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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The many-body expansion for aqueous systems revisited: III. Hofmeister ion – water interactions

We report a Many Body Energy (MBE) analysis of aqueous ionic clusters containing anions and cations at the two opposite ends of the Hofmeister series, viz. the kosmotropes Ca2+, SO42- and chaotropes NH4+ and ClO4- with 9 water molecules to quantify the how these ions in altering the interaction between the water molecules in their immediate surrounding. The current results are contrasted to the ones reported earlier for water clusters as well as for alkali metal and halide ion aqueous clusters of the same size, which lie in the middle of the Hofmeister series. Through this analysis, noteworthy differences between the MBE of kosmotropes and chaotropes were identified. The MBE of kosmotropes is dominated by ion-water interactions that extends beyond the 4-body term, the point at which the MBE of pure water converges. The percentage contribution of the 2- B to the total cluster binding energy is noticeably larger. The disruption due to the dominant ion results in weak, unfavorable water-water interactions. The MBE for chaotropes, on the other hand, was found to converge more quickly as it more closely resembles that of pure water clusters. Chaotropes exhibit weaker overall binding energies and ion-water interactions with more favorable water-water interactions, somewhat recovering the pattern of the 2-4 body terms exemplified by pure water clusters. More importantly, both kosmotropic and chaotropic ions exhibit an anticorrelation between the 2-B ion-water (I-W) and water-water (W-W) interactions as well as between the 3-B (I-W-W) and (I-W) interactions. The consideration of two different structural arrangements (ion inside and outside of a water cluster) suggests that fully solvated (ion inside) chaotropes disrupt the hydrogen bonding network in a similar manner as partially solvated (ion outside) kosmotropes and offer useful insights into the modeling requirements of bulk vs. an interface. Finally, the 2-B contribution to the total Basis Set Superposition Error (BSSE) correction for the kosmotropic and chaotropic ions follows the previously reported erf profile vs. intermolecular distance. When scaled for the corresponding dimer energies and distances, a single profile fits the current results together with all previously reported ones for the pure water and halide water clusters.

Herman, Kristina M.↗
DOE OSTI2021

The many-body expansion for aqueous systems revisited: II. Alkali metal and halide ion – water interactions

We present a detailed study of the Many-Body Expansion (MBE) for alkali metal and halide ion-water interactions and quantify the effect of these ions on the strength of the surrounding aqueous hydrogen bonding environment. Building on our previous work on neutral water clusters [J. P. Heindel and S. S. Xantheas, J. Chem. Theor. Comput. 16 (11), 6843–6855 (2020)], we carry out the complete MBE for ion-water clusters, Z+/-(H2O)9, where Z = Li+, K+, Cs+, Cl-, Br-, I- and compare with the results for (H2O)10. The 2-B ion-water (I-W) interaction represents a larger percentage of the total cluster binding energy compared to a pure water cluster of the same size with the total 3-B term being smaller and of opposite sign (repulsive) whereas higher order terms are essentially negligible. The same oscillating behavior around zero for MBE terms higher than the 5-B with basis set that was reported for water clusters is also observed for the ion-water clusters considered with Basis Set Superposition Error (BSSE) corrections amending this like in the water cluster case. A remarkable, linear anti-correlation between the total 2-B ion-water and the total 2-B and 3-B water-water interactions is found, quantifying the effect of the different ions in disrupting and altering (weakening) the neighboring hydrogen bonded water network. Our results suggest a universal behavior of the two different families of ions (alkali metals and halides) for both the correlations of the various components of the total binding energies as well as the estimate of the 2-B BSSE correction which is reported to follow a common profile for ion-water and water-water interactions when cast in terms of reduced distances and energies. We expect our insights into the nature of BSSE will be important for future ab initio based, many-body molecular dynamics studies.

ion-water interactions, water-water interaction, m↗
NASA NTRS1993

The effect of Na vapor on the Na content of chondrules

Chondrules contain higher concentrations of volatiles (Na) than expected for melt droplets in the solar nebula. Recent studies have proposed that chondrules may have formed under non-canonical nebular conditions such as in particle/gas-rich clumps. Such chondrule formation areas may have contained significant Na vapor. To test the hypothesis of whether a Na-rich vapor would minimize Na volatilization reaction rates in a chondrule analog and maintain the Na value of the melt, experiments were designed where a Na-rich vapor could be maintained around the sample. A starting material with a melting point lower that typical chondrules was required to keep the logistics of working with Na volatilization from NaCl within the realm of feasibility. The Knippa basalt, a MgO-rich alkali olivine basalt with a melting temperature of 1325 +/- 5 C and a Na2O content of 3.05 wt%, was used as the chondrule analog. Experiments were conducted in a 1 atm, gas-mixing furnace with the fO2 controlled by a CO/CO2 gas mixture and fixed at the I-W buffer curve. To determine the extent of Na loss from the sample, initial experiments were conducted at high temperatures (1300 C - 1350 C) for duration of up to 72 h without a Na-rich vapor present. Almost all (up to 98%) Na was volatilized in runs of 72 h. Subsequent trials were conducted at 1330 C for 16 h in the presence of a Na-rich vapor, supplied by a NaCl-filled crucible placed in the bottom of the furnace. Succeeding Knudsen cell weight-loss mass-spectrometry analysis of NaCl determined the P(sub Na) for these experimental conditions to be in the 10(exp -6) atm range. This value is considered high for nebula conditions but is still plausible for non-canonical environments. In these trials the Na2O content of the glass was maintained or in some cases increased; Na2O values ranged from 2.62% wt to 4.37% wt. The Na content of chondrules may be controlled by the Na vapor pressure in the chondrule formation region. Most heating events capable of producing chondrules are sufficient to volatile Na. Sodium volatilization reaction rates will be reduced to varying degrees from melt droplets, depending on the magnitude of the P(sub Na) generated. A combination of Na vapor during, and Na diffusion back into chondrules after, formation could maintain and/or enrich Na concentrations in chondrules.

Lewis, R. Dean↗
NASA NTRS2000

Mars Global Surveyor Ka-Band Frequency Data Analysis

The Mars Global Surveyor (MGS) spacecraft, launched on November 7, 1996, carries an experimental space-to-ground telecommunications link at Ka-band (32 GHz) along with the primary X-band (8.4 GHz) downlink. The signals are simultaneously transmitted from a 1.5-in diameter parabolic high gain antenna (HGA) on MGS and received by a beam-waveguide (BWG) R&D 34-meter antenna located in NASA's Goldstone Deep Space Network (DSN) complex near Barstow, California. The projected 5-dB link advantage of Ka-band relative to X-band was confirmed in previous reports using measurements of MGS signal strength data acquired during the first two years of the link experiment from December 1996 to December 1998. Analysis of X-band and Ka-band frequency data and difference frequency (f(sub x)-f(sub ka)/3.8) data will be presented here. On board the spacecraft, a low-power sample of the X-band downlink from the transponder is upconverted to 32 GHz, the Ka-band frequency, amplified to I-W using a Solid State Power Amplifier, and radiated from the dual X/Ka HGA. The X-band signal is amplified by one of two 25 W TWTAs. An upconverter first downconverts the 8.42 GHz X-band signal to 8 GHz and then multiplies using a X4 multiplier producing the 32 GHz Ka-band frequency. The frequency source selection is performed by an RF switch which can be commanded to select a VCO (Voltage Controlled Oscillator) or USO (Ultra-Stable Oscillator) reference. The Ka-band frequency can be either coherent with the X-band downlink reference or a hybrid combination of the USO and VCO derived frequencies. The data in this study were chosen such that the Ka-band signal is purely coherent with the X-band signal, that is the downconverter is driven by the same frequency source as the X-band downlink). The ground station used to acquire the data is DSS-13, a 34-meter BWG antenna which incorporates a series of mirrors inside beam waveguide tubes which guide the energy to a subterranean pedestal room, providing a stable environment for the feed and electronics equipment. A dichroic plate is used to reflect the X-band energy and pass the Ka-band energy to another mirror. The RF energy for each band is then focused onto a feed horn and low-noise amplifier package. After amplification and RF/IF downconversion, the IF signals are sent to the Experimental Tone Tracker (ETT), a digital phase-lock-loop receiver, which simultaneously tracks both X-band and Ka-band carrier signals. Once a signal is detected, the ETT outputs estimates of the SNR in a I -Hz bandwidth (Pc/No), baseband phase and frequency of the signals every I -sec. Between December 1996 and December 1998, the Ka-band and X-band signals from MGS were tracked on a regular basis using the ETT. The Ka-band downlink frequencies described here were referenced to the spacecraft's on-board USO which was also the X-band frequency reference (f(sub ka)= 3.8 f(sub x)). The ETT estimates of baseband phase at I -second sampled time tags were converted to sky frequency estimates. Frequency residuals were then generated for each band by removing a model frequency from each observable frequency at each time tag. The model included Doppler and other effects derived from spacecraft trajectory files obtained from the MGS Navigation Team. A simple troposphere correction was applied to the data. In addition to residuals, the USO frequencies emitted by the spacecraft were estimated. For several passes, the USO frequencies were determined from X-band data and from Ka-band data (referred to X-band by dividing by 3.8) and were found to be in good agreement. In addition, X-band USO frequency estimates from MGS Radio Science data acquired from operational DSN stations were available for comparison and were found to agree within the I Hz level. The remaining sub-Hertz differences were attributed to the different models and software algorithms used by MGS Radio Science and KaBLE-11. A summary of the results of a linear fit of the USO frequency versus time (day of year) is presented in Table I for an initial segment of passes.

Morabito, D.↗
NASA NTRS2010

A First-Order Radiative Transfer Model for Microwave Radiometry of Forest Canopies at L-Band

In this study, a new first-order radiative transfer (RT) model is developed to more accurately account for vegetation canopy scattering by modifying the basic r-co model (the zero-order RT solution). In order to optimally utilize microwave radiometric data in soil moisture (SM) retrievals over moderately to densely vegetated landscapes, a quantitative understanding of the relationship between scattering mechanisms within vegetation canopies and the microwave brightness temperature is desirable. A first-order RT model is used to investigate this relationship and to perform a physical analysis of the scattered and emitted radiation from vegetated terrain. The new model is based on an iterative solution (successive orders of scattering) of the RT equations up to the first order. This formulation adds a new scattering term to the i-w model. The additional term represents emission by particles (vegetation components) in the vegetation layer and emission by the ground that is scattered once by particles in the layer. The new model is tested against 1.4 GHz brightness temperature measurements acquired over deciduous trees by a truck-mounted microwave instrument system called ComRAD in 2007. The model predictions are in good agreement with the data and they give quantitative understanding for the influence of first-order scattering within the canopy on the brightness temperature. The model results show that the scattering term is significant for trees and modifications are necessary to the T-w model when applied to dense vegetation. Numerical simulations also indicate that the scattering term has a negligible dependence on SM and is mainly a function of the angle and polarization of the microwave observation.

Kurum, Mehmet↗
DOE OSTI2020

Materials Data on W3I8 by Materials Project

W3I8 crystallizes in the monoclinic P2_1/c space group. The structure is one-dimensional and consists of two W3I8 ribbons oriented in the (0, 1, 0) direction. there are six inequivalent W+2.67+ sites. In the first W+2.67+ site, W+2.67+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.78–2.81 Å. In the second W+2.67+ site, W+2.67+ is bonded to five I1- atoms to form a mixture of edge and corner-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.78–2.94 Å. In the third W+2.67+ site, W+2.67+ is bonded to five I1- atoms to form a mixture of edge and corner-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.78–3.00 Å. In the fourth W+2.67+ site, W+2.67+ is bonded to five I1- atoms to form a mixture of edge and corner-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.79–2.94 Å. In the fifth W+2.67+ site, W+2.67+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.79–2.82 Å. In the sixth W+2.67+ site, W+2.67+ is bonded to five I1- atoms to form a mixture of edge and corner-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.78–2.99 Å. There are sixteen inequivalent I1- sites. In the first I1- site, I1- is bonded in a 10-coordinate geometry to two W+2.67+ atoms. In the second I1- site, I1- is bonded in a 8-coordinate geometry to two W+2.67+ atoms. In the third I1- site, I1- is bonded in a 3-coordinate geometry to two W+2.67+ atoms. In the fourth I1- site, I1- is bonded in a 12-coordinate geometry to two W+2.67+ atoms. In the fifth I1- site, I1- is bonded in a 12-coordinate geometry to two W+2.67+ atoms. In the sixth I1- site, I1- is bonded in a 8-coordinate geometry to two W+2.67+ atoms. In the seventh I1- site, I1- is bonded in a single-bond geometry to one W+2.67+ atom. In the eighth I1- site, I1- is bonded in a bent 120 degrees geometry to two W+2.67+ atoms. In the ninth I1- site, I1- is bonded in a bent 120 degrees geometry to two W+2.67+ atoms. In the tenth I1- site, I1- is bonded in a 3-coordinate geometry to two W+2.67+ atoms. In the eleventh I1- site, I1- is bonded in a 8-coordinate geometry to two W+2.67+ atoms. In the twelfth I1- site, I1- is bonded in a 9-coordinate geometry to two W+2.67+ atoms. In the thirteenth I1- site, I1- is bonded in a 12-coordinate geometry to two W+2.67+ atoms. In the fourteenth I1- site, I1- is bonded in a 3-coordinate geometry to two W+2.67+ atoms. In the fifteenth I1- site, I1- is bonded in a 9-coordinate geometry to two W+2.67+ atoms. In the sixteenth I1- site, I1- is bonded in a single-bond geometry to one W+2.67+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on WI3 by Materials Project

WI3 crystallizes in the tetragonal P4_12_12 space group. The structure is three-dimensional. there are three inequivalent W3+ sites. In the first W3+ site, W3+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are four shorter (2.79 Å) and one longer (2.82 Å) W–I bond lengths. In the second W3+ site, W3+ is bonded to five I1- atoms to form a mixture of corner and edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.78–2.96 Å. In the third W3+ site, W3+ is bonded to five I1- atoms to form a mixture of corner and edge-sharing WI5 square pyramids. There are four shorter (2.79 Å) and one longer (2.96 Å) W–I bond lengths. There are nine inequivalent I1- sites. In the first I1- site, I1- is bonded in a 12-coordinate geometry to two W3+ atoms. In the second I1- site, I1- is bonded in a 8-coordinate geometry to two W3+ atoms. In the third I1- site, I1- is bonded in a 10-coordinate geometry to two W3+ atoms. In the fourth I1- site, I1- is bonded in a single-bond geometry to one W3+ and one I1- atom. The I–I bond length is 3.58 Å. In the fifth I1- site, I1- is bonded in a 8-coordinate geometry to two W3+ atoms. In the sixth I1- site, I1- is bonded in a bent 120 degrees geometry to two W3+ atoms. In the seventh I1- site, I1- is bonded in a 7-coordinate geometry to two W3+ atoms. In the eighth I1- site, I1- is bonded in a 12-coordinate geometry to two W3+ atoms. In the ninth I1- site, I1- is bonded in a 1-coordinate geometry to two I1- atoms. The I–I bond length is 2.79 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on W5I16 by Materials Project

W5I16 crystallizes in the orthorhombic Pna2_1 space group. The structure is one-dimensional and consists of two W5I16 ribbons oriented in the (1, 1, 0) direction. there are five inequivalent W+3.20+ sites. In the first W+3.20+ site, W+3.20+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.81–2.91 Å. In the second W+3.20+ site, W+3.20+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.75–2.82 Å. In the third W+3.20+ site, W+3.20+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are two shorter (2.77 Å) and three longer (2.84 Å) W–I bond lengths. In the fourth W+3.20+ site, W+3.20+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.76–2.86 Å. In the fifth W+3.20+ site, W+3.20+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.76–2.84 Å. There are sixteen inequivalent I1- sites. In the first I1- site, I1- is bonded in a 9-coordinate geometry to three W+3.20+ atoms. In the second I1- site, I1- is bonded in a 5-coordinate geometry to three W+3.20+ atoms. In the third I1- site, I1- is bonded in a 8-coordinate geometry to three W+3.20+ atoms. In the fourth I1- site, I1- is bonded in a 4-coordinate geometry to three W+3.20+ atoms. In the fifth I1- site, I1- is bonded in a 12-coordinate geometry to two W+3.20+ atoms. In the sixth I1- site, I1- is bonded in a 12-coordinate geometry to two W+3.20+ atoms. In the seventh I1- site, I1- is bonded in a 10-coordinate geometry to two W+3.20+ atoms. In the eighth I1- site, I1- is bonded in a 12-coordinate geometry to two W+3.20+ atoms. In the ninth I1- site, I1- is bonded in a 1-coordinate geometry to one W+3.20+ and one I1- atom. The I–I bond length is 2.96 Å. In the tenth I1- site, I1- is bonded in a single-bond geometry to one W+3.20+ atom. In the eleventh I1- site, I1- is bonded in a distorted single-bond geometry to one W+3.20+ and one I1- atom. The I–I bond length is 3.31 Å. In the twelfth I1- site, I1- is bonded in a 1-coordinate geometry to one W+3.20+ and one I1- atom. The I–I bond length is 2.96 Å. In the thirteenth I1- site, I1- is bonded in a single-bond geometry to one W+3.20+ atom. In the fourteenth I1- site, I1- is bonded in a 2-coordinate geometry to two I1- atoms. In the fifteenth I1- site, I1- is bonded in a distorted linear geometry to two I1- atoms. The I–I bond length is 2.82 Å. In the sixteenth I1- site, I1- is bonded in a 1-coordinate geometry to one I1- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on W15I47 by Materials Project

W5I18W10I29 crystallizes in the monoclinic C2 space group. The structure is one-dimensional and consists of two W10I29 ribbons oriented in the (0, 0, 1) direction and two W5I18 ribbons oriented in the (0, 0, 1) direction. In each W10I29 ribbon, there are five inequivalent W+3.13+ sites. In the first W+3.13+ site, W+3.13+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.80–2.83 Å. In the second W+3.13+ site, W+3.13+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.76–2.84 Å. In the third W+3.13+ site, W+3.13+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.76–2.90 Å. In the fourth W+3.13+ site, W+3.13+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.77–2.89 Å. In the fifth W+3.13+ site, W+3.13+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.76–2.87 Å. There are fifteen inequivalent I1- sites. In the first I1- site, I1- is bonded in a 6-coordinate geometry to three W+3.13+ atoms. In the second I1- site, I1- is bonded in a 12-coordinate geometry to two W+3.13+ atoms. In the third I1- site, I1- is bonded in a distorted single-bond geometry to one W+3.13+ and one I1- atom. The I–I bond length is 2.98 Å. In the fourth I1- site, I1- is bonded in a distorted linear geometry to two I1- atoms. The I–I bond length is 3.02 Å. In the fifth I1- site, I1- is bonded in a distorted single-bond geometry to one W+3.13+ and one I1- atom. In the sixth I1- site, I1- is bonded in a distorted single-bond geometry to one W+3.13+ and one I1- atom. The I–I bond length is 3.01 Å. In the seventh I1- site, I1- is bonded in a linear geometry to two equivalent I1- atoms. In the eighth I1- site, I1- is bonded in a single-bond geometry to one W+3.13+ atom. In the ninth I1- site, I1- is bonded in a single-bond geometry to one W+3.13+ atom. In the tenth I1- site, I1- is bonded in a 4-coordinate geometry to three W+3.13+ atoms. In the eleventh I1- site, I1- is bonded in a 2-coordinate geometry to two W+3.13+ atoms. In the twelfth I1- site, I1- is bonded in a 10-coordinate geometry to three W+3.13+ atoms. In the thirteenth I1- site, I1- is bonded in a 12-coordinate geometry to two W+3.13+ atoms. In the fourteenth I1- site, I1- is bonded in a 10-coordinate geometry to three W+3.13+ atoms. In the fifteenth I1- site, I1- is bonded in a 11-coordinate geometry to two W+3.13+ atoms. In each W5I18 ribbon, there are three inequivalent W+3.13+ sites. In the first W+3.13+ site, W+3.13+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are three shorter (2.82 Å) and two longer (2.84 Å) W–I bond lengths. In the second W+3.13+ site, W+3.13+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.77–2.89 Å. In the third W+3.13+ site, W+3.13+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.79–2.89 Å. There are ten inequivalent I1- sites. In the first I1- site, I1- is bonded in a 11-coordinate geometry to two W+3.13+ atoms. In the second I1- site, I1- is bonded in a 10-coordinate geometry to three W+3.13+ atoms. In the third I1- site, I1- is bonded in a 12-coordinate geometry to two W+3.13+ atoms. In the fourth I1- site, I1- is bonded in a distorted single-bond geometry to one W+3.13+ and one I1- atom. The I–I bond length is 3.11 Å. In the fifth I1- site, I1- is bonded in a distorted linear geometry to two I1- atoms. The I–I bond length is 2.85 Å. In the sixth I1- site, I1- is bonded in a 1-coordinate geometry to one I1- atom. In the seventh I1- site, I1- is bonded in a distorted single-bond geometry to one W+3.13+ and one I1- atom. The I–I bond length is 2.98 Å. In the eighth I1- site, I1- is bonded in a distorted linear geometry to two equivalent I1- atoms. In the ninth I1- site, I1- is bonded in a single-bond geometry to one W+3.13+ atom. In the tenth I1- site, I1- is bonded in a 10-coordinate geometry to three W+3.13+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on WI2 by Materials Project

WI2 crystallizes in the orthorhombic Cmce space group. The structure is two-dimensional and consists of two WI2 sheets oriented in the (0, 1, 0) direction. there are three inequivalent W2+ sites. In the first W2+ site, W2+ is bonded to five I1- atoms to form edge-sharing WI5 square pyramids. There are four shorter (2.83 Å) and one longer (2.84 Å) W–I bond lengths. In the second W2+ site, W2+ is bonded to five I1- atoms to form a mixture of corner and edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.81–2.96 Å. In the third W2+ site, W2+ is bonded to five I1- atoms to form a mixture of corner and edge-sharing WI5 square pyramids. There are a spread of W–I bond distances ranging from 2.81–2.96 Å. There are four inequivalent I1- sites. In the first I1- site, I1- is bonded in a distorted bent 150 degrees geometry to two W2+ atoms. In the second I1- site, I1- is bonded in a 11-coordinate geometry to three W2+ atoms. In the third I1- site, I1- is bonded in a single-bond geometry to one W2+ atom. In the fourth I1- site, I1- is bonded in a 12-coordinate geometry to three W2+ atoms.

36 MATERIALS SCIENCE↗