Deeply Reduced Chiral Mo IV 6 -Polyoxometalates with Highly Enhanced Electronic Conductivity.

A series of deeply reduced Mo IV 6 -polyoxometalates (POMs), [Mo IV 6 (bpy) 6 Mo VI 2 O 16 S 2 ]·10H 2 O ( 1 ) (bpy = 2,2'-bipyridine), [Mo IV 6 (bpy) 4 (L-TrA) 2 Mo V 4 (bpy) 2 O 14 S 4 ] 2 ·36.5H 2 O ( 2 ), and [Mo IV 6 (bpy) 4 (D-TrA) 2 Mo V 4 (bpy) 2 O 14 S 4 ] 2 ( 3 ) (TrA = tartaric acid), were obtained from one-pot hydrothermal syntheses. They feature the bioxo-bridged [Mo IV 3 O 3 S] 4+ incomplete cuboidal cores stabilized by strong triangular metal-metal bonds and datively chelated bpy π-ligands. The two apical Mo VI O 4 in 12e-Mo 8 ( 1 ) and two [Mo V 2 O 3 STrAbpy] in 16e-Mo 10 ( 2 , 3 ) complete the octahedral coordination geometry of the deeply reduced Mo IV , not counting the Mo IV -Mo IV d 2 -d 2 bonds. The aromatic planar bpy π ligands form a two-dimensional face-to-face π stacking supramolecular structure, which are further strengthened by point-to-face C-H···π interactions in the π stacked layers. 16e-Mo 10 ( 2, 3 ) has stronger intramolecular face-to-face π stacking interactions, which are interconnected by intermolecular C-H···π into a three-dimensional framework structure. These structural features account for their highly enhanced electronic conductivities ( 1 , 6.19 × 10 -8 S cm -1 ; 2 , 2.18 × 10 -7 S cm -1 ), providing a new way of thinking to improve electronic conductivity of POMs. 1 - 3 have been described by first-principles density function theory (DFT) calculations and also characterized by elemental analyses, powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), solid UV-visible spectra, and circular dichroic (CD) spectra.