Redetermination of Sr2PdO3 from single-crystal X-ray data.

The crystal structure redetermination of Sr2PdO3 (distrontium palladium trioxide) was carried out using high-quality single-crystal X-ray data. The Sr2PdO3 structure has been described previously in at least three reports [Wasel-Nielen & Hoppe (1970 ▸). Z. Anorg. Allg. Chem. 375, 209-213; Muller & Roy (1971 ▸). Adv. Chem. Ser. 98, 28-38; Nagata et al. (2002 ▸). J. Alloys Compd. 346, 50-56], all based on powder X-ray diffraction data. The current structure refinement of Sr2PdO3, as compared to previous powder data refinements, leads to more precise cell parameters and fractional coordinates, together with anisotropic displacement parameters for all sites. The compound is confirmed to have the ortho-rhom-bic Sr2CuO3 structure type (space group Immm) as reported previously. The structure consists of infinite chains of corner-sharing PdO4 plaquettes inter-spersed by SrII atoms. A brief comparison of Sr2PdO3 with the related K2NiF4 structure type is given.

Chemical context

Low-dimensional transition-metal oxides with chain structures have received attention since they can enable inter­esting physical phenomena such as spin 1/2 anti­ferromagnetic Heisenberg coupling (Motoyama et al., 1996 ▸; Takigawa et al., 1996 ▸), superconductivity (Hiroi et al., 1993 ▸), ultrafast non-linear optical response (Ogasawara et al., 2000 ▸) or even glucose sensing (El-Ads et al., 2016 ▸). The particularly relevant sub-family based on square-planar MO4 (M = divalent metal) primary building units is dominated by oxidocuprates(II), while the chemistry of respective palladates(II), showing the same preference for a square-planar coordination by oxygen, is much less explored.

Here we address Sr2PdO3, which has previously been obtained as a microcrystalline material (Wasel-Nielen & Hoppe, 1970 ▸; Muller & Roy, 1971 ▸; Nagata et al., 2002 ▸). Based on evaluations of powder X-ray diffractograms, Sr2PdO3 was identified as being isostructural with Sr2CuO3 (Teske & Müller-Buschbaum, 1969 ▸; Weller & Lines, 1989 ▸) and Sr2FeO3 (Tassel et al., 2013 ▸). However, structural details derived from the given atomic parameters have only been reported with large uncertainties (Muller & Roy, 1971 ▸; Nagata et al., 2002 ▸). Therefore, a redetermination of Sr2PdO3 based on single crystal X-ray data seemed appropriate.

Structural commentary

The crystal structure of Sr2PdO3 is essentially the same as determined previously (Wasel-Nielen & Hoppe, 1970 ▸; Muller & Roy, 1971 ▸; Nagata et al., 2002 ▸). The lattice parameters (Table 1 ▸) are almost identical to those in the previous reports but with higher precision. The PdII atom occupies the 2d crystallographic sites with mmm site symmetry. We would like to point out that we chose a different cell setting as compared to all the previous reports, where the PdII atom was chosen to be located at the cell origin (site 2a; 0, 0, 0; hence the different site designations). The PdII atom forms distorted PdO4 square planes, which are linked by sharing oxygen atoms in the trans-position to form infinite chains extending along the b-axis direction as shown in Fig. 1 ▸. Corresponding to this connectivity pattern, the Pd—O bond lengths are longer for the shared oxygen atoms, 2.052 (2) Å, and shorter for the terminal ones, 1.9911 (2) Å. The Sr atom is situated at the 4j Wyckoff site having mm2 site symmetry. It is seven-coordinate in a monocapped trigonal–prismatic fashion by oxygen with three different bond lengths (Table 1 ▸, Fig. 2 ▸). In addition to the square-planar first coordination of PdII with oxygen, the second consists of eight SrII atoms present at the corner of a cuboid with dimension 3.5342 (2) × 3.7887 (2) × 3.9822 (3) Å3 (Fig. 2 ▸). Of the two kinds of oxygen atoms, both surrounded by six metal ions that form distorted octa­hedra, O1 is coordinated by one PdII atom [2.052 (2) Å] and five SrII atoms with one short [2.474 (2) Å] and four long distances [2.6668 (2) Å] (Fig. 3 ▸). O2 is connected to four equidistant SrII [2.5906 (3) Å] and two PdII atoms [1.9911 (2) Å] (Fig. 3 ▸). In our current structure determination, much more precise values of the cell parameters along with the z parameters of Sr and O1 have been determined, consequently, yielding very precise values for the bond lengths (see Table 1 ▸). The quality of the current refinement is also clearly reflected by better reliability factors (see Table 2 ▸) as compared to the previous refinements. The atomic arrangement described here is same as provided by Wasel-Nielen & Hoppe (1970 ▸).

Table 1

Comparison of lattice parameters and bond lengths (Å) in Sr2PdO3 determined in different studies

	1970 worka	1971 workb	2002 workc	This work
a	3.977	3.97	3.985	3.5342 (2)
b	3.53	3.544	3.539	3.9822 (3)
c	12.82	12.84	12.847	12.8414 (8)
Pd—O1 (×2)	2.08	2.045	2.068	2.052 (2)
Pd—O2 (×2)	1.99	1.985	1.993	1.9911 (1)
Sr—O1	2.45	2.504	2.467	2.474 (2)
Sr—O1 (×4)	2.67	2.668	2.671	2.6668 (2)
Sr—O2 (×2)	2.58	2.57	2.588	2.5906 (3)

References: (a) Wasel-Nielen & Hoppe (1970 ▸); (b) Muller & Roy (1971 ▸); (c) Nagata et al. (2002 ▸).

Figure 1

Crystal structure of Sr2PdO3 viewed along the a axis (left) and along the b axis (right).

Figure 2

Coordination around the SrII (left) and PdII atoms (right). All atoms are drawn with displacement ellipsoids at the 80% probability level. Distances are in Å.

Figure 3

Coordination polyhedra of two types of oxygen atoms, O1 (left) and O2 (right). All atoms are drawn with displacement ellipsoids at the 80% probability level. Distances are in Å.

Table 2

Experimental details

Crystal data
Chemical formula	Sr2PdO3
M r	329.64
Crystal system, space group	Orthorhombic, I m m m
Temperature (K)	296
a, b, c (Å)	3.5342 (2), 3.9822 (3), 12.8414 (8)
V (Å3)	180.73 (2)
Z	2
Radiation type	Mo Kα
μ (mm−1)	34.15
Crystal size (mm)	0.18 × 0.16 × 0.12
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2009 ▸)
T min, T max	0.062, 0.102
No. of measured, independent and observed [I > 2σ(I)] reflections	8304, 178, 176
R int	0.035
(sin θ/λ)max (Å−1)	0.702
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.009, 0.021, 1.27
No. of reflections	178
No. of parameters	16
Δρmax, Δρmin (e Å−3)	0.43, −0.51

Computer programs: APEX2 and, SAINT (Bruker, 2009 ▸), SHELXS97 and SHELXTL (Sheldrick, 2008 ▸), SHELXL2014/7 (Sheldrick, 2015 ▸), DIAMOND (Brandenburg, 2006 ▸).

The structural features discussed above are closely related to those of the K2NiF4 type of structure, which is regarded as the prototype structure for all the high T cuprates. K2NiF4 consists of layers of corner-shared NiF6 octa­hedra extending in the ab plane. One can derive the Sr2PdO3 structure from the K2NiF4 structure by systematically removing the bridging F atoms from the NiF6 octa­hedra lying in the a-axis direction (Fig. 4 ▸). This would reduce the dimensionality of the layer, resulting in linear chains of square planes connected by edges along only one direction.

Figure 4

Inter­conversion of the Sr2PdO3 and K2NiF4 structures.

Synthesis and crystallization

Millimeter-sized block-shaped crystals of dark-yellow colour with composition Sr2PdO3 as confirmed by SEM–EDS, were obtained from a mixture of different phases while attempting to synthesize SrPd3O4 using a KOH flux (Smallwood et al., 2000 ▸). SrCO3 and Pd metal powder were mixed in the molar ratio of 2:3, placed in an alumina crucible, and 15 grams of KOH pellets were added on top. The crucible was heated in a muffle furnace to 1023 K in 24 h with a 6 h dwell time. The furnace was then cooled slowly to 873 K over 125 h after which it was switched off and allowed to cool naturally. The product was washed several times with water to remove the solidified flux and subsequently rinsed with ethanol.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸.

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989018017176/wm5474sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989018017176/wm5474Isup2.hkl

CCDC reference: 1882781

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

Sr2PdO3	Dx = 6.057 Mg m−3
Mr = 329.64	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Immm	Cell parameters from 1490 reflections
a = 3.5342 (2) Å	θ = 3.2–29.9°
b = 3.9822 (3) Å	µ = 34.15 mm−1
c = 12.8414 (8) Å	T = 296 K
V = 180.73 (2) Å3	Block, yellow-brown
Z = 2	0.18 × 0.16 × 0.12 mm
F(000) = 292

Bruker APEXII CCD diffractometer	176 reflections with I > 2σ(I)
φ and ω scans	Rint = 0.035
Absorption correction: multi-scan (SADABS; Bruker, 2009)	θmax = 29.9°, θmin = 3.2°
Tmin = 0.062, Tmax = 0.102	h = −4→4
8304 measured reflections	k = −5→5
178 independent reflections	l = −18→18

Refinement on F2	0 restraints
Least-squares matrix: full	w = 1/[σ2(Fo2) + (0.0092P)2 + 0.2817P] where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.009	(Δ/σ)max < 0.001
wR(F2) = 0.021	Δρmax = 0.43 e Å−3
S = 1.27	Δρmin = −0.51 e Å−3
178 reflections	Extinction correction: SHELXL-2014/7 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
16 parameters	Extinction coefficient: 0.0059 (5)

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

	x	y	z	Uiso*/Ueq
Pd1	0.5000	0.0000	0.5000	0.00493 (11)
Sr1	0.5000	0.0000	0.14752 (2)	0.00656 (11)
O1	0.5000	0.0000	0.34021 (18)	0.0085 (5)
O2	0.5000	0.5000	0.5000	0.0128 (8)

	U11	U22	U33	U12	U13	U23
Pd1	0.00765 (19)	0.00396 (17)	0.00320 (18)	0.000	0.000	0.000
Sr1	0.00752 (17)	0.00760 (16)	0.00456 (17)	0.000	0.000	0.000
O1	0.0117 (13)	0.0101 (12)	0.0037 (11)	0.000	0.000	0.000
O2	0.021 (2)	0.0035 (15)	0.0134 (18)	0.000	0.000	0.000

Pd1—O2i	1.9911 (1)	Sr1—O1ix	2.6668 (2)
Pd1—O2	1.9911 (1)	Sr1—O1vii	2.6668 (2)
Pd1—O1	2.052 (2)	Sr1—Pd1xi	3.2674 (2)
Pd1—O1ii	2.052 (2)	Sr1—Pd1xii	3.2674 (2)
Pd1—Sr1iii	3.2674 (2)	Sr1—Pd1xiii	3.2674 (2)
Pd1—Sr1iv	3.2674 (2)	Sr1—Pd1xiv	3.2674 (2)
Pd1—Sr1v	3.2674 (2)	Sr1—Sr1xv	3.5342 (2)
Pd1—Sr1vi	3.2674 (2)	O1—Sr1viii	2.6668 (2)
Pd1—Sr1vii	3.2674 (2)	O1—Sr1iii	2.6668 (2)
Pd1—Sr1viii	3.2674 (2)	O1—Sr1vii	2.6668 (2)
Pd1—Sr1ix	3.2674 (2)	O1—Sr1ix	2.6668 (2)
Pd1—Sr1x	3.2674 (2)	O2—Pd1xvi	1.9911 (1)
Sr1—O1	2.474 (2)	O2—Sr1ix	2.5906 (3)
Sr1—O2xi	2.5906 (3)	O2—Sr1iv	2.5906 (3)
Sr1—O2xii	2.5906 (3)	O2—Sr1viii	2.5906 (3)
Sr1—O1viii	2.6668 (2)	O2—Sr1vi	2.5906 (3)
Sr1—O1iii	2.6668 (2)
O2i—Pd1—O2	180.0	O1—Sr1—O1vii	86.61 (5)
O2i—Pd1—O1	90.0	O2xi—Sr1—O1vii	119.68 (4)
O2—Pd1—O1	90.0	O2xii—Sr1—O1vii	65.87 (4)
O2i—Pd1—O1ii	90.0	O1viii—Sr1—O1vii	96.597 (9)
O2—Pd1—O1ii	90.0	O1iii—Sr1—O1vii	83.000 (8)
O1—Pd1—O1ii	180.0	O1ix—Sr1—O1vii	173.22 (10)
O2i—Pd1—Sr1iii	52.455 (3)	O1—Sr1—Pd1xi	125.435 (5)
O2—Pd1—Sr1iii	127.545 (3)	O2xi—Sr1—Pd1xi	37.546 (3)
O1—Pd1—Sr1iii	54.565 (5)	O2xii—Sr1—Pd1xi	86.845 (8)
O1ii—Pd1—Sr1iii	125.435 (5)	O1viii—Sr1—Pd1xi	147.95 (5)
O2i—Pd1—Sr1iv	127.545 (3)	O1iii—Sr1—Pd1xi	38.82 (5)
O2—Pd1—Sr1iv	52.455 (3)	O1ix—Sr1—Pd1xi	97.52 (3)
O1—Pd1—Sr1iv	125.435 (5)	O1vii—Sr1—Pd1xi	86.43 (3)
O1ii—Pd1—Sr1iv	54.565 (5)	O1—Sr1—Pd1xii	125.435 (5)
Sr1iii—Pd1—Sr1iv	180.0	O2xi—Sr1—Pd1xii	86.845 (8)
O2i—Pd1—Sr1v	52.455 (4)	O2xii—Sr1—Pd1xii	37.546 (3)
O2—Pd1—Sr1v	127.545 (3)	O1viii—Sr1—Pd1xii	97.52 (3)
O1—Pd1—Sr1v	125.435 (5)	O1iii—Sr1—Pd1xii	86.43 (3)
O1ii—Pd1—Sr1v	54.565 (5)	O1ix—Sr1—Pd1xii	147.95 (5)
Sr1iii—Pd1—Sr1v	70.871 (10)	O1vii—Sr1—Pd1xii	38.82 (5)
Sr1iv—Pd1—Sr1v	109.129 (10)	Pd1xi—Sr1—Pd1xii	65.481 (6)
O2i—Pd1—Sr1vi	127.545 (3)	O1—Sr1—Pd1xiii	125.435 (5)
O2—Pd1—Sr1vi	52.455 (4)	O2xi—Sr1—Pd1xiii	86.845 (9)
O1—Pd1—Sr1vi	125.435 (5)	O2xii—Sr1—Pd1xiii	37.546 (3)
O1ii—Pd1—Sr1vi	54.565 (5)	O1viii—Sr1—Pd1xiii	38.82 (5)
Sr1iii—Pd1—Sr1vi	114.520 (6)	O1iii—Sr1—Pd1xiii	147.95 (5)
Sr1iv—Pd1—Sr1vi	65.480 (6)	O1ix—Sr1—Pd1xiii	86.43 (3)
Sr1v—Pd1—Sr1vi	75.090 (7)	O1vii—Sr1—Pd1xiii	97.52 (3)
O2i—Pd1—Sr1vii	52.455 (3)	Pd1xi—Sr1—Pd1xiii	109.130 (10)
O2—Pd1—Sr1vii	127.545 (3)	Pd1xii—Sr1—Pd1xiii	75.091 (7)
O1—Pd1—Sr1vii	54.565 (5)	O1—Sr1—Pd1xiv	125.435 (5)
O1ii—Pd1—Sr1vii	125.435 (5)	O2xi—Sr1—Pd1xiv	37.546 (3)
Sr1iii—Pd1—Sr1vii	65.480 (5)	O2xii—Sr1—Pd1xiv	86.845 (8)
Sr1iv—Pd1—Sr1vii	114.520 (6)	O1viii—Sr1—Pd1xiv	86.43 (3)
Sr1v—Pd1—Sr1vii	104.910 (7)	O1iii—Sr1—Pd1xiv	97.52 (3)
Sr1vi—Pd1—Sr1vii	180.0	O1ix—Sr1—Pd1xiv	38.82 (5)
O2i—Pd1—Sr1viii	127.545 (3)	O1vii—Sr1—Pd1xiv	147.95 (5)
O2—Pd1—Sr1viii	52.455 (3)	Pd1xi—Sr1—Pd1xiv	75.091 (7)
O1—Pd1—Sr1viii	54.565 (5)	Pd1xii—Sr1—Pd1xiv	109.130 (10)
O1ii—Pd1—Sr1viii	125.435 (5)	Pd1xiii—Sr1—Pd1xiv	65.481 (6)
Sr1iii—Pd1—Sr1viii	109.129 (10)	O1—Sr1—Sr1xv	90.0
Sr1iv—Pd1—Sr1viii	70.871 (10)	O2xi—Sr1—Sr1xv	133.011 (5)
Sr1v—Pd1—Sr1viii	180.0	O2xii—Sr1—Sr1xv	46.991 (5)
Sr1vi—Pd1—Sr1viii	104.910 (7)	O1viii—Sr1—Sr1xv	48.500 (3)
Sr1vii—Pd1—Sr1viii	75.090 (7)	O1iii—Sr1—Sr1xv	131.500 (4)
O2i—Pd1—Sr1ix	127.545 (4)	O1ix—Sr1—Sr1xv	131.500 (4)
O2—Pd1—Sr1ix	52.455 (3)	O1vii—Sr1—Sr1xv	48.500 (4)
O1—Pd1—Sr1ix	54.565 (5)	Pd1xi—Sr1—Sr1xv	122.741 (3)
O1ii—Pd1—Sr1ix	125.435 (5)	Pd1xii—Sr1—Sr1xv	57.260 (3)
Sr1iii—Pd1—Sr1ix	75.090 (7)	Pd1xiii—Sr1—Sr1xv	57.260 (3)
Sr1iv—Pd1—Sr1ix	104.910 (7)	Pd1xiv—Sr1—Sr1xv	122.741 (3)
Sr1v—Pd1—Sr1ix	114.520 (6)	Pd1—O1—Sr1	180.0
Sr1vi—Pd1—Sr1ix	70.871 (10)	Pd1—O1—Sr1viii	86.61 (5)
Sr1vii—Pd1—Sr1ix	109.129 (10)	Sr1—O1—Sr1viii	93.39 (5)
Sr1viii—Pd1—Sr1ix	65.480 (6)	Pd1—O1—Sr1iii	86.61 (5)
O2i—Pd1—Sr1x	52.455 (3)	Sr1—O1—Sr1iii	93.39 (5)
O2—Pd1—Sr1x	127.545 (3)	Sr1viii—O1—Sr1iii	173.23 (10)
O1—Pd1—Sr1x	125.435 (5)	Pd1—O1—Sr1vii	86.61 (5)
O1ii—Pd1—Sr1x	54.565 (5)	Sr1—O1—Sr1vii	93.39 (5)
Sr1iii—Pd1—Sr1x	104.910 (7)	Sr1viii—O1—Sr1vii	96.597 (9)
Sr1iv—Pd1—Sr1x	75.090 (7)	Sr1iii—O1—Sr1vii	83.001 (8)
Sr1v—Pd1—Sr1x	65.480 (5)	Pd1—O1—Sr1ix	86.61 (5)
Sr1vi—Pd1—Sr1x	109.129 (10)	Sr1—O1—Sr1ix	93.39 (5)
Sr1vii—Pd1—Sr1x	70.871 (10)	Sr1viii—O1—Sr1ix	83.001 (8)
Sr1viii—Pd1—Sr1x	114.520 (6)	Sr1iii—O1—Sr1ix	96.597 (9)
Sr1ix—Pd1—Sr1x	180.0	Sr1vii—O1—Sr1ix	173.23 (10)
O1—Sr1—O2xi	136.990 (5)	Pd1xvi—O2—Pd1	180.0
O1—Sr1—O2xii	136.990 (5)	Pd1xvi—O2—Sr1ix	90.0
O2xi—Sr1—O2xii	86.020 (11)	Pd1—O2—Sr1ix	90.0
O1—Sr1—O1viii	86.61 (5)	Pd1xvi—O2—Sr1iv	90.0
O2xi—Sr1—O1viii	119.68 (4)	Pd1—O2—Sr1iv	90.0
O2xii—Sr1—O1viii	65.87 (4)	Sr1ix—O2—Sr1iv	180.0
O1—Sr1—O1iii	86.61 (5)	Pd1xvi—O2—Sr1viii	90.0
O2xi—Sr1—O1iii	65.87 (4)	Pd1—O2—Sr1viii	90.0
O2xii—Sr1—O1iii	119.68 (4)	Sr1ix—O2—Sr1viii	86.018 (11)
O1viii—Sr1—O1iii	173.22 (10)	Sr1iv—O2—Sr1viii	93.982 (11)
O1—Sr1—O1ix	86.61 (5)	Pd1xvi—O2—Sr1vi	90.0
O2xi—Sr1—O1ix	65.87 (4)	Pd1—O2—Sr1vi	90.0
O2xii—Sr1—O1ix	119.68 (4)	Sr1ix—O2—Sr1vi	93.982 (11)
O1viii—Sr1—O1ix	83.000 (8)	Sr1iv—O2—Sr1vi	86.018 (11)
O1iii—Sr1—O1ix	96.597 (9)	Sr1viii—O2—Sr1vi	180.0