Synthesis and Characterization of Trinuclear Ni^II₃ and Cu^II₃ Triplesalophen Complexes: Evaluation of Ligand Folding and Heteroradialene Formation and their Impact on the Magnetic Properties

Abstract

The coordination chemistry of the triplesalophen ligands H 6 baron R (R = Me, Cl, Br) with Cu II and Ni II has been studied. The triplesalophen ligand system is an extension of the triplesalen ligand system and is composed of a bridging phloroglucinol ring with three meta-phenylene salophen coordination compartments. The completely sp 2 hybridized backbone of the triplesalophen ligands should favor a more planar molecular structure of the trinuclear complexes in comparison to the triplesalen complexes. Reaction of the ligands with the metal acetates in n-butanol/CHCl 3 provided the complexes [(baron Me )Ni 3 ]a, [(baron Cl )Ni 3 ]a, [(baron Br )-Ni 3 ]a, [(baron Me )Cu 3 ], [(baron Cl )Cu 3 ], and [(baron Br )Cu 3 ]. For the Ni II complexes, recrystallization from pyridine or performing the reaction in pyridine provided the compounds [(baron Me )Ni 3 ]b and [(baron Cl )Ni 3 ]b, whereas for the bromo derivative the complex [(baron Br ){Ni(py) 2 } 2 Ni] with one fourcoordinate and two six-coordinate Ni II ions have been obtained. In contrast, for the Cu II complexes, two [(baron R ){Cu(py)} 2 Cu] (R = Me, Cl, Br) units dimerize via [a] Lehrstuhl für Anorganische Chemie I, 5934bridging of a coordinated phenolate. The structural analysis reveals a strong tendency for π stacking of the trinuclear complexes resulting in a planarization of the complexes. The trinuclear triplesalophen complexes exhibit the four signatures of heteroradialene formation, which were extracted from single-crystal X-ray diffraction, NMR, FTIR, and UV/ Vis spectroscopy. Analysis of these experimental data with regard to the respective data of the free ligands H 6 baron R (R = Me, Cl, Br) and the mononuclear analogue H 2 carl Cl and its complexes [(carl Cl )Ni] and [(carl Cl )Cu] clearly demonstrates that the heteroradialene resonance structure, which has been established as the dominant resonance structure for the free ligands, still has a strong but smaller contribution in the trinuclear triplesalophen complexes. The magnetic properties demonstrate weak intramolecular ferromagnetic interactions mediated by the triplesalophen ligands in the trinuclear Cu II 3 complexes, which are experimentally difficult to determine due to intermolecular antiferromagnetic interactions of the same order of magnitude. molecular structures of the trinuclear Ni II 3 complexes [2] and the trinuclear Cu II 3 complexes [11] of the tert-butyl ligand H 6 talen tBu 2 exhibit a strong ligand folding along the central O-N vectors, resulting in overall bowl-shaped molecular structures. This ligand folding preorganizes the axial coordination sites of the metal salen subunits for the complementary binding of a hexacyanometallate. In combination with a strong tendency of two [(talen tBu 2 )M t 3 ] m+ complexes to dimerize due to van der Waals interaction of the tertbutyl phenyl groups, [12] a high driving force results for the formation of heptanuclear complexes [M t 6 M c ] n+ (= [{(talen tBu 2 )M t 3 } 2 {M c (CN) 6 }] n+ ) by the supramolecular assembly of two [(talen tBu ...

Increasing the π–π Interactions in Trinuclear NiII3 Triplesalophen Complexes

“…Thus, a strategy to increase the anisotropy is to align the local anisotropy tensors collinear, which was confirmed by calculations . In this respect, we have developed the optimized ligand system triplesalophen (Scheme ), which consists of a completely sp 2 ‐hybridized backbone . This should allow the synthesis of planar trinuclear triplesalophen complexes with almost collinear anisotropy tensors.…”

“…In this respect, we synthesized the triplesalophen ligands H 6 baron R ( R = Me, Cl, Br) . With these ligands, trinuclear Ni II 3 , Co II 3 , and Cu II 3 complexes were synthesized and characterized . Although the trinuclear triplesalophen complexes show a significantly lower ligand folding than the analogous triplesalen complexes,, their molecular structures still show significant deviations from planarity.…”

“…With these ligands, trinuclear Ni II 3 , Co II 3 , and Cu II 3 complexes were synthesized and characterized . Although the trinuclear triplesalophen complexes show a significantly lower ligand folding than the analogous triplesalen complexes,, their molecular structures still show significant deviations from planarity. Furthermore, several attempts to use trinuclear triplesalophen building blocks for the construction of nonanuclear complexes failed so far.…”

Aromatic Versus Heteroradialene Character in Extended Thiophloroglucinol Ligands and their Trinuclear Nickel(II) Complexes

“…[69][70][71][72][73] For example, nature utilizes strong metal-sulfur covalent bonds in iron-sulfur clusters and blue copper centers for biological electron-transfer sites. [38,[80][81][82][83][84] This ketoenamine resonance structure is reminiscent of [6]radialenes and has been termed heteroradialene. [38,[80][81][82][83][84] This ketoenamine resonance structure is reminiscent of [6]radialenes and has been termed heteroradialene.…”

“…[74][75][76][77][78][79] However, during our efforts to synthesize such extended thiophloroglucinol ligands we realized that in the triplesalen ligands and in extended phloroglucinol ligands in general, the central backbone must be described as the N-protonated tautomer rather than the Oprotonated tautomer, with a major contribution of resonance structure IV with exocyclic C=C and C=O bonds (Scheme 1 d). [38,[80][81][82][83][84] This ketoenamine resonance structure is reminiscent of [6]radialenes and has been termed heteroradialene. [85,86] Radialenes are alicyclic compounds exhibiting cross-conjugation of the double-bond system, that is, radialenes do not have a delocalized aromatic p system.…”