Assembling [M(P4Mo6)2] (M = Na, Mn, Na/Cu) dimeric clusters via transition metal/sodium ions into 0D to 3D phosphomolybdates

Abstract

Six phosphomolybdate compounds based on the sandwich-type cluster [M(P₄Mo₆X₃₁)₂] (M = Na, Mn, Na/Cu; X = O or OH) have been solvothermally synthesized by using various organic/inorganic cations as templates, namely, (H₃AEP)₄[Na(P₄Mo₆O₃₁H_5.5)₂]·4H₂O (1), (Me₂NH₂)₇[NaMn(H₂O)][Mn(P₄Mo₆O₃₁H₆)₂]·5H₂O (2), (H₄tpc)_0.5(H₄tpb)_0.5(H_0.5bpp)[Na_2.5(H₂O)][Na(P₄Mo₆O₃₁H₈)₂]·2H₂O (3), (Me₂NH₂)_6.5[Na₄(H₂O)₈][Cu_0.25Na_0.75(P₄Mo₆O₃₁H_6.25)₂] (4), (Me₂NH₂)_1.5(NH₄)₄[Mn_1.5Na_4.5(H₂O)₇][Mn(P₄Mo₆O₃₁H_4.5)₂]·3.5H₂O (5), and (DMIm)₄[Mn_1.5Na₂(H₂O)₈][Mn(P₄Mo₆O₃₁H_6.5)₂]·1.5H₂O (6) (AEP = 1-(2-aminoethyl) piperazine, Me₂NH = dimethylamine, bpp = 1,3-bis(4-pyridyl)propane, tpb = 1,2,4,5-tetra(4-pyridyl)-benzene, tpc = a,a-1,4-dihydroxy-e,e,e,e-1,2,4,5-tetra-(4-pyridyl)cyclohexane, and [DMIm] = 1,3-dimethylimidazolium). These compounds were characterized by elemental analysis, PXRD, IR, TGA, and single-crystal X-ray diffraction. Compound 1 features a classical zero-dimensional (0D) dimeric cluster [Na(P₄Mo₆O₃₁H_5.5)₂]. Compound 2 possesses a 1-D chain constructed from the linkage of [Mn(P₄Mo₆O₃₁H₆)₂] dimeric clusters and M (M = Na⁺, Mn²⁺) linking metal ions. Compounds 3 and 4 are characteristic of 2-D layers, which are built up by connecting [Na(Mo₆P₄O₃₁H₈)₂] and [M(Mo₆P₄O₃₁H_6.5)₂] (M = Cu_0.25/Na_0.75) dimeric clusters, respectively, via Na⁺ ions. Compounds 5 and 6 feature 3D frameworks, where the dimeric clusters are interconnected by M (M = Na⁺, Mn²⁺) ions. Thus, the application of linking metal ions with different coordination modes and valence states to assemble [M(P₄Mo₆X₃₁)₂] clusters is promising for harvesting new phosphomolybdates. In particular, compounds 1 and 5 exhibited visible light degradation performance for Rhodamine B.