Wide Spectral Range Nonlinear Optical Crystals of One-Dimensional Coordination Solids [Et4N][Cd(SCN)3] and [Et4N][Cd(SeCN)3] and the General Design Criteria for [R4N][Cd(XCN)3] (Where R = Alkyl and X = S, Se, Te) as NLO Crystals

• Published in: Inorganic chemistry Vol. 39; no. 9; pp. 1868 - 1873
• Main Authors: Zhang, Hong, Zelmon, David E, Price, Gary E, Teo, Boon K
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01-05-2000
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic9912833

We report herein two new nonlinear optical (NLO) crystals, [Et4N][Cd(XCN)3], where X = S (1) and Se (2), that are transparent from 220 to 3300 nm, covering the entire near-ultraviolet, the visible, and the near-infrared spectral regions and giving rise to a very wide and continuous optical window, which is useful for many frequency conversion applications. Both 1 and 2 exhibit highly efficient second harmonic generation (SHG) as measured via the Kurtz−Perry method. The corresponding [Me4N]+ salts, [Me4N][Cd(XCN)3 where X = S (3) and Se (4), show no SHG effects. All four structures adopt noncentrosymmetric space groups (Cmc21 for 1 and 2 and Pna21 for 3 and presumably 4) and are based on one-dimensional anionic [Cd(XCN)3 -]∞ zigzag chains. However, a detailed analysis of the structures of [R4N][Cd(XCN)3], where R = Et, Me, and X = S, Se revealed that the difference in the second-order nonlinear responses of the Et4N+ salts (1 and 2) and the Me4N+ salts (3 and 4) is attributable to the relative alignment of the [Cd(XCN)3 -]∞ zigzag chains, being parallel in the crystals of 1 and 2 but antiparallel in the crystals of 3 and 4. Also reported, for the first time, are the synthesis and crystal structure of [Et4N][Cd(SeCN)3] (2). Compound 2 crystallizes in an orthorhombic unit cell of Cmc21 space group symmetry with lattice parameters of 9.938(1) Å, 16.868(2) Å, 11.054(1) Å, and Z = 4. Other issues related to the molecular and crystal engineering of this class of NLO materials are also discussed.