The future use of single-molecule magnets in applications will require the ability to control and manipulate the spin state and magnetization of the magnets by external means. There are different approaches to this control, one being the modification of the magnets by adsorption of small ligand molecules. In this paper we use iron phthalocyanine supported by an Au(111) surface as a model compound and demonstrate, using x-ray photoelectron spectroscopy and density functional theory, that the spin state of the molecule can be tuned to different values (S ∼ 0, [Formula: see text], 1) by adsorption of ammonia, pyridine, carbon monoxide or nitric oxide on the iron ion. The interaction also leads to electronic decoupling of the iron phthalocyanine from the Au(111) support.

Considerable interest in calcite crystallization has prompted many studies on organic molecule adsorption. However, each study has explored only a few compounds, using different methods and conditions, so it is difficult to combine the results into a general model that describes the fundamental mechanisms. Our goal was to develop a comprehensive adsorption model from the behavior of a range of organic compounds by exploring how common functional groups interact with calcite and the effects of various side groups and hydrogen on adsorption. We used density functional theory, with semiempirical dispersion corrections (DFT-D2), to determine adsorption energy on calcite {10.4} for nonpolar (benzene, ethane, and carbon dioxide) and oxygen containing polar molecules (water, methanol, ethanol, phenol, formic acid, acetic acid, propanoic acid, benzoic acid, formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, dimethyl ether, acetone, and furan). From the adsorption energies, within the transition state theory approximation, we derived desorption temperature for each molecule. Then we used X-ray photoelectron spectroscopy (XPS) to determine the desorption temperature for four representative molecules and compared the experimental results with those predicted. Carboxylic acids (R-COOH) adsorb more strongly than water and alcohols (R−OH), which in turn adsorb more strongly than the aldehydes (R-CHO). Attachment of a hydrogen atom or a side group changes adsorption behavior for hydroxyl and aldehyde functional groups but does not affect the carboxyl functional group significantly.

Zinc-protoporphyrin, adsorbed on the rutile TiO(2)(110) surface, has been studied using photoemission spectroscopy and near-edge absorption fine structure spectroscopy to deduce the nature of the molecule-surface bonding and the chemical environment of the central metal atom. To overcome the difficulties associated with sublimation of the porphyrin molecules, samples were prepared in situ using ultrahigh vacuum electrospray deposition, a technique which facilitates the deposition of nonvolatile and fragile molecules. Monolayers of Zn protoporphyrin are found to bond to the surface via the oxygen atoms of the deprotonated carboxyl groups. The molecules initially lie largely parallel to the surface, reorienting to an upright geometry as the coverage is increased up to a monolayer. For those molecules directly chemisorbed to the surface, the interaction is sufficiently strong to pull the central metal atom out of the molecule.

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The interaction between monolayers of iron phthalocyanine on a Au(111) support and carbon monoxide and nitric oxide is studied by X-ray photoelectron spectroscopy and density functional theory calculations. We find several carbon monoxide and nitric oxide adsorbate species, and in particular species that bind to the iron ions of the phthalocyanine compound. The formation of phthalocyanine carbonyl and nitrosyl complexes leads to a redistribution of the electrons in the iron 3d levels resulting in a change of the spin state. Further, the adsorption results in an electronic decoupling of the iron phthalocyanine adsorbates from the substrate. The extent of the spin change and adsorbate–substrate decoupling depends on which ligand is used. The X-ray photoelectron spectroscopy results suggest that a covalent bond is formed between the NO and CO adsorbates and the FePc iron ion, and that the NO and CO valence states hybridize with metal ion d states. The density functional theory calculations show that CO adsorbs in a linear configuration, while NO adsorption assumes a tilted geometry.

The adsorption of ammonia on Au(111)-supported monolayers of iron phthalocyanine has been investigated by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and density functional theory calculations. The ammonia-induced changes of the x-ray photoemission lines show that a dative bond is formed between ammonia and the iron center of the phthalocyanine molecules, and that the local spin on the iron atom is quenched. This is confirmed by density functional theory, which also shows that the bond between the iron center of the metalorganic complex and the Au (111) substrate is weakened upon adsorption of ammonia. The experimental results further show that additional adsorption sites exist for ammonia on the iron phthalocyanine monolayer.

Sulfur and nitrogen are two common constituents of natural and synthetic organic molecules, especially in systems where organisms play a role. There is evidence in the literature that nitrogen and sulfur containing functional groups have an influence on adsorption of organic molecules to calcite surfaces. The purpose of this work was to investigate the interaction of these functional groups with CaCO3 and to explore how adsorption is affected by various side groups and the H atom. First, we used density functional theory with semiempirical dispersion corrections (DFT-D2) to determine the energy of adsorption on the dominant calcite face, {10.4} for molecules containing nitrogen (ammonia, methylamine, ethylamine, aniline, hydrogen cyanide, acetonitrile, propionitrile, benzonitrile, dimethylamine, pyrrole, trimethylamine, and pyridine) and sulfur (hydrogen sulfide, methanethiol, ethanethiol, thiophenol, dimethyl sulfide, and thiophene). Second, based on the determined adsorption energies, we predicted desorption temperature for each molecule within the transition state theory approximation. Finally, we used X-ray photoelectron spectroscopy (XPS) to determine the desorption temperature for four molecules for comparison with the predicted values. Our results show that ammonia and primary amines (R−NH2) adsorb more strongly than nitriles (R−CN) and hydrogen sulfide and thiols (R−SH). On average, the adsorption energy of nitriles is slightly higher than hydrogen sulfide and thiols. Attachment of side groups or a H atom changes the strength of the surface–molecule interactions and significantly affects the adsorption behavior of all three functional groups.

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