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In the crystal, mol­ecules are linked by pairs of N—H⋯O hydrogen bonds into ribbons along the c-axis direction. The layered crystal packing is further consolidated by van der Waals and C—H⋯π inter­actions., In the crystal, the whole mol­ecule of the title compound, C14H12N4O7·0.224H2O, is nearly planar with a maximum deviation from the least-squares plane of 0.352 (1) Å. The mol­ecular conformation is stabilized by an intra­molecular N—H⋯O hydrogen bond, generating an S(6) ring motif. In the crystal, mol­ecules are linked by centrosymmetric pairs of N—H⋯O hydrogen bonds, forming ribbons along the c-axis direction. These ribbons connected by van der Waals contacts, forming sheets parallel to the ac plane. There are also inter­molecular van der Waals contacts and and C—H⋯π inter­actions between the sheets. A Hirshfeld surface analysis indicates that the most prevalent inter­actions are O⋯H/H⋯O (41.2%), H⋯H (19.2%), C⋯H/H⋯C (12.2%) and C⋯O/ O⋯C (8.4%).

Two known lanthanide complexes, [KLa(HL 1 ) 2 {(CH 3 ) 2 NCHO} 2 (H 2 O) 3 ] ( 1 ) and [Sm(H 2 O) 9 ]( E -H 2 L 2 ) 3 ·2H 2 O ( 2 ) were prepared by reaction of lanthanum(III) and samarium(III) nitrates with potassium 3-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonate (KH 2 L 1 ) and potassium ( E,Z )-5-chloro-3-(2-(1,3-dioxo-1-phenylbutan-2-ylidene)hydrazinyl)-2-hydroxybenzenesulfonate (KH 2 L 2 ), respectively. Catalytic activities of 1 and 2 were evaluated in the cyanosilylation of aldehydes with trimethylsilyl cyanide in different solvents such as tetrahydrofuran, dichloromethane or methanol. Complex 1 was found to be efficient catalyst for the cyanosilylation reaction in methanol medium at room temperature, producing cyanohydrin trimethylsilyl ethers with good yields (76–99%).

The title compound has a nonplanar conformation. In the crystal, the anions are linked to the cations and the water mol­ecules by N—H⋯O and O—H⋯O hydrogen bonds, forming a three-dimensional network. Face-to-face π–π stacking inter­actions are also observed., In the anion of the title hydrated salt, C2H10N2 2+·C21H13N3O8S2−·2H2O, the planes of the phenyl rings and the benzene ring of the 5-nitro-2-oxido­benzene­sulfonate group are inclined to one another by 44.42 (11), 56.87 (11) and 77.70 (12)°. In the crystal, the anions are linked to the cations and the water mol­ecules by N—H⋯O and O—H⋯O hydrogen bonds, forming a three-dimensional network. Furthermore, there are face-to-face π–π stacking inter­actions between the centroids of one phenyl ring and the benzene ring of the 5-nitro-2-oxido­benzene­sulfonate group [centroid–centroid distance = 3.8382 (13) Å and slippage = 1.841 Å]. A Hirshfeld surface analysis was conducted to verify the contributions of the different inter­molecular inter­actions.

The new mononuclear nickel(II) complexes [Ni(HL 1 )(H 2 O) 2 (CH 3 OH)] ( 1 , NaH 2 L 1 = sodium ( Z )-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazinyl)benzenesulfonate) and [Ni(H 2 L 2 ) 2 (H 2 O) 4 ] [(CH 3 ) 2 S O) 2 ] ( 2 , H 3 L 2 = (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazinyl)benzoic acid) were synthesized and characterized by IR and ESI-MS spectroscopies, elemental and X-ray crystal structural analyses. Both compounds 1 and 2 act as homogenous catalysts for the diastereoselective nitroaldol (Henry) reaction of aliphatic and aromatic aldehydes with nitroethane in different solvents such as acetonitrile, methanol or water. Complex 1 was found to be the more efficient catalyst for the Henry reaction in aqueous medium, providing β-nitroalcohols with good yields (67–82%) and diastereoselectivities ( syn/anti 59:41–70:30).

Two known organotin(IV) complexes, [Sn(C6H5)3HL1] (1) and [Sn(C2H5)2(1κO,2κO-H3L2) (1κO2-H3L2) (μ3-O)]2 (2), were prepared upon interaction of Ph3SnCl and Et2SnO with 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)benzoic acid (H2L1) and 2-(2-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene) hydrazinyl)benzoic acid (H4L2), respectively, in toluene solution. Both complexes are applied as catalysts in cyanosilylation of aldehydes. Complex 2 shows a high catalytic activity in the cyanosilylation reaction of a variety of aliphatic and aromatic aldehydes with trimethylsilyl cyanide yielding to the corresponding cyanohydrin trimethylsilyl ethers (yields up to 99%) in methanol and at room temperature.

The 1D and the 2D copper(II) coordination polymers [{Cu(κN,OO′-L)}2(μ-1κN:2κN′-bpy)2]n (1) and [{Cu(μ-1κN,OO′:2κO″-L)}2(μ-1κN:2κN′-hmt)]n (2), respectively, were synthesized from copper(II) nitrate and sodium 2-(2-(1,3-dioxo-1H-inden-2(3H)-ylidene) hydrazinyl)benzenesulfonate (NaHL), in the presence of 4,4′-bipyridine (4,4′-bpy) (for 1) or hexamethylenetetramine (hmt) (for 2). 1 and 2 are water soluble and are characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction. Depending on the neutral linkers, the dianionic ligand L2− displays tri- (in 1) or tetradentate (in 2) binding modes. The Cu2+ in 1 adopts a distorted N3O2 square-pyramid coordination environment, while in 2 it displays a distorted N2O3 trigonal bipyramid geometry. The catalytic activity of 1 and 2 was evaluated in the diastereoselective Henry reaction of nitroethane with a variety of aromatic and aliphatic aldehydes, in water and in organic solvents. β-Hydroxy nitroalkanes were obtained in high yields (up to 92%), and moderate-to-good syn/anti diastereoselectivities (up to 79:21), in water at room temperature.