Nowotny phase

In inorganic chemistry, a Nowotny chimney ladder phase (NCL phase) is a particular intermetallic crystal structure found with certain binary compounds. NLC phases are generally tetragonal and are composed of two separate sublattices. The first is a tetragonal array of transition metal atoms, generally from group 4 through group 9 of the periodic table. Contained within this array of transition metal atoms is a second network of main group atoms, typically from group 13 (boron group) or group 14 (carbon group). The transition metal atoms form a chimney with helical zigzag chain. The main-group elements form a ladder spiraling inside the transition metal helix.

The phase is named after one of the early investigators H. Nowotny. Examples are RuGa₂, Mn₄Si₇, Ru₂Ge₃, Ir₃Ga₅, Ir₄Ge₅ V₁₇Ge₃₁, Cr₁₁Ge₁₉, Mn₁₁Si₁₉, Mn₁₅Si₂₆, Mo₉Ge₁₆, Mo₁₃Ge₂₃, Rh₁₀Ga₁₇, and Rh₁₇Ge₂₂.

In RuGa₂ the ruthenium atoms in the chimney are separated by 329 pm. The gallium atoms spiral around the Ru chimney with a Ga–Ga intrahelix distance of 257 pm. The view perpendicular to the chimney axis is that of a hexagonal lattice with gallium atoms occupying the vertices and ruthenium atoms occupying the center. Each gallium atom bonds to 5 other gallium atoms forming a distorted trigonal bipyramid. The gallium atoms carry a positive charge and the ruthenium atoms have a formal charge of −2 (filled 4d shell).

In Ru₂Sn₃ the ruthenium atoms spiral around the tin inner helix. In two dimensions, the Ru atoms form a tetragonal lattice with the tin atoms appearing as triangular units in the Ru channels.

The occurrence of a LCP phase can be predicted by the so-called 14 electron rule. In it the total number of valence electrons per transition metal atom is 14.

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