ABSTRACT
The π-π stacking interaction, one of the main intermolecular forces, sometimes leads to amazing magnetic properties. Although the concept has been raised that spin density is one of the main factors that contribute to the magnetic coupling strength in intermolecular magnetic coupling systems, it has not been confirmed either experimentally or theoretically to date. Herein we present a study on the magnetostructural data of seven unpublished Cu(II) complexes and ten reported radicals. It is confirmed for the first time that the spin density on short contact atoms is a major factor that contributes to the π-π stacking magnetic coupling strength. Based on the reported data to date, when the short contact distance is larger than the default contact radius, medium or relatively strong magnetic coupling strength could be obtained only if the spin density on the short contact atoms is greater than 0.1350; when the C···C short contact is less than the default contact radius of 3.4 Å, but not less than 3.351 Å, and the spin density is less than 0.1, neither medium nor strong magnetic coupling strength could be observed. Further, when the short contact distance decreases with a temperature drop, the spin densities on the relevant short contact atoms increase. In the complexes reported the small spin densities on the relevant short contact atoms are the major factors that result in the weak π-π magnetic coupling strength.
Subject(s)
Copper/chemistry , Magnetic Phenomena , Organometallic Compounds/chemistry , Crystallography, X-Ray , Models, Molecular , Molecular ConformationABSTRACT
The asymmetric unit of the title compound, [Zn(NCS)(C(12)H(7)ClN(2))(2)][Zn(NCS)(3)(C(12)H(7)ClN(2))], contains two cations and two anions. In the cations, the Zn(II) ions have distorted trigonal-bipyramidal environments formed by four N atoms from two 2-chloro-1,10-phenanthroline (cphen) ligands and one N atom from a thio-cyanate ligand. The Zn(II) atoms in the complex anions also have distorted trigonal-bipyramidal environments, formed by two N atoms from a cphen ligand and three N atoms from three thio-cyanato ligands. The crystal packing exhibits π-π inter-actions between the rings of the cphen ligands [shortest centroid-centroid distance = 3.586â (5)â Å] and short inter-molecular Sâ¯Cl [3.395â (5)â Å] and Sâ¯S [3.440â (4)â Å] contacts.
ABSTRACT
In the title complex, [Cd(NO(2))(C(22)H(20)N(6))(CH(3)OH)]ClO(4), the Cd(II) ion is in a distorted penta-gonal-bipyramidal CdN(4)O(3) coordination geometry. The dihedral angles formed between the mean planes of the pyrazole rings and the phenanthroline ring system are 4.37â (19) and 5.84â (21)°. In the crystal, the anions and cations are connected by inter-molecular O-Hâ¯O hydrogen bonding, while pairs of weak inter-molecular C-Hâ¯O hydrogen bonds connect the cations into centrosymmetric dimers. In addition, there is a π-π stacking inter-action involving two symmetry-related benzene rings, with a centroid-centroid distance of 3.437â (3)â Å.
ABSTRACT
The ferromagnetic couplings were observed in an unpublished crystal that consists of binuclear copper(II) complexes, namely, [Cu(2)(µ(1,3)-SCN)(2)(PhenOH)(OCH(3))(2)(HOCH(3))(2)] (PhenOH = 2-hydroxy-1,10-phenanthroline), and in the binuclear complex Cu(ii) ion assumes a distorted octahedral geometry and thiocyanate anion functions as a µ(1,3)-SCN(-) equatorial-axial (EA) bridging ligand. The analysis for the crystal structure indicates that there are three types of magnetic coupling pathways, in which two pathways involve π-π stacking between the adjacent complexes and the third one is the µ(1,3)-SCN(-) bridged pathway. The fitting for the data of the variable-temperature magnetic susceptibilities shows that there is a ferromagnetic coupling between adjacent Cu(II) ions with J = 50.02 cm(-1). Theoretical calculations reveal that the two types of π-π stacking resulted in ferromagnetic couplings with J = 4.16 cm(-1) and J = 2.75 cm(-1), respectively, and the bridged thiocyanate anions pathway led to a weaker ferromagnetic interaction with J = 0.88 cm(-1). The theoretical calculations also indicate that the ferromagnetic coupling sign from the two types of π-π stacking does not accord with McConnell I spin-polarization mechanism. The analysis for the Wiberg bond indexes that originate from the π-π stacking atoms indicates that the Wiberg bond indexes are relevant to the associated magnetic coupling magnitude and the Wiberg bond index is one of the key factors that dominates the associated magnetic coupling magnitude.
Subject(s)
Copper/chemistry , Organometallic Compounds/chemistry , Computer Simulation , Crystallography, X-Ray , Models, Molecular , Organometallic Compounds/chemical synthesisABSTRACT
In the title complex, [Cd(NCS)(2)(C(22)H(20)N(6))], the Cd(II) ion is in a CdN(6) coordination geometry which is inter-mediate between octa-hedral and trigonal-prismatic. The dihedral angles formed between the mean planes of the pyrazole rings and the phenanthroline system are 15.74â (15) and 16.30â (13)°. In the crystal, there is a π-π stacking inter-action involving two symmetry-related pyrazole rings, with a centroid-centroid distance of 3.664â (3)â Å. In addition, there is a relatively short inter-molecular contact between C atoms [Câ¯C = 3.399â (6)â Å] involving symmetry-related pyridine rings along the a axis.
