Bismuth is the heaviest stable element of the periodic table (the half-life of 209 Bi τ1/2 = 2.0 × 10 yr is nine orders of magnitude longer than the age of the universe, t = 1.4 × 10 10 yr). This property makes it and its compounds interesting for studying effects of strong spin orbit coupling (SOC) on physical properties of materials. Relativistic effects often result in Bi compounds behaving differently than isoelectronic species. For example, the most common cationic oxidation state of Bi is +3, with +5 compounds being generally unstable towards reduction. Bi 3+ cation is very often lone-pair active, leading to complicated coordination environments. Less known are the effects of relativistic phenomena on structural chemistry of Bi intermetallic compounds. Bi is known to form several stable hypervalent polyanions, such as Bi -square network found in LiBi and NaBi but not observed in the isoelectronic NaSb . Similarly, CaBi2 and the recently reported SrBi2 both host a hypervalent Bi -square lattice , which is missing in the isoelectronic CaSb2 .