1. Crystallography of AgsCn lamellae. Crystal structures of AgSCn are determined at atomic resolution by simply coupling X-ray/electron diffractions with reduced radiation dosage and first-principles calculations. The former is sufficient to extract most crystallographic information, whereas the latter refines the coordinates of each atom, especially the radiation-sensitive ligands. Two distinct orientations of –(Ag-S)∞– and –(Ag-Ag)∞– with different bonding types are identified for the anisotropic Ag-S network, leading to a preferred long cleaved edge in single crystal AgSCn. The in-plane lattice evolution as a function of chain length demonstrates that the rigid Ag-S network constructed via strong covalent and argentophilic bonds is, in turn, deformable, as a result of accommodating the inter-chain vdW force among ligands. We conclude that the introduction of alkyl chains to the backbone breaks its orthogonal symmetry and such inter-chain vdW interaction becomes stronger for AgSCn with longer chain lengths, and thus induces more deformation of the overall structure towards the packing of triclinic n-alkane (6, 8, and 10) crystals with minimal symmetry. Another finding is the odd/even effect of in-plane lattice constants. The odd/even effect is present only along –(Ag-S)∞– (or a-c) direction, but absent (or minimal, if any) in –(Ag-Ag)∞– (or a+c) direction. Such contrast may originate from the fact that the zig-zag chain of –(Ag-S)∞– is more vulnerable to the ligand-induced tensile/compressive regulation via the change of Ag-S-Ag bond angles than the directly bonded, –(Ag-Ag)∞– structure. Such modulation stems from the configurational distinction (orthogonal H-H interaction between terminal CH3 groups) of the interlayer interfaces formed by odd or even alkyl chains, based on the DFT-relaxed atomic coordinates.
2. Anisotropic optical properties of AgSCn. Such in-plane anisotropy gives rise to novel electrical/optical properties. With sample rotation, single-crystal AgSCn exhibits varying transmitted light intensity and color under polarized illumination, while no modulation is observed with the single polarizer setup. The results indicate a strong birefringence in AgSCn crystals. We establish a phenomenological model to describe the measured transmittance and found strong wavelength dependence in (1) the magnitude of birefringence (∆n) and (2) a phenomenal rotation of the dielectric frame. Such wavelength dependence gives rise to the asymmetric color shift in single-crystal AgSCn with different sample orientations. The rotation of the dielectric frame is only observed in monoclinic or triclinic lattices with low symmetry because of the inconsistency between its three orthonormal dielectric frames and the corresponding, non-orthonormal, crystal axes. As a result, the magnitude of the rotation exhibits a similar parity effect since the even-chain AgSCn deviates more from the symmetric configuration compared to its odd-chain counterparts.
