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

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.