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While ionothermal synthesis using deep eutectic solvents based on the combination of choline chloride and urea derivatives has been widely explored for metal–organic framework (MOF) synthesis, the alternative approach consisting in using urea derivatives on their own as solvents, albeit promising, remains comparatively underemployed. This highlight article aims to review the field of urothermal synthesis, covering the state of the art of this approach and its potential development. The use of e-urea (2-imidazolidinone, ethyleneurea), the most extensively employed species in this context, is detailed, showing its ability to play diverse roles in MOF construction. Beyond its role as solvent and soft regulator of solution acidity, it can be present in the pore or as a ligand, most commonly in a bridging mode with divalent metal cations via coordination of the carbonyl group assisted by hydrogen bonding of the NH moieties, or yield ethylenediamine as a decomposition product incorporated in the MOF. Furthermore, urothermal synthesis has demonstrated potential for the preparation of chiral architectures and their enantio-enrichment. Alternatives to e-urea in pure form or as a hemihydrate are also presented. The combination of e-urea with other organic solvents or the use of co-ligands have been shown to modulate its tendency to act as a bridging ligand, while fully N-alkylated urea derivatives represent appealing solvents. They have low melting point or can even be liquid at room temperature, making them media of choice, prone to ligation to the metal center in a terminal fashion given the absence of hydrogen bonding donor, favoring removal towards activation. The structures of the materials reported under urothermal conditions are described as well as their properties and applications. [ABSTRACT FROM AUTHOR]

New iron and cobalt bis(dithiolene) complexes [M(3cbdt)2] (3cbdt = 3-cyanobenzene-1,2-dithiolate) were prepared as tetraphenylphosphonium (Ph4P+) salts for Fe in the monoanionic state and for Co in both the dianionic and monoanionic states: (Ph4P)2[Fe(III)(3cbdt)2]2 (1); (Ph4P)2[Co(III)(3cbdt)2]2 (2); (Ph4P)2[Co(II)(3cbdt)2] (3). These compounds were characterized by single-crystal X-ray diffraction, cyclic voltammetry, EPR, and static magnetic susceptibility. Their properties are discussed in comparison with the corresponding complexes based on the isomer ligand 4-cyanobenzene-1,2-dithiolate (4cbdt) and 4,5-cyanobenzene-1,2-dithiolate (dcbdt), previously described by us. The Fe(III) and the Co(III) compounds (1 and 2) are isostructural, crystallizing in the triclinic P 1 ¯ space group, with cis [M(III)(3cbdt)2] complexes dimerized in a trans fashion, and the transition metal (M = Fe, Co) has a distorted 4+1 square pyramidal coordination geometry. The Co(II) compound (3) crystallizes in the triclinic P 1 ¯ space group, with the unit cell containing one cis and three trans inequivalent [Co(II)(3cbdt)2] complexes with the transition metal (Co) and having a square planar coordination geometry. The Fe(III) complex (1) is EPR-silent, and the static magnetic susceptibility shows a temperature dependence typical of dimers of antiferromagnetically coupled S = 3/2 spins with −J/kB = 233.6 K and g = 1.8. Static magnetic susceptibility measurements of compound (3) show that this Co(II) complex is paramagnetic, corresponding to an S = ½ state with g = 2, in agreement with EPR spectra showing in solid state a hyperfine structure typical of the I(59Co) = 7/2. Static susceptibility measurements of Co(III) complex (2) showed an increase in the paramagnetic susceptibility upon warming above 100 K, which is consistent with strong AFM coupling between dimerized S = 1 units with a constant −J/kB ~1286 K. [ABSTRACT FROM AUTHOR]

A green alternative approach to the chiral induction of a metal–organic framework (MOF) has been explored using the natural deep eutectic solvents (DES) proline : thymol (1 : 7) and menthol : thymol (1 : 1). These solvents have been successfully employed for the preparation of the MIL-103 MOF and lead to an enantioenrichment of the porous material when used in enantiopure form, as demonstrated by circular dichroism. [ABSTRACT FROM AUTHOR]

New nickel and copper bisdithiolene complexes were prepared as tetraphenylphosphonium (Ph4P+) salts, (Ph4P)n[M(3cbdt)2], [n = 1, 2; M = Ni, Cu; 3cbdt = 3-cyanobenzene-1,2-dithiolate]: (Ph4P)2[Ni(3cbdt)2] (1); Ph4P[Ni(3cbdt)2] (2); (Ph4P)2[Cu(3cbdt)2] (3); Ph4P[Cu(3cbdt)2] (4), and characterised by single crystal X-ray diffraction, cyclic voltammetry, EPR and static magnetic susceptibility for the paramagnetic species. These Cu and Ni complexes obtained as stable monoanionic and dianionic anions are the first members of this family of cyano benzene functionalized bisdithiolene transition metal complexes, opening the way to the preparation of analogous compounds with other transition metals and their future use as building blocks for the preparation of molecular materials. Their properties are discussed in comparison with the corresponding complexes based on the 4-cyanobenzene-1,2-dithiolate (4cbdt) ligand previously described by us. The salts (Ph4P)n[M(3cbdt)2], [n = 1, 2; M = Ni, Cu] present the metal complexes always in a square-planar coordination geometry with a ligand trans configuration, but revealing a rich polymorphism. The Ni and Cu compounds are isostructural and occur as two polymorphs (α, β) with the exception of the salt of the monoanionic Ni complex, that was found only as the α-polymorph. The salt of the dianionic Ni complex was found to crystallise also with one acetonitrile molecule, when recrystallised from this solvent. The salts of monoanionic [Ni(3cbdt)2] and dianionic [Cu(3cbdt)2] complexes have been characterised by EPR and static magnetic susceptibility as paramagnetic S = 1/2 species. [ABSTRACT FROM AUTHOR]

Giant octahedral M32 coordination cages were prepared via self-assembly of sulfonylcalix[4]arene-supported tetranuclear M(II) clusters (M = Co, Ni) with hybrid linker based on tris(dipyrrinato)cobalt(III) complexes appended with peripherical carboxylic groups. Due to intrinsic and extrinsic porosity, the obtained solid-state supramolecular architectures demonstrated good performance as adsorbents for the separation of industrially important gases mixtures. [ABSTRACT FROM AUTHOR]