The title compound, C₂₄H₂₀P⁺·ClO₄^-, undergoes a sudden reversible phase change in the region of 173-180 K which involves ordering of three quarters of the perchlorate anions.

The title complex, [Ni(C₆H₄NO₂)₂(H₂O)₄], consists of an Ni atom coordinated to two trans pyridine­carboxyl­ate ligands, coordinated through the N atoms, and four water ligands. The Ni atom lies on a site of 2/m symmetry, and the pyridine­carboxyl­ate ligand lies on a mirror plane. Extensive inter-complex hydrogen bonding occurs between the water ligands and the carboxyl­ate groups, resulting in a three-dimensional network.

The title complex, [Ni(C₆H₄NO₂)₂(H₂O)₄], consists of Ni atoms coordinated to two trans pyridyl­carboxyl­ate ligands, coordinated through the N atoms, and four water ligands. The Ni atom lies on a centre of symmetry. Extensive inter-complex hydrogen bonding occurs between the water ligands and the carboxyl­ate groups, resulting in a three-dimensional network.

In the title complex, [FeCl₂(C₃₀H₂₈N₆)], the Fe atom is five-coordinated by two terminal chloride ligands and one end of the bis-tridentate ligand. The complexes display intermolecular C—Hπ, π-stacking and C—HX (X = N, Cl) interactions.

The Cu atom in the title compound, [Cu(NO₃)(C₉H₂₁N₃)]ClO₄, is coordinated facially by the tridentate tri­aza­cyclo­nonane ligand, and also by a chelating nitrate anion. In addition, the copper makes a sixth much longer interaction [2.828 (3) Å] with an O atom of the perchlorate anion.

The title compound, [(CH₃)₄N]₃[La(NO₃)₆]·MeOH, contains an anionic hexa­nitratolanthanate(III) complex with the nitrate ligands octa­hedrally disposed around the metal. The incorporated methanol solvent is involved in hydrogen bonding to one nitrate ligand.

The title compound, [Ni(C₁₆H₂₈N₂O₈)], is isostructural with its Cu^II and Co^II analogues. The Ni^II atom lies on a centre of inversion and exhibits a distorted octa­hedral coordination environment involving two carboxyl­ate O atoms, two ether O atoms and two amino N atoms.

The title compound, [Co(C₁₆H₂₈N₂O₈)], is isostructural with its Cu^II and Ni^II analogues. The Co^II atom lies on a centre of inversion and exhibits a distorted octa­hedral coordination environment involving two carboxyl­ate O atoms, two ether O atoms and two amino N atoms.

The title compound, {[Cu(C₇H₄O₄)₂]·2CH₃OH}_n, forms a square-planar complex through two N,O-chelating pyridine-2,3-dicarboxyl­ate ligands. Axial inter­actions between Cu^II and O atoms of the CO₂H groups in the meta-positions of adjacent ligands form one-dimensional chains. Incorporation of methanol into the structure results in O—HO hydrogen-bond inter­actions, which cross-link the chains into a three-dimensional network.