A rich variety of chalcogenidoarsenate anions and ligands have been prepared under mild solvothermal conditions in strongly polarizing solvents such as water, methanol and amines in the temperature range 100 -200 • C. This review covers synthetic and structural aspects of such species As x E y z− with particular emphasis being placed on the trends and differences observed for E = S, Se, Te and on developments within the past decade. These include the preparation of quaternary Main Group element chalcogenidoarsenates(III) such as Cs 3 AsGeSe 5 and polymeric selenidoarsenates(II, III) such as Cs 2 As 4 Se 6 . A currently expanding area of interest involves the employment of transition metal-polyamine or -polyimine fragments such as {Mn(tren)} 2+ or {Mn(terpy)} 2+ as structuredirecting agents. The metal atoms of such cations can be connected to the terminal chalcogen atoms of oligomeric or polymeric anions As x E y z− to prevent their further condensation or can be directly incorporated into anionic or neutral networks when at least two free coordination sites are available in the fragment. This strategy has led to the characterization of novel ligands including cyclo-

Heating CsAsSe3 · 0.5H2O in methanol to 190 °C leads to formation of black Cs2As4Se6 (1) together with red Cs4As4Se8 and a colourless solution from which the substituted caesium selenidoarsenates(V) Cs2[As(CH3)Se3] · 2H2O (2) and Cs[As(CH3)2Se2] can be obtained as crystalline fractions. Cs2As4Se6 contains catena‐hexaselenidotetraarsenate(II,III) anions in which cyclic As3Se5 units are linked through corner‐sharing AsSe3 pyramids into infinite chains $^{1}_{\infty}\rm [As_{4}Se_{6}^{\phantom{\infty}2-}]$. The Cs symmetric As3Se2 five‐membered rings of the As3Se5 units display an envelope conformation with an As‐As bond length 2.528(3) Å and As‐Se distances of 2.449(2) and 2.447(2) Å. Cs symmetry is also observed for the discrete tetrahedral [As(CH3)Se3]2− anions of (2).

enH 2 )[{Mn(en) 2 (enH)} 2 (µ-en)](Ge 2 Se 7 ) 2 (1) and [Mn-(dien) 2 ] 2 Ge 2 Se 7 (2) can be prepared by solvothermal reaction of elemental Ge and Se with Mn(OOCCH 3 ) 2 ·4H 2 O in respectively superheated ethylenediamine/methanol (3:2 mixture, 150°) and diethylenetriamine (dien, 130°C). The cyclic Ge 2 Se 7 4Ϫ anion contains two tetrahedral GeSe 4 building units linked at one corner Se Condenzation of tetrahedral [GeSe 4 ] 4Ϫ ortho-anions in polar solvents leads to formation of respectively corner-and edge-bridged dinuclear [Ge 2 Se 7 ] 6Ϫ and [Ge 2 Se 6 ] 4Ϫ anions or adamantane-like [Ge 4 Se 10 ] 4Ϫ species, all of which have been structurally characterized in the presence of alkali metal counter cations [1]. Corner-bridging of GeSe 4 building units has also been observed in the

Mn(en) 3 ] 2 [Ge 4 O 6 Te 4 ]·1.5en (1) and (enH) 3 [Mn(en) 3 ] 3 -[Ge 4 O 6 Te 4 ] 2 I·4.7en (2) may be prepared at 150°C by solvothermal reaction of elemental Ge and Te with Mn(OOCCH 3 ) 2 ·4H 2 O in the presence of [CH 3 ) 4 N]I as a mineralizer in respectively superheated ethylenediamine (en) or an en/CH 3 OH (3:2) mixture. Both contain the novel [Ge 4 O 6 Te 4 ] 4Ϫ anion with a central adamantanoid Ge 4 O 6 core and four terminal Te atoms and represent the first examples

Cs3AsGeSe5 and Cs4Ge2Se6 can be prepared by methanolothermal reaction of elemental As, Ge and Se with Cs2CO3 at 190 °C. The former quaternary phase contains zweier $^{1}_{\infty}$[{AsGeSe5}3−] chains consisting of corner‐bridged GeSe4 tetrahedra and AsSe3 pyramids and represents the first GeIV‐AsIII chalcogenidometalate. Cs4Ge2Se6 exhibits discrete [Ge2Se6]4− anions formed by two edge‐sharing GeSe4 tetrahedra.