Structural diversity in molecular nickel phosphide carbonyl nanoclusters

The reaction of [Ni6(CO)12]2- as a [NBu4]+ salt in CH2Cl2 with 0.8 equiv of PCl3 afforded [Ni14P2(CO)22]2-. In contrast, the reactions of [Ni6(CO)12]2- as a [NEt4]+ salt with 0.4-0.5 equiv of POCl3 afforded [Ni22-xP2(CO)29-x]4- (x = 0.84) or [Ni39P3(CO)44]6- by using CH3CN and thf as a solvent, respectively. Moreover, by using 0.7-0.9 mol of POCl3 per mole of [NEt4]2[Ni6(CO)12] both in CH3CN and thf, [Ni23-xP2(CO)30-x]4- (x = 0.82) was obtained together with [Ni22P6(CO)30]2- as a side product. [Ni23-xP2(CO)30-x]4- (x = 0.82) and [Ni22P6(CO)30]2- were separated owing to their different solubility in organic solvents. All the new molecular nickel phosphide carbonyl nanoclusters were structurally characterized through single crystal X-ray diffraction (SC-XRD) as [NBu4]2[Ni14P2(CO)22] (two different polymorphs, P21/n and C2/c), [NEt4]4[Ni23-xP2(CO)30-x]·CH3COCH3·solv (x = 0.82), [NEt4]2[Ni22P6(CO)30]·2thf, [NEt4]4[Ni22-xP2(CO)29-x]·2CH3COCH3(x = 0.84) and [NEt4]6[Ni39P3(CO)44]·C6H14·solv. The metal cores’ sizes of these clusters range from 0.59 to 1.10 nm, and their overall dimensions including the CO ligands are 1.16-1.63 nm. In this respect, they are comparable to ultrasmall metal nanoparticles, molecular nanoclusters, or atomically precise metal nanoparticles. The environment of the P atoms within these molecular Ni-P-CO nanoclusters displays a rich diversity, that is, Ni5P pentagonal pyramid, Ni7P monocapped trigonal prism, Ni8P bicapped trigonal prism, Ni9P monocapped square antiprism, Ni10P sphenocorona, Ni10P bicapped square antiprism, and Ni12P icosahedron.