Long range antiferromagnetic exchange in dinuclear copper(II) complexes containing 1,4-dicyanamidobenzene dianion bridging ligands

Abstract

Six Cu(I1) dimers, [(Cu(dien) ),(p-dicyd)][CF3SO3I2 (1). [(Cu(dien) ),(p-Me2dicyd)][CF3SO3j2 (2), [ ICu(dien1 l,(p-Cl,dicyd)l[CF3S0312 (31, [ ICu(L) I&-dicydll (4). lCu(L) I&-Me,dicyd)l (51, and [(Cu(L)),(p-Cl,dicyd)] (6), where dicyd2-, ~e , d i c~d ' -and cl,dicyd2-are unsubstituted, 2,Sdimethyl-and 2,5-dichloro-l,4-dicyanamidobenzene dianions, respectively, dien is diethylenetriamine, and L-= 1,3-bis(2-pyridylimino)isoindolinato, have been synthesized and characterized by elemental analysis, IR, UV-vis, and EPR spectroscopy, and magnetic studies. Temperature-dependent magnetic susceptibility measurements of the complexes 1-6 from 5 to 300 K are reported. The data for 2 , 3 , 5 , and 6 have been fitted to a dimer model with a modified Bleaney-Bowers expression which derived antiferromagnetic exchange constants -J = 10.6,4.5, 5.2, and 3.0 cm-', respectively (where the Hamiltonian is of the form .7/' = -2JS;S,). For 4, an approach to a maximum in X, with decreasing temperature gave an estimated -J < 3.5 cm-I. Only complex 1 showed CurieWeiss behavior. This is far weaker antiferromagnetic exchange compared to that observed for dinuclear Ru(II1) complexes incorporating the dicyd2-bridging ligands (J. Am. Chem Soc. 114, 5 130 (1992)) and is attributed to a symmetry and energy mismatch between Cu(I1) a* magnetic orbitals and the T,, molecular orbitals of the bridging ligand which are important for superexchange.Key words: superexchange, copper dimer, dicyanamidobenzene.

From an ST = 3 Single-Molecule Magnet to Diamagnetic Ground State Depending on the Molecular Packing of MnIIIsalen-type Dimers Decorated by N,N‘-Dicyano-1,4-naphthoquinonediiminate Radicals

“…Hence, the position of the ν(C⋮N) stretch obviously indicates that the DCNNQI moiety in 1 and 2 is reduced to its radical DCNNQI •- form by the redox reaction with [Mn II (5-MeOsaltmen)]. It is interesting to note that a similar shift of the ν(C⋮N) band was observed for the series of 2,5-dimethyl- N , N ‘ -dicyanoquinonediimine (DM-DCNQI): 2188 cm -1 for the free neutral DM-DCNQI, 2216 cm -1 for the coordinated neutral DM-DCNQI in [Rh 2 (O 2 CCF 3 ) 4 (DM-DCNQI)], 2140 cm -1 for the partially reduced form in [TTF][DM-DCNQI] (TTF = tetrathiafulvalene), and 2093 cm -1 for the dianionic form in (AsPh 4 ) 2 DM-DCNQI 1 …”

Ferrimagnetic ordering of one-dimensional N,N′-dicyanoquinone diimine (DCNQI) electron transfer salts with porphyrinatomanganese(II)

“…These values are also shifted to lower energy compared with those of the ETSs with partial electron transfer, e.g., the corresponding tetrathiafulvalene (TTF)-based ETSs, 2150 cm 21 for [TTF][DMeO-DCNQI] 24 and 2140 cm 21 for [TTF][DMe-DCNQI], 24,25 and are shifted to higher energy than those for the dianion, e.g., 2093 cm 21 for [DMe-DCNQI] 22 . 26 The values of 1 and 2 are comparable to that for the anion radical, e.g., 2118 cm 21 for [DMe-DCNQI] 2 ? .…”

N,N‘-Dicyanoquinone Diimines (DCNQIs): Versatile Acceptors for Organic Conductors

“…These structures prevent polymerization. 366 Another class of compounds deserves special attention. As mentioned above, on cooling, acetonitrile solutions of the DCNQIs from Table 11 and CuI black salts (DCNQI) 2 Cu are precipitated.…”