Mixed-terminal-ligand oxo-centered carboxylate-bridged trinuclear complexes: gas phase generation by means of electrospray ionization FT-ICR MS, condensed phase synthesis, and X-ray structure of K+[Cr3O(C6H5COO)6(F)2(H2O)]−·2(CH3)2CO

The current state of knowledge concerning mixed-terminal-ligand oxo-centered carboxylate-bridged trinuclear complexes is summarized and the application of mass spectrometric techniques to the study of trinuclear basic carboxylates is briefly reviewed. The exchange/substitution reactions of terminal ligands with other molecules in both liquid and gas phase have been investigated using electrospray ionization Fourier transform-ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), studying the clusters [Fe3O(pivalato)6(H2O)3]+ClO4 − (1), [Cr3O(RCOO)6(L)3]+ClO4 − (R=C(CH3)3, L=H2O (2); R=C6H5, L=H2O (3), CH3OH (4), or piperidine (5)) as well as [(C2H5)2NH2]+ 2[Fe3O((CH3)2CHCH2COO)6(F)3]2−·CH3CN·2CHCl3 (6) and K+[Cr3O(C6H5COO)6(F)2(H2O)]−·2(CH3)2CO (7). It was established that factors influencing the quantitative and qualitative yields of products in the ion–molecule collisions/reactions occurring in the ESI source are: skimmer voltage, capillary voltage, ion accumulation time in the hexapole, capillary temperature, pressure in the hexapole region, and the properties of the atomic or molecular system used for concomitant creation of background pressure and providing reagent for ion–molecule reactions. Under ‘soft’ ESI conditions coordinatively saturated gaseous ions [(core)(L)3]+ (where [core]+=[Cr3O(RCOO)6]+) could be generated and supramolecular self-assembled entities [(Anion)(core)2(L)6]+ (where Anion−=ClO4 − for coordination compounds 2–5 or F− for 7) and [(ClO4){(core)(H2O)(L)2}3]2+ (for compound 3 in methanol) pre-existing in solution were detected. The ESI FT-ICR MS study revealed that the [(core)(L)3]+ ions lose L molecules as a result of undergoing dissociation by the absorption of blackbody infrared radiation. Based on studies of exchange/substitution reactions in the liquid phase, two new methods of condensed phase synthesis of mixed-terminal-ligand species are proposed: (a) an ‘aged solutions’ strategy; and (b) site-directed gradual replacement of terminal ligands via supramolecular assemblies. Also, a new compound, K+[Cr3O(C6H5COO)6(F)2(H2O)]−·2(CH3)2CO, was synthesized and X-ray crystallographic analysis (at 120 K) was employed to confirm its ‘unsymmetric’ structure.