Metamagnetic copper(II) diphosphonates with layered structures

Compounds [NH3(CH2)(4)NH3]Cu-3(hedp)(2).2H(2)O (1) and [NH3(CH2)(3)NH3]Cu-3(hedp)(2).3.5H(2)O (2), where hedp represents 1-hydroxyethylidenediphosphonate, exhibit two-dimensional structures closely related to each other. The anionic layers with composition {Cu-3(hedp)(2)}(n)(2n)-contain four- and eight-membered rings assembled from vertex-sharing {CuO4} units and {CPO3} tetrahedra. The protonated diamines and lattice water fill the interlayer spaces. Crystal data for 2: space group P (1) over bar, a = 8.0315(4), b = 11.3713(6), c = 13.3117(7) Angstrom, alpha = 97.122(1), beta = 103.187(1), gamma = 108.668(1)degrees, V = 1095.5(1) Angstrom(3), Z = 2. Magnetic properties of the two compounds have been investigated. Both show typical metamagnetic behaviors at low temperature. The critical field at which the antiferromagnetic ground-state switches to a ferrimagnetic state is similar to48 Oe for 1 and 185 Oe for 2 at about 2 K.