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

Self-assembly reactions between AgNO3, L (PPh3, PPh2Py, AsPh3, SbPh3) and [beta-Mo8O26](4-) in DMF led to the formation of [beta-{AgL}(2)Mo8O26](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 [beta-{AgL(DMF)}(2)Mo8O26](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 [beta-{AgL}(2)Mo8O26](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 [beta-{AgL}(2)Mo8O26](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 [Ag-2(PyPPh2)(2)(DMF)(4)][Mo6O19] (12).