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

Abstract

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]­(As^VS₄)}·phen (<b>1</b> and <b>1′</b>), (CH₃NH₃)₂{[Mn­(phen)]₂(As^VS₄)₂} (<b>2</b>), {[Mn­(phen)₂]­(As^III₂S₄)}_<i>n</i> (<b>3</b>), {[Mn­(phen)]₃(As^IIIS₃)₂}·H₂O (<b>4</b>), and {[Mn­(2,2′-bipy)₂]₂(As^VS₄)}­[As^IIIS­(S₅)] (<b>5</b>). Compound <b>1</b> comprises a {[Mn­(phen)₂]­(As^VS₄)}⁻ complex anion, a monoprotonated methylamine cation and a phen molecule. Compound <b>2</b> contains a butterfly like {[Mn­(phen)]₂(As^VS₄)₂}^2– anion charge compensated by two monoprotonated methylamine cations. Compound <b>3</b> is a neutral chain formed by a helical ¹_∞(As^IIIS₂^–) <i>vierer</i> chain covalently bonds to [Mn^II(phen)]²⁺ complexes via all its terminal S atoms. Compound <b>4</b> features a neutral chain showing the stabilization of noncondensed (As^IIIS₃)^3– anions in the coordination of [Mn^II(phen)]²⁺ complex cations. Compound <b>5</b> features a mixed-valent As^III/As^V 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 (As^VS₄)^3– anion acts as a countercation for a polythioarsenate anion, [As^IIIS­(S₅)]⁻. The title compounds exhibit optical gaps in the range 1.58–2.48 eV and blue photoluminescence. Interestingly, compound <b>1</b> displays a weak second harmonic generation (SHG) response being about 1/21 times of KTP (KTiOPO₄). Magnetic measurements show paramagnetic behavior for <b>1</b> and dominant antiferromagnetic behavior for <b>2</b>–<b>5</b>. Of particular interest is <b>4</b>, which is the first manganese chalcogenide showing spin-canting characteristic