Rational Design of Homo and Hetero Hexanuclear Coordination Compounds: Syntheses and Magnetic Properties of [Cu2IIM4II] (M = Cu, Ni) Species and the Crystal Structure of {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}(ClO4)4 · 2 H2O

Abstract

New homo‐ and heterometallic hexanuclear complexes of formula {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}(ClO4)4 · 2 H2O [Cu6‐tmen] {[Cu(pmdien)]4[Cu2L]}(ClO4)4 · 4 H2O [Cu6‐pmdien] and {[Ni(cyclam)]4[Cu2L]}(ClO4)4 · 4 H2O [Cu2Ni4‐cyclam] [H8L = tetrakis(aminomethylene)methanetetrakis(oxamic acid), tmen = N,N,N′,N′‐tetramethylethylenediamine, pmdien = N,N,N′,N′,N″‐pentamethyldiethylenetriamine, and cyclam = 1,4,8,11‐tetraazacyclotetradecane] have been synthesized. The crystal structure of [Cu6‐tmen] has been determined by single‐crystal X‐ray diffraction. The structure consists of cationic {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}4+ hexanuclear units. The hexanuclear cation is made up of two symmetry‐related oxamato‐bridged trinuclear units connected through the central carbon atom C(6) of the L8– ligand. Variable‐temperature magnetic susceptibility measurements (1.8–300K) have been performed for these series of complexes including the dinuclear precursors of formula Na4[Cu2L] · 10.5 H2O [Cu2‐Na], (NMe4)4[Cu2L] · 4 H2O [Cu2‐NMe4] and (PPh4)4[Cu2L] · 6 H2O [Cu2‐PPh4]. The magnetic data have been interpreted. Evidence of a weak intramolecular ferromagnetic interaction between the two CuII ions in [Cu2L]4– has been observed. For the hexanuclear species, the interaction through the oxamato bridge was found to be equal to –6790, –2650, and –1643 yJ (–342, –133, and –82cm–1) for [Cu6‐tmen], [Cu6‐pmdien], and [Cu2Ni4‐cyclam], respectively. In these complexes, the weak intramolecular ferromagnetic coupling between the two CuII ions within the dinuclear synthon was masked by intermolecular interactions or local anisotropy.

Magnetic Anisotropy of a High-Spin Octanuclear Nickel(II) Complex with a meso-Helicate Core

“…The small J eff /| J | ratio confirms the validity of the perturbational treatment. The − J value in 2b is comparable to that reported for related oxalate-bridged (22.0−39.0 cm -1 ) and oxamidate-bridged (25.0−57.0 cm -1 ) binuclear nickel(II) complexes. , In this model, the value of J eff is related to that of J ‘ between the two central Ni II ions through the meta -phenylenediamidate bridges by J eff = 1 / 9 J ‘, that is, J ‘ = +3.1 cm -1 . The calculated J ‘ value in 2b agrees both in sign and in magnitude with that found in the binuclear precursor 1b (+3.6 cm -1 ) .…”

“…The magnetic susceptibility data of 2b were fitted according to an effective spin Hamiltonian for a dimer-of-tetramers model that takes into account the coupling between the S = 2 ground state of each Ni II 4 unit [ H = − J ( S 1A S 3A + S 1A S 4A + S 1A S 5A + S 2B S 6B + S 2B S 7B + S 2B S 8B ) − J eff S A S B + g β( S 1A + S 3A + S 4A + S 5A + S 2B + S 6B + S 7B + S 8B ) B , with S i A = S j B = 1 for i = 1, 3−5; j = 2, 6−8; and S A = S B = 2] . A least-squares fit gave J = −26.6 cm -1 , J eff = +0.34 cm -1 , and g = 2.13.…”

Oxamato-Bridged Trinuclear NiIICuIINiII Complexes: A New (NiIICuIINiII)2 Hexanuclear Complex and Supramolecular Structures. Characterization and Magnetic Properties

“…All attempts to fit the full experimental curve were unsuccessful, either assuming D = 0 or introducing the ZFS in the ground quartet state. The raised χ M T values at low temperatures can be due to the possibility of weak ferromagnetic coupling between the trinuclear entities associated with structural parameters such as hydrogen bonds, as indicated in a previous work on similar trinuclear Ni II Cu II Ni II complexes 14b 8 Experimental and calculated () variations of χ M T versus T for {[Ni(H 2 O)(dien)] 2 (μ-Cu(OHpba))}(ClO 4 ) 2 ·4H 2 O ( 6 ). 5 Magnetic Parameters for Complexes 2 − 6 and Some Previously Reported Species complex J cm -1 g Ni g Cu ref {[Ni(H 2 O)(dien)] 2 (μ-Cu(pba))}- (ClO 4 ) 2 ·6H 2 O ( 2 ) −98.7 2.23 2.29 a {[Ni(H 2 O)(Medpt)] 2 (μ-Cu(OHpba))}- (ClO 4 ) 2 ·4H 2 O ( 3 ) −102.2 2.12 2.24 a {[Ni(H 2 O)(dien)] 2 (μ-Cu(Me 2 pba))}- (ClO 4 ) 2 ·2.5H 2 O ( 4 ) −101.1 2.30 2.24 a {[Ni(H 2 O)(dpt)] 2 (μ-Cu(Me 2 pba))}- (ClO 4 ) 2 ·2H 2 O ( 5 ) −111.2 2.30 2.30 a {[Ni(H 2 O)(dien)] 2 (μ-Cu(OHpba))}- (ClO 4 ) 2 ·4H 2 O ( 6 ) −88.8 2.3 2.3 a {[Ni(bapa)(H 2 O)] 2 (μ-Cu(pba))}(ClO 4 ) 2 b −90.3 2.19 2.12 8 {[Ni(bispictn)] 2 (μ-Cu(pba))}(ClO 4 ) 2 ·2.5H 2 O b −107.2 2.15 2.19 9 {[Ni(cth)] 2 (μ-Cu(pba))}(ClO 4 ) 2 b −109.2 2.13 2.15 9 {[Ni(bispictn)] 2 (μ-Cu(OHpba))}(ClO 4 ) 2 ·H 2 O −102.0 2.13 2.15 9 {[Ni(cth)] 2 (μ-Cu(opba))}(ClO 4 ) 2 ·H 2 O −104.2 2.13 2.18 9 {[Ni(cth)] 2 (μ-Cu(OHpba))}(ClO 4 ) 2 −90.0 2.29 2.20 10 {[Ni(Me 3 [12N 3 ])] 2 (μ-Cu(Me 2 pba))}(ClO 4 ) 2 −110.0 2.30 2.32 10 a This work.…”

“…The N,N ‘-substituted bis(oxamato)copper(II) complexes have an important function in the preparation of this kind of system . The use of these anionic mononuclear complexes and related ones in the “complex as a ligand” approach provided the preparation of several oxamato-bridged compounds: heterotrinuclear complexes Mn II Cu II Mn II , − Ni II Cu II Ni II , − Co II Cu II Co II , and Fe III Ni II Fe III ;14a hexanuclear complex (Ni II Cu II Ni II ) 2 ;14b ferrimagnetic chains Mn II Cu II , , Ni II Cu II , , Fe II Cu II , and Co II Cu II ; and more complex structures with radical species, Mn II Cu II , and Co II Cu II . Despite the number of oxamato-bridged heterotrinuclear systems reported, however, to our knowledge, only three Ni II Cu II Ni II complexes have been characterized by X-ray crystallography: {[Ni(bapa)(H 2 O)] 2 Cu(pba)}(ClO 4 ) 2 [bapa = bis(3-aminopropyl)amine and pba = 1,3-propylenebis(oxamato)] reported by some of us, {[Ni(bispictn)] 2 Cu(pba)}(ClO 4 ) 2 · 2.5H 2 O and {[Ni(cth)] 2 Cu(pba)}(ClO 4 ) 2 [bispictn = N , N ‘-bis(2-pyridylmethyl)-1,3-propanediamine, cth = rac -5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) recently reported by Gao et al Only one heterohexanuclear (Ni II Cu II Ni II ) 2 has been reported, but without crystal structure determination 14b…”

Spin Control in Ladderlike Hexanuclear Copper(II) Complexes with Metallacyclophane Cores

“…In the search of rationally designed polynuclear complexes with oxamate-based ligands, we recently reported the two binuclear copper(II) metallacyclophanes 1 and 2 built upon the binucleating ligands N , N ‘ -1,3-phenylenebis(oxamate) (mpba) and N , N ‘ -1,4-phenylenebis(oxamate) (ppba), respectively (Chart ) . Complexes 1 and 2 constitute a rare example of the control of spin in metal complexes by the topology of the bridging ligand. , Thus, the two Cu II ions of 1 are moderately ferromagnetically coupled, while those of 2 are strongly antiferromagnetically coupled, both effects resulting from a spin polarization mechanism through the π-conjugated bond system of the phenylenediamidate bridges with meta - and para -substitution patterns.…”