A copper(II) paddle-wheel structure of tranexamic acid: di­chloro-tetra­kis­[μ-4-(ammonio­meth­yl)cyclo­hexane-1-carboxyl­ato-O,O′]dicopper(II) dichloride hexa­hydrate

Tranexamic acid [systematic name: trans-4-(amino-meth-yl)cyclo-hexane-1-carb-oxy-lic acid], is an anti-fibrinolytic amino acid that exists as a zwitterion [trans-4-(ammonio-meth-yl)cyclo-hexane-1-carboxyl-ate] in the solid state. Its reaction with copper chloride leads to the formation of a compound with a copper(II) paddle-wheel structure that crystallizes as a hexa-hydrate, [Cu2Cl2(C8H15NO2)4]2+·2Cl-·6H2O. The asymmetric unit is composed of a copper(II) cation, two zwitterionic tranexamic acid units, a coordinating Cl- anion and a free Cl- anion, together with three water mol-ecules of crystallization. The whole structure is generated by inversion symmetry, with the Cu⋯Cu axle of the paddle-wheel dication being located about a center of symmetry. The cyclo-hexane rings of the zwitterionic tranexamic acid units have chair conformations. The carboxyl-ate groups that bridge the two copper(II) cations are inclined to one another by 88.4 (8)°. The copper(II) cation is ligated by four carboxyl-ate O atoms in the equatorial plane and by a Cl- ion in the axial position. Hence, it has a fivefold O4Cl coordination sphere with a perfect square-pyramidal geometry and a τ5 index of zero. In the crystal, the paddle-wheel dications are linked by a series of N-H⋯Cl hydrogen bonds, involving the coordinating and free Cl- ions, forming a three-dimensional network. This network is strengthened by a series of N-H⋯Owater, Owater-H⋯Cl and Owater-H⋯O hydrogen bonds.