Stepwise Assembly of M7II Clusters Revealed by Mass Spectrometry, EXAFS, and Crystallography

The square-planar monomer NiL2 (Ni-1), L=2-ethoxy-6-(N-methyl-iminomethyl)phenolate, reacts with M(H2O)(6)(ClO4)(2), M=Ni or Co, to form heptanuclear disks [CoxNi7-x(OH)(6)(L)(6)](ClO4)(2)2CH(3)CN (CoxNi7-x, x=0-7) and the co-crystal [CoxNi7-x(OH)(6)L-6][NiL2](ClO4)(2)2CH(3)CN (CoxNi7-x-Ni-1) under ambient conditions. It has proved possible to explore the bottom-up assembly process of CoxNi7-x and CoxNi7-x-Ni-1 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: Ni-1[M2L3](+)[M-4(OH)(2)L-4](2+)[M-7(OH)(6)L-6](2+). In contrast, the reaction of Ni-1 with Zn2+ only reaches halfway, and crystallographic evidence indicates a butterfly structure for [Zn2Ni2(OH)(2)Cl-2] (Zn2Ni2), 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.