Cyclopentadienylindium, C₅H₅In, is an organoindium compound  containing indium

Indium

Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...

 in the +1 oxidation state. Commonly abbreviated to CpIn, it is a cyclopentadienyl complex

Cyclopentadienyl complex

A cyclopentadienyl complex is a metal complex with one or more cyclopentadienyl groups . Based on the type of bonding between the metals and the cyclopentadienyl]] moieties, cyclopentadienyl complexes are classified into the following three categories: a) π-complexes, b) σ-complexes, and c) ionic...

 with a half-sandwich

Sandwich compound

In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic covalent bonds to two arene ligands. The arenes have the formula CnHn, substituted derivatives and heterocyclic derivatives...

 structure.
It was the first (1957) low valent organoindium compound reported.

Preparation and chemistry

CpIn can be readily prepared by reacting indium(I) chloride with cyclopentadienyllithium:

InCl + CpLi → CpIn + LiCl

InCp reacts with BF₃

Boron trifluoride

Boron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...

, BCl₃

Boron trichloride

Boron trichloride is a chemical compound with the formula BCl3. This colorless gas is a valuable reagent in organic synthesis. It is also dangerously reactive.-Production and properties:Boron reacts with halogens to give the corresponding trihalides...

, BBr₃

Boron tribromide

Boron tribromide, BBr3, is a colorless, fuming liquid compound containing boron and bromine. It is usually made by heating boron trioxide with carbon in the presence of bromine: this generates free boron which reacts vigorously with the bromine...

, BI₃

Boron triiodide

Boron triiodide is a chemical compound of boron and iodine with chemical formula BI3. It has a trigonal planar molecular geometry. It is a crystalline solid. Its dielectric constant is 5.38 and its heat of vaporization is 40.5 kJ/mol....

 and trimethylborane

Trimethylborane

Trimethylborane is a toxic compound normally occurring as a gas that spontaneously catches fire in air. The formula is B3, which can also be expressed as Me3B, with Me representing methyl. Its melting point is -161.5 °C and boiling point is -20.2 °C.Vapour pressure is given by log P =...

 B(CH₃)₃ to form adducts, e. g.:

CpIn + BF₃ → CpIn.BF₃

In these adducts the bonding of the Cp ligand to the indium atom changes from η

Hapticity

The term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...

⁵ (π complexing) to η¹

Hapticity

The term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...

 (σ bonding).

Salts containing the InX₂⁻ anion containing indium in the +1 oxidation state have been prepared, for example:

CpIn + HCl

Hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

 + N(Et₄)Cl → N(Et₄)InCl₂+ C₅H₆

Cyclopentadiene

Cyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction...

Structure and bonding

Solid CpIn is polymeric consisting of zigzag chains of alternating indium atoms and C₅H₅ units. Two indium atoms interact with the opposite faces of each C₅H₅⁻ ring, nearly perpendicularly to the ring plane, and two rings interact with each indium atom, forming an angle of about 128°. In the CpIn monomer present in the vapour phase the indium atom sits on the central axis of the aromatic cyclopentadienyl anion, C₅H₅⁻.

Bonding studies have shown that the aromatic ring electrons of the cyclopentadienyl anion interact with the indium 5s and 5p atomic orbital

Atomic orbital

An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

s, and that the lone pair on the indium atom is a dominant feature.

Ball-and-stick Ball-and-stick model In chemistry, the ball-and-stick model is a molecular model of a chemical substance which is to display both the three-dimensional position of the atoms and the bonds between them...  and space-filling model Space-filling model In chemistry a space-filling model, also known as calotte model, is a type of three-dimensional molecular model where the atoms are represented by spheres whose radii are proportional to the radii of the atoms and whose center-to-center distances are proportional to the distances between the atomic... s of CpIn chains in the crystal structure of cyclopentadienylindium(I)