4,4'-Bipyridine-2-hydroxy-propane-1,2,3-tricarboxylic acid (3/2).

The combination of 2-hydroxy-propane-1,2,3-tricarboxylic acid (H(3)hypta, also called citric acid) and 4,4'-bipyridine (4,4'-bipy) in a 1:1.5 molar ratio leads to the formation of the title mol-ecular cocrystal, 1.5C(10)H(8)N(2)·C(6)H(8)O(7). The asymmetric unit contains one and a half 4,4'-bipy units, with one lying across a centre of inversion, and one H(3)hypta mol-ecule. The significant differences in the C-O bond distances support the existence of the un-ionized acid mol-ecule and confirm the formation of a cocrystal. There are π-π and C-H⋯π stacking inter-actions between the aromatic rings of 4,4'-bipy [with inter-planar distances of 3.7739 (8) and 3.7970 (8) Å] and between CH groups of H(3)hypta [with an H⋯π distance of 2.63 Å]. In the crystal structure, intermolecular O-H⋯N hydrogen bonds occur and an O-H⋯O hydrogen bond occurs within the citric acid moiety.

(2,9-Dimethyl-1,10-phenanthroline)(4-hydroxy-pyridine-2,6-dicarboxyl-ato)copper(II) trihydrate.

In the title complex, [Cu(C(7)H(3)NO(5))(C(14)H(12)N(2))]·3H(2)O, there are two independent neutral mol-ecules of the Cu complex along with six mol-ecules of water of hydration in the asymmetric unit. The Cu(II )atoms in each complex adopt a distorted square-pyramidal coordination geometry being penta-coordinated by one N and two O atoms of 4-hydroxy-pyridine-2,6-dicarboxyl-ate anions and two N atoms of 2,9-dimethyl-1,10-phenanthroline (dmp) molecules. In the crystal structure, there are O-H⋯O and C-H⋯O hydrogen bonds and five π-π stacking inter-actions with centroid-centroid distances in the range 3.620 (1)-3.712 (1) Å. In addition, a C-H⋯π inter-action between a heterocyclic ring of dmp is observed to reinforce the crystal cohesion.