A copper(II) paddle-wheel structure of tranexamic acid: di-chloro-tetra-kis-[μ-4-(ammonio-meth-yl)cyclo-hexane-1-carboxyl-ato-O,O']dicopper(II) dichloride hexa-hydrate.

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, [Cu(2)Cl(2)(C(8)H(15)NO(2))(4)](2+)·2Cl(-)·6H(2)O. 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 O(4)Cl coordination sphere with a perfect square-pyramidal geometry and a τ(5) 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⋯O(water), O(water)-H⋯Cl and O(water)-H⋯O hydrogen bonds.