Syntheses and crystal structures of a series of new divalent metal phosphonates with imino-bis(methylphosphonic acid)

Hydrothermal reactions of divalent transition metal salts with imino-bis(methylphosphonic acid), NH(CH2PO3H2)2 (H4L) afforded three new metal phosphonates, namely, Cu[NH(CH2PO3H)2] 1, {Co[NH2(CH2PO3H)(CH2PO3)](H2O)2}·H2O 2 and Mn[NH2(CH2PO3H)(CH2PO3)](H2O) 3. When HO2C(CH2)3N(CH2PO3H2)2 was used as the phosphonate ligand and 4,4′-bipy as the second metal linker, {Cu4[NH(CH2PO3)2]2(4,4′-bipy)(H2O)4}·9H2O 4 with a pillared layered architecture was obtained. The NH(CH2PO3)2 anion resulted from the cleavage of the HO2C(CH2)3-group during the reaction. Although compounds 1–3 have a same M/L ratio (1:1), they exhibit totally different structures.Compound 1 has a linear chain structure, in which each pair of square-pyramidal coordinated copper(II) ions are bridged by two phosphonate oxygen atoms to form a Cu2O2 dimeric unit, and such dimeric units are further interconnected via phosphonate groups to form a [010] chain. Compound 2 has a layered architecture built from CoO6 octahedra bridged by phosphonate ligands. In compound 3, the interconnection of the manganese(II) ions by bridging imino-diphosphonate ligands leads to a 3D network. Compound 4 has a pillar-layered structure, the layers composed of Cu(II) ions bridged by aminodiphosphonate ligands are interconnected by 4,4′-bipy ligands to form channels along c-axis. Several factors that affect the structures of the metal phosphonates formed have also been discussed. Compounds 2 and 3 show predominant antiferromagnetic interactions between magnetic centers.