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 (ψ) 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 (ϕ) 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 = −J S1·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 (ψ = 0° and ϕ = 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 pdiphenylethyne (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 [λ1 = 308 (1) and 316 nm (2)]. In the series of orthogonal model complexes 1−5 with linear oligo(p-phenylene-ethynylene) (OPE) spacers, −C6H4(CCC6H4)n− (n = 1−5), a linear increase of the IL π−π* transition energy with the reciprocal of the intermetallic distance is theoretically predicted [νmax = 1.99 × 104 + 2.15 × 105 (1/r) (S = 0) or ν = 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.

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 (ψ) 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 (ϕ) 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 = −J S1·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 (ψ = 0° and ϕ = 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 pdiphenylethyne (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 [λ1 = 308 (1) and 316 nm (2)]. In the series of orthogonal model complexes 1−5 with linear oligo(p-phenylene-ethynylene) (OPE) spacers, −C6H4(CCC6H4)n− (n = 1−5), a linear increase of the IL π−π* transition energy with the reciprocal of the intermetallic distance is theoretically predicted [νmax = 1.99 × 104 + 2.15 × 105 (1/r) (S = 0) or ν = 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 × 10 3 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.

### Dicopper(II)Metallacyclophanes with Oligo(p‑phenylene-ethynylene) Spacers: Experimental Foundations and Theoretical Predictions on Potential Molecular Magnetic Wires

#####
*DE MUNNO, Giovanni;ARMENTANO, Donatella;*

##### 2013-01-01

#### Abstract

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 (ψ) 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 (ϕ) 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 = −J S1·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 (ψ = 0° and ϕ = 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 pdiphenylethyne (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 [λ1 = 308 (1) and 316 nm (2)]. In the series of orthogonal model complexes 1−5 with linear oligo(p-phenylene-ethynylene) (OPE) spacers, −C6H4(CCC6H4)n− (n = 1−5), a linear increase of the IL π−π* transition energy with the reciprocal of the intermetallic distance is theoretically predicted [νmax = 1.99 × 104 + 2.15 × 105 (1/r) (S = 0) or ν = 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.