Preparative and structural studies of halodimolybdates(II). I. Preparation and crystal structure of (picH)₂Mo₂Br₆(H₂O)₂

Abstract (picH) 2 Mo 2 Br 6 (H 2 O) 2 (picH = 4‐methylpyridinium cation) was prepared from (NH 4 ) 3 Mo 2 CI 9 · H 2 O and picHBr in 4 M aqueous HBr at −20°C. The compound crystallizes in the triclinic P 1 space group. The cell dimensions are: a = 7.822(5); b = 7.937(2), c = 10.163(7) Å α = 73.08(5)°; β = 85.46(3)°; γ = 74.25(1)°. For z = 1, d(calcd) = 2.55 gcm −3 , d(obsd) = 2.53(2) gcm −3 . The structure has been solved from 1191 independent reflections within the sphere bounded by θ = 30°, collected on a counter diffractometer, using MoK α radiation. Refinement led to final unweighted and weighted residuals of 0.035 and 0.041. Hydrogen atoms were not included. Structure consists of Mo 2 Br 6 (H 2 0)2 − of crystallographic Ci symmetry and two picH + ions. Br atoms and H 2 O molecules surround Mo 2 pair forming eclipsed configuration. The distance MoMo is 2.122(2) Å three independent MoBr bond lengths 2.589(2), 2.568(2) and 2.593(2) Å. H 2 O molecule is coordinated to Mo at 2.185(10) Å. Bond lengths and angles within the aromatic ring are normal. The compound is diamagnetic. Two water molecules are evolved when the substance is heated to 160°C in the inert atmosphere. The reaction with pyridine gives Mo 2 Br 4 Py 4 .