Polyfunctional Inorganic−Organic Hybrid Materials: An Unusual Kind of NLO Active Layered Mixed Metal Oxalates with Tunable Magnetic Properties and Very Large Second Harmonic Generation

Mixed M(II)/M(III) metal oxalates, as “stripes” connected through strong hydrogen bonding by
para-dimethylaminobenzaldeide (DAMBA) and water, form an organic−inorganic 2D network that enables
segregation in layers of the cationic organic NLO-phore trans-4-(4-dimethylaminostyryl)-1-methylpyridinium,
[DAMS+]. The crystalline hybrid materials obtained have the general formula [DAMS]4[M2M‘(C2O4)6]·2DAMBA·2H2O (M = Rh, Fe, Cr; M‘ = Mn, Zn), and their overall three-dimensional packing is
non-centrosymmetric and polar, therefore suitable for second harmonic generation (SHG). All the compounds
investigated are characterized by an exceptional SHG activity, due both to the large molecular quadratic
hyperpolarizability of [DAMS+] and to the efficiency of the crystalline network which organizes [DAMS+]
into head-to-tail arranged J-type aggregates. The tunability of the pairs of metal ions allows exploiting also
the magnetic functionality of the materials. Examples containing antiferro-, ferro-, and ferri-magnetic
interactions (mediated by oxalato bridges) are obtained by coupling proper M(III) ions (Fe, Cr, Rh) with
M(II) (Mn, Zn). This shed light on the role of weak next-nearest-neighbor interactions and main nearest-neighbor couplings along “stripes” of mixed M(II)/M(III) metal oxalates of the organic−inorganic 2D network,
thus suggesting that these hybrid materials may display isotropic 1D magnetic properties along the mixed
M(II)/M(III) metal oxalates “stripes”.