137-26-8

Basic information

• Product Name: Tetramethylthiuram Disulfide
• Synonyms: 1,1’-dithiobis(n,n-dimethylthio-formamid;1,1’-dithiobis(n,n-dimethylthioformamide);Aapirol;Accel TMT;Accelerator T;Accelerator Thiuram;acceleratort;acceleratorthiuram
• CAS NO: 137-26-8
• Molecular Formula: C₆H₁₂N₂S₄
• Molecular Weight: 240.43
• EINECS: 205-286-2
• Product Categories: Rubber Chemicals;Flame retardants;Organics;FUNGICIDE;Agro-Products;Intermediates & Fine Chemicals;Pharmaceuticals;Sulfur & Selenium Compounds;IMDUR;dispersed masterbatch
• Mol File: 137-26-8.mol
• Article Data: 55

Chemical Properties

• Melting Point: 156-158 °C(lit.)
• Boiling Point: 129 °C (20 mmHg)
• Flash Point: 89°C
• Appearance: /solid
• Density: 1.43
• Vapor Pressure: 0.000726mmHg at 25°C
• Refractive Index: 1.5500 (estimate)
• Storage Temp.: 0-6°C
• Solubility: 0.0184g/l
• PKA: 0.87±0.50(Predicted)
• Water Solubility: 16.5 mg/L (20 ºC)
• Merck: 14,9371
• BRN: 1725821
• CAS DataBase Reference: Tetramethylthiuram Disulfide(CAS DataBase Reference)
• NIST Chemistry Reference: Tetramethylthiuram Disulfide(137-26-8)
• EPA Substance Registry System: Tetramethylthiuram Disulfide(137-26-8)

Safety Data

• Hazard Codes: Xn,N
• Statements: 20/22-36/38-43-48/22-50/53
• Safety Statements: 26-36/37-60-61
• RIDADR: UN 2771/2811
• WGK Germany: 3
• RTECS: JO1400000
• TSCA: Yes
• HazardClass: 9
• PackingGroup: III
• Hazardous Substances Data: 137-26-8(Hazardous Substances Data)

Usage

Chemical properties

pure colorless crystal; no smell; m.p.155~156°C; relative density 1.29; easily soluble in benzene, chloroform (230g/L), acetone (80g/L), carbon disulfide and other organic solvents; slightly soluble in ether and ethanol (<10g/L); insoluble in water (30mg/L); decomposing under acid condition;? industrial products are white or light yellow powder, with a m.p. of more than 146℃.

Uses

Different sources of media describe the Uses of 137-26-8 differently. You can refer to the following data:
1. 1. Tetramethylthiuram Disulfide belongs to protective fungicides of broad spectrum, with a residual effect period of up to 7d or so. It is mainly used for dealing with seeds and soil and preventing powdery mildew, smut and rice seedlings damping-off of cereal crops. It can also be used for some fruit trees and vegetable diseases. For example, dressing seed with 500g of 50% wettable powder can control rice blast, rice leaf spot, barley and wheat smut. 2. As pesticides, Tetramethylthiuram Disulfide is often referred to as thiram and is mainly used for the treatment of seeds and soil and the prevention and controlling of cereal powdery mildew, smut and vegetable diseases. This product, as the super accelerator of natural rubber, synthetic rubber and latex, is often referred to as accelerator TMTD and is the representative of thiuram vulcanization accelerator, accounting for 85% of the total amount of similar products. Accelerator T is also the super accelerator of natural rubber, diene synthetic rubber, Ⅱ, R and EPDM, with the highest utilization rate of all. The vulcanization promoting force of accelerator T is very strong, but, without the presence of zinc oxide, it is not vulcanized at all. 3. Used for the manufacture of cables, wires, tires and other rubber products. 4. Used as the super accelerator of natural rubber, synthetic rubber and latex. 5. Used as the late effect promoter of natural rubber, butadiene rubber, styrene-butadiene rubber and polyisoprene rubber. 6. Used for the pest control of rice, wheat, tobacco, sugar beet, grapes and other crops, as well as for the seed dressing and soil treatment. 7. Tetramethylthiuram Disulfide is suitable for the manufacture of natural rubber, synthetic rubber and latex, and can also be used as curing agent. This product is the second accelerator of thiazole accelerators, which can be used with other accelerators as the continuous vulcanization accelerator. 8. In rubber industry, Tetramethylthiuram Disulfide can be used as the super-vulcanization accelerator, and aften used with thiazole accelerator. It can also be used in combination with other accelerators as the continuous rubber accelerator. For slowly decomposing out of free sulfur at more than 100 ℃, it can be used as curing agent too. Its products have excellent resistance to aging and heat, so it is applicable to natural rubber, synthetic rubber and is mainly used in the manufacture of tires, tubes, shoes, cables and other industrial products. In agriculture, it can be used as fungicide and insecticide, and it can also be used as lubricant additives. 9.? Production methods from dimethylamine, carbon disulfide, ammonia condensation reaction was dimethyl dithiocarbamate, and then by the oxidation of hydrogen peroxide to the finished product.
2. Thiram is a protective fungicide applied to foliage to control Botrytis spp. on grapes, soft fruit, lettuce, vegetables and ornamentals. It also controls rust on ornamentals, scab and storage diseases on apple and pear and leaf curl and Monilia on stone fruit. It is used in seed treatments alone or in combination with added insecticides or fungicides to control damping off diseases such as Pythium spp., and other diseases like Fusarium spp. of maize, cotton, cereals, legumes, vegetables and ornamentals.
3. Seed disinfectant
4. antianginal
5. Thiram is an ectoparasiticide. Thiram is used in agriculture to prevent fungal diseases in seed and crops. Thiram has other applications ranging from use as a topical bactericide to animal repellent.
6. Rubber accelerator; vulcanizer; seed disinfectant; fungicide; bacteriostat in soap; animal repellent.
7. Tetramethylthiuram disulfide is used as fungicide; bacteriostat; pesticide; rubber vulcanization accelerator; scabicide; seed disinfectant; animal repellent; insecticide; lube-oil additive; wood preservative; in antiseptic sprays; in the blending of lubrieant oils; used against Botrytis, rusts and downy mildews; seed dressing against "damping off' and verticillium wilt; ethanol antagonist and deterrent in mixtures of the methyl, ethyl, propyl, and butyl derivatives; antioxidant in polyolefin plastics; peptizing agent in polysulphide elastomers; in soaps and rodent repellents; nut, fruit, and mushroom disinfectant.

Toxicity

Acute oral-rat: LD50 780~865mg/kg; Acute oral-mice: LD50 1500~2000mg/kg. Accelerator T has an irritation effect on the human mucous membrane and skin. People long-term exposure to it have allergic reactions while drinking alcohol. Carp LC50 4mg/L.

Production method

The preparation of sodium dimethyl dithiocarbamate(SDD): the reaction of dimethylamine hydrochloride and carbon disulfide in the presence of sodium hydroxide can generate sodium dimethylamino dithiocarbamate . The reaction temperature is 50~55℃ and the pH value is 8~9. The preparation of thiram: the reaction of SDD (or Diram) and hydrogen peroxide in the presence of sulfuric acid can produce thiram. The reaction temperature is controlled at 10 ℃ below and the end pH value is 3 to 4. Chlorine can also be used instead of hydrogen peroxide and sulfuric acid. The reaction is performed in the sieve tray tower, from the bottom of which the diluted chlorine is introduced and from the top of which 5% sodium solution is sprayed, which is called chlorine-air oxidation method. There are also other methods, such as sodium nitrite oxidation or electrolytic oxidation.

Hazards & Safety Information

Category :Toxic substances Toxicity classification :? moderate toxicity Acute Toxicity : Oral-Rat LD50: 560 mg/kg; Oral-mouse LD50: 1250 mg/kg Stimulation Data: Eye-Rabbit 100 mg/24hours Moderate Flammability Hazardous characteristics: The products can decompose into toxic nitrogen oxides and sulfur oxides when meeting heat. Storage and transportation characteristics : Storehouse should be low-temperature, well-ventilated and dry; the storage and transportation should be separated form food raw materials. Extinguishing agent : sand, dry powder, foam Occupational Standard :TWA 5 mg/m3; STEL 10 mg/m3

Description

Tetramethylthiuram disulfide is a rubber chemieal, an accelerator of vulcanization. It represents the most commonly positive allergen contained in the "thiuram mix". The most frequent occupational categories are the metal industry, homemakers, health services and laboratories, building industries, and shoemakers.

Chemical Properties

Different sources of media describe the Chemical Properties of 137-26-8 differently. You can refer to the following data:
1. Thiram is a colorless to yellow, crystalline solid. Characteristic odor. Commercial pesticide products may be dyed blue.
2. white to almost white powder

Physical properties

Colorless to white to cream-colored crystals. May darken on exposure to air or light.

Definition

ChEBI: An organic disulfide that results from the formal oxidative dimerisation of N,N-dimethyldithiocarbamic acid. It is widely used as a fungicidal seed treatment.

General Description

A liquid solution of a white crystalline solid. Primary hazard is to the environment. Immediate steps should be taken to limit spread to the environment. Easily penetrates the soil to contaminates groundwater and waterways.

Air & Water Reactions

Insoluble in water. Decomposes in acidic media to give toxic products. Decomposes to an extent on prolonged exposure to heat, air or moisture.

Reactivity Profile

TMTD is incompatible with oxidizing materials and strong acids. Also incompatible with strong alkalis and nitrating agents .

Hazard

Toxic by ingestion and inhalation, irritant to skin and eyes. Body weight and hematologic effects. Questionable carcinogen.

Health Hazard

Inhalation of dust may cause respiratory irritation. Liquid irritates eyes and skin and may cause allergic eczema in sensitive individuals. Ingestion causes nausea, vomiting, and diarrhea, all of which may be persistent; paralysis may develop.

Fire Hazard

Special Hazards of Combustion Products: Toxic and irritating oxides of sulfur are formed. Carbon disulfide may be formed from unburned material.

Agricultural Uses

Fungicide, Rodenticide: Thiram is used as a fungicide to prevent crop damage in the field and to prevent crops from deterioration in storage or transport. Thiram is also used as a seed, nut, fruit, and mushroom disinfectant from a variety of fungal diseases. In addition, it is used as an animal repellent to protect fruit trees and ornamentals from damage by rabbits, rodents, and deer. Thiram has been used in the treatment of human scabies, as a sun screen, and as a bactericide applied directly to the skin or incorporated into soap. Thiram is used as a rubber accelerator and vulcanizer and as a bacteriostat for edible oils and fats. It is also used as a rodent repellent, wood preservative, and may be used in the blending of lubricant oils. Registered for use in EU countries. Registered for use in the U.S.

Trade name

AAPIROL?; AATACK?; AATIRAM?; ACCELERATOR T?; ACCELERATOR THIURAM?; ACCEL TMT?; AGROSOL POUR-ON?; ANLES?; ARASAN?[C]; ATIRAM?; ATTACK?; AULES?; CHIPCO THIRAM 75?; CRYLCOAT?; CUNITEX?; CYURAM DS?; DELSAN?; EBECRYL?; EKAGOM TB?; EVERSHIELD T SEED PROTECTORANT?; FALITIRAM?; FERMIDE?; FERNACOL?; FERNASAN?; FERNIDE?; FLO PRO T SEED PROTECTANT?; FMC 2070?[C]; FORMALSOL?; HERMAL?; HERYL?; HEXATHIR?; HY-VIC?; KODIAK T?; KREGASAN?; LIQUID MOLY-CO-THI?; MERCURAM?; METIURAC?; MOLY-T?; NA2771?; NOBECUTAN?; NOMERSAN?; NORMERSAN?; OPTIMA?; PANORAM 75?; POLYRAM ULTRA?; POMARSOL?; POMARSOL FORTE?; POMASOL?; PRO-GRO?; PURALIN?; RAXIL?; REZIFILM?; ROOTONE?; ROYAL TMTD?; RTUBAYTAN- THIRAM?; RTU FLOWABLE SOYBEAN FUNGICIDE?; SADOPLON?; SOLUCRYL?; SPOTRETE?; SPOTRETE-F?; SQ 1489?; SRANANSF- X?; TERSAN 75?[C]; TERSANTETRAMETHYL DIURANE SULFIDE?; TETRAPOM?; TETRASIPTON?; THIANOSAN?; THILLATE?; THIMAR?; THIMER?; THIOKNOCK?; THIOSAN?; THIOSCABIN?; THIOTEX?; THIOTOX?; THIRAM 75?; THIRAM 80?; THIRAMAD?; THIRAM B?; THIRAMPA?; THIRASAN?; THIULIN?; THIULIX?; THIURAD?; THIURAMIN?; THIURAMYL?; THYLATE?; TIRAMPA?; TITAN FL?; TRAMETAN?; TRIDIPAM?; TRIPOMOL?; TUADS?; TUEX?; TULISAN?; UCECOAT?; UCECRYL?; UVECRYL?; VANCIDA TM-95?; VANCIDE TM?; VITAFLO 280?; VITAVAX? Thiram; VITAVAX-T?; VUAGT-1-4?; VULCAFOR TMTD?; VULKACIT MTIC?; VULKACIT THIURAM?; VULKACIT THIURAM/C?

Contact allergens

Different sources of media describe the Contact allergens of 137-26-8 differently. You can refer to the following data:
1. TITD is a rubber vulcanization accelerator
2. This rubber chemical, accelerator of vulcanization, represents the most commonly positive allergen contained in “thiuram mix.” The most frequent occupational categories are the metal industry, homemakers, health services and laboratories, the building industry, and shoemakers. It is also widely used as a fungicide, belonging to the dithiocarbamate group of carrots, bulbs, and woods, and as an insecticide. Thiram is the agricultural name for thiuram.

Safety Profile

Poison by ingestion and intraperitoneal routes. Questionable carcinogen with experimental tumorigenic and teratogenic data. Other experimental reproductive effects. Mutation data reported, Affects human pulmonary system. A rmld allergen and irritant. Acute poisoning in experimental animals produced liver, hdney, and brain damage. Dangerous in a fire; see NITROGEN MONOXIDE and SULFUR DIOXIDE.

Potential Exposure

Thiram is a dithiocarbamate. Some thiurams have been used as rubber components: thiram is used as a rubber accelerator and vulcanizer; a seed, nut, fruit, and mushroom disinfectant; a bacteriostat for edible oils and fats; and as an ingredient in suntan and antiseptic sprays and soaps. It is also used as a fungicide, rodent repellent; wood preservative; and may be used in the blending of lubricant oils.

Carcinogenicity

Thiram also was not carcinogenic in rats by gavage or in mice by single subcutaneous injection. In skin painting studies in mice thiram had tumor-initiating and -promoting activity but was not a complete carcinogen. Thiram was genotoxic to insects, plants, fungi, and bacteria: it induced sister chromatid exchange and unscheduled DNA synthesis in cultured human cells. Despite established genotoxicity in vitro, it showed no clastogenic and/or aneugenic activity in vivo after oral administration to mice at the maximum tolerated dose.

Environmental Fate

Biological. In both soils and water, chemical and biological mediated reactions can transform thiram to compounds containing the mercaptan group (Alexander, 1981). Odeyemi and Alexander (1977) isolated three strains of Rhizobium sp. that degraded thiram. One of these strains, Rhizobium meliloti, metabolized thiram to yield dimethy- lamine (DMA) and carbon disul?de which formed spontaneously from dimethyldithiocar- bamate (DMDT). The conversion of DMDT to DMA and carbon disul?de occurred via enzymatic and nonenzymatic mechanisms (Odeyemi and Alexander, 1977).When thiram (100 ppm) was inoculated with activated sludge (30 ppm) at 25°C and pH 7.0 for two weeks, 30% degraded. Metabolites included methionine, elemental sulfur, formaldehyde, dimethyldithiocarbamate-α-aminobutyric acid and the corresponding keto aciTo a non-autoclaved alluvial sandy loam (pH 7.3) fortified and inoculated with the bacterium Pseudomonas aeruginosa, 40 and 86% degradation were observed after 4 and 24 days, respectively. In autoclaved soil, thiram degradation was not affected. DegradatSoil. Decomposes in soils to carbon disul?de and dimethylamine (Sisler and Cox, 1954; Kaars Sijpesteijn et al., 1977). When a spodosol (pH 3.8) pretreated with thiram was incubated for 24 days at 30°C and relative humidity of 60–90%, dimethylamine formed as the major product. Minor degradative products included nitrite ions (nitration reduction) and dimethylnitrosamine (Ayanaba et al., 1973).Plant. Major plant metabolites are ethylene thiourea, thiram monosul?de, ethylene thiram disul?de and sulfur (Hartley and Kidd, 1987).

Metabolic pathway

Dialkyldithiocarbamates chelate copper and inhibit pyruvate dehydrogenase. It is likely that the mode of action of chelators is principally through their effect on lipoamide containing dehydrogenases (Corbett et al., 1984). Thiram generates dimethyldithiocarbamic acid by being cleaved in acidic conditions and in biological media. The acid is conjugated with glucose and alanine in plants and with glucuronic acid in mammals. Dimethyldithiocarbamic acid is further degraded to dimethylamine and CS2. An extensive review of the properties of dithiocarbamate pesticides was published by the World Health Organisation (WHO, 1988) from which much of the following information is taken.

Shipping

UN2771 Thiocarbamate pesticides, solid, toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials.

Purification Methods

Crystallise thiram (three times) from boiling CHCl3, then recrystallise it from boiling CHCl3 by adding EtOH dropwise to initiate crystallisation, and allow it to cool. Finally it is precipitated from cold CHCl3 by adding EtOH (which retains the monosulfide in solution). [Ferington & Tobolsky J Am Chem Soc 77 4510 1955, Beilstein 4 IV 242.]

Degradation

Thiram is decomposed in acidic media. It deteriorates on prolonged exposure to heat, air or moisture. DT50 values are estimated as 128 days, 18 days and 9 hours at pH 4, 7 and 9, respectively (PM). The dimethyldithiocarbamate (2) is stable in alkaline media but unstable in acidic conditions, decomposing to dimethylamine and carbon disulfide. In water, the dimethyldithiocarbamate can be oxidatively degraded to a number of products. The rate of degradation depends on pH and the type of any cations that might be present. The rate of decomposition and production of CS2 is decreased by cations in the following order Na+ > Zn2+> Fe3+> Cu2+. Thiram was completely degraded in sewage water in 12 days. An ethanolic solution of unlabelled thiram (4 g l-1) was exposed to UV light for 48 hours. The reaction tube was encircled by low pressure Hg lamps that gave more than 85% of their total radiation at 253.7 nm. Pure nitrogen was bubbled through the solutions. Photo-oxidation studies were done similarly except that oxygen was bubbled through the solution. In further experiments, irradiation was by visible light from a tungsten lamp and again oxygen was bubbled through the solution. The outlet gases from the UV study were condensed in a cold trap and analysed by GC-MS. Traces of carbon disulfide and dimethylamine were identified. The reaction mixture was also analysed by GC-MS and three products were identified as tetramethyl hydrazine (3), N,N-dimethylthioformamide (4) and tetramethylthiourea (5). The identity of the latter was confirmed by IR and NMR. The reaction mixture was concentrated and applied to TLC plates and sulfur and tetramethylthiourea (5) were identified as the main products of photolysis. The same products with the addition of sulfur dioxide and carbon dioxide were produced by UV light and oxygen. Oxidation of thiram in the presence of visible light together with Rose Bengal as a photosensitiser also gave the same products in almost identical yields. The results confirm that C-S and S-S bond fissions are primary photochemical steps with dithiocarbamates.

Toxicity evaluation

Thiram cytotoxicity appears to result from its potential to disrupt cellular defense mechanisms against oxidative stress. In cultured human skin fibroblast, thiram results in an increase in oxidative markers such as lipid peroxidation and oxidation of reduced glutathione and decrease in other endogenous antioxidant. Toxic effects of thiram have been described in humans and animal model systems ranging from liver injury, testicular toxicity, ophthalmological changes, and development of micronuclei in bone marrow. However, the mechanisms of these effects are not characterized and inconsistent across various studies.

Incompatibilities

Dust may form explosive mixture with air. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine,fluorine, etc.); contact may cause fires or explosions. Keep away from strong alkaline materials, strong acids, strong bases and nitrating agents.

Waste Disposal

Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal. Thiram can be dissolved in alcohol or other flammable solvent and burned in an incinerator with an afterburner and scrubber.

InChI:InChI=1/C6H12N2S4/c1-7(2)5(9)11-12-6(10)8(3)4/h1-4H3

Upstream product

• 75-15-0 carbon disulfide 
• 14548-16-4 Dimethyl-(1-phenyl-vinyl)-amine 
• 7664-93-9 sulfuric acid 
• 7722-84-1 dihydrogen peroxide 
• 598-64-1 dimethylammonium dimethyldithiocarbamate 
• 67-56-1 methanol 
• 128-04-1 sodium dimethyldithiocarbamate 
• 53297-68-0 4-amino-3-chlorobenzenesulfonamide 
• 148-18-5 sodium N,N-diethyldithiocarbamate 
• 506-59-2 N,N-dimethylammonium chloride 
• 2129-20-6 bis(dimethylamino)sulfide 
• 110-01-0 thiophene 
• 110-66-7 n-pentanethiol 
• 124-40-3 dimethyl amine 

Downstream Products

• 97-74-5 bis(dimethylthiocarbamoyl)sulfide 
• 3878-45-3 triphenylphosphine sulfide 
• 24171-17-3 N-(N,N-dimethylthiocarbamoyldithioyl)morpholine 
• 66232-66-4 N-(N,N-dimethylthiocarbamoyldithioyl)piperidine 
• 98-77-1 piperidinium piperidyldithiocarbamate 
• 5327-10-6 morpholinium morpholine-1-carbodithioate 
• 23766-26-9 5?(4?methoxyphenyl)?1,3,4?oxadiazole?2?thiol 
• 7250-18-2 benzyl dimethyldithiocarbamate 
• 16906-70-0 phenyl N,N-dimethyl dithiocarbamate 
• 56905-27-2 cyclohexyl N,N-dimethyl dithiocarbamate 
• 23726-35-4 bis(N,N-dimethylcarbamodithioato-κS,κS')-copper(II) 
• 121413-30-7 Ph₃PAuSC(S)NMe₂ 
• 123324-78-7 NCCH₂Au{SC(S)N(CH₃)2}2 
• 15521-65-0 bis(N,N-dimethyldithiocarbamate)nickel(II) 

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Relevant articles and documents

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Irradiation at 460 nm of [Mo3(μ3-S)(μ2-S2)3(S2CNR2)3]I ([2a]I, R = Me; [2b]I, R = Et; [2c]I, R = iBu; [2d]I, R = CH2C6H5) in a mixed aqueous-polar organic medium with [Ru(bipy)3]2+ as photosensitizer and Et3N as electron donor leads to H2 evolution. Maximum activity (300 turnovers, 3 h) is found with R = iBu in 1:9 H2O:MeCN; diminished activity is attributed to deterioration of [Ru(bipy)3]2+. Monitoring of the photolysis mixture by mass spectrometry suggests transformation of [Mo3(μ3-S)(μ2-S2)3(S2CNR2)3]+ to [Mo3(μ3-S)(μ2-S)3(S2CNR2)3]+ via extrusion of sulfur on a time scale of minutes without accumulation of the intermediate [Mo3S6(S2CNR2)3]+ or [Mo3S5(S2CNR2)3]+ species. Deliberate preparation of [Mo3S4(S2CNEt2)3]+ ([3]+) and treatment with Et2NCS21- yields [Mo3S4(S2CNEt2)4] (4), where the fourth dithiocarbamate ligand bridges one edge of the Mo3 triangle. Photolysis of 4 leads to H2 evolution but at ～25% the level observed for [Mo3S7(S2CNEt2)3]+. Early time monitoring of the photolyses shows that [Mo3S4(S2CNEt2)4] evolves H2 immediately and at constant rate, while [Mo3S7(S2CNEt2)3]+ shows a distinctive incubation prior to a more rapid H2 evolution rate. This observation implies the operation of catalysts of different identity in the two cases. Photolysis solutions of [Mo3S7(S2CNiBu2)3]+ left undisturbed over 24 h deposit the asymmetric Mo6 cluster [(iBu2NCS2)3(μ2-S2)2(μ3-S)Mo3](μ3-S)(μ3-η2,η1-S′,η1-S″-S2)[Mo3(μ2-S)3(μ3-S)(S2CNiBu2)2(μ2-S2CNiBu2)] in crystalline form, suggesting that species with this hexametallic composition and core topology are the probable H2-evolving catalysts in photolyses beginning with [Mo3S7(S2CNR2)3]+. When used as solvent, N,N-dimethylformamide (DMF) suppresses H2-evolution but to a greater degree for [Mo3S4(S2CNEt2)4] than for [Mo3S7(S2CNEt2)3]+. Recrystallization of [Mo3S4(S2CNEt2)4] from DMF affords [Mo3S4(S2CNEt2)4(η1,κO-DMF)] (5), implying that inhibition by DMF arises from competition for a Mo coordination site that is requisite for H2 evolution. Computational assessment of [Mo3S4(S2CNMe2)3]+ following addition of 2H+ and 2e- suggests a Mo(H)-μ2(SH) intermediate as the lowest energy species for H2 elimination. An analogous pathway may be available to the Mo6 cluster via dissociation of one end of the μ2-S2CNR2 ligand, a known hemilabile ligand type, in the [Mo3S4]4+ fragment.