Two different copper sites in hexakis(1-methyltetrazole)copper(II) bis(tetrafluoroborate)

EPR study of manganese(II) and copper(II) in single crystals of the spin-crossover complex hexakis(1-propyltetrazole)iron(2+) tetrafluoroborate(1-)

“…Analogous 1-methyltetrazole complexes have been shown to crystallize in the P2\jn group with two Cu sites of different local symmetries. 27 The formation of species of lower symmetry (diamagnetic phase II) must be caused by processes peculiar to the spin transition, involving some rearrangement of the molecules. Our results indicate that the crystallographic phase transformation is rapid near the magnetic transition temperature if the molecules are already in the low-spin state but is slow if both the spin state and crystal structure must change at the same time.…”

Disordered CuN6 Jahn−Teller Centers in Hexakis(1-methyltetrazole)copper(II) Tetrafluoroborate: A Temperature-Dependent X-ray Diffraction and EPR Study

“…Both the frequency of transitions between the energy minima and the populations of the differently elongated octahedra may be temperature dependent, and while EPR experiments can give information on both of these, X-ray diffraction experiments only show the population distribution. The above description certainly applies to Cu(mtz) 6 (BF 4 ) 2 , since the variable-temperature EPR measurements on powder and single-crystal samples 4 give a single nearly axially symmetric g tensor for both inequivalent CuN 6 centers, consistent with tetragonally elongated geometries, despite the low-symmetry crystalline fields at the copper atoms. Likewise the X-ray structural results for Cu(mtz) 6 (BF 4 ) 2 are also in accord with this description.…”

“…In addition, EPR experiments on pure and on copper-doped Zn(mtz) 6 (BF 4 ) 2 have been carried out, and a preliminary communication dealing with part of the EPR work has appeared previously. 4 There are several other literature examples of copper(II) complexes containing two crystallographically inequivalent Jahn-Teller-active centers, namely, Cu(hb(pz) 3 ) 2 5 [hb(pz) 3 ) hydrotris(pyrazolyl)borate], Cu(en) 3 Cl 2 ‚ 3 / 4 en 6 (en ) 1,2-ethylenediamine), Cu(Et-cPO) 2 7 [Et-cPO ) cyclopentadienyl)tris(diethyl phosphito-P)cobaltate ion], [Cu(H 2 O) 6 ](bs) 2 8 (bs ) benzenesulfonate), and very recently Cu(ttcn) 2 (BF 4 ) 2 ‚ 2MeCN 9 (ttcn ) trithiacyclononane). However, this appears to be the first example where an attempt has been made to understand the difference between the two centers in terms of the local-site strains arising from the crystal packing.…”

“…Therefore, in order to obtain more precise information about the Jahn−Teller states of the two centers, extensive temperature-dependent X-ray diffraction measurements were undertaken on the copper complex and the isomorphous zinc compound. In addition, EPR experiments on pure and on copper-doped Zn(mtz) 6 (BF 4 ) 2 have been carried out, and a preliminary communication dealing with part of the EPR work has appeared previously . There are several other literature examples of copper(II) complexes containing two crystallographically inequivalent Jahn−Teller-active centers, namely, Cu(hb(pz) 3 ) 2 [hb(pz) 3 = hydrotris(pyrazolyl)borate], Cu(en) 3 Cl 2 · 3 / 4 en (en = 1,2-ethylenediamine), Cu(Et-cPO) 2 [Et−cPO = cyclopentadienyl)tris(diethyl phosphito- P )cobaltate ion], [Cu(H 2 O) 6 ](bs) 2 (bs = benzenesulfonate), and very recently Cu(ttcn) 2 (BF 4 ) 2 · 2MeCN (ttcn = trithiacyclononane).…”

Electron paramagnetic resonance of penta-ammino copper fluoroborate: coexistence of isotropic and anisotropic spectra in tetragonal phase

“…The second component of the spectrum in the low temperature phase is an anisotropic pattern of a SQP fivecoordinated copper ion. In some cases it has been observed that iso-and anisotropic spectra coexist in Cu(II) six-coordinated complexes [9][10][11] even in monocrystals [12]. However, the temperature dependence of relative integral intensities of both components points to thermally activated processes.…”