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Poly{[μ‐(2,5‐dicarboxypyrazine‐ 3,6‐dicarboxylato)‐ trans ‐diaquairon(II) dihydrate]}, a Member of a New Class of Quasi‐Linear Chain Compounds. Preparation, Structure, and Magnetic Susceptibility
Author(s) -
Marioni PierreAlain,
SteeckliEvans Helen,
Marty Werner,
Güdel HansUlrich,
Williams Alan F.
Publication year - 1986
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19860690507
Subject(s) - chemistry , crystallography , pyrazine , magnetic susceptibility , monoclinic crystal system , steric effects , antiferromagnetism , octahedron , crystal structure , ligand (biochemistry) , molecule , stereochemistry , denticity , bridging ligand , biochemistry , physics , receptor , organic chemistry , condensed matter physics
Abstract The title compound 1 , {[Fe(H 2 pztc)(H 2 O) 2 ] · 2 H 2 O} ∞ , has been prepared from pyrazinetetracarboxylic acid (H 4 pztc) and Fe(II) salt in H 2 O. It crystallizes in the monoclinic space group P 2 1 / a with cell parameters a = 13.56(1) Å, b = 7.17(1) Å, c = 6.48(1) Å, β = 101.0(2)°, V = 618.4 Å 3 . The molecules form infinite parallel chains with bis(bidentate) coordination (through N and O) of the bridging pyrazine ligands. Two trans ‐COOH groups of the ligand remain uncoordinated, and two trans ‐H 2 O ligands complete a pseudo‐octahedral Fe(II) coordination which is distorted by the steric effect of the free COOH groups. The parallel polynuclear chains are linked through an extended network of H‐bonds involving the COO functions of the bridging ligand and the coordinated and lattice H 2 O molecules. Mössbauer and magnetic‐susceptibility data suggest normal paramagnetic behaviour of high‐spin Fe 2+ . An observed drop below 15 K in effective magnetic moment for 1 was attributed to temperature‐dependent population changes of the levels of the ground state 5 Γ, and not to antiferromagnetic coupling ( J < 1 cm −1 ). This result establishes that the obvious potential magnetic exchange pathway through the pyrazine bridges is inefficient, and this may be attributed, in part, to the high planarity of Fe(H 2 pztc) moieties.