Structural and Complexation Properties of 2,11-Diselena[3.3](2,6)pyridinophane

2,11-Diselena[3.3](2,6)pyridinophane (PyPySe₂) has been synthesized in excellent yield by the high dilution method. Its conformational behavior in solution has been unambiguously determined by variable temperature (VT)¹H,¹³C{¹H}, and⁷⁷Se{¹H} NMR. PyPySe₂exists predominantly in the syn conformation, which undergoes flip of the pyridine rings and twist of the methylene bridges. The syn forms arising from pyridine flips cannot be distinguished by VT NMR as the energy barrier is low for this process. The syn forms arising from methylene twists can be differentiated by the nonequivalency of the bridge protons in VT NMR. The coalescence temperature for the bridge protons yields an activation barrier, AG*, of 37.4 kJ mol^-1for this process. The activation barrier for this process in the phenyl analogue is 30.4 kJ mol^-1. The difference in the activation barriers (7 kJ mol^-1) is due to the electrostatic interaction of the nitrogen lone pairs in the transition state of the methylene twist where the two pyridine rings are horizontal with respect to each other. PyPySe₂complexed Ni²⁺and Cu²⁺in CH₃NO₂with these complexes exhibiting similar stability constants, indicating that both metal ions fit equally well in the cavity of the heterophane. The stability constant values indicate a typical host-guest interaction. The X-ray structure determined from a single crystal of [NiPyPySe₂(H₂O)₂][C1O₄]₂-CH₃NO₂belonging to the Pnma space group shows that the heterophane is in a syn conformation and highly symmetrical. This is in contrast to the Ni²⁺complex of the thia analogue where the heterophane is distorted from the syn conformation. Interesting differences in the spectral and conductivity properties of the Cu(II) complex are observed when the coordinated H₂0 is replaced by Cl^-. The heterophane and its metal and charge-transfer complexes are semiconductors at room temperature with the CuPyPySe₂Cl₂complex exhibiting the best conductivity.