Synthesis, Crystal Growth, and Optical and Magnetic Properties of Three Bimetallic Thiocyanates: Na ₂ Zn(NCS) ₄ ·8H ₂ O, K ₂ Zn(NCS) ₄ ·3H ₂ O, and (NH ₄ ) ₂ Co(N

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)₄]^2- 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)₄]^2- 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.