ja943960s_si_001.html (0.59 kB)
Download fileNovel Hybrid Spin Systems of 7,7‘,8,8‘-Tetracyanoquinodimethane (TCNQ) Radical Anions and 4-Amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (abpt). Crystal Structure of [Fe(abpt)2(TCNQ)2] at 298 and 100 K, Mössbauer Spectroscopy, Magnetic Properties, and Infrared Spectroscopy of the Series [MII(abpt)2(TCNQ)2] (M = Mn, Fe, Co, Ni, Cu, Zn)
dataset
posted on 06.03.1996, 00:00 by Paul J. Kunkeler, Petra J. van Koningsbruggen, Joost P. Cornelissen, André N. van der Horst, Adri M. van der Kraan, Anthony L. Spek, Jaap G. Haasnoot, Jan ReedijkThe compound
[Fe(abpt)2(TCNQ)2], where TCNQ is
the radical anion 7,7‘,8,8‘-tetracyanoquinodimethane
and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, is an
Fe(II) complex containing coordinated radical anions
which undergoes a thermally induced spin-crossover with
Tc = 280 K. Variable-temperature magnetic
susceptibility
(7−460 K) and 57Fe Mössbauer spectroscopy data
give evidence for a complete S = 2 (high-spin) ↔
S = 0 (low-spin) transition, taking place gradually, without hysteresis. The
X-ray structure has been determined at 298 K
(1)
and 100 K (2). The compound crystallizes in the
triclinic space group P1̄ with one molecule in the unit
cell of
dimensions a = 9.277(2) Å, b =
9.876(3) Å, c = 12.272(2) Å, α =
69.52(2)°, β = 86.92(2)°, and γ =
81.73(2)°
for 1 and a = 9.236(2) Å, b
= 9.684(1) Å, c = 12.137(2) Å, α =
69.26(1)°, β = 87.53(2)°, and γ =
82.38(1)° for
2. Two abpt ligands coordinating via
pyridyl-N1A and triazole-N1 are in the equatorial positions.
Fe−N1 and
Fe−N1A distances are 2.08(1) and 2.12(1) Å for
1 and 2.00(2) and 2.02(1) Å for 2,
respectively. TCNQ molecules
coordinate axially at remarkably short distances
i.e., Fe−N1T = 2.16(1) Å for
1 and 1.93(1) Å for 2. The
TCNQ
molecules are stacked in pairs yielding diamagnetic entities. The
FT-IR spectra (100−300 K) show that the TCNQ
νCN vibrations are a fingerprint for the different spin
states. In the series of the isostructural
[MII(abpt)2(TCNQ)2]
(M = Mn, Fe, Co, Ni, Cu, Zn) compounds, the νCN
absorptions show a shift to higher frequencies as a function
of
the crystal field stabilization energy. Above
Tc, the Cu(II)-doped Fe(II) species
shows a broad signal with g⊥ =
2.09 and g∥ = 2.25 and hyperfine structure
(A∥ = 180 G). At
Tc and below, the spectrum becomes better
resolved
and now shows superhyperfine structure (AN∥
= 16 G; nine lines). Above Tc, the
Mn(II)-doped Fe(II) compound
shows a very broad signal at g = 2.00. The spectrum
sharpens at Tc to give a clearly resolved
spectrum corresponding
to a magnetically isolated Mn(II) ion in a tetragonal environment.
The signal is split by the zero-field splitting,
yielding major signals at g = 1.6 and g = 5.5
and six hyperfine lines (A∥ = 80 G) that are
clearly visible on both
signals.