The first water-soluble polynuclear metallamacrocyclic Sr(II)–Cu(II) complex based on simple glycinehydroximate ligands

Recently, the aminohydroximate ligands have found wide applications in fascinated class of polynuclear metallamacrocyclic compounds named as 15-MC-5 metallacrowns. The enhanced imterest in water-soluble aminohydroximate Ln(III)-Cu(II) complexes is largely due to their rich coordination chemistry, diverse properties and ease of synthesis. We examined the glycinehydroxamic acid as a simple ligand for preparation of the first water‐soluble polynuclear metallamacrocyclic Sr(II)‐Cu(II) compound. The complex Sr(H2O)3[15-MCCuGlyha‐5](Cl)2 was synthesized and characterized structurally and spectroscopically. The single‐crystal structure reveals the classic metallamacrocyclic 15‐MC‐5 configuration. The Sr(II) ion is located at the center of the 15‐MCCu(II)Glyha‐5 ring and coordinated by five oxygen atoms of the cycle in the equatorial plane and additional three oxygenatoms of the water molecules in apical positions. Detailed DFT and QT AIM studies were carried out for the hydrated isoelectronic Sr[15MCCuGlyha-5]2+ and Y[15MCCuGlyha-5]3+ systems. The ionic contribution to the metal-ligand interactions appears to be higher for the Sr(II) derivative despite of the smaller charge separation. DFT calculations suggest a thermodynamically favorable substitution of the Sr(II) central ion with Y(III). Indeed, it was shown experimentally that the strontium ion can be easily replaced by yttrium. Preliminary cytotoxic studies revealed low toxicity of the strontium complex and its yttrium analogue so the water-soluble Sr(II) and Y(III) metallacrowns can be further investigated as possible platforms for development of new 90Sr and 90Y radiotherapy drugs.