ABAB Homoleptic Bis(phthalocyaninato)lutetium(III) Complex: Toward the Real Octupolar Cube and Giant Quadratic Hyperpolarizability

The concept of octupolar molecules has considerably enlarged
the
engineering of second-order nonlinear optical materials by giving
access to 2D and 3D architectures. However, if the archetype of octupolar
symmetry is a cube with alternating donor and acceptor groups at the
corners, no translation of this ideal structure into a real molecule
has been realized to date. This may be achieved by designing a bis­(phthalocyaninato)­lutetium­(III)
double-decker complex with a crosswise ABAB phthalocyanine bearing
alternating electron-donor and electron-acceptor groups. In this communication,
we present the first step toward this goal with the synthesis, crystal
structure determination, and measurement of the molecular first-order
hyperpolarizability β by harmonic light diffusion, of an original
lutetium­(III) sandwich complex displaying the required ABAB-type alternation
for one face of the cube. This structure is characterized by an intense
absorption in the near-IR due to an intervalence transition and exhibits
the highest quadratic hyperpolarizability ever reported for an octupolar
molecule, ⟨βHLS2⟩1907 = 5750 × 10–30 esu.