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Reaction of H3L1, the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3-carboxaldehyde, with manganese(ii)perchlorate or iron(ii)tetrafluoroborate results in the isolation of [MH3L1]X2(M = Mn and X = ClO4and M = Fe and X = BF4). These complexes are high spin d5and d6, respectively, as inferred from the long M–N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and Mössbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH3L1]2+with three equivalents of potassium hydroxide produced [CoL1]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH3L1](BF4)2with 1.5 equivalents of potassium hydroxide to give {[FeH1.5L1](BF4)}2or by the metathesis reaction of [FeH2L1][FeHL1](ClO4)2with sodium hexafluorophosphate to give [FeH3L1][FeL1](PF6)2. The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal xray diffraction and Mössbauer spectroscopy. The iron(iii) atom is low spin while the iron(ii) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1 : 1 reaction of [FeH3L1](BF4)2or [MnH3L1](ClO4)2with [CoL1]. [MH3L1][CoL1](X)2(M = Fe and X = BF4or M = Mn and X = ClO4), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and Mössbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(ii) and manganese(ii), respectively. DFT calculations demonstrate that the spin state of the iron(ii) atom in {[FeH3L1][FeL1]}2+changes from high spin to low spin as the iron(ii)-iron(iii) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(ii)-Npyrazolebond distances. [ABSTRACT FROM AUTHOR]

Reaction of H(3)L(1), the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3-carboxaldehyde, with manganese(II)perchlorate or iron(II)tetrafluoroborate results in the isolation of [MH(3)L(1)]X(2) (M = Mn and X = ClO(4) and M = Fe and X = BF(4)). These complexes are high spin d(5) and d(6), respectively, as inferred from the long M-N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and Mössbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH(3)L(1)](2+) with three equivalents of potassium hydroxide produced [CoL(1)]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH(3)L(1)](BF(4))(2) with 1.5 equivalents of potassium hydroxide to give {[FeH(1.5)L(1)](BF(4))}(2) or by the metathesis reaction of [FeH(2)L(1)][FeHL(1)](ClO(4))(2) with sodium hexafluorophosphate to give [FeH(3)L(1)][FeL(1)](PF(6))(2). The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal x-ray diffraction and Mössbauer spectroscopy. The iron(III) atom is low spin while the iron(II) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1:1 reaction of [FeH(3)L(1)](BF(4))(2) or [MnH(3)L(1)](ClO(4))(2) with [CoL(1)]. [MH(3)L(1)][CoL(1)](X)(2) (M = Fe and X = BF(4) or M = Mn and X = ClO(4)), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and Mössbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(II) and manganese(II), respectively. DFT calculations demonstrate that the spin state of the iron(II) atom in {[FeH(3)L(1)][FeL(1)]}(2+) changes from high spin to low spin as the iron(II)-iron(III) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(II)-N(pyrazole) bond distances.