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

摘要

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[M_2M'(C_2O_4)_6]· 2DAMBA·2H_2O (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 fern-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".