Metal-organic macrocycles (MOMs), metal-organic polyhedra (MOPs) and metal-organic frameworks (MOFs) are metal-organic systems (MOSs) developed from appropriately designed ligands and selected metal ions. Metalladiazamacrocycles, a class of MOMs, are finite 2D MOSs formed from tricationic hexacoordinate metal ions and ditopic bridging ligands, N-acylsalicylhydrazide, containing diaza residues, where the size and shape of the systems have been modulated by controlling the steric repulsions between the ligands. The 2D MOM systems could be expanded to 3D MOP systems by self-assembling C(3) symmetric components and C(4) symmetric components to octahedral MOPs. By substituting some replaceable solvent sites of MOMs or MOPs, MOFs based on MOMs or MOPs as SBBs have been constructed, where the properties of the SBBs have been directly transferred to the MOF systems.

Among the several approaches developed for the fabrication of molecular crystals with noncentrosymmetric lattices, incorporation of chirality is the only one which guarantees it for fundamental symmetry reasons. One of the few quadratic nonlinear optical chromophores which form a large number of noncentric cocrystals/salts without the assistance of chirality is 4-nitrophenolate; hence it is an ideal candidate to explore new avenues to noncentric lattice formation. The utility of a structure-directing counterion in such an approach is explored in the present study. In contrast to para-aminopyridine, it is found that ortho-aminopyridines (2-aminopyridine and 2,6-diaminopyridine) which support bent pathways of supramolecular assembly through H-bond formation lead to noncentric cocrystalline salts with 4-nitrophenol. The molecular assembly in the crystals can be visualized in the form of H-bonded helical structures. The second harmonic generation observed in the new materials is analyzed in terms of the contributions from the partners in the ternary system consisting of 4-nitrophenolate, pyridinium, and 4-nitrophenol.

A general strategy was developed for edge-directed self-assembly of tetragonal metal-organic polyhedra (MOPs) having a C(4) symmetry Cu(II)(2)(COO)(4) paddle-wheel as a secondary building unit, using C(2) symmetric dicarboxylic ligands as pincer-type primary building units.

Optical second harmonic generation (SHG) from molecular crystals is largely controlled by the molecular hyperpolarizability and the relative disposition of the molecules in the crystal lattice. Even though it is known that intermolecular interactions can modify the bulk SHG, strong and direct influence of such effects in crystals has not been widely demonstrated. We present a new family of crystals based on the achiral remote functionalized nonlinear optical (NLO) chromophore, N-(2-aminoethyl)-4-nitroaniline, combined with a homologous series of carboxylic acids, in which the overwhelming impact of supramolecular interactions on the solid-state SHG is clearly manifested. Crystallographic investigations reveal a systematic variation in the superstructure formation of the NLO-phore unit across the series, and the intensities of the SHG from microcrystalline samples are found to correlate with the assembly pattern. Failure of simple additive models in explaining the SHG trend is analyzed using quantum chemical computations of the hyperpolarizability of molecular clusters which establishes the dominant influence of noncovalent intermolecular interactions. The present study illustrates the feasibility of exploiting supramolecular structural features to enhance the NLO response of molecular materials.

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