Synthesis and Crystal Packing of trans ‐Bis(2‐aminotroponato)palladium(II) Complexes Bearing Linear Alkyl Chains – Hard Lamellar Structures Self‐Locked by Cross‐Shaped Molecular Units

The synthesis, structure, and three‐dimensional lamellar array of a series of trans ‐bis(2‐aminotroponato‐κ N ,κ O )palladium(II) complexes bearing linear alkyl chains ( 1a: n = 5; 1b: n = 8; 1c: n = 14; 1d: n = 16; 1e: n = 18, where n is the number of carbon atoms in the chain) attached to trans nitrogen donor atoms are described. The trans ‐coordination of the ligands, the cross‐shaped molecular structures, and the crystal packing of 1b and 1c have been unequivocally established from single‐crystal XRD studies. Highly regulated multilayered lamellar structures are observed for 1b and 1c , where every lamellar layer in the crystallographic ab plane, formed by π‐stacking interactions of metal cores and van der Waals interactions between alkyl chains, is laminated alternately on the c axis with an orthogonal lamellar array of the identical unit. Powder XRD analysis showed that 1b – 1e exhibit diffraction peaks attributed to periodic ( n 00) reflections of a typical lamellar structure. A linear correlation between the d ‐spacing and chain lengths in these compounds indicates that they form the same type of three‐dimensional layer‐by‐layer structure of lamellar aggregates. The correlation between the cross‐shaped molecular structures of 1b – 1e and the dimensionality of molecular constraint in the crystal packing is discussed by comparison with those of rod‐shaped analogues that exhibit high liquid crystallinity.