Metal dependent coordination of biomolecular ligand: X-ray crystal structures of copper, cobalt and calcium complexes of (3-hydroxy-5-(hydroxymethyl)-2-methylisonicotinic acid) 5-phosphate, an oxidized pyridoxal 5-phosphate

X-ray crystal analyses of divalent copper, cobalt and calcium complexes of monoanionic (3-hydroxy-5-(hydroxymethyl)-2-methylisonicotinic acid) 5-phosphate (L₁C₈H₉NO₇P⁻) revealed the chemical compositions of Cu---L·3H₂O(1), Co---L·5H₂O(2) and Ca·L₂·7H₂O (3) and the coordination structures which depend on the coordination abilities and chemical properties of the respective metal ions. Although 1 and 2 crystals showed similar features, i.e., presence of the metal ion at the crystallographic center of symmetry and octahedral six-coordination, the patterns of coordination with the ligand molecules differed. While direct coordination to the L carboxyl oxygen was observed in 1 crystals, all ligation positions in 2 crystals were occupied by water molecules. On the other hand, 3 crystals formed a pentagonal bipyramidal structure (seven-coordination), where oxygens of L phosphates and water molecules coordinated to the calcium ion. Each of the complex structures showed characteristic molecular packing depending on the pattern of coordination to the respective metal ion. L is monoanionic in all complex crystals, where the phosphate and carboxyl groups are deprotonated and pyridine nitrogen is protonated, and is neutralized by each metal ion. Crystal data: 1, monoclinic, space group P2₁/c, A = 5.4129(6), B = 10.515(2), C = 22.770(2) Å, β = 91.853(9)°, Z = 4, R = 0.0404 for 1834 observed reflections; 2, triclinic, space group

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, c = 6.789(3) Å, α = 96.84(3), β = 109.10(3), γ = 100.50(2)°, Z = 2, R = 0.0684 for 1605 observed reflections; 3, triclinic, , a = 10.069(2), B = 14.501(3), c = 10.051(1) Å, α = 100.75(1), β = 97.28(2), γ = 76.18(2)°, Z = 2, R = 0.0540 for 3637 observed reflections.