Diastereoselective solid-state crossed photocycloaddition of olefins in a 3D Zn(ii) coordination polymer.

1,2-Bis(4-pyridyl)ethylene undergoes a photoinitiated [2+2] cross-cycloaddition reaction with allyl groups of allylmalonate in pores of a 3D metal-organic framework (MOF) [Zn2(H2O)2(Amal)2(bpe)] to produce a 3D MOF with a new topology.

Exploitation of knowledge databases in the synthesis of zinc(II) malonates with photo-sensitive and photo-insensitive N,N'-containing linkers.

Photoinitiated solid-state reactions are known to affect the physical properties of coordination polymers, such as fluorescence and sorption behaviour, and also afford extraordinary architectures (e.g. three-periodic structures with polyorganic ligands). However, the construction of novel photo-sensitive coordination polymers requires an understanding of the factors which govern the mutual disposition of reactive fragments. A series of zinc(II) malonate complexes with 1,2-bis(pyridin-4-yl)ethylene and its photo-insensitive analogues has been synthesized for the purpose of systematic analysis of their underlying nets and mutual disposition of N-donor ligands. The application of a big data-set analysis for the prediction of a variety of possible complex compositions, coordination environments and networks for a four-component system has been demonstrated for the first time. Seven of the nine compounds possess one of the highly probable topologies for their underlying nets; in addition, two novel closely related four-coordinated networks were obtained. Complexes containing 1,2-bis(pyridin-4-yl)ethylene and 1,2-bis(pyridin-4-yl)ethane form isoreticular compounds more readily than those with 4,4'-bipyridine and 1,2-bis(pyridin-4-yl)ethylene. The effects of the precursor, either zinc(II) nitrate or zinc(II) acetate, on the composition and dimensionality of the resulting architecture are discussed. For three of the four novel complexes containing 1,2-bis(pyridin-4-yl)ethylene, the single-crystal-to-single-crystal [2 + 2] cycloaddition reactions were carried out. UV irradiation of these crystals afforded either the 0D→1D or the 3D→3D transformations, with and without network changes. One of the two 3D→3D transformations was accompanied by solvent (H2O) cleavage.

Temperature-dependent zero-field splitting in a copper(II) dimer studied by EPR.

We report on the synthesis and temperature-dependent magnetic properties observed in an exchange-coupled copper(II) dimer using X/Q-band Electron Paramagnetic Resonance (EPR) spectroscopy (9/34 GHz). It has been found that the zero-field splitting (D) in the dimer changes gradually by a factor close to two in the temperature range from T = 50 to 300 K. X-ray diffraction data show that this dimer consists of two five-coordinated copper ions, one of which has a highly asymmetric geometry intermediate between square pyramid and trigonal bipyramid. The copper-copper distance in the dimer is temperature-independent, whereas the degree of trigonality in an asymmetric unit decreases as the temperature is lowered. Therefore we suppose that the observed dependence D(T) originates from the interplay of different exchange interaction pathways driven by these thermal changes. Magnetic susceptibility measurements reveal weak ferromagnetic interactions, whose anisotropic parts should indeed be very sensitive to the subtle changes in the geometry and may result in apparent D(T). Apart from being a very unusual example of magneto-structural correlations, this and similar dimeric systems can be considered as an interesting type of new materials exhibiting strongly temperature-dependent magnetic properties.