Incorrect atom connectivity in X-ray structure solutions associated with a "partial polar ambiguity":: a non-macrocyclic structure for the macrocyclic lead complex, [η4-Me8taa]Pb

The divalent lead complex [eta(4)-Me(8)taa]Pb has been synthesized by metathesis of PbI2 with Li-2[Me(8)taa] in THF (Me(8)taaH(2) = octamethyldibenzotetraaza[14] annulene). [eta(4)-Me(6)taa]Pb exists as (at least) three structural of each of these modifications have been determined by single crystal X-ray diffraction. Of most si the modifications, namely the triclinic chloroform solvate [eta(4)-Me(8)taa]Pb . CHCl3, and the primitive an C-centered orthorhombic polymorphs of the dichloromethane solvate [eta(4)-Me(8)taa]Pb . CH2Cl2. structures C-centered orthorhombic polymorph [eta(4)-Me(8)taa]Pb . CH2Cl2 is subject to the existence of a false um in the structure solution refinement procedure, the result of which is the generation of a non-macrocyclic structure for a compound that is actually macrocyclic. Significantly, even though it does not exhibit the true connectivity of the molecule, the errant structure is characterized by a low R value and well-behaved displacement parameters. The manifestation of the false minimum is a consequence of the crystal belonging to a pc group, which results in a "partial polar ambiguity." As such, the result serves to emphasize that care taken to ensure that, for polar space groups, all atoms of the derived structure belong to a single true configuration, rather than a hybrid of the two possible true polar configurations.