Polymorphism of Copper(I) Halide π‐Complexes: Synthesis and Structure of a New Modification of [Cu₂Cl₂(CH₂=CH–CH₂)₂O]

Abstract

A new polymorph of [Cu2Cl2(CH2=CH–CH2)2O] has been obtained by an alternating‐current electrochemical synthesis starting from CuCl2 and triallylphosphite. Diallylether was obtained in statu nascendi via transetherification of triallylphosphite. The structure is monoclinic, space group P21/n, a = 7.6738(7), b = 6.5128(4), c = 18.2689(18) Å, β = 91.644(11)°, V = 912.67(13) Å3 (at 150 K), Z = 4; R1 = 0.0339, wR2 = 0.0822. Flexibility of the organic ligand and weak interactions copper···halogen have been identified as the main reasons enabling polymorphism in molecular π‐complexes of copper(I).

Coordination environment friendly silicon in copper(I) chloride π-complexes with tetravinylsilane and dimethyltetravinyldisiloxane

“…It would lead to reduction of number of independent copper atoms as it was observed for some other CuCl pcomplexes. Thus, any symmetry change is directly related to a conformational flexibility of the organic component which promotes a transformation of the copper(I) halide fragment and therefore facilitating polymorphism [22]. Table 2 Selected bond distances (Å) and bond angles (°) for I.…”

Trimorphism of Zn(NCS)2(4-dimethylaminopyridine)2: Crystal Structures, Thermodynamic Relations, and Comparison with the Co(II) Polymorphs

“…Finally, these results are sometimes discussed in context of the crystal structure, where, for example, some short intermolecular contacts are held to be responsible for the stability of a given form. 37,38 All these might be incomplete because for definite conclusions the exact thermodynamic relations must be known, which for coordination compounds is difficult to investigate. In contrast to organic compounds, usually no melting or polymorphic transition is observable, and therefore, helpful thermodynamic rules like the heat of transition, the melting enthalpy or melting entropy rule cannot be used.…”

“…In this case, on the one hand, the chemical composition is constant, and all differences in the physical properties, including thermodynamic parameters, depend entirely on the differences in the crystal structures and can be compared directly. − On the other hand, even if several polymorphic or isomeric coordination compounds are reported, in most cases their thermodynamic relations are usually not investigated. − Sometimes conclusions on the stability were drawn based on the comparison of the densities, the fact that one form transforms into another or by computational methods. − In other cases, crystals of two modifications were obtained, and one of these forms can be prepared pure, whereas no access to the other form was found, and thus, it is concluded that the latter, frequently called “disappearing polymorph”, is metastable, which is not necessarily the case. Finally, these results are sometimes discussed in context of the crystal structure, where, for example, some short intermolecular contacts are held to be responsible for the stability of a given form. , All these might be incomplete because for definite conclusions the exact thermodynamic relations must be known, which for coordination compounds is difficult to investigate. In contrast to organic compounds, usually no melting or polymorphic transition is observable, and therefore, helpful thermodynamic rules like the heat of transition, the melting enthalpy or melting entropy rule cannot be used. − Therefore, there are only a few examples where the thermodynamic relations of coordination compounds are investigated in more detail. ,− In some cases, the transformation of one form into the other is observed by, for example, X-ray diffraction.…”