One of the promising areas of development of modern coordination chemistry is the creation of new ampolydentate ligands that are able to form kinetically, thermodynamically and thermally stable metal complexes with valuable properties. Due to phosphoryl group has a high affinity for most metals, phosphoryl-containing ligands attract a special attention of researchers in the synthesis of new metal complexes for modern technologies.
One way to create the new ligand systems is to modify the structure of known classes of ligands, which already have a wide and diverse application. The substitution of carbon atoms in the structure of widely used β-diketones by heteroatoms leads to the formation of their structural analogues - carbacyl- and sulfonylamidophosphates, which have recently proved to be powerful ligand systems. The possibility of varying the nature and size of the substituents at the functional core allows obtaining new complexes with potentially useful properties.
The aim of this work was to trace the relationship between the structure of ligands, the method of their coordination to transition metal ions, the structure of the resulting complexes and their properties. Two representatives of phosphorylated ureas - (CAPh) ligands, containing 2-aminothiazole and 2-aminopyridine fragments, and two phosphorylated sulfamide (SAPh) ligands, which differ by nature of substituents near the phosphorus atom, were synthesized. In the structure of dimethyl[(1,3-thiazol-2-ylamino)carbonyl]amidophosphate, the binding of molecules to a centrosymmetric dimer by four hydrogen bonds was recorded for the first time for urea derivatives. For 2-aminopyridine-containing ligand a polymeric structure is realized.
As a result of the study, three new types of coordination mode for CAPh and SAPh ligands were found for the first time:
1) the [dimethyl[(1,3-thiazol-2-ylamino)carbonyl]-amidophosphate (H2L1) and dimethyl-[(pyridin-3-ylamino)carbonyl]amidophosphate (H2L2)) are coordinated in bidentate manner via the carbonyl oxygen and the nitrogen atom of heterocycle with the formation of a six-membered chelated metalcycle in both neutral and acidoform.
2) bidentate-bridge coordination for N-[bis(diethylamino)phosphoryl]benzene-sulfonamide (HL3) to the silver ion via the oxygen atoms of the phosphoryl group and amide nitrogen atoms, resulting formation of polymer one-dimensional chains {AgL3}n;
3) monodentate coordination of SAPh ligands in molecular form via the oxygen atom of the phosphoryl group was registered (in UO2(HL3,4)2(NO3)2 complexes).
As a result of biological studies the time- and dose-dependent cytotoxic effect of the urea obtained on L1210 leukemia cells was demonstrated.
In this study it was possible to trace the influence of steric factor on the coordination capabilities of sulfamide-type ligands and the structure of complexes. Due to steric peculiarities created by the presence of shielding ethyl substituents near the phosphorus atom, which are able to prevent the formation of intermolecular contacts, it was not possible to obtain tetrakis-lanthanide complexes with the HL3 ligand. In addition, the steric complications that create ethyl substituents allowed obtaining a molecular tris-complex of lanthanide Lu(L3)3 with an uncharacteristic low coordination number Lu3+ 6.
On the other hand, the spatial structure of dimorpholine[phenylsulfonyl]-amidophosphate (HL4) allowed to obtain tetrakis-complexes of the composition {Na[Nd(L4)4]}n with a polymer structure that is typical for similar anionic complexes with sodium cation. The crystal structure of this complex contains large pores (790 Å3), and the thermogravimetric analysis showed the absence of solvent molecules.
Upon UV light photoexcitation, the europium complexes Eu(L3)3Phen and Na[Eu(L4)4] show bright red luminescence with an emission lifetime of 1.44 ms and 1.3 ms.
Thermogravimetric studies of all complexes showed their thermal stability up to 200°C, which opens new opportunities for practical use of the compounds obtained.
Keywords: phosphorylated ureas, sulfamides, lanthanides coordination compounds, CAPh, SAPh, spectroscopy, crystal structure, luminescence, HOMO, LUMO.
