Observation of ferromagnetic and antiferromagnetic coupling in 1-D and 2-Dextended structures of copper(II) terephthalates

The reaction between CuCl2. 2H(2)O and disodium terephthalate, Na(2)tp, in aqueous solution simultaneously produces chain, bis(aqua)[mu-(terephthalato -kappa O:kappa O')]copper(II), monohydrate, Cutp(OH2)(2). H2O (1), and laye red, bis(aqua)[mu-(terephthalato-kappa O)]copper(II), Cutp(OH2)(2) (2), str uctured materials. 1 (C8H10CuO7) belongs to the orthorhombic P2(1)2(1)2 spa ce group [a = 6.3015(4) Angstrom, b = 6.8743(4) Angstrom, c = 22.9972(14) A ngstrom, and Z = 4] and incorporates tp in a bridging bis-monodentate bindi ng mode and Cu(II) in a tetragonally elongated octahedron. 2 (C8H10CuO6) wh ich belongs to the orthorhombic Pmc2(1) space group [a = 10.7421(8) Angstro m, b = 7.2339(10) Angstrom, c = 5.7143(13) Angstrom, and Z = 2] incorporate s tp in a mono-bidentate binding mode and Cu(II) in a distorted square pyra mid. 1 and 2 exhibit axial X-band powder EPR spectra with g(perpendicular t o) = 2.08, g(parallel to) = 2.29 (1) and g(perpendicular to) = 2.07, g(para llel to) = 2.29 (2) at 300 K. 1 obeys the Curie-Weiss law at high temperatu res (theta = -7.2 K) and at low temperatures behaves as 1-D magnetic chains with an exchange-coupling constant of J/k(B) = -9.15 K (H = -2JS(1). S-2). This material displays a spontaneous moment below 2 K under small applied magnetic fields, consistent with the presence of spin canting. 2 exhibits f erromagnetic interactions with theta = +0.8 K. Along the 1-D chain where co ordinated water forms the bridge between metal centers, the coupling betwee n Cu(II) is J/k(B) = +0.6 K. The fit of the magnetic susceptibility for 2 u sing a molecular field correction, which takes into consideration antiferro magnetic interactions between chains via the tp Ligand, yields J'/k(B) = -0 .13 K.