Manganese(2+) (16397-91-4) Physical and Chemical Properties
Manganese(2+)
Divalent manganese (Mn2+) supplied as salts or solutions for use in formulation, catalysis, materials synthesis and analytical standards.
| CAS Number | 16397-91-4 |
| Family | Transition metal cations |
| Typical Form | Salt (solid) or aqueous solution |
| Common Grades | EP |
Manganese(2+) is the divalent cation of the transition metal manganese and belongs to the class of monoatomic inorganic cations. Structurally it exists as a bare metal center in formal notation Mn2+ and, in condensed-phase chemistry, is most commonly encountered as an inner-sphere hexaaqua complex, [Mn(H2O)6]2+, or as coordinated species with oxygen- and nitrogen-donor ligands. Electronic configuration and ligand-field considerations place Mn2+ in a high-spin d5 configuration (half-filled d-shell) which imparts relatively small ligand-field stabilization energy; as a consequence, Mn2+ typically forms labile, kinetically fast-exchanging complexes with octahedral coordination being dominant in aqueous chemistry.
Chemically, Mn2+ behaves as a hard Lewis acid that preferentially binds hard bases (O, N donors) and shows limited covalency. In aqueous solution the hydrated ion undergoes slight hydrolysis and commonly imparts a mildly acidic character to concentrated solutions; under alkaline conditions Mn2+ is readily converted to insoluble hydroxide precipitates. Redox chemistry is central to manganese speciation: Mn2+ is relatively stable under reducing conditions but can be oxidized to higher oxidation states such as Mn3+ or Mn4+ in the presence of oxidants or enzymatic oxidases; biological systems effect Mn2+ → Mn3+ conversion via proteins such as ceruloplasmin.
Manganese ions are widely important industrially and biologically. Mn2+ is an essential micronutrient and a catalytic cofactor for numerous enzymes (for example, Mn superoxide dismutase, arginase, pyruvate carboxylase), and it is administered clinically as a trace element in total parenteral nutrition formulations. Industrially, manganese and its compounds are integral to metallurgy, alloy production, battery manufacturing and as catalysts or additives in chemical processes. Common commercial grades reported for this substance include: EP.
Basic Physical Properties
Density
No experimentally established value for this property is available in the current data context.
Melting or Decomposition Point
Reported melting values in the available data include: 1246 and 1244 °C. These values are presented as reported; no single standardized melting point with additional experimental detail is available here.
Solubility in Water
No experimentally established value for this property is available in the current data context.
Solution pH (Qualitative Behavior)
As a hydrated divalent transition-metal cation, Mn2+ in aqueous solution exists primarily as the hexaaqua complex and undergoes limited hydrolysis; aqueous solutions of Mn2+ are mildly acidic at higher concentrations due to proton release from coordinated water ligands. Increasing pH promotes stepwise deprotonation and ultimately precipitation of manganese hydroxide phases (e.g., Mn(OH)2). Mn2+ also forms stable soluble complexes with chelating ligands (e.g., EDTA, polycarboxylates), shifting speciation and apparent solution acidity accordingly.
Chemical Properties
Acid–Base Behavior
Mn2+ functions as a hard Lewis acid with preference for coordination to oxygen and nitrogen donor ligands. Hydration produces the hexaaqua ion, which can donate protons from coordinated water molecules in stepwise hydrolysis equilibria; however, no specific hydrolysis pKa values are provided in the current data context. Complexation with multidentate ligands stabilizes the divalent state and suppresses hydrolysis and precipitation.
Reactivity and Stability
Mn2+ is kinetically labile relative to many transition‑metal complexes and readily undergoes ligand exchange. Under oxidizing conditions Mn2+ can be converted to Mn3+ or Mn4+ species; biological oxidation of Mn2+ to Mn3+ by ceruloplasmin is documented. In alkaline aqueous environments Mn2+ tends to form insoluble hydroxides or oxides, whereas under reducing and complexing conditions it remains soluble. Mn2+ binds to biomolecular carriers (transferrin, albumin to a small extent) which affects distribution and bioavailability.
Molecular and Ionic Parameters
Formula and Molecular Weight
- Molecular formula: Mn+2
- Molecular weight: 54.93804 \(\mathrm{g}\,\mathrm{mol}^{-1}\)
- Exact mass: 54.938043
- Monoisotopic mass: 54.938043
Additional computed descriptors: topological polar surface area (TPSA) 0; complexity 0.
Constituent Ions
- Constituent ion: Mn2+ (formally a monoatomic dication; formal charge 2)
- Element: Manganese (symbol Mn, atomic number 25)
Computed counts and formal descriptors from molecular data include: Heavy Atom Count 1; Formal Charge 2; Hydrogen Bond Donor Count 0; Hydrogen Bond Acceptor Count 0; Rotatable Bond Count 0; Covalently-Bonded Unit Count 1.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS: 16397-91-4
- Additional CAS and registry strings appearing in source annotations: 7439-96-5; 15365-82-9
- UNII: H6EP7W5457
- InChI: InChI=1S/Mn/q+2
- InChIKey: WAEMQWOKJMHJLA-UHFFFAOYSA-N
- SMILES: [Mn+2]
- ChEBI: CHEBI:29035
- DrugBank: DB06757
- DSSTox Substance ID: DTXSID00167687
- HMDB: HMDB0001333
- KEGG: C19610
- NCI Thesaurus Code: C68267
- Wikidata: Q27095727
Synonyms and Common Names
Reported synonyms and common names include (selected from depositor-supplied synonyms): Manganese(2+), Manganese(II), Manganous ion, Manganese (Mn2+), Manganese ion(2+), Mn2+, MANGANESE(II) ION, Manganese cation (2+), Manganous cation, Manganese dication, Mn(II), Mn++, Mn(2+), Manganese cation (Mn2+), Manganous dication, hexaaquamanganese(2+) ion, Manganese(2+), hexaaqua-, ion.
Industrial and Commercial Applications
Functional Roles and Use Sectors
Mn2+ serves multiple functional roles. Biomedically it is used as an essential trace element in nutritional supplements and as a component of parenteral trace-element preparations for total parenteral nutrition to prevent deficiency. In biochemical and pharmaceutical contexts Mn2+ is used as a cofactor in enzyme assays and as a reagent in mechanistic studies. Industrial sectors utilizing manganese chemistry include metallurgy and alloy production (improving hardness and strength), battery manufacturing (additives and electrode materials), welding and smelting operations, and as catalytic or promotive additives in chemical syntheses and processes.
Typical Application Examples
- Trace-element supplement in parenteral nutrition formulations to maintain physiological Mn levels.
- Laboratory reagent and biochemical cofactor for enzymology and redox studies.
- Component or additive in metallurgical processes and battery materials where manganese compounds impart desired mechanical or electrochemical properties.
- Use in industrial catalysts and as a promoter in oxidation and polymerization reactions where manganese redox cycling is functionally employed.
Safety and Handling Overview
Health and Environmental Hazards
Manganese is an essential micronutrient but exhibits toxicity at elevated exposures, with chronic overexposure associated with neurological effects and accumulation in brain regions such as the basal ganglia. Mn2+ can cross biological membranes and the blood–brain barrier; dysregulated systemic or occupational exposure can lead to hypermanganesemia and associated motor and neurobehavioral disturbances. Inhalation exposure to fine particulates or aerosols of manganese compounds is a principal occupational concern. Mn2+ interacts with biological transport proteins (transferrin, serum carriers), influencing distribution and clearance, which occurs primarily via biliary excretion.
Storage and Handling Considerations
Handle manganese(II) compounds using standard industrial hygiene controls: avoid inhalation of dust or aerosols, minimize skin and eye contact, and use appropriate personal protective equipment (gloves, eye protection) and local exhaust ventilation for operations generating airborne particulate. Store in a cool, dry, well-ventilated area away from strong oxidizers and incompatible reagents; maintain containers tightly closed to prevent contamination and moisture uptake. For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
