Structural Diversity, Optical and Magnetic Properties of a Series of Manganese Thioarsenates with 1,10-Phenanthroline or 2,2′-Bipyridine Ligands: Using Monodentate Methylamine as an Alkalinity Regulator

The exploration in two hydro­(solvo)­thermal reaction systems As/S/Mn2+/phen/methylamine aqueous solution and As/S/Mn2+/2,2′-bipy/H2O affords five new manganese thioarsenates with diverse structures, namely, (CH3NH3)­{[Mn­(phen)2]­(AsVS4)}·phen (1 and 1′), (CH3NH3)2{[Mn­(phen)]2(AsVS4)2} (2), {[Mn­(phen)2]­(AsIII2S4)}n (3), {[Mn­(phen)]3(AsIIIS3)2}·H2O (4), and {[Mn­(2,2′-bipy)2]2(AsVS4)}­[AsIIIS­(S5)] (5). Compound 1 comprises a {[Mn­(phen)2]­(AsVS4)}− complex anion, a monoprotonated methylamine cation and a phen molecule. Compound 2 contains a butterfly like {[Mn­(phen)]2(AsVS4)2}2– anion charge compensated by two monoprotonated methylamine cations. Compound 3 is a neutral chain formed by a helical 1∞(AsIIIS2–) vierer chain covalently bonds to [MnII(phen)]2+ complexes via all its terminal S atoms. Compound 4 features a neutral chain showing the stabilization of noncondensed (AsIIIS3)3– anions in the coordination of [MnII(phen)]2+ complex cations. Compound 5 features a mixed-valent AsIII/AsV character and an interesting chalcogenidometalates structure, where a polycation formed by the connection of two [Mn­(2,2′-bipy)2]2+ complex cation and a (AsVS4)3– anion acts as a countercation for a polythioarsenate anion, [AsIIIS­(S5)]−. The title compounds exhibit optical gaps in the range 1.58–2.48 eV and blue photoluminescence. Interestingly, compound 1 displays a weak second harmonic generation (SHG) response being about 1/21 times of KTP (KTiOPO4). Magnetic measurements show paramagnetic behavior for 1 and dominant antiferromagnetic behavior for 2–5. Of particular interest is 4, which is the first manganese chalcogenide showing spin-canting characteristic.