Twelve quaternary rare-earth selenides Ba₂REGaSe₅ and Ba₂REInSe₅ were prepared in the form of single crystals from reactions of BaSe, RE, M₂Se₃ (M = Ga, In), and Se at 1373 K. The compounds Ba₂REGaSe₅ fall into two separate series adopting an orthorhombic (RE = La, Ce; space group Pnma, Z = 4, a = 12.49–12.50 Å, b = 9.60–9.63 Å, c = 8.74 Å) or a triclinic structure (RE = Tb, Ho, Tm, Yb, Lu; space group $\mathit{P}\overline{1}$, Z = 2, a = 7.28–7.31 Å, b = 8.61–8.72 Å, c = 9.37–9.43 Å, α = 103.4–103.5°, β = 103.0–103.1°, γ = 107.3–107.5°). The compounds Ba₂REInSe₅ adopt an orthorhombic structure (RE = Pr, Tb, Ho, Tm, Lu; space group Cmc2₁, Z = 4, a = 4.23–4.33 Å, b = 18.75–18.96 Å, c = 13.29–13.31 Å). All structures contain anionic M-centred tetrahedra, isolated Se^2– anions, Ba²⁺ cations in eight-fold coordination, and RE³⁺ cations in either six- or seven-fold coordination. A structure map developed based on radius ratios involving the RE³⁺, M³⁺, and Ch^2– ions is effective in segregating four structures (in space groups Cmc2₁, $\mathit{P}\overline{1}$, Pnma, and I4/mcm) found for Ba₂REMCh₅ (M = Ga, In; Ch = S, Se, Te). Bond valence sum calculations reveal that the upper limit for the largest RE components that can be substituted within a given structural series is set by the need to avoid overbonding of the RE atoms. An optical band gap of 1.34(2) eV was measured for the compound Ba₂LaGaSe₅, slightly less than a value of 1.76 eV obtained from electronic band structure calculations, which suggest an indirect transition.

十二季稀土硒化物的Ba ₂ RE GASE ₅和Ba ₂ RE InSe系₅在单晶的形式制备来自基地，反应RE，中号₂硒₃（中号在1373 K. =镓，铟），和Se化合物Ba ₂ RE GaSe ₅分为两个独立的系列，采用正交晶系（ RE = La，Ce;空间群Pnma， Z  = 4， a = 12.49–12.50Å， b = 9.60–9.63Å， c= 8.74Å）或三斜结构（RE = Tb，Ho，Tm，Yb，Lu;空间群$\mathit{P}\overline{\mathrm{1个}}$，Z  = 2，a = 7.28–7.31Å，b = 8.61–8.72Å，c = 9.37–9.43Å，α  = 103.4–103.5°，β  = 103.0–103.1°，γ  = 107.3–107.5°）。化合物Ba ₂ RE InSe ₅采用正交结构（RE = Pr，Tb，Ho，Tm，Lu；空间群Cmc 2 ₁，Z  = 4，a = 4.23–4.33Å，b = 18.75–18.96Å，c = 13.29–13.31Å）。所有结构均包含阴离子M中心四面体，分离的Se ^2–阴离子，Ba8配位的²⁺阳离子和6或7配位的RE ³⁺阳离子。根据包含RE ³⁺，M ³⁺和Ch ^2–离子的半径比得出的结构图可有效分离四种结构（在空间群Cmc 2 _1中，$\mathit{P}\overline{\mathrm{1个}}$，发现Ba ₂ REMCh ₅（M = Ga，In; Ch = S，Se，Te）的Pnma和Pnma和I 4 / mcm ）。键合价的计算表明，在给定结构系列中可以取代的最大RE组分的上限由避免RE原子过度键合的需要确定。对于化合物Ba ₂ LaGaSe ₅测得的光学带隙为1.34（2）eV ，略小于通过电子能带结构计算获得的1.76 eV的值，这表明存在间接跃迁。