Transformation of a Tetranuclear Copper(II) Complex Bridged by Sugar Phosphates into Nucleotide-Containing Cu4 Aggregations

Abstract

Reaction of [Cu4(μ-OH){μ-(α-D-Glc-1P)}2(L)4(H2O)2]X3 (1a: L = bpy, X = NO3, α-D-Glc-1P = α-D-glucopyranose-1-phosphate) with Na2[H2ATP] (ATP = adenosine 5′-triphosphate) readily afforded the ATP-bridged tetranuclear copper(II) complex [Cu4(μ-ATP)2(bpy)4] (3), which was characterized by X-ray crystallographic analysis to consist of four linearly dispersed {CuII(bpy)}2+ fragments bridged by two triphosphate groups of the ATP tetravalent anions. The sugar and adenine base parts of the ATP moieties are away from the copper(II) centers, but the structure was stabilized by weak intramolecular π–π stacking between the ATP purine ring and two bpy ligands and intermolecular hydrogen bonding between the adenine base pairs. The variable-temperature magnetic susceptibility of complex 3 exhibited only weak antiferromagnetic couplings between the four linearly dispersed CuII ions. A similar reaction of 1a or 2 (L = phen, X = NO3) with Na2[IMP] (IMP = inosine 5′-monophosphate) yielded a different type of tetracopper(II) complex formulated as [Cu4{μ-(IMP-H)}2(L)4(H2O)4](NO3)2 [L = bpy (5), phen (6)], in which the IMP moieties are deprotonated at the N-1 position of the nucleobase, forming IMP-H trianions, and four {Cu(bpy)(H2O)}2+ fragments are connected through the N-1, N-7, and O-6 atoms of the nucleobase and the monodentate 5′-phosphate group. Reaction of 1b (L = bpy, X = Cl) with Na2[UMP] (UMP = uridine 5′-monophosphate) resulted in a polymeric compound formulated as {[Cu{μ-(UMP-H)}(bpy)(H2O)]2[Cu4(μ-OH){μ-(α-d-Glc-1P)}2(bpy)4(H2O)2]Cl}n (7). The N-3 deprotonated [UMP-H]3– anions connect {Cu(bpy)(H2O)}2+ fragments through the N-3 nitrogen atom and the phosphate oxygen atoms to afford C2-helical coordination polymers and the tetracopper(II) complex cations, [Cu4(μ-OH){μ-(α-d-Glc-1P)}2(bpy)4(H2O)2]3+, are incorporated between the polymer chains with a C2-chiral arrangement of the {Cu4(μ-OH)(μ-PO4)2(bpy)4(H2O)2} framework constrained to the Λ-form through inter- and intramolecular stacking interactions between the bpy ligands.