Stepwise Assembly of MII7 Clusters Revealed by Mass Spectrometry, EXAFS, and Crystallography.

Abstract

The square-planar monomer NiL2 (Ni1 ), L=2-ethoxy-6-(N-methyl-iminomethyl)phenolate, reacts with M(H2 O)6 (ClO4 )2 , M=Ni or Co, to form heptanuclear disks [Cox Ni7-x (OH)6 (L)6 ](ClO4 )2 ⋅2 CH3 CN (Cox Ni7-x , x=0-7) and the co-crystal [Cox Ni7-x (OH)6 L6 ][NiL2 ](ClO4 )2 ⋅2 CH3 CN (Cox Ni7-x -Ni1 ) under ambient conditions. It has proved possible to explore the bottom-up assembly process of Cox Ni7-x and Cox Ni7-x -Ni1 in real time. The final products have been characterized by thermogravimetric analysis, IR, elemental analysis, ICP-MS, and single-crystal X-ray diffraction. Time-dependent mass spectrometry (MS) revealed the following reaction steps: Ni1 →[M2 L3 ]+ →[M4 (OH)2 L4 ]2+ →[M7 (OH)6 L6 ]2+ . In contrast, the reaction of Ni1 with Zn2+ only reaches halfway, and crystallographic evidence indicates a butterfly structure for [Zn2 Ni2 (OH)2 Cl2 ] (Zn2 Ni2 ), an intermediate that is difficult to isolate in the above Ni-Co series. A summation method has been used to analyze the MS of bimetallic clusters with very similar atomic masses, as is the case for Co and Ni. The results provide ample information on the distribution of Co and Ni within each cluster and their statistical distribution within selected crystals.