The importance of 3d/4f-metal cluster chemistry is outlined, and the employment of 2-pyridyl ketone- and 2-pyridyl oxime-based ligands for the preparation of low-nuclearity NiII/LnIII complexes (Ln = lanthanide) is reviewed. The synthetic utility of the “metal complexes as ligands” and “one-pot” approaches is critically discussed. The small nuclearity of the products permits the in-depth analysis of their magnetic properties.

The incorporation of spin crossover (SCO) properties into metal–organic frameworks (MOFs) has led to an appealing subclass of multifunctional MOFs. Because temperature is the most common way to manipulate the SCO phenomenon, the spin state of relevant complexes is conveniently monitored by variable‐temperature magnetic susceptibility (χMT) measurements. Other physical and spectroscopic techniques may also monitor the SCO behavior. In this context, the present work focuses on the use of variable‐temperature micro‐Raman spectroscopy. More specifically, the SCO behavior of the two‐dimensional Hofmann‐type MOF [FeII(2‐mpz)2Ni(CN)4], (2‐mpz = 2‐methylpyrazine), in the form of both bulk microcrystalline powder and nanoparticles is in depth analyzed via temperature‐dependent Raman spectroscopy. Magnetic susceptibility measurements were used in order to benchmark the vibrational spectroscopic ones. A brief introduction on the basic synthetic features of the samples and the morphological characteristics of representative samples are described, while the detailed syntheses of the MOF compounds in the microscale and the nanoscale were recently comprehensively addressed. It is unambiguously revealed for the samples in the different particle sizes that the SCO characteristics, such as Tc values, hysteretic behavior, and high spin (HS) population curves as a function of temperature, derived from Raman measurements are in close comparison with those of the magnetic susceptibility. In addition, spectroscopic analysis in the high‐ and low‐wavenumber regions suggests the 2D network structure of the specific compound and reveals the alterations at molecular level associated with the HS and low spin (LS) states. The significance of Raman spectroscopy for the study of SCO materials is demonstrated, because the technique offers combined structural characterization and detailed study of the transition.

The diamagnetic two-dimensional Hofmann-type metal–organic framework [ZnII(2-mpz)2Ni­(CN)4] has been successfully synthesized along with its isostructural hysteretic spin-crossover FeII analogue in the form of both bulk microcrystalline powder and nanoparticles. Detailed atomic force microscopy topographic study revealed a nanogrowth relationship between the height and length of the nanoparticle.

The use of methyl 2-pyridyl ketone oxime (mpkoH) for the synthesis of Ni(II)/Ln(III) (Ln = lanthanide) complexes, using "one-pot" reactions in the absence of an external base, is described. Depending on the reaction and crystallization conditions employed, two families of complexes have been obtained. The first family consists of true heterometallic species and involves complexes [NiLn(mpko)(3)(mpkoH)(3)](ClO(4))(2), where Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er. The second family contains the pseudo heterometallic complexes [Ni(mpkoH)(3)](2)[Ln(NO(3))(6)](ClO(4)), where Ln = La, Ce, Pr, Nd and Sm. The crystal structures of [NiCe(mpko)(3)(mpkoH)(3)](ClO(4))(2) (1), [NiDy(mpko)(3)(mpkoH)(3)](ClO(4))(2) (8) and [Ni(mpkoH)(3)](2)[La(NO(3))(6)](ClO(4)) (11) have been determined by single-crystal, X-ray crystallography. Complexes 1·1.2MeOH·0.6H(2)O and 8·1.2MeOH·0.6H(2)O crystallise in the monoclinic space group P2(1)/a and are isomorphous; there are two crystallographically independent cations in the unit cell, but their interatomic distances and angles differ little. The Ni(II) and Ln(III) ions are bridged by three oximate groups belonging to the η(1):η(1):η(1):μ mpko(-) ligands. The Ni(II) centre is octahedrally coordinated by the six nitrogen atoms of the mpko(-) ligands in a facial arrangement. The Ln(III) centre is bound to an (O(oximate))(3)N(6) set of donor atoms, the nitrogen atoms belonging to the three N,N'-bidentate chelating mpkoH ligands. The stereochemistry of the Ln(III) atoms has been evaluated by means of continuous shape measures (CShM). The two crystallographically independent Ce(III) atoms in 1 have tricapped trigonal prismatic and capped square antiprismatic coordination geometries, while the polyhedra of the Dy(III) atoms in 8 are both close to a tricapped trigonal prism. The octahedral Ni(II) atoms in 11 are both facially bound to a N(6) set of donor atoms from three N,N'-bidentate chelating mpkoH ligands, while the 12-coordinate La(III) centre in [La(NO(3))(6)](3-) is coordinated by six bidentate chelating nitrato groups. Variable-temperature, solid state dc magnetic susceptibility studies were carried out on complexes 2, 6, 7 and 8. The dc susceptibility data for 6 in the 2.0-300 K range have been fit to a model with one J value, revealing an antiferromagnetic Ni(II)···Gd(III) exchange interaction [J = -1.1 cm(-1) based on H = -J (Ŝ(Ni)·Ŝ(Gd))]. Antiferromagnetic Ni(II)···Pr(III), Ni(II)···Tb(III) and Ni(II)···Dy(III) exchange interactions have also been suggested for 2, 7 and 8, respectively. The combined work demonstrates the usefulness of mpko(-) in the preparation of interesting Ni(II)/Ln(III) compounds, without requiring the presence of external base and ancillary organic ligands.

Metal-ion mediated reactions of 2-pyridinealdoxime and hexafluorophosphate lead to Zn(II) complexes containing picolinic acid, picolinamide and monofluorophosphate (-2) as ligands.

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The use of 2-pyridinealdoxime (paoH), methyl 2-pyridyl ketone oxime (mepaoH), phenyl 2-pyridyl ketone oxime (phpaoH) and pyridine-2-amidoxime (NHpaoH) for the synthesis of dinuclear Co/Dy complexes is described in the absence or presence of an external base. Complexes [CoDy(pao)(NO)] (1), [CoDy(mepao)(NO)] (2), [CoDy(phpao)(NO)] (3) and [CoDy(NHpao)(NO)]·3MeOH (4·3MeOH) have been isolated and their structures have been determined by single-crystal X-ray crystallography. The complexes crystallize in non-centrosymmetric (2, 3) or centrosymmetric (1, 4·3MeOH) trigonal space groups and form a family of triply-oximate bridged dinuclear Co(iii)-Dy(iii) complexes. The crystals of 1, 3 and 4·3MeOH contain mixtures of Δ and Λ enantiomers, whereas complex 2 is enantiomerically pure (Λ). A 3-fold crystallographic axis (C) passes through two metal ions in all complexes. The low-spin Co and Dy ions are bridged by three oximate groups belonging to the η:η:η:μ 2-pyridyloximate ligands. The Co centre is octahedrally coordinated by the six nitrogen atoms of the deprotonated organic ligands in a facial arrangement. The Dy centre is bound to an O set of donor atoms, its coordination sphere being completed by three bidentate chelating nitrato groups. The coordination polyhedron around Dy in 1 is best described as the Johnson tricapped trigonal prism, while the coordination geometries of the Dy centres in 2, 3 and 4·3MeOH are best described as consisting of spherical tricapped trigonal prismatic coordination polyhedra. The spectroscopic data of the complexes are also reported and discussed in the infra-red region in terms of the coordination modes of the ligands involved. The magnetic properties of these complexes were studied between 300 and 1.8 K revealing mainly the depopulation of the Dym sublevels of the ground H state. The intrinsic magnetic anisotropy of the Dy centers is clearly observed by the non-superimposed magnetization (M) versus H/T data, but single-molecule magnet (SMM) properties were detected only for the mepao-containing complex 2. The origin of these properties in 2 is critically discussed and supported by computational studies.

The first use of the cyanoacetate ligand in 3d/4f-metal chemistry leads to {Fe2IIIM4III} (M = Dy, Gd, Y) coordination clusters with a squashed octahedral core structure; the DyIII compound exhibits slow relaxation of the magnetisation.