The molecule of the title compound, [Ni4(CH3O)4(C8H7O3)4(CH3OH)4], has S 4 symmetry. Each of the four NiII atoms occupies every other corner of a cube, with the alternate corners occupied by μ3-methano­late bridging groups linking to three NiII atoms. Each NiII atom is in an O6 octa­hedral coordination environment formed by three O atoms from three μ3-methano­late groups, one from methanol, and two others from a bidentate 2-formyl-6-meth­oxy­phenolate ligand. The Ni—O bond distances range from 2.0020 (14) to 2.0938 (14) Å, the cis bond angles range from 81.74 (6) to 97.63°, and the trans bond angles range from 168.76 (5) to 175.22 (6)°. There are bifurcated hydrogen-bonding inter­actions between the coordinated methanol OH groups and both the phenolic and meth­oxy O atoms of an adjoining 2-formyl-6-meth­oxy­phenolate moiety. In addition, there are weak inter­molecular C—H⋯O inter­actions involving the meth­oxy O atoms.

In the title compound, [Ni(C18H18N2O4)]·C3H7NO, the central NiII atom is in a square-planar O2N2 coordination environment. The planar Ni–salen moieties (r.m.s. deviation for the plane through the conjugated part of the Ni–salen group = 0.07 Å) form parallel stacks in the a-axis direction, with alternating Ni⋯Ni separations of 3.5339 (7) and 3.6165 (7) Å. In the crystal, there are weak inter­molecular C—H⋯O inter­actions involving the dimethyl­formamide O and phenolate O atoms.

In the title compound, [Ni(C11H13N2O4)2]·C3H7NO, the NiII ion is octa­hedrally coordinated in an N2O4 environment by two identical Schiff base ligands. The Ni—O bond lengths range from 2.004 (2) to 2.106 (2) Å, while the Ni—N bond lengths are 2.038 (2) and 2.0465 (19) Å. The cis bond angles range from 78.64 (8) to 97.30 (8)°, with the former being due to the small bite of the amino­alcohol ligand, while the trans bond angles range from 167.86 (8) to 171.23 (8)°. One of the alcohol H atoms forms a hydrogen bond with the dimethyl­formamide (DMF) solvent mol­ecule, while the other links mol­ecules into chains along the b axis through inter­molecular O—H⋯O hydrogen bonds. There are bifurcated C—H⋯O inter­actions involving one of the nitro groups between parallel stacks of mol­ecules in the b-axis direction.

In the title compound, [Ni(C8H7O3)(NO3)(C12H12N2)2], the asymmetric unit contains a NiII atom, two mol­ecules of 2-(benzyl­amino)pyridine, a mol­ecule of deprotonated o-vanillin (3-methoxy­salicylaldehydate) and a bidentate nitrate anion. The NiII center is six-coordinated by two pyridine N atoms from 2-(benzyl­amino)pyridine, two O atoms from o-vanillin and two O atoms from the nitrate anion. The crystal packing shows two hydrogen bonds from the amine N—H group to the deprotonated phenol O atom of the o-vanillin moieties, as well as weak C—H⋯O secondary inter­actions. These inter­actions link the mol­ecules into ribbons in the c direction. The steric requirement of the bidentate nitrate and its small bite angle [61.01 (3)°] cause some orientation of the two 2-(benzyl­amino)pyridine groups. As a result, this coordination environment of the NiII center is distorted octa­hedral, as the trans angles range from 158.65 (3) to 175.76 (3)° and the cis angles range from 61.01 (3) (for the bidentate nitrate O atoms) to 102.30 (4)°.

In the title complex, [Ni(C7H5O2)2(C12H12N2)2], the NiII atom lies on a center of inversion and is coordinated in an octa­hedral geometry by two 2-(benzyl­amino)­pyridine (2-BAP) and two 2-formyl­phenolate ligands with the O-atom donors in the equatorial plane and the pyridine N atoms in axial positions. There are hydrogen-bonding inter­actions between the secondary amine H atom and the phenolate O atom, as well as C—H⋯O inter­actions, which result in the dihedral angle between the aromatic phenyl ring of the 2-formyl­phenolate moiety and the pyridine ring being 80.23 (4)°. In the packing, there are both C—H⋯π inter­actions, which link the mol­ecules into chains along the b axis, and offset π–π inter­actions involving both the pyridine and phenyl rings of the 2-BAP ligands [centroid–centroid distances = 4.0100 (8) Å for the pyridine rings and 3.6601 (8) and 4.8561 (8) Å for the phenyl rings].