Molybdenum Cluster Halide Compound Mo6Cl12(OH2)2 with Six-Handed Linkage Hydrogen Bonding

Abstract

Abstract A hexanuclear Mo cluster compound Mo6Cl12(OH2)2 was synthesized for the first time and its crystal structure was analyzed by powder X-ray diffraction and Rietveld analysis. The initial structure model for the Rietveld analysis was developed by a cut and try method of manipulating the hexanuclear molecule(s) in the unit cell using a computer modeling program. In this paper the characteristic network structure of hydrogen bonding is discussed. In the refined structure (I4/m, Z = 2, a = 0.89869(3) nm, c = 1.14471(3) nm), the Mo6Cl12(OH2)2 molecules are connected to form a three-dimensional network by hydrogen-bonding of the aquo ligands. This is a newly reported compound and is isostructural to Mo6Br12(OH2)2 in an earlier report (L. J. Guggenberger et al., Inorg. Chem.1969, 8, 2041) which focused on the skeletal structure of the molecule. The Mo6Cl12(OH2)2 molecule has four terminal Cl atoms at equatorial positions and two aquo ligands at axial positions. The four terminal Cl atoms from four different molecules and two aquo ligands from two different molecules formed a linkage to connect the six molecules via H-bonding, where the two aquo ligands engaged with each other. Infrared absorption in the OH stretching region gave sharp peaks at 3159 and 3235 cm−1, of which the low wavenumbers indicate strong hydrogen bonding of the water molecules. 1H MAS NMR gave a signal at 6.8 ppm as the major species accompanied by well-resolved spinning side bands, indicating that the large cluster molecules separate the water molecules to weaken the dipole–dipole interaction between the protons. The flexible hydrogen-bonding linkages adopt angles such that the cluster molecules contact each other and form the densely packed crystal structure. This compound highlights an example in which molecules at nanometer scale have multisites for bonding that form a unique network structure.