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Mo(CO)6 is Cubic alpha N2-derived structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of twenty-four formaldehyde molecules and four molybdenum(6+) molecules.
A two-step solar thermochemical looping cycle based on Co 3 Mo 3 N/Co 6 Mo 6 N reduction/nitridation reactions offers a pathway for green NH 3 production that utilizes concentrated solar irradiation, H 2 O, and air as feedstocks. The NH 3 production cycle steps both derive process heat from concentrated solar irradiation and encompass 1) the reduction of Co 3 Mo 3 N in H 2 to Co 6 Mo 6 N and NH 3 ; and 2) nitridation of Co 6 Mo 6 N to Co 3 Mo 3 N with N 2 . Co 3 Mo 3 N reduction/nitridation reactions are examined at different H 2 and/or N 2 partial pressures and temperatures. NH 3 production is quantified in situ using liquid conductivity measurements coupled with mass spectrometry (MS). Solid-state characterization is performed to identify a surface oxygen layer that necessitates the addition of H 2 during cycling to prevent surface oxidation by trace amounts of O 2 . H 2 concentrations of > 5% H 2 /Ar and temperatures >500 °C are required to reduce Co 3 Mo 3 N to Co 6 Mo 6 N and form NH 3 at 1 bar. Complete regeneration of Co 3 Mo 3 N from Co 6 Mo 6 N is achieved at conditions of 700 °C under 25–75% H 2 /N 2 . H 2 pressure-swings are observed to increase NH 3 production during Co 3 Mo 3 N reduction. In conclusion, the results represent the first comprehensive characterization of and definitive non-catalytic production of NH 3 via chemical looping with metal nitrides and provide insights for technology development.
Electrocatalytic nitrate to ammonia conversion is a key reaction for energy and environmental sustainability. This reaction involves complex multi electron and proton transfer steps, and is impeded by the lack of catalyst for promoting both reactivity and ammonia selectivity. Here, we demonstrate active motifs based on the Chevrel phase Co 2 Mo 6 S 8 exhibit an enzyme-like high turnover frequency of ~95.1 s –1 for nitrate electroreduction to ammonia. We reveal strong synergy of multiple binding sites on this catalyst, such that the ligand effect of Co steers H ad* toward hydrogenation other than hydrogen evolution, the ensemble effect of Co, and the spatial confinement effect that promote the full hydrogenation of NO x to ammonia without N–N coupling. The catalyst exhibits almost exclusive ammonia conversion with a Faradaic efficiency of 97.1% and ammonia yielding rate of 115.5 mmol·g cat –1 ·h –1 in neutral electrolytes. The high activity was also confirmed in electrolytes with dilute nitrate and high chloride concentrations.
Solar Thermal Ammonia Production has the potential to synthesize ammonia in a green, renewable process that can greatly reduce the carbon footprint left by the conventional Haber-Bosch reaction. Co 3 Mo 3 N has been identified as a potential candidate for ammonia production. It is synthesized via oxide precursor synthesis followed by nitridation under 10% H 2 /N 2 . The synthesis method can be extended to other candidate nitrides. The Co 3 Mo 3 N → Co 6 Mo 6 N reduction is demonstrated on TGA with rapid kinetics. The formation of NH 3 is qualitatively observed, but not quantitatively determined. The material retains crystal structure, but no secondary phases are observed in XRD. Partial re-nitridation back to CMN331 of ~35% of max nitridation is observed. Reaction parameters in TGA differ from experimental conditions in the literature. Experiments at Georgia Tech better mimic re-nitridation conditions with more sensitive, quantitative analytical techniques (GC-MS). The ASU NH 3 synthesis/re-nitridation reactor is under development and will permit experiments (reduction/re-nitridation) under precisely controlled T, pH 2 .
As one of the most attractive transition metal dichalcogenides (TMDs), the growth of molybdenum disulfide (MoS 2 ) with industrial compatibility is of great importance. Atomic layer deposition (ALD) has been shown to be a promising method to achieve the growth of high-quality TMD materials. However, MoS 2 films deposited by ALD often are amorphous with nonideal stoichiometry and require high-temperature post-deposition annealing. Here, we introduce a modified ALD recipe using Mo(CO) 6 and H 2 S, resulting in controllable linear growth behavior, a S-to-Mo ratio of 2:1, and crystalline films at a temperature as low as 190 °C. The growth mechanisms and key factors leading to this improvement are proposed and complemented by kinetics calculations. This newly developed methodology relies on aligning the process time with the reaction kinetics of carbonyl disassociation. The MoS 2 films prepared herein were shown to be active hydrogen evolution reaction catalysts.
Molybdenum carbide nanoparticles (α-MoC 1−x NPs) are promising catalysts that offer noble-metal-like performance at lower cost. We report a mild continuous-flow synthesis of α-MoC 1−x NPs from Mo(CO) 6 , coupled with in-line spectroscopic monitoring and machine learning (ML)-based analysis to quantify precursor conversion and product formation in real time. A multilayer perceptron ML model was found to accurately deconvolute complex, nonlinear spectral patterns, enabling identification of a two-step reaction pathway, involving precursor conversion to an amorphous intermediate followed by intraparticle crystallization to α-MoC 1−x NPs, with the first step being rate limiting. Ex situ small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) validation confirm the predicted concentration profiles and crystallization behavior. This integrated approach showcases how ML can empower insights into NP nucleation and growth, paving the way for self-driving, flow-based platforms for NP synthesis.
Ternary nitrides in the family A 3 B x N (A=Co, Ni, Fe; B=Mo; x=2,3) identified and synthesized. Experiments with Co 3 Mo 3 N in Ammonia Synthesis Reactor demonstrate cyclable NH3 production from bulk nitride under pure H 2 . Production rates were approx. constant in all the reduction steps with no evident dependence on the consumed solid-state nitrogen up to formation of 661. Material can be re-nitridized under pure N 2 (or 10% H 2 /N 2 ). Bulk N utilization per reduction step averaged between 25 – 40% of the total (2-3 hours). Rate equations and parameters extracted from data. NH 3 selectivity exceeds gas phase equilibrium at higher temperatures (in a large excess of H 2 ). Selectivity begins to decrease significantly above 650 C, N 2 production rapidly increases above 650 C seemingly due to reaction that is zero order in H 2 (thermal reduction of the nitride?). Poised to begin the systematics studies of relationships between materials and reactions.
Reaction of the aryltin( ii ) hydrides with molybdenum carbonyl afforded Mo(CO) 5 {Sn(Ar iPr 6 )H}, (1), or Mo(CO) 5 {Sn(Ar iPr 4 )(THF)H} (2), respectively, in which 1 reacted with carbon dioxide, to yield Mo(CO) 5 {Sn(Ar iPr 6 )(κ 2 -O,O′-O 2 CH)}, (3).
Polyoxometalates (POMs) featuring 7, 12, 18, or more redox-accessible transition metal ions are ubiquitous as selective catalysts, especially for oxidation reactions. The corresponding synthetic and catalytic chemistry of stable, discrete, capping-ligand-free polythiometalates (PTMs), which could be especially attractive for reduction reactions, is much less well developed. Among the challenges are the propensity of PTMs to agglomerate and the tendency for agglomeration to block reactant access of catalyst active sites. Nevertheless, the pervasive presence of transition metal sulfur clusters metalloenzymes or cofactors that catalyze reduction reactions and the justifiable proliferation of studies of two-dimensional (2D) metal-chalcogenides as reduction catalysts point to the promise of well-defined and controllable PTMs as reduction catalysts. Here, we report the fabrication of agglomeration-immune, reactant-accessible, capping-ligand-free Co II Mo 6 IV S 24 n– clusters as periodic arrays in a water-stable, hierarchically porous Zr-metal–organic framework (MOF; NU1K) by first installing a disk-like Anderson polyoxometalate, Co III Mo 6 VI O 24 m– , in size-matched micropores where the siting is established via difference electron density (DED) X-ray diffraction (XRD) experiments. Flowing H 2 S, while heating, reduces molybdenum(VI) ions to Mo(IV) and quantitatively replaces oxygen anions with sulfur anions (S 2– , HS – , S 2 2– ). DED maps show that MOF-templated POM-to-PTM conversion leaves clusters individually isolated in open-channel-connected micropores. Importantly, the structure of the immobilized cluster as determined, in part, by X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) analysis, and pair distribution function (PDF) analysis of total X-ray scattering agrees well with the theoretically simulated structure. PTM@MOF displays both electrocatalytic and photocatalytic competency for hydrogen evolution. Nevertheless, the initially installed PTM appears to be a precatalyst, gaining competency only after the loss of ~3 to 6 sulfurs and exposure to hydride-forming metal ions.
Heterometallic clusters have attracted broad interests in the synthetic chemistry due to their various coordination modes and potential applications in heterogeneous catalysis. Here we report the synthesis, experimental, and theoretical characterizations of four ternary clusters ([M 2 (CO) 6 Sn 2 Sb 5 ] 3- (M = Cr, Mo), and [(MSn 2 Sb 5 ) 2 ] 4- , (M = Cu, Ag)) in the process of capturing the hypho - [Sn 2 Sb 5 ] 3- in ethylenediamine (en) solution. We show that the coordination of the binary anion to transition-metal ions or fragments provides additional stabilization due to the formation of locally σ-aromatic units, producing a spherical aromatic shielding region in the cages. While in the case of [Mo 2 (CO) 6 Sn 2 Sb 5 ] 3- stabilization arises from locally σ-aromatic three-centre and five-centre two-electron bonds, aromatic islands in [(AgSn 2 Sb 5 ) 2 ] 4- and [(CuSn 2 Sb 5 ) 2 ] 4- render them globally antiaromatic. This work describes the coordination chemistry of the versatile building block [Sn 2 Sb 5 ] 3- , thus providing conceptual advances in the field of metal-metal bonding in clusters.
Direct CO 2 electrolysis using solid oxide electrolysis cells (CO 2 -SOECs) holds promise to efficiently convert carbon dioxide to carbon monoxide and oxygen. Cathodes with desirable catalytic activity and chemical stability play a critical role in the development of direct CO 2 -SOECs. Although Sr 2 Fe 1.5 Mo 0.5 O 6–δ (SFM) has exhibited promise for direct CO 2 -SOECs due to its redox stability, it suffers from insufficient activity for the CO 2 reduction reaction (CO 2 RR). Here we report interface engineering of nanosized Pr 6 O 11 on the SFM cathode obtained through infiltration to promote the CO 2 RR performance for direct CO 2 -SOECs. The effect of Pr 6 O 11 loading on the performance of the CO 2 RR is systematically investigated. At 800 °C, the current density of the Pr 6 O 11 infiltrated SFM cathode with an optimum Pr 6 O 11 loading of 14.8 wt% reaches 1.61 A cm –2 at 1.5 V, more than double that of the SFM cathode (0.76 A cm –2 ) under the same operating conditions. X-ray photoelectron spectroscopy (XPS) characterization and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis indicate that the adsorption ability of CO 2 on the SFM cathode has been significantly improved by the formation of Pr 6 O 11 . Temperature-programmed desorption (TPD) of CO 2 measurements further manifest that a 14.8 wt% Pr 6 O 11 -SFM cathode has better CO desorption capacity. In addition, polarization resistance of the SFM cathode has significantly decreased with the addition of Pr 6 O 11 . Three-electrode measurement was used to analyze the improved electrode kinetics. Finally, these results demonstrate that the formation of Pr 6 O 11 in the SFM cathode through infiltration is a promising approach for increasing CO 2 RR activity for CO 2 -SOECs.
Sr20FeCo9(MoO6)10 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are ten inequivalent Sr sites. In the first Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, a faceface with one FeO6 octahedra, faces with three CoO6 octahedra, and faces with four MoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.63–3.04 Å. In the second Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four MoO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.63–3.06 Å. In the third Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four MoO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.65–3.06 Å. In the fourth Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, a faceface with one FeO6 octahedra, faces with three CoO6 octahedra, and faces with four MoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.64–3.05 Å. In the fifth Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, a faceface with one FeO6 octahedra, faces with three CoO6 octahedra, and faces with four MoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.63–3.05 Å. In the sixth Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four MoO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.62–3.05 Å. In the seventh Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four MoO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.63–3.05 Å. In the eighth Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four MoO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.64–3.06 Å. In the ninth Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four MoO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.66–3.05 Å. In the tenth Sr site, Sr is bonded to twelve O atoms to form distorted SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, a faceface with one FeO6 octahedra, faces with three CoO6 octahedra, and faces with four MoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.64–3.03 Å. There are five inequivalent Mo sites. In the first Mo site, Mo is bonded to six O atoms to form MoO6 octahedra that share a cornercorner with one FeO6 octahedra, corners with five CoO6 octahedra, and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–17°. There are a spread of Mo–O bond distances ranging from 1.93–1.99 Å. In the second Mo site, Mo is bonded to six O atoms to form MoO6 octahedra that share corners with six CoO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–16°. There are a spread of Mo–O bond distances ranging from 1.93–1.96 Å. In the third Mo site, Mo is bonded to six O atoms to form MoO6 octahedra that share corners with six CoO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–16°. There are a spread of Mo–O bond distances ranging from 1.93–1.96 Å. In the fourth Mo site, Mo is bonded to six O atoms to form MoO6 octahedra that share a cornercorner with one FeO6 octahedra, corners with five CoO6 octahedra, and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–16°. There are a spread of Mo–O bond distances ranging from 1.94–2.03 Å. In the fifth Mo site, Mo is bonded to six O atoms to form MoO6 octahedra that share a cornercorner with one FeO6 octahedra, corners with five CoO6 octahedra, and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–17°. There are a spread of Mo–O bond distances ranging from 1.93–1.98 Å. Fe is bonded to six O atoms to form FeO6 octahedra that share corners with six MoO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–15°. There are two shorter (2.02 Å) and four longer (2.05 Å) Fe–O bond lengths. There are five inequivalent Co sites. In the first Co site, Co is bonded to six O atoms to form CoO6 octahedra that share corners with six MoO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–17°. There are a spread of Co–O bond distances ranging from 2.05–2.10 Å. In the second Co site, Co is bonded to six O atoms to form CoO6 octahedra that share corners with six MoO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–16°. There are a spread of Co–O bond distances ranging from 2.07–2.10 Å. In the third Co site, Co is bonded to six O atoms to form CoO6 octahedra that share corners with six MoO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–16°. There are a spread of Co–O bond distances ranging from 2.07–2.10 Å. In the fourth Co site, Co is bonded to six O atoms to form CoO6 octahedra that share corners with six MoO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–17°. There are two shorter (2.07 Å) and four longer (2.09 Å) Co–O bond lengths. In the fifth Co site, Co is bonded to six O atoms to form CoO6 octahedra that share corners with six MoO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–16°. There are a spread of Co–O bond distances ranging from 2.05–2.11 Å. There are thirty inequivalent O sites. In the first O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–4°. In the second O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–4°. In the third O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–4°. In the fourth O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–4°. In the fifth O site, O is bonded to four Sr, one Mo, and one Fe atom to form a mixture of distorted edge and corner-sharing OSr4FeMo octahedra. The corner-sharing octahedra tilt angles range from 0–2°. In the sixth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the seventh O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the eighth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the ninth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the tenth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Fe atom. In the eleventh O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Fe atom. In the twelfth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the thirteenth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the fourteenth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the fifteenth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the sixteenth O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–2°. In the seventeenth O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–3°. In the eighteenth O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–4°. In the nineteenth O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–3°. In the twentieth O site, O is bonded to four Sr, one Mo, and one Co atom to form a mixture of distorted edge and corner-sharing OSr4CoMo octahedra. The corner-sharing octahedra tilt angles range from 0–3°. In the twenty-first O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the twenty-second O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the twenty-third O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the twenty-fourth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the twenty-fifth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the twenty-sixth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the twenty-seventh O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the twenty-eighth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the twenty-ninth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom. In the thirtieth O site, O is bonded in a 6-coordinate geometry to four Sr, one Mo, and one Co atom.
Heterotrimetallic complexes with (N 2 S 2 )M metallodithiolates, M = Ni 2+ , [Fe(NO)] 2+ , and [Co(NO)] 2+ , as bidentate chelating ligands to a central trans-Cr(NO)(MeCN) unit were characterized as the first members of a new class, NiCrNi, FeCrFe, CoCrCo. The complexes exhibit a cisoid structural topology, ascribed to the stereoactivity of the available lone pair(s) on the sulfur donors, resulting in a dispersed, electropositive pocket from the N/N and N/S hydrocarbon linkers wherein the Cr-NO site is housed. Computational studies explored alternative isomers (transoid and inverted cisoid) that suggest a combination of electronic and steric effects govern the geometrical selectivity. Electrostatic potential maps readily display the dominant electronegative potential from the sulfurs which force the NO to the electropositive pocket. The available S lone pairs work in synergy with the π-withdrawing ability of NO to lift Cr out of the S 4 plane toward the NO and stabilize the geometry. The metallodithiolate ligands bound to Cr(NO) thus find structural consistency across the three congeners. Although the dinitrosyl [(bme-dach)Co(NO)-Mo(NO)(MeCN)-(bme-dach)Co(MeCN)][PF 6 ] 2 (CoMoCo') analogue displays chemical noninnocence and a partial Mo–Co bond toward (N 2 S 2 )Co'(NCCH 3 ) in an “asymmetric butterfly” topology, the stability of the {Cr(NO)} 5 unit prohibits such bond rearrangement. Magnetism and EPR studies illustrate spin coupling across the sulfur thiolate sulfur bridges.
CoMo is Frank-Kasper $\mu$ Phase-like structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are seven inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to four Mo and twelve Co atoms. There are one shorter (2.65 Å) and three longer (2.85 Å) Mo–Mo bond lengths. There are a spread of Mo–Co bond distances ranging from 2.70–2.88 Å. In the second Mo site, Mo is bonded in a 10-coordinate geometry to seven Mo and nine equivalent Co atoms. There are a spread of Mo–Mo bond distances ranging from 2.69–2.85 Å. There are three shorter (2.75 Å) and six longer (2.91 Å) Mo–Co bond lengths. In the third Mo site, Mo is bonded in a 8-coordinate geometry to eight Mo and six equivalent Co atoms. There are a spread of Mo–Mo bond distances ranging from 2.52–3.04 Å. All Mo–Co bond lengths are 2.60 Å. In the fourth Mo site, Mo is bonded in a 8-coordinate geometry to eight Mo and six equivalent Co atoms. There are three shorter (3.02 Å) and three longer (3.05 Å) Mo–Mo bond lengths. All Mo–Co bond lengths are 2.60 Å. In the fifth Mo site, Mo is bonded in a 6-coordinate geometry to six Mo and six Co atoms. There are three shorter (2.63 Å) and three longer (2.69 Å) Mo–Co bond lengths. In the sixth Mo site, Mo is bonded in a 6-coordinate geometry to six Mo and six Co atoms. There are three shorter (2.65 Å) and three longer (2.69 Å) Mo–Co bond lengths. In the seventh Mo site, Mo is bonded to six equivalent Mo and six equivalent Co atoms to form distorted MoCo6Mo6 cuboctahedra that share corners with twelve equivalent CoCo4Mo8 cuboctahedra, edges with six equivalent MoCo6Mo6 cuboctahedra, and faces with eighteen equivalent CoCo4Mo8 cuboctahedra. All Mo–Co bond lengths are 2.47 Å. There are three inequivalent Co sites. In the first Co site, Co is bonded to eight Mo and four equivalent Co atoms to form distorted CoCo4Mo8 cuboctahedra that share corners with two equivalent MoCo6Mo6 cuboctahedra, corners with thirteen CoCo4Mo8 cuboctahedra, edges with five CoCo4Mo8 cuboctahedra, faces with three equivalent MoCo6Mo6 cuboctahedra, and faces with ten equivalent CoCo4Mo8 cuboctahedra. There are two shorter (2.34 Å) and two longer (2.43 Å) Co–Co bond lengths. In the second Co site, Co is bonded to seven Mo and five Co atoms to form CoCo5Mo7 cuboctahedra that share corners with fifteen CoCo4Mo8 cuboctahedra, edges with five CoCo5Mo7 cuboctahedra, and faces with thirteen CoCo5Mo7 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.38–2.41 Å. In the third Co site, Co is bonded to six equivalent Mo and six equivalent Co atoms to form CoCo6Mo6 cuboctahedra that share corners with twelve equivalent CoCo5Mo7 cuboctahedra, edges with six equivalent CoCo6Mo6 cuboctahedra, and faces with eighteen equivalent CoCo5Mo7 cuboctahedra.
Co7Mo6 is Frank-Kasper $\mu$ Phase structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to nine Mo and six equivalent Co atoms. There are a spread of Mo–Mo bond distances ranging from 2.74–3.03 Å. There are three shorter (2.65 Å) and three longer (2.69 Å) Mo–Co bond lengths. In the second Mo site, Mo is bonded in a 6-coordinate geometry to four Mo and twelve Co atoms. There are one shorter (2.63 Å) and three longer (2.83 Å) Mo–Mo bond lengths. There are a spread of Mo–Co bond distances ranging from 2.70–2.87 Å. In the third Mo site, Mo is bonded in a 8-coordinate geometry to eight Mo and six equivalent Co atoms. The Mo–Mo bond length is 2.54 Å. All Mo–Co bond lengths are 2.59 Å. There are two inequivalent Co sites. In the first Co site, Co is bonded to seven Mo and five Co atoms to form a mixture of corner, edge, and face-sharing CoCo5Mo7 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.37–2.40 Å. In the second Co site, Co is bonded to six equivalent Mo and six equivalent Co atoms to form CoCo6Mo6 cuboctahedra that share corners with twelve equivalent CoCo5Mo7 cuboctahedra, edges with six equivalent CoCo6Mo6 cuboctahedra, and faces with eighteen equivalent CoCo5Mo7 cuboctahedra.
Mo4Co2C crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are two inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to six equivalent Co atoms. All Mo–Co bond lengths are 2.43 Å. In the second Mo site, Mo is bonded in a 2-coordinate geometry to four equivalent Co and two equivalent C atoms. There are two shorter (2.71 Å) and two longer (2.91 Å) Mo–Co bond lengths. Both Mo–C bond lengths are 2.12 Å. Co is bonded in a 12-coordinate geometry to nine Mo and three equivalent Co atoms. All Co–Co bond lengths are 2.60 Å. C is bonded to six equivalent Mo atoms to form corner-sharing CMo6 octahedra. The corner-sharing octahedral tilt angles are 39°.
Mo4Co2N crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are two inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to six equivalent Co atoms. All Mo–Co bond lengths are 2.43 Å. In the second Mo site, Mo is bonded in a distorted bent 150 degrees geometry to four equivalent Co and two equivalent N atoms. There are two shorter (2.69 Å) and two longer (2.88 Å) Mo–Co bond lengths. Both Mo–N bond lengths are 2.12 Å. Co is bonded in a 12-coordinate geometry to nine Mo and three equivalent Co atoms. All Co–Co bond lengths are 2.61 Å. N is bonded to six equivalent Mo atoms to form corner-sharing NMo6 octahedra. The corner-sharing octahedral tilt angles are 41°.
Fourteen nickel-base superalloy single crystals containing 0 to 5 wt% chromium (Cr), 0 to 11 wt% cobalt (Co), 6 to 12 wt% molybdenum (Mo), 0 to 4 wt% rhenium (Re), and fixed amounts of aluminum (Al) and tantalum (Ta) were examined to determine the effect of bulk composition on basic microstructural parameters, including gamma' solvus, gamma' volume fraction, volume fraction of topologically close-packed (TCP) phases, phase chemistries, and gamma - gamma'. lattice mismatch. Regression models were developed to describe the influence of bulk alloy composition on the microstructural parameters and were compared to predictions by a commercially available software tool that used computational thermodynamics. Co produced the largest change in gamma' solvus over the wide compositional range used in this study, and Mo produced the largest effect on the gamma lattice parameter and the gamma - gamma' lattice mismatch over its compositional range, although Re had a very potent influence on all microstructural parameters investigated. Changing the Cr, Co, Mo, and Re contents in the bulk alloy had a significant impact on their concentrations in the gamma matrix and, to a smaller extent, in the gamma' phase. The gamma phase chemistries exhibited strong temperature dependencies that were influenced by the gamma and gamma' volume fractions. A computational thermodynamic modeling tool significantly underpredicted gamma' solvus temperatures and grossly overpredicted the amount of TCP phase at 982 C. Furthermore, the predictions by the software tool for the gamma - gamma' lattice mismatch were typically of the wrong sign and magnitude, but predictions could be improved if TCP formation was suspended within the software program. However, the statistical regression models provided excellent estimations of the microstructural parameters based on bulk alloy composition, thereby demonstrating their usefulness.