Ca2CuO2Cl2, a redetermination from single-crystal X-ray diffraction data

Baptiste, B.; Azuma, M.; Yu, R.; Giura, P.; d'Astuto, M.

doi:10.1107/S2414314618016450

inorganic compounds

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ISSN: 2414-3146

Volume 3| Part 11| November 2018| x181645

https://doi.org/10.1107/S2414314618016450

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Ca₂CuO₂Cl₂, a redetermination from single-crystal X-ray diffraction data

Benoît Baptiste,^a ^* Masaki Azuma,^b Runze Yu,^b Paola Giura ^a and Matteo d'Astuto ^c

^aInstitut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Sorbonne Université, UMR CNRS 7590 Muséum National d'Histoire Naturelle, IRD UMR 206, 4 place Jussieu, F-75005 Paris, France, ^bLaboratory for Materials and Structures, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan, and ^cUniv. Grenoble Alpes, CNRS, Institut Néel, 38000 Grenoble, France
^*Correspondence e-mail: benoit.baptiste@upmc.fr

Edited by M. Weil, Vienna University of Technology, Austria (Received 25 September 2018; accepted 19 November 2018; online 27 November 2018)

The crystal structure of Ca₂CuO₂Cl₂, dicalcium oxidocuprate(II) dichloride, was redetermined on the basis of single-crystal X-ray diffraction data using a laboratory Mo anode. Previous structure determinations based on single-crystal X-ray data [Grande & Müller-Buschbaum (1977 ). Z. Anorg. Allg. Chem. 429, 88–90], powder X-ray diffraction data [Yamada et al. (2005 ). Phys. Rev. B, 72, 224503–1–5] or neutron diffraction data [Argyriou et al. (1995 ). Phys. Rev. B, 51, 8434–8437] were confirmed. The present study allowed the refinement of anisotropic displacement parameters for all crystallographic sites, accompanied with higher accuracy and precision for bond lengths and angles. The layered title compound comprises of [CuO₄] square-planar and [CaO₄Cl₄] square-antiprismatic coordination polyhedra, and is the undoped parent compound of a high-temperature superconducting cuprate.

Keywords: crystal structure; cuprates; high-temperature-superconductors; oxychlorides.

CCDC reference: 1879872

Structure description

The layered crystal structure of Ca₂CuO₂Cl₂ (Fig. 1) has tetragonal symmetry (space group I4/mmm), and is the undoped parent compound of a high-temperature superconducting cuprate (Hiroi et al., 1994 ; Kohsaka et al., 2002 ; Yamada et al., 2005).

Figure 1
The crystal structure of Ca₂CuO₂Cl₂, showing displacement ellipsoids drawn at the 90% probability level.

The principal building blocks in the structure are square-planar [CuO₄] and square-antiprismatic [CaO₄Cl₄] polyhedra, both with point group symmetry 4/mmm. Relevant bond lengths are listed in Table 1. The building units are fused together by sharing O and Cl atoms into layers extending parallel to (001). Square-planar [CuO₄] polyhedra are typical of oxocuprates(II) (Müller-Buschbaum, 1977 ), and are found in other high-temperature superconducting cuprates (Raveau et al., 1991 ). However, here the [CuO₄] units are complemented to elongated [CuO₄Cl₂] octahedra with the Cl atoms at the axial sites.

Table 1
Selected bond lengths (Å)

Cu1—Cl1	2.7452 (14)	Ca1—Cl1ⁱ	2.9775 (7)
Cu1—O1	1.9340 (1)	Ca1—O1ⁱⁱ	2.4900 (7)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[x-{\script{1\over 2}}, y-{\script{1\over 2}}, z-{\script{1\over 2}}]$ .

Previous structure determinations of Ca₂CuO₂Cl₂ based on single-crystal X-ray data (Grande & Müller-Buschbaum, 1977), powder X-ray diffraction data (Yamada et al., 2005) or neutron diffraction data (Argyriou et al., 1995) are confirmed by the current study. The first determination of the crystal structure of Ca₂CuO₂Cl₂ converged with rather high residuals (R₁ = 0.105; Grande & Müller-Buschbaum, 1977). Another previous attempt to determine anisotropic displacement parameters for all crystallographic sites has been made on basis of neutron powder diffraction data (Argyriou et al., 1995). We note that most of the refined values are compatible with our refinement within uncertainty, with the notable exception of U₃₃ for the chlorine and oxygen sites, which have larger values in our refinement. Although a direct comparison between the results of the two techniques is difficult, we note that neutrons are more sensitive to oxygen but the number of measured reflections is much smaller in powder diffraction. The much higher redundancy resulting from single-crystal X-ray data collection allows a better data-to-parameter ratio and hence a more reliable refinement. We also estimate that our model shows a lower correlation between fitted parameters.

Synthesis and crystallization

Powders of CaO and CuCl₂ were mixed in a molar ratio of 2:1 and put into an alumina crucible. The mixed powder was heated at 1053 K for 24 h with intermediate grindings. Subsequently, the as-obtained Ca₂CuO₂Cl₂ material was again heated to 1053 K at a ramp rate of 60 K h⁻¹ and kept at this temperature for 5 h. It was then heated to 1203 K at a ramp rate of 60 K h⁻¹ and kept at that temperature for 10 h. Finally, it was cooled down to room temperature at a ramp rate of 60 K h⁻¹. Single crystals with a size up to 2 mm × 2 mm × 0.1 mm could be harvested by cleaving the as-grown bulks.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. Coordinates from an isotypic compound were used in the structure solution.

Table 2
Experimental details

Crystal data
Chemical formula	Ca₂CuO₂Cl₂
M_r	246.60
Crystal system, space group	Tetragonal, I4/mmm
Temperature (K)	293
a, c (Å)	3.8680 (2), 15.0321 (15)
V (Å³)	224.90 (3)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	8.16
Crystal size (mm)	0.80 × 0.40 × 0.16

Data collection
Diffractometer	Agilent Xcalibur, Sapphire3
Absorption correction	Analytical [CrysAlis PRO (Agilent, 2013 ), using a multi-faceted crystal model based on expressions derived by Clark & Reid (1995 )]
T_min, T_max	0.056, 0.287
No. of measured, independent and observed [I > 2σ(I)] reflections	634, 101, 101
R_int	0.019
(sin θ/λ)_max (Å⁻¹)	0.652

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.018, 0.047, 1.24
No. of reflections	101
No. of parameters	12
Δρ_max, Δρ_min (e Å⁻³)	0.51, −0.43
Computer programs: CrysAlis PRO (Agilent, 2013), OLEX2 (Dolomanov et al., 2009 ), VESTA (Momma & Izumi, 2011 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 1879872

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314618016450/wm4087sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314618016450/wm4087Isup2.hkl

checkCIF report

Computing details top

Data collection: CrysAlis PRO (Agilent, 2013); cell refinement: CrysAlis PRO (Agilent, 2013); data reduction: CrysAlis PRO (Agilent, 2013); program(s) used to solve structure: coordinates from isotypic compound; program(s) used to refine structure: OLEX2 (Dolomanov et al., 2009); molecular graphics: VESTA (Momma & Izumi, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).

Dicalcium oxidocuprate(II) dichloride top

Crystal data top

Ca₂CuO₂Cl₂	D_x = 3.641 Mg m⁻³
M_r = 246.60	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4/mmm	Cell parameters from 440 reflections
a = 3.8680 (2) Å	θ = 5.4–27.4°
c = 15.0321 (15) Å	µ = 8.16 mm⁻¹
V = 224.90 (3) Å³	T = 293 K
Z = 2	Block, black
F(000) = 238	0.80 × 0.4 × 0.16 mm

Data collection top

Agilent Xcalibur, Sapphire3 diffractometer	101 independent reflections
Radiation source: Enhance (Mo) X-ray Source	101 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.019
Detector resolution: 16.0318 pixels mm^-1	θ_max = 27.6°, θ_min = 5.4°
ω scans	h = −4→4
Absorption correction: analytical [CrysAlis PRO (Agilent, 2013), using a multi-faceted crystal model based on expressions derived by Clark & Reid (1995)]	k = −4→4
T_min = 0.056, T_max = 0.287	l = −18→18
634 measured reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F² > 2σ(F²)] = 0.018	Secondary atom site location: difference Fourier map
wR(F²) = 0.047	w = 1/[σ²(F_o²) + (0.0248P)² + 0.4487P] where P = (F_o² + 2F_c²)/3
S = 1.24	(Δ/σ)_max < 0.001
101 reflections	Δρ_max = 0.51 e Å⁻³
12 parameters	Δρ_min = −0.43 e Å⁻³

Special details top

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.

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 > 2sigma(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
Cu1	0.0000	0.0000	0.5000	0.0090 (3)
Cl1	0.0000	0.0000	0.31738 (9)	0.0158 (4)
Ca1	0.0000	0.0000	0.10434 (7)	0.0128 (3)
O1	0.5000	0.0000	0.5000	0.0120 (7)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.0049 (4)	0.0049 (4)	0.0171 (5)	0.000	0.000	0.000
Cl1	0.0152 (5)	0.0152 (5)	0.0171 (6)	0.000	0.000	0.000
Ca1	0.0101 (4)	0.0101 (4)	0.0183 (6)	0.000	0.000	0.000
O1	0.0049 (16)	0.0114 (17)	0.0198 (16)	0.000	0.000	0.000

Geometric parameters (Å, º) top

Cu1—Cl1ⁱ	2.7451 (14)	Ca1—Cl1^vi	2.9775 (7)
Cu1—Cl1	2.7452 (14)	Ca1—Cl1^vii	2.9775 (7)
Cu1—O1ⁱⁱ	1.9340 (1)	Ca1—Cl1^viii	2.9775 (7)
Cu1—O1ⁱⁱⁱ	1.9340 (1)	Ca1—O1^ix	2.4900 (7)
Cu1—O1^iv	1.9340 (1)	Ca1—O1^x	2.4900 (7)
Cu1—O1	1.9340 (1)	Ca1—O1^xi	2.4900 (7)
Ca1—Cl1^v	2.9775 (7)	Ca1—O1^xii	2.4900 (7)

Cl1ⁱ—Cu1—Cl1	180.0	Ca1^vii—Cl1—Ca1^viii	133.44 (6)
O1ⁱⁱ—Cu1—Cl1	90.0	Ca1^viii—Cl1—Ca1^vi	81.01 (2)
O1ⁱⁱⁱ—Cu1—Cl1	90.0	Ca1^vii—Cl1—Ca1^v	81.01 (2)
O1—Cu1—Cl1	90.0	Ca1^viii—Cl1—Ca1^v	81.01 (2)
O1^iv—Cu1—Cl1	90.0	O1^ix—Ca1—O1^xi	66.63 (2)
O1^iv—Cu1—Cl1ⁱ	90.0	O1^x—Ca1—O1^xi	101.92 (4)
O1—Cu1—Cl1ⁱ	90.0	O1^x—Ca1—O1^ix	66.63 (2)
O1ⁱⁱ—Cu1—Cl1ⁱ	90.0	O1^xi—Ca1—O1^xii	66.63 (2)
O1ⁱⁱⁱ—Cu1—Cl1ⁱ	90.0	O1^ix—Ca1—O1^xii	101.92 (4)
O1ⁱⁱ—Cu1—O1	90.0	O1^x—Ca1—O1^xii	66.63 (2)
O1ⁱⁱⁱ—Cu1—O1	90.0	Cu1^xiii—O1—Cu1	180.0
O1ⁱⁱⁱ—Cu1—O1ⁱⁱ	180.0	Cu1^xiii—O1—Ca1^vii	90.0
O1—Cu1—O1^iv	180.0	Cu1—O1—Ca1^vii	90.0
O1ⁱⁱ—Cu1—O1^iv	90.0	Cu1—O1—Ca1^xiv	90.0
O1ⁱⁱⁱ—Cu1—O1^iv	90.0	Cu1^xiii—O1—Ca1^xiv	90.0
Cu1—Cl1—Ca1^vi	66.72 (3)	Cu1—O1—Ca1^v	90.0
Cu1—Cl1—Ca1^v	66.72 (3)	Cu1^xiii—O1—Ca1^xv	90.0
Cu1—Cl1—Ca1	180.0	Cu1^xiii—O1—Ca1^v	90.0
Cu1—Cl1—Ca1^viii	66.72 (3)	Cu1—O1—Ca1^xv	90.0
Cu1—Cl1—Ca1^vii	66.72 (3)	Ca1^v—O1—Ca1^xiv	78.08 (4)
Ca1^v—Cl1—Ca1	113.28 (3)	Ca1^xv—O1—Ca1^xiv	101.92 (4)
Ca1^vii—Cl1—Ca1	113.28 (3)	Ca1^vii—O1—Ca1^xiv	180.0
Ca1^vi—Cl1—Ca1	113.28 (3)	Ca1^v—O1—Ca1^xv	180.0
Ca1^vi—Cl1—Ca1^v	133.44 (6)	Ca1^v—O1—Ca1^vii	101.92 (4)
Ca1^viii—Cl1—Ca1	113.28 (3)	Ca1^xv—O1—Ca1^vii	78.08 (4)
Ca1^vii—Cl1—Ca1^vi	81.01 (2)

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

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