Cation-cation interactions often occur between molecular

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s of

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. The lanthanide and actinid ...

s and f-elements (so-called yl cations). They are distinguished as a separate type of

intermolecular interactions An intermolecular force (IMF; also secondary force) is the force that mediates interaction between molecules, including the electromagnetic forces of attraction or repulsion which act between atoms and other types of neighbouring particles (e.g. ...

, since without taking them into account, cations usually repel each other in accordance with

Coulomb's law Coulomb's inverse-square law, or simply Coulomb's law, is an experimental scientific law, law of physics that calculates the amount of force (physics), force between two electric charge, electrically charged particles at rest. This electric for ...

Cation-cation interactions in f-elements

Of particular interest are cation-cation interactions between actinide cations -

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

, in the form of uranyl UO₂²⁺,

neptunium Neptunium is a chemical element; it has chemical symbol, symbol Np and atomic number 93. A radioactivity, radioactive actinide metal, neptunium is the first transuranic element. It is named after Neptune, the planet beyond Uranus in the Solar Syste ...

in the form of neptunoyl NpO₂²⁺,

plutonium Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...

and

americium Americium is a synthetic element, synthetic chemical element; it has Chemical symbol, symbol Am and atomic number 95. It is radioactive and a transuranic member of the actinide series in the periodic table, located under the lanthanide element e ...

, which are essentially a manifestation of specific complex formation. They are a special case of

that occur in molecular ions. It was first discovered when studying the behavior of netunium(V) compounds in

solutions Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Solutio ...

of uranyl perchlorate. Great impact to crystallochemistry of cation-cation bonds was made by Mikhail Grigoriev. The cation-cation interaction pO₂sup>+ determines the

crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...

of Np(V) compounds, and the strength of cation-cation bonds between neptunoyl ions in a solid is comparable to the strength of ordinary bonds with acid

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s, although in an aqueous solution, apparently, the role There are somewhat fewer of these connections. In an organic solution, the intensity of C-C interactions can remain high In the absence of mutual coordination of neptunium ions, Np(V) compounds can exhibit both structural similarity with An(VI) compounds and fundamental differences (showing a tendency to unite Np coordination polyhedra through common equatorial edges. Cation-cation interactions can be detected not only by data from structural studies, but also according to

vibrational spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functio ...

data. For uranyl, cation-cation interactions are also recorded in the gas phase.

Cation-cation interactions in transition metal ions

For

s, cation-cation interactions appear in nitrene complexes. Nitrenium ligands provide an excellent platform for the simple and efficient synthesis of extremely rare complexes that have positively charged ligands coordinated to positively charged metals to form stable cation-cation and cation-dication coordination bonds.

References

{{Reflist Cations Chemical bonding