LAUSR

Abstract Metal borides represent a class of materials with a large variety of crystal structures, yet their physical and catalytic properties are overwhelmingly understudied. In this review, we present the structural variations, relationships and properties of metal borides with a metal-to-boron ratio (M:B) of 2:1, which have over 130 known phases (from binaries to quaternaries) that crystallize with 21 structure types. While most of these structure types contain isolated boron atoms only, B−B-bonds (d(B−B) Except for the anti-MoS2-type (Pt2B, existence is still debated), the unit cell length of the short axis in these structures is always close to 3.0 A, which corresponds to the height of a typical B[M6] prism. In the case of URu3B2 and ZrCo3B2 the short axis is doubled respectively tripled due to their superstructure in comparison to the related CeCo3B2-type. Even though interesting magnetic and superconducting properties have been reported in many phases (especially in the CeCo3B2-type) as well as some fascinating catalytic behaviors (such as in CuAl2-type phases), more must be done in the future to capitalize on the structural diversity from this 2:1 borides composition space.