Conformational preferences of bis(acetonitrile)tetrachloro molybdenum(IV) and tungsten(IV). Crystal structure of WCl4(CH3CN)2 and DFT calculations
Abstract
Crystalline MoCl4(NCCH3)2 and WCl4(NCCH3)2 have been obtained by an electrocrystallization process and are shown to be isostructural. They crystallize in the monoclinic space group C2 with a=11.668(3), b=7.616(5), c=5.901(2) Å, β=103.04(3)° and a=11.679(2), b=7.631(3), c=5.896(2) Å, β=103.11(2)°, respectively. The structure of the tungsten compound determined on a single crystal was refined to a final R(F2) value of 0.046 [Rw(F2)=0.112] using 745 observed reflections. The metal is in a distorted octahedral environment with 4 chlorine atoms in the equatorial plane and 2 acetonitrile groups in axial positions. DFT optimization of the geometry was done at the B3LYP/LANLD1Z/LANLD2Z/6–31G*/6–31G** and BPW91/LANLD1Z/LANLD2Z/6–31G*/ 6–31G** levels of theory for singlet and triplet spin states for WCl4(NCCH3)2 in cis and trans conformations, and for WCl4(NCCH3)x (x=1 or 2) with an η2 coordination of acetonitrile. At the two levels, the energy minimum corresponds to the trans structure with a triplet spin state. The electronic spectra were assigned and the vibrational, 13C and 1H NMR spectroscopies confirm that the previously reported cis and η2 structures are incorrect.