[{AgL}₂Mo₈O₂₆]^n– complexes: a combined experimental and theoretical study

Abstract

Self-assembly reactions between AgNO₃, L (PPh₃, PPh₂Py, AsPh₃, SbPh₃) and [β-Mo₈O₂₆]^4- in DMF led to the formation of [β-{AgL}₂Mo₈O₂₆]^2- anions, which were isolated as Bu₄N⁺ salts (1-4) and characterized by XRD, IR and elemental analysis. In the crystal structures Ag⁺ can switch the coordination number from 5 (P, As) to 6 (Sb) by uptake of a DMF molecule. High-level QAIM analysis of the coordination sphere around Ag shows critical points even in the case of longer Ag-O distances. Changing the ligand type to a family of substituted pyridines results in novel Ag-L-POM complexes with different environments around Ag⁺. For 3-X-pyridine ligands (X = Cl, Br, I), complexes with additional DMF molecules [β-{AgL(DMF)}₂Mo₈O₂₆]^2- (5-7) have been isolated. Halogen bonding of the XO type was detected in the crystal structures of 5-7 and studied by DFT calculations, providing estimated energies from 0.9 to 3.4 kcal mol^-1. Variation of substituents at the pyridine ring results in the formation of [β-{AgL}₂Mo₈O₂₆]^2- in the case of 2-NH₂-py (8), 2-CH₃-Py (9), 2,4,6-collidine (10) and 2,6-NH₂-py (11). Solution behavior of 1-4 in CH₃CN was studied by a hyphenated HPLC-ICP-AES technique. According to the results, the [β-{AgL}₂Mo₈O₂₆]^2- anions are largely dissociated in this medium. An attempt to change the [Mo₈O₂₆]^4- precursor to [Mo₆O₁₉]^2- (in the case of AgNO₃ and PyPPh₂) resulted in the crystallization of [Ag₂(PyPPh₂)₂(DMF)₄][Mo₆O₁₉] (12).