In the title compound, [Cr₂Nd₂F₄(NO₂)₈(C₁₂H₈N₂)₄]·4CH₃OH·H₂O, two cis-difluoridobis(1,10-phenanthroline)chromium(III) fragments containing octa­hedrally coordinated chromium(III) bridge via fluoride ions to two tetra­nitratoneodymate(III) fragments, forming an uncharged tetra­nuclear square-like core. The fluoride bridges are fairly linear, with Cr—F—Nd angles of 168.74 (8)°. Cr—F bond lengths are 1.8815 (15) Å, slightly elongated compared to those of the parent chromium(III) complex, which has bond lengths ranging from 1.8444 (10) to 1.8621 (10) Å. The tetra­nuclear complex is centered at a fourfold rotoinversion axis, with the Cr and Nd atoms situated on two perpendicular twofold rotation axes. The uncoordinated water mol­ecule resides on a fourfold rotation axis. The four methanol solvent mol­ecules are located around this axis, forming a cyclic hydrogen-bonded arrangement. The title compound is the first structurally characterized example of unsupported fluoride bridges between lanthanide and transition metal ions.

The structures of the diastereoisomers Λ(+)₅₇₈-, (I), and Δ(−)₅₇₈-bis­(ethane-1,2-diamine)[β-ethyl (S)-aspartato-κ²N,O¹]cobalt(III) bis­(perchlorate) monohydrate, (II), both [Co(C₆H₁₀N₂O₄)(C₂H₈N₂)₂](ClO₄)₂·H₂O, are compared. In both structures, the ester group of the amino acid side chain is engaged only in intra­molecular hydrogen bonding to coordinated amine groups. This inter­action is stronger in (I) and correlates with previously observed diastereoisomeric equilibrium ratios for related metal complex systems in aqueous media. The two perchlorate anions of (II) are located on twofold axes. Both perchlorates in (I) and one of the perchlorates in (II) are affected by disorder. Both structures exhibit extensive three-dimensional hydrogen-bonding net­works.

The salts hexa­aqua­magnesium furan-2,5-dicarboxyl­ate, [Mg(H₂O)₆](C₆H₂O₅), (I), and hexa­aqua­nickel furan-2,5-di­carboxyl­ate, [Ni(H₂O)₆](C₆H₂O₅), (II), provide the first crystallographic characterization of the furan-2,5-dicarboxyl­ate dianion. Both structures exhibit extensive three-dimensional hydrogen-bonding networks between the octa­hedral coordinated hexa­aquametal(II) ions and the dicarboxyl­ate anions. Although the two structures are not isomorphous, they contain essentially identical two-dimensional slabs. The distinction between the structures is that these slabs are related by translation in (II), whereas adjacent slabs in (I) are reflected relative to each other by the action of a glide plane. The reflection occurs so that the local contacts between slabs are not changed, and thus the hydrogen-bond networks are identical except for the orientation of the water mol­ecules at the inter­face between slabs.

In the title compound, (C₂₄H₂₀P)₂[Cr(CN)₄(N)]·2H₂O, the complex anion exhibits a square-based pyramidal geometry around the central Cr^V atom, which is coordinated by a nitride ligand in the apical position and by four cyanide ligands in the equatorial plane. The chromium atom is located 0.4493 (13) Å out of the plane formed by the ligating C atoms of the cyanide ligands. The water mol­ecules of crystallization form inter­molecular O—HN hydrogen bonds to the N atoms of two cyanide ligands of neighbouring complex anions, forming an infinite hydrogen-bonded chain parallel to [011] of water mol­ecules and [Cr(N)(CN)₄]²⁻ anions. The terminal nitride ligands are not engaged in inter­molecular inter­actions.