Article Cite This: Inorg. Chem. 2017, 56, 14291-14299
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High-Pressure Synthesis and Characterization of the Ammonium Yttrium Borate (NH4)YB8O14 Martin K. Schmitt, Maren Podewitz, Klaus R. Liedl, and Hubert Huppertz* Institut für Allgemeine, Anorganische und Theoretische Chemie, Universität Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
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ABSTRACT: The first high-pressure yttrium borate (NH4)YB8O14 was synthesized at 12.8 GPa/1300 °C using a Walker-type multianvil module. The compound crystallizes in the orthorhombic space group Pnma (no. 62) with the lattice parameters a = 17.6375(9), b = 10.7160(5), and c = 4.2191(2) Å. (NH4)YB8O14 constitutes a novel structure type but exhibits similarities to the crystal structure of β-BaB4O7. X-ray single-crystal and powder diffraction, EDX, vibrational spectroscopy as well as quantum chemical calculations were used to characterize (NH4)YB8O14.
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INTRODUCTION The first high-pressure experiments in the field of transition metal borates were carried out by Brachtel, Jansen, and Depmeier on silver and palladium borates in the early 1980s.1−4 Over the following 20 years, however, only little progress was made in this research area. In 2003, Huppertz and Heymann took up this topic again by synthesizing β-ZnB4O7.5 Since then, our group has continuously explored the field of transition metal borates via high-pressure syntheses revealing the existence of approximately 30 new phases to date. Apart from compounds exhibiting hitherto unknown compositions (such as Co7B24O42(OH)2·2H2O6) or striking new structural features (e.g., the first ammine borate Cd(NH3)2[B3O5(NH3)]27 or the first transition metal cluster containing borate Mo2B4O98), we observed an impressive structural diversity in some M−B−O(−H) (M = transition metal) systems. Our most recent investigations in the system Ni−B−O(−H), for example, yielded three novel high-pressure compounds, γ-NiB4O7,9 Ni3B18O28(OH)4·H2O,10 and NiB3O5(OH),11 within a very narrow p−T range (4−5 GPa/700−900 °C). Inspired by these findings, we turned our attention to yttrium borates because no high-pressure studies have yet been published on these compounds. The Inorganic Crystal Structure Database (ICSD) lists the following compounds for the system Y−B−O(−H): Y[B2O3(OH)]3,12,13 Y17.33(BO3)4(B2O5)2O1614 (revised formula of Y3BO6), and YBO315,16 (several entries exist for various space groups of this phase). Searching the ICSD for compounds consisting of yttrium, boron, oxygen, and an arbitrary additional element yields 46 entries with predominantly alkali, alkaline earth, or transition metals being the fourth component. In this article, we report on the first yttrium-bearing borate synthesized under high-pressure conditions. The pseudoquaternary compound (NH4)YB8O14 was characterized via X-ray single-crystal and powder diffraction, IR and Raman spectroscopy, energy-dispersive © 2017 American Chemical Society
X-ray spectroscopy (EDX), as well as quantum chemical calculations. In addition to (NH4)YB8O14 being the first high-pressure yttrium borate, another interesting aspect of this compound is the incorporation of ammonium. Only very recently was the ammonium fluoridoborate NH4B4O6F discovered to be a promising deep-ultraviolet nonlinear optical material.17
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EXPERIMENTAL SECTION
Synthesis. The high-pressure/high-temperature synthesis of (NH4)YB8O14 was carried out in a Walker-type multianvil module in combination with a 1000 t downstroke press (both Max Voggenreiter GmbH, Germany). A 1:8 molar mixture consisting of Y2O3 (SigmaAldrich, USA, 99.99%) and H3BO3 (Carl Roth, Germany, ≥ 99.8%) was weighed and ground in an agate mortar under ambient conditions. Subsequently, the mixture was filled into a crucible, closed with a lid (both made of α-BN; Henze Boron Nitride Products AG, Germany), and placed into an 18/11 assembly. The compression was accomplished through a two-step mechanism consisting of six steel wedges (outer anvils) and eight tungsten carbide cubes (inner anvils). A more detailed description of the experimental setup can be found in the literature.18−20 The assembly was compressed to approximately 12.8 GPa within 1010 min and subsequently heated to 1300 °C in 10 min. The temperature was maintained for 20 min and afterward reduced to ∼410 °C within 30 min before the heating was switched off to quench the sample to ambient temperature. Subsequently, the pressure was released within 36 h. A colorless reaction product was recovered and mechanically separated from the crucible material. Despite several attempts, a phase pure sample of (NH4)YB8O14 could not be synthesized. Single-Crystal Structure Analysis. A Bruker D8 Quest Kappa diffractometer equipped with a Photon 100 detector was used to collect the single-crystal intensity data at room temperature. An Incoatec microfocus X-ray tube (power settings: 50 kV/1 mA) and a multilayer optic were used to generate monochromatized Mo Kα radiation Received: September 19, 2017 Published: November 1, 2017 14291
DOI: 10.1021/acs.inorgchem.7b02402 Inorg. Chem. 2017, 56, 14291−14299
Article
Inorganic Chemistry (λ = 0.7107 Å). The absorption correction was carried out with SADABS.21 SHELXT22 (version 2014/4) was employed to solve the structure before it was further refined using SHELXL23 (version 2016/6) as implemented in WINGX24 (version 2013/3). The structure was solved and refined (full-matrix least-squares on F2) in space group Pnma (no. 62) and afterward checked with the ADDSYM tool of PLATON25 (version 160117). All non-hydrogen atoms were refined using anisotropic displacement parameters. The positions of the electron density corresponding to the bonds to the four hydrogen atoms were located on the difference Fourier map. Restraints were applied for the N−H distances. X-ray Powder Diffraction. A flat sample of the reaction product was analyzed on a Stoe Stadi P powder diffractometer in transmission geometry using Ge(111)-monochromatized Mo Kα1 radiation (λ = 0.7093 Å). The diffracted radiation was collected with a Dectris Mythen 1K detector. Owing to the strong fluorescence of yttrium by molybdenum radiation, a horizontal background line was subtracted from the measured diffractogram. The Rietveld refinement was carried out with TOPAS 4.226 between 2.0 and 42.0° 2θ using the structural models obtained via single-crystal diffraction. Vibrational Spectroscopy. The absorption spectrum of a singlecrystal was measured in the range 600−4000 cm−1 on a Bruker Vertex 70 FT-IR spectrometer (spectral resolution 4 cm−1) equipped with a Globar mid-IR source (nonpolarized radiation) and a KBr beam splitter.
The spectrometer is connected to a Bruker Hyperion 3000 microscope and equipped with a mercury cadmium telluride (MCT) detector.
Table 1. Crystal and Structure Refinement Data for (NH4)YB8O14 empirical formula molar mass, g mol−1 crystal system space group
(NH4)YB8O14 417.43 orthorhombic Pnma (no. 62) Single-Crystal Data T, °C 24(2) radiation Mo Kα (λ = 0.71073 Å) a, Å 17.6375(9) b, Å 10.7160(5) c, Å 4.2191(2) V, Å3 797.42(7) Z 4 calcd density, g cm−3 3.48 absorption coeff, mm−1 7.4 F(000), e 808 crystal size, mm3 0.06 × 0.05 × 0.02 θ range, deg 2.31−37.82 index ranges −30 ≤ h ≤ 30, −18 ≤ k ≤ 18, −7≤ l ≤ 7 reflections collected 53278 independent reflections 2236 [Rint = 0.094] completeness to θ = 25.24° 100% refinement method Full-matrix least-squares on F2 data/restraints/parameters 2236/3/125 goodness-of-fit on F2 1.071 final R indices [I > 2σ(I)] R1 = 0.034, wR2 = 0.074 R indices (all data) R1 = 0.050, wR2 = 0.080 largest diff. peak/hole, e Å−3 1.17/−1.04 Powder Data radiation Mo Kα1 (λ = 0.7093 Å) a, Å 17.6425(9) b, Å 10.7200(5) c, Å 4.2200(3) V, Å3 798.11(7) range, ° 2θ 2.0−42.0 step width, ° 2θ 0.015 Rexp, % 3.10 Rwp, % 8.99 Rp , % 5.68
Figure 1. Crystal structure of (NH4)YB8O14 viewed along [001̅]. The unit cell is penetrated by two ribbons (dark blue: background; light blue: foreground) formed by “sechser” rings of [BO4] tetrahedra. Along [100], the channels are alternately occupied by yttrium or ammonium ions. All nonhydrogen atoms are drawn with 90% displacement ellipsoids.
Figure 2. Tetrahedra forming the ribbons (dark blue: foreground; light blue: background) vary their orientation with regard to the c-axis resulting in a chain periodicity of eight. As a result, the ribbons are slightly undulated. All nonhydrogen atoms are drawn with 90% displacement ellipsoids. 14292
DOI: 10.1021/acs.inorgchem.7b02402 Inorg. Chem. 2017, 56, 14291−14299
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Inorganic Chemistry
structure optimizations using density functional theory with periodic boundary conditions as implemented in the program suite CRYSTAL14.29,30 For the structure optimizations, two different density functionals were employed, the pure PBESOL31 and the hybrid range-separated HSESOL functional,32 both developed to describe solids. These were used in combination with Basis 1, which provided an effective core potential for Y,33 Pople-type basis sets for B,34 O,35 and N36 as well as Gatti et al.’s 1994 basis set for H.37 For test cases, the structure was also optimized employing mostly triple-ζ basis sets, denoted here as Basis 2, in combination with PBESOL. Basis 2 described B, O, N, and H by Peintinger et al.’s triple-ζ basis sets38 while providing the same effective core potential as in Basis 1 for Y.33 The convergence criterion for the energy was set to 10−7 a.u. in all calculations. IR and Raman frequencies as well as IR intensities were calculated within the harmonic approximation using HSESOL/Basis 1. Calculated modes were analyzed in terms of atomic contribution and classified as stretching or bending mode by CRYSTAL’s vibrational analysis tool and visual inspection. Obtained IR intensities were fitted with Lorentzian functions using J-ICE.39
A BaF2 window was used to carry the single crystal during the measurement in transmittance mode. Then, 160 scans of the sample were recorded employing a 15× IR objective. Data processing was accomplished using OPUS.27 A Horiba Jobin Yvon Labram-HR-800 Raman spectrometer (focal length 800 mm) was used to acquire the Raman spectrum of an arbitrarily oriented single crystal. A 50× objective lens, a 100 μm slit, a 1000 μm confocal pinhole, and an optical grating with 1800 lines mm−1 were used for the measurement. The analyzed area (∼5 μm in diameter) was excited via a 532 nm frequency-doubled Nd:YAG laser. The scattered light was collected by a 1024 × 256 Andor CCD detector in the range of 100−3600 cm−1. Two spectra with an acquisition time of 60 s each were averaged using LABSPEC28 (version 5.93.20). The background was manually fitted and subtracted from the original spectrum. EDX. A semiquantitative EDX measurement was performed on a Jeol JSM-6010LA scanning electron microscope (SEM) in high vacuum. The crystals were mounted on a carbon tape and coated with carbon. An acceleration voltage of 15 kV and a working distance of 14 mm were used for the measurement. The measurement time was 60 s, and the output signal was between 3600 and 4200 cps. The chemical composition was measured on different spots on several crystals and eventually averaged. The final composition was normalized to 100% neglecting hydrogen. Quantum Chemical Methodology. The experimentally obtained crystal structure of (NH4)YB8O14 was subjected to quantum chemical
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RESULTS AND DISCUSSION Synthesis. (NH4)YB8O14 was synthesized in a highpressure/high-temperature experiment at 12.8 GPa/1300 °C using a reactant mixture of Y2O3 and H3BO3. The formation of ammonium ions is the result of a reaction between the BN crucible and water released by the boric acid upon heating and was already observed previously (see experimental section of the cited literature).9,40 More details concerning the synthesis are given in the Experimental Section. Crystal Structure. (NH4)YB8O14 crystallizes in the orthorhombic space group Pnma (no. 62) with the following lattice parameters: a = 17.6375(9), b = 10.7160(5), and c = 4.2191(2) Å. The unit cell (V = 797.42(7) Å3) comprises Z = 4 formula units. Altogether, 17 atom positions (1 × Y, 4 × B, 8 × O, 1 × N, and 3 × H) distributed over the Wyckoff sites 4c and 8d were located during the refinement. More details on crystallographic and refinement data are given in Table 1. The crystal structure consists of “sechser” rings41,42 forming infinite ribbons parallel a (Figure 1). Each ring shares two common tetrahedra with the preceding and succeeding ring, respectively. Alternatively, this arrangement can be viewed as a double chain of [BO4] tetrahedra connected through every second tetrahedron. The tetrahedra vary their orientation with regard to the c-axis. Viewed along a, four tetrahedra point toward −c, followed by four tetrahedra pointing toward +c, which results in a chain periodicity of eight tetrahedra. This leads to a slight undulation of the aforementioned infinite ribbons of “sechser” rings (Figure 2). Every unit cell is penetrated by a second ribbon, which is equivalent to the first one and offset along [011̅] (Figure 1). The tetrahedra forming
Figure 3. View on the crystal structure of (NH4)YB8O14 along the a-axis. The framework of [BO4] tetrahedra exhibits channels parallel to [001] (not visible in this depiction) and [100]. All nonhydrogen atoms are drawn with 90% displacement ellipsoids.
Table 2. Selected Interatomic Distances (Å) for (NH4)YB8O14 Y1−O4 −O6 −O3 −O2 −O6 −O3 −O7 −O8 −O5 −O5 Ø
2.367(2) 2.407(2) 2.579(2) 2.641(2) 2.852(2) 2.906(2) 3.124(2) 3.225(2) 3.229(2) 3.424(2) 2.836
2× 2× 2× 2× 2× 2×
B1−O5 −O2 −O6 −O7
B2−O1 −O4 −O3 −O8
Ø
1.416(2) 1.457(2) 1.475(2) 1.507(2) 1.464
B4−O1 −O4 −O7 −O8
Ø
1.419(2) 1.477(2) 1.509(2) 1.528(2) 1.483
B3−O2 −O6 −O8 −O7
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Ø
1.417(2) 1.466(2) 1.485(2) 1.570(2) 1.485
Ø
1.409(2) 1.447(2) 1.529(2) 1.532(2) 1.479
DOI: 10.1021/acs.inorgchem.7b02402 Inorg. Chem. 2017, 56, 14291−14299
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Inorganic Chemistry
Table 4. Hydrogen Bonds (Å and deg) for (NH4)YB8O14a
the second ribbon point toward the opposite direction (with respect to the a-axis) compared to the ones building up the first ribbon (Figure 1). Both ribbons are connected via common oxygen atoms, which results in the formation of an anionic borate framework exhibiting channels parallel to the a- and c-axis (Figure 3). These channels host the yttrium and ammonium cations. Every channel running parallel to the c-axis contains only one species (e.g., ammonium), whereas the adjacent channels along the a-axis host the other species (in this example, yttrium; Figure 1). The individual interatomic B−O distances vary between 1.416(2) and 1.570(2) Å (Table 2), where the largest bond lengths are those to the oxygen atoms O7 and O8. This is due to the fact that both oxygen atoms are coordinated by three boron atoms, respectively. The average bond lengths and angles (Table 3) within the [BO4] tetrahedra (ØB1 = 1.464/109.5, ØB2 = 1.485/109.4, ØB3 = 1.483/109.4, and ØB4 = 1.479 Å/ 109.3°) are in line with those reported in the literature (Ø = 1.476(35) Å/109.44(2.78)°).43 The yttrium atoms are located between two “sechser” rings. They coordinate to the oxygen atoms belonging to the adjacent rings and the tetrahedra connecting these rings (Figure 4). Their coordination number (CN) can be considered as 10 + 6 (see below). The Y−O bond lengths within the first coordination sphere are larger in (NH4)YB8O14 (2.367(2) ≤ Y−O ≤ 2.906(2) Å; CN = 10 + 6; see Table 2) compared to Y[B2O3(OH)]312,13 (2.339(6) ≤ Y−O ≤ 2.465(3) Å; CN = 9) or YBO316 (2.323(4) ≤ Y−O ≤ 2.386(2) Å, CN = 8). Y−O
Ø O6−B3−O8 O6−B3−O7 O2−B3−O7 O8−B3−O7 O2−B3−O8 O2−B3−O6 Ø
105.9(2) 106.3(2) 109.4(2) 109.6(2) 112.1(2) 113.5(2) 109.5 104.6(2) 105.0(2) 108.3(2) 109.2(2) 111.3(2) 118.1(2) 109.4
O4−B2−O8 O4−B2−O3 O3−B2−O8 O1−B2−O8 O1−B2−O3 O1−B2−O4 Ø O4−B4−O7 O7−B4−O8 O4−B4−O8 O1−B4−O7 O1−B4−O8 O1−B4−O4 Ø
d(D−H)
d(H···A)
d(D···A)
∠(DHA)
0.84(2) 0.84(2) 0.84(2) 0.85(2) 0.85(2) 0.85(2) 0.87(2) 0.87(2) 0.87(2)
2.04(3) 2.58(3) 2.27(3) 1.90(2) 2.65(2) 2.65(2) 2.29(3) 2.29(3) 2.26(4)
2.687(2) 3.180(3) 2.922(2) 2.738(3) 3.152(2) 3.152(2) 2.860(2) 2.860(2) 2.931(3)
134(3) 130(3) 136(3) 166(5) 119(1) 119(1) 123(2) 123(2) 133(5)
a
D: donor; A: acceptor. Symmetry transformations used to generate equivalent atoms: $5: x, −y + 3/2, z; $6: x, y, z − 1; $11: −x + 3/2, y + 1/2, z − 1/2; $12: x, −y + 3/2, z − 1.
Table 5. Charge Distributions and Bond Valence Sums (vu) in (NH4)YB8O14 According to CHARDI (∑Q) and BLBS (∑V) Y1 B1 B2 B3 B4 O1 O2 O3 O4 O5 O6 O7 O8 N1 H1 H2 H3
Table 3. Selected Bond Angles (deg) for (NH4)YB8O14 O2−B1−O6 O5−B1−O7 O5−B1−O6 O2−B1−O7 O6−B1−O7 O5−B1−O2
D−H···A N1−H1···O1_$5 N1−H1···O3 N1−H1···O4_$11 N1−H2···O5 N1−H2···O7 N1−H2···O7_$5 N1−H3···O1_$6 N1−H3···O1_$12 N1−H3···O5_$6
104.8(2) 106.6(2) 107.5(2) 107.6(2) 114.5(2) 115.2(2) 109.4 101.8(2) 105.8(2) 106.1(2) 109.2(2) 113.8(2) 118.8(2) 109.3
∑Q
∑Va
2.96 3.15 3.10 3.16 3.11 −1.94 −1.96 −1.86 −2.14 −1.81 −2.04 −1.84 −1.74 −4.00 0.75 0.75 0.75
2.58 3.13 3.00 2.97 3.02 −2.21 −1.85 −1.84 −2.10 −2.19 −1.96 −2.20 −1.99 (−2.56) (1.00) (1.00) (1.00)
a
Valences in parentheses were determined by assuming that the BVS of H is 1.00.
Figure 4. Yttrium (left) and ammonium (right) ions coordinate to nearby oxygen atoms belonging to the adjacent “sechser” rings (dark blue) and the tetrahedra connecting these rings (light blue). D−H (D: donor) bonds are shown as solid lines; H···A (A: acceptor) bonds are shown as dashed lines. All nonhydrogen atoms are drawn with 90% displacement ellipsoids.
Figure 5. Crystal structure of β-BaB4O7 viewed along [100]. Here, the ribbons run parallel to the b-axis because of the nonstandard setting Pmnb. The chain periodicity is reduced to four (in contrast to eight in (NH4)YB8O14; see also Figure 2). 14294
DOI: 10.1021/acs.inorgchem.7b02402 Inorg. Chem. 2017, 56, 14291−14299
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Inorganic Chemistry Table 6. Atomic Coordinates and Equivalent Isotropic Displacement Parameters Ueq (Å2) for (NH4)YB8O14a
a
atom
Wyckoff position
x
y
z
Ueq
Y1 B1 B2 B3 B4 O1 O2 O3 O4 O5 O6 O7 O8 N1 H1 H2 H3
4c 8d 8d 8d 8d 8d 8d 4c 8d 4c 8d 8d 8d 4c 8d 4c 4c
0.57720(2) 0.5407(1) 0.7974(1) 0.5778(1) 0.66831(9) 0.72054(7) 0.53996(7) 0.8237(1) 0.68217(6) 0.56850(9) 0.46127(7) 0.59184(6) 0.65268(6) 0.6757(2) 0.709(2) 0.637(2) 0.671(3)
0.25 0.6298(2) 0.6262(2) 0.5030(2) 0.5019(2) 0.5992(2) 0.6041(2) 0.75 0.3818(2) 0.75 0.6188(2) 0.5379(2) 0.4757(2) 0.75 0.798(3) 0.75 0.75
0.23738(6) 0.3029(4) 0.2999(4) 0.7913(4) 0.2819(4) 0.2300(3) 0.6420(3) 0.1870(4) 0.1361(3) 0.2262(4) 0.1969(3) 0.1375(3) 0.6328(3) 0.7570(5) 0.827(8) 0.88(2) 0.552(5)
0.00824(6) 0.0030(3) 0.0029(3) 0.0032(3) 0.0031(3) 0.0045(2) 0.0043(2) 0.0042(3) 0.0034(2) 0.0038(3) 0.0043(2) 0.0027(2) 0.0031(2) 0.0058(3) 0.05(2) 0.04(2) 0.06(2)
Ueq is defined as one third of the trace of the orthogonalized Uij tensor.
Table 7. Anisotropic Displacement Parameters Uij (Å2) for (NH4)YB8O14 atom
U11
U22
U33
U12
U13
U23
Y1 B1 B2 B3 B4 O1 O2 O3 O4 O5 O6 O7 O8 N1
0.0083(1) 0.0028(6) 0.0028(6) 0.0032(6) 0.0026(6) 0.0024(4) 0.0063(5) 0.0062(7) 0.0049(5) 0.0037(6) 0.0032(4) 0.0022(4) 0.0033(4) 0.0066(7)
0.0067(1) 0.0042(6) 0.0037(6) 0.0039(6) 0.0042(6) 0.0053(5) 0.0042(5) 0.0021(6) 0.0030(4) 0.0022(6) 0.0028(4) 0.0042(4) 0.0043(5) 0.0042(7)
0.0098(2) 0.0021(6) 0.0024(6) 0.0025(6) 0.0026(6) 0.0056(5) 0.0024(4) 0.0043(6) 0.0023(4) 0.0055(7) 0.0068(5) 0.0015(4) 0.0016(4) 0.0067(8)
0 0.0004(5) −0.0005(5) 0.0000(5) 0.0000(5) −0.0013(3) 0.0019(4) 0 0.0011(4) 0 −0.0007(3) 0.0013(3) 0.0013(4) 0
0.00077(8) −0.0007(5) −0.0004(5) 0.0000(5) 0.0007(5) −0.0003(4) −0.0002(4) 0.0014(5) 0.0005(3) 0.0012(5) −0.0011(3) −0.0008(3) 0.0013(3) −0.0002(7)
0 0.0002(5) 0.0003(5) 0.0007(5) 0.0004(5) 0.0009(4) 0.0010(4) 0 −0.0004(4) 0 −0.0001(4) −0.0010(4) 0.0014(3) 0
Figure 7. EDX spectrum of (NH4)YB8O14. The unindexed peak at ∼0.3 keV originates from carbon used for the sputtering process.
Table 8. Measured and Expected Compositions (Neglecting Hydrogen; Normalized to 100%) (wt %) of (NH4)YB8O14
Figure 6. Rietveld refinement plot.
distances similar to those in the first coordination sphere of (NH4)YB8O14 can be found in Y17.33(BO3)4(B2O5)2O1614 (d(Y−O)max = 2.88(7) Å; CN = 7)44 as well as in Y2B4O945 14295
composition/element
N
Y
B
O
measured expected
4(1) 3.4
23(1) 21.5
25(4) 20.9
49(6) 54.2
DOI: 10.1021/acs.inorgchem.7b02402 Inorg. Chem. 2017, 56, 14291−14299
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Inorganic Chemistry
Table 9. Structural Parameters of (NH4)YB8O14 such as Lattice Vectors and Unit Cell Volume of the Experimentally Obtained Structure as well as of the Quantum Chemically Optimized Structuresa a, Å b, Å c, Å V, Å3 ρ, g cm−3 dN−O, Å dB−O, Å dY−O, Å dmin,Y−Y, Å a
experiment
PBESOL/Basis 1
PBESOL/Basis 2
HSESOL/Basis 1
17.6375(9) 10.7160(5) 4.2191(2) 797.42(7) 3.48 2.687(3)−3.180(3) 1.409(2)−1.570(2) 2.367(2)−3.424(2) 6.335(1)
17.587 10.694 4.207 791.14 3.526 2.68−3.24 1.41−1.53 2.36−3.42 6.39
17.623 10.742 4.212 797.32 3.498 2.70−3.21 1.41−1.57 2.35−3.44 6.34
17.475 10.635 4.179 776.63 3.592 2.68−3.21 1.41−1.52 2.35−3.38 6.33
For details, see Quantum Chemical Methodology.
ammonium. The BVS of N1 was calculated according to a procedure described in The Chemical Bond in Inorganic Chemistry: The Bond Valence Model by I. D. Brown:53 First, the N−H distances were increased to ∼1 Å. The resulting H···O acceptor distances were then used to obtain the corresponding bond valences via the graphical method (details are given in the book). The valences of the N−H bonds were then calculated by subtracting the H···O valences from the atomic valence of H (1.0 vu; vu = valence units). The CN of Y1 can be considered as 10 + 6 because both the contribution to the effective coordination number (c-ECoN) and the calculated bond valences (v) exhibit a significant decrease beyond the tenth oxygen atom [d(Y−O3) = 2.906(2) Å; c-ECoN = 0.218; v = 0.09 versus d(Y−O7) = 3.124(2) Å; c-ECoN = 0.045; v = 0.05]. However, as their contribution to the ECoN or BVS is still significant (they add up to 9% of the total BVS of Y1), the six oxygen atoms up to a distance of 3.424(2) Å were considered as second-sphere ligands of yttrium. The c-ECoN and v values from oxygen atoms even more distant are 0.0 and
