High-Nuclearity 3d-4f Clusters as Enhanced Magnetic Coolers and MolecularMagnets. -The Co II /Co III (9:1) mixed compounds (III) and the Ni II compounds (V) are isostructural and crystallize in the monoclinic space group P21/m with Z = 2 (single crystal XRD). (IIIa) and (Va) exhibit the largest magnetocaloric effects among any known 3d-4f complexes, which is significant for their potential applications in magnetic cooling technology in the ultralow temperature range. Compounds (IIIb) and (Vb) display slow relaxation of the magnetization.

The long-sought-after crystal structure of Fe(tpa)(NCS)(2) (1, tpa = tris(2-pyridylmethyl)amine), an otherwise well-studied spin-crossover (SCO) complex, has been obtained, and its one-step, incomplete spin transition was correlated to its solid-state structures at different temperatures. Upon exposure to methanol vapor, single-crystal-to-single-crystal transformation of 1 to a new SCO compound, 2, formulated as {[Fe(tpa)(NCS)(2)] x [Fe(tpa)(NCS)(2) x CH(3)OH]}, occurs with a dramatic color change from yellow to red. Crystallographic studies revealed that the asymmetric unit of the structure of 2 contains two independent Fe(II) centers. Studies by magnetic measurements and Mossbauer spectroscopy revealed a two-step complete spin transition for compound 2, between LS-LS and HS-HS, via an unambiguous intermediate LS-HS phase; the two SCO centers of disparate spin states were resolved crystallographically. That a significant portion of the original crystal structure is maintained indicates that the present approach is a more subtle means of altering the properties associated with SCO phenomenon than by changing counteranions or crystallization using different solvents. Furthermore, the dramatic changes in crystal structure and SCO behaviors triggered by mere solvent sorption suggest that this approach is rather efficient in modifying and hopefully fine-tuning and optimizing properties of SCO compounds. Coupled with the aforementioned gentleness and subtlety, the present approach of heterogeneously introducing perturbations to pre-existing supramolecular arrays of SCO units is more conducive to systematic studies aiming at the discovery of new SCO systems and phenomenon toward their ultimate materials applications.

When p-aminothiophenol (PATP) is used as a probe molecule and adsorbs on silver and gold nanogaps, a significant change of relative SERS intensities can be observed. Our DFT calculations show that surface photocatalytic coupling reactions yield a new surface species of p,p'-dimercaptoazobenzene (DMAB) causing the significant change in the SERS spectra.

NNSFC[20825103, 20901064, 90922031, 2007CB815304, 21021061]; Fundamental Research Funds for the Central Universities[2010121016