Post-Synthetic Modification of a Stepwise-Assembled [3 × 3] {Co₉} Grid with Heterometallic Cd(II) and Homometallic Co(II) Salts

The controllable construction and assembly of sophisticated aggregates with specific metal centers or skeletons has become a hot topic in coordination chemistry. However, monitoring the assembly process remains a significant challenge. In this paper, the stepwise formation of a {Co9} grid with a [3 × 3] skeleton was monitored by electrospray ionization mass spectrometry (ESI–MS). Based on the observed intermediates, a possible formation pathway was proposed as follows: [Co2L2] → [Co3L2] → [Co4L3] → [Co5L3] → [Co6L4] → [Co7L4] → [Co8L5] → [Co9L6]. From the {Co9} grid precursor, homometallic {Co9Co2} and heterometallic {Co9Cd2} clusters with similar skeletons were prepared from the postsynthetic modification strategy when dotted with para-magnetic Co2+ ions and dia-magnetic Cd2+ ions. Furthermore, the detailed structures of {Co9Co2} and {Co9Cd2} were characterized by single-crystal X-ray diffraction, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP–MS), scanning electron microscopy coupled (SEM) with energy-dispersive X-ray spectroscopy (EDS), and ESI–MS. Compared with {Co9} precursor, the magnetic signal of {Co9Co2} was enhanced after postmodificated with paramagnetic Co(II) ions, but in {Co9Cd2}, which keep silence upon the introducing of diamagnetic Cd(II) ions.