Inorganics — Open Access Journal

Molecular magnetic resonance imaging (MRI) provides information non-invasively at cellular and molecular levels, for both early diagnosis and monitoring therapeutic follow-up. This imaging technique requires the development of a new class of contrast agents, which signal changes (typically becomes enhanced) when in presence of the cellular or molecular process to be evaluated. Even if molecular MRI has had a prominent role in the advances in medicine over the past two decades, the large majority of the developed probes to date are still in preclinical level, or eventually in phase I or II clinical trials. The development of novel imaging probes is an emergent active research domain. This review focuses on gadolinium-based specific-targeted contrast agents, providing rational design considerations and examples of the strategies recently reported in the literature. Full article

The potential of fluorolytic sol–gel synthesis for a wide variety of applications in the field of optical materials is reviewed. Based on the fluorolytic sol–gel synthesis of nanometal fluorides, sols of complex fluorometalates have become available that exhibit superior optical properties over known classical binary metal fluorides as, for instance, magnesium fluoride, calcium fluoride, or strontium fluoride, respectively. The synthesis of transparent sols of magnesium fluoroaluminates of the general composition Mg_xAlF_y, and fluoroperovskites, [K_1−xNa_x]MgF₃, is reported. Antireflective coatings fabricated from MgF₂, CaF₂, Mg_xAlF_y, and [K_1−xNa_x]MgF₃ sols and their relevant properties are comprehensively described. Especially the heavier alkaline earth metal fluorides and the fluorperovskites crystallizing in a cubic crystal structure are excellent hosts for rare earth (RE) metals. Thus, the second chapter reflects the synthesis approach and the properties of luminescent systems based on RE-doped alkaline earth metal fluorides and [K_1−xNa_x]MgF₃ phases. Full article

trans-Platinum complexes have been the landmark in unconventional drugs prompting the development of innovative structures that might exhibit chemical and biological profiles different to cisplatin. Iodido complexes signaled a new turning point in the platinum drug design field when their cytotoxicity was reevaluated and reported. In this new study, we have synthesized and evaluated diodidoplatinum complexes trans-[PtI₂(amine)(pyridine)] bearing aliphatic amines (isopropylamine and methylamine) and pyridines in trans configuration. X-ray diffraction data support the structural characterization. Their cytotoxicity has been evaluated in tumor cell lines such as SAOS-2, A375, T-47D, and HCT116. Moreover, we report their solution behavior and reactivity with biological models. Ultraviolet-a (UVA) irradiation induces an increase in their reactivity towards model nucleobase 5′-GMP in early stages, and promotes the release of the pyridine ligand (spectator ligand) at longer reaction times. Density Functional calculations have been performed and the results are compared with our previous studies with other iodido derivatives. Full article

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body. Full article

Complexes displaying multiple bonds between different metal atoms have considerable synthetic potential because of the combination of the high electronic and coordinative unsaturation associated to multiple bonds with the intrinsic polarity of heterometallic bonds but their number is scarce and its chemistry has been relatively little explored. In a preliminary study, our attempted synthesis of the unsaturated hydrides [MoMCp(μ-H)(μ-PR₂)(CO)₅] from anions [MoMCp(μ-PR₂)(CO)₅]⁻ and (NH₄)PF₆ yielded instead the ammonia complexes [MoMCp(μ-H)(μ-PR₂)(CO)₅(NH₃)] (M = Mn, R = Ph; M = Re, R = Cy). We have now examined the structure and behaviour of the MoMn complex (Mo–Mn = 3.087(3) Å) and found that it easily dissociates NH₃ (this requiring some 40 kJ/mol, according to DFT calculations), to yield the undetectable unsaturated hydride [MoMnCp(μ-H)(μ-PPh₂)(CO)₅] (computed Mo–Mn = 2.796 Å), the latter readily adding simple donors L such as CNR (R = Xyl, p-C₆H₄OMe) and P(OMe)₃, to give the corresponding electron-precise derivatives [MoMnCp(μ-H)(μ-PPh₂)(CO)₅(L)]. Thus the ammonia complex eventually behaves as a synthetic equivalent of the unsaturated hydride [MoMnCp(μ-H)(μ-PPh₂)(CO)₅]. The isocyanide derivatives retained the stereochemistry of the parent complex (Mo–Mn = 3.0770(4) Å when R = Xyl) but a carbonyl rearrangement takes place in the reaction with phosphite to leave the entering ligand trans to the PPh₂ group, a position more favoured on steric grounds. Full article

By applying first principles density functional theory (DFT) methods, different metal fluorides and their surfaces have been characterized. One of the most investigated metal fluorides is AlF₃ in different polymorphs. Its chloride-doped analogon AlCl_xF_3−x (ACF) has recently attracted much attention due to its application in catalysis. After presenting a summary of different first-principle studies on the bulk and surface properties of different main group fluorides, we will revisit the problem of the stability of different $\alpha$-AlF₃ surfaces and extend the investigation to chloride-doped counterparts to simulate the surface properties of amorphous ACF. For each material, we have considered ten different surface cuts with their respective terminations. We found that terminations of ($01\overline{1}0$) and ($11\overline{2}0$) yield the most stable surfaces for $\alpha$-AlF₃ and for the chlorine substituted surfaces. A potential equilibrium shape of the crystal for both $\alpha$-AlF₃ and ACF is visualized by a Wulff construction. Full article

Gold compounds have been proven to be novel and versatile tools for biological applications, including as anticancer agents. Recently, we explored the potential of Au(III) complexes with bi-dentate N-donor ligands as inhibitors of the membrane water and glycerol channels aquaporins (AQPs), involved in different physiological and pathophysiological pathways. Here, eight new Au(III) complexes featuring a pyridine-benzimidazole scaffold have been synthesized and characterized via different methods. The stability of all the compounds in aqueous solution and their reactivity with glutathione have been investigated by UV–visible spectroscopy. The Au(III) compounds, tested for their AQPs inhibition properties in human Red Blood Cells (hRBC), are potent and selective inhibitors of AQP3. Furthermore, the compounds’ antiproliferative effects have been studied in a small panel of human cancer cells expressing AQP3. The complexes show only very moderate anticancer effects in vitro and are mostly active against the melanoma A375 cells, with marked expression of AQP3 at the level of the nuclear membrane. In general, the AQP3 inhibition properties of these complexes hold promises to develop them as chemical probes to study the function of this protein isoform in biological systems. Full article

Addition of the bulky redox-active diphosphine 1,8-bis(diphenylphosphino)naphthalene (dppn) to [Fe₂(CO)₆(µ-edt)] (1) (edt = 1,2-ethanedithiolate) affords [Fe₂(CO)₄(κ²-dppn)(µ-edt)] (3) as the major product, together with small amounts of a P–C bond cleavage product [Fe₂(CO)₅{κ¹-PPh₂(1-C₁₀H₇)}(µ-edt)] (2). The redox properties of 3 have been examined by cyclic voltammetry and it has been tested as a proton-reduction catalyst. It undergoes a reversible reduction at E_1/2 = −2.18 V and exhibits two overlapping reversible oxidations at E_1/2 = −0.08 V and E_1/2 = 0.04 V. DFT calculations show that while the Highest Occupied Molecular Orbital (HOMO) is metal-centred (Fe–Fe σ-bonding), the Lowest Unoccupied Molecular Orbital (LUMO) is primarily ligand-based, but also contains an antibonding Fe–Fe contribution, highlighting the redox-active nature of the diphosphine. It is readily protonated upon addition of strong acids and catalyzes the electrochemical reduction of protons at E_p = −2.00 V in the presence of CF₃CO₂H. The catalytic current indicates that it is one of the most efficient diiron electrocatalysts for the reduction of protons, albeit operating at quite a negative potential. Full article

A sustainable route to ketones is described where stearone is produced via ketonic decarboxylation of stearic acid mediated by solid base catalysts in yields of up to 97%, at 250 °C. A range of Mg/Al layered double hydroxide (LDH) and mixed metal oxide (MMO) solid base catalysts were prepared with Mg/Al ratios of between 2 and 6 via two synthetic routes, co-precipitation and co-hydration, with each material tested for their catalytic performance. For a given Mg/Al ratio, the LDH and MMO materials showed similar reactivity, with no correlation to the method of preparation. The presence of co-produced oxide phases in the co-hydration catalysts had negligible impact on reactivity. Full article

The catalytic activity of nickel complexes in hydrophosphination involving secondary phosphines is not a commonly studied transformation. Beyond a small number of stand-out examples, many reports in the literature focus on the use of simple nickel salts. β-Diketiminates have been proven to be incredibly effective ligands for catalysis using a range of metal centers. This synthetic study investigates the catalytic ability of a Ni(II) β-diketiminate complex in the hydrophosphination of alkenes and alkynes, with a serendipitous discovery of its ability to effect alkyne cyclotrimerization and phosphine dehydrocoupling. Full article

Proceeding our initial studies of compounds with formally dative TM→Si bonds (TM = Ni, Pd, Pt), which feature a paddlewheel arrangement of four (N,S) or (N,N) bridging ligands around the TM–Si axis, the current study shows that the (N,O)-bidentate ligand 2-pyridyloxy (pyO) is also capable of bridging systems with TM→Si bonds (shown for TM = Pd, Cu). Reactions of MeSi(pyO)₃ with [PdCl₂(NCMe)₂] and CuCl afforded the compounds MeSi(µ-pyO)₄PdCl (1) and MeSi(µ-pyO)₃CuCl (2), respectively. In the latter case, some crystals of the Cu(II) compound MeSi(µ-pyO)₄CuCl (3) were obtained as a byproduct. Analogous reactions of Si(pyO)₄, in the presence of HpyO, with [PdCl₂(NCMe)₂] and CuCl₂, afforded the compounds [(HpyO)Si(µ-pyO)₄PdCl]Cl (4), (HpyO)₂Si[(µ-pyO)₂PdCl₂]₂ (5), and (HpyO)₂Si[(µ-pyO)₂CuCl₂]₂ (6), respectively. Compounds 1–6 and the starting silanes MeSi(pyO)₃ and Si(pyO)₄ were characterized by single-crystal X-ray diffraction analyses and, with exception of the paramagnetic compounds 3 and 6, with NMR spectroscopy. Compound 2 features a pentacoordinate Si atom, the Si atoms of the other complexes are hexacoordinate. Whereas compounds 1–4 feature a TM→Si bond each, the Si atoms of compounds 5 and 6 are situated in an O₆ coordination sphere, while the TMCl₂ groups are coordinated to pyridine moieties in the periphery of the molecule. The TM–Si interatomic distances in compounds 1–4 are close to the sum of the covalent radii (1 and 4) or at least significantly shorter than the sum of the van-der-Waals radii (2 and 3). The latter indicates a noticeably weaker interaction for TM = Cu. For the series 1, 2, and 3, all of which feature the Me–Si motif trans-disposed to the TM→Si bond, the dependence of the TM→Si interaction on the nature of TM (Pd(II), Cu(I), and Cu(II)) was analyzed using quantum chemical calculations, that is, the natural localized molecular orbitals (NLMO) analyses, the non-covalent interaction (NCI) descriptor, Wiberg bond order (WBO), and topological characteristics of the bond critical points using the atoms in molecules (AIM) approach. Full article

A series of cyclometalated iridium(III) complexes that have the general formula [(C^N)₂Ir(NR)(X)] (C^N = monoanionic bidentate cyclometalating ligands; NR = pyridine derivatives; X = Cl⁻ or I⁻) are designed, prepared, and applied for the transformation of toluene to benzaldehyde using a clean, highly efficient, and environmentally-friendly process. The activation energies that are needed for the catalytic oxidation of toluene when using these complexes as catalysts are quite low: between 22.9 and 30.8 kcal mol⁻¹. The catalytic frequencies (TOF) are fairly high (up to 7.0 × 10² h⁻¹) with excellent reliability, and the turnover number (TON) can reach 4.2 × 10³ after 6 h of processing time. Catalytic tests, X-ray absorption near-edge structure (XANES), and kinetic modeling are used to derive detailed insights into the characteristics of the catalysts and their effects on the reactions that are featured in the catalytic oxidation of toluene. Full article

Lithium titanates are used in various applications, such as anode materials for lithium intercalation (Li₄Ti₅O₁₂) or breeding materials in fusion reactors (Li₂TiO₃). Here, we report the formation of nano-crystalline lithium titanates by a mechanochemical approach and present a deeper insight into their structural characteristics by X-ray diffraction (XRD) and solid-state NMR spectroscopy. The compounds were synthesized in a high-energy planetary ball mill with varying milling parameters and different grinding tools. NaCl type Li₂TiO₃ (α-Li₂TiO₃) was formed by dry milling of lithium hydroxide with titania (rutile or anatase) and by a milling induced structure transformation of monoclinic β-Li₂TiO₃ or spinel type Li₄Ti₅O₁₂. Heating of mechanochemical prepared α-Li₂TiO₃ induces a phase transformation to the monoclinic phase similar to hydrothermal reaction products, but a higher thermal stability was observed for the mechanochemical formed product. Microstructure and crystallographic structure were characterized by XRD via Rietveld analysis. Detailed phase analysis shows the formation of the cubic phase from the various educts. A set of two lattice parameters for α-Li₂TiO₃ was refined, depending on the presence of OH⁻ during the milling process. An average crystallite size of less than 15 nm was observed for the mechanochemical generated products. The local Li environment detected by ⁶Li NMR revealed Li defects in the form of tetrahedral instead of octahedral site occupation. Subsequent adjustment of the structural model for Rietveld refinement leads to better fits, supporting this interpretation. Full article

A semi-empirical equation to estimate the hydration number of Mn(II) complexes was derived from a database of 49 previously published ¹H longitudinal Nuclear Magnetic Relaxation Dispersion profiles. This equation has the longitudinal ¹H relaxivity and the molecular weight of the Mn(II) complex under consideration as parameters. Full article

We herein report the synthesis, single-crystal structures of coordination polymers, and structural transformations of complexes employing 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile (tdpd²⁻) and pyrazine (pyz) as bridging ligands. {[M(H₂O)₄(pyz)][M(tdpd)₂(pyz)]·6(H₂O)}_n, [1·10H₂O and 2·10H₂O where M = Co (1) and Zn (2)], consists of two types of crystallographically independent one-dimensional (1D) structures packed together. One motif, [M(tdpd)₂(pyz)]²⁻ (A), is an anionic infinite pyz bridged 1D array with chelating tdpd²⁻ ligands, and the other motif is a cationic chain, [M(H₂O)₄(pyz)]²⁺ (B), which is decorated with four terminal water molecules. The 1D arrays (A) and (B) are arranged in parallel by multi-point hydrogen-bonding interactions in an alternate (A)(B)(A)(B) sequence extending along the c-axis. Both compounds exhibit structural transformations driven by thermal dehydration processes around 350 K to give partially dehydrated forms, 1·2H₂O and 2·2H₂O. The structural determination of the partially dehydrated form, 2·2H₂O, reveals a solid-state structural transformation from a 1D chain structure to a two-dimensional (2D) coordination sheet structure, [Zn₂(tdpd)₂(H₂O)₂(pyz)]_n (2·2H₂O). Further heating to 500 K yields the anhydrous form 2. While the virgin samples of 1·10H₂O and 2·10H₂O crystallize in different crystal systems, powder X-ray diffraction (PXRD) measurements of the dehydrated forms, 1·2H₂O and 2·2H₂O, are indicative of the same structure. The structural transformation is irreversible for 1·10H₂O at ambient conditions. On the other hand, compound 2·10H₂O shows a reversible structural change. The solid-state structural transformation for 1·10H₂O was also confirmed by monitoring in-situ magnetic susceptibility, which is consistent with other thermally-induced measurements. Full article

Bis(guanidine) copper complexes are known for their ability to activate dioxygen. Unfortunately, until now, no bis(guanidine) copper-dioxygen adduct has been able to transfer oxygen to substrates. Using an aromatic backbone, fluorescence properties can be added to the copper(I) complex which renders them useful for later reaction monitoring. The novel bis(guanidine) ligand DMEG₂tol stabilizes copper(I) and copper(II) complexes (characterized by single crystal X-ray diffraction, IR spectroscopy, and mass spectrometry) and, after oxygen activation, bis(µ-oxido) dicopper(III) complexes which have been characterized by low-temperature UV/Vis and Raman spectroscopy. These bis(guanidine) stabilized bis(µ-oxido) complexes are able to mediate tyrosinase-like hydroxylation activity as first examples of bis(guanidine) stabilized complexes. The experimental study is accompanied by density functional theory calculations which highlight the special role of the different guanidine donors. Full article

Mn₂Sb is ferrimagnetic below its Curie temperature (T_C) and passes through a spin flip transition with decreasing temperature. The Co substitution induces an additional first-order phase transition from the ferrimagnetic (FRI) to an antiferromagnetic (AFM) state. This phase transition is connected to a sizable magnetocaloric effect (MCE). To understand the underlying mechanisms, the temperature dependence of structural and magnetic changes was analyzed. At the same time, the influence of the Co substitution was explored. Three Mn_2−xCo_xSb (x = 0.1, 0.15, 0.2) compounds were synthesized by cold crucible induction melting. Neutron powder diffraction was performed to determine the magnetic structures and to obtain the individual magnetic moments on both symmetrically independent Mn sites. In combination with the temperature-dependent magnetization measurements, the magnetic phase transition temperatures were identified. In the low-temperature range, additional antiferromagnetic peaks were detected, which could be indexed with a propagation vector of (0 0 ½). In Mn_1.9Co_0.1Sb at 50 K and in Mn_1.8Co_0.2Sb at 200 K, a co-existence of the FRI and the AFM state was observed. The pure AFM state only occurs in Mn_1.8Co_0.2Sb at 50 K. Full article

The catalytic fragmentation of hydrophobic proteins by polyoxometalates (POMs) requires the presence of surfactants in order to increase the solubility of the protein. Depending on the nature of the surfactant, different effects on the kinetics of protein hydrolysis are observed. As the molecular interactions between the POMs and surfactants in solutions have been scarcely explored, in this study, the interaction between the catalytically active Keggin polyoxometalate [Zr(α-PW₁₁O₃₉)₂]¹⁰⁻ and four different surfactants—sodium dodecyl sulfate (SDS), dodecyldimethyl(3-sulfopropyl)ammonium (Zw3-12), dodecyldimethyl(3-sulfopropyl) ammonium (CHAPS), and polyethylene glycol tert-octylphenyl ether (TX-100)—have been studied in aqueous media. The effect of polyoxometalate on the self-assembly of surfactant molecules into micelles and on the critical micellar concentration (CMC) has been examined by fluorescence spectroscopy and diffusion ordered NMR spectroscopy (DOSY). Full article

Considerable attention has been given to the research field of bioorganometallic chemistry, which is a hybrid chemistry field between biology and organometallic chemistry. The introduction of biomolecules, which have hydrogen bonding sites and chiral centers, into organometallic compounds is a promising strategy to construct chirality-organized bioorganometallic conjugates. This feature paper sketches an outline of induction of helical chirality into bioorganometallic conjugates by the control of a torsional twist of the organometallic moiety. Topics covered included control of the helical chirality of 1,n′-disubstituted ferrocene moieties in ferrocene-dipeptide conjugates, and the chirality induction of the Au(I)–Au(I) axis in the dinuclear organogold(I)-uracil conjugates. Full article