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In general, molecules with certain functional groups such as amine (-NH2) and carboxyl (-COOH) can promote the growth of co-crystals leading to the formation of supramolecular networks. However, if the differences in the pKa values of the two molecules are large [pKa (base)—pKa (acid)], salts can result instead of ‘real’ co-crystals. Here, we report the formation of such salt by letting pyrazine-2-carboxylic acid (pKa = 2.9) crystallize together with aminoguanidine (pKa = 11.5; high Δpka = 8.6) a nitrogen-rich organic base. The title salt has been prepared by slow evaporation of an equimolar ratio of guanylhydrazine bicarbonate (i.e., aminoguanidine bicarbonate (AgunH.HCO3)) and pyrazine-2-carboxylic acid (Pymca) in aqueous medium. The salt was characterized by IR spectroscopy, powder and single-crystal X-ray diffraction techniques. This material shows enhanced antioxidant activity and this is due to the crucial role of hydrazinic moiety in the aminoguanidinium salt.

A new set of lighter lanthanide complexes having general formula (GunH)3[Ln(tdp)3]·3H2O (Ln = La, Pr, Nd, and Sm) derived from thiodipropionic acid (H2tdpa) and guanidine carbonate [Gun.(H2CO3)1/2] were synthesized by template method in aqueous medium. These complexes were characterized by various physico-chemical techniques, such as elemental analysis, molar conductance, FT-IR, UV–Vis, TG–DTA (air and nitrogen atmosphere), and PXRD studies. In this manuscript, for first time, the sulfur content of the acid in the complexes has been estimated by simple volumetric analysis. From the thermal analysis, all of the complexes are assisted with water molecules, which decompose endothermic followed by exothermic decomposition to yield Ln2(SO4)3 as the end residue. All the complexes are stabilized by nine coordinated monocapped square antiprismatic or tricapped trigonal prismatic geometry and found to be monomeric in compositions, which is proposed by various physico-chemical techniques. The isomorphism of these complexes is revealed by PXRD technique. Furthermore, the luminescence properties of free acid and the synthesized complexes were studied at room temperature in solid state.

Glyoxylic acid and ethyl carbazate condense in situ in the reaction medium and react with metal nitrates of Co, Ni or Cu to yield isostructural metal complexes with the general formula [M(gly-ec)2(H2O)2] (M = Co2+ (1), Ni2+ (2) and Cu2+ (3); Hgly-ec = ethoxycarbonyl-hydrazono-acetic acid). These products are elucidated through various physicochemical techniques including powder and single-crystal X-ray diffraction. X-ray crystallography of complexes 1 and 3 reveals that two anionic Schiff base ligands are coordinated to the metal ion via (N, O) bidentate chelation and situated trans to each other in equatorial positions and are nearly coplanar with the metal atom. The two coordinated water molecules occupy the trans axial positions, with a slightly distorted octahedral geometry. The thermal behavior of complexes 1–3 is studied in air and nitrogen atmosphere from 30 to 800 °C. In both mediums, all of the complexes show endothermic followed by exothermic decomposition to yield metal oxides as the end products at low temperature. Hence, these isotypic complexes may be used as solid-state precursors for the preparation of respective metal oxides due to their low temperatures of decomposition.

Supplementary data related to this article can be found at https://doi.org/10.1016/j.molstruc.2018.12.076.

The title compound was prepared by a template method starting from manganese(II) nitrate with a Schiff base ligand. The product of condensation was between methyl carbazate and glyoxylic acid, and formed in situ in aqueous solution containing ammonium thio­cyanate. The manganese compound crystallized in the monoclinic space group P21/n and exists as a centrosymmetric dimer., The title compound, [Mn2(C4H5N2O4)2(NCS)2(H2O)4]·4H2O (I), exists as a centrosymmetric dimer. Each dimeric unit consists of tridentate (O,O,N)-chelating Schiff bases with symmetry-maintained μ-O-bridged carboxyl­ate anions, terminally bound thio­cyanate anions, and ligated and solvated water mol­ecules. The complex exhibits a distorted octa­hedron geometry and the centrosymmetric μ-O-bridged carboxyl­ate anions connect the two manganese atoms to form an M 2O2 ring. In the crystal, the mol­ecules are inter­linked via strong N—H⋯O and O—H⋯O hydrogen-bonding contacts and weak O—H⋯S inter­molecular inter­actions, forming a three-dimensional mol­ecular network.

New-fangled water mediated and air stable thorium complex of molecular formula (AgunH)2[Th(dip)3].H2O have been prepared by reacting thorium(IV) nitrate, dipicolinic acid (H2dip) and aminoguanidine bicarbonate (AgunH.HCO3) at appropriate molar ratio via., template method. The complex has been systematically characterized by chemical analysis, elemental, spectral, thermal and single crystal studies including luminescence and antioxidant properties. The IR spectrum of the resulting complex infers that the carboxylate anion behaves as a monodentate and facilitates to form a monomeric rather than polymeric environment. This is further confirmed by single crystal X-ray diffraction studies. Thermal stability of the title compound undergoes step-wise decomposition to endure ThO(CO3) as the end residue. The single crystal X-ray study reveals that the thorium complex crystallizes in the triclinic crystal system with centric space group (P-1) of Z = 2. Each dipicolinate anion (dip2−) exhibits tridentate coordination modes through a nitrogen atom of pyridine ring and oxygen atoms of the carboxylate groups to form nine coordination with tri-capped trigonal prismatic geometry. Further, the anionic complex is neutralized by two aminoguanidinium (AgunH+) cations and stabilized along with a lattice water molecule. This material shows enhanced luminescent properties, this is due to the crucial role of dipicolinate anion not for aminoguanidinium moiety. Whereas, the aminoguanidinium species is promote to act as a secondary antioxidant.

New hydrazone ligands methoxycarbonyl-hydrazono-acetic acid, (HL1) and ethoxycarbonyl-hydrazono-acetic acid, (HL2) generated from methyl and ethyl carbazates with glyoxylic acid, and their respective silver(I) complexes [Ag(HL1)(L1)].H2O (1) and [Ag(HL2)2]+1[Ag(L2)2]−1 (2) were synthesized and characterized by various physico-chemical techniques. Single crystal X-ray structures of the ligand, HL1 and complexes (1 & 2) were determined. In complex 1, the five coordination sites around silver are occupied by one each of a neutral bidentate (N, O) HL1 ligand, with a free carboxyl group and an anionic tridentate (O, N, O) L1 carboxylate ligand, while complex 2 is unique with a homo nuclear ion-pair nature. In the cationic moiety, the silver ion is hexa-coordinated to two neutral tridentate (O, N, O) hydrazone ligands with the binding carboxyl groups protonated; whereas in the anionic moiety, the silver ion is penta-coordinated with two negatively charged carboxylate ligands with one of them as bidentate (N, O) and the other as tridentate (O, N, O). Thermal data for the prepared complexes 1 and 2 show a low temperature endo-followed by an exothermic decomposition pattern as that of the Schiff base ligands (HL1 & HL2), in the range 175–350 °C to give metallic silver as the end residue, which was confirmed by PXRD, FTIR and FESEM analyses. All of the compounds are water soluble and hence used for biological studies, such as antimicrobial (antibacterial and antifungal stains) and anticancer activities (Hela, MCF-7, and compared with a normal cell HBL-100). From a biological screening test, the silver complexes tend to be a potential applicant expandable as efficient cytotoxic agents. Further, the path of cell death (apoptosis) was also examined through fluorescence staining methods (AO/EtBr and DAPI).