Crystal structure and X-ray powder diffraction data of barium copper iodate Ba₂Cu(IO₃)₆

Abstract

X-ray powder diffraction data, unit-cell parameters, and space group for the barium copper iodate, Ba₂Cu(IO₃)₆, are reported [a = 7.48540(15) Å, b = 7.51753(19) Å, c = 7.64259(17) Å, α = 98.8823(7)°, β = 95.0749(7)°, γ = 97.6297(7)°, V = 418.528(9) ų, Z = 1, and space group P$\bar{1}$]. All measured lines are indexed and are consistent with the corresponding space group. The single-crystal diffraction data of Ba₂Cu(IO₃)₆ are also reported [a = 7.493(3) Å, b = 7.521(6) Å, c = 7.644(5) Å, α = 98.855(18)°, β = 95.060(16)°, γ = 97.62(2)°, V = 419.3(5) ų, Z = 1, and space group P$\bar{1}$]. The crystal structure of Ba₂Cu(IO₃)₆ features isolated [Cu(IO₃)₆]⁴⁻ anionic clusters separated by Ba²⁺ cations. The experimental powder diffraction pattern matches well with the simulated pattern derived from the single crystal data.

I. INTRODUCTION

Metal iodates are an attractive inorganic compound system with a diversity of unusual structures and various physical properties, which mainly arise from the stereochemical active lone pair electrons on the I⁵⁺ ion and the asymmetric pyramidal coordination geometry of IO₃ building units. Over the past two decades, the incorporation of d ⁰ transition-metal ions (Ti⁴⁺, Nb⁵⁺, V⁵⁺, and Mo⁶⁺) into ternary metal iodates afforded abundant new quaternary iodates, many of which exhibit non-centrosymmetric structures and promising nonlinear optical properties (Hu and Mao, 2015; Chen et al., 2021). The quaternary metal iodates containing magnetic transition-metal ions (Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, and Cu²⁺) have also been explored, and their magnetic properties have been studied, such as (LiFe_1/3)(IO₃)₂ (Lan et al., 2002a, 2002b). The Cu²⁺ ion possesses a partially filled d-orbital and usually occupies a distorted octahedral CuO₆ coordination geometry; hence, the combination of copper cations with iodate groups is expected to form novel structures with various connection fashion of CuO₆ units, and may further afford interesting magnetic properties. As far, only seven Cu-containing quaternary iodates, NaCu(IO₃)₃ (Sen Gupta et al., 1987), AgCu(IO₃)₃ (Wang et al., 2017), KCu(IO)₃ (Mitoudi-Vagourdi et al., 2019), and LnCu(IO₃)₅ (Ln = La, Ce, Pr, and Nd) (Geng et al., 2022), have been reported. In this study, a new Cu-containing quaternary iodate, namely, Ba₂Cu(IO₃)₆, has been synthesized. The crystal structure and powder X-ray diffraction data of Ba₂Cu(IO₃)₆ are reported.

II. EXPERIMENTAL

A. Sample preparation

Crystal samples of Ba₂Cu(IO₃)₆ were synthesized by hydrothermal reactions of a mixture of BaCO₃, CuO, and I₂O₅ sealed in a 25 ml Teflon-lined stainless-steel autoclave. The loaded compositions were BaCO₃ (19.7 mg, 0.1 mmol), CuO (4.0 mg, 0.05 mmol), I₂O₅ (2670.4 mg, 8.0 mmol), and H₂O (2.0 ml). The mixture was heated at 220 °C for 70 h, followed by slow cooling to ambient temperature at a rate of 3.0 °C/h. Colorless Ba₂Cu(IO₃)₆ crystals were obtained as a single phase. The as-grown Ba₂Cu(IO₃)₆ crystals exhibit long granular shapes with sizes ranging from 0.1 to 0.5 mm (Supplementary Figure S1). Elemental analyses were carried out on a field emission scanning electron microscope (FEI, NovaNanoSEM450) equipped with an energy-dispersive X-ray spectroscope (EDS; Oxford, X-MaxN). The Ba:Cu:I:O molar ratio based on the EDS analyses was given to be 2.08:1.00:6.11:18.58 (Supplementary Figure S2). The Ba₂Cu(IO₃)₆ crystals were ground into powder and screened through 50 μm mesh for the X-ray powder diffraction measurement.

B. Powder diffraction data collection

X-ray powder diffraction data were collected at room temperature on a Bruker D8 ADVANCE X-ray diffractometer with a LynxEye detector and graphite-filtered Cu Kα radiation (Kα ₁: 1.54059 Å, Kα ₂: 1.54439 Å, Kα ₂/Kα ₁ ratio: 0.5). The X-ray generator operated with voltage and electric current set at 40 kV and 40 mA. The measurement was performed over the 2θ range from 5° to 95° with a scanning step width of 0.02° and a counting time of 1.5 s per step. The profile fitting and refinement of the experimental X-ray powder diffraction pattern were performed using the software package GSAS-II (Toby and Von Dreele, 2013). The Rietveld method (Rietveld, 2014) was adopted for the refinement. In addition, the software package MDI Jade 7.5 (MDI, 2002) was used to fit the background, strip off the Cu Kα ₂ component, and perform the assignment of Miller indices (h, k, l) to the observed peaks in the experimental X-ray powder diffraction pattern. The values of 2θ _obs, d _obs, (I/I _o)_obs, h, k, l, 2θ _cal, d _cal, (I/I _o)_cal, and Δ2θ were obtained (Supplementary Table SI). The Cu Kα ₁ wavelength (λ = 1.5405981 Å) was used in converting observed line positions to d-spacing.

C. Single-crystal diffraction data collection

X-ray single-crystal diffraction data were collected on a Rigaku SCXMini CCD diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at 293(2) K. Data reduction was performed with the software CrystalClear, and absorption correction based on multi-scan method (Blessing, 1995) was applied. The structure was solved by the direct method and refined by the full-matrix least-squares fitting on F ² using the structure solution program package SHELX (Sheldrick, 2015).

III. RESULTS AND DISCUSSION

Through the Rietveld refinements based on the experimental X-ray powder diffraction patterns using the software package GSAS-II, the profile fitting has been performed, and the unit cell and atomic coordinates have been refined. Ba₂Cu(IO₃)₆ is identified to crystallize in the triclinic space group P $\bar{1}$ with unit-cell parameters of a = 7.48540(15) Å, b = 7.51753(19) Å, c = 7.64259(17) Å, α = 98.8823(7)°, β = 95.0749(7)°, γ = 97.6297(7)°, V = 418.528(9) Å³, Z = 1, ρ = 5.5055 g/cm³. The calculated XRD pattern of the Rietveld refinement fits well with the observed pattern (Figure 1), and the final reliability factors wR and GOF are 0.0529 and 2.52, respectively. All observed diffraction peaks of the experimental pattern are well indexed, and no detectable impurities were observed. Using the software package MDI Jade 7.5, the peak positions and intensities have been obtained. The Cu Kα ₁ radiation (λ = 1.5405981 Å) has been used for the d-values calculation. The values of 2θ _obs, d _obs, (I/I _o)_obs, h, k, l, 2θ _cal, d _cal, (I/I _o)_cal, and Δ2θ are listed in Supplementary Table SI. The figure of merit is F ₃₀ = 16.1 (0.0026, 647) (Smith and Snyder, 1979).

Figure 1. The Rietveld refinement plot of the powder XRD patterns for Ba₂Cu(IO₃)₆: experimental data (blue crosses), calculated data (green line), calculated Bragg positions (red tick marks), and difference curves (cyan line). The experimental XRD pattern was measured using the graphite-filtered Cu Kα radiation (Kα ₁: 1.54059 Å, Kα ₂: 1.54439 Å, Kα ₂/Kα ₁ ratio: 0.5).

The crystal structure of Ba₂Cu(IO₃)₆ has also been determined using the X-ray single-crystal diffraction data, which gives the unit cell as a = 7.493(3) Å, b = 7.521(6) Å, c = 7.644(5) Å, α = 98.855(18)°, β = 95.060(16)°, γ = 97.62(2)°, V = 419.3(5) Å³, Z = 1, ρ = 5.495 g/cm³, and space group P $\bar{1}$. The detailed crystallographic information is summarized in Table I. As shown in Figure 2, the crystal structure of Ba₂Cu(IO₃)₆, features isolated [Cu(IO₃)₆]⁴⁻ anionic clusters separated by Ba²⁺ cations. The asymmetric unit contains one Ba, one Cu, three I, and nine O atoms [Figure 2(a)]. I(1), I(2), and I(3) atoms are all three-coordinated in IO₃ trigonal-pyramidal geometry. The Cu(1) atom is located in a CuO₆ distorted octahedral geometry. Each CuO₆ unit is corner-sharing with six IO₃ groups [two I(1)O₃, two I(2)O₃, and two I(3)O₃] all in a monodentate fashion, leading to the formation of [Cu(IO₃)₆]⁴⁻ clusters [Figure 2(b)]. Such [Cu(IO₃)₆]⁴⁻ anions are discrete from each other and further connected by the Ba²⁺ counter cations [Figure 2(c)].

TABLE I. Single-crystal crystallographic data for Ba₂Cu(IO₃)_6.

Figure 2. (a) ORTEP representations of the asymmetric unit shown in thermal ellipsoid with 30% probability (Symmetry codes for the generated equivalent atoms: (a) = 1–x, 1–y, 1–z); (b) view of the [Cu(IO₃)₆]⁴⁻; (c) view of the 3D structure along [001] direction.

The lattice parameters obtained by the Rietveld refinement of experimental X-ray powder diffraction data are very close to these determined by the X-ray single-crystal diffraction data, and the deviations of the lengths of unit-cell axis a, b, c, and unit-cell volume are as minor as 0.10, 0.05, 0.02, and 0.18%, respectively. In addition, the experimental powder diffraction pattern and the simulated pattern derived from single-crystal data show excellent matching (Supplementary Figure S3). These results confirm the accuracy of the reported crystal structure and the X-ray powder diffraction of Ba₂Cu(IO₃)₆.

IV. DEPOSITED DATA

The Crystallographic Information Framework (CIF) file and powder X-ray diffraction data were deposited with the ICDD. You may request this data from ICDD at [email protected].