Crystal structure of the inter-metallic compound SrCdPt.

The crystal structure of the title compound, strontium cadmium platinum, adopts the TiNiSi structure type with the Sr atoms on the Ti, the Cd atoms on the Ni and the Pt atoms on the Si positions, respectively. The Pt atoms form cadmium-centred tetra-hedra that are condensed into a three-dimensional network with channels parallel to the b-axis direction in which the Sr atoms are located. The latter are bonded to each other in the form of six-membered rings with chair conformations. All atoms in the SrCdPt structure are situated on a mirror plane.

Chemical context

Exploratory synthesis of polar inter­metallic phases has proven to be productive in terms of novel compositions, new and unprecedented structures, and unusual bonding regimes (Corbett, 2010 ▶). Platinum has participated significantly in the formation of ternary inter­metallic compounds. Together with indium, a number of platinum phases have been reported, for example BaPtIn3 (Palasyuk & Corbett, 2007 ▶), SrPtIn (Hoffmann & Pöttgen, 1999 ▶), CaPtIn2 (Hoffmann et al., 1999 ▶) or Ca2Pt2In (Muts et al., 2007 ▶). Some other ternary inter­metallic compounds of platinum with cadmium, viz. Ca2CdPt2 (Samal & Corbett, 2012 ▶), Ca6Pt8Cd16, (Ba/Sr)Cd4Pt2 (Samal et al., 2013 ▶), Ca6Cd11Pt (Gulo et al., 2013 ▶) and CaCdPt (Kersting et al., 2013 ▶) have been isolated recently. They demonstrate the diversity of the structures types adopted. In this communication, we present the crystal structure of SrCdPt.

Structural commentary

SrCdPt crystallizes in the TiNiSi structure type. The titanium, nickel, and silicon sites are occupied by strontium, cadmium, and platinum, respectively, in the structure of the title compound. Although platinum and nickel are in the same group in the periodic table, the platinum in SrCdPt occupies the silicon site and not the nickel site because platinum is the most electronegative metal in this structure, just like silicon in TiNiSi. A count of 56 valence electrons per cell is found in SrCdPt [(Sr:2 + Cd:2 +Pt:10) × 4] whilst TiNiSi contains only 32 valence electrons per cell.

In the compounds of the TiNiSi structure family, the metals listed first in the formula are linked to each other, forming six-membered rings in chair, half-chair, or boat conformations. The adopted conformation is not a function of the electron count, but is due to the nature of the respective metal (Landrum et al., 1998 ▶). In the SrCdPt structure, the strontium atoms construct six-membered rings with chair conformations and Sr—Sr distances of 3.870 (2) Å, which is significantly shorter than the sum of the covalent radii of 4.30 Å (Emsley, 1999 ▶), indicating strong bonding inter­actions between them (Fig. 1 ▶). The existence of such strong Sr—Sr bonds is not noticeable in SrCd4Pt2 (Samal et al., 2013 ▶). The platinum atoms in the structure of SrCdPt form zigzag chains of edge-sharing cadmium-centred tetra­hedra parallel to the b-axis direction. These chains are condensed via common corners with adjacent chains, building up the three-dimensional network with channels parallel to the b-axis direction in which the Sr atoms reside, as illustrated in Fig. 2 ▶.

Figure 1

Projection of the crystal structure of SrCdPt approximately along [100]. Displacement ellipsoids are represented at the 90% probability level.

Figure 2

View of zigzag chains of cadmium-centred tetra­hedra of Pt atoms forming channels along the b-axis direction in the structure of SrCdPt.

Strontium has an overall coordination number of 15 and is surrounded by four other strontium, six cadmium, and five platinum atoms. The Sr—Cd distances range from 3.3932 (13) to 3.6124 (17) Å, whereas the Sr—Pt distances vary only slightly, from 3.1943 (11) to 3.2238 (10) Å. Cadmium is located at a site that is surrounded by six strontium and four platinum atoms, whilst platinum has a coordination number of 9 defined by five strontium and four cadmium atoms. The environment of each atom in this structure is represented in Fig. 3 ▶. The inter­atomic distances (Sr—Cd, Sr—Pt, and Cd—Pt) are in good agreement with those found in the structures of some other ternary compounds in the alkaline earth–Cd–Pt system (Samal & Corbett, 2012 ▶; Samal et al., 2013 ▶; Gulo et al., 2013 ▶; Kersting et al., 2013 ▶). In SrCdPt, the shortest Cd—Cd distance of 3.3197 (15) Å is too long to be considered as a bond. It is significantly longer than the sum of the covalent radii of 2.90 Å (Emsley, 1999 ▶). In contrast, cadmium atoms are bonded together, forming Cd4 tetra­hedra in SrCd4Pt2, Cd8 tetra­hedral stars in Ca6Cd16Pt8, and Cd7 penta­gonal bipyramids in Ca6Cd11Pt.

Figure 3

Coordination polyhedra of Sr, Cd, and Pt atoms in the structure of SrCdPt.

Database survey

A search of the Pearson’s Crystal Data – Crystal Structure Database for Inorganic Compounds (Villars & Cenzual, 2011 ▶) for the TiNiSi family of compounds returned 1101 entries with the same prototype. Two ternary compounds of them include strontium and platinum, one compound includes strontium with cadmium, and no compound had formed so far including both cadmium and platinum.

Synthesis and crystallization

Starting materials for the synthesis of the title compound were ingots of strontium (99.9+%, Alfa Aesar), cadmium powder (99.9+%, Alfa Aesar) and platinum powder (99.95%, Chempur). A stoichiometric mixture of these elements was weighed and loaded into a tantalum ampoule in an argon-filled dry box. The tantalum ampoule was then weld-sealed under an argon atmosphere and subsequently enclosed in an evacuated silica jacket. The sample was then heated to 1123 K for 15 h, followed by equilibration at 923 K for 4 days, and slow cooling to room temperature. The synthesis procedures were similar to general methods applied in some previous experiments (Gulo et al., 2013 ▶).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▶. The highest remaining electron density is located 0.98 Å from the Pt site.

Table 1

Experimental details

Crystal data
Chemical formula	SrCdPt
M r	395.11
Crystal system, space group	Orthorhombic, P n m a
Temperature (K)	298
a, b, c ()	7.5748(15), 4.4774(9), 8.6383(17)
V (3)	292.97(10)
Z	4
Radiation type	Mo K
(mm1)	72.61
Crystal size (mm)	0.05 0.04 0.03
Data collection
Diffractometer	Bruker SMART CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2001 ▶)
T min, T max	0.043, 0.113
No. of measured, independent and observed [I > 2(I)] reflections	2231, 381, 338
R int	0.061
(sin /)max (1)	0.664
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.030, 0.066, 1.07
No. of reflections	381
No. of parameters	19
max, min (e 3)	2.22, 1.87

Computer programs: SMART and SAINT (Bruker, 2001 ▶), SHELXS97 and SHELXL97 (Sheldrick, 2008 ▶) and DIAMOND (Brandenburg, 2006 ▶).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S1600536814025823/wm5093sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536814025823/wm5093Isup2.hkl

CCDC reference: 1036051

Additional supporting information: crystallographic information; 3D view; checkCIF report

SrCdPt	F(000) = 656
Mr = 395.11	Dx = 8.958 Mg m−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 25 reflections
a = 7.5748 (15) Å	θ = 12–18°
b = 4.4774 (9) Å	µ = 72.61 mm−1
c = 8.6383 (17) Å	T = 298 K
V = 292.97 (10) Å3	Block, brown
Z = 4	0.05 × 0.04 × 0.03 mm

Bruker SMART CCD diffractometer	381 independent reflections
Radiation source: fine-focus sealed tube	338 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.061
Detector resolution: 0 pixels mm-1	θmax = 28.1°, θmin = 3.6°
ω scans	h = −9→9
Absorption correction: multi-scan (SADABS; Bruker, 2001)	k = −5→5
Tmin = 0.043, Tmax = 0.113	l = −11→11
2231 measured reflections

Refinement on F2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.030	Secondary atom site location: difference Fourier map
wR(F2) = 0.066	w = 1/[σ2(Fo2) + (0.0307P)2] where P = (Fo2 + 2Fc2)/3
S = 1.07	(Δ/σ)max < 0.001
381 reflections	Δρmax = 2.22 e Å−3
19 parameters	Δρmin = −1.87 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
Pt	0.27016 (7)	0.2500	0.37717 (7)	0.0150 (2)
Cd	0.14353 (12)	0.2500	0.06550 (12)	0.0140 (3)
Sr	0.02883 (16)	0.2500	0.68094 (16)	0.0141 (3)

	U11	U22	U33	U12	U13	U23
Pt	0.0175 (3)	0.0114 (3)	0.0160 (4)	0.000	0.0005 (2)	0.000
Cd	0.0173 (6)	0.0120 (5)	0.0127 (6)	0.000	0.0013 (4)	0.000
Sr	0.0161 (7)	0.0116 (6)	0.0147 (7)	0.000	0.0006 (5)	0.000

Pt—Cdi	2.8435 (8)	Cd—Srxi	3.4336 (17)
Pt—Cdii	2.8435 (8)	Cd—Srv	3.4879 (13)
Pt—Cd	2.8581 (13)	Cd—Sriv	3.4879 (13)
Pt—Cdiii	2.8713 (12)	Cd—Sriii	3.6124 (17)
Pt—Sriv	3.1943 (11)	Sr—Pti	3.1943 (11)
Pt—Srv	3.1943 (11)	Sr—Ptii	3.1943 (11)
Pt—Sr	3.1980 (15)	Sr—Ptvi	3.2238 (10)
Pt—Srvi	3.2238 (10)	Sr—Ptvii	3.2238 (10)
Pt—Srvii	3.2238 (10)	Sr—Cdvii	3.3932 (13)
Cd—Ptiv	2.8435 (8)	Sr—Cdvi	3.3932 (13)
Cd—Ptv	2.8435 (8)	Sr—Cdxii	3.4336 (17)
Cd—Ptviii	2.8713 (12)	Sr—Cdi	3.4879 (13)
Cd—Cdix	3.3197 (15)	Sr—Cdii	3.4879 (13)
Cd—Cdx	3.3197 (15)	Sr—Cdviii	3.6124 (17)
Cd—Srvii	3.3932 (13)	Sr—Srvi	3.870 (2)
Cd—Srvi	3.3932 (13)
Cdi—Pt—Cdii	103.87 (4)	Ptviii—Cd—Sriv	130.66 (3)
Cdi—Pt—Cd	128.03 (2)	Cdix—Cd—Sriv	97.51 (2)
Cdii—Pt—Cd	128.03 (2)	Cdx—Cd—Sriv	175.11 (5)
Cdi—Pt—Cdiii	71.03 (3)	Srvii—Cd—Sriv	120.84 (3)
Cdii—Pt—Cdiii	71.03 (3)	Srvi—Cd—Sriv	70.47 (2)
Cd—Pt—Cdiii	119.54 (3)	Srxi—Cd—Sriv	117.17 (3)
Cdi—Pt—Sriv	138.23 (3)	Srv—Cd—Sriv	79.86 (4)
Cdii—Pt—Sriv	69.04 (3)	Ptiv—Cd—Sriii	58.47 (2)
Cd—Pt—Sriv	70.13 (3)	Ptv—Cd—Sriii	58.47 (2)
Cdiii—Pt—Sriv	67.79 (3)	Pt—Cd—Sriii	106.50 (4)
Cdi—Pt—Srv	69.04 (3)	Ptviii—Cd—Sriii	153.82 (4)
Cdii—Pt—Srv	138.23 (3)	Cdix—Cd—Sriii	109.17 (4)
Cd—Pt—Srv	70.13 (3)	Cdx—Cd—Sriii	109.17 (4)
Cdiii—Pt—Srv	67.79 (3)	Srvii—Cd—Sriii	133.73 (2)
Sriv—Pt—Srv	88.99 (4)	Srvi—Cd—Sriii	133.73 (2)
Cdi—Pt—Sr	70.24 (3)	Srxi—Cd—Sriii	68.55 (3)
Cdii—Pt—Sr	70.24 (3)	Srv—Cd—Sriii	66.02 (3)
Cd—Pt—Sr	125.53 (4)	Sriv—Cd—Sriii	66.02 (3)
Cdiii—Pt—Sr	114.93 (4)	Pti—Sr—Ptii	88.99 (4)
Sriv—Pt—Sr	135.06 (2)	Pti—Sr—Pt	99.38 (3)
Srv—Pt—Sr	135.06 (2)	Ptii—Sr—Pt	99.38 (3)
Cdi—Pt—Srvi	142.88 (3)	Pti—Sr—Ptvi	154.71 (5)
Cdii—Pt—Srvi	72.78 (3)	Ptii—Sr—Ptvi	86.033 (18)
Cd—Pt—Srvi	67.51 (3)	Pt—Sr—Ptvi	105.89 (3)
Cdiii—Pt—Srvi	135.959 (18)	Pti—Sr—Ptvii	86.033 (18)
Sriv—Pt—Srvi	76.441 (19)	Ptii—Sr—Ptvii	154.71 (5)
Srv—Pt—Srvi	137.64 (2)	Pt—Sr—Ptvii	105.89 (3)
Sr—Pt—Srvi	74.11 (3)	Ptvi—Sr—Ptvii	87.96 (4)
Cdi—Pt—Srvii	72.78 (3)	Pti—Sr—Cdvii	51.57 (2)
Cdii—Pt—Srvii	142.88 (3)	Ptii—Sr—Cdvii	107.65 (4)
Cd—Pt—Srvii	67.51 (3)	Pt—Sr—Cdvii	138.55 (2)
Cdiii—Pt—Srvii	135.959 (18)	Ptvi—Sr—Cdvii	106.76 (4)
Sriv—Pt—Srvii	137.64 (2)	Ptvii—Sr—Cdvii	51.10 (2)
Srv—Pt—Srvii	76.441 (19)	Pti—Sr—Cdvi	107.65 (4)
Sr—Pt—Srvii	74.11 (3)	Ptii—Sr—Cdvi	51.57 (2)
Srvi—Pt—Srvii	87.96 (4)	Pt—Sr—Cdvi	138.55 (2)
Ptiv—Cd—Ptv	103.87 (4)	Ptvi—Sr—Cdvi	51.10 (2)
Ptiv—Cd—Pt	117.50 (2)	Ptvii—Sr—Cdvi	106.76 (4)
Ptv—Cd—Pt	117.50 (2)	Cdvii—Sr—Cdvi	82.56 (4)
Ptiv—Cd—Ptviii	108.97 (3)	Pti—Sr—Cdxii	50.65 (2)
Ptv—Cd—Ptviii	108.97 (3)	Ptii—Sr—Cdxii	50.65 (2)
Pt—Cd—Ptviii	99.68 (3)	Pt—Sr—Cdxii	130.48 (4)
Ptiv—Cd—Cdix	54.88 (2)	Ptvi—Sr—Cdxii	109.17 (3)
Ptv—Cd—Cdix	119.11 (5)	Ptvii—Sr—Cdxii	109.17 (3)
Pt—Cd—Cdix	122.75 (4)	Cdvii—Sr—Cdxii	58.19 (3)
Ptviii—Cd—Cdix	54.10 (3)	Cdvi—Sr—Cdxii	58.19 (3)
Ptiv—Cd—Cdx	119.11 (5)	Pti—Sr—Cdi	50.41 (2)
Ptv—Cd—Cdx	54.88 (2)	Ptii—Sr—Cdi	105.21 (4)
Pt—Cd—Cdx	122.75 (4)	Pt—Sr—Cdi	50.11 (2)
Ptviii—Cd—Cdx	54.10 (3)	Ptvi—Sr—Cdi	154.30 (5)
Cdix—Cd—Cdx	84.81 (5)	Ptvii—Sr—Cdi	90.55 (2)
Ptiv—Cd—Srvii	167.74 (3)	Cdvii—Sr—Cdi	92.00 (2)
Ptv—Cd—Srvii	86.46 (2)	Cdvi—Sr—Cdi	151.86 (5)
Pt—Cd—Srvii	61.38 (3)	Cdxii—Sr—Cdi	95.54 (3)
Ptviii—Cd—Srvii	60.64 (3)	Pti—Sr—Cdii	105.21 (4)
Cdix—Cd—Srvii	114.39 (5)	Ptii—Sr—Cdii	50.41 (2)
Cdx—Cd—Srvii	61.52 (3)	Pt—Sr—Cdii	50.11 (2)
Ptiv—Cd—Srvi	86.46 (2)	Ptvi—Sr—Cdii	90.55 (2)
Ptv—Cd—Srvi	167.74 (3)	Ptvii—Sr—Cdii	154.30 (5)
Pt—Cd—Srvi	61.38 (3)	Cdvii—Sr—Cdii	151.86 (5)
Ptviii—Cd—Srvi	60.64 (3)	Cdvi—Sr—Cdii	92.00 (2)
Cdix—Cd—Srvi	61.52 (3)	Cdxii—Sr—Cdii	95.54 (3)
Cdx—Cd—Srvi	114.39 (5)	Cdi—Sr—Cdii	79.86 (4)
Srvii—Cd—Srvi	82.56 (4)	Pti—Sr—Cdviii	134.25 (2)
Ptiv—Cd—Srxi	60.31 (2)	Ptii—Sr—Cdviii	134.25 (2)
Ptv—Cd—Srxi	60.31 (2)	Pt—Sr—Cdviii	88.75 (4)
Pt—Cd—Srxi	175.05 (4)	Ptvi—Sr—Cdviii	48.75 (2)
Ptviii—Cd—Srxi	85.27 (3)	Ptvii—Sr—Cdviii	48.75 (2)
Cdix—Cd—Srxi	60.30 (3)	Cdvii—Sr—Cdviii	93.99 (3)
Cdx—Cd—Srxi	60.30 (3)	Cdvi—Sr—Cdviii	93.99 (3)
Srvii—Cd—Srxi	121.81 (3)	Cdxii—Sr—Cdviii	140.77 (5)
Srvi—Cd—Srxi	121.81 (3)	Cdi—Sr—Cdviii	113.98 (3)
Ptiv—Cd—Srv	120.35 (4)	Cdii—Sr—Cdviii	113.98 (3)
Ptv—Cd—Srv	59.65 (2)	Pti—Sr—Srvi	152.61 (6)
Pt—Cd—Srv	59.46 (3)	Ptii—Sr—Srvi	94.42 (2)
Ptviii—Cd—Srv	130.66 (3)	Pt—Sr—Srvi	53.25 (3)
Cdix—Cd—Srv	175.11 (5)	Ptvi—Sr—Srvi	52.64 (2)
Cdx—Cd—Srv	97.51 (2)	Ptvii—Sr—Srvi	101.34 (5)
Srvii—Cd—Srv	70.47 (2)	Cdvii—Sr—Srvi	149.28 (6)
Srvi—Cd—Srv	120.84 (3)	Cdvi—Sr—Srvi	95.53 (3)
Srxi—Cd—Srv	117.17 (3)	Cdxii—Sr—Srvi	144.11 (3)
Ptiv—Cd—Sriv	59.65 (2)	Cdi—Sr—Srvi	102.75 (5)
Ptv—Cd—Sriv	120.35 (4)	Cdii—Sr—Srvi	58.53 (3)
Pt—Cd—Sriv	59.46 (3)	Cdviii—Sr—Srvi	55.44 (3)