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The crystal structure of the title compound has been determined from photographic X-ray data. Crystals are monoclinic, space group Cc, with cell dimensions a = 1430, b = 2467, c = 630 pm, p = 92.52" and Z = 4. The structure was solved by Patterson and Fourier methods and refined by least squares to R 0.1 01 for 1480 observed reflections. The compound is unusual in having two types of copper-containing anion, a [CuCI,-1, chain and a [CuC1412-tetrahedron. The symmetry of the crystal lattice is almost hexagonal, and the distortion from hexagonal symmetry is attributed to the Jahn-Teller effect in the [CuCI,-1, chains. The distortion of the tetrahedron differs from that usually found in tetrahedral tetrachlorocuprate( 11) complexes in that it approximates to C,, rather than D,, symmetry.

Enthalpies of formation of copper( 11) and zinc(ii) complexes with three tetra-aza macrocyclic ligands of differing ring size have been determined directly by rnicrocalorimetry. The values for the copper( 11) complexes, which reach a maximum with the ligand 1.4.8.1 1 -tetra-azacyclotetradecane, have been correlated with the calculated ideal size of the aperture in the macrocyclic ligand required to maintain the ligand in a minimum-strain conformation. The macrocyclic effect has been interpreted as being due to a favourable entropy term and to a normally favo_urable enthalpy term, the magnitude of which is critically dependent on matching the size of the metal ion to that of the aperture in the macrocyclic iigand.

The calorimetric determination of the enthalpy of formation of (1,4,8,1 l-tetraazacyclotetradecane)nickel(II) has been made by displacing the macrocyclic ligand with cyanide and following the reaction to completion (5 h) in a batch microcalorimeter of the heat-flow type. The 770 value found (-20.3 kcal mol™1) is 11 kcal moL1 less than that previously reported. Thermodynamic parameters of both octahedral and square-planar forms of the complex have been calculated. The macrocyclic effect in Ni(II) complexes has been rationalized with that already established for Cu(II) complexes.

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