Solvent-induced syntheses of 2D/3D [AgSCN]n-based supramolecular isomers with unusual topologies: structural, theoretical and nonlinear optical studies

Abstract

Reactions of hexamethylenetetramine (hmt) and AgSCN in different solvents generated three distinct [AgSCN]_n-based coordination polymers (CPs): [Ag(1,3-μ₂-SCN)(μ₂-hmt)]_n (1), {[Ag(1,1,3-μ₃-SCN)]₂(μ₂-hmt)}_n (2) and [Ag(1,1,3-μ₃-SCN)(μ₄-hmt)_0.5]_n (3). The identities of the coordination polymers (CPs) 1–3 have been unambiguously established by elemental analysis, IR, UV-vis spectra and single-crystal X-ray diffraction studies. Interestingly, 1 displays a two-dimensional (2D) (4,4) network involving one-dimensional (1D) zigzag [Ag(1,3-μ₂-SCN)]_n chains bridged by μ₂-hmt linkers. 2 and 3 are novel 2D and three-dimensional (3D) supramolecular isomers: 2 presents an unusual 2D threaded-loop type (3,4)-connected {(3·4·5)(5²·7)}{(3·4·5³·6³·7²)(3·5⁴·6³·7²)} network containing puckered [Ag(1,1,3-μ₃-SCN)]_n networks linked by μ₂-hmt bridges, while 3 exhibits a unique 3D pillared-layer (3,4,6)-connected (4·6²)(6⁶)₂(4²·6¹⁰·8³) framework in which the undulating [Ag(1,1,3-μ₃-SCN)]_n layers are supported by μ₄-hmt pillars. 1–3 all possess good third-order nonlinear optical (NLO) properties. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations have afforded insight into the electronic transitions and spectral characterization of these functionalized NLO molecular materials.