Enhancing Photocatalysis: Understanding the Mechanistic Diversity in Photocatalysts Modified with Single-Atom Catalytic Sites.

Surface modification of heterogeneous photocatalysts with single-atom catalysts (SACs) is an attractive approach for achieving enhanced photocatalytic performance. However, there is limited knowledge of the mechanism of photocatalytic enhancement in SAC-modified photocatalysts, which makes the rational design of high-performance SAC-based photocatalysts challenging. Herein, a series of photocatalysts for the aerobic degradation of pollutants based on anatase TiO2 modified with various low-cost, non-noble SACs (vanadate, Cu, and Fe ions) is reported. The most active SAC-modified photocatalysts outperform TiO2 modified with the corresponding metal oxide nanoparticles and state-of-the-art benchmark photocatalysts such as platinized TiO2 and commercial P25 powders. A combination of in situ electron paramagnetic resonance spectroscopy and theoretical calculations reveal that the best-performing photocatalysts modified with Cu(II) and vanadate SACs exhibit significant differences in the mechanism of activity enhancement, particularly with respect to the rate of oxygen reduction. The superior performance of vanadate SAC-modified TiO2 is found to be related to the shallow character of the SAC-induced intragap states, which allows for both the effective extraction of photogenerated electrons and fast catalytic turnover in the reduction of dioxygen, which translates directly into diminished recombination. These results provide essential guidelines for developing efficient SAC-based photocatalysts.

An Investigation into the Surface Integrity of Micro-Machined High-Speed Steel and Tungsten Carbide Cutting Tools.

The performance and lifespan of cutting tools are significantly influenced by their surface quality. The present report highlights recent advances in enhancing the surface characteristics of tungsten carbide and high-speed steel cutting tools using a novel micro-machining technique for polishing and edge-honing. Notably, the main aim was to reduce the surface roughness while maintaining the hardness of the materials at an optimal level. By conducting a thorough analysis of surfaces obtained using different techniques, it was found that the micro-machining method effectively decreased the surface roughness of the cutting tools the most effectively out of the techniques investigated. Significantly, the surface roughness was reduced from an initial measurement of 400 nm to an impressive value of 60 nm. No significant change in hardness was observed, which guarantees the maintenance of the mechanical properties of the cutting tools. This analysis enhances the comprehension of surface enhancement methodologies for cutting tools through the presentation of these findings. The observed decrease in surface roughness, along with the consistent hardness, exhibits potential for improving tool performance. These enhancements possess the capacity to optimise manufacturing processes, increase tool reliability, and minimise waste generation.

Tuning Catalyst Selectivity for Ammonia vs Hydrogen: An Investigation into the Coprecipitation of Mo and Fe Sulfides.

Iron sulfides are key materials in metalloprotein catalysis. One interesting aspect of iron sulfides in biology is the incorporation of secondary metals, for example, Mo, in nitrogenase. These secondary metals may provide vital clues as to how these enzymes first emerged in nature. In this work, we examined the materials resulting from the coprecipitation of molybdenum with iron sulfides using X-ray absorption spectroscopy (XAS). The materials were tested as catalysts, and direct reductants using nitrite (NO2-) and protons (H+) as test substrates. It was found that Mo will coprecipitate with iron as sulfides, however, in distinct ways depending on the stoichiometric ratios of Mo, Fe, and HS-. It was observed that the selectivity of reduction products depends on the amount of molybdenum, with the presence of approximately at 10% Mo optimizing ammonium/ammonia (NH4+/NH3) production from NO2- and minimizing competitive hydrogen (H2) formation from protons (H+) with a secondary reductant.

Understanding the Role of (W, Mo, Sb) Dopants in the Catalyst Evolution and Activity Enhancement of Co3 O4 during Water Electrolysis via In Situ Spectroelectrochemical Techniques.

Unlocking the potential of the hydrogen economy is dependent on achieving green hydrogen (H2 ) production at competitive costs. Engineering highly active and durable catalysts for both oxygen and hydrogen evolution reactions (OER and HER) from earth-abundant elements is key to decreasing costs of electrolysis, a carbon-free route for H2 production. Here, a scalable strategy to prepare doped cobalt oxide (Co3 O4 ) electrocatalysts with ultralow loading, disclosing the role of tungsten (W), molybdenum (Mo), and antimony (Sb) dopants in enhancing OER/HER activity in alkaline conditions, is reported. In situ Raman and X-ray absorption spectroscopies, and electrochemical measurements demonstrate that the dopants do not alter the reaction mechanisms but increase the bulk conductivity and density of redox active sites. As a result, the W-doped Co3 O4 electrode requires ≈390 and ≈560 mV overpotentials to reach ±10 and ±100 mA cm-2 for OER and HER, respectively, over long-term electrolysis. Furthermore, optimal Mo-doping leads to the highest OER and HER activities of 8524 and 634 A g-1 at overpotentials of 0.67 and 0.45 V, respectively. These novel insights provide directions for the effective engineering of Co3 O4 as a low-cost material for green hydrogen electrocatalysis at large scales.

Monometallic interphasic synergy via nano-hetero-interfacing for hydrogen evolution in alkaline electrolytes.

Electrocatalytic synergy is a functional yet underrated concept in electrocatalysis. Often, it materializes as intermetallic interaction between different metals. We demonstrate interphasic synergy in monometallic structures is as much effective. An interphasic synergy between Ni(OH)2 and Ni-N/Ni-C phases is reported for alkaline hydrogen evolution reaction that lowers the energy barriers for hydrogen adsorption-desorption and facilitates that of hydroxyl intermediates. This makes ready-to-serve Ni active sites and allocates a large amount of Ni d-states at Fermi level to promote charge redistribution from Ni(OH)2 to Ni-N/Ni-C and the co-adsorption of Hads and OHads intermediates on Ni-N/Ni-C moieties. As a result, a Ni(OH)2@Ni-N/Ni-C hetero-hierarchical nanostructure is developed, lowering the overpotentials to deliver -10 and -100 mA cm-2 in alkaline media by 102 and 113 mV, respectively, compared to monophasic Ni(OH)2 catalyst. This study unveils the interphasic synergy as an effective strategy to design monometallic electrocatalysts for water splitting and other energy applications.

Implanting Ni-O-VOx sites into Cu-doped Ni for low-overpotential alkaline hydrogen evolution.

Nickel-based catalysts are most commonly used in industrial alkaline water electrolysis. However, it remains a great challenge to address the sluggish reaction kinetics and severe deactivation problems of hydrogen evolution reaction (HER). Here, we show a Cu-doped Ni catalyst implanted with Ni-O-VOx sites (Ni(Cu)VOx) for alkaline HER. The optimal Ni(Cu)VOx electrode exhibits a near-zero onset overpotential and low overpotential of 21 mV to deliver -10 mA cm-2, which is comparable to benchmark Pt/C catalyst. Evidence for the formation of Ni-O-VOx sites in Ni(Cu)VOx is established by systematic X-ray absorption spectroscopy studies. The VOx can cause a substantial dampening of Ni lattice and create an enlarged electrochemically active surface area. First-principles calculations support that the Ni-O-VOx sites are superactive and can promote the charge redistribution from Ni to VOx, which greatly weakens the H-adsorption and H2 release free energy over Ni. This endows the Ni(Cu)VOx electrode high HER activity and long-term durability.

Extraction of metals from mildly acidic tropical soils: Interactions between chelating ligand, pH and soil type.

Naturally occurring and synthetic chelating ligands can act as suppressants for fungal pathogens, nematodes and weeds, based on their ability to alter micronutrient bioavailability in soil, particularly iron. Chelators are also used as detergents, for remediation of heavy metal contamination and for supplying metals as fertiliser. The aim of this work was to test the ability of chelators to solubilise metals, in particular iron, in tropical soils over an environmentally relevant pH range. Six topsoils from farms in North Queensland, Australia were adjusted to pH 5, 6 and 7 and then extracted with CaCl2, EDTA, DTPA, EDDHA and mimosine. The extracts were analysed for concentrations of aluminium, copper, iron, magnesium, manganese, potassium, strontium and zinc. EDDHA solubilised iron effectively under all of the conditions tested, indicating its likely suitability for pest suppression. The concentration of aluminium in EDDHA extracts was positively correlated with pH, and at pH 7 the concentration of aluminium was far greater than that of iron. An increase in the mobility of aluminium from EDDHA application to soil may lead to aluminium toxicity in plants, which should be considered further in any practical application of EDDHA. Mimosine, which is also a strong chelator, was a poor extractor of all metals, possibly due to adsorption to the soil.

Overall electrochemical splitting of water at the heterogeneous interface of nickel and iron oxide.

Efficient generation of hydrogen from water-splitting is an underpinning chemistry to realize the hydrogen economy. Low cost, transition metals such as nickel and iron-based oxides/hydroxides have been regarded as promising catalysts for the oxygen evolution reaction in alkaline media with overpotentials as low as ~200 mV to achieve 10 mA cm-2, however, they are generally unsuitable for the hydrogen evolution reaction. Herein, we show a Janus nanoparticle catalyst with a nickel-iron oxide interface and multi-site functionality for a highly efficient hydrogen evolution reaction with a comparable performance to the benchmark platinum on carbon catalyst. Density functional theory calculations reveal that the hydrogen evolution reaction catalytic activity of the nanoparticle is induced by the strong electronic coupling effect between the iron oxide and the nickel at the interface. Remarkably, the catalyst also exhibits extraordinary oxygen evolution reaction activity, enabling an active and stable bi-functional catalyst for whole cell water-splitting with, to the best of our knowledge, the highest energy efficiency (83.7%) reported to date.

A Surfactant-Free and Scalable General Strategy for Synthesizing Ultrathin Two-Dimensional Metal-Organic Framework Nanosheets for the Oxygen Evolution Reaction.

Metal-organic framework (MOFs) two-dimensional (2D) nanosheets have many coordinatively unsaturated metal sites that act as active centres for catalysis. To date, limited numbers of 2D MOFs nanosheets can be obtained through top-down or bottom-up synthesis strategies. Herein, we report a 2D oxide sacrifice approach (2dOSA) to facilely synthesize ultrathin MOF-74 and BTC MOF nanosheets with a flexible combination of metal sites, which cannot be obtained through the delamination of their bulk counterparts (top-down) or the conventional solvothermal method (bottom-up). The ultrathin iron-cobalt MOF-74 nanosheets prepared are only 2.6 nm thick. The sample enriched with surface coordinatively unsaturated metal sites, exhibits a significantly higher oxygen evolution reaction reactivity than bulk FeCo MOF-74 particles and the state-of-the-art MOF catalyst. It is believed that this 2dOSA could provide a new and simple way to synthesize various ultrathin MOF nanosheets for wide applications.

Defect-Induced Pt-Co-Se Coordinated Sites with Highly Asymmetrical Electronic Distribution for Boosting Oxygen-Involving Electrocatalysis.

Rational design and synthesis of hetero-coordinated moieties at the atomic scale can significantly raise the performance of the catalyst and obtain mechanistic insight into the oxygen-involving electrocatalysis. Here, a facile plasma-photochemical strategy is applied to construct atomically coordinated Pt-Co-Se moieties in defective CoSe2 (CoSe2- x ) through filling the plasma-created Se vacancies in CoSe2- x with single Pt atomic species (CoSe2- x -Pt) under ultraviolet irradiation. The filling of single Pt can remarkably enhance the oxygen evolution reaction (OER) activity of CoSe2 . Optimal OER specific activity is achieved with a Pt content of 2.25 wt% in CoSe2- x -Pt, exceeding that of CoSe2- x by a factor of 9. CoSe2- x -Pt shows much better OER performance than CoSe2- x filled with single Ni and even Ru atomic species (CoSe2- x -Ni and CoSe2- x -Ru). Noticeably, it is general that Pt is not a good OER catalyst but Ru is; thus the design of active sites for electrocatalysis at an atomic level should follow a different intrinsic mechanism. Mechanism studies unravel that the single Pt can induce much higher electronic distribution asymmetry degree than both single Ni and Ru, and benefit the interaction between the Co sites and adsorbates (OH*, O*, and OOH*) during the OER process, leading to a better OER activity.

Evolution of Oxygen-Metal Electron Transfer and Metal Electronic States During Manganese Oxide Catalyzed Water Oxidation Revealed with In†Situ Soft X-Ray Spectroscopy.

Manganese oxide (MnOx ) electrocatalysts are examined herein by in situ soft X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) during the oxidation of water buffered by borate (pH 9.2) at potentials from 0.75 to 2.25 V vs. the reversible hydrogen electrode. Correlation of L-edge XAS data with previous mechanistic studies indicates MnIV is the highest oxidation state involved in the catalytic mechanism. MnOx is transformed into birnessite at 1.45 V and does not undergo further structural phase changes. At potentials beyond this transformation, RIXS spectra show progressive enhancement of charge transfer transitions from oxygen to manganese. Theoretical analysis of these data indicates increased hybridization of the Mn-O orbitals and withdrawal of electron density from the O ligand shell. In situ XAS experiments at the O K-edge provide complementary evidence for such a transition. This step is crucial for the formation of O2 from water.

The Oxidation of Peroxide by Disordered Metal Oxides: A Measurement of Thermodynamic Stability "By Proxy".

It is often noted that disordered materials have different chemical properties to their more "ordered" cousins. Quantifying these effects in terms of thermodynamics is challenging in part because disordered materials can be difficult to characterise and are frequently relatively unstable. During the course of our experiments to understand the effects of disorder in catalysts for water oxidation we observed that many disordered manganese and cobalt oxide water oxidation catalysts directly oxidised peroxide in contrast to their more ordered analogues which catalysed its disproportionation, that is, MnO2 +2 H+ +H2 O2 →Mn2+ +2 H2 O+O2 (oxidation) versus H2 O2 →H2 O+ 1 / 2 O2 (disproportionation). By measuring the efficiency for one reaction over the other as a function of pH, we were able to quantify the relative stability of materials in two series of metal oxides and thereby quantify their relative thermodynamic stability, "by proxy". We found that for the series of catalysts investigated the disorder made the materials stronger chemical oxidants and worse catalysts for the disproportionation of peroxide.

Insight into pH-Dependent Formation of Manganese Oxide Phases in Electrodeposited Catalytic Films Probed by Soft X-Ray Absorption Spectroscopy.

MnOx films electrodeposited under basic, neutral, and acidic conditions from an ionic liquid were investigated by means of X-ray absorption spectroscopy at the manganese L2,3 -edges and the oxygen K-edge. Such films can serve as catalysts for the water oxidation reaction. Previous studies showed that the catalytic activity could be controlled by varying the deposition parameters, which influence the formation of MnOx phases and the film composition. Herein the film compositions are investigated in detail, indicating different ratios of MnOx structural phases in the films. All films in the series predominately consist of varying proportions of three MnOx phases-Mn2 O3 , Mn3 O4 , and birnessite, while an increase of the average Mn oxidation state in the film is identified when going from basic to acidic conditions during electrodeposition. The contribution of these three phases shows a systematic dependency on the pH during electrodeposition. While no specific single MnOx phase was found to dominate the composition of samples that were previously found to show high catalytic activity, the X-ray spectroscopic results revealed the compositions of those samples prepared under close to neutral conditions to be most sensitive to changes in pH.

NiFeCr Hydroxide Holey Nanosheet as Advanced Electrocatalyst for Water Oxidation.

By introducing chromium into a nickel-iron layered double hydroxide (LDH), a nickel iron chromium hydroxide nanomesh catalyst has been achieved on nickel foam substrate via electrodeposition followed by partial etching of chromium. The electrodeposited chromium acts as a sacrificial template to introduce holes in the LDH to increase the electrochemically active surface area, and the remaining chromium synergistically modulates the electronic structure of the composite. The obtained electrode shows extraordinary performance for oxygen evolution reaction and excellent electrochemical stability. The onset potential of the as-prepared electrode in 1 M KOH is only 1.43 V vs RHE, and the overpotential to achieve a high current density of 100 mA·cm-2 is only 255 mV, outperforming benchmark nonprecious NiFe hydroxide composite electrode in alkaline media.

Tunable Biogenic Manganese Oxides.

Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnOx ) is explored. Physical characterisation of MnOx includes scanning and transmission electron microscopy, and X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopy. This characterisation reveals that the MnOx materials share the structural features of birnessite, yet differ in the degree of structural disorder. Importantly, these biogenic products exhibit strikingly different morphologies that can be easily controlled. Changing the substrate-to-protein ratio produces MnOx either as nm-thin sheets, or rods with diameters below 20 nm, or a combination of the two. Mineralisation in solutions that contain Fe2+(aq) makes solids with significant disorder in the structure, while the presence of Ca2+(aq) facilitates formation of more ordered materials. The (photo)oxidation and (photo)electrocatalytic capacity of the MnOx minerals is examined and correlated with their structural properties.

Counting vacancies and nitrogen-vacancy centers in detonation nanodiamond.

Detonation nanodiamond particles (DND) contain highly-stable nitrogen-vacancy (N-V) centers, making it important for quantum-optical and biotechnology applications. However, due to the small particle size, the N-V concentrations are believed to be intrinsically very low, spawning efforts to understand the formation of N-V centers and vacancies, and increase their concentration. Here we show that vacancies in DND can be detected and quantified using simulation-aided electron energy loss spectroscopy. Despite the small particle size, we find that vacancies exist at concentrations of about 1 at%. Based on this experimental finding, we use ab initio calculations to predict that about one fifth of vacancies in DND form N-V centers. The ability to directly detect and quantify vacancies in DND, and predict the corresponding N-V formation probability, has a significant impact to those emerging technologies where higher concentrations and better dispersion of N-V centres are critically required.

Catalytic Activity and Impedance Behavior of Screen-Printed Nickel Oxide as Efficient Water Oxidation Catalysts.

We report that films screen printed from nickel oxide (NiO) nanoparticles and microballs are efficient electrocatalysts for water oxidation under near-neutral and alkaline conditions. Investigations of the composition and structure of the screen-printed films by X-ray diffraction, X-ray absorption spectroscopy, and scanning electron microscopy confirmed that the material was present as the cubic NiO phase. Comparison of the catalytic activity of the microball films to that of films fabricated by using NiO nanoparticles, under similar experimental conditions, revealed that the microball films outperform nanoparticle films of similar thickness owing to a more porous structure and higher surface area. A thinner, less-resistive NiO nanoparticle film, however, was found to have higher activity per Ni atom. Anodization in borate buffer significantly improved the activity of all three films. X-ray photoelectron spectroscopy showed that during anodization, a mixed nickel oxyhydroxide phase formed on the surface of all films, which could account for the improved activity. Impedance spectroscopy revealed that surface traps contribute significantly to the resistance of the NiO films. On anodization, the trap state resistance of all films was reduced, which led to significant improvements in activity. In 1.00 m NaOH, both the microball and nanoparticle films exhibit high long-term stability and produce a stable current density of approximately 30 mA cm(-2) at 600 mV overpotential.

Electrosynthesis of highly transparent cobalt oxide water oxidation catalyst films from cobalt aminopolycarboxylate complexes.

Efficient catalysis of water oxidation represents one of the major challenges en route to efficient sunlight-driven water splitting. Cobalt oxides (CoOx ) have been widely investigated as water oxidation catalysts, although the incorporation of these materials into photoelectrochemical devices has been hindered by a lack of transparency. Herein, the electrosynthesis of transparent CoOx catalyst films is described by utilizing cobalt(II) aminopolycarboxylate complexes as precursors to the oxide. These complexes allow control over the deposition rate and morphology to enable the production of thin, catalytic CoOx films on a conductive substrate, which can be exploited in integrated photoelectrochemical devices. Notably, under a bias of 1.0 V (vs. Ag/AgCl), the film deposited from [Co(NTA)(OH2 )2 ](-) (NTA=nitrilotriacetate) decreased the transmission by only 10 % at λ=500 nm, but still generated >80 % of the water oxidation current produced by a [Co(OH2 )6 ](2+) -derived oxide film whose transmission was only 40 % at λ=500 nm.

Forward and reverse (retro) iron(III) or gallium(III) desferrioxamine E and ring-expanded analogues prepared using metal-templated synthesis from endo-hydroxamic acid monomers.

A metal-templated synthesis (MTS) approach was used to preorganize the forward endo-hydroxamic acid monomer 4-[(5-aminopentyl)(hydroxy)amino]-4-oxobutanoic acid (for-PBH) about iron(III) in a 1:3 metal/ligand ratio to furnish the iron(III) siderophore for-[Fe(DFOE)] (ferrioxamine E) following peptide coupling. Substitution of for-PBH with the reverse (retro) hydroxamic acid analogue 3-(6-amino-N-hydroxyhexanamido)propanoic acid (ret-PBH) furnished ret-[Fe(DFOE)] (ret-ferrioxamine E). As isomers, for-[Fe(DFOE)] and ret-[Fe(DFOE)] gave identical mass spectrometry signals ([M + H(+)](+), m/zcalc 654.3, m/zobs 654.3), yet for-[Fe(DFOE)] eluted in a more polar window (tR = 23.44 min) than ret-[Fe(DFOE)] (tR = 28.13 min) on a C18 reverse-phase high-performance liquid chromatography (RP-HPLC) column. for-[Ga(DFOE)] (tR = 22.99 min) and ret-[Ga(DFOE)] (tR = 28.11 min) were prepared using gallium(III) as the metal-ion template and showed the same trend for the retention time. Ring-expanded analogues of for-[Fe(DFOE)] and ret-[Fe(DFOE)] were prepared from endo-hydroxamic acid monomers with one additional methylene unit in the amine-containing region, 4-[(6-aminohexyl)(hydroxy)amino]-4-oxobutanoic acid (for-HBH) or 3-(7-amino-N-hydroxyheptanamido)propanoic acid (ret-HBH), to give the corresponding tris(homoferrioxamine E) macrocycles, for-[Fe(HHDFOE)] or ret-[Fe(HHDFOE)] ([M + H(+)](+), m/zcalc 696.3, m/zobs 696.4). The MTS reaction using a constitutional isomer of for-HBH that transposed the methylene unit to the carboxylic acid containing region, 5-[(5-aminopentyl)(hydroxy)amino]-5-oxopentanoic acid (for-PPH), gave the macrocycle for-[Fe(HPDFOE)] in a yield significantly less than that for for-[Fe(HHDFOE)], with the gallium(III) analogue for-[Ga(HPDFOE)] unable to be detected. The work demonstrates the utility and limits of MTS for the assembly of macrocyclic siderophores from endo-hydroxamic acid monomers. Indirect measures (RP-HPLC order of elution, c log P values, molecular mechanics, and density functional theory calculations) of the relative water solubility of the ligands, the iron(III) macrocycles, and the apomacrocycles were consistent in identifying for-DFOE as the most water-soluble macrocycle from for-DFOE, ret-DFOE, for-HHDFOE, ret-HHDFOE, and for-HPDFOE. From this group, only for-DFOE is known in nature, which could suggest that water solubility is an important trait in its natural selection.

Redox activity and two-step valence tautomerism in a family of dinuclear cobalt complexes with a spiroconjugated bis(dioxolene) ligand.

A family of dinuclear cobalt complexes with bridging bis(dioxolene) ligands derived from 3,3,3',3'-tetramethyl-1,1'-spirobis(indane-5,5',6,6'-tetrol) (spiroH4) and ancillary ligands based on tris(2-pyridylmethyl)amine (tpa) has been synthesized and characterized. The bis(dioxolene) bridging ligand is redox-active and accessible in the (spiro(cat-cat))(4-), (spiro(SQ-cat))(3-), and (spiro(SQ-SQ))(2-) forms, (cat = catecholate, SQ = semiquinonate). Variation of the ancillary ligand (Mentpa; n = 0-3) by successive methylation of the 6-position of the pyridine rings influences the redox state of the complex, governing the distribution of electrons between the cobalt centers and the bridging ligands. Pure samples of salts of the complexes [Co2(spiro)(tpa)2](2+) (1), [Co2(spiro)(Metpa)2](2+) (2), [Co2(spiro)(Me2tpa)2](2+) (3), [Co2(spiro)(Me3tpa)2](2+) (4), [Co2(spiro)(tpa)2](3+) (5), and [Co2(spiro)(tpa)2](4+) (6) have been isolated, and 1, 4, and 6 have been characterized by single crystal X-ray diffraction. Studies in the solid and solution states using multiple techniques reveal temperature invariant redox states for 1, 2, and 4-6 and provide clear evidence for four different charge distributions: 1 and 2 are Co(III)-(spiro(cat-cat))-Co(III), 4 is Co(II)-(spiro(SQ-SQ))-Co(II), 5 is Co(III)-(spiro(SQ-cat))-Co(III), and 6 is Co(III)-(spiro(SQ-SQ))-Co(III). Of the six complexes, only 3 shows evidence of temperature dependence of the charge distribution, displaying a rare thermally induced two-step valence tautomeric transition from the Co(III)-(spiro(cat-cat))-Co(III) form to Co(II)-(spiro(SQ-cat))-Co(III) and then to Co(II)-(spiro(SQ-SQ))-Co(II) in both solid and solution states. This is the first time a two-step valence tautomeric (VT) transition has been observed in solution. Partial photoinduction of the VT transition is also possible in the solid. Magnetic and spectroscopic studies of 5 and 6 reveal that spiroconjugation of the bis(dioxolene) ligand allows electronic interaction across the spiro bridge, suggesting that thermally activated vibronic coupling between the two cobalt-dioxolene moieties plays a key role in the two-step transition evident for 3.