(μ-Benzene-1,2,4,5-tetracarboxylato-κ²O¹:O⁴)bis[aquabis(2,2-methylpropane-1,3-diamine-κ²N,N′)nickel(II)] methanol disolvate tetrahydrate, [Ni₂(C₁₀H₂O₈)(C₅H₁₄N₂)₄(H₂O)₂]·2CH₄O·4H₂O, (I), is dinuclear, with elemental units built up around an inversion centre halving the benzene-1,2,4,5-tetracarboxylate (btc) anion, which bridges two symmetry-related Ni^II cations. The octahedral Ni polyhedron is completed by two chelating 2,2-methylpropane-1,3-diamine (dmpda) groups and a terminal aqua ligand. Two methanol and four water solvent molecules are involved in a number of N–H⋯O and O–H⋯O hydrogen bonds which define a strongly bound two-dimensional supramolecular structure. The structure of catena-poly[[[bis(2,2-methylpropane-1,3-diamine-κ²N,N′)nickel(II)]-μ-pyridine-2,5-dicarboxylato-κ³O⁵:N,O²-[(2,2-methylpropane-1,3-diamine-κ²N,N′)nickel(II)]-μ-pyridine-2,5-dicarboxylato-κ³N,O²:O⁵] octahydrate], {[Ni₂(C₇H₃NO₄)₂(C₅H₁₄N₂)₃]·8H₂O}_n, (II), is polymeric, forming twisted chains around three independent Ni centres, two of which lie on inversion centres and the third in a general position. There are three chelating dmpda ligands (one disordered over two equally populated positions), which are each attached to a different cation, and two pyridine-2,5-dicarboxylate (pdc) anions, both chelating the Ni centre in general positions through an -O-C-C-N- loop, while acting as bridges to the remaining two centrosymmetric Ni atoms. There are, in addition, eight noncoordinated water molecules in the structure, some of which are disordered.