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

Abstract

Hydrothermal reactions of divalent transition metal salts with imino-bis(methylphosphonic acid), NH(CH 2PO 3H 2) 2 (H 4L) afforded three new metal phosphonates, namely, Cu[NH(CH 2PO 3H) 2] 1, {Co[NH 2(CH 2PO 3H)(CH 2PO 3)](H 2O) 2}·H 2O 2 and Mn[NH 2(CH 2PO 3H)(CH 2PO 3)](H 2O) 3. When HO 2C(CH 2) 3N(CH 2PO 3H 2) 2 was used as the phosphonate ligand and 4,4′-bipy as the second metal linker, {Cu 4[NH(CH 2PO 3) 2] 2(4,4′-bipy)(H 2O) 4}·9H 2O 4 with a pillared layered architecture was obtained. The NH(CH 2PO 3) 2 anion resulted from the cleavage of the HO 2C(CH 2) 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 Cu 2O 2 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 CoO 6 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.