inorganic compounds
LaZn12.37 (1), a zinc-deficient variant of the NaZn13 structure type
aDepartment of Inorganic Chemistry, Ivan Franko Lviv National University, Kyryla i Mefodia 6,79005 Lviv, Ukraine, and bAgilent Technologies UK Ltd, 10 Mead Road, Oxford Industrial Park, Yarnton, Oxfordshire, OX5 1QU, England
*Correspondence e-mail: romaniuk@ua.fm
The title compound (lanthanum dodecazinc), LaZn12.37 (1), is confirmed to be a nonstoichiometric (zinc-deficient) modification of the NaZn13 structure type, in which one Zn atom (Wyckoff site 8b, m) has a fractional site occupancy of 0.372 (11). The other Zn atom (96i, m) and the La atom (8a, 432) are fully occupied. The coordination polyhedra of the Zn atoms are distorted icosahedra, whereas the La atoms are surrounded by 24 Zn atoms, forming pseudo-Frank–Kasper polyhedra. Electronic structure calculations indicate that Zn—Zn bonding is much stronger than La—Zn bonding.
Related literature
For general background to intermetallics, see: Berche et al. (2009); Oshchapovsky et al. (2010); Pavlyuk et al. (2009); Rolla & Iandelli (1941). For isotypic structures, see: Iandelli & Palenzona (1967); Kuz'ma et al. (1966); Veleckis et al. (1967). For electronic structure calculations with the TB-LMTO-ASA package, see: Andersen et al. (1986).
Experimental
Crystal data
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Data collection: CrysAlis PRO (Agilent, 2011); cell CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006) and VESTA (Momma & Izumi, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).
Supporting information
10.1107/S1600536811028893/hb5947sup1.cif
contains datablocks I, New_Global_Publ_Block. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536811028893/hb5947Isup2.hkl
Small irregularly shaped single-crystal of the LaZn12.37 (1) binary compound was selected by mechanical fragmentation of sample with nominal composition LaZn20Sn2. Alloy was prepared by mixing stoichiometric amounts of powders of zinc, tin and LaZn ligature with subsequent pressing them into pellets. These pellets were enclosed in evacuated silica ampoules and heated in the resistance oven. After that alloys were annealed at 600°C for 30 days and quenched in cold water. No reaction between alloys and quartz containers was observed.
Data collection: CrysAlis PRO (Agilent, 2011); cell
CrysAlis PRO (Agilent, 2011); data reduction: CrysAlis PRO (Agilent, 2011); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006)and VESTA (Momma & Izumi, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).LaZn12.37 | Dx = 7.113 Mg m−3 |
Mr = 947.00 | Mo Kα radiation, λ = 0.71073 Å |
Cubic, Fm3c | Cell parameters from 811 reflections |
Hall symbol: -F 4c 2 3 | θ = 3.4–28.9° |
a = 12.0940 (9) Å | µ = 37.49 mm−1 |
V = 1768.9 (2) Å3 | T = 293 K |
Z = 8 | Irregular platelet, grey |
F(000) = 3426.0 | 0.05 × 0.03 × 0.01 mm |
Agilent Gemini Ultra diffractometer with Eos CCD detector | 110 independent reflections |
Radiation source: Enhance (Mo) X-ray Source | 108 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.122 |
ω scans | θmax = 28.3°, θmin = 3.4° |
Absorption correction: multi-scan CrysAlis PRO (Agilent, 2011) | h = −14→16 |
Tmin = 0.368, Tmax = 1.0 | k = −16→16 |
1543 measured reflections | l = −9→16 |
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)] = 0.024 | w = 1/[σ2(Fo2) + (0.0097P)2] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.052 | (Δ/σ)max < 0.001 |
S = 1.22 | Δρmax = 0.81 e Å−3 |
110 reflections | Δρmin = −1.08 e Å−3 |
12 parameters | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.00058 (8) |
LaZn12.37 | Z = 8 |
Mr = 947.00 | Mo Kα radiation |
Cubic, Fm3c | µ = 37.49 mm−1 |
a = 12.0940 (9) Å | T = 293 K |
V = 1768.9 (2) Å3 | 0.05 × 0.03 × 0.01 mm |
Agilent Gemini Ultra diffractometer with Eos CCD detector | 110 independent reflections |
Absorption correction: multi-scan CrysAlis PRO (Agilent, 2011) | 108 reflections with I > 2σ(I) |
Tmin = 0.368, Tmax = 1.0 | Rint = 0.122 |
1543 measured reflections |
R[F2 > 2σ(F2)] = 0.024 | 12 parameters |
wR(F2) = 0.052 | 0 restraints |
S = 1.22 | Δρmax = 0.81 e Å−3 |
110 reflections | Δρmin = −1.08 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 | Occ. (<1) | |
La1 | 0.2500 | 0.2500 | 0.2500 | 0.0081 (5) | |
Zn2 | 0.0000 | 0.17786 (6) | 0.11938 (6) | 0.0113 (4) | |
Zn3 | 0.0000 | 0.0000 | 0.0000 | 0.006 (2) | 0.372 (11) |
U11 | U22 | U33 | U12 | U13 | U23 | |
La1 | 0.0081 (5) | 0.0081 (5) | 0.0081 (5) | 0.000 | 0.000 | 0.000 |
Zn2 | 0.0120 (5) | 0.0097 (5) | 0.0123 (5) | 0.000 | 0.000 | 0.0031 (3) |
Zn3 | 0.006 (2) | 0.006 (2) | 0.006 (2) | 0.000 | 0.000 | 0.000 |
La1—Zn2i | 3.5211 (4) | Zn2—Zn2ii | 2.6854 (8) |
La1—Zn2ii | 3.5211 (4) | Zn2—Zn2i | 2.6854 (8) |
La1—Zn2 | 3.5211 (4) | Zn2—Zn2ix | 2.6859 (12) |
La1—Zn2iii | 3.5211 (4) | Zn2—Zn2xv | 2.6859 (12) |
La1—Zn2iv | 3.5211 (4) | Zn2—Zn2xvi | 2.8875 (15) |
La1—Zn2v | 3.5211 (4) | Zn2—La1xvii | 3.5211 (4) |
La1—Zn2vi | 3.5211 (4) | Zn3—Zn2xviii | 2.5906 (7) |
La1—Zn2vii | 3.5211 (4) | Zn3—Zn2xix | 2.5906 (7) |
La1—Zn2viii | 3.5211 (4) | Zn3—Zn2xx | 2.5906 (7) |
La1—Zn2ix | 3.5211 (4) | Zn3—Zn2i | 2.5906 (7) |
La1—Zn2x | 3.5211 (4) | Zn3—Zn2ii | 2.5906 (7) |
La1—Zn2xi | 3.5211 (4) | Zn3—Zn2xiii | 2.5906 (7) |
Zn2—Zn2xii | 2.5522 (10) | Zn3—Zn2xxi | 2.5906 (7) |
Zn2—Zn2x | 2.5522 (10) | Zn3—Zn2xxii | 2.5906 (7) |
Zn2—Zn3 | 2.5906 (7) | Zn3—Zn2xxiii | 2.5906 (7) |
Zn2—Zn2xiii | 2.6854 (8) | Zn3—Zn2xvi | 2.5906 (7) |
Zn2—Zn2xiv | 2.6854 (8) | Zn3—Zn2xiv | 2.5906 (7) |
Zn2i—La1—Zn2ii | 44.832 (17) | Zn2ii—Zn2—Zn2xv | 161.98 (3) |
Zn2i—La1—Zn2 | 44.832 (17) | Zn2i—Zn2—Zn2xv | 108.22 (3) |
Zn2ii—La1—Zn2 | 44.832 (17) | Zn2ix—Zn2—Zn2xv | 65.03 (3) |
Zn2i—La1—Zn2iii | 163.67 (2) | Zn2xii—Zn2—Zn2xvi | 106.09 (2) |
Zn2ii—La1—Zn2iii | 128.82 (2) | Zn2x—Zn2—Zn2xvi | 163.91 (2) |
Zn2—La1—Zn2iii | 146.29 (2) | Zn3—Zn2—Zn2xvi | 56.130 (16) |
Zn2i—La1—Zn2iv | 128.82 (2) | Zn2xiii—Zn2—Zn2xvi | 57.477 (19) |
Zn2ii—La1—Zn2iv | 146.29 (2) | Zn2xiv—Zn2—Zn2xvi | 105.27 (2) |
Zn2—La1—Zn2iv | 163.67 (2) | Zn2ii—Zn2—Zn2xvi | 105.27 (2) |
Zn2iii—La1—Zn2iv | 44.832 (17) | Zn2i—Zn2—Zn2xvi | 57.477 (19) |
Zn2i—La1—Zn2v | 146.29 (2) | Zn2ix—Zn2—Zn2xvi | 57.484 (14) |
Zn2ii—La1—Zn2v | 163.67 (2) | Zn2xv—Zn2—Zn2xvi | 57.484 (14) |
Zn2—La1—Zn2v | 128.82 (2) | Zn2xii—Zn2—La1 | 68.752 (6) |
Zn2iii—La1—Zn2v | 44.832 (17) | Zn2x—Zn2—La1 | 68.752 (6) |
Zn2iv—La1—Zn2v | 44.832 (17) | Zn3—Zn2—La1 | 117.115 (12) |
Zn2i—La1—Zn2vi | 119.133 (3) | Zn2xiii—Zn2—La1 | 173.86 (2) |
Zn2ii—La1—Zn2vi | 106.477 (13) | Zn2xiv—Zn2—La1 | 122.82 (4) |
Zn2—La1—Zn2vi | 151.31 (2) | Zn2ii—Zn2—La1 | 67.584 (9) |
Zn2iii—La1—Zn2vi | 44.84 (2) | Zn2i—Zn2—La1 | 67.584 (9) |
Zn2iv—La1—Zn2vi | 42.496 (13) | Zn2ix—Zn2—La1 | 67.580 (12) |
Zn2v—La1—Zn2vi | 78.388 (9) | Zn2xv—Zn2—La1 | 122.80 (3) |
Zn2i—La1—Zn2vii | 151.31 (2) | Zn2xvi—Zn2—La1 | 116.657 (11) |
Zn2ii—La1—Zn2vii | 119.133 (3) | Zn2xii—Zn2—La1xvii | 68.752 (6) |
Zn2—La1—Zn2vii | 106.477 (13) | Zn2x—Zn2—La1xvii | 68.752 (6) |
Zn2iii—La1—Zn2vii | 42.496 (13) | Zn3—Zn2—La1xvii | 117.115 (12) |
Zn2iv—La1—Zn2vii | 78.388 (9) | Zn2xiii—Zn2—La1xvii | 67.584 (9) |
Zn2v—La1—Zn2vii | 44.84 (2) | Zn2xiv—Zn2—La1xvii | 67.584 (9) |
Zn2vi—La1—Zn2vii | 86.486 (17) | Zn2ii—Zn2—La1xvii | 122.82 (4) |
Zn2i—La1—Zn2viii | 106.477 (13) | Zn2i—Zn2—La1xvii | 173.86 (2) |
Zn2ii—La1—Zn2viii | 151.31 (2) | Zn2ix—Zn2—La1xvii | 122.80 (3) |
Zn2—La1—Zn2viii | 119.133 (3) | Zn2xv—Zn2—La1xvii | 67.580 (12) |
Zn2iii—La1—Zn2viii | 78.388 (9) | Zn2xvi—Zn2—La1xvii | 116.657 (11) |
Zn2iv—La1—Zn2viii | 44.84 (2) | La1—Zn2—La1xvii | 118.34 (2) |
Zn2v—La1—Zn2viii | 42.496 (13) | Zn2xviii—Zn3—Zn2xix | 62.436 (7) |
Zn2vi—La1—Zn2viii | 86.486 (17) | Zn2xviii—Zn3—Zn2xx | 62.436 (7) |
Zn2vii—La1—Zn2viii | 86.486 (17) | Zn2xix—Zn3—Zn2xx | 62.436 (7) |
Zn2i—La1—Zn2ix | 42.496 (13) | Zn2xviii—Zn3—Zn2 | 117.564 (7) |
Zn2ii—La1—Zn2ix | 78.388 (9) | Zn2xix—Zn3—Zn2 | 117.564 (7) |
Zn2—La1—Zn2ix | 44.84 (2) | Zn2xx—Zn3—Zn2 | 180.00 (3) |
Zn2iii—La1—Zn2ix | 151.31 (2) | Zn2xviii—Zn3—Zn2i | 180.00 (3) |
Zn2iv—La1—Zn2ix | 119.133 (3) | Zn2xix—Zn3—Zn2i | 117.564 (7) |
Zn2v—La1—Zn2ix | 106.477 (13) | Zn2xx—Zn3—Zn2i | 117.564 (7) |
Zn2vi—La1—Zn2ix | 146.29 (2) | Zn2—Zn3—Zn2i | 62.436 (7) |
Zn2vii—La1—Zn2ix | 121.00 (2) | Zn2xviii—Zn3—Zn2ii | 117.564 (7) |
Zn2viii—La1—Zn2ix | 77.04 (2) | Zn2xix—Zn3—Zn2ii | 180.00 (3) |
Zn2i—La1—Zn2x | 78.388 (9) | Zn2xx—Zn3—Zn2ii | 117.564 (7) |
Zn2ii—La1—Zn2x | 44.84 (2) | Zn2—Zn3—Zn2ii | 62.436 (7) |
Zn2—La1—Zn2x | 42.496 (13) | Zn2i—Zn3—Zn2ii | 62.436 (7) |
Zn2iii—La1—Zn2x | 106.477 (13) | Zn2xviii—Zn3—Zn2xiii | 67.74 (3) |
Zn2iv—La1—Zn2x | 151.31 (2) | Zn2xix—Zn3—Zn2xiii | 62.436 (7) |
Zn2v—La1—Zn2x | 119.133 (3) | Zn2xx—Zn3—Zn2xiii | 117.564 (7) |
Zn2vi—La1—Zn2x | 121.00 (2) | Zn2—Zn3—Zn2xiii | 62.436 (7) |
Zn2vii—La1—Zn2x | 77.04 (2) | Zn2i—Zn3—Zn2xiii | 112.26 (3) |
Zn2viii—La1—Zn2x | 146.29 (2) | Zn2ii—Zn3—Zn2xiii | 117.564 (7) |
Zn2ix—La1—Zn2x | 86.486 (17) | Zn2xviii—Zn3—Zn2xxi | 117.564 (7) |
Zn2i—La1—Zn2xi | 44.84 (2) | Zn2xix—Zn3—Zn2xxi | 67.74 (3) |
Zn2ii—La1—Zn2xi | 42.496 (13) | Zn2xx—Zn3—Zn2xxi | 62.436 (7) |
Zn2—La1—Zn2xi | 78.388 (9) | Zn2—Zn3—Zn2xxi | 117.564 (7) |
Zn2iii—La1—Zn2xi | 119.133 (3) | Zn2i—Zn3—Zn2xxi | 62.436 (7) |
Zn2iv—La1—Zn2xi | 106.477 (13) | Zn2ii—Zn3—Zn2xxi | 112.26 (3) |
Zn2v—La1—Zn2xi | 151.31 (2) | Zn2xiii—Zn3—Zn2xxi | 117.564 (7) |
Zn2vi—La1—Zn2xi | 77.04 (2) | Zn2xviii—Zn3—Zn2xxii | 62.436 (7) |
Zn2vii—La1—Zn2xi | 146.29 (2) | Zn2xix—Zn3—Zn2xxii | 117.564 (7) |
Zn2viii—La1—Zn2xi | 121.00 (2) | Zn2xx—Zn3—Zn2xxii | 67.74 (3) |
Zn2ix—La1—Zn2xi | 86.486 (17) | Zn2—Zn3—Zn2xxii | 112.26 (3) |
Zn2x—La1—Zn2xi | 86.486 (17) | Zn2i—Zn3—Zn2xxii | 117.564 (7) |
Zn2xii—Zn2—Zn2x | 90.0 | Zn2ii—Zn3—Zn2xxii | 62.436 (7) |
Zn2xii—Zn2—Zn3 | 162.22 (4) | Zn2xiii—Zn3—Zn2xxii | 117.564 (7) |
Zn2x—Zn2—Zn3 | 107.78 (4) | Zn2xxi—Zn3—Zn2xxii | 117.564 (7) |
Zn2xii—Zn2—Zn2xiii | 113.70 (3) | Zn2xviii—Zn3—Zn2xxiii | 112.26 (3) |
Zn2x—Zn2—Zn2xiii | 116.33 (3) | Zn2xix—Zn3—Zn2xxiii | 117.564 (7) |
Zn3—Zn2—Zn2xiii | 58.782 (3) | Zn2xx—Zn3—Zn2xxiii | 62.436 (7) |
Zn2xii—Zn2—Zn2xiv | 134.159 (17) | Zn2—Zn3—Zn2xxiii | 117.564 (7) |
Zn2x—Zn2—Zn2xiv | 61.64 (4) | Zn2i—Zn3—Zn2xxiii | 67.74 (3) |
Zn3—Zn2—Zn2xiv | 58.782 (3) | Zn2ii—Zn3—Zn2xxiii | 62.436 (7) |
Zn2xiii—Zn2—Zn2xiv | 60.0 | Zn2xiii—Zn3—Zn2xxiii | 180.0 |
Zn2xii—Zn2—Zn2ii | 134.159 (17) | Zn2xxi—Zn3—Zn2xxiii | 62.436 (7) |
Zn2x—Zn2—Zn2ii | 61.64 (4) | Zn2xxii—Zn3—Zn2xxiii | 62.436 (7) |
Zn3—Zn2—Zn2ii | 58.782 (3) | Zn2xviii—Zn3—Zn2xvi | 117.564 (7) |
Zn2xiii—Zn2—Zn2ii | 111.18 (2) | Zn2xix—Zn3—Zn2xvi | 62.436 (7) |
Zn2xiv—Zn2—Zn2ii | 65.05 (4) | Zn2xx—Zn3—Zn2xvi | 112.26 (3) |
Zn2xii—Zn2—Zn2i | 113.70 (3) | Zn2—Zn3—Zn2xvi | 67.74 (3) |
Zn2x—Zn2—Zn2i | 116.33 (3) | Zn2i—Zn3—Zn2xvi | 62.436 (7) |
Zn3—Zn2—Zn2i | 58.782 (3) | Zn2ii—Zn3—Zn2xvi | 117.564 (7) |
Zn2xiii—Zn2—Zn2i | 106.450 (14) | Zn2xiii—Zn3—Zn2xvi | 62.436 (7) |
Zn2xiv—Zn2—Zn2i | 111.18 (2) | Zn2xxi—Zn3—Zn2xvi | 62.436 (7) |
Zn2ii—Zn2—Zn2i | 60.0 | Zn2xxii—Zn3—Zn2xvi | 180.0 |
Zn2xii—Zn2—Zn2ix | 61.62 (4) | Zn2xxiii—Zn3—Zn2xvi | 117.564 (7) |
Zn2x—Zn2—Zn2ix | 134.15 (2) | Zn2xviii—Zn3—Zn2xiv | 62.436 (7) |
Zn3—Zn2—Zn2ix | 103.88 (3) | Zn2xix—Zn3—Zn2xiv | 112.26 (3) |
Zn2xiii—Zn2—Zn2ix | 108.22 (3) | Zn2xx—Zn3—Zn2xiv | 117.564 (7) |
Zn2xiv—Zn2—Zn2ix | 161.98 (3) | Zn2—Zn3—Zn2xiv | 62.436 (7) |
Zn2ii—Zn2—Zn2ix | 111.90 (3) | Zn2i—Zn3—Zn2xiv | 117.564 (7) |
Zn2i—Zn2—Zn2ix | 56.74 (3) | Zn2ii—Zn3—Zn2xiv | 67.74 (3) |
Zn2xii—Zn2—Zn2xv | 61.62 (4) | Zn2xiii—Zn3—Zn2xiv | 62.436 (7) |
Zn2x—Zn2—Zn2xv | 134.15 (2) | Zn2xxi—Zn3—Zn2xiv | 180.00 (3) |
Zn3—Zn2—Zn2xv | 103.88 (3) | Zn2xxii—Zn3—Zn2xiv | 62.436 (7) |
Zn2xiii—Zn2—Zn2xv | 56.74 (3) | Zn2xxiii—Zn3—Zn2xiv | 117.564 (7) |
Zn2xiv—Zn2—Zn2xv | 111.90 (3) | Zn2xvi—Zn3—Zn2xiv | 117.564 (7) |
Symmetry codes: (i) y, z, x; (ii) z, x, y; (iii) −z+1/2, −y+1/2, x+1/2; (iv) x+1/2, −z+1/2, −y+1/2; (v) −y+1/2, −x+1/2, −z+1/2; (vi) x+1/2, y, −z+1/2; (vii) y, −z+1/2, x+1/2; (viii) −z+1/2, x+1/2, y; (ix) z, −y+1/2, x; (x) x, z, −y+1/2; (xi) −y+1/2, −x, z; (xii) −x, −z+1/2, y; (xiii) −y, z, −x; (xiv) −z, x, y; (xv) −z, −y+1/2, x; (xvi) x, y, −z; (xvii) −x, −y+1/2, −z+1/2; (xviii) −y, −z, −x; (xix) −z, −x, −y; (xx) −x, −y, −z; (xxi) z, −x, −y; (xxii) −x, −y, z; (xxiii) y, −z, x. |
Experimental details
Crystal data | |
Chemical formula | LaZn12.37 |
Mr | 947.00 |
Crystal system, space group | Cubic, Fm3c |
Temperature (K) | 293 |
a (Å) | 12.0940 (9) |
V (Å3) | 1768.9 (2) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 37.49 |
Crystal size (mm) | 0.05 × 0.03 × 0.01 |
Data collection | |
Diffractometer | Agilent Gemini Ultra diffractometer with Eos CCD detector |
Absorption correction | Multi-scan CrysAlis PRO (Agilent, 2011) |
Tmin, Tmax | 0.368, 1.0 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1543, 110, 108 |
Rint | 0.122 |
(sin θ/λ)max (Å−1) | 0.667 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.024, 0.052, 1.22 |
No. of reflections | 110 |
No. of parameters | 12 |
Δρmax, Δρmin (e Å−3) | 0.81, −1.08 |
Computer programs: CrysAlis PRO (Agilent, 2011), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2006)and VESTA (Momma & Izumi, 2008), publCIF (Westrip, 2010).
Footnotes
‡also at Institute of Chemistry and Environmental Protection, Jan Dlugosz University, Armii Krajowej 13/15 Ave, 42-200 Czestochowa, Poland.
Acknowledgements
The single crystal investigations were supported by Agilent Technologies.
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The results presented in this paper are the part of systematic investigation of ternary rare earth–Zn–Sn systems (see Pavlyuk et al., (2009) and Oshchapovsky et al., (2010)). The corresponding binary La—Zn system is not completely explored yet (Berche et al., 2009).
LaZn12.37 (1) is the only nonstoichiometric compound in the binary La—Zn system. It was found by Rolla et al.(Rolla & Iandelli,1941) for the first time. Later Kuz'ma et al., (1966), Veleckis et al.,(1967) and Iandelli & Palenzona, (1967) determined the cell parameters of LaZn12.37 (1). These parameters vary a little so Veleckis et al. supposed that LaZn12.37 (1) was nonstoichiometric. However, according to Berche et al. (2009) the homogeneity range was not determined accurately. Until now there were no single-crystal data indicating positions with partial occupation. In this article we will try to fill this gap. Unit cell projection of the LaZn12.37 (1) compound together with coordination polyhedra of atoms are given in Figure 1. La1 atoms are surrounded by 24 fully occupied positions of zinc atoms forming pseudo-Frank-Kasper polyhedra [LaZn24] (CN = 24). Coordination polyhedron of the Zn2 atom is distorted icosahedron [ZnLa2Zn10] (CN = 12) made of two lanthanum atoms and ten or nine zinc atoms (one position is partially occupied). Zn3 atom in partially occupied position is surrounded by twelve zinc atoms forming isosahedron [ZnZn12].
Electronic structure of LaZn12.37 (1) was calculated using TB-LMTO-ASA (Andersen et al., 1986) program package. According to the results of calculations by TB-LMTO-ASA package this compound has metallic bonding (see Fig.2). In this compound the formation of bonds is close to those in Zintl phases, however they have different coordination polyhedra. Lanthanum atoms donate their electrons to zinc atoms. So positive charge density can be observed around lanthanum atoms and negative charge density is around zinc atoms. This indicates that besides of metallic bonding which is dominate in this compound the weak covalent interaction also exists. ELF which indicates bond formation is mostly located at zinc atoms (see Fig. 3 a, b, c). Thus zinc - zinc bonding is much stronger than lanthanum - zinc bonding. So this compound can be treated as insertion of lanthanum atoms into framework made of zinc atoms.