions were calculated as the average of the five points and provided the composition Ba1.00 (4)In2.023 (6)P2.020 (3), in good agreement with the refined structure.
There are a number of residual peaks in the final difference map of BaIn2P2 that do not appear to be due to twinning or disorder, but may arise from inadequate absorption correction or from stacking faults.
For all compounds, data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).
CaIn2P2 | Dx = 4.517 Mg m−3 |
Mr = 331.66 | Mo Kα radiation, λ = 0.71073 Å |
Hexagonal, P63/mmc | Cell parameters from 814 reflections |
Hall symbol: -P 6c 2c | θ = 2.3–28.6° |
a = 4.0220 (17) Å | µ = 10.97 mm−1 |
c = 17.408 (8) Å | T = 90 K |
V = 243.87 (18) Å3 | Plate, black |
Z = 2 | 0.42 × 0.40 × 0.12 mm |
F(000) = 296 |
Bruker SMART 1000 diffractometer | 179 independent reflections |
Radiation source: sealed tube | 153 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.055 |
Detector resolution: 8.3 pixels mm-1 | θmax = 30.5°, θmin = 2.3° |
ω scans | h = −5→5 |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | k = −5→5 |
Tmin = 0.021, Tmax = 0.268 | l = −24→24 |
3448 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.028 | w = 1/[σ2(Fo2) + (0.0336P)2 + 2.2105P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.073 | (Δ/σ)max < 0.001 |
S = 1.27 | Δρmax = 1.14 e Å−3 |
179 reflections | Δρmin = −2.15 e Å−3 |
10 parameters | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.012 (2) |
CaIn2P2 | Z = 2 |
Mr = 331.66 | Mo Kα radiation |
Hexagonal, P63/mmc | µ = 10.97 mm−1 |
a = 4.0220 (17) Å | T = 90 K |
c = 17.408 (8) Å | 0.42 × 0.40 × 0.12 mm |
V = 243.87 (18) Å3 |
Bruker SMART 1000 diffractometer | 179 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | 153 reflections with I > 2σ(I) |
Tmin = 0.021, Tmax = 0.268 | Rint = 0.055 |
3448 measured reflections |
R[F2 > 2σ(F2)] = 0.028 | 10 parameters |
wR(F2) = 0.073 | 0 restraints |
S = 1.27 | Δρmax = 1.14 e Å−3 |
179 reflections | Δρmin = −2.15 e Å−3 |
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. |
x | y | z | Uiso*/Ueq | ||
Ca1 | 0.0000 | 0.0000 | 0.5000 | 0.0062 (6) | |
In1 | 0.6667 | 0.3333 | 0.32934 (4) | 0.0059 (3) | |
P1 | 0.3333 | 0.6667 | 0.39679 (16) | 0.0050 (6) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Ca1 | 0.0062 (8) | 0.0062 (8) | 0.0064 (13) | 0.0031 (4) | 0.000 | 0.000 |
In1 | 0.0062 (4) | 0.0062 (4) | 0.0054 (4) | 0.00308 (18) | 0.000 | 0.000 |
P1 | 0.0057 (8) | 0.0057 (8) | 0.0035 (11) | 0.0028 (4) | 0.000 | 0.000 |
Ca1—P1 | 2.936 (2) | In1—P1 | 2.6021 (16) |
Ca1—In1 | 3.7706 (14) | In1—In1i | 2.7625 (19) |
P1—Ca1—P1ii | 93.54 (7) | P1iv—In1—Ca1iv | 50.93 (4) |
P1—Ca1—In1ii | 89.72 (6) | P1viii—In1—Ca1iv | 50.93 (4) |
In1ii—Ca1—In1iii | 64.46 (3) | P1viii—In1—Ca1 | 50.93 (4) |
P1—Ca1—In1 | 43.48 (3) | In1i—In1—Ca1 | 141.987 (19) |
P1iv—In1—P1 | 101.22 (7) | Ca1v—In1—Ca1 | 64.46 (3) |
P1—In1—In1i | 116.82 (6) | Ca1iv—In1—Ca1 | 64.46 (3) |
In1i—In1—Ca1iv | 141.987 (19) | In1ix—P1—In1vi | 101.22 (7) |
P1—In1—Ca1iv | 101.19 (7) | In1ix—P1—In1 | 101.22 (7) |
Ca1v—In1—Ca1iv | 64.46 (3) | In1ix—P1—Ca1vi | 85.60 (3) |
P1—In1—Ca1 | 50.93 (4) | In1vi—P1—Ca1vi | 85.60 (3) |
In1vi—P1—In1 | 101.22 (7) | In1ix—P1—Ca1v | 169.09 (10) |
In1—P1—Ca1vi | 169.09 (10) | In1vi—P1—Ca1v | 85.60 (3) |
In1—P1—Ca1 | 85.60 (3) | In1—P1—Ca1v | 85.60 (3) |
P1—Ca1—P1vii | 86.46 (7) | Ca1vi—P1—Ca1v | 86.46 (7) |
P1iv—In1—P1viii | 101.22 (7) | In1ix—P1—Ca1 | 85.60 (3) |
P1viii—In1—P1 | 101.22 (7) | In1vi—P1—Ca1 | 169.09 (10) |
P1iv—In1—Ca1v | 50.93 (4) | Ca1vi—P1—Ca1 | 86.46 (7) |
P1viii—In1—Ca1v | 101.19 (7) | Ca1v—P1—Ca1 | 86.46 (7) |
In1i—In1—Ca1v | 141.987 (19) |
Symmetry codes: (i) x, y, −z+1/2; (ii) −x+1, −y+1, −z+1; (iii) −x, −y, −z+1; (iv) x+1, y, z; (v) x+1, y+1, z; (vi) x, y+1, z; (vii) x−1, y−1, z; (viii) x, y−1, z; (ix) x−1, y, z. |
SrIn2P2 | Dx = 4.870 Mg m−3 |
Mr = 379.20 | Mo Kα radiation, λ = 0.71073 Å |
Hexagonal, P63/mmc | Cell parameters from 1023 reflections |
Hall symbol: -P 6c 2c | θ = 4.5–31.3° |
a = 4.0945 (16) Å | µ = 19.55 mm−1 |
c = 17.812 (7) Å | T = 90 K |
V = 258.61 (18) Å3 | Plate, black |
Z = 2 | 0.34 × 0.24 × 0.19 mm |
F(000) = 332 |
Bruker SMART 1000 diffractometer | 189 independent reflections |
Radiation source: sealed tube | 168 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.035 |
Detector resolution: 8.3 pixels mm-1 | θmax = 30.5°, θmin = 2.3° |
ω scans | h = −5→5 |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | k = −5→5 |
Tmin = 0.014, Tmax = 0.057 | l = −25→25 |
3694 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.015 | w = 1/[σ2(Fo2) + (0.0168P)2 + 0.5106P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.037 | (Δ/σ)max < 0.001 |
S = 1.25 | Δρmax = 0.60 e Å−3 |
189 reflections | Δρmin = −0.78 e Å−3 |
10 parameters | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.0236 (15) |
SrIn2P2 | Z = 2 |
Mr = 379.20 | Mo Kα radiation |
Hexagonal, P63/mmc | µ = 19.55 mm−1 |
a = 4.0945 (16) Å | T = 90 K |
c = 17.812 (7) Å | 0.34 × 0.24 × 0.19 mm |
V = 258.61 (18) Å3 |
Bruker SMART 1000 diffractometer | 189 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | 168 reflections with I > 2σ(I) |
Tmin = 0.014, Tmax = 0.057 | Rint = 0.035 |
3694 measured reflections |
R[F2 > 2σ(F2)] = 0.015 | 10 parameters |
wR(F2) = 0.037 | 0 restraints |
S = 1.25 | Δρmax = 0.60 e Å−3 |
189 reflections | Δρmin = −0.78 e Å−3 |
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. |
x | y | z | Uiso*/Ueq | ||
Sr1 | 0.0000 | 0.0000 | 0.5000 | 0.00493 (19) | |
In1 | 0.6667 | 0.3333 | 0.32753 (2) | 0.00542 (16) | |
P1 | 0.3333 | 0.6667 | 0.39116 (8) | 0.0053 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Sr1 | 0.0050 (2) | 0.0050 (2) | 0.0047 (3) | 0.00252 (12) | 0.000 | 0.000 |
In1 | 0.00595 (19) | 0.00595 (19) | 0.0044 (2) | 0.00297 (9) | 0.000 | 0.000 |
P1 | 0.0048 (4) | 0.0048 (4) | 0.0062 (6) | 0.0024 (2) | 0.000 | 0.000 |
Sr1—P1 | 3.0572 (12) | In1—P1 | 2.6216 (11) |
Sr1—In1 | 3.8763 (11) | In1—In1i | 2.7620 (13) |
P1—Sr1—P1ii | 95.92 (4) | P1—In1—Sr1iv | 101.96 (4) |
P1—Sr1—In1ii | 91.77 (4) | Sr1v—In1—Sr1iv | 63.76 (3) |
In1ii—Sr1—In1iii | 63.76 (3) | P1—In1—Sr1 | 51.86 (2) |
P1—Sr1—In1 | 42.411 (17) | In1vi—P1—In1 | 102.69 (4) |
P1iv—In1—P1 | 102.69 (4) | In1—P1—Sr1vi | 166.26 (5) |
P1—In1—In1i | 115.62 (3) | In1—P1—Sr1 | 85.73 (2) |
In1i—In1—Sr1v | 142.421 (16) | Sr1vi—P1—Sr1 | 84.08 (4) |
Symmetry codes: (i) x, y, −z+1/2; (ii) −x+1, −y+1, −z+1; (iii) −x, −y, −z+1; (iv) x+1, y, z; (v) x+1, y+1, z; (vi) x, y+1, z. |
BaIn2P2 | F(000) = 736 |
Mr = 428.92 | Dx = 5.292 Mg m−3 |
Monoclinic, P21/m | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yb | Cell parameters from 1863 reflections |
a = 9.9652 (8) Å | θ = 2.7–30.6° |
b = 4.1789 (3) Å | µ = 16.15 mm−1 |
c = 12.9834 (10) Å | T = 90 K |
β = 95.326 (2)° | Whisker, black |
V = 538.34 (7) Å3 | 0.23 × 0.15 × 0.09 mm |
Z = 4 |
Bruker SMART 1000 diffractometer | 1753 independent reflections |
Radiation source: sealed tube | 1452 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.037 |
ω scans | θmax = 30.0°, θmin = 1.6° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | h = −13→14 |
Tmin = 0.119, Tmax = 0.324 | k = −5→5 |
7899 measured reflections | l = −18→18 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.038 | w = 1/[σ2(Fo2) + (0.0566P)2 + 1.6205P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.093 | (Δ/σ)max = 0.001 |
S = 1.03 | Δρmax = 2.56 e Å−3 |
1753 reflections | Δρmin = −2.48 e Å−3 |
62 parameters | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.0039 (3) |
BaIn2P2 | V = 538.34 (7) Å3 |
Mr = 428.92 | Z = 4 |
Monoclinic, P21/m | Mo Kα radiation |
a = 9.9652 (8) Å | µ = 16.15 mm−1 |
b = 4.1789 (3) Å | T = 90 K |
c = 12.9834 (10) Å | 0.23 × 0.15 × 0.09 mm |
β = 95.326 (2)° |
Bruker SMART 1000 diffractometer | 1753 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | 1452 reflections with I > 2σ(I) |
Tmin = 0.119, Tmax = 0.324 | Rint = 0.037 |
7899 measured reflections |
R[F2 > 2σ(F2)] = 0.038 | 62 parameters |
wR(F2) = 0.093 | 0 restraints |
S = 1.03 | Δρmax = 2.56 e Å−3 |
1753 reflections | Δρmin = −2.48 e Å−3 |
Experimental. numerical corrections could not be made due to crystal faces not visible |
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. |
x | y | z | Uiso*/Ueq | ||
Ba1 | 0.55267 (6) | 0.2500 | 0.84462 (5) | 0.00507 (16) | |
Ba2 | 0.15873 (6) | −0.7500 | 0.41054 (5) | 0.00517 (16) | |
In1 | 0.44833 (7) | −0.2500 | 0.59588 (5) | 0.00439 (17) | |
In2 | 0.95400 (7) | 0.2500 | 0.83627 (6) | 0.00499 (17) | |
In3 | 0.81312 (7) | −0.2500 | 1.03287 (6) | 0.00490 (17) | |
In4 | 0.22825 (7) | −0.2500 | 0.71717 (5) | 0.00386 (17) | |
P1 | 0.7963 (3) | −0.2500 | 0.8329 (2) | 0.0047 (5) | |
P2 | 0.6090 (3) | 0.2500 | 0.6055 (2) | 0.0047 (5) | |
P3 | 0.0781 (3) | −0.7500 | 0.6624 (2) | 0.0057 (5) | |
P4 | 0.3241 (3) | −0.2500 | 0.9114 (2) | 0.0054 (5) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Ba1 | 0.0060 (3) | 0.0036 (3) | 0.0057 (3) | 0.000 | 0.0014 (2) | 0.000 |
Ba2 | 0.0046 (3) | 0.0040 (3) | 0.0071 (3) | 0.000 | 0.0010 (2) | 0.000 |
In1 | 0.0044 (3) | 0.0037 (4) | 0.0053 (3) | 0.000 | 0.0015 (3) | 0.000 |
In2 | 0.0053 (3) | 0.0045 (4) | 0.0052 (3) | 0.000 | 0.0007 (3) | 0.000 |
In3 | 0.0052 (3) | 0.0049 (4) | 0.0045 (3) | 0.000 | 0.0001 (2) | 0.000 |
In4 | 0.0038 (3) | 0.0033 (3) | 0.0046 (3) | 0.000 | 0.0005 (2) | 0.000 |
P1 | 0.0059 (12) | 0.0048 (13) | 0.0032 (12) | 0.000 | 0.0000 (9) | 0.000 |
P2 | 0.0031 (11) | 0.0065 (13) | 0.0042 (12) | 0.000 | −0.0008 (9) | 0.000 |
P3 | 0.0064 (12) | 0.0046 (13) | 0.0064 (12) | 0.000 | 0.0021 (9) | 0.000 |
P4 | 0.0036 (12) | 0.0052 (13) | 0.0074 (12) | 0.000 | 0.0007 (9) | 0.000 |
Ba1—P2 | 3.206 (3) | In2—P1i | 2.6122 (17) |
Ba1—P1i | 3.218 (2) | In2—P3viii | 2.673 (3) |
Ba1—P1 | 3.218 (2) | In2—In3ix | 2.7460 (10) |
Ba1—P4 | 3.267 (2) | In2—Ba2iv | 3.9024 (8) |
Ba1—P4i | 3.267 (2) | In2—Ba2iii | 3.9024 (8) |
Ba1—P4ii | 3.290 (3) | In3—P1 | 2.587 (3) |
Ba1—In1 | 3.9055 (8) | In3—P4x | 2.6350 (17) |
Ba1—In1i | 3.9055 (8) | In3—P4ii | 2.6350 (17) |
Ba1—In3i | 3.9873 (8) | In3—In2ix | 2.7460 (10) |
Ba1—In3 | 3.9873 (8) | In3—Ba1vii | 3.9873 (8) |
Ba1—In2 | 4.0108 (10) | In4—P4 | 2.612 (3) |
Ba1—In4 | 4.0697 (8) | In4—P3 | 2.6296 (18) |
Ba2—P2iii | 3.139 (2) | In4—P3i | 2.6296 (17) |
Ba2—P2iv | 3.139 (2) | In4—Ba2vi | 4.0539 (10) |
Ba2—P3v | 3.227 (2) | In4—Ba1vii | 4.0697 (8) |
Ba2—P3vi | 3.227 (2) | P1—In2vii | 2.6122 (17) |
Ba2—P1iv | 3.233 (3) | P1—Ba1vii | 3.218 (2) |
Ba2—P3 | 3.438 (3) | P1—Ba2iv | 3.233 (3) |
Ba2—In2iv | 3.9024 (8) | P2—In1iii | 2.624 (3) |
Ba2—In2iii | 3.9024 (8) | P2—In1i | 2.6283 (17) |
Ba2—In1iv | 3.9244 (10) | P2—Ba2iii | 3.139 (2) |
Ba2—In4vi | 4.0539 (10) | P2—Ba2iv | 3.139 (2) |
Ba2—Ba2i | 4.1789 (3) | P3—In4vii | 2.6296 (17) |
Ba2—Ba2vii | 4.1789 (3) | P3—In2xi | 2.673 (3) |
In1—P2iii | 2.624 (3) | P3—Ba2v | 3.227 (2) |
In1—P2 | 2.6283 (17) | P3—Ba2vi | 3.227 (2) |
In1—P2vii | 2.6283 (17) | P4—In3x | 2.6350 (17) |
In1—In4 | 2.8161 (10) | P4—In3ii | 2.6350 (17) |
In1—Ba1vii | 3.9055 (8) | P4—Ba1vii | 3.267 (2) |
In1—Ba2iv | 3.9244 (10) | P4—Ba1ii | 3.290 (3) |
In2—P1 | 2.6122 (17) | ||
P2—Ba1—P1i | 75.72 (6) | P2iii—In1—In4 | 116.64 (7) |
P2—Ba1—P1 | 75.72 (6) | P2—In1—In4 | 118.43 (6) |
P1i—Ba1—P1 | 80.99 (7) | P2vii—In1—In4 | 118.43 (6) |
P2—Ba1—P4 | 116.48 (6) | P2iii—In1—Ba1 | 147.201 (13) |
P1i—Ba1—P4 | 167.36 (7) | P2—In1—Ba1 | 54.64 (6) |
P1—Ba1—P4 | 98.34 (5) | P2vii—In1—Ba1 | 105.78 (6) |
P2—Ba1—P4i | 116.48 (6) | In4—In1—Ba1 | 72.48 (2) |
P1i—Ba1—P4i | 98.34 (5) | P2iii—In1—Ba1vii | 147.201 (13) |
P1—Ba1—P4i | 167.36 (7) | P2—In1—Ba1vii | 105.78 (6) |
P4—Ba1—P4i | 79.52 (6) | P2vii—In1—Ba1vii | 54.64 (6) |
P2—Ba1—P4ii | 148.14 (7) | In4—In1—Ba1vii | 72.48 (2) |
P1i—Ba1—P4ii | 80.20 (6) | Ba1—In1—Ba1vii | 64.689 (16) |
P1—Ba1—P4ii | 80.20 (6) | P2iii—In1—Ba2iv | 95.98 (6) |
P4—Ba1—P4ii | 87.23 (6) | P2—In1—Ba2iv | 52.87 (5) |
P4i—Ba1—P4ii | 87.23 (6) | P2vii—In1—Ba2iv | 52.87 (5) |
P2—Ba1—In1 | 41.95 (3) | In4—In1—Ba2iv | 147.38 (3) |
P1i—Ba1—In1 | 116.89 (5) | Ba1—In1—Ba2iv | 80.095 (17) |
P1—Ba1—In1 | 75.97 (5) | Ba1vii—In1—Ba2iv | 80.095 (17) |
P4—Ba1—In1 | 74.84 (5) | P1—In2—P1i | 106.24 (10) |
P4i—Ba1—In1 | 115.01 (5) | P1—In2—P3viii | 108.08 (7) |
P4ii—Ba1—In1 | 147.484 (9) | P1i—In2—P3viii | 108.08 (7) |
P2—Ba1—In1i | 41.95 (3) | P1—In2—In3ix | 118.88 (6) |
P1i—Ba1—In1i | 75.97 (5) | P1i—In2—In3ix | 118.88 (6) |
P1—Ba1—In1i | 116.89 (5) | P3viii—In2—In3ix | 95.28 (7) |
P4—Ba1—In1i | 115.01 (5) | P1—In2—Ba2iv | 55.31 (6) |
P4i—Ba1—In1i | 74.84 (5) | P1i—In2—Ba2iv | 106.71 (6) |
P4ii—Ba1—In1i | 147.484 (9) | P3viii—In2—Ba2iv | 55.02 (5) |
In1—Ba1—In1i | 64.689 (16) | In3ix—In2—Ba2iv | 132.10 (2) |
P2—Ba1—In3i | 115.54 (4) | P1—In2—Ba2iii | 106.71 (6) |
P1i—Ba1—In3i | 40.33 (5) | P1i—In2—Ba2iii | 55.31 (6) |
P1—Ba1—In3i | 85.31 (4) | P3viii—In2—Ba2iii | 55.02 (5) |
P4—Ba1—In3i | 127.07 (5) | In3ix—In2—Ba2iii | 132.10 (2) |
P4i—Ba1—In3i | 86.13 (4) | Ba2iv—In2—Ba2iii | 64.747 (16) |
P4ii—Ba1—In3i | 41.07 (3) | P1—In2—Ba1 | 53.18 (5) |
In1—Ba1—In3i | 153.57 (2) | P1i—In2—Ba1 | 53.18 (5) |
In1i—Ba1—In3i | 109.556 (12) | P3viii—In2—Ba1 | 124.29 (6) |
P2—Ba1—In3 | 115.54 (4) | In3ix—In2—Ba1 | 140.43 (3) |
P1i—Ba1—In3 | 85.31 (4) | Ba2iv—In2—Ba1 | 79.071 (17) |
P1—Ba1—In3 | 40.33 (5) | Ba2iii—In2—Ba1 | 79.071 (17) |
P4—Ba1—In3 | 86.13 (4) | P1—In3—P4x | 106.80 (7) |
P4i—Ba1—In3 | 127.07 (5) | P1—In3—P4ii | 106.80 (7) |
P4ii—Ba1—In3 | 41.07 (3) | P4x—In3—P4ii | 104.93 (10) |
In1—Ba1—In3 | 109.556 (12) | P1—In3—In2ix | 126.40 (7) |
In1i—Ba1—In3 | 153.57 (2) | P4x—In3—In2ix | 105.08 (6) |
In3i—Ba1—In3 | 63.206 (15) | P4ii—In3—In2ix | 105.08 (6) |
P2—Ba1—In2 | 73.09 (5) | P1—In3—Ba1vii | 53.62 (5) |
P1i—Ba1—In2 | 40.54 (3) | P4x—In3—Ba1vii | 55.12 (6) |
P1—Ba1—In2 | 40.54 (3) | P4ii—In3—Ba1vii | 105.02 (6) |
P4—Ba1—In2 | 136.78 (4) | In2ix—In3—Ba1vii | 147.557 (10) |
P4i—Ba1—In2 | 136.78 (4) | P1—In3—Ba1 | 53.62 (5) |
P4ii—Ba1—In2 | 75.05 (5) | P4x—In3—Ba1 | 105.02 (6) |
In1—Ba1—In2 | 99.630 (18) | P4ii—In3—Ba1 | 55.12 (6) |
In1i—Ba1—In2 | 99.630 (18) | In2ix—In3—Ba1 | 147.557 (10) |
In3i—Ba1—In2 | 54.733 (15) | Ba1vii—In3—Ba1 | 63.206 (15) |
In3—Ba1—In2 | 54.733 (15) | P4—In4—P3 | 114.16 (7) |
P2—Ba1—In4 | 79.06 (4) | P4—In4—P3i | 114.16 (7) |
P1i—Ba1—In4 | 152.69 (5) | P3—In4—P3i | 105.23 (10) |
P1—Ba1—In4 | 102.81 (4) | P4—In4—In1 | 107.81 (6) |
P4—Ba1—In4 | 39.85 (5) | P3—In4—In1 | 107.57 (6) |
P4i—Ba1—In4 | 83.63 (4) | P3i—In4—In1 | 107.57 (6) |
P4ii—Ba1—In4 | 127.08 (4) | P4—In4—Ba2vi | 130.06 (6) |
In1—Ba1—In4 | 41.291 (15) | P3—In4—Ba2vi | 52.65 (5) |
In1i—Ba1—In4 | 78.346 (16) | P3i—In4—Ba2vi | 52.65 (5) |
In3i—Ba1—In4 | 164.93 (2) | In1—In4—Ba2vi | 122.13 (3) |
In3—Ba1—In4 | 115.309 (10) | P4—In4—Ba1 | 53.28 (5) |
In2—Ba1—In4 | 138.201 (15) | P3—In4—Ba1 | 158.24 (5) |
P2iii—Ba2—P2iv | 83.45 (7) | P3i—In4—Ba1 | 96.48 (5) |
P2iii—Ba2—P3v | 159.23 (7) | In1—In4—Ba1 | 66.23 (2) |
P2iv—Ba2—P3v | 94.20 (5) | Ba2vi—In4—Ba1 | 148.862 (8) |
P2iii—Ba2—P3vi | 94.20 (5) | P4—In4—Ba1vii | 53.28 (5) |
P2iv—Ba2—P3vi | 159.23 (7) | P3—In4—Ba1vii | 96.48 (5) |
P3v—Ba2—P3vi | 80.70 (7) | P3i—In4—Ba1vii | 158.24 (5) |
P2iii—Ba2—P1iv | 76.43 (6) | In1—In4—Ba1vii | 66.23 (2) |
P2iv—Ba2—P1iv | 76.43 (6) | Ba2vi—In4—Ba1vii | 148.862 (8) |
P3v—Ba2—P1iv | 82.95 (6) | Ba1—In4—Ba1vii | 61.784 (14) |
P3vi—Ba2—P1iv | 82.95 (6) | In3—P1—In2 | 90.01 (7) |
P2iii—Ba2—P3 | 107.57 (6) | In3—P1—In2vii | 90.01 (7) |
P2iv—Ba2—P3 | 107.57 (6) | In2—P1—In2vii | 106.24 (10) |
P3v—Ba2—P3 | 92.85 (6) | In3—P1—Ba1vii | 86.05 (7) |
P3vi—Ba2—P3 | 92.85 (6) | In2—P1—Ba1vii | 166.90 (8) |
P1iv—Ba2—P3 | 174.47 (7) | In2vii—P1—Ba1vii | 86.28 (2) |
P2iii—Ba2—In2iv | 117.38 (5) | In3—P1—Ba1 | 86.05 (7) |
P2iv—Ba2—In2iv | 75.35 (5) | In2—P1—Ba1 | 86.28 (2) |
P3v—Ba2—In2iv | 42.74 (5) | In2vii—P1—Ba1 | 166.90 (8) |
P3vi—Ba2—In2iv | 87.65 (4) | Ba1vii—P1—Ba1 | 80.99 (6) |
P1iv—Ba2—In2iv | 41.64 (3) | In3—P1—Ba2iv | 168.38 (11) |
P3—Ba2—In2iv | 134.90 (3) | In2—P1—Ba2iv | 83.04 (7) |
P2iii—Ba2—In2iii | 75.35 (5) | In2vii—P1—Ba2iv | 83.04 (7) |
P2iv—Ba2—In2iii | 117.38 (5) | Ba1vii—P1—Ba2iv | 102.71 (6) |
P3v—Ba2—In2iii | 87.65 (4) | Ba1—P1—Ba2iv | 102.71 (6) |
P3vi—Ba2—In2iii | 42.74 (5) | In1iii—P2—In1 | 82.96 (7) |
P1iv—Ba2—In2iii | 41.64 (3) | In1iii—P2—In1i | 82.96 (7) |
P3—Ba2—In2iii | 134.90 (3) | In1—P2—In1i | 105.31 (9) |
In2iv—Ba2—In2iii | 64.747 (16) | In1iii—P2—Ba2iii | 91.59 (7) |
P2iii—Ba2—In1iv | 41.87 (3) | In1—P2—Ba2iii | 167.33 (9) |
P2iv—Ba2—In1iv | 41.87 (3) | In1i—P2—Ba2iii | 85.26 (2) |
P3v—Ba2—In1iv | 134.24 (4) | In1iii—P2—Ba2iv | 91.59 (7) |
P3vi—Ba2—In1iv | 134.24 (4) | In1—P2—Ba2iv | 85.26 (2) |
P1iv—Ba2—In1iv | 75.53 (5) | In1i—P2—Ba2iv | 167.33 (9) |
P3—Ba2—In1iv | 110.00 (5) | Ba2iii—P2—Ba2iv | 83.45 (7) |
In2iv—Ba2—In1iv | 101.204 (18) | In1iii—P2—Ba1 | 157.44 (11) |
In2iii—Ba2—In1iv | 101.204 (18) | In1—P2—Ba1 | 83.41 (7) |
P2iii—Ba2—In4vi | 130.70 (4) | In1i—P2—Ba1 | 83.41 (7) |
P2iv—Ba2—In4vi | 130.70 (4) | Ba2iii—P2—Ba1 | 105.10 (6) |
P3v—Ba2—In4vi | 40.37 (3) | Ba2iv—P2—Ba1 | 105.10 (6) |
P3vi—Ba2—In4vi | 40.37 (3) | In4—P3—In4vii | 105.23 (10) |
P1iv—Ba2—In4vi | 79.22 (5) | In4—P3—In2xi | 93.88 (7) |
P3—Ba2—In4vi | 95.25 (5) | In4vii—P3—In2xi | 93.88 (7) |
In2iv—Ba2—In4vi | 58.244 (15) | In4—P3—Ba2v | 167.46 (8) |
In2iii—Ba2—In4vi | 58.244 (15) | In4vii—P3—Ba2v | 86.98 (2) |
In1iv—Ba2—In4vi | 154.75 (2) | In2xi—P3—Ba2v | 82.23 (6) |
P2iii—Ba2—Ba2i | 48.27 (3) | In4—P3—Ba2vi | 86.98 (2) |
P2iv—Ba2—Ba2i | 131.73 (3) | In4vii—P3—Ba2vi | 167.46 (8) |
P3v—Ba2—Ba2i | 130.35 (3) | In2xi—P3—Ba2vi | 82.23 (6) |
P3vi—Ba2—Ba2i | 49.65 (3) | Ba2v—P3—Ba2vi | 80.70 (7) |
P1iv—Ba2—Ba2i | 90.0 | In4—P3—Ba2 | 94.58 (7) |
P3—Ba2—Ba2i | 90.0 | In4vii—P3—Ba2 | 94.58 (7) |
In2iv—Ba2—Ba2i | 122.373 (8) | In2xi—P3—Ba2 | 166.04 (11) |
In2iii—Ba2—Ba2i | 57.627 (8) | Ba2v—P3—Ba2 | 87.15 (6) |
In1iv—Ba2—Ba2i | 90.0 | Ba2vi—P3—Ba2 | 87.15 (6) |
In4vi—Ba2—Ba2i | 90.0 | In4—P4—In3x | 96.47 (7) |
P2iii—Ba2—Ba2vii | 131.73 (3) | In4—P4—In3ii | 96.47 (7) |
P2iv—Ba2—Ba2vii | 48.27 (3) | In3x—P4—In3ii | 104.93 (10) |
P3v—Ba2—Ba2vii | 49.65 (3) | In4—P4—Ba1 | 86.87 (7) |
P3vi—Ba2—Ba2vii | 130.35 (3) | In3x—P4—Ba1 | 166.52 (8) |
P1iv—Ba2—Ba2vii | 90.0 | In3ii—P4—Ba1 | 87.60 (2) |
P3—Ba2—Ba2vii | 90.0 | In4—P4—Ba1vii | 86.87 (7) |
In2iv—Ba2—Ba2vii | 57.627 (8) | In3x—P4—Ba1vii | 87.60 (2) |
In2iii—Ba2—Ba2vii | 122.373 (8) | In3ii—P4—Ba1vii | 166.52 (8) |
In1iv—Ba2—Ba2vii | 90.0 | Ba1—P4—Ba1vii | 79.52 (6) |
In4vi—Ba2—Ba2vii | 90.0 | In4—P4—Ba1ii | 179.53 (11) |
Ba2i—Ba2—Ba2vii | 180.00 (3) | In3x—P4—Ba1ii | 83.81 (7) |
P2iii—In1—P2 | 97.04 (7) | In3ii—P4—Ba1ii | 83.81 (7) |
P2iii—In1—P2vii | 97.04 (7) | Ba1—P4—Ba1ii | 92.77 (6) |
P2—In1—P2vii | 105.31 (9) | Ba1vii—P4—Ba1ii | 92.77 (6) |
Symmetry codes: (i) x, y+1, z; (ii) −x+1, −y, −z+2; (iii) −x+1, −y, −z+1; (iv) −x+1, −y−1, −z+1; (v) −x, −y−2, −z+1; (vi) −x, −y−1, −z+1; (vii) x, y−1, z; (viii) x+1, y+1, z; (ix) −x+2, −y, −z+2; (x) −x+1, −y−1, −z+2; (xi) x−1, y−1, z. |
Experimental details
(CaIn2P2) | (SrIn2P2) | (BaIn2P2) | |
Crystal data | |||
Chemical formula | CaIn2P2 | SrIn2P2 | BaIn2P2 |
Mr | 331.66 | 379.20 | 428.92 |
Crystal system, space group | Hexagonal, P63/mmc | Hexagonal, P63/mmc | Monoclinic, P21/m |
Temperature (K) | 90 | 90 | 90 |
a, b, c (Å) | 4.0220 (17), 4.0220 (17), 17.408 (8) | 4.0945 (16), 4.0945 (16), 17.812 (7) | 9.9652 (8), 4.1789 (3), 12.9834 (10) |
α, β, γ (°) | 90, 90, 120 | 90, 90, 120 | 90, 95.326 (2), 90 |
V (Å3) | 243.87 (18) | 258.61 (18) | 538.34 (7) |
Z | 2 | 2 | 4 |
Radiation type | Mo Kα | Mo Kα | Mo Kα |
µ (mm−1) | 10.97 | 19.55 | 16.15 |
Crystal size (mm) | 0.42 × 0.40 × 0.12 | 0.34 × 0.24 × 0.19 | 0.23 × 0.15 × 0.09 |
Data collection | |||
Diffractometer | Bruker SMART 1000 diffractometer | Bruker SMART 1000 diffractometer | Bruker SMART 1000 diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2003) | Multi-scan (SADABS; Sheldrick, 2003) | Multi-scan (SADABS; Sheldrick, 2003) |
Tmin, Tmax | 0.021, 0.268 | 0.014, 0.057 | 0.119, 0.324 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3448, 179, 153 | 3694, 189, 168 | 7899, 1753, 1452 |
Rint | 0.055 | 0.035 | 0.037 |
(sin θ/λ)max (Å−1) | 0.714 | 0.714 | 0.703 |
Refinement | |||
R[F2 > 2σ(F2)], wR(F2), S | 0.028, 0.073, 1.27 | 0.015, 0.037, 1.25 | 0.038, 0.093, 1.03 |
No. of reflections | 179 | 189 | 1753 |
No. of parameters | 10 | 10 | 62 |
Δρmax, Δρmin (e Å−3) | 1.14, −2.15 | 0.60, −0.78 | 2.56, −2.48 |
Computer programs: SMART (Bruker, 2003), SAINT (Bruker, 2003), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
Ca1—P1 | 2.936 (2) | In1—In1i | 2.7625 (19) |
In1—P1 | 2.6021 (16) | ||
P1—Ca1—P1ii | 93.54 (7) | P1—In1—In1i | 116.82 (6) |
P1iii—In1—P1 | 101.22 (7) | In1iv—P1—In1 | 101.22 (7) |
Symmetry codes: (i) x, y, −z+1/2; (ii) −x+1, −y+1, −z+1; (iii) x+1, y, z; (iv) x, y+1, z. |
Sr1—P1 | 3.0572 (12) | In1—In1i | 2.7620 (13) |
In1—P1 | 2.6216 (11) | ||
P1—Sr1—P1ii | 95.92 (4) | P1—In1—In1i | 115.62 (3) |
P1iii—In1—P1 | 102.69 (4) | In1iv—P1—In1 | 102.69 (4) |
Symmetry codes: (i) x, y, −z+1/2; (ii) −x+1, −y+1, −z+1; (iii) x+1, y, z; (iv) x, y+1, z. |
Ba1—P2 | 3.206 (3) | In1—P2 | 2.6283 (17) |
Ba1—P1 | 3.218 (2) | In1—In4 | 2.8161 (10) |
Ba1—P4 | 3.267 (2) | In2—P1 | 2.6122 (17) |
Ba1—P4i | 3.290 (3) | In2—P3v | 2.673 (3) |
Ba2—P2ii | 3.139 (2) | In2—In3vi | 2.7460 (10) |
Ba2—P3iii | 3.227 (2) | In3—P1 | 2.587 (3) |
Ba2—P1iv | 3.233 (3) | In3—P4vii | 2.6350 (17) |
Ba2—P3 | 3.438 (3) | In4—P4 | 2.612 (3) |
In1—P2ii | 2.624 (3) | In4—P3 | 2.6296 (18) |
Symmetry codes: (i) −x+1, −y, −z+2; (ii) −x+1, −y, −z+1; (iii) −x, −y−2, −z+1; (iv) −x+1, −y−1, −z+1; (v) x+1, y+1, z; (vi) −x+2, −y, −z+2; (vii) −x+1, −y−1, −z+2. |
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Layered ternary compounds, AB2X2 (A = rare earth or alkaline earth metal, B = main group, metalloid, X = main group 14–17 element) or 1–2–2 phases, favor the ThCr2Si2 (I4/mmm) structure type, with the CaAl2Si2 structure type (P3m1) as a distant second (Grytsiv et al., 2002; Hellmann et al., 2007). There are a few other less commonly observed structure types for layered main group metalloids, such as α-BaCu2S2 (Pnma) (Leoni et al., 2003) observed for BaAl2Si2 (Condron et al., 2007), and EuIn2P2 (Jiang & Kauzlarich, 2006). In addition to layered structure types, there is at least one example of a 1–2–2 phase with a three-dimensional structure, as found in BaGa2Sb2 (Kim & Kanatzidis, 2001). More complex two-dimensional and three-dimensional structures composed of alkaline earth, In and P have also been reported, such as Ba2In5P5 (Mathieu et al., 2008), Ba14InP11 (Carrillo-Cabrera et al., 1996) and Ba3In2P4 (Somer et al., 1998).
The rare earth Zintl phase EuIn2P2 contains two-dimensional layers of Eu2+ cations dispersed between layers of [In2P2]2- anions. EuIn2P2 has been shown to exhibit colossal magnetoresistance (Jiang & Kauzlarich, 2006). The temperature-dependent magnetoresistance and the magneto-optical behavior of this compound suggest interaction between conduction electrons and local spins (Jiang & Kauzlarich, 2006; Pfuner et al., 2008). The alkaline earth analogs of the EuIn2P2 were prepared in order to provide a non-magnetic analog for heat capacity and electrical transport studies. The existence of the Sr analog has been alluded to in a recent publication (Mathieu et al., 2008), although the structural details were not provided. Here, two new members of the P63/mmc structure type are presented, along with one new structure type, P21/m. Both structures can be described as composed of In2P6 ethane-like moieties (either eclipsed or staggered), connected through the P atoms in such a fashion as to form layers separated by alkaline earth cations.
CaIn2P2 and SrIn2P2 are isostructural in the space group P63/mmc. A view of SrIn2P2 emphasizing the layered structure is provided in Fig. 1. AIn2P2 (A = Ca, Sr) contains alternating layers of [In2P2]2- that are parallel to (001) and charge balanced by A2+ cationic layers stacked along the c axis. The alkaline earth element resides on Wyckoff position a (multiplicity 2) with 3m site symmetry. As shown in Fig. 1, its coordination environment consists of six P atoms in a trigonal antiprismatic arrangement. The In atom resides on Wyckoff position f (multiplicity 4) with 3m symmetry. There are three surrounding P atoms in a pyramidal arrangement and an apical In atom. The centroid of the In—In bond is a site of 6m2 (D3h) symmetry; thus, the ethane-related unit P3In–InP3 moiety has eclipsed P atoms. Each P atom [also at Wyckoff position f (multiplicity 4) with 3m symmetry] has three equal bonds to In, as well as three equal bonds to Ca (Sr). The P3In–InP3 moieties are connected in parallel via bridging P atoms to form a double layer of six-membered rings. The Ca or Sr cations are centered above each ring and form layers above and below each double layer of rings, as shown in Fig. 2.
The In—P bonds are considered to be covalent, whereas the In—Ca (Sr) interactions are electrostatic in origin. By Zintl electron counting (Kauzlarich, 1996), each P has a lone pair. The lone pair may have largely an s character, since its simultaneous interaction with three Sr [atoms] (Ca [atoms]) shows it to be non-directional. The majority of the bond distances increase from the Ca to the Sr compound, as expected; the In—Ini [symmetry code: (i) = x, y, -z + 1/2] distances are equal within experimental error for both compounds. The previously reported Eu phase contains intermediate distances (Jiang & Kauzlarich, 2006).
BaIn2P2 adopts a new structure type with greater complexity and geometric distortion in the space group P21/m. Each atom resides on a crystallographic mirror plane. The structure is similar to CaIn2P2 and SrIn2P2 in that it contains alternating layers of [In2P2]2- sheets, parallel to the (101) plane, that are charge balanced by A2+ cationic layers, as shown in Fig. 3. The In—In distances of 2.7625 (19) and 2.7620 (13) Å, corresponding to CaIn2P2 and SrIn2P2, respectively, are bracketed by the two In—In bond distances of 2.7460 (10) (In2—In3vi) [symmetry code:(v) 2 - x, -y, 2 - z] and 2.8161 (10) Å (In1—In4) observed in BaIn2P2. There are two crystallographic sites for Ba cations in this structure. Each Ba is coordinated by six P atoms in a distorted trigonal antiprismatic conformation, as shown in Fig. 3. The In coordination in BaIn2P2 is similar to that in CaIn2P2 and SrIn2P2 in that it is comprised of another In atom and three P atoms forming a P3In–InP3 unit. However, in this structure the ethane-like moiety is staggered and has non-crystallographic D3d symmetry. The [In2P2]2- layers are markedly different in BaIn2P2 and consist of four-, five- and six-membered rings. A view roughly perpendicular to the (InP) layer (Fig. 4) emphasizes this difference when compared with Fig. 2. The lower symmetry in the layer in BaIn2P2 is likely related to the necessity to accommodate the larger Ba2+ cation (Shannon, 1976). If one assumes that the separation between cations is tied to the repeat distances of the six-membered (InP)3 rings [4.0220 (17) in CaIn2P2 and 4.0945 (16) Å in SrIn2P2], it is apparent that the EuIn2P2 structure type cannot accommodate Ba. In BaIn2P2, the shortest Ba···Ba distance is 4.1789 (3) Å.
There are many examples where the identity of the cation provides different structures for isoelectronic series of compounds and this is also the case for Zintl and intermetallic phases (Kauzlarich, 1996; Nesper, 1990). For example, AMn2P2 (A = Sr, Ba) assumes different structure types depending on the identity of the cation: SrMn2P2 crystallizes in the CaAl2Si2 structure type, whereas BaMn2P2 crystallizes in the ThCr2Si2 structure type (Brock et al., 1994). This was attributed to the difference in cation coordination: octahedral for the cation site in CaAl2Si2 versus cubic in the ThCr2Si2 structure type. Electronic considerations have been shown to play an important role in dictating structure and properties for other isoelectronic series (Alemany et al., 2008; Xia & Bobev, 2007, 2008; Kim et al., 2008). For AIn2P2 (A = Ca, Sr), the EuIn2P2 structure type, the six-membered ring structure of the non-metal layer cannot accommodate the size of the Ba cation and a new structure type is adopted.
Of the published structures of the combination of alkaline earth cation and group 13 and 15 elements, Ba2In5P5 is a recent example of a layered structure that is built up from ethane-like moieties (Mathieu et al., 2008). The bond distances and angles in this compound are very similar to those observed in BaIn2P2 presented herein. The structure of Ba2In5P5 can be described as containing two staggered ethane-like moieties similar to that observed in the BaIn2P2 structure type, with the In—In bonds arranged parallel to each other and connected via P atoms. However, in Ba2In5P5 two of the parallel moieties are joined through a P atom by a highly distorted InP4 tetrahedron.
The ethane-like moiety is also observed in the three-dimensional framework structures of BaGa2Sb2 (Kim & Kanatzidis, 2001) and Ba3Ga4Sb5 (Park et al., 2003). Both BaGa2Sb2 and Ba3Ga4Sb5 adopt unique structure types that contain tunnels wherein the Ba2+ cations reside (Kim & Kanatzidis, 2001; Park et al., 2003).
AIn2P2 (A = Ca, Sr, Ba) can be considered Zintl phases where there is electrostatic bonding between the alkaline earth cation and the layered anion (Kauzlarich, 1996). The basic building block of the ethane-like moiety is a common element in compounds composed of alkaline earth, group 13 and group 15 elements. Similar to the molecule ethane, this moiety can have a staggered or eclipsed conformation. This moiety is connected through shared P atoms to form extended structures in these compounds. The interaction of the P atoms with the cation, rather than In—In bond length, may determine whether the moiety is eclipsed or staggered, as the In—In bond is both the shortest and longest in the BaIn2P2 compound (moiety is staggered) compared with the Ca (Sr) compounds (moiety is eclipsed).