Zn₃(4-OOCC₆H₄PO₃)₂: A polar metal phosphonate with pillared layered structure showing SHG-activity and large dielectric anisotropy

A new metal phosphonate Zn₃(4-OOCC₆H ₄PO₃)₂ (1) is reported which crystallizes in orthorhombic space group Pca2₁. It shows a pillared layered structure in which the {ZnO₄}, {ZnO₅} and {PO₃C} polyhedra are connected through corner- or edge-sharing to form an inorganic layer in the ab plane which contains 4- and 5-member rings. These layers are pillared by the uni-oriented 4-carboxylatephenylphosphonate ligands, thus leading to a polar 3D architecture. The dielectric anisotropy measurements of a single crystal of 1 reveal that dielectric constant along the inter-layer is larger than that along the intra-layer with a ratio of about 2.3. Second harmonic generation (SHG) activity is observed.