In this work, two new thiocyanate compounds, Na2Zn(NCS)4·8H2O and (NH4)2Co(NCS)4·3H2O, are reported. A previously reported compound of K2Zn(NCS)4·3H2O was reexamined by single-crystal X-ray diffraction to determine a more accurate structure model. Millimeter-sized high-quality crystals were grown in water via evaporation at room temperature. Na2Zn(NCS)4·8H2O is isostructural to Na2Co(NCS)4·8H2O. (NH4)2Co(NCS)4·3H2O was found to be of the A2M(NCS)4·3H2O (A = K, NH4, M = Co, Zn) structure type. Both structure types feature independent M(NCS)42– tetrahedra that are connected through noncovalent interactions for the sodium and ammonium compounds, forming one-dimensional (1D) and zero-dimensional (0D) structures, respectively. K2Zn(NCS)4·3H2O has potassium bridging the M(NCS)42– tetrahedra together to form a three-dimensional (3D) structure. The second harmonic generation responses of K2Zn(NCS)4·3H2O and (NH4)2Co(NCS)4·3H2O were found to be 1.74× KDP and 0.04× KDP for the samples of a particle size of 90–125 μm with an incident laser of 1064 nm, respectively, confirming their acentric structure nature. The magnetic properties of (NH4)2Co(NCS)4·3H2O were investigated, with an antiferromagnetic transition found at 2 K and a metamagnetic transition also found to occur at a field of 1.4 T. Density functional theory was employed to explore the electronic structures of thiocyanates, which confirmed the similarity of their electronic structures.
Rich et al. (2026) studied this question.