A comparison of the crystal structures of (dabcoH2)CuCl4 and (dabcoH2)CuCl4⋅H2O

The crystal structures of the anhydrous and monohydrated (dabcoH2)CuCl4⋅nH2O salts (n = 0,1) have been determined and a comparison of their crystal structures has been reported. The anhydrous salt is monoclinic P21/c with a = 9.045(2) Å, b = 6.9270(10) Å, c = 18.767(4) Å and β = 90.07(3)° with V = 1175.8(4) Å3. The hydrated salt is also monoclinic P21/c with a = 9.266(2) Å, b = 9.395(2) Å, c = 14.386(3) Å and β = 93.32(3)° with V = 1250.3(5) Å3. The structures of the two salts are closely related. Both compounds contain isolated distorted (compressed) tetrahedral CuCl42− anions, diprotonated dabco cations, and in the case of the hydrated salt, lattice H2O molecules. In the anhydrous salt, each of the two N–H+ groups of the dabcoH22+ dications form bifurcated hydrogen bonds to chloride ions on adjacent CuCl42− anions along the c axis, thus forming chains running parallel to the c axis. In the hydrated salt, a water molecule is inserted into one of the pair of bifurcated hydrogen bonds, forming instead N–H ⋅ ⋅ ⋅ O–H ⋅ ⋅ ⋅ CuCl42− linkages. The chains thus formed are cross-linked by O–H ⋅ ⋅ ⋅ Cl hydrogen bonds between the chains. Because of this additional hydrogen bonding, the CuCl42− anions in the hydrated salt are distorted further from tetrahedral geometry.