Crystal structure of Sr2CdPt2 containing linear platinum chains.

The ternary inter-metallic title phase, distrontium cadmium diplatinum, was prepared from stoichiometric amounts of the elements at 1123 K for one day. The crystal structure adopts the ortho-rhom-bic Ca2GaCu2 structure type in space group Immm. Its main features are characterized by linear (Pt-Pt⋯Pt-Pt) n chains that are aligned along [010] and condensed through cadmium atoms forming Cd-centred Pt2Cd2/2 rectangles to build up sheets parallel to (001). These sheets are connected to each other via alternating (001) sheets of strontium atoms along [001]. The strontium sheets consists of corrugated Sr4 units that are condensed to each other through edge-sharing parallel to [100].

Chemical context

A large number of transition metal-based ternary inter­metallic phases have been studied in terms of metal–metal inter­actions and structure–property relationships (Corbett, 2010 ▸). Exploratory synthetic approaches in systems A/Cd/Pt (A = alkaline earth metal) have revealed a great compositional and structural diversity. The calcium phase Ca6Cd16Pt8 contains a three-dimensional array of isolated Cd8 tetra­hedral stars (TS) and a face-centred cube of Pt@Ca6 octa­hedra (Samal et al., 2013 ▸) whilst the structure of Ca6Cd11Pt crystallizes in its own structure type consisting of apically inter­bonded Cd7 penta­gonal bipyramids and five-membered rings of Ca atoms (Gulo et al., 2013 ▸). The strontium phase SrCd4Pt2 is made up of chains of edge-sharing Cd4 tetra­hedra bridged by four-bonded Sr atoms (Samal et al., 2013 ▸) and SrCdPt presents six-membered rings of Sr atoms in a chair conformation (Gulo & Köhler, 2014 ▸). The barium phase BaCd2Pt exhibits zigzag chains of Ba atoms and Pt-centred boat and anti-boat conformations formed by six-membered rings of Cd atoms (Gulo & Köhler, 2015 ▸). The Pt-based ternary inter­metallic compounds with general formula A 2 XPt2 (A = alkaline-earth or rare-earth metal; X = diel, triel, or tetrel element) adopt five different structure types. Sr2InPt2 (Muts et al., 2007 ▸) crystallizes in the monoclinic Ca2Ir2S type (Schoolaert & Jung, 2002 ▸), Pu2SnPt2 (Pereira et al., 1997 ▸) in the tetra­gonal Mo2FeB2 type (Gladyshevskii et al., 1996 ▸) while U2CdPt2 has its own structure type (Gravereau et al., 1994 ▸). Ce2CdPt2 (Pöttgen et al., 2000 ▸) adopts the tetra­gonal U3Si2 type (Zachariasen, 1948 ▸), and Ca2CdPt2 (Samal & Corbett, 2012 ▸) the ortho­rhom­bic Ca2GaCu2 type (Fornasini & Merlo, 1988 ▸).

In this article we present the crystal structure of the novel inter­metallic phase Sr2CdPt2 containing linear (Pt—Pt⋯Pt—Pt) chains as a principal structural motif.

Structural commentary

The ternary inter­metallic title phase adopts the ortho­rhom­bic Ca2GaCu2 structure type (Fornasini & Merlo, 1988 ▸) with the Ca, Ga, and Cu sites replaced by Sr, Cd, and Pt sites, respectively. The three atoms occupy three independent sites in the unit cell. The Sr atom resides on a special position with site symmetry mm2 (Wyckoff site 4 j), the Cd atom occupies a special positions with site symmetry mmm (2 a) and the Pt atom is on a special positions with site symmetry m2m (4 h). In the two structures, the transition metals (platinum and copper, respectively) occupy the same positions. In contrast, in the structure of SrCd4Pt2 (Samal et al., 2013 ▸) which is isotypic with ZrFe4Si2 (Yarmolyuk et al., 1975 ▸), the transition metals (platinum and iron, respectively) occupy different positions and the Pt atoms reside on the respective Si sites because silicon and platinum atoms are the most electronegative atoms in the two systems. The new phase Sr2CdPt2 contains 26 valence electrons and, as already mentioned, is isotypic with Ca2GaCu2. However, in comparison the structure of Sr2CdPt2 is appreciably distorted along the platinum chains, presumably because Ca2GaCu2 contains much smaller Cu atoms and a larger valence electron count of 29. Coordination spheres of each atomic site in the title structure are illustrated in Fig. 1 ▸. The Sr atom is coordinated by five other Sr, four Cd, and four Pt atoms. The Sr—Sr bond lengths vary from 3.674 (3) to 3.854 (1) Å, the Sr—Cd distances range from 3.490 (1) to 3.577 (1) Å, whereas the Sr—Pt values vary only slightly, from 3.188 (1) to 3.231 (1) Å. Six Sr atoms construct a square-planar pyramid, Sr@Sr5. The existence of Sr—Sr strong bonds is observable in SrCdPt (Gulo & Köhler, 2014 ▸) but not in SrCd4Pt2 (Samal et al., 2013 ▸). The Cd atom exhibits a coordination number of twelve and has eight Sr and four Pt atoms in its environment with Cd—Pt distances of 2.785 (1) Å. The Pt atom is surrounded by six Sr, two Cd and one Pt atoms with a Pt—Pt distance of 2.734 (1) Å. This distance is slightly longer than those found in Ca2CdPt2 (2.659 Å; Samal & Corbett, 2012 ▸) or Sr2InPt2 (2.707 Å; Muts et al., 2007 ▸) but shorter than those in Pu2SnPt2 (Pereira et al., 1997 ▸), U2CdPt2 (Gravereau et al., 1994 ▸) or Ce2CdPt2 (Pöttgen et al., 2000 ▸). All other inter­atomic distances (Sr—Cd, Sr—Pt, and Cd—Pt) are in agreement with those found in some ternary compounds in A/Cd/Pt systems (A = alkaline earth metal).

Figure 1

Coordination of strontium, cadmium, and platinum atoms in Sr2CdPt2. Displacement ellipsoids are displayed at the 90% probability level.

Packing features

Sr atoms are bound together into corrugated sheets consisting of edge-sharing Sr4-units. These sheets spread parallel to (001) and are linked by another Sr—Sr bond of 3.674 (3) Å along [001]. (Fig. 2 ▸). The crystal structure is also characterized by the existence of linear (Pt—Pt⋯Pt—Pt) chains along [010] with longer distances of 3.2010 (14) Å between pairs of tightly bound Pt—Pt dumbbells, a significant distortion in the direction of dimerization. The platinum chains are condensed into (001) sheets through Cd atoms, forming Cd-centred rectangles with composition Pt2Cd2/2 (Fig. 3 ▸). The Pt2Cd2/2 layers are stacked along [001] and are linked through the corrugated sheets of Sr atoms.

Figure 2

Projection of the crystal structure of Sr2CdPt2 approximately along the b axis.

Figure 3

Projection of linear platinum chains that are aligned along the b axis and condensed via cadmium atoms forming Pt2Cd2/2-rectangles in the ab-plane

Database survey

A search of the Pearson’s Crystal Data – Crystal Structure Database for Inorganic Compounds (Villars & Cenzual, 2015 ▸) for the Sr/Cd/Pt family of compounds returned two compounds only: SrCd4Pt2 (Samal et al., 2013 ▸) and SrCdPt (Gulo & Köhler, 2014 ▸).

Synthesis and crystallization

The title compound was synthesized from starting materials of Sr granules (99.9+%, Alfa Aesar), Cd powder (99.9+%, Alfa Aesar) and Pt powder (99.95%, Chempur). A stoichiometric mixture of these elements was loaded into a Nb ampoule in an Ar-filled dry box. The Nb ampoule was then weld-sealed under an Ar atmosphere and subsequently enclosed in an evacuated silica jacket. The sample was then heated to 1123 K for 15 h, equilibrated at 923 K for 4 days, and followed by slow cooling to room temperature.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▸. The maximum and minimum remaining electron densities are located 1.66 and 0.81 Å, respectively, from the Pt site.

Table 1

Experimental details

Crystal data
Chemical formula	CdPt2Sr2
M r	677.82
Crystal system, space group	Orthorhombic, I m m m
Temperature (K)	293
a, b, c (Å)	4.5596 (9), 5.9351 (12), 9.1874 (18)
V (Å3)	248.63 (9)
Z	2
Radiation type	Mo Kα
μ (mm−1)	81.39
Crystal size (mm)	0.08 × 0.06 × 0.05
Data collection
Diffractometer	Bruker P4
Absorption correction	Multi-scan (SADABS; Bruker, 2001 ▸)
T min, T max	0.004, 0.017
No. of measured, independent and observed [I > 2σ(I)] reflections	1069, 190, 172
R int	0.025
(sin θ/λ)max (Å−1)	0.666
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.022, 0.058, 1.16
No. of reflections	190
No. of parameters	13
Δρmax, Δρmin (e Å−3)	1.84, −2.51

Computer programs: XSCANS (Bruker, 2001 ▸), SHELXS97 and SHELXL97 (Sheldrick, 2008 ▸) and DIAMOND (Brandenburg, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989015024937/wm5254sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015024937/wm5254Isup2.hkl

CCDC reference: 1444811

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

CdPt2Sr2	F(000) = 560
Mr = 677.82	Dx = 9.054 Mg m−3
Orthorhombic, Immm	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -I 2 2	Cell parameters from 25 reflections
a = 4.5596 (9) Å	θ = 12–18°
b = 5.9351 (12) Å	µ = 81.39 mm−1
c = 9.1874 (18) Å	T = 293 K
V = 248.63 (9) Å3	Block, brown
Z = 2	0.08 × 0.06 × 0.05 mm

Bruker P4 4-circle diffractometer	190 independent reflections
Radiation source: fine-focus sealed tube	172 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
Detector resolution: 0 pixels mm-1	θmax = 28.3°, θmin = 4.1°
ω–scans	h = −5→6
Absorption correction: multi-scan (SADABS; Bruker, 2001)	k = −7→7
Tmin = 0.004, Tmax = 0.017	l = −11→11
1069 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)] = 0.022	w = 1/[σ2(Fo2) + (0.0337P)2 + 3.9776P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.058	(Δ/σ)max < 0.001
S = 1.16	Δρmax = 1.84 e Å−3
190 reflections	Δρmin = −2.51 e Å−3
13 parameters	Extinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraints	Extinction coefficient: 0.0024 (4)

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	0.0000	0.23034 (10)	0.5000	0.0172 (3)
Cd	−0.5000	0.5000	0.5000	0.0172 (4)
Sr	0.0000	0.5000	0.19995 (16)	0.0162 (4)

	U11	U22	U33	U12	U13	U23
Pt	0.0156 (4)	0.0205 (4)	0.0155 (4)	0.000	0.000	0.000
Cd	0.0157 (8)	0.0152 (8)	0.0207 (9)	0.000	0.000	0.000
Sr	0.0171 (8)	0.0169 (8)	0.0146 (8)	0.000	0.000	0.000

Pt—Pti	2.7341 (13)	Cd—Srvii	3.4901 (10)
Pt—Cdii	2.7855 (5)	Cd—Srviii	3.5773 (12)
Pt—Cd	2.7855 (5)	Cd—Sriii	3.5773 (13)
Pt—Sriii	3.1876 (14)	Cd—Sr	3.5773 (12)
Pt—Sr	3.1876 (14)	Cd—Srix	3.5773 (13)
Pt—Ptiii	3.2010 (14)	Sr—Ptiii	3.1876 (14)
Pt—Sriv	3.2312 (10)	Sr—Ptiv	3.2312 (10)
Pt—Srv	3.2312 (10)	Sr—Ptxii	3.2312 (10)
Pt—Srvi	3.2312 (10)	Sr—Ptxiii	3.2312 (10)
Pt—Srvii	3.2312 (10)	Sr—Ptv	3.2312 (10)
Cd—Ptiii	2.7855 (5)	Sr—Cdxiv	3.4901 (10)
Cd—Ptviii	2.7855 (5)	Sr—Cdxiii	3.4901 (10)
Cd—Ptix	2.7855 (5)	Sr—Cdii	3.5773 (12)
Cd—Sriv	3.4901 (10)	Sr—Srxv	3.674 (3)
Cd—Srx	3.4901 (10)	Sr—Srxvi	3.8535 (9)
Cd—Srxi	3.4901 (10)
Pti—Pt—Cdii	125.070 (13)	Srviii—Cd—Sriii	180.0
Pti—Pt—Cd	125.070 (13)	Ptiii—Cd—Sr	58.560 (14)
Cdii—Pt—Cd	109.86 (3)	Ptviii—Cd—Sr	121.440 (14)
Pti—Pt—Sriii	120.139 (18)	Ptix—Cd—Sr	121.440 (14)
Cdii—Pt—Sriii	73.232 (13)	Pt—Cd—Sr	58.560 (14)
Cd—Pt—Sriii	73.232 (13)	Sriv—Cd—Sr	66.071 (12)
Pti—Pt—Sr	120.139 (18)	Srx—Cd—Sr	113.929 (12)
Cdii—Pt—Sr	73.232 (13)	Srxi—Cd—Sr	66.071 (12)
Cd—Pt—Sr	73.232 (13)	Srvii—Cd—Sr	113.929 (12)
Sriii—Pt—Sr	119.72 (4)	Srviii—Cd—Sr	79.18 (3)
Pti—Pt—Ptiii	180.0	Sriii—Cd—Sr	100.82 (3)
Cdii—Pt—Ptiii	54.930 (13)	Ptiii—Cd—Srix	121.440 (14)
Cd—Pt—Ptiii	54.930 (13)	Ptviii—Cd—Srix	58.560 (14)
Sriii—Pt—Ptiii	59.861 (18)	Ptix—Cd—Srix	58.560 (14)
Sr—Pt—Ptiii	59.861 (18)	Pt—Cd—Srix	121.440 (14)
Pti—Pt—Sriv	64.971 (13)	Sriv—Cd—Srix	113.929 (12)
Cdii—Pt—Sriv	145.14 (2)	Srx—Cd—Srix	66.071 (12)
Cd—Pt—Sriv	70.466 (13)	Srxi—Cd—Srix	113.929 (12)
Sriii—Pt—Sriv	134.76 (2)	Srvii—Cd—Srix	66.071 (12)
Sr—Pt—Sriv	73.786 (15)	Srviii—Cd—Srix	100.82 (3)
Ptiii—Pt—Sriv	115.029 (13)	Sriii—Cd—Srix	79.18 (3)
Pti—Pt—Srv	64.971 (13)	Sr—Cd—Srix	180.0
Cdii—Pt—Srv	70.466 (13)	Ptiii—Sr—Pt	60.28 (4)
Cd—Pt—Srv	145.14 (2)	Ptiii—Sr—Ptiv	134.76 (2)
Sriii—Pt—Srv	134.76 (2)	Pt—Sr—Ptiv	106.214 (15)
Sr—Pt—Srv	73.786 (15)	Ptiii—Sr—Ptxii	106.214 (15)
Ptiii—Pt—Srv	115.029 (13)	Pt—Sr—Ptxii	134.76 (2)
Sriv—Pt—Srv	89.75 (3)	Ptiv—Sr—Ptxii	50.06 (3)
Pti—Pt—Srvi	64.971 (13)	Ptiii—Sr—Ptxiii	106.214 (15)
Cdii—Pt—Srvi	70.466 (13)	Pt—Sr—Ptxiii	134.76 (2)
Cd—Pt—Srvi	145.14 (2)	Ptiv—Sr—Ptxiii	110.71 (5)
Sriii—Pt—Srvi	73.786 (15)	Ptxii—Sr—Ptxiii	89.75 (3)
Sr—Pt—Srvi	134.76 (2)	Ptiii—Sr—Ptv	134.76 (2)
Ptiii—Pt—Srvi	115.029 (13)	Pt—Sr—Ptv	106.214 (15)
Sriv—Pt—Srvi	129.94 (3)	Ptiv—Sr—Ptv	89.75 (3)
Srv—Pt—Srvi	69.29 (5)	Ptxii—Sr—Ptv	110.71 (5)
Pti—Pt—Srvii	64.971 (13)	Ptxiii—Sr—Ptv	50.06 (3)
Cdii—Pt—Srvii	145.14 (2)	Ptiii—Sr—Cdxiv	151.90 (4)
Cd—Pt—Srvii	70.466 (13)	Pt—Sr—Cdxiv	91.620 (18)
Sriii—Pt—Srvii	73.786 (15)	Ptiv—Sr—Cdxiv	48.779 (16)
Sr—Pt—Srvii	134.76 (2)	Ptxii—Sr—Cdxiv	93.47 (3)
Ptiii—Pt—Srvii	115.029 (13)	Ptxiii—Sr—Cdxiv	93.47 (3)
Sriv—Pt—Srvii	69.29 (5)	Ptv—Sr—Cdxiv	48.779 (16)
Srv—Pt—Srvii	129.94 (3)	Ptiii—Sr—Cdxiii	91.620 (19)
Srvi—Pt—Srvii	89.75 (3)	Pt—Sr—Cdxiii	151.90 (4)
Ptiii—Cd—Ptviii	180.0	Ptiv—Sr—Cdxiii	93.47 (3)
Ptiii—Cd—Ptix	109.86 (3)	Ptxii—Sr—Cdxiii	48.779 (16)
Ptviii—Cd—Ptix	70.14 (3)	Ptxiii—Sr—Cdxiii	48.779 (16)
Ptiii—Cd—Pt	70.14 (3)	Ptv—Sr—Cdxiii	93.47 (3)
Ptviii—Cd—Pt	109.86 (3)	Cdxiv—Sr—Cdxiii	116.48 (4)
Ptix—Cd—Pt	180.0	Ptiii—Sr—Cdii	48.21 (2)
Ptiii—Cd—Sriv	119.245 (13)	Pt—Sr—Cdii	48.21 (2)
Ptviii—Cd—Sriv	60.755 (13)	Ptiv—Sr—Cdii	152.59 (2)
Ptix—Cd—Sriv	119.245 (13)	Ptxii—Sr—Cdii	152.59 (2)
Pt—Cd—Sriv	60.755 (13)	Ptxiii—Sr—Cdii	89.339 (16)
Ptiii—Cd—Srx	60.755 (13)	Ptv—Sr—Cdii	89.339 (16)
Ptviii—Cd—Srx	119.245 (13)	Cdxiv—Sr—Cdii	113.929 (12)
Ptix—Cd—Srx	60.755 (13)	Cdxiii—Sr—Cdii	113.929 (12)
Pt—Cd—Srx	119.245 (13)	Ptiii—Sr—Cd	48.21 (2)
Sriv—Cd—Srx	180.00 (4)	Pt—Sr—Cd	48.21 (2)
Ptiii—Cd—Srxi	60.755 (13)	Ptiv—Sr—Cd	89.339 (16)
Ptviii—Cd—Srxi	119.245 (13)	Ptxii—Sr—Cd	89.339 (16)
Ptix—Cd—Srxi	60.755 (13)	Ptxiii—Sr—Cd	152.59 (2)
Pt—Cd—Srxi	119.245 (13)	Ptv—Sr—Cd	152.59 (2)
Sriv—Cd—Srxi	116.48 (4)	Cdxiv—Sr—Cd	113.929 (12)
Srx—Cd—Srxi	63.52 (4)	Cdxiii—Sr—Cd	113.929 (12)
Ptiii—Cd—Srvii	119.245 (13)	Cdii—Sr—Cd	79.18 (3)
Ptviii—Cd—Srvii	60.755 (13)	Ptiii—Sr—Srxv	149.861 (18)
Ptix—Cd—Srvii	119.245 (13)	Pt—Sr—Srxv	149.861 (18)
Pt—Cd—Srvii	60.755 (13)	Ptiv—Sr—Srxv	55.35 (2)
Sriv—Cd—Srvii	63.52 (4)	Ptxii—Sr—Srxv	55.35 (2)
Srx—Cd—Srvii	116.48 (4)	Ptxiii—Sr—Srxv	55.35 (2)
Srxi—Cd—Srvii	180.0	Ptv—Sr—Srxv	55.35 (2)
Ptiii—Cd—Srviii	121.440 (14)	Cdxiv—Sr—Srxv	58.24 (2)
Ptviii—Cd—Srviii	58.560 (14)	Cdxiii—Sr—Srxv	58.24 (2)
Ptix—Cd—Srviii	58.560 (14)	Cdii—Sr—Srxv	140.409 (17)
Pt—Cd—Srviii	121.440 (14)	Cd—Sr—Srxv	140.409 (17)
Sriv—Cd—Srviii	66.071 (12)	Ptiii—Sr—Srxvi	53.63 (3)
Srx—Cd—Srviii	113.929 (12)	Pt—Sr—Srxvi	100.38 (5)
Srxi—Cd—Srviii	66.071 (12)	Ptiv—Sr—Srxvi	151.51 (5)
Srvii—Cd—Srviii	113.929 (12)	Ptxii—Sr—Srxvi	103.14 (3)
Ptiii—Cd—Sriii	58.560 (14)	Ptxiii—Sr—Srxvi	52.59 (2)
Ptviii—Cd—Sriii	121.440 (14)	Ptv—Sr—Srxvi	92.53 (2)
Ptix—Cd—Sriii	121.440 (14)	Cdxiv—Sr—Srxvi	141.30 (3)
Pt—Cd—Sriii	58.560 (14)	Cdxiii—Sr—Srxvi	58.05 (2)
Sriv—Cd—Sriii	113.929 (12)	Cdii—Sr—Srxvi	55.88 (3)
Srx—Cd—Sriii	66.071 (12)	Cd—Sr—Srxvi	101.13 (5)
Srxi—Cd—Sriii	113.929 (12)	Srxv—Sr—Srxvi	103.81 (4)
Srvii—Cd—Sriii	66.071 (12)