Histamine Molecule and Dianion Oxalate are Efficient Blocks for Building 2D Supramolecular Networks

Abstract

One salt and two Cu(II) complexes (H₂hsm)(ox), 1, [Cu(hsm)(ox)], 2, and [Cu(hsm)(ox)H₂O], 3, have been synthesized and X-ray characterized (hsm is histamine and ox²⁻ is the oxalate dianion). Starting from the prochiral tetracoordinated complex 2, pentacoordinated complex 3 crystallizes as a racemic mixture of the enantiomeric Δ and Λ isomers, in space group P2₁/c. In all cases, the side chain of the hsm group is gauche, allowing the formation of strong hydrogen bonds in the salt 1, and to chelate the metal center in complexes 2 and 3. The combination hsm/ox seems to favor the formation of 2D supramolecular structures (planes or wavy planes), through efficient networks of N–H···O hydrogen bonds. Cell parameters: 1, P2₁/c, a = 6.260 (2) Å, b = 11.500 (4) Å, c = 12.525 (4) Å, β = 104.047 (17)º; 2, C2/c, a = 10.7966 (13) Å, b = 15.5622 (16) Å, c = 11.3996 (15) Å, β = 106.261 (11)º; 3, P2₁/c, a = 7.0627 (6) Å, b = 7.1323 (6) Å, c = 20.0296 (19) Å, β = 91.529 (7)º.

Graphical Abstract

Crystal structures based on histamine, histaminium and oxalate revealed that 2D supramolecular networks are stabilized with these building blocks, both in an organic salt and in two Cu(II) coordination complexes.