Ion-bearing stairs: alkali metal complexes of 1,2-diaza-4-phospholides.

In this work, eight alkali metal complexes with 1,2-diaza-4-phospholide ligands were prepared and characterized by X-ray single-crystal structural analysis and NMR spectroscopy. Their structures showed varied coordination motifs: (i) a dimeric 1,2-diaza-4-phospholide lithium complex with -bidentate bridging coordination (4) consists of two lithium atoms that are linked two μ-bridging, κ,κ-coordinated ligands; (ii) the polymeric chain 1,2-diaza-4-phospholide potassium complex (5) showed an ion-bearing stair-shaped chain structure running through axis , where the steps are η interactions, and there is a transition platform between every two stairs; (iii) the polymeric chain 1,2-diaza-4-phospholide potassium complex (6) also presented a polymeric chain structure in the solid state but displayed a head-to-tail arrangement of two 1,2-diaza-4-phospholides; (iv) in comparison to 6, the 1,2-diaza-4-phospholide sodium complex (7) displayed a tetrameric structure, in which the sodium ions are arranged in a distorted tetrahedral fashion and each of them occupies a vertex of the tetrahedron; (v) the polymeric chain 1,2-diaza-4-phospholide potassium complex (8) presented a solvent-free chain structure, in which potassium ions each is η-bonded by two 1,2-diaza-4-phospholides and η-coordinated by another, consisting of a stair-shaped chain structure running through axis but without significant intermolecular contacts between the adjacent stairs in comparison to that of 5; (vi) the polymeric chain 1,2-diaza-4-phospholide sodium complex (9) presented a solvent-free chain structure, in which sodium ions each is η(),η(,),η()-bonded by three 1,2-diaza-4-phospholides, consisting of a chain structure running through axis ; and (vii) the treatment complex 8 with elemental sulphur or selenium in the presence of crown ether gave rare thiophosphonato potassium [η(,,)-3,5-Budp-(μ-K)(S)([18]crown-6)] (10) or a selenophosphonato potassium [η(,,)-3,5-Budp-(μ-K)(Se)([18]crown-6)] (11). Both of the complexes crystallized in the orthorhombic space group as pale-yellow (or red) crystals. The X-ray diffraction analysis revealed 10 or 11 as a terminal complex with the η,η-,-coordination mode (X = S and Se). The H DOSY NMR spectroscopy study of the species 8 in DMSO- suggested that polymeric complexes (4-9) in the solid state should dissociate into the related monomers in the solutions when the donor solvents were used.