Assembling metal phosphonates in the presence of monodentate-terminal and bidentate-bridging pyridineligands. Use of non-covalent and covalent-coordinate interactions to build polymeric metal–phosphonate architectures

Abstract

The cubic transition metal phosphonates [^tBuPO₃M(2-apy)]₄ (M= Zn (1), Co (2)), whose core resembles the D4R SBU of zeolites, have been synthesized from a reaction between the corresponding metal acetate, tert-butylphosphonic acid and 2-aminopyridine (2-apy) at room temperature. X-Ray structure determination reveals that the molecules of 1 and 2, which crystallize in the tetragonal I4₁/a space group with crystallographically imposed symmetry, form a 3-D supramolecular assembly aided by N–H⋯O hydrogen bonding. When the same reaction was carried out by using a bridging bidentate Lewis base such as 4,4′-bipyridine, insoluble precipitate is obtained for both zinc and cobalt. In the case of other metal salts such as copper, manganese and nickel, however, one-dimensional polymeric compounds such as [M(^tBuPO₃H)₂(4,4′-bipy)(H₂O)₂]_n (M= Cu (3), Mn (4)), [{Ni(4,4′-bipy)(H₂O)₄}{^tBuPO₃H}₂{H₂O}]_n (5) have been isolated. The solid-state structures of 3–5 have been determined by single crystal X-ray diffraction studies. Compounds 3 and 4 are isostructural and crystallize in the triclinic P space group with two phosphonate ligands coordinated to the metal centers in a [1.100] fashion, whereas in the case of compound 5, the polymeric backbone is formed by Ni-4,4′-bipy units and the phosphonate anions show no bonding interaction to the metal. The 1-D polymeric chains of 3–5 organize in the solid-state as 3-D supramolecular assemblies with the aid of extensive hydrogen bonding interaction between coordinated water molecules and P–OH or PO groups of the phosphonate ligands.