Crystal Structure of pyridinium isopolymolybdate (C 5 H 6 N) 2n [Mo 4 O 13 ] n

Synthesis and crystal structure are described for pyridinium isopolymolybdate of chemical composition (C 5 H 6 N) 2n [Mo 4 O 13 ] n . The crystals are triclinic, space group P1, with the following unit‐cell parameters: a =8.2695(11) Å, b =10.544(4) Å, c =11.177(4) Å, α = 71.76(5)°, β = 89.68(3)°, γ = 78.79(3)°, V =906.4(4) Å 3 , Z = 2 (chemical formula (C 5 H 6 N) 2 [Mo 4 O 13 ]), D calcd = 2.755 g·cm –3 . Crystal structure was solved by Patterson methods and refined to a final R value 0.085 for 4045 independent reflections. The studied compound, considered in analogy to triclinic (NH 4 ) 2 Mo 4 O 13 as pyridinium polyoctamolybdate, is proposed to be better described as pyridinium isopolytetramolybdate (C 5 H 6 N) 2n [Mo 4 O 13 ] n . It seems that the proper coordination number of molybdenum (VI) ions is five, resulting in pyramidal coordination polyhedra [MoO 5 ]. Coordination polyhedra joined by common edges form tetramolybdate monomeric unit [Mo 4 O 13 ]. The mers are connected by oxygen bridges Mo ‐ O ‐ Mo into infinite ribbon chains. Each two infinite chains are hold together by weaker intermolecular interactions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)