Elucidation of the Fe(III) Gallate Structure in Historical Iron Gall Ink.

Synthetic, structural, spectroscopic and aging studies conclusively show that the main colorant of historical iron gall ink (IGI) is an amorphous form of Fe(III) gallate·xH2O (x = ∼1.5-3.2). Comparisons between experimental samples and historical documents, including an 18th century hand-written manuscript by George Washington, by IR and Raman spectroscopy, XRD, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy confirm the relationship between the model and authentic samples. These studies settle controversy in the cultural heritage field, where an alternative structure for Fe(III) gallate has been commonly cited.

Synthesis and characterization of homo- and heterodinuclear M(II)-M'(III) (M(II) = Mn or Fe, M'(III) = Fe or Co) mixed-valence supramolecular pseudo-dimers. The effect of hydrogen bonding on spin state selection of M(II).

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.

Composition and particle size of superparamagnetic corrosion products in tap water.

Chemical analyses, magnetization, Mössbauer spectrum, and x-ray diffraction measurements were made on solids removed from tap water by means of membrane filters. The taps from which this water was obtained had previously been unused for prolonged periods of time. When these taps were reactivated and water was first drawn, it was observed that the quantity of coarse solids in the water gradually decreased with flow, while at the same time the quantity of fine solids gradually increased. The magnetization, Mössbauer spectra, and x-ray diffraction patterns of the solids showed the presence of a significant number of superparamagnetic particles of magnetite. In the temperature range of our measurements (77 K

A DFT computational study of spin crossover in iron(III) and iron(II) tripodal imidazole complexes. A comparison of experiment with calculations.

B3LYP* functionals were used to model the sixteen iron(II) (1A, LS and 5T, HS) and iron(III) (2T, LS and 6A, HS) complexes of the 1 : 3 Schiff base condensate of tris(2-aminoethyl)amine and imidazole-4-carboxaldehyde, H3L1, and its deprotonated forms, [H2L1]1-, [HL1]2-, and [L1]3-. This ligand system is unusual in that [FeH3L1]3+, [FeH3L1]2+ and [FeL1]- all exhibit a spin crossover between 100-300 K. This makes these complexes ideal for a hybrid DFT computational approach and provides an opportunity to refine the value of the exact exchange admixture parameter, c3, and to predict properties of partially protonated complexes that are not experimentally available. The accepted value of 0.20 is larger than the value of approximately 0.13 that was found to best reproduce experimental data in terms of spin state predictions. With iron(III) B3LYP calculations showed that all of the complexes were low spin at 298 K with the exception of [FeH3L1]3+ which is spin crossover in agreement with experimental results. It was also shown for iron(III) that the ligand field increased as the number of protons decreased. In contrast all of the iron(II) complexes were close to the spin crossover region regardless of protonation state. Experimental structures are fairly well modeled by this system in regard to the key structural indicators of spin state, which are the bite and trans angles. The calculated iron to nitrogen atom distances are always larger in the high spin form than the low spin form but all iron to nitrogen bond distances are larger than the experimental values. In general non-bonded interactions are not well modeled by this methodology.

Synthesis and characterization of a spin crossover iron(II)-iron(III) mixed valence supramolecular pseudo-dimer exhibiting chiral recognition, hydrogen bonding, and pi-pi interactions.

Reaction of iron(II) and the 3 : 1 Schiff base condensate of 5-methylpyrazole-3-carboxaldehyde and tris(2-aminoethyl)amine in air gives a pseudo-dimer complex with a triple helix structure made of Delta-Delta and Lambda-Lambda pairings of spin crossover iron(II) and low spin iron(III) cations that are held together by three pi-pi and hydrogen bonding interactions.

Synthesis and characterization of manganese(II) and iron(III) d5 tripodal imidazole complexes. Effect of oxidation state, protonation state and ligand conformation on coordination number and spin state.

The 1 : 3 Schiff base condensates of tris(2-aminoethyl)amine (tren) or tris(3-aminopropyl)amine (trpn) with 4-methyl-5-imidazolecarboxaldehyde, H3L1 and H3L2, respectively, were generated in situ and used to prepare complexes with manganese(II) and iron(III). The resultant complexes, [MnH3L1](ClO4)2, [MnH3L1](ClO4)2.EtOH.H2O, [MnH3L2](ClO4)2, [FeH3L1](ClO4)3.1.5(EtOH) and [FeHL1](I3) (0.525)(I)(0.475).2.625H2O, have been characterized by EA, IR, ES MS, variable temperature magnetic susceptibility, X-ray crystallography, and Mössbauer spectroscopy for the iron complexes. The three manganese(II) complexes are high spin with [MnH3L2](ClO4)2 exhibiting coordination number seven while the others are six coordinate. [FeH3L1](ClO4)3.1.5(EtOH) has two iron sites, a seven coordinate and a pseudo seven coordinate site. The complex is high spin at room temperature but exhibits a magnetic moment that decreases with temperature corresponding to conversion of one of the sites to low spin. [FeHL1](I3) (0.525)(I)(0.475).2.625H2O is low spin even at room temperature. In the present complexes the apical nitrogen atom, N(ap), of the tripodal ligand is pyramidal and directed toward the metal atom. The data show that the M-N(ap) distance decreases as the oxidation state of the metal increases, as the number of bound imidazole protons on the ligand increases, and as the number of carbon atoms in the backbone of the ligand (tren vs. trpn) increases. In a limiting sense, short M-N(ap) distances result in high spin seven coordinate mono capped octahedral complexes and long M-N(ap) distances result in low spin six coordinate octahedral complexes.

A DFT computational study of spin crossover in iron(III) and iron(II) tripodal imidazole complexes. A comparison of experiment with calculations.

B3LYP* functionals were used to model the sixteen iron(II) (1A, LS and 5T, HS) and iron(III) (2T, LS and 6A, HS) complexes of the 1:3 Schiff base condensate of tris(2-aminoethyl)amine and imidazole-4-carboxaldehyde, H3L1, and its deprotonated forms, [H2L1]1-, [HL1]2-, and [L1]3-. This ligand system is unusual in that [FeH3L1]3+, [FeH3L1]2+ and [FeL1]- all exhibit a spin crossover between 100-300 K. This makes these complexes ideal for a hybrid DFT computational approach and provides an opportunity to refine the value of the exact exchange admixture parameter, c3, and to predict properties of partially protonated complexes that are not experimentally available. The accepted value of 0.20 is larger than the value of approximately 0.13 that was found to best reproduce experimental data in terms of spin state predictions. With iron(III) B3LYP calculations showed that all of the complexes were low spin at 298 K with the exception of [FeH3L1]3+ which is spin crossover in agreement with experimental results. It was also shown for iron(III) that the ligand field increased as the number of protons decreased. In contrast all of the iron(II) complexes were close to the spin crossover region regardless of protonation state. Experimental structures are fairly well modeled by this system in regard to the key structural indicators of spin state, which are the bite and trans angles. The calculated iron to nitrogen atom distances are always larger in the high spin form than the low spin form but all iron to nitrogen bond distances are larger than the experimental values. In general non-bonded interactions are not well modeled by this methodology.

Synthesis and characterization of seven-coordinate tripodal imidazole complexes of iron(II) and manganese(II).

The iron(II) and manganese(II) complexes of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 1-methyl-2-imidazolecarbaldehyde and the manganese(II) complex of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 4-imidazolecarbaldehyde are high-spin mono capped octahedral seven-coordinate complexes with a short, approximately 2.44 è, metal to apical nitrogen bond.

Proton control of oxidation and spin state in a series of iron tripodal imidazole complexes.

Reaction of iron salts with three tripodal imidazole ligands, H(3)(1), H(3)(2), H(3)(3), formed from the condensation of tris(2-aminoethyl)amine (tren) with 3 equiv of an imidazole carboxaldehyde yielded eight new cationic iron(III) and iron(II), [FeH(3)L](3+or2+), and neutral iron(III), FeL, complexes. All complexes were characterized by EA(CHN), IR, UV, Mössbauer, mass spectral techniques and cyclic voltammetry. Structures of three of the complexes, Fe(2).3H(2)O (C(18)H(27)FeN(10)O(3), a = b = c = 20.2707(5), cubic, I3d, Z = 16), Fe(3).4.5H(2)O (C(18)H(30)FeN(10)O(4.5), a = 20.9986(10), b = 11.7098(5), c = 19.9405(9), beta = 109.141(1), monoclinic, P2(1)/c), Z = 8), and [FeH(3)(3)](ClO(4))(2).H(2)O (C(18)H(26)Cl(2)FeN(10)O(9), a = 9.4848(4), b = 23.2354(9), c = 12.2048(5), beta = 111.147(1) degrees, monoclinic, P2(1)/n, Z = 4) were determined at 100 K. The structures are similar to one another and feature an octahedral iron with facial coordination of imidazoles and imine nitrogen atoms. The iron(III) complexes of the deprotonated ligands, Fe(1), Fe(2), and Fe(3), are low-spin while the protonated iron(III) cationic complexes, [FeH(3)(1)](ClO(4))(3) and [FeH(3)(2)](ClO(4))(3), are high-spin and spin-crossover, respectively. The iron(II) cationic complexes, [FeH(3)(1)]S(4)O(6), [FeH(3)(2)](ClO(4))(2), [FeH(3)(3)](ClO(4))(2), and [FeH(3)(3)][B(C(6)H(5))(4)](2) exhibit spin-crossover behavior. Cyclic voltammetric measurements on the series of complexes show that complete deprotonation of the ligands produces a negative shift in the Fe(III)/Fe(II) reduction potential of 981 mV on average. Deprotonation in air of either cationic iron(II) or iron(III) complexes, [FeH(3)L](3+or2+), yields the neutral iron(III) complex, FeL. The process is reversible for Fe(3), where protonation of Fe(3) yields [FeH(3)(3)](2+).