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Barium iodide

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Barium iodide^[1]
Names

IUPAC name Barium iodide
Other names Barium iodide, anhydrous
Identifiers
CAS Number	13718-50-8 (anhydrous)^Y 7787-33-9 (dihydrate)^N 13477-15-1 (hexahydrate)^N
3D model (JSmol)	Interactive image Interactive image
ChemSpider	75507^Y
ECHA InfoCard	100.033.873
EC Number	237-276-9
PubChem CID	83684
UNII	WKC4T7680A^Y
CompTox Dashboard (EPA)	DTXSID2065597
InChI InChI=1S/Ba.2HI/h;21H/q+2;;/p-2^Y Key: SGUXGJPBTNFBAD-UHFFFAOYSA-L^Y InChI=1/Ba.2HI/h;21H/q+2;;/p-2 Key: SGUXGJPBTNFBAD-NUQVWONBAS
SMILES I[Ba]I [Ba+2].[I-].[I-]
Properties
Chemical formula	BaI₂ (anhydrous) BaI₂·2H₂O (dihydrate)
Molar mass	391.136 g/mol (anhydrous) 427.167 g/mol (dihydrate)
Appearance	White orthorhombic crystals (anhydrous) colorless crystals (dihydrate)
Odor	odorless
Density	5.15 g/cm³ (anhydrous) 4.916 g/cm³ (dihydrate)
Melting point	711 °C (1,312 °F; 984 K) (anhydrous) decomposes at 740 °C (dihydrate)
Solubility in water	166.7 g/100 mL (0 °C) 221 g/100 mL (20 °C) 246.6 g/100 mL (70 °C)
Solubility	soluble in ethanol, acetone
Magnetic susceptibility (χ)	−124.0·10⁻⁶ cm³/mol
Structure
Crystal structure	PbCl₂-type (Orthorhombic oP12)
Space group	Pnma (No. 62)
Thermochemistry
Std enthalpy of formation (Δ_fH^⦵₂₉₈)	−602.1 kJ·mol⁻¹
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	toxic
Related compounds
Other anions	barium fluoride barium chloride barium bromide
Other cations	beryllium iodide magnesium iodide calcium iodide strontium iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is ^YN ?) Infobox references

Barium iodide is an inorganic compound with the formula BaI₂. The compound exists as an anhydrous and a hydrate (BaI₂(H₂O)₂), both of which are white solids. When heated, hydrated barium iodide converts to the anhydrous salt. The hydrated form is freely soluble in water, ethanol, and acetone.

Structure

[edit]

The structure of the anhydrous form resembles that of lead(II) chloride with each Ba center bound to nine iodide ligands^[2] and has a crystalline packing structure that is quite similar to BaCl₂.^[3]

Reactions

[edit]

Anhydrous BaI₂ can be prepared by treating Ba metal with 1,2-diiodoethane in ether.^[4]

BaI₂ reacts with alkyl potassium compounds to form organobarium compounds.^[5]

BaI₂ can be reduced with lithium biphenyl, to give a highly active form of barium metal.^[6]

Safety

[edit]

Like other soluble salts of barium, barium iodide is toxic.

References

[edit]

^ Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, FL: CRC Press, pp. 4–44, ISBN 0-8493-0594-2
^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
^ Brackett, E. B.; Brackett, T. E.; Sass, R. L.; The Crystal Structures of Barium Chloride, Barium Bromide, and Barium Iodide. J. Phys. Chem., 1963, volume 67, 2132 – 2135
^ Duval, E.; Zoltobroda, G.; Langlois, Y.; A new preparation of BaI2: application to (Z)-enol ether synthesis. Tetrahedron Letters, 2000, 41, 337-339
^ Walter, M. D.; Wolmershauser, G.; Sitzmann, H.; Calcium, Strontium, Barium, and Ytterbium Complexes with Cyclooctatetraenyl or Cyclononatetraenyl Ligands. J. Am. Chem. Soc., 2005, 127 (49), 17494 – 17503.
^ Yanagisawa, A.; Habaue, S.; Yasue, K.; Yamamoto, H.; Allylbarium Reagents: Unprecedented Regio- and Stereoselective Allylation Reactions of Carbonyl Compounds. J. Am. Chem. Soc.1994, 116,6130-6141

Barium compounds

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Barium iodide is an inorganic compound with the chemical formula BaI₂. It is a white, hygroscopic solid that occurs in both anhydrous and dihydrate forms, the latter being BaI₂·2H₂O. The compound serves primarily as a precursor in chemical synthesis, materials preparation, and various laboratory applications, and it is commercially available in high-purity grades specifically for research purposes. As a barium salt of hydroiodic acid, barium iodide exhibits typical properties of alkaline earth metal halides, including high solubility in water and sensitivity to moisture due to its hygroscopic nature. The anhydrous form is obtained by dehydration of the dihydrate, and both forms are used in controlled environments to prevent hydration or deliquescence. In research settings, high-purity barium iodide is valued for its role in preparing other barium compounds, as a source of iodide ions in synthetic reactions, and in specialized materials science experiments where its optical or electronic properties may be exploited. The compound is handled with care due to the toxicity associated with barium and iodide ions, requiring standard laboratory precautions to avoid ingestion or inhalation. Its availability in high-purity forms reflects its niche but important role in academic and industrial research rather than large-scale commercial production.

Physical and chemical properties

Appearance and physical state

Barium iodide (BaI₂) is a colorless or white solid that is highly hygroscopic.^[1] It typically appears as a crystalline solid or in the form of colorless beads and is encountered in both anhydrous and dihydrate forms, with the hygroscopic nature causing it to readily absorb moisture from the air.^[1]

Solubility and hygroscopicity

Barium iodide (BaI₂) is highly soluble in water, reflecting its ionic character and the favorable hydration of Ba²⁺ and I⁻ ions. Reported solubility values for the anhydrous form include approximately 182 g per 100 g of water at 0 °C and 223 g per 100 g of water at 20 °C.^[2] Solubility increases with temperature, a typical behavior for many ionic compounds. The compound is also soluble in polar organic solvents such as ethanol and methanol, but essentially insoluble in non-polar solvents like diethyl ether.^[3] The anhydrous form of barium iodide is strongly hygroscopic and deliquescent, readily absorbing atmospheric moisture to form the dihydrate BaI₂·2H₂O or, under high humidity conditions, dissolving into an aqueous solution.^[4] This property requires careful handling and storage in tightly sealed containers, often under inert gas or with desiccants, to maintain the anhydrous state. The dihydrate form is also hygroscopic but less aggressively so than the anhydrous material, and it can lose water of hydration under reduced humidity or upon heating.^[5]^[4]

Melting and boiling points

The anhydrous form of barium iodide melts at 711 °C. ^[6] Some commercial and safety data sources report a melting point of 740 °C. ^[7] ^[8] No boiling point is reported for the anhydrous compound, as it decomposes upon further heating rather than boiling. ^[7] The dihydrate form (BaI₂·2H₂O) does not exhibit a distinct melting point. Upon heating, it undergoes dehydration to the anhydrous form prior to reaching temperatures where melting would occur. The hygroscopic nature of barium iodide can influence the precision of thermal measurements if moisture is present in the sample.

Density and crystal data

The anhydrous form of barium iodide has a density of 5.15 g/cm³, while the dihydrate form has a density of 4.916 g/cm³. The anhydrous barium iodide crystallizes in the orthorhombic crystal system with space group Pnma (No. 62), adopting the PbCl₂ structure type. The structure is characterized by a coordination environment typical for such halides, with Z = 4 formula units per unit cell. No polymorphism is reported for either form under standard conditions. The dihydrate form has a different crystal arrangement due to the incorporation of water molecules, resulting in its lower density.

Structure

Anhydrous barium iodide

The anhydrous form of barium iodide (BaI₂) crystallizes in an orthorhombic structure analogous to that of lead(II) chloride (PbCl₂ structure type), which is distinct from the structure of the dihydrate form.^[6] In this structure, each Ba²⁺ ion is coordinated to nine I⁻ ligands, resulting in a nine-coordinate environment around the barium center. The coordination geometry is a distorted tricapped trigonal prism, with varying Ba–I bond lengths that reflect the asymmetric arrangement typical of this lattice type. Each iodide ion is bound to four barium ions, contributing to a three-dimensional network.^[6] The PbCl₂-type lattice accommodates the large ionic radii of Ba²⁺ and I⁻, enabling the high coordination number observed, and features a sawtooth-like arrangement in the packing of the ions. This structural motif is common among heavier alkaline earth diiodides and dihalides with larger anions.^[6]

Barium iodide dihydrate

Barium iodide dihydrate (BaI₂·2H₂O) is the hydrated form of barium iodide, featuring two water molecules per formula unit. It appears as a white hygroscopic solid that can be dehydrated to the anhydrous form upon heating.^[9]^[10] The crystal structure of barium iodide dihydrate incorporates water molecules that coordinate to the barium ions and participate in hydrogen bonding within the lattice, resulting in structural differences from the anhydrous form. Detailed crystallographic data, including precise coordination geometry and hydrogen bonding network, are not widely detailed in accessible sources.

Preparation

Synthesis from barium compounds and hydroiodic acid

Barium iodide is commonly prepared in the laboratory by reacting barium carbonate with hydroiodic acid, a method that exploits the acid-base reaction and gas evolution to drive completion. The balanced equation is BaCO₃ + 2HI → BaI₂ + CO₂ + H₂O. ^[11] ^[12] The procedure typically involves adding solid barium carbonate gradually to concentrated hydroiodic acid in an aqueous medium, resulting in effervescence from CO₂ release. The mixture is stirred and gently heated to ensure complete reaction, after which any unreacted barium carbonate is removed by filtration. The clear filtrate is then concentrated by evaporation, often under reduced pressure to avoid excessive heating, yielding crystals of barium iodide dihydrate (BaI₂·2H₂O) upon cooling. An analogous method uses barium hydroxide in place of barium carbonate: Ba(OH)₂ + 2HI → BaI₂ + 2H₂O. This variant proceeds without gas evolution, requiring careful control of stoichiometry to prevent excess base or acid, followed by similar filtration and evaporation steps to isolate the dihydrate. The resulting product is highly hygroscopic and generally obtained as the dihydrate unless further processed.

Alternative methods and dehydration

Metathesis reactions, such as the exchange between barium chloride and sodium iodide in a suitable solvent, have been reported but are less commonly used for large-scale preparation due to the high solubility of barium iodide, which complicates isolation of the product in high purity. The dihydrate form, BaI₂·2H₂O, is frequently obtained from aqueous preparations and can be converted to the anhydrous material by dehydration. This is typically achieved by heating the dihydrate under vacuum at temperatures between 200°C and 300°C or by prolonged drying over phosphorus pentoxide (P₂O₅) in a desiccator. Higher temperatures or extended heating may be required to ensure complete removal of water, with some protocols recommending stepwise heating to avoid decomposition or hydrolysis. Obtaining pure anhydrous barium iodide presents challenges due to its extreme hygroscopicity, which can lead to rapid rehydration during handling or incomplete dehydration if conditions are not sufficiently dry. Special precautions, such as working in a glovebox under inert gas or using rigorous vacuum techniques, are often necessary to maintain the anhydrous state.

Reactions

Behavior in water and air

Barium iodide dissolves readily in water, dissociating into Ba²⁺ cations and I⁻ anions.^[13] The anhydrous form is highly hygroscopic and readily absorbs atmospheric moisture, converting to the dihydrate BaI₂·2H₂O.^[13] Barium iodide is sensitive to light, air, and moisture; exposure to light can cause decomposition with the formation of iodine, particularly in acidic conditions.^[14]

Thermal decomposition and redox reactions

Barium iodide exhibits considerable thermal stability, with decomposition not occurring readily under normal heating conditions. Safety data sheets indicate that when thermal decomposition does occur, it produces hazardous products including hydrogen iodide and barium oxides.^[8]^[15] Certain sources also list iodine among the decomposition products, suggesting possible redox processes involving oxidation of iodide ions, potentially in the presence of oxygen or other oxidants during heating.^[16] Specific decomposition temperatures are not commonly reported in available safety documentation, with some indicating that such data are unavailable.^[17]

Uses

Chemical synthesis and laboratory applications

Barium iodide serves primarily as a precursor and reagent in chemical synthesis, particularly in organometallic and inorganic preparations. Due to its hygroscopic nature, it requires careful handling under dry conditions for laboratory use. High-purity grades are commercially available for research applications.^[18]^[19] It is notably employed as a reagent in the facile synthesis of poly(phenylcarbyne), a polymer precursor to diamond-like carbon materials. This application highlights its utility in specialized carbon-based polymer syntheses.^[18]^[20]^[21] Barium iodide reacts with alkyl potassium compounds to form organobarium species, making it valuable in the preparation of organobarium compounds for organometallic studies.^[19] In salt metathesis reactions, barium iodide is commonly used as a metal source to prepare alkaline earth metal complexes, such as adducts with polyethers or amides, due to its favorable solubility and reactivity in these systems.^[22]^[23] More recently, barium iodide has served as a precursor in the mechanochemical reduction of β-diketiminate complexes to yield novel barium inverse sandwich structures with benzene ligands.^[24]

Materials preparation and specialized uses

Barium iodide is utilized as a precursor in the preparation of high-performance scintillator crystals, particularly europium-doped variants (BaI₂:Eu), for gamma-ray detection applications. These materials exhibit promising scintillation properties, including notable light yield and suitability for radiation detection.^[25]^[26] Single crystals of barium iodide, often activated with Eu²⁺, are grown using the Bridgman technique, which allows for reliable crystal production with reduced susceptibility to cracking compared to certain other high-Z halides such as lanthanum-based scintillators. This growth method supports the development of large, high-quality crystals suitable for detector fabrication.^[26]^[27] Experimental scintillator detectors incorporating BaI₂:Eu crystals have been constructed and evaluated, demonstrating performance in gamma-ray spectroscopy and related detection tasks. These applications leverage the compound's high atomic number and scintillation characteristics for specialized radiation detection needs.^[27]^[28] Patents describe the use of barium iodide-based crystals and scintillators for gamma-ray detection, highlighting their implementation in advanced detector systems.^[29]^[30] High-purity grades of barium iodide are commercially available to support such research-grade and materials preparation efforts.

Safety and handling

Toxicity and health hazards

Barium iodide is toxic if swallowed and may cause damage to organs through prolonged or repeated exposure, primarily due to the barium ion in this soluble compound. Soluble barium compounds are systemic poisons that interfere with potassium ion channels, leading to hypokalemia and disruption of neuromuscular and cardiovascular function. Acute exposure via ingestion can cause severe gastrointestinal symptoms such as vomiting, abdominal pain, and diarrhea, followed by muscle weakness, paralysis, cardiac arrhythmias, ventricular fibrillation, and potentially fatal respiratory failure or circulatory collapse. The toxicity is mainly attributed to the barium component, with the iodide ion contributing lesser acute effects but potentially leading to thyroid dysfunction (iodism) in cases of prolonged or high exposure. No specific LD50 values for barium iodide are widely reported in authoritative sources, but soluble barium salts generally exhibit oral LD50 values in rodents on the order of 100-500 mg/kg, reflecting high acute toxicity. Chronic exposure to soluble barium compounds may result in adverse effects on the cardiovascular system, kidneys, and bones, though data specific to barium iodide remain limited. Barium iodide is classified under GHS as Acute Tox. 4 (oral), Acute Tox. 4 (inhalation), and STOT RE 1 (cardiovascular system), with hazard statements including H302 (harmful if swallowed) and H372 (causes damage to organs through prolonged or repeated exposure). It is not considered carcinogenic, mutagenic, or reproductive toxin based on available data.^[31]

Storage and handling precautions

Barium iodide (BaI₂) is highly hygroscopic and absorbs moisture readily from the air, which can lead to degradation or clumping of the material. Store the anhydrous form and the dihydrate in tightly sealed containers under dry conditions, preferably in a desiccator over a suitable drying agent (such as silica gel or phosphorus pentoxide) or in a dry inert atmosphere (e.g., argon or nitrogen) to prevent hydration and maintain purity.^[32] Keep in a cool, well-ventilated area away from incompatible materials such as strong oxidizers, acids, and moisture sources. Handle barium iodide only in a fume hood or well-ventilated area to minimize dust inhalation. Wear appropriate personal protective equipment (PPE), including nitrile or neoprene gloves, safety goggles or face shield, and a lab coat. In case of dust formation, use a NIOSH-approved respirator with particulate filter. Avoid skin contact and ingestion.^[32] For spills, sweep or vacuum up the material carefully to avoid generating dust, then transfer to a suitable waste container. Do not flush to sewer. Dispose of barium iodide waste as hazardous chemical waste in accordance with local, regional, and national regulations (e.g., as barium-containing hazardous waste under RCRA in the US). Contaminated packaging should be disposed of similarly.^[33]

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Barium iodide

Structure

Reactions

Safety

References

Barium iodide

Physical and chemical properties

Appearance and physical state

Solubility and hygroscopicity

Melting and boiling points

Density and crystal data

Structure

Anhydrous barium iodide

Barium iodide dihydrate

Preparation

Synthesis from barium compounds and hydroiodic acid

Alternative methods and dehydration

Reactions

Behavior in water and air

Thermal decomposition and redox reactions

Uses

Chemical synthesis and laboratory applications

Materials preparation and specialized uses

Safety and handling

Toxicity and health hazards

Storage and handling precautions

References

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