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.