Structural effects: disordering twinning, polymorphism, and morphotrop
ism due to substitution of halide atoms are considered using the resul
ts of X-ray diffraction analysis of 18 olefinic pi-complexes of Cu(I).
These effects are associated with the heterodesmic character of compo
unds, in particular, with weak interactions such as lengthened coordin
ation bonds and hydrogen contacts.