Binuclear copper(II) complexes of new dinucleating ligands with a pyrazolate group as an endogenous bridge. Effects of exogenous azide and acetate bridges on magnetic properties

Abstract

N e w dinucleating ligands containing pyrazole as an endogenous bridging group, 3,5-bis-[N-(2-pyridylmethyl)carbamoyl] pyrazole ( H3L1), 3,5-bis{N-[2-(diethylamino)ethyl]carbamoyl}pyrazole ( H3L2), and 3,5-bis{N-[3-(dimethylamino)propyl]carbamoyl}pyrazole ( H3L3), and their binuclear copper(i1) complexes with azide or acetate ion as an exogenous bridge, [Cu,L(N,) (H,O),]-H,O (L = L1--L3) and [Cu,L1 (02CMe)]-2MeOH, have been obtained. Cryomagnetic investigations (5-300 K) reveal a significant antiferromagnetic spin exchange for the azide-bridged complexes ( -J = 371-297 cm-'), but a ferromagnetic spin exchange (J > +8.9 cm-l) for the acetate-bridged complex. The azide-bridged complexes are e.s.r. silent. The acetate-bridged complex is unstable in dimethylformamide (dmf) but a quickly prepared dmf frozen solution of the sample givesX-band signals characteristic of a spin-triplet ( S = 1 ) state, together with signals due to a spin doublet (S = $) attributable to monomeric copper(i1). Signals at 81 2, 1 292, and 4 380 G show a seven-line hyperfine structure (Azz = 0.01 03 cm-'); the first and third signals are assigned t o AMs = 1 transitions and the second to the AMs = 2 transition of the parallel resonance of the spintriplet state. E.s.r. simulation based on the spin Hamiltonian for the spin triplet of a dicopper(ii) system gives g , , = 2.533, D = 0.21 0 cm-l, and E = 0.020 cm-l. Only t w o components of the perpendicular resonances are recognizable at 2 11 3 and 3 81 2 G which give g, = 2.055.

Pyrazolate‐Based Dinucleating Ligands in L2M2 Scaffolds: Effects of Bulky Substituents and Coligands on Structures and M···H−C Interactions

“…[5,6] Further control of the metalϪmetal separation, as well as of the steric and electronic properties of the individual metal ions, can be achieved by appropriate chelating side arms attached to the 3-and 5-positions of the heterocycle, [7,8] usually giving rise to either bis(µ-pyrazolato) bridged species L 2 M 2 (A, Scheme 1) [9][10][11][12][13][14][15] or LM 2 X complexes featuring secondary bridges within the dimetallic pocket (B). [16][17][18][19][20][21][22][23][24] [a] Institut für Anorganische Chemie der Georg-AugustUniversität Göttingen Tammannstraße 4, 37077 Göttingen, Germany Fax: (internat.) ϩ 49-(0)551-393063 E-mail: franc.meyer@chemie.uni-goettingen.de [b] Anorganisch-Chemisches Institut der Universität Heidelberg Im Neuenheimer Feld 270, 69120 Heidelberg, Germany [ ‡] New address: Crompton GmbH, Ernst-Schering-Straße 14, 59192 Bergkamen, Germany close proximity to the low-spin nickel(II) center.…”

Crystal structure and ferromagnetic properties of the oxamidato-bridged Cu(II)–VO(IV) complex containing macrocyclic ligands

“…Finally, below 18 K, the dominant phenomenon is one of intermolecular antiferromagnetic interactions and/or zero-field splitting effects in the ground state. The magnetic analysis was carried out by using the theoretical expression of the magnetic susceptibility deduced from the Heisenberg spin Hamiltonian: H ¼ À2JŜ 1Ŝ2 À DŜ z and v M is given by [29] …”

Theoretical Study on Magnetic Interaction in Pyrazole-Bridged Dinuclear Metal Complex: Possibility of Intramolecular Ferromagnetic Interaction by Orbital Counter-Complementarity

“…The orbital orthogonality found in such PBA analogues, however, requires the linearly aligned metal-ligand-metal structures, as well as the specific combination of metal ions such as Cr(III)/Cr(II), so that it is considered to have less degrees of freedom in molecular structures. On the other hand, it has been known that some heterogeneous bridging ligands between two Cu(II) ions make different contributions to the magnetic exchange interactions [9,10]. A pyrazole, which is a heterocyclic five-membered ring compound, is often used as a bridging ligand between two metal ions [9][10][11][12].…”

“…On the other hand, it has been known that some heterogeneous bridging ligands between two Cu(II) ions make different contributions to the magnetic exchange interactions [9,10]. A pyrazole, which is a heterocyclic five-membered ring compound, is often used as a bridging ligand between two metal ions [9][10][11][12]. Kida, Okawa, and co-workers reported that pyrazole-bridged dinuclear-Cu(II) complexes with azide and acetate as counter bridging-ligands shown in Figure 1 exhibit anti-ferromagnetic (AFM) and ferromagnetic (FM) behavior, respectively [9,10].…”

“…A pyrazole, which is a heterocyclic five-membered ring compound, is often used as a bridging ligand between two metal ions [9][10][11][12]. Kida, Okawa, and co-workers reported that pyrazole-bridged dinuclear-Cu(II) complexes with azide and acetate as counter bridging-ligands shown in Figure 1 exhibit anti-ferromagnetic (AFM) and ferromagnetic (FM) behavior, respectively [9,10]. They explained this phenomenon by an orbital complementarity/counter-complementarity that originates in the orbital interaction between Cu(II) and bridging-ligands.…”