Exploring the Effect of Metal Ions and Counteranions on the Structure and Magnetic Properties of Five Dodecanuclear Co^II and Ni^II Clusters

Abstract

We present the synthesis, characterization of the structures, and magnetic properties of five isostructural dodecanuclear coordination clusters of Ni(II) and Co(II): [Co(12)(bm)(12)(NO(3))(O(2)CMe)(6)(EtOH)(6)](NO(3))(5) (1), [Ni(12)(bm)(12)(NO(3))(O(2)CMe)(6)(H(2)O)(3)(EtOH)(3)](NO(3))(5)·2H(2)O (2), mixed-metal composition (Ni/Co 1:1) [Co(6)Ni(6)(bm)(12)(NO(3))(O(2)CMe)(6)(NO(3))(5) (3), and [M(12)(bm)(12)(NO(3))(O(2)CMe)(6)(EtOH)(6)](ClO(4))(5) (M=Co (4), Ni (5)), in which Hbm=(1H-benzimidazol-2-yl)methanol. They consist of analogous structural cores that are constructed by three cubanes (M(4)O(4)) that surround the templating nitrate and bridging auxiliary acetate and the directing ligands bm. They have different magnetic behaviors. Whereas there is the absence of the out-of-phase ac susceptibility (χ'') for the Ni(II)-based compounds 2 and 5, the Co(II)-containing compounds 1, 3, and 4 have prominent χ'' signals that exhibit frequency dependence, which indicates slow magnetic relaxation behavior above 1.8 K. In particular, the larger perchlorate counterions in 4 further change the overall correlation interaction between clusters, thus leading to an enhanced blocking temperature for the less-symmetrical 4 (pseudo-C(3)) relative to 1 and 3 (true C(3)). Interestingly, electrospray ionization mass spectrometry (ESI-MS) indicates that the three dodecanuclear clusters of 1-3 retain their compositions in solution. The mixed-metal cluster cores of 3 are formed based on the nature of the interchangeability between metal centers in solution.

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

“…As these two metals differ in their magnetic moments, that is, S=1 for Ni 2+ and S=0 for Zn 2+ , magnetic susceptibility measurements could provide direct evidence of the site of each metal ion within the cluster. The susceptibility data exhibited a peak at 20 K that fitted well to a dimer model at all temperatures (Figure S15) with g =2.146(9) and J =−9.86(8) K ,. The large negative J value suggests that the two Ni atoms are close to each other.…”

“…Elucidating the stepwise assembly of coordination clusters may provide insight into the formation of crystallized polymers and frameworks . However, it is quite difficult to rationally construct high‐nuclear clusters of desired shape with precisely controlled positions of neighboring atoms of the periodic table with similar coordination tendencies and crystallographic characteristics, as for example Ni 2+ and Co 2+ . The distributions of such metal ions within clusters are generally difficult to determine by X‐ray diffraction analysis.…”

“…The distributions of such metal ions within clusters are generally difficult to determine by X‐ray diffraction analysis. To clearly understand the assembly process involved, there is a real need to overcome these challenges …”

“…As such, it is desirable to study reactions in real time at ambient temperature and pressure, rather than under solvothermal conditions as reported previously . Rigorous studies of homometallic and mixed‐metal systems are necessary for a deep insight into the details of their formation and to improve our knowledge of specific systems . Based on the above considerations, herein we present a study of the formation of [M 7 (μ 3 ‐X) 6 L 6 ] clusters from a monomeric precursor, NiL 2 ( Ni 1 ).…”

Iterative Mass Spectrometry and X-Ray Crystallography to Study Ion-Trapping and Rearrangements by a Flexible Cluster

“…However, when such reactions involve big molecules such as supramolecular cages2122 and high nuclearity coordination clusters232425, it is often difficult to follow the changes due to the complicated dynamics involving bond breaking and reforming in solution. Techniques such as nuclear magnetic resonance (NMR) spectroscopy can provide information that allows one to follow certain events and propose a mechanism26.…”