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(NCS) 4 ·3H 2 O

In this work, two new thiocyanate compounds, Na 2 Zn(NCS) 4 ·8H 2 O and (NH 4 ) 2 Co(NCS) 4 ·3H 2 O, are reported. A previously reported compound of K 2 Zn(NCS) 4 ·3H 2 O 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. Na 2 Zn(NCS) 4 ·8H 2 O is isostructural to Na 2 Co(NCS) 4 ·8H 2 O. (NH 4 ) 2 Co(NCS) 4 ·3H 2 O was found to be of the A 2 M(NCS) 4 ·3H 2 O (A = K, NH 4, 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. K 2 Zn(NCS) 4 ·3H 2 O has potassium bridging the [M(NCS) 4 ] 2– tetrahedra together to form a three-dimensional (3D) structure. The second harmonic generation responses of K 2 Zn(NCS) 4 ·3H 2 O and (NH 4 ) 2 Co(NCS) 4 ·3H 2 O 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 (NH 4 ) 2 Co(NCS) 4 ·3H 2 O 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.