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Phase‐transformation‐induced twinning of an iron(III) calix[4]pyrrolidine complex
Author(s) -
Journot Guillaume,
Neier Reinhard,
StoeckliEvans Helen
Publication year - 2014
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229614012157
Subject(s) - triclinic crystal system , monoclinic crystal system , pyrrolidine , crystallography , chemistry , crystal twinning , molecule , crystal structure , stereochemistry , organic chemistry , microstructure
The title compound, tetrachlorido‐1κ Cl ;2κ 3 Cl ‐(2,2,7,7,12,12,17,17‐octamethyl‐21,22,23,24‐tetraazapentacyclo[16.2.1.1 3,6 .1 8,11 .1 13,16 ]tetracosane‐1κ 4 N , N ′, N ′′, N ′′′)‐μ 2 ‐oxido‐diiron(III), [Fe 2 Cl 4 O(C 28 H 52 N 4 )], undergoes a slow phase transformation at ca 173 K from monoclinic space group P 2 1 / n , denoted form (I), to the maximal non‐isomorphic subgroup, triclinic space group P , 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 FeCl 3 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 Fe III atoms are coordinated to the macrocyclic ligand and have distorted octahedral FeN 4 OCl coordination spheres. These Fe III atoms lie out of the mean plane of the four N atoms, displaced towards the O atom of the [OFeCl 3 ] 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 [OFeCl 3 ] units are similar, with each Fe III 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].