Table 1. Comparative compilation of structure types with kröhnkite-type chains.
| Type | Generalized formula(e) | Space group | Z | Generalized unit-cell parameters (Å, °) | No. of representatives |
|---|---|---|---|---|---|
| A | M1II 2 M2II(TO4)2(H2O)2: M1 = Ca, Sr; M II = Mg, Mn, Fe, Co, Ni, Zn; T = P, As. M1I 2 M2II(TO4)2(H2O)2: M1 = Na, K, NH4; M II = Mg, Fe, Co, Ni, Cu, Zn; T = S, Se, Cr, Mo, W | P\overline{1} | 1 | a ≃ 5.7–7.1, b ≃ 6.7–7.9, c ≃ 5.3–6.0, α ≃ 93–105, β ≃ 105–112, γ ≃ 103–111 | 32 |
| B | M1II 2 M2II(TO4)2(H2O)2: M1 = Ca; M2 = Mn, Fe; T = P | P\overline{1} | 1 | a ≃ 5.8–6.0, b ≃ 6.5–6.6, c ≃ 5.5, α ≃ 102–103, β ≃ 108–109, γ ≃ 90–91 | 2 |
| C | M1I 2 M2II(TO4)2(H2O)2: M1 = K, Rb; M2 = Mn, Cd; T = S, Se, Cr | P\overline{1} | 2 | a ≃ 6.6–6.9, b ≃ 7.3–7.7, c ≃ 10.7–11.4, α ≃ 72–73, β ≃ 74–75, γ ≃ 70 | 4 |
| C1 | K2Fe(SO4)2(H2O)2 | P1a | 2 | a ≃ 6.6, b ≃ 7.3, c ≃ 10.7, α ≃ 73, β ≃ 74, γ ≃ 70 | 1 |
| D | M1II 2 M2II(TO4)2(H2O)2: M1 = Ca; M2 = Mg, Mn, Co, Cu, Zn; T = As. M1I 2 M2II(TO4)2(H2O)2: M1 = Na, NH4, Rb; M2 = Cr, Mn, Fe, Cu, Cd; T = S, Se, Cr, Mo | P21/c | 2 | a ≃ 5.8–6.8, b ≃ 12.8–14.3, c ≃ 5.4–5.9, β ≃ 106–111 | 14 |
| E | M1I M2IIH(TO4)2(H2O)2: M1 = K, NH4, Cs; M2 = Mg, Mn, Fe, Co, Zn; T = S, Se | P\overline{1} | 1 | a ≃ 4.6–4.8, b ≃ 5.7–5.9, c ≃ 8.1–8.6, α ≃ 103–104, β ≃ 96–100, γ ≃ 94–97 | 8 |
| E1 b | (NH4)Mg(HSO4)(SO4)(H2O)2 (at 100 K) | P\overline{1} | 2 | a ≃ 7.1, b ≃ 7.7, c ≃ 8.3, α ≃ 84.6, β ≃ 73.3, γ ≃ 77.4 | 1 |
| F1 c | M1I M2III(TO4)2(H2O)2: M1 = Na; M2 = Al, Sc, Fe; T = Cr | C2/c | 4 | a ≃ 14.1–14.5, b ≃ 5.3–5.6, c ≃ 10.7–10.8, β ≃ 109–110 | 3 |
| F2 c | M1I M2III(TO4)2(H2O)2: M1 = Na, K, NH4, Tl; M2 = Al, Fe, In; T = Cr | C2/m | 2 | a ≃ 10.7–11.0, b ≃ 5.4–5.6, c ≃ 7.5–7.6, β ≃ 114 | 5 |
| G | AgSc(CrO4)2(H2O)2 | P\overline{1} | 1 | a ≃ 5.6, b ≃ 6.1, c ≃ 7.4, α ≃ 111, β ≃ 90, γ ≃ 117 | 1 |
| H d | K2Zn(CrO4)2(H2O)2 | C2/c | 4 | a ≃ 15.0, b ≃ 5.7, c ≃ 12.3, β ≃ 117 | 1 |
Notes: (a) Type C1 is represented only by the low-temperature modification of K2Fe(SO4)2(H2O)2 and has an uncertain space group. (b) Type E1 is described for the first time in the present work; it is an ordered variant of type E (see text). (c) Types F1 and F2 are closely related (see text). (d) Type H (Stoilova et al., 2008 ▸) is closely related to type A.