Crystals of Ba3.81K0.19Mo22O34, a metal-metal bonded oligomer, were synthesized. The Mo22 clusters consisted of 5  trans  edge-shared Mo octahedra, and predominant features included 4 short, and 4 long, apical-apical Mo bond distances within the cluster, relatively long inter-cluster metal-metal bond distances, and cluster interconnections which involved a stair-step arrangement from one Mo22 unit to the next. The material crystallized in the centro-symmetrical space group, P21/a (a = 0.9908, b = 0.9353, c = 1.5951nm,  = 98.78). Five cations per formula unit could be accommodated in pockets which were created by the interconnected Mo22O50 clusters. However, this phase contained 4 fully occupied cation sites and 1 vacancy. The magnetic susceptibility indicated that it was spin-paired, with a small paramagnetic tail at low temperatures. Electron spin resonance results indicated that the tail was perhaps due to Mo-containing impurities or defects at which electrons were trapped.

G.L.Schimek, R.E.McCarley: Journal of Solid State Chemistry, 1994, 113[2], 345-54