Download citation
Download citation
link to html
The crystal structure of the already known binary title compound LaZn5 (lanthanum penta­zinc) (space group P6/mmm, Pearson symbol hP6, CaCu5 structure type) has been redetermined from single-crystal X-ray diffraction data. In contrast to previous determinations based on X-ray powder data [Nowotny (1942). Z. Metallkd. 34, 247-253; de Negri et al. (2008). Inter­metallics, 16, 168-178], where unit-cell parameters and assignment of the structure type were reported, the present study reveals anisotropic displacement parameters for all atoms. The crystal structure consists of three crytallographically distinct atoms. The La atom (Wyckoff site 1a, site symmetry 6/mmm) is surrounded by 18 Zn atoms and two La atoms. The coordination polyhedron around one of the Zn atoms (Wyckoff site 2c, site symmetry -6m2) is an icosa­hedron made up from three La and nine Zn atoms. The other Zn atom (Wyckoff site 3g, site symmetry mmm) is surrounded by four La and eight Zn atoms. Bonding between atoms is explored by means of the TB-LMTO-ASA (tight-binding linear muffin-tin orbital atomic spheres approximation) program package. The positive charge density is localized around La atoms, and the negative charge density is around Zn atoms, with weak covalent bonding between the latter.

Supporting information


Crystallographic Information File (CIF)
Contains datablocks I, global


Structure factor file (CIF format)
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 296 K
  • Mean [sigma](La-Zn) = 0.001 Å
  • R factor = 0.018
  • wR factor = 0.037
  • Data-to-parameter ratio = 8.1

checkCIF/PLATON results

No syntax errors found

Alert level C PLAT088_ALERT_3_C Poor Data / Parameter Ratio .................... 8.11 PLAT752_ALERT_4_C Angle Calc 126.54, Rep 126.54(1) ...... Senseless su ZN2 -ZN1 -LA1 1.555 1.555 1.555 # 104 PLAT973_ALERT_2_C Large Calcd. Positive Residual Density on La1 1.02 eA-3
Alert level G PLAT004_ALERT_5_G Info: Polymeric Structure Found with Dimension . 1 PLAT005_ALERT_5_G No _iucr_refine_instructions_details in CIF .... ? PLAT152_ALERT_1_G The Supplied and Calc. Volume s.u. Differ by ... 3 Units
0 ALERT level A = Most likely a serious problem - resolve or explain 0 ALERT level B = A potentially serious problem, consider carefully 3 ALERT level C = Check. Ensure it is not caused by an omission or oversight 3 ALERT level G = General information/check it is not something unexpected 1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 1 ALERT type 2 Indicator that the structure model may be wrong or deficient 1 ALERT type 3 Indicator that the structure quality may be low 1 ALERT type 4 Improvement, methodology, query or suggestion 2 ALERT type 5 Informative message, check

Comment top

This paper is part of a systematic investigation of binary RE—Zn (Oshchapovsky et al., 2011a; Zelinska et al., 2004) and ternary RE—Zn—M systems (where RE is a rare earth metal and M is a p-element of group IV) (Oshchapovsky et al., 2011b; Pavlyuk et al., 2009). The binary La—Zn system is not completely investigated yet (Berche et al., 2009), especially with respect to the structure of the compound LaZn4. In order to determine its crystal structure a sample with the same composition was synthesized. However, this sample was prepared under non-equilibrium conditions and phase analysis from X-ray powder data revealed the presence of LaZn5, LaZn2, trace amounts of LaZn and strong reflections of unknown phase(s). The lattice parameters of the title LaZn5 phase were determined for the first time based on X-ray powder diffraction data (Nowotny, 1942). Previous authors (Nowotny, 1942; de Negri et al., 2008) also assigned the structure type. However, a complete crystal structure determination including anisotropic displacement parameters was not carried out before. Therefore a high-quality single-crystal of LaZn5 was selected and the results of the full structure determination are presented in this paper.

The crystal structure consists of three crytallographically distinct atoms. La1 (Wyckoff site 1a, site symmetry 6/mmm) is surrounded by 18 Zn atoms and 2 La atoms. The coordination polyhedron around Zn1 atom (Wyckoff site 2c, site symmetry -6m2) is an icosahedron formed by 3 La and 9 Zn atoms. Zn2 (Wyckoff site 3g, site symmetry mmm) is surrounded by 4 La and 8 Zn atoms. The projection of the LaZn5 unit cell is given in Fig. 1. The thermal displacement of the lanthanum atom is almost isotropic. The thermal ellipsoids of the Zn1 atoms are oblate along the c axis. The thermal ellipsoids of the Zn2 atoms are extended along the a and b axes due to the largest space for displacement in this direction (the distances of corresponding atoms to each other and to La atoms are larger than for Zn1 atoms).

The electronic structure of LaZn5 was calculated using the TB-LMTO-ASA package (Andersen et al., 1986). The dominant type of bonding in this compound is metallic. The La atoms donate their electrons to the Zn atoms. Therefore positive charge density can be observed around the rare earth atom and negative charge density is around the transition metal atoms. This fact, together with significant electron density (~0.4 e/Å3) and significant ELF density (~0.4) between Zn atoms, confirms the weak covalent bonding between them. In other words, an ion–metallic bonding between La and Zn atoms and a covalent–metallic bonding between Zn atoms is evident (Figure 2). A similar way of bond formation is also observed for LaZn12.37 (Oshchapovsky et al., 2011a) and La5Zn2Sn (Oshchapovsky et al., 2011b) which were investigated previously. The density of states (DOS) plot confirms a metallic-type of conductivity of the title compound (Figure 3), and it is rather similar to the DOS plot for the LaZn12.37 compound.

Related literature top

For previous structural studies of the title compound, see: de Negri et al. (2008); Nowotny (1942). For general background, see: Andersen et al. (1986); Berche et al. (2009); Oshchapovsky et al. (2011a,b); Pavlyuk et al. (2009); Zelinska et al. (2004).

Experimental top

A small irregularly shaped single crystal of LaZn5 was selected by mechanical fragmentation of a sample with nominal composition LaZn4. The sample was prepared by mixing stoichiometric amounts of Zn and LaZn powders with subsequent pressing into a pellet. This pellet was sealed in an evacuated silica ampoule and annealed in a resistance furnace at 873 K for 30 days and subsequently quenched in cold water. No reaction between the alloy and the silica container was observed.

Refinement top

The highest peak of 1.11 e/Å3 is at (0; 0; 0.1905) and 0.81 Å away from the La1 atom. The deepest hole -0.71 e/Å3 is at (0; 0; 1/2) and 2.13 Å away from the same atom.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); 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).

Figures top
[Figure 1] Fig. 1. Projection of the unit cell, coordination polyhedra of the atoms and the covalent bonds in the LaZn5 compound. Atoms are given with their anisotropic displacement ellipsoids at the 99.99% probability level.
[Figure 2] Fig. 2. Isosurfaces of ELF drawn at the level 0.3 at z=0 and z=0.5 and sections for the LaZn5 compound.
[Figure 3] Fig. 3. Density of states plot for the LaZn5 compound.
lanthanum pentazinc top
Crystal data top
LaZn5Dx = 7.024 Mg m3
Mr = 465.86Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P6/mmmCell parameters from 1123 reflections
Hall symbol: -P 6 2θ = 4.3–27.5°
a = 5.4654 (17) ŵ = 36.05 mm1
c = 4.2574 (15) ÅT = 296 K
V = 110.13 (6) Å3Irregular shape, metallic grey
Z = 10.04 × 0.02 × 0.02 mm
F(000) = 207
Data collection top
73 independent reflections
Radiation source: fine-focus sealed tube62 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.069
ϕ and ω scansθmax = 27.5°, θmin = 4.3°
Absorption correction: multi-scan
(SADABS; Bruker, 2004)
h = 67
Tmin = 0.410, Tmax = 0.478k = 67
1123 measured reflectionsl = 55
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)] = 0.018 w = 1/[σ2(Fo2) + (0.P)2 + 0.1413P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.037(Δ/σ)max < 0.001
S = 1.17Δρmax = 1.11 e Å3
73 reflectionsΔρmin = 0.71 e Å3
9 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.022 (4)
0 constraints
Crystal data top
LaZn5Z = 1
Mr = 465.86Mo Kα radiation
Hexagonal, P6/mmmµ = 36.05 mm1
a = 5.4654 (17) ÅT = 296 K
c = 4.2574 (15) Å0.04 × 0.02 × 0.02 mm
V = 110.13 (6) Å3
Data collection top
73 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2004)
62 reflections with I > 2σ(I)
Tmin = 0.410, Tmax = 0.478Rint = 0.069
1123 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0189 parameters
wR(F2) = 0.0370 restraints
S = 1.17Δρmax = 1.11 e Å3
73 reflectionsΔρmin = 0.71 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
La10.00000.00000.00000.0099 (4)
Zn10.33330.66670.00000.0124 (4)
Zn20.50001.00000.50000.0121 (4)
Atomic displacement parameters (Å2) top
La10.0106 (4)0.0106 (4)0.0085 (6)0.0053 (2)0.0000.000
Zn10.0146 (5)0.0146 (5)0.0081 (8)0.0073 (3)0.0000.000
Zn20.0162 (5)0.0104 (6)0.0079 (6)0.0052 (3)0.0000.000
Geometric parameters (Å, º) top
La1—Zn1i3.1554 (10)Zn1—Zn2xiii2.6496 (7)
La1—Zn1ii3.1554 (10)Zn1—Zn1i3.1554 (10)
La1—Zn1iii3.1554 (10)Zn1—La1xiv3.1555 (10)
La1—Zn13.1555 (10)Zn1—La1xv3.1555 (10)
La1—Zn1iv3.1555 (10)Zn1—Zn1xvi3.1555 (10)
La1—Zn1v3.1555 (10)Zn1—Zn1v3.1555 (10)
La1—Zn2vi3.4640 (8)Zn2—Zn1xvii2.6496 (7)
La1—Zn2vii3.4640 (8)Zn2—Zn1xvi2.6496 (7)
La1—Zn2viii3.4640 (8)Zn2—Zn1xviii2.6496 (7)
La1—Zn2ix3.4640 (8)Zn2—Zn2xix2.7327 (8)
La1—Zn2iv3.4640 (8)Zn2—Zn2viii2.7327 (8)
La1—Zn2x3.4640 (8)Zn2—Zn2xx2.7327 (8)
Zn1—Zn2xi2.6496 (7)Zn2—Zn2vi2.7327 (8)
Zn1—Zn22.6496 (7)Zn2—La1xxi3.4640 (8)
Zn1—Zn2viii2.6496 (7)Zn2—La1xiv3.4640 (8)
Zn1—Zn2xii2.6496 (7)Zn2—La1xv3.4640 (8)
Zn1—Zn2vi2.6496 (7)Zn2—La1xxii3.4640 (8)
Zn1i—La1—Zn1ii120.0Zn2xiii—Zn1—La1xv72.679 (6)
Zn1i—La1—Zn160.0Zn2xi—Zn1—La172.679 (6)
Zn1ii—La1—Zn1180.0Zn2—Zn1—La1126.545 (13)
Zn1iii—La1—Zn1120.0Zn2viii—Zn1—La172.679 (6)
Zn1i—La1—Zn1iv60.0Zn2xii—Zn1—La1126.545 (13)
Zn1ii—La1—Zn1iv60.0Zn2vi—Zn1—La172.679 (5)
Zn1iii—La1—Zn1iv120.0Zn2xiii—Zn1—La172.679 (6)
Zn1iii—La1—Zn1v60.0Zn2xi—Zn1—Zn1xvi107.321 (5)
Zn1—La1—Zn1v60.0Zn2—Zn1—Zn1xvi53.455 (13)
Zn1iv—La1—Zn1v180.0Zn2viii—Zn1—Zn1xvi107.321 (6)
Zn1i—La1—Zn2vi46.905 (10)Zn2xii—Zn1—Zn1xvi53.455 (13)
Zn1ii—La1—Zn2vi133.095 (10)Zn2vi—Zn1—Zn1xvi107.321 (6)
Zn1iii—La1—Zn2vi133.095 (10)Zn2xiii—Zn1—Zn1xvi107.321 (6)
Zn1—La1—Zn2vi46.906 (10)Zn1i—Zn1—Zn1xvi120.0
Zn1i—La1—Zn2vii133.095 (10)La1—Zn1—Zn1xvi180.0
Zn1ii—La1—Zn2vii46.905 (10)Zn2xi—Zn1—Zn1v53.455 (13)
Zn1iii—La1—Zn2vii46.905 (10)Zn2—Zn1—Zn1v107.321 (5)
Zn1—La1—Zn2vii133.094 (10)Zn2viii—Zn1—Zn1v53.455 (13)
Zn1iv—La1—Zn2vii90.0Zn2xii—Zn1—Zn1v107.321 (6)
Zn1v—La1—Zn2vii90.0Zn2vi—Zn1—Zn1v107.321 (6)
Zn2vi—La1—Zn2vii180.0Zn2xiii—Zn1—Zn1v107.321 (6)
Zn1ii—La1—Zn2viii133.094 (9)La1xiv—Zn1—Zn1v60.0
Zn1—La1—Zn2viii46.906 (10)La1—Zn1—Zn1v60.0
Zn1iv—La1—Zn2viii133.094 (10)Zn1xvi—Zn1—Zn1v120.0
Zn1v—La1—Zn2viii46.906 (10)Zn1—Zn2—Zn1xvii180.0
Zn2vi—La1—Zn2viii46.463 (8)Zn1—Zn2—Zn1xvi73.09 (3)
Zn2vii—La1—Zn2viii133.537 (8)Zn1xvii—Zn2—Zn1xvi106.91 (3)
Zn1i—La1—Zn2ix90.0Zn1—Zn2—Zn1xviii106.91 (3)
Zn1ii—La1—Zn2ix46.906 (9)Zn1xvii—Zn2—Zn1xviii73.09 (3)
Zn1—La1—Zn2ix133.094 (10)Zn1—Zn2—Zn2xix121.043 (10)
Zn1iv—La1—Zn2ix46.906 (10)Zn1xvii—Zn2—Zn2xix58.958 (10)
Zn1v—La1—Zn2ix133.094 (10)Zn1xvi—Zn2—Zn2xix58.958 (10)
Zn2vi—La1—Zn2ix133.537 (8)Zn1xviii—Zn2—Zn2xix121.042 (10)
Zn2vii—La1—Zn2ix46.463 (8)Zn1—Zn2—Zn2viii58.957 (10)
Zn2viii—La1—Zn2ix180.0Zn1xvii—Zn2—Zn2viii121.042 (11)
Zn1i—La1—Zn2iv46.906 (9)Zn1xvi—Zn2—Zn2viii121.042 (10)
Zn1ii—La1—Zn2iv90.0Zn1xviii—Zn2—Zn2viii58.958 (10)
Zn1iii—La1—Zn2iv133.094 (9)Zn2xix—Zn2—Zn2viii180.0
Zn1—La1—Zn2iv90.0Zn1—Zn2—Zn2xx121.043 (10)
Zn1iv—La1—Zn2iv46.906 (10)Zn1xvii—Zn2—Zn2xx58.957 (10)
Zn1v—La1—Zn2iv133.094 (10)Zn1xvi—Zn2—Zn2xx58.957 (10)
Zn2vi—La1—Zn2iv46.463 (8)Zn1xviii—Zn2—Zn2xx121.043 (10)
Zn2vii—La1—Zn2iv133.537 (8)Zn2xix—Zn2—Zn2xx60.0
Zn2viii—La1—Zn2iv86.189 (19)Zn2viii—Zn2—Zn2xx120.0
Zn2ix—La1—Zn2iv93.811 (19)Zn1—Zn2—Zn2vi58.957 (10)
Zn1i—La1—Zn2x133.094 (9)Zn1xvii—Zn2—Zn2vi121.043 (10)
Zn1ii—La1—Zn2x90.0Zn1xvi—Zn2—Zn2vi121.043 (10)
Zn1iii—La1—Zn2x46.906 (9)Zn1xviii—Zn2—Zn2vi58.957 (10)
Zn1iv—La1—Zn2x133.094 (10)Zn2viii—Zn2—Zn2vi60.0
Zn1v—La1—Zn2x46.906 (10)Zn2xx—Zn2—Zn2vi180.0
Zn2vi—La1—Zn2x133.537 (8)Zn1—Zn2—La1xxi119.585 (15)
Zn2vii—La1—Zn2x46.463 (8)Zn1xvii—Zn2—La1xxi60.416 (15)
Zn2viii—La1—Zn2x93.811 (19)Zn1xvi—Zn2—La1xxi119.585 (15)
Zn2ix—La1—Zn2x86.189 (19)Zn1xviii—Zn2—La1xxi60.415 (15)
Zn2iv—La1—Zn2x180.0Zn2xix—Zn2—La1xxi66.768 (4)
Zn2xi—Zn1—Zn2145.358 (11)Zn2viii—Zn2—La1xxi113.232 (4)
Zn2xi—Zn1—Zn2viii106.91 (3)Zn2xx—Zn2—La1xxi113.232 (4)
Zn2—Zn1—Zn2viii62.09 (2)Zn2vi—Zn2—La1xxi66.768 (4)
Zn2xi—Zn1—Zn2xii62.09 (2)Zn1—Zn2—La1xiv60.415 (15)
Zn2—Zn1—Zn2xii106.91 (3)Zn1xvii—Zn2—La1xiv119.584 (15)
Zn2viii—Zn1—Zn2xii145.358 (11)Zn1xvi—Zn2—La1xiv60.415 (15)
Zn2xi—Zn1—Zn2vi145.358 (11)Zn1xviii—Zn2—La1xiv119.585 (15)
Zn2—Zn1—Zn2vi62.09 (2)Zn2xix—Zn2—La1xiv113.232 (5)
Zn2viii—Zn1—Zn2vi62.09 (2)Zn2viii—Zn2—La1xiv66.768 (4)
Zn2xii—Zn1—Zn2vi145.358 (11)Zn2xx—Zn2—La1xiv66.768 (5)
Zn2xi—Zn1—Zn2xiii62.09 (2)Zn2vi—Zn2—La1xiv113.232 (4)
Zn2—Zn1—Zn2xiii145.358 (11)La1xxi—Zn2—La1xiv180.0
Zn2viii—Zn1—Zn2xiii145.358 (11)Zn1—Zn2—La1xv60.415 (15)
Zn2xii—Zn1—Zn2xiii62.09 (2)Zn1xvii—Zn2—La1xv119.585 (15)
Zn2vi—Zn1—Zn2xiii106.91 (3)Zn1xvi—Zn2—La1xv60.416 (15)
Zn2xi—Zn1—Zn1i107.321 (6)Zn1xviii—Zn2—La1xv119.584 (15)
Zn2—Zn1—Zn1i107.321 (6)Zn2xix—Zn2—La1xv66.768 (4)
Zn2viii—Zn1—Zn1i107.321 (6)Zn2viii—Zn2—La1xv113.232 (4)
Zn2xii—Zn1—Zn1i107.321 (6)Zn2xx—Zn2—La1xv113.232 (4)
Zn2vi—Zn1—Zn1i53.455 (13)Zn2vi—Zn2—La1xv66.768 (4)
Zn2xiii—Zn1—Zn1i53.455 (13)La1xxi—Zn2—La1xv75.84 (3)
Zn2xi—Zn1—La1xiv72.679 (6)La1xiv—Zn2—La1xv104.16 (3)
Zn2—Zn1—La1xiv72.679 (6)Zn1—Zn2—La1xxii119.585 (15)
Zn2viii—Zn1—La1xiv72.679 (6)Zn1xvii—Zn2—La1xxii60.415 (15)
Zn2xii—Zn1—La1xiv72.679 (6)Zn1xvi—Zn2—La1xxii119.584 (15)
Zn2vi—Zn1—La1xiv126.545 (13)Zn1xviii—Zn2—La1xxii60.416 (15)
Zn2xiii—Zn1—La1xiv126.545 (13)Zn2xix—Zn2—La1xxii113.232 (4)
Zn1i—Zn1—La1xiv180.0Zn2viii—Zn2—La1xxii66.768 (4)
Zn2xi—Zn1—La1xv126.545 (13)Zn2xx—Zn2—La1xxii66.768 (4)
Zn2—Zn1—La1xv72.679 (6)Zn2vi—Zn2—La1xxii113.232 (4)
Zn2viii—Zn1—La1xv126.545 (13)La1xxi—Zn2—La1xxii104.16 (3)
Zn2xii—Zn1—La1xv72.679 (6)La1xiv—Zn2—La1xxii75.84 (3)
Zn2vi—Zn1—La1xv72.679 (6)La1xv—Zn2—La1xxii180.0
Symmetry codes: (i) x+1, y+1, z; (ii) x, y, z; (iii) x1, y1, z; (iv) x, y1, z; (v) x, y+1, z; (vi) xy+1, x, z; (vii) xy, x1, z1; (viii) y+1, xy+1, z; (ix) y+1, xy, z1; (x) x1, y1, z1; (xi) y+1, xy+1, z1; (xii) x, y, z1; (xiii) xy+1, x, z1; (xiv) x, y+1, z; (xv) x+1, y+1, z; (xvi) x+1, y+2, z; (xvii) x+1, y+2, z+1; (xviii) x, y, z+1; (xix) y+2, xy+2, z; (xx) xy+1, x+1, z; (xxi) x+1, y+1, z+1; (xxii) x, y+1, z+1.

Experimental details

Crystal data
Chemical formulaLaZn5
Crystal system, space groupHexagonal, P6/mmm
Temperature (K)296
a, c (Å)5.4654 (17), 4.2574 (15)
V3)110.13 (6)
Radiation typeMo Kα
µ (mm1)36.05
Crystal size (mm)0.04 × 0.02 × 0.02
Data collection
DiffractometerBruker APEXII CCD
Absorption correctionMulti-scan
(SADABS; Bruker, 2004)
Tmin, Tmax0.410, 0.478
No. of measured, independent and
observed [I > 2σ(I)] reflections
1123, 73, 62
(sin θ/λ)max1)0.650
R[F2 > 2σ(F2)], wR(F2), S 0.018, 0.037, 1.17
No. of reflections73
No. of parameters9
Δρmax, Δρmin (e Å3)1.11, 0.71

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2006) and VESTA (Momma & Izumi, 2008), publCIF (Westrip, 2010).


Follow Acta Cryst. E
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds