Ab initio crystal structure of copper(II) hydroxy-terephthalate by synchrotron powder diffraction and magnetic properties

The structure of Cu2(OH)2(C8H4O4) has been determined by ab initio XRPD methods from synchrotron data. The compound crystallizes in P-1 space group, a=10.1423(4)Å, b=6.3388(2)Å, c=3.4841(1)Å, α=99.170(2)°, β=96.567(2)°, γ=98.760(3)°, Dx=2.497g cm−3. The structure has been fully refined by the Rietveld method down to Rp=0.077 for 9651 observed data points (513 reflections of which 193 are independent). The structure consists of layered hydroxides Cu(OH)2 intercalated by terephthalate anions, at the interlayer space forming a 3D framework similar to Co(II)-based compound. The apticity of the tp anion and the octahedral coordination of the metal ions are similar in both compounds and can be formulated as M2(μ3-OH)2(μ6-η1, η2, η1, η2-tp) with M = Cu and Co. Although Cu(II)-based structure is very similar to the monoclinic (C2/m) Co(II)-based analogue, the former is completely ordered in contrast with the later which is disordered. The lower symmetry in Cu(II)-based compound due to the Jahn-Teller effects inducing an elongation of the octahedrons CuO6 with four short distances of about 2.0 Å and two long distances CuO up to 2.8 Å is also observed to be different from Co(II)-based compound. Whereas the Co(II) derivative exhibits noncollinear antiferromagnetic coupling between the ferrimagnetic hydroxide layers, the magnetic behavior of the copper(II) analogue indicate a ferromagnetic coupling through the terephthalate bridge between ferromagnetic sheets with in-plane interaction J=+5.5K.