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Phase-transformation-induced twinning of an iron(III) calix[4]pyrrolidine complex

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2014
Author Journod Guillaume, Neier Reinhard, Stoeckli-Evans Helen,
Project The hydrogenation of calix[4]pyrroles leading to the novel ligand system calix[4]pyrrolidine: Their properties and their application
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Original article (peer-reviewed)

Journal Acta Crystallogr., Sect. C Struct. Chem
Volume (Issue) 70(7)
Page(s) 644 - 649
Title of proceedings Acta Crystallogr., Sect. C Struct. Chem


The title compound, tetra­chlorido-1[kappa]Cl;2[kappa]3Cl-(2,2,7,7,12,12,17,17-octa­methyl-21,22,23,24-tetra­aza­penta­cyclo­[,6.18,11.113,16]tetra­cosane-1[kappa]4N,N',N'',N''')-[mu]2-oxido-diiron(III), [Fe2Cl4O(C28H52N4)], undergoes a slow phase transformation at ca 173 K from monoclinic space group P21/n, denoted form (I), to the maximal non-isomorphic subgroup, triclinic space group P\overline{1}, denoted form (II), which is accompanied by nonmerohedral twinning [twin fractions of 0.693 (4) and 0.307 (4)]. The transformation was found to be reversible, as on raising the temperature the crystal reverted to monoclinic form (I). In the asymmetric unit of form (I), Z' = 1, while in form (II), Z' = 2, with a very small reduction (ca 1.8%) in the unit-cell volume. The two independent mol­ecules (A and B) in form (II) are related by a pseudo-twofold screw axis along the b axis. The mol­ecular overlay of mol­ecule A on mol­ecule B has an r.m.s. deviation of 0.353 Å, with the largest distance between two equivalent atoms being 1.202 Å. The reaction of calix[4]pyr­roli­dine, the fully reduced form of meso-octa­methyl­porphyrinogen, with FeCl3 gave a red-brown solid that was recrystallized from ethanol in air, resulting in the formation of the title compound. In both forms, (I) and (II), the FeIII atoms are coordinated to the macrocyclic ligand and have distorted octa­hedral FeN4OCl coordination spheres. These FeIII atoms lie out of the mean plane of the four N atoms, displaced towards the O atom of the [OFeCl3] unit by 0.2265 (5) Å in form (I), and by 0.2210 (14) and 0.2089 (14) Å, respectively, in the two independent mol­ecules (A and B) of form (II). The geometry of the [OFeCl3] units are similar, with each FeIII atom having a tetra­hedral coordination sphere. The NH H atoms are directed below the planes of the macrocycles and are hydrogen bonded to the coordinated Cl- ions. There are also intra­molecular C-H...Cl hydrogen bonds present in both (I) and (II). In form (I), there are no significant inter­molecular inter­actions present. In form (II), the individual mol­ecules are arranged in alternate layers parallel to the ac plane. The B mol­ecules are linked by a C-H...Cl hydrogen bond, forming chains along [100].