Preparative and Structural Studies of trans‐Tetrachloro and Tetrabromodipyridinemolybdate(III) and Tungstate(III)

The first products of reactions between (PyH) 3 MoX 6 (PyH = pyridinium, C 5 H 6 N + ; X = Cl, Br) and pyridine are trans‐(PyH)MoCl 4 Py 2 and trans‐(Py) 2 HMoBr 4 Py 2 . Trans‐(Py) 2 H MoCl 4 Py 2 can be obtained from the cold solution of trans‐(PyH)MoCl 4 Py 2 in pyridine. NaBH 4 suspended in the mixture of isopropanol and pyridine reduces WX 4 Py 2 to trans‐(Py) 2 HWX 4 Py 2 (X = Cl, Br). Trans‐(Py) 2 HMX 4 Py 2 (M = Mo, W; X = Cl, Br) decompose at room temperature to trans‐(PyH)MX 4 Py 2 . Four trans‐(Py) 2 HMX 4 Py 2 compounds are isostructural and three of them crystallize in the triclinic unit cell. Pairs of trans‐(PyH)MCl 4 Py 2 and (PyH)MBr 4 Py 2 have nearly equal sequence of interplanar spacings. Crystal structure of trans‐(Py) 2 HWCl 4 Py 2 has been solved. The compound has a triclinic P 1 space group with: a = 9.373(3), b = 9.563(3), c = 15.009(6) Å, α = 78.21(1), β = 77.94(2), γ = 78.63(2)° and Z = 2. Two independent WCl 4 Py 2 − groups are located on the symmetry center. Average WCl and WN (pyridine) bond lengths are 2.435(5) and 2.18(2) Å. The cation (Py) 2 H + contains a hydrogen bond between pyridinium ion and pyridine. The NN distance is 2,76 Å. (PyH)MX 4 Py 2 react with pyridine giving mer‐MX 3 Py 3 (M = Mo, W; X = Cl, Br).