Non-isovalent substitution in a Zintl phase with the TiNiSi type structure, CaMg1–xAgxGe [x = 0.13 (3)]

Banenzoué, C.; Ponou, S.; Lambi, J.N.

doi:10.1107/S1600536809048454

inorganic compounds

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ISSN: 2056-9890

Volume 65| Part 12| December 2009| Page i90

doi:10.1107/S1600536809048454

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Non-isovalent substitution in a Zintl phase with the TiNiSi type structure, CaMg_1–xAg_xGe [x = 0.13 (3)]

Charles Banenzoué,^a Siméon Ponou ^b ^*‡ and John Ngolui Lambi ^c

^aDepartement de Chimie Inorganique, Université de Douala, Cameroon, ^bDepartment of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, SE 106 91 Stockholm, Sweden, and ^cDepartment of Chemistry, E.N.S. de Yaounde, BP 47 Yaounde, Cameroon
^*Correspondence e-mail: simeonp@inorg.su.se

(Received 31 October 2009; accepted 15 November 2009; online 21 November 2009)

Single crystals of the title Ag-substituted calcium magnesium germanide, CaMg_1–xAg_xGe [x = 0.13 (3)] were obtained from the reaction of the corresponding elements at high temperature. The compound crystallizes with the TiNiSi structure type (Pearson code oP12) and represents an Ag-substituted derivative of the Zintl phase CaMgGe in which a small fraction of the divalent Mg atoms have been replaced by monovalent Ag atoms. All three atoms in the asymmetric unit (Ca, Mg/Ag, Ge) occupy special positions with the same site symmetry (.m.). Although the end member CaAgGe has been reported in an isomorphic superstructure of the same TiNiSi type, higher Ag content in solid solutions could not be achieved due to competitive formation of other, perhaps more stable, phases.

Related literature

For the KHg₂ structure type, see: Duwell & Baenziger (1955 ) and for the TiNiSi structure type, see: Shoemaker & Shoemaker (1965 ); Eisenmann et al. (1972 ); Villars & Calvert (1991 ). For the structural systematics and properties of the TiNiSi structure type, see: Kauzlarich (1996 ); Landrum et al. (1998 ). For related compounds, see: Ponou & Lidin (2008 ); Ponou et al. (2007 ). For atomic radii, see: Pauling (1960 ).

Experimental

Crystal data

CaMg_0.87Ag_0.13Ge
M_r = 147.84
Orthorhombic, P n m a
a = 7.5128 (2) Å
b = 4.4573 (1) Å
c = 8.3911 (2) Å
V = 280.99 (1) Å³
Z = 4
Mo Kα radiation
μ = 13.43 mm⁻¹
T = 293 K
0.10 × 0.06 × 0.04 mm

Data collection

Oxford Xcalibur3 diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2007 $[Oxford Diffraction (2007). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ) T_min = 0.396, T_max = 0.584
2462 measured reflections
516 independent reflections
481 reflections with I > 2σ(I)
R_int = 0.026

Refinement

R[F² > 2σ(F²)] = 0.019
wR(F²) = 0.041
S = 1.10
516 reflections
21 parameters
Δρ_max = 0.89 e Å⁻³
Δρ_min = −0.44 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2007 $[Oxford Diffraction (2007). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ); cell refinement: CrysAlis RED (Oxford Diffraction, 2007 $[Oxford Diffraction (2007). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999 ); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809048454/hb5206sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809048454/hb5206Isup2.hkl

checkCIF report

Comment top

The solid solution CaMg_1–_xAg_xGe [x = 0.13 (3)] is iso-structural with the non-substituted ternary phase CaMgGe (Eisenmann et al., 1972). It crystallizes in the TiNiSi type (Space Group Pnma) with Ca, Mg/Ag, and Ge at Ti, Ni, and Si-positions, respectively. The TiNiSi type (Shoemaker & Shoemaker, 1965) which is well represented among ternary equiatomic phases (Villars & Calvert, 1991), is an ordered ternary derivative of the KHg₂ type (Duwell & Baenziger, 1955; Pearson code oI12). Hence, the structure consist of a three-dimensional four-connected anionic [Mg_1–_xAg_xGe] networks with the Ca cations sitting in large channels (Fig. 1). The anionic network may be constructed from two-dimensional sheets, similar to those in black phosphorus and running perpendicular to the a-axis, which are linked along the a-direction to form one-dimensional ladders of edge-sharing four-rings and channels of eight-rings running along the b-direction. The TiNiSi type is known to be very versatile and shows remarkable structural and electronic flexibility (Landrum et al., 1998). Meanwhile, a large number of compounds with the TiNiSi type like CaMgGe can be rationalized as Zintl phases (Kauzlarich, 1996) according to the ionic formulation Ca²⁺(Mg²⁺Ge^4–). Zinlt phases are known to be very sensitive to the electron count (Ponou et al., 2007). But, because of the above mentioned flexibility of the TiNiSi type, non-isovalent substitutions was expected without major structural distortion. Thus, since CaAgGe crystallizes in the isomorphic (i₃) superstructure of the TiNiSi type with a tripling of the a-axis (Ponou & Lidin, 2008), a wide stoichiometry breadth was expected in the system CaMg_1–_xAg_xGe. Eventually, the reaction of different starting mixtures with x = 1/4, 1/2, and 3/4, yielded almost the same composition (x = 0.10 – 0.13) within 3σ standard deviation. This indicates a narrow homogeneity range, meaning that in this class of materials, the inherent electronic rigidity of the Zintl phase may be conflicting with the otherwise remarkable flexibility of TiNiSi type.

CaMg_0.87 (1)Ag_0.13 (1)Ge is the Ag-richest phase that was structurally characterized. The unit-cell volume here (V = 280.99 (1) Å³) is quite similar to that of the non-substituted phase CaMgGe (V = 280.89 Å³), though the size of Mg is significantly larger than [Pauling's (1960) radii: Mg 1.600 Å, Ag 1.440 Å]. But, it should be noted that the later cell parameters were determined with much higher standard deviation (Eisenmann et al., 1972). In a reinvestigation of the CaMgGe structure (not reported), no indications of any superstructure were found.

Related literature top

For the KHg₂ structure type, see: Duwell & Baenziger (1955) and for the TiNiSi structure type, see: Shoemaker & Shoemaker (1965); Eisenmann et al. (1972); Villars & Calvert (1991). For the structural systematics and properties of the TiNiSi structure type, see: Kauzlarich (1996); Landrum et al. (1998). For related compounds, see: Ponou & Lidin (2008); Ponou et al. (2007).

For related literature, see: Pauling (1960).

Experimental top

Three different mixtures of the elements (all from ABCR GmbH, Karlsruhe, Germany) Ca (granule, 99.5%), Mg (pieces, 99.9%), Ag (60m powder, 99.9%), and Ge (50m powder, 99.999%), with compositions along the CaMg_1–xAg_xGe series with x = 1/4, 1/2, and 0.75 were loaded in a Niobium ampoules (approx. 9 mm diameter and 30 mm length) which were sealed on both ends by arc-melting and, in turn, enclosed in evacuated fused silica Schlenk tube to protect the former from air oxidation at high temperature. The ampoules were heated at 1273 K for 2 h, and cooled at a rate of 6 K/h to 923 K, where they are annealed for 24 h, then cooled down to room temperature by turning off the furnace. Semi quantitative EDX analysis of the single crystals confirmed the presenced of the four elements, and no eventual contaminant at the detection limit could be observed.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2007); cell refinement: CrysAlis RED (Oxford Diffraction, 2007); data reduction: CrysAlis RED (Oxford Diffraction, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

Fig. 1. : A perspective view of (I) with displacement ellipsoids drawn at 95% probability level. Ca, Mg/Ag, and Ge atoms are drawn as grey crossed, orange and blue spheres, respectively.

calcium magnesium silver germanide top

Crystal data top

CaMg_0.87Ag_0.13Ge	F(000) = 273.5
M_r = 147.84	D_x = 3.495 Mg m⁻³
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 2462 reflections
a = 7.5128 (2) Å	θ = 4.9–32.1°
b = 4.4573 (1) Å	µ = 13.43 mm⁻¹
c = 8.3911 (2) Å	T = 293 K
V = 280.99 (1) Å³	Irregular block, grey
Z = 4	0.10 × 0.06 × 0.04 mm

Data collection top

Oxford Xcalibur3 diffractometer	516 independent reflections
Radiation source: Enhance (Mo) X-ray Source	481 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.026
Detector resolution: 16.5467 pixels mm^-1	θ_max = 32.1°, θ_min = 4.6°
ω scans	h = −8→10
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2007)	k = −5→6
T_min = 0.396, T_max = 0.584	l = −12→12
2462 measured reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0233P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.019	(Δ/σ)_max < 0.001
wR(F²) = 0.041	Δρ_max = 0.89 e Å⁻³
S = 1.10	Δρ_min = −0.44 e Å⁻³
516 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
21 parameters	Extinction coefficient: 0.084 (3)

Crystal data top

CaMg_0.87Ag_0.13Ge	V = 280.99 (1) Å³
M_r = 147.84	Z = 4
Orthorhombic, Pnma	Mo Kα radiation
a = 7.5128 (2) Å	µ = 13.43 mm⁻¹
b = 4.4573 (1) Å	T = 293 K
c = 8.3911 (2) Å	0.10 × 0.06 × 0.04 mm

Data collection top

Oxford Xcalibur3 diffractometer	516 independent reflections
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2007)	481 reflections with I > 2σ(I)
T_min = 0.396, T_max = 0.584	R_int = 0.026
2462 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.019	21 parameters
wR(F²) = 0.041	0 restraints
S = 1.10	Δρ_max = 0.89 e Å⁻³
516 reflections	Δρ_min = −0.44 e Å⁻³

Special details top

Experimental. CrysAlis RED, (Oxford Diffraction, 2007) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
Ge1	0.76875 (4)	0.2500	0.38457 (3)	0.00994 (12)
Ag1	0.14396 (8)	0.2500	0.43738 (7)	0.0140 (2)	0.1309 (15)
Mg1	0.14396 (8)	0.2500	0.43738 (7)	0.0140 (2)	0.8691 (15)
Ca1	0.51982 (7)	0.2500	0.68206 (7)	0.01280 (14)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ge1	0.00976 (16)	0.00827 (16)	0.01178 (17)	0.000	−0.00007 (9)	0.000
Ag1	0.0172 (4)	0.0124 (3)	0.0124 (3)	0.000	−0.0020 (2)	0.000
Mg1	0.0172 (4)	0.0124 (3)	0.0124 (3)	0.000	−0.0020 (2)	0.000
Ca1	0.0119 (3)	0.0134 (3)	0.0131 (3)	0.000	−0.00085 (18)	0.000

Geometric parameters (Å, º) top

Ge1—Mg1ⁱ	2.7621 (4)	Ag1—Ag1^viii	3.2788 (9)
Ge1—Ag1ⁱ	2.7621 (4)	Ag1—Mg1^ix	3.2788 (9)
Ge1—Mg1ⁱⁱ	2.7621 (4)	Ag1—Ag1^ix	3.2788 (9)
Ge1—Ag1ⁱⁱ	2.7621 (4)	Ag1—Ca1^x	3.3267 (8)
Ge1—Ag1ⁱⁱⁱ	2.8535 (7)	Ag1—Ca1^xi	3.3273 (6)
Ge1—Mg1ⁱⁱⁱ	2.8535 (7)	Ag1—Ca1^xii	3.3273 (6)
Ge1—Mg1^iv	2.8596 (7)	Ag1—Ca1	3.4912 (8)
Ge1—Ag1^iv	2.8596 (7)	Ca1—Ge1ⁱⁱ	3.1590 (4)
Ge1—Ca1	3.1191 (6)	Ca1—Ge1ⁱ	3.1590 (4)
Ge1—Ca1ⁱⁱ	3.1590 (4)	Ca1—Ge1^xiii	3.2214 (4)
Ge1—Ca1ⁱ	3.1590 (4)	Ca1—Ge1^xiv	3.2214 (4)
Ge1—Ca1^v	3.2214 (4)	Ca1—Mg1^xv	3.3267 (8)
Ag1—Ge1ⁱ	2.7621 (4)	Ca1—Ag1^xv	3.3267 (8)
Ag1—Ge1ⁱⁱ	2.7621 (4)	Ca1—Mg1^xvi	3.3273 (6)
Ag1—Ge1^vi	2.8535 (7)	Ca1—Ag1^xvi	3.3273 (6)
Ag1—Ge1^vii	2.8596 (7)	Ca1—Mg1^xvii	3.3273 (6)
Ag1—Mg1^viii	3.2788 (9)	Ca1—Ag1^xvii	3.3273 (6)

Mg1ⁱ—Ge1—Ag1ⁱ	0.00 (2)	Ge1ⁱ—Ag1—Ca1^x	63.086 (14)
Mg1ⁱ—Ge1—Mg1ⁱⁱ	107.58 (2)	Ge1ⁱⁱ—Ag1—Ca1^x	63.086 (14)
Ag1ⁱ—Ge1—Mg1ⁱⁱ	107.58 (2)	Ge1^vi—Ag1—Ca1^x	82.653 (19)
Mg1ⁱ—Ge1—Ag1ⁱⁱ	107.58 (2)	Ge1^vii—Ag1—Ca1^x	177.14 (3)
Ag1ⁱ—Ge1—Ag1ⁱⁱ	107.58 (2)	Mg1^viii—Ag1—Ca1^x	60.49 (2)
Mg1ⁱⁱ—Ge1—Ag1ⁱⁱ	0.0	Ag1^viii—Ag1—Ca1^x	60.49 (2)
Mg1ⁱ—Ge1—Ag1ⁱⁱⁱ	71.425 (16)	Mg1^ix—Ag1—Ca1^x	60.49 (2)
Ag1ⁱ—Ge1—Ag1ⁱⁱⁱ	71.425 (16)	Ag1^ix—Ag1—Ca1^x	60.49 (2)
Mg1ⁱⁱ—Ge1—Ag1ⁱⁱⁱ	71.425 (16)	Ge1ⁱ—Ag1—Ca1^xi	167.565 (19)
Ag1ⁱⁱ—Ge1—Ag1ⁱⁱⁱ	71.425 (16)	Ge1ⁱⁱ—Ag1—Ca1^xi	84.010 (9)
Mg1ⁱ—Ge1—Mg1ⁱⁱⁱ	71.425 (16)	Ge1^vi—Ag1—Ca1^xi	62.269 (13)
Ag1ⁱ—Ge1—Mg1ⁱⁱⁱ	71.425 (16)	Ge1^vii—Ag1—Ca1^xi	60.851 (14)
Mg1ⁱⁱ—Ge1—Mg1ⁱⁱⁱ	71.425 (16)	Mg1^viii—Ag1—Ca1^xi	60.470 (16)
Ag1ⁱⁱ—Ge1—Mg1ⁱⁱⁱ	71.425 (16)	Ag1^viii—Ag1—Ca1^xi	60.470 (16)
Ag1ⁱⁱⁱ—Ge1—Mg1ⁱⁱⁱ	0.00 (2)	Mg1^ix—Ag1—Ca1^xi	114.69 (3)
Mg1ⁱ—Ge1—Mg1^iv	126.076 (12)	Ag1^ix—Ag1—Ca1^xi	114.69 (3)
Ag1ⁱ—Ge1—Mg1^iv	126.076 (12)	Ca1^x—Ag1—Ca1^xi	120.958 (16)
Mg1ⁱⁱ—Ge1—Mg1^iv	126.075 (12)	Ge1ⁱ—Ag1—Ca1^xii	84.010 (9)
Ag1ⁱⁱ—Ge1—Mg1^iv	126.075 (12)	Ge1ⁱⁱ—Ag1—Ca1^xii	167.565 (19)
Ag1ⁱⁱⁱ—Ge1—Mg1^iv	118.073 (19)	Ge1^vi—Ag1—Ca1^xii	62.269 (13)
Mg1ⁱⁱⁱ—Ge1—Mg1^iv	118.073 (19)	Ge1^vii—Ag1—Ca1^xii	60.851 (14)
Mg1ⁱ—Ge1—Ag1^iv	126.076 (12)	Mg1^viii—Ag1—Ca1^xii	114.69 (3)
Ag1ⁱ—Ge1—Ag1^iv	126.076 (12)	Ag1^viii—Ag1—Ca1^xii	114.69 (3)
Mg1ⁱⁱ—Ge1—Ag1^iv	126.075 (12)	Mg1^ix—Ag1—Ca1^xii	60.470 (16)
Ag1ⁱⁱ—Ge1—Ag1^iv	126.075 (12)	Ag1^ix—Ag1—Ca1^xii	60.470 (16)
Ag1ⁱⁱⁱ—Ge1—Ag1^iv	118.073 (19)	Ca1^x—Ag1—Ca1^xii	120.958 (16)
Mg1ⁱⁱⁱ—Ge1—Ag1^iv	118.073 (19)	Ca1^xi—Ag1—Ca1^xii	84.104 (19)
Mg1^iv—Ge1—Ag1^iv	0.00 (2)	Ge1ⁱ—Ag1—Ca1	59.328 (12)
Mg1ⁱ—Ge1—Ca1	73.110 (14)	Ge1ⁱⁱ—Ag1—Ca1	59.328 (12)
Ag1ⁱ—Ge1—Ca1	73.110 (14)	Ge1^vi—Ag1—Ca1	152.91 (2)
Mg1ⁱⁱ—Ge1—Ca1	73.110 (14)	Ge1^vii—Ag1—Ca1	106.88 (2)
Ag1ⁱⁱ—Ge1—Ca1	73.110 (14)	Mg1^viii—Ag1—Ca1	110.19 (2)
Ag1ⁱⁱⁱ—Ge1—Ca1	117.905 (19)	Ag1^viii—Ag1—Ca1	110.19 (2)
Mg1ⁱⁱⁱ—Ge1—Ca1	117.905 (19)	Mg1^ix—Ag1—Ca1	110.19 (2)
Mg1^iv—Ge1—Ca1	124.022 (18)	Ag1^ix—Ag1—Ca1	110.19 (2)
Ag1^iv—Ge1—Ca1	124.022 (18)	Ca1^x—Ag1—Ca1	70.261 (14)
Mg1ⁱ—Ge1—Ca1ⁱⁱ	145.884 (18)	Ca1^xi—Ag1—Ca1	132.669 (11)
Ag1ⁱ—Ge1—Ca1ⁱⁱ	145.884 (18)	Ca1^xii—Ag1—Ca1	132.669 (11)
Mg1ⁱⁱ—Ge1—Ca1ⁱⁱ	71.906 (14)	Ge1—Ca1—Ge1ⁱⁱ	105.655 (14)
Ag1ⁱⁱ—Ge1—Ca1ⁱⁱ	71.906 (14)	Ge1—Ca1—Ge1ⁱ	105.655 (14)
Ag1ⁱⁱⁱ—Ge1—Ca1ⁱⁱ	134.864 (8)	Ge1ⁱⁱ—Ca1—Ge1ⁱ	89.738 (15)
Mg1ⁱⁱⁱ—Ge1—Ca1ⁱⁱ	134.864 (8)	Ge1—Ca1—Ge1^xiii	97.268 (13)
Mg1^iv—Ge1—Ca1ⁱⁱ	66.910 (14)	Ge1ⁱⁱ—Ca1—Ge1^xiii	156.90 (2)
Ag1^iv—Ge1—Ca1ⁱⁱ	66.910 (14)	Ge1ⁱ—Ca1—Ge1^xiii	86.771 (6)
Ca1—Ge1—Ca1ⁱⁱ	74.345 (14)	Ge1—Ca1—Ge1^xiv	97.268 (13)
Mg1ⁱ—Ge1—Ca1ⁱ	71.906 (14)	Ge1ⁱⁱ—Ca1—Ge1^xiv	86.771 (6)
Ag1ⁱ—Ge1—Ca1ⁱ	71.906 (14)	Ge1ⁱ—Ca1—Ge1^xiv	156.90 (2)
Mg1ⁱⁱ—Ge1—Ca1ⁱ	145.884 (18)	Ge1^xiii—Ca1—Ge1^xiv	87.548 (14)
Ag1ⁱⁱ—Ge1—Ca1ⁱ	145.884 (18)	Ge1—Ca1—Mg1^xv	126.88 (2)
Ag1ⁱⁱⁱ—Ge1—Ca1ⁱ	134.864 (8)	Ge1ⁱⁱ—Ca1—Mg1^xv	111.240 (16)
Mg1ⁱⁱⁱ—Ge1—Ca1ⁱ	134.864 (8)	Ge1ⁱ—Ca1—Mg1^xv	111.240 (16)
Mg1^iv—Ge1—Ca1ⁱ	66.910 (14)	Ge1^xiii—Ca1—Mg1^xv	49.866 (10)
Ag1^iv—Ge1—Ca1ⁱ	66.910 (14)	Ge1^xiv—Ca1—Mg1^xv	49.866 (10)
Ca1—Ge1—Ca1ⁱ	74.345 (14)	Ge1—Ca1—Ag1^xv	126.88 (2)
Ca1ⁱⁱ—Ge1—Ca1ⁱ	89.738 (15)	Ge1ⁱⁱ—Ca1—Ag1^xv	111.240 (16)
Mg1ⁱ—Ge1—Ca1^v	136.591 (17)	Ge1ⁱ—Ca1—Ag1^xv	111.240 (16)
Ag1ⁱ—Ge1—Ca1^v	136.591 (17)	Ge1^xiii—Ca1—Ag1^xv	49.866 (10)
Mg1ⁱⁱ—Ge1—Ca1^v	67.048 (15)	Ge1^xiv—Ca1—Ag1^xv	49.866 (10)
Ag1ⁱⁱ—Ge1—Ca1^v	67.048 (15)	Mg1^xv—Ca1—Ag1^xv	0.000 (6)
Ag1ⁱⁱⁱ—Ge1—Ca1^v	66.097 (13)	Ge1—Ca1—Mg1^xvi	137.481 (10)
Mg1ⁱⁱⁱ—Ge1—Ca1^v	66.097 (13)	Ge1ⁱⁱ—Ca1—Mg1^xvi	109.433 (18)
Mg1^iv—Ge1—Ca1^v	70.325 (14)	Ge1ⁱ—Ca1—Mg1^xvi	52.239 (12)
Ag1^iv—Ge1—Ca1^v	70.325 (14)	Ge1^xiii—Ca1—Mg1^xvi	51.633 (12)
Ca1—Ge1—Ca1^v	135.874 (8)	Ge1^xiv—Ca1—Mg1^xvi	107.823 (18)
Ca1ⁱⁱ—Ge1—Ca1^v	75.935 (6)	Mg1^xv—Ca1—Mg1^xvi	59.042 (16)
Ca1ⁱ—Ge1—Ca1^v	137.148 (11)	Ag1^xv—Ca1—Mg1^xvi	59.042 (16)
Ge1ⁱ—Ag1—Ge1ⁱⁱ	107.58 (2)	Ge1—Ca1—Ag1^xvi	137.481 (10)
Ge1ⁱ—Ag1—Ge1^vi	108.575 (16)	Ge1ⁱⁱ—Ca1—Ag1^xvi	109.433 (18)
Ge1ⁱⁱ—Ag1—Ge1^vi	108.575 (16)	Ge1ⁱ—Ca1—Ag1^xvi	52.239 (12)
Ge1ⁱ—Ag1—Ge1^vii	115.669 (14)	Ge1^xiii—Ca1—Ag1^xvi	51.633 (12)
Ge1ⁱⁱ—Ag1—Ge1^vii	115.669 (14)	Ge1^xiv—Ca1—Ag1^xvi	107.823 (18)
Ge1^vi—Ag1—Ge1^vii	100.20 (2)	Mg1^xv—Ca1—Ag1^xvi	59.042 (16)
Ge1ⁱ—Ag1—Mg1^viii	122.12 (3)	Ag1^xv—Ca1—Ag1^xvi	59.042 (16)
Ge1ⁱⁱ—Ag1—Mg1^viii	55.586 (12)	Mg1^xvi—Ca1—Ag1^xvi	0.00 (3)
Ge1^vi—Ag1—Mg1^viii	52.990 (18)	Ge1—Ca1—Mg1^xvii	137.481 (10)
Ge1^vii—Ag1—Mg1^viii	121.27 (2)	Ge1ⁱⁱ—Ca1—Mg1^xvii	52.239 (12)
Ge1ⁱ—Ag1—Ag1^viii	122.12 (3)	Ge1ⁱ—Ca1—Mg1^xvii	109.433 (18)
Ge1ⁱⁱ—Ag1—Ag1^viii	55.586 (12)	Ge1^xiii—Ca1—Mg1^xvii	107.823 (18)
Ge1^vi—Ag1—Ag1^viii	52.990 (18)	Ge1^xiv—Ca1—Mg1^xvii	51.633 (12)
Ge1^vii—Ag1—Ag1^viii	121.27 (2)	Mg1^xv—Ca1—Mg1^xvii	59.042 (16)
Mg1^viii—Ag1—Ag1^viii	0.000 (16)	Ag1^xv—Ca1—Mg1^xvii	59.042 (16)
Ge1ⁱ—Ag1—Mg1^ix	55.586 (12)	Mg1^xvi—Ca1—Mg1^xvii	84.104 (19)
Ge1ⁱⁱ—Ag1—Mg1^ix	122.12 (3)	Ag1^xvi—Ca1—Mg1^xvii	84.104 (19)
Ge1^vi—Ag1—Mg1^ix	52.990 (18)	Ge1—Ca1—Ag1^xvii	137.481 (10)
Ge1^vii—Ag1—Mg1^ix	121.27 (2)	Ge1ⁱⁱ—Ca1—Ag1^xvii	52.239 (12)
Mg1^viii—Ag1—Mg1^ix	85.64 (3)	Ge1ⁱ—Ca1—Ag1^xvii	109.433 (18)
Ag1^viii—Ag1—Mg1^ix	85.64 (3)	Ge1^xiii—Ca1—Ag1^xvii	107.823 (18)
Ge1ⁱ—Ag1—Ag1^ix	55.586 (12)	Ge1^xiv—Ca1—Ag1^xvii	51.633 (12)
Ge1ⁱⁱ—Ag1—Ag1^ix	122.12 (3)	Mg1^xv—Ca1—Ag1^xvii	59.042 (16)
Ge1^vi—Ag1—Ag1^ix	52.990 (18)	Ag1^xv—Ca1—Ag1^xvii	59.042 (16)
Ge1^vii—Ag1—Ag1^ix	121.27 (2)	Mg1^xvi—Ca1—Ag1^xvii	84.104 (19)
Mg1^viii—Ag1—Ag1^ix	85.64 (3)	Ag1^xvi—Ca1—Ag1^xvii	84.104 (19)
Ag1^viii—Ag1—Ag1^ix	85.64 (3)	Mg1^xvii—Ca1—Ag1^xvii	0.00 (2)
Mg1^ix—Ag1—Ag1^ix	0.000 (16)

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

Experimental details

Crystal data
Chemical formula	CaMg_0.87Ag_0.13Ge
M_r	147.84
Crystal system, space group	Orthorhombic, Pnma
Temperature (K)	293
a, b, c (Å)	7.5128 (2), 4.4573 (1), 8.3911 (2)
V (Å³)	280.99 (1)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	13.43
Crystal size (mm)	0.10 × 0.06 × 0.04

Data collection
Diffractometer	Oxford Xcalibur3 diffractometer
Absorption correction	Multi-scan (CrysAlis RED; Oxford Diffraction, 2007)
T_min, T_max	0.396, 0.584
No. of measured, independent and observed [I > 2σ(I)] reflections	2462, 516, 481
R_int	0.026
(sin θ/λ)_max (Å⁻¹)	0.747

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.019, 0.041, 1.10
No. of reflections	516
No. of parameters	21
Δρ_max, Δρ_min (e Å⁻³)	0.89, −0.44

Computer programs: CrysAlis CCD (Oxford Diffraction, 2007), CrysAlis RED (Oxford Diffraction, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 1999), SHELXTL (Sheldrick, 2008).

Footnotes

‡Permanent address: Department of Chemistry, E.N.S. de Yaounde BP 47 Yaounde Cameroon.

Acknowledgements

Financial support from the Wenner-Gren Foundation in gratefully acknowledged. The authors thank Professor Sven Lidin (Stockholm University, Sweden) for continuous support.

References

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