The first lead cobalt phosphite, PbCo2(HPO3)3

Abstract

Single crystals of a new lead cobalt phosphite, PbCo₂(HPO₃)₃, have been synthesized using mild hydrothermal techniques and characterized by X-ray diffraction analysis, SQUID magnetic measurements, IR spectroscopy, UV/vis spectroscopy, thermogravimetric analysis, and scanning electron microscopy. PbCo₂(HPO₃)₃ crystallizes in the non-centrosymmetric (NCS) R3m space group, a = 5.3145(15) Å, c = 25.494(7) Å, V = 623.6(4) ų. The crystal structure of PbCo₂(HPO₃)₃ is based upon 2D heteropolyhedral blocks built up from Co₂O₉ octahedral dimers and HPO₃ pseudo-tetrahedra. Lead cations reside in the interlayer space of the structure. Here, the NCS character results reasonably from the cooperative Pb²⁺ lone electron pair arrangements, by analogy to the centrosymmetric compound (NH₄)₂Co₂(HPO₃)₃ with similar but disordered blocks. A local twisting of specific HPO₃ groups arises due to unreasonably short H⋯H contacts between two phosphite oxoanions. In terms of the magnetic behavior, the new PbCo₂(HPO₃)₃ phase demonstrates weak antiferromagnetic interactions inside the Co₂O₉ dimers between cobalt ions as expected from the phosphite μ-O bridges.