Copper Selenidophosphates Cu₄P₂Se₆, Cu₄P₃Se₄, Cu₄P₄Se₃, and CuP₂Se, Featuring\nZero‑, One‑, and Two-Dimensional Anions

Abstract

Five new compounds\nin the Cu/P/Se phase diagram have been synthesized, and their crystal\nstructures have been determined. The crystal structures of these compounds\ncomprise four previously unreported zero-, one-, and two-dimensional\nselenidophosphate anions containing low-valent phosphorus. In addition\nto two new modifications of Cu₄P₂Se₆ featuring the well-known hexa­selenido­hypodiphosphate­(IV)\nion, there are three copper selenidophosphates with low-valent P:\nCu₄P₃Se₄ contains two different new\nanions, (i) a monomeric (zero-dimensional) selenidophosphate anion\n[P₂Se₄]^4– and (ii) a one-dimensional\nselenidophosphate anion [P(−Se)]−∞1, which is related to the well-known gray-Se-like [P]−∞1 Zintl anion. Cu₄P₄Se₃ contains one-dimensional [P4(−Se)2]2−∞1 polyanions, whereas CuP₂Se contains the 2D selenidophosphate [P2(−Se)]−∞2 polyanion. It consists\nof charge-neutral CuP₂Se layers separated by a van der\nWaals gap which is very rare for a Zintl-type phase. Hence, besides\nblack P, CuP₂Se constitutes a new possible source of 2D\noxidized phosphorus containing layers for intercalation or exfoliation\nexperiments. Additionally, the electronic structures and some fundamental\nphysical properties of the new compounds are reported. All compounds\nare semiconducting with indirect band gaps of the orders of around\n1 eV. The phases reported here add to the structural diversity of\nchalcogenido phosphates. The structural variety of this family of\ncompounds may translate into a variety of tunable physical properties.