2013-11-13 09:51:09
ACS Publications
ERMMES
POLE 2
ermmes
Dicopper(II) Metallacyclophanes with Oligo(p-phenylene-ethynylene) Spacers: Experimental Foundations and Theoretical Predictions on Potential Molecular Magnetic Wires
Two novel double-stranded dicopper(II) metallacyclophanes of formula (nBu4N)4[Cu2(dpeba)2]·4MeOH·2Et2O (1) and (nBu4N)4[Cu2(tpeba)2]·12H2O (2) have been prepared by the CuII-mediated self-assembly of the rigid (?rod-like?) bridging ligands N,N?-4,4?-diphenylethynebis(oxamate) (dpeba) and N,N?-1,4-di(4-phenylethynyl)phenylenebis(oxamate) (tpeba), respectively. Single crystal X-ray diffraction analysis of 1 confirms the presence of a dicopper(II)tetraaza[3.3]4,4?-diphenylethynophane metallacyclic structure featuring a very long intermetallic distance between the two square planar CuII ions [r = 14.95(1) Å]. The overall parallel-displaced π-stacked conformation of the two nearly planar para substituted diphenylethyne spacers [dihedral angle (?) of 7.8(1)°] leads to important deviations from the perpendicular orientation of the copper mean basal planes with respect to the facing benzene planes [dihedral angles (?) of 56.4(1) and 58.4(1)°]. X-band EPR spectra together with variable-temperature magnetic susceptibility and variable-field magnetization measurements of 1 and 2, both in solution and in the solid state, show the occurrence of a non-negligible, moderate to weak intramolecular antiferromagnetic coupling [?J = 3.9?4.1 (1) and 0.5?0.9 cm?1 (2); H = ?JS1·S2 with S1 = S2 = SCu = 1/2]. Density functional calculations on the BS singlet (S = 0) and triplet (S = 1) spin states of the model complexes 1 and 2 with an ideal orthogonal molecular geometry (? = 0° and ? = 90°) support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction between the two unpaired electrons occupying the dxy orbital of each square planar CuII ion through the predominantly π-type orbital pathway of the double p-diphenylethyne (1) and di(phenylethynyl)phenylene spacers (2). Time-dependent density functional calculations reproduce the observed bathochromic shift of the main intraligand (IL) π?π* transition in the electronic absorption spectra of 1 and 2 [?1 = 308 (1) and 316 nm (2)]. In the series of orthogonal model complexes 1?5 with linear oligo(p-phenylene-ethynylene) (OPE) spacers, ?C6H4(C≡CC6H4)n? (n = 1?5), a linear increase of the IL π?π* transition energy with the reciprocal of the intermetallic distance is theoretically predicted [?max = 1.99 ? 104 + 2.15 ? 105 (1/r) (S = 0) or ? = 2.01 ? 104 + 2.18 ? 105 (1/r) (S = 1)], which clearly indicates that the effective π-conjugation length increases with the number of phenylethyne repeating units. This is accompanied by an exponential decay of the antiferromagnetic coupling with the intermetallic distance [?J = 1.08 ? 103 exp(?0.31r)], which supports the ability of the extended π-conjugated OPEs to mediate the exchange interaction between the unpaired electrons of the two CuII centers with intermetallic distances in the range of 1.5?4.3 nm. Further developments may be then envisaged for this new family of oxamato-based dicopper(II) oligo-p-phenylethynophanes on the basis of the unique ligand capacity to act as a molecular antiferromagnetic wire.
7645-7657
10.1021/ic400754m
Dicopper(II) Metallacyclophanes with Oligo(p-phenylene-ethynylene) Spacers
http://dx.doi.org/10.1021/ic400754m
52
13
juillet 1, 2013
Inorganic Chemistry
Inorg. Chem.
0020-1669
María
Castellano
Francisco R.
Fortea-Pérez
Abdeslem
Bentama
Salah-Eddine
Stiriba
MiguelJulve
Francesc
Lloret
Giovanni
De Munno
Donatella
Armentano
YanglingLi
Rafael
Ruiz-García
JoanCano