The analysis of noncovalent interactions in several complexes constructed from 2,3,5,6-tetramethylpyrazine with different acid ligands, 1,4-cyclohexanedicarboxylic acid, 2,6-dihydroxybenzoic acid, 2,6-pyridinedicarboxylic acid, 6-hydroxy-2-naphthoic acid, 3-nitrophthalic acid, o-phthalic acid and 3-hydroxybenzoic acid, supported by single crystal X-ray diffraction analysis is presented. It reveals that all of these forms except 2 are organic supramolecular cocrystals without charge-transfer between the multicomponent acids and the base. The noncovalent interactions directing the assemblies of the eight structures are managed by classical O–H⋯O, O–H⋯N, weak C–H⋯O and π–π stacking interactions to generate 2D or 3D supermolecular architectures. For 5, 6, 7 and 8, carboxyl/pyrazine supramolecular heterosynthons R22(6) and R22(8) containing classical O–H⋯N and weak C–H⋯O interactions, usually observed in organic cocrystals of carboxylic acid and heterocyclic base, are again confirmed to participate in constructing these hydrogen-bonding supermolecular networks. In addition, weak C–H⋯O interactions were involved in building and consolidating their structures in all organic complexes. The thermal stability of crystals 1–8 has been investigated by thermogravimetric analysis (TGA) of mass loss.

Employing [Fe(C2O4)3]3− (C2O42− = oxalate) metallotectons as building units, a series of 3D iron–organic compounds with formulae [K(H-L1)2{Fe(C2O4)3}·2H2O] 1, [(H-Phen){Fe (C2O4)2}(Phen)·3H2O] 2, [(H2-L2)2{Fe2(C2O4)3Cl4}] 3, [K(H2-L3){Fe(C2O4)3}·2H2O] 4, [K(H2-L4){Fe(C2O4)3}·H2O] 5, [(H-L5){Fe(C2O4)(L5)}] 6, [(H2-L6)2{Fe2(C2O4)4(OH)2}·2H2O] 7, [(H-L7)4{Fe(C2O4)3}Cl·2H2O] 8 (with L1 = 2-methylbenzimidazole, Phen = 1,10-phenanthroline, L2 = 1,4-bis(imidazol-1-ylmethyl)benzene, L3 = 1,4-bis((2-methylimidazol-1-yl)methyl)benzene, L4 = 1,1′-butane-1,4-diylbis(1H-imidazole), H-L5 = 1H-benzotriazole, L6 = 1,2-ethylenediamine, L7 = melamine) have been synthesized and characterized by single-crystal X-ray diffraction. Compounds 1 and 5 possess different 2D [KFe(C2O4)3]2− layers. Compound 2 features a 2D hydrogen bonded network completed by trimer water clusters and [Fe(C2O4)2(Phen)]− anions via hydrogen bonds. Compounds 3–6 feature a series of 2D layers, which are further extended into a 3D supramolecular structure through C–H⋯O hydrogen bonds. Distinct [Fe2(C2O4)3Cl4]4− units and [Fe2(C2O4)4(OH)2]4− units are shown in compounds 3 and 7, respectively. Trinary hydrogen bonds and double hydrogen bonds are simultaneously displayed in 8 as well as N–H⋯Cl and O–H⋯Cl hydrogen bonds. Furthermore, in order to examine the thermal stability of all compounds, TGA was carried out.

Tetrafluoroterephthalic acid, (H2tfBDC), forms nine novel crystals with a series of N-containing heterocycles: 2,3-dimethyl pyrazine (2,3-Pyr), 2,6-dimethyl pyrazine (2,6-Pyr), 2,4-diamino-6-methyl-1,3,5-triazine (dmt), Benzoguanamine (bga), 2-methylbenzimidazole (2-MeBzlmH), 1,4-bis(imidazol) butane (bimb), 2-amino-4-hydroxy-6-methyl pyrimidine (ahmp), 1,2-bis[(2-methylimidazol-1-yl)methyl] benzene (L7), and 1,4-bis[(2-methylimidazol-1-yl)methyl] benzene (L5). These crystal structures including salts/co-crystals/hydrates were analyzed and characterized by single crystal X-ray diffraction, IR, and TGA. Single crystal X-ray diffraction studies show that the huge numbers of hydrogen bonds play a significance part in assembling individual molecules into larger architectures, especially the strong N–H⋯O, O–H⋯O hydrogen bonds, and weak but highly directional C–H⋯O and C–H⋯F interactions exist commonly in all nine novel crystals. Crystal structure analysis shows that the F atom of the H2tfBDC participates in C–H⋯F hydrogen bond formation, producing different supramolecular synthons. More importantly, the N–H⋯O, O–H⋯O, and C–H⋯O hydrogen bonds are mainly involved in the supramolecular assembly of these molecules, but C–H⋯F hydrogen bonds convert two-dimensional networks into three dimensional, hence, the C–H⋯F interactions have a crucial role in the formation of higher-order supramolecular structures.

Single crystals of LaKNaTaO5 is facilely obtained in corundum crucible at 600 °C by adding a certain amount of water to the hydroxide flux of KOH/NaOH additionally, which is a green method to avoid the heavy metal silver pollution compared with the silver tuber. The addition of water plays a critical role in the reaction process by changing the auto-dissociation of OH− in hydroxide melts. In addition, we have synthesized samples doped with Eu3+ and Tb3+ by the same route respectively and have investigated the effects of concentration and temperature on the photoluminescence (PL) properties. The results demonstrate that rare-earth-doped LaKNaTaO5 is an ideal material for white light emitting diodes (WLEDs).Highlights► Single crystal of LaKNaTaO5 was facilely obtained in corundum crucible. ► SEM and EDS results demonstrated the feasibility of the method. ► Photoluminescence properties of LaKNaTaO5 and samples doped with Eu3+ and Tb3+.