An Unstable Paramagnetic Isopolyoxomolybdate Intermediate Non-Homogeneously Reduced at Different Sites and Trapped in a Host Based on Chemical Adaptability

摘要

Under special conditions, solutions of polyoxometalates can "behave" as unique constitutional dynamic libraries (CDLs) containing building blocks that may reversibly associate, thereby allowing a continuous change in constitution through reorganization, while external stimulants can influence the scenario. This is especially valid in case of polyoxomolyb-date chemistry; for related basic aspects of CDLs see Refs. [2,3]. In this context, a variety of nanosized clusters with fascinating structures and properties could be even deliberately obtained.The mentioned solution proper-ties can be related to the chemical adaptability of related clusters based on the flexibility of their building blocks, for example, in case of the giant molecular wheels of the type {Mo_(154)} and {Mo_(176)} with the formulas [{Mo1}{Mo2}-{Mo8}]_n~(m-) (n-=14, 16; m = 28, 32).Here we report on a reduction pathway of an aqueous solution of the diamag-netic [Mo_(36)O_(112)(H2O)_(16)] (structure in Figure S1, Supporting Information), which leads to an unprecedentedly reduced polyoxomolybdate, that is, a paramagnetic unstable derivative of the {Mo_(36)}-type cluster trapped in an appropri- ately enlarged {Mo_(154)}-type wheel/host formed on the release of special building blocks. Results from X-ray crystallography, EPR spectra, and DFT calculations prove that the paramagnetic {Mo_(36)} cluster shows an unprecedented type of electronic and magnetic structure with different uncoupled Mo~V centers—an interesting result, as all known reduced polyoxomolybdates with an even number of 4d electrons are according to a literature search diamagnetic. This offers the option to study not only new types of exchange interactions, but also interesting reactivities of the Mo~V centers. The whole system and especially the trapped cores are stabilized by an unprecedented dense hydrogen-bonding system in between the two mentioned highly reduced components. Altogether we can refer here to an extremely complex system in which several parts are intrinsically related, that is, structurally, electronically, and magnetically.