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".

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The inorganic−organic hybrid layered material of stoichiometry [DAMS+][Ag5I6 -], characterized by a strong SHG activity, has been prepared mechanochemically by room-temperature ball-milling a mixture of AgI and [DAMS+][I-], eventually followed by a moderate heating. By means of electronic absorption spectra, XRPD, and second harmonic generation (SHG) experiments we proved that the intralayer ordering of the [DAMS+] nonlinear optical chromophores into J-aggregates precedes the interlayer one, on the whole producing, by a sequential process, the “macropolarity” responsible for the strong SHG. The mechanochemical approach was shown to be of general use, as it was successfully applied to the synthesis of the analogous [DAMS+][Cu5I6 -], [DAZOP+][Ag5I6 -], and [DAES+][Ag5I6 -] materials.

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