Cobalt and Manganese Diphosphonates with One-, Two-, and Three-Dimensional Structures and Field-Induced Magnetic Transitions

Abstract

Reactions of 2-(1-Imidazole)-1-hydroxyl-1,1'-ethylidenediphosphonic acid (ImhedpH(4)) and cobalt or manganese salts under hydrothermal conditions result in three new metal diphosphonates: β-Co(3)(ImhedpH)(2)(H(2)O)(4)·2H(2)O (1), Co(3)(ImhedpH)(2)(H(2)O)(4) (2), and Mn(ImhedpH(2))·H(2)O (3). In compound 1, the columns made up of {Co1(2)O(2)} dimers and {PO(3)C} tetrahedra through corner-sharing are cross-linked through {Co2O(6)} octahedra, forming an inorganic layer. Neighboring layers are pillared by coordinated imidazole groups of ImhedpH(-) ligands, leading to a three-dimensional open framework containing two kinds of channels with sizes of 8.256 × 9.851 Å and 8.030 × 4.745 Å (van der Waals radii not accounted for). Compound 2 shows a layer structure, in which Co(3)(ImhedpH)(2)(H(2)O)(4) trimer units are connected through the corner-sharing of {Co1O(5)} trigonal bipyramids and {PO(3)C} tetrahedra, forming an inorganic layer containing 20-member rings composed of six Co atoms, two μ(3)-O1 units, and four O-P-O units. The noncoordinated imidazole groups protrude from two sides of the layer. Compound 3 shows a ladder structure, where the Mn(II) ions are bridged by ImhedpH(2)(2-) ligands through double O-P-O units to form a single chain, and two such chains are further fused together by sharing edges of {MnO(5)} trigonal bipyramids. The magnetic properties of 1-3 have been studied. Ferrimagnetism and field-induced magnetic transition from ferrimagnetism to a fully polarized state are observed in 1. Compounds 2 and 3 reveal dominant antiferromagnetic interactions between metal centers, and two-step field-induced magnetic phase transitions are found in 2.