Amino-acid based coordination polymers

作者：Maclaren Jana K; Janiak Christoph^*

来源：Inorganica Chimica Acta, 2012, 389: 183-190.

DOI：10.1016/j.ica.2012.03.010

• Amino acids
• Copper
• Cadmium
• Coordination polymer
• Helices

Five new transition metal-amino acid coordination polymers, including two copper compounds 1D-{Cu(D-alpha-PhGly)(2)} (1), 1D-{Cu(L-Trp)(2)} (2) and three cadmium compounds 2D-{Cd(D-Leu)(2)} (3) 2D-{Cd(D-Phe)(2)} (4) and 2D-{[Cd(D-Phe)(4,4%26apos;-bipy)H2O][NO3]} (5) are structurally characterized (PhGly = phenylglycinato, Trp = tryptophanato, Leu = leucinato, Phe = phenylalaninato in enantiopure form, 4,4%26apos;-bipy = 4,4%26apos;-bipyridine). Single crystals were obtained by slow diffusion of the metal salt and the ligand in a water-methanol mixture. The enantiopure amino acetate ligands led to homochiral crystallization of 1-5 in the non-centrosymmetric space group P2(1). Characterization by single-crystal X-ray diffraction, infrared and Raman spectroscopy showed that the copper compounds 1 and 2 form twofold helices around the 2(1) screw axis and the cadmium compounds 3-5 yield two-dimensional coordinative layers also with twofold helices around the 2(1) axes for 3 and 4. The Cu-amino-acetate/carboxlyate helices are connected by N-H center dot center dot center dot O hydrogen bonds and very long Cu center dot center dot center dot O-carboxylate contacts to supramolecular 2D layers. Crystal packings of 2D layer structures in 1-4 show a separation of the hydrophobic alkyl groups from the hydrophilic M-aminocarboxylate region. Charge-assisted Cu(+)center dot center dot center dot(-)O interactions and N-H center dot center dot center dot O(-) hydrogen-bonding interactions in the hydrophilic region are the driving force of %26quot;hydrophobic exterior layer%26quot; formation with a hydrophilic interior exposing the hydrophobic alkyl groups to the exterior. Stacking of the layers occurs through weak van der Waals interactions between the alkyl groups. This correlates with the crystal morphology, with formation of thin crystal plates along the stacking direction. %26lt;br%26gt;In 5 the Cd-mu-amino carboxylate-kappa N,O:O%26apos; units with a pentagonal-bipyramidal Cd atom form strands, and these strands are then joined through the rigid 4,4%26apos;-bipy linkers to a coordinative 2D layer. The nitrate anions connect these layers with charge-assisted (aqua)O-H center dot center dot center dot O(-)(nitrate) and (amino)N-H center dot center dot center dot O(-)(nitrate) hydrogen bonds to a supramolecular 3D network.

• 出版日期2012-7-1