Crystal structures of sulfamates MeLi(NH2SO3)2 (Me: K, Rb and Cs) and physical properties of KLi(NH2SO3)2 (refractive indices, thermal expansion, elastic properties)

Abstract

Abstract New sulfamates KLi(NH2SO3)2, RbLi ⋅ (NH2SO3)2 and CsLi(NH2SO3)2 were prepared from non-stoichiometric (ratio Li: Me = 3:1) aqueous solutions of LiNH2SO3 and MeNH2SO3 (Me = K, Rb, Cs) at room temperature. Large single crystals of KLi(NH2SO3)2 were grown from these solutions by controlled lowering of the temperature between 293 K and 288 K. The crystal structures were investigated using single-crystal X-ray diffraction methods. KLi(NH2SO3)2: space group P21, Z = 2, a = 5.196(1) Å, b = 8.475(1) Å, c = 8.868(1) Å, β = 105.05(1)°, T meas. = 293 K, R1 = 0.026; RbLi(NH2SO3)2: space group P1̅, Z = 4, a = 7.844(1) Å, b = 9.804(1) Å, c = 10.825(1) Å, α = 108.77(1)°, β = 93.29(1)°, γ = 98.64(1)°, T meas. = 293 K, R1 = 0.033; CsLi(NH2SO3)2 : space group P1̅, Z = 2, a = 5.535(1) Å, b = 7.877(1) Å, c = 9.857(1) Å, α = 74.07(1)°, β = 76.33(1)°, γ = 87.07(1)°, T meas. = 200 K; R1 = 0.023. The common feature of the three crystal structures are alternating layers of Me+ and lithium cations together with anionic [NH2SO3]– tetrahedra. Li+ coordination polyhedra and [NH2SO3]– anions, linked via common corners, form one type of these sheets. Additionally, these layers are stabilized by hydrogen bonds. Me+ coordination polyhedra are linked to each other and to the above mentioned layers by common corners and edges. RbLi(NH2SO3)2 and CsLi(NH2SO3)2 possess similar structures. Generally, the observed interatomic distances and angles agree with crystal chemical expectations. Differential scanning calorimetry measurements showed that KLi(NH2SO3)2 undergoes a first-order structural phase transition at 401 K and melts at 423 K. Between 153 K and 423 K no indications of further phase transitions were observed. In addition, the refractive indices and the tensor of thermal expansion were measured. Further, the elastic and thermoelastic constants of KLi(NH2SO3)2 were determined from ultrasonic resonant frequencies of thick plane-parallel plates and their shift upon variation of temperature, respectively. The elastic behaviour of KLi(NH2SO3)2 is similar to the average elastic properties of LiNH2SO3 and KNH2SO3.