Alkaline Earth Metal Complexes Research Articles

Square-planar Tetranuclear Cluster-based Alkaline Earth Metal-organic Frameworks with Enhanced Proton Conductivity.

Alkaline earth (AE) metal complexes have garnered significant interest in various functional fields due to their nontoxicity, low density, and low cost. However, there is a lack of systematic investigation into the structural characteristics and physical properties of AE-metal-organic frameworks (MOFs). In this research, we synthesized isostructural MOFs consisting of AE4(μ4-Cl) clusters bridged by benzo-(1,2;3,4;5,6)-tris(thiophene-2'-carboxylic acid) (BTTC3-) ligands. The resulting structure forms a truncated octahedral cage denoted as [AE4(m4-Cl)]6(BTTC)8, which further linked to a porous three-dimensional framework. Among the investigated AE ions (Ca, Sr, and Ba), the Ca4-MOF demonstrated good chemical stability in water compared to Sr4-MOF and Ba4-MOF. The N2 adsorption and solid-state UV-vis-NIR absorption behaviors were evaluated for all AE4-MOFs, showing similar trends among the different metal ions. Additionally, the proton conduction study revealed that the Ca4-MOF exhibited ultra-high proton conductivity, reaching 3.52×10-2 S cm-1 at 343 K and 98 % RH. Notably, the introduction of LiCl via guest exchange resulted in an improved proton conduction of up to 6.36×10-2 S cm-1 under similar conditions in the modified LiCl@Ca4-MOF. The findings shed light on the regulation of physical properties and proton conductivity of AE-MOFs, providing valuable insights for their potential applications in various fields.

Synthesis, characterization, and evaluation of the antimicrobial, cytotoxic properties of alkaline earth metal complexes containing the nucleobase guanine

Synthesis, characterization, and evaluation of the antimicrobial, cytotoxic properties of alkaline earth metal complexes containing the nucleobase guanine

Bis(phenoxy-imine) Alkaline–Earth Complexes with Competing Binding Pockets

Bis(phenoxy-imine) Alkaline–Earth Complexes with Competing Binding Pockets

1D and 2D Coordination Polymers of Calcium with Nonsteroidal Anti-Inflammatory Drugs: Synthesis, Crystal Structures, Hirshfeld Surfaces, Antimicrobial and Antioxidant Activities.

Four alkaline earth metal complexes of ketoprofen (Hket) and indomethacin (Hind) were synthesized and characterized: [Ca(ket)2(H2O)2]n (1), [Mg(ket)2(H2O)2] (2), [Ca(ind)2(EtOH)2]n (3), and [Mg(ind)2(EtOH)2] (4). All compounds were studied by elemental analysis (EA), flame atomic absorption spectrometry (FAAS), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Crystal structures of 1 and 3 were determined by single crystal X-ray diffraction technique T=100 K. The structure of 1 is dominated by a one-dimensional coordination polymer, while 3 is formed by a two-dimensional layer stabilized by the calcium zig-zag chains and π⋅⋅⋅π stacking interactions. Crystal packing arrangements were characterized by fingerprint plots (FPs) that were derived from the Hirshfeld surfaces (HSs). The antioxidant and antimicrobial activities of complexes were evaluated against Gram-positive and Gram-negative bacteria as well as yeasts.

Alkaline earth metals: homometallic bonding.

The study of alkaline earth metal complexes is undergoing a renaissance. Stable molecular species featuring Mg-Mg bonds were reported in 2007 and their reactivity has since been intensively investigated. Motivated by this work, efforts have also been devoted to the synthesis of complexes featuring Be-Be and Ca-Ca bonds. These collective endeavours have revealed that the chemistry of the group 2 metals is richer and more complex than had previously been appreciated. Here, a discussion of the nature of homometallic alkaline earth bonding is presented, recent synthetic advances are described, and future directions are considered.

Phenoxy imine NOON complexes of heavy alkaline earth ions for the ring-opening polymerisation of cyclic esters

The polymerisation of lactide monomers by heavier alkaline earth complexes supported by a phenoxy-imine NOON ligand, DippLM(thf)x (DippL = ([2,7-(CNDipp)-1,8-O-C10H4]2− where Dipp = 2,6-iPr-C6H3; M = Ca (1), Sr (2) and Ba (3)) is described.

A Blueprint for the Stabilization of Sub-Valent Alkaline Earth Complexes.

The study of sub-valent Group 2 chemistry is a relatively new research field, being established in 2007 with the report of the first Mg(I) dimers. These species are stabilized by the formation of a Mg-Mg covalent bond; however, the extension of this chemistry to heavier alkaline earth (AE) metals has been frustrated by significant synthetic challenges, primarily associated with the instability of heavy AE-AE interactions. Here we present a new blueprint for the stabilization of heavy AE(I) complexes, based upon the reduction of AE(II) precursors with planar coordination geometries. We report the synthesis and structural characterisation of homoleptic trigonal planar AE(II) complexes of the monodentate amides {N(SiMe3 )2 }- and {N(Mes)(SiMe3 )}- . DFT calculations showed that the LUMOs of these complexes all show some d-character for AE = Ca-Ba. DFT analysis of the square planar Sr(II) complex [Sr{N(SiMe3 )2 }(dioxane)2 ]∞ revealed analogous frontier orbital d-character. AE(I) complexes that could be accessed by reduction of these AE(II) precursors were modelled computationally, revealing exergonic formation in all cases. Crucially, NBO calculations show that some d-character is preserved in the SOMO of theoretical AE(I) products upon reduction, showing that d-orbitals could play a crucial role in achieving stable heavy AE(I) complexes.

Azo-azomethine complex activity and sensor potential toward Ca(II) ion in life samples: The spectroscopic and morphological studies

Current coordination chemistry trends are designing and synthesizing new azo-azomethine alkaline earth metal complexes for medicinal, diagnostic, and catalytic uses. Because of their many uses, it has been noted for decades that azo-azomethine metal complex chemistry is receiving particular attention. Therefore the present work involves the synthesis of a new azo-azomethine ligand (L) by condensation of 4-((3-formyl-4-hydroxy-5-methoxyphenyl)diazenyl)benzoic acid and 3-methoxy aniline. From that azo-azomethine ligand, complex Ca(II) has been prepared (L-Ca(II)). EDX, FT-IR, 1H NMR, 13C NMR, UV–vis, thermal analytic techniques, mass spectrometry, FESEM, AFM, and magnetic susceptibility examinations were used to describe the structure. The new complex of azo-azomethine was used to fabricate coated carbon brush electrode as an ionophore of the membrane sensor for the analytical determination of Ca2+. The response of Ca(II) was linear over the concentration ranging from 1.0 × 10−6 –1.0 × 10−1 mol/L, with selectivity coefficients between 0.001455–0.411661, and detection limit for 1.9 × 10−6 mol/L. The membrane responded within 8 s, depending on the concentration of Ca2+. The fabricated CBE demonstrated excellent selectivity, as well as remarkable repeatability and reproducibility, in the determination of Ca2+ ions. The experimental results provided compelling evidence of the sensor's effectiveness in accurately measuring the Ca2+ levels in various real-life samples.

Periodic trends in the hydration energies and critical sizes of alkaline earth and transition metal dication water complexes.

This review encompasses guided ion beam tandem mass spectrometry studies of hydrated metal dication complexes. Metals include the Group 2 alkaline earths (Mg, Ca, Sr, and Ba), late first-row transition metals (Mn, Fe, Co, Ni, Cu, and Zn), along with Cd. In all cases, threshold collision-induced dissociation experiments are used to quantitatively determine the sequential hydration energies for M2+ (H2 O)x complexes ranging in size from one to 11 water molecules. Periodic trends in these bond dissociation energies are examined and discussed. Values are compared to other experimental results when available. In addition to dissociation by simple water ligand loss, complexes at a select size (which differs from metal to metal) are also observed to undergo charge separation to yield a hydrated metal hydroxide cation and a hydrated proton. This leads to the concept of a critical size, xcrit , and the periodic trends in this value are also discussed.

Exploring the Development of Undergraduate Scientific Research Ability in Basic Course Instruction: A Case Study of Alkali and Alkaline Earth Metal Complexes in Inorganic Chemistry

Exploring the Development of Undergraduate Scientific Research Ability in Basic Course Instruction: A Case Study of Alkali and Alkaline Earth Metal Complexes in Inorganic Chemistry

Activation of the N2 molecule by means of low-valence complexes of calcium and magnesium.

Nitrogen gas is a highly inert molecule and its activation under mild conditions represents a crucial goal in current research. In a recent study, the discovery of low-valence Ca(I) compounds capable of coordinating and reducing N2 was reported [B. Rösch, T. X. Gentner, J. Langer, C. Färber, J. Eyselein, L. Zhao, C. Ding, G. Frenking and S. Harder, Science, 2021, 371, 1125]. The study of low-valence alkaline earth complexes represents a new horizon in inorganic chemistry and demonstrates examples of spectacular reactivity. For example, complexes of the [BDI]2Mg2 type are selective reducing reagents in both organic and inorganic synthesis reactions. To date, however, no activity of Mg(I) complexes in the activation of the nitrogen molecule has been reported. By computational studies, in the present work, we investigated the analogies and differences of low-valence Ca(I) and Mg(I) complexes in the coordination, activation and protonation of N2. We have shown that the possibility of alkaline earth metals to employ atomic orbitals of the d type is reflected in the differences in the N2 binding energy and its coordination mode (end-on vs. side-on), as well as in the spin state of the resulting adduct (singlet vs. triplet). These divergences are finally observed in the subsequent protonation reaction, which turned out to be prohibitive in the presence of Mg.

Atom-economic access to cationic magnesium complexes.

Cationic alkaline-earth complexes attract interest for their enhanced Lewis acidity and reactivity compared with their neutral counterparts. Synthetic protocols to these complexes generally utilize expensive specialized reagents in reactions generating multiple by-products. We have studied a simple ligand transfer approach to these complexes using (NacNac)MgR and ER3 (NacNac = β-diketiminate anion; E = group 13 element; R = aryl/amido anion) which demonstrates high atom economy, opening up the ability to target these species in a more sustainable manner. The success of this methodology is dependent on the identity of the group 13 element with the heavier elements facilitating faster ligand exchange. Furthermore, while this reaction is successful with aromatic ligands such as phenyl and pyrrolyl, the secondary amide piperidide (pip) fails to transfer, which we attribute to the stronger 3-centre-4-electron dimerization interaction of Al2(pip)6.

Red Emitting Cerium(III) and Versatile Luminescence Chromaticity of 1D‐Coordination Polymers and Heterobimetallic Ln/AE Pyridylpyrazolate Complexes

AbstractTen homoleptic lanthanide containing 1D‐coordination polymers, three heterobimetallic lanthanide/alkaline earth complexes as well as two alkaline earth complexes of the formula 1∞[Ln(2‐PyPz)3], [Tb2AE(2‐PyPz)8], and [AE(2‐PyPz)2(2‐PyPzH)2], Ln=La−Nd, Sm−Ho, AE=Ca, Sr, Ba were obtained by reactions of the lanthanide (Ln) and/or the alkaline earth metals (AE) with the ligand 3‐(2‐pyridyl)pyrazole. Organic melt based and/or solvothermal synthesis results in a redox reaction. The investigated compounds exhibit fair thermal stability up to 400 °C. The Ce3+ compound exhibits a bright and red 5d‐based broad band emission with a maximum at around 640 nm under UV excitation marking an example of a strong reduction of the exited 5d states of Ce(III). The co‐doping of the Gd‐containing coordination polymers with Eu3+ and Tb3+ allows for a shift in the chromaticity from the ion specific 4 f‐based emission colors close to white light emission and thus for a versatile tuning of the chromaticity. The co‐doping of Eu3+ with Tb3+ and vice versa shows metal‐to‐metal energy transfer (MMET) between 4 f‐levels of Tb3+ and Eu3+, which influences the tuning of the emission colour.

Synthesis and characterisation of divalent di(1,3‐bis(diphenylphosphano)cyclopentadienyl)lanthanoid and alkaline earth complexes as potential platforms for heterometallic complexes

AbstractNew divalent lanthanoid and alkaline earth metal complexes bearing the 1,3‐bis(diphenylphosphano)cyclopentadienyl ligand have been synthesised using the redox‐transmetallation protolysis (RTP) approach. From the reaction of the corresponding metal, diphenylmercury and the proligand C5H4(PPh2)2, the compounds [M(η5‐C5H3(PPh2)2‐1,3)2(S)] (with M=Yb, S=(thf)2 or M=Yb, Eu, Ca, Sr, Ba, S=dme) were isolated and characterised by X‐ray diffraction and multinuclear NMR spectroscopy. These compounds may provide a platform for early‐late heterobimetallic complexes.

Metalation of 2‐Quinolyl‐Linked (Boranophosphinoyl)methane −Alkali Metal, Alkaline Earth Metal, and Ytterbium(II) Complexes of Monoanionic [CH(iPr2P−BH3)(C9H6N‐2)]− Ligand

AbstractA series of alkali and alkaline earth metal complexes, and an ytterbium(II) complex of monoanionic [CH(iPr2P−BH3)(C9H6N‐2)]− ligand (abbreviated as LQPB−) were synthesized. Lithium complexes [Li(LQPB)(TMEDA)] (2, TMEDA=Me2NCH2CH2NMe2) and [Li(LQPB)(12‐crown‐4)] (3) were prepared by lithiation of 1 with LinBu in the presence of TMEDA and 12‐crown‐4 ether, respectively. Treatment of 2 with NaOtBu and KOtBu, respectively, followed by addition of 18‐crown‐6 ether yielded monomeric sodium complex [Na(LQPB)(18‐crown‐6)] (4) and polymeric potassium derivative [K(LQPB)(18‐crown‐6)]n (5). Metalation of 1 with MgnBu2/TMEDA afforded [Mg(LQPB)2(TMEDA)] (6). Heavier group 2 complexes [Ca(LQPB)2(DME)2] (7), [Sr(LQPB)2]2 (8) and [Ba(LQPB)2(DME)] (9) were synthesized by metalation of 1 with the corresponding alkaline earth metal amide M[N(SiMe3)2]2(DME)n (M=Ca or Ba, n=2; M=Sr, n=0) in toluene under reflux conditions. Treatment of YbI2(THF)2 with potassium complex 5 led to isolation of mononuclear Yb(II) complex [Yb(LQPB)2(18‐crown‐6)] (10).

Synthesis and reactivity of low-oxidation-state alkaline earth metal complexes

Synthesis and reactivity of low-oxidation-state alkaline earth metal complexes

Alkaline-earth metal(II) complexes of salinomycin – spectral properties and antibacterial activity

Abstract In the present paper the synthesis and structural characterization of alkaline-earth metal(II) complexes of the polyether ionophorous antibiotic salinomycinic acid (SalH.H2O) are discussed. The complexes [M(Sal)2(H2O)2] (M = Mg2+, 1; Ca2+, 2; Sr2+, 3; Ba2+, 4) were obtained reacting salinomycinic acid and Et4NOH with the corresponding metal(II) salts at metal-to-ligand-to-base molar ratio of 1:1:1. The spectral properties of 1–4 were characterized using infrared spectroscopy, fast atom bombardment-mass spectrometry, nuclear magnetic resonance and elemental analysis data. The crystallinity degree and morphology of complex 2 were studied by X-ray powder diffraction and transmission electron microscopy. The biometal(II) salinomycinate complexes 1 and 2 possess an enhanced antimicrobial activity compared to the parent antibiotic against Gram-positive bacteria. The comparison between the effectiveness of the complexes, reported here, and the already known isostructural coordination species of salinomycin and monensin (MonH.H2O), revealed that magnesium(II) and calcium(II) monensinates appear to be promising antibacterial agents against Bacillus subtilis, Bacillus cereus and Micrococcus luteus.

2-Imino-2,3-dihydrobenzoxazole-a useful platform for designing rare- and alkaline earth complexes with variable di- and trianionic O,N,N, ligands.

The reactions of 2-imino-2,3-dihydrobenzoxazole LH with M[N(SiMe3)2]2(THF)2 (M = Yb and Ca) and Y(CH2SiMe3)3(THF)2 proceed with the opening of the dihydrobenzoxazole ring and the elimination of HN(SiMe3)2 or SiMe4. Besides, in the case of Yb[N(SiMe3)2]2(THF)2, an electron transfer from Yb(II) to L takes place and Yb(III) complex 1 is coordinated by a dianionic phenolate ligand containing a pendant radical-anionic diazabutadiene fragment form. When LH is reacted with Ca[N(SiMe3)2]2(THF)2, C-H bond activation of a methyl fragment by imino nitrogen occurs and affords a dimeric calcium complex 2. In 2, the phenolate ligand is dianionic due to the presence of the amido-imino fragment [R-NC(CH3)-C(CH2)-NR']- (R = 2,4-tBu2-C6H2O; R' = 2,6-iPr2C6H3). In situ generated ate-complex {Na(Et2O)n}{Ca[N(SiMe3)2]3} also enables C-H bond activation, however the dianionic phenolate ligand in the resulting complex 3 contains an amido-imino fragment [R-N-C(CH2)-C(CH3)NR']- featuring the sequence of N-C and NC bonds opposite to that in 2. The reaction of Y(CH2SiMe3)3(THF)2 with LH affords mono(alkyl) yttrium complex 4. 4 contains a dianionic amido-imino phenolate ligand resulting from the migration of one alkyl group to the CN bond [R-N-C(Me)(CH2SiMe3)-C(Me)NR']. 4 undergoes slow intramolecular C-H bond activation of the residual CH3 group to afford a yttrium complex coordinated by a trianionic diamido-phenolate ligand [R-N-C(Me)(CH2SiMe3)-C(CH2)NR'].

Synthesis and Oligonuclear Structures of Strontium and Barium Complexes with Protonated and Deprotonated N-Mesityl-P,P-diphenylphosphinic Amide Ligands.

Metalation of N-mesityl-P,P-diphenylphosphinic amide Ph2P(O)-NHMes (HL, I) with MgBu2 and Ae{N(SiMe3)2}2 (Ae = Ca, Sr, and Ba) yields alkaline-earth metal complexes with the compositions of [(thf)nAe(L·HL)2] [Ae/n = Mg/0 (II), Ca/2 (III)] as well as of [Sr2L3(L·HL)(HL)] (1), [Ba2L3(L·HL)(HL)] (2), [Ba3L6] (3), and [(thf)2Ba3L6] (4). In III, 1, 2, and 3, the alkaline-earth metal atoms are in severely distorted octahedral environments, and the structural distortions are partially caused by the small O-Ae-N bite angles of the chelating Ph2P(O)-NMes anions. The substructures (L·HL) contain N–H···N hydrogen bridges, stabilizing the arrangement of the ligands in complexes II, III, 1, and 2. In the trinuclear barium complex [Ba(μ-L)3Ba(μ-L)3Ba] (3), a rigid adjustment of the anionic L bases leads to a C3-symmetric molecule in the crystalline state with bridging oxygen atoms. Due to the small O–Ba–N bite angles of the chelating anions, vacant coordination sites are available at the outer barium centers. Coordination of thf bases in these gaps yields the complex [(thf)Ba(μ-L)3Ba(μ-L)3Ba(thf)] (4). However, THF is unable to deaggregate the trinuclear complexes into smaller barium-containing moieties. Increasing the radius of the alkaline-earth metals and increasing the nuclearity of these compounds lead to decreasing solubility in common organic solvents. NMR studies verify that the molecular structures of these alkaline-earth metal complexes are maintained in ethereal solvents and toluene.

Cover Picture: Alkali and Alkaline Earth Metal Complexes as Versatile Catalysts for Ring‐Opening Polymerization of Cyclic Esters (Chem. Rec. 8/2021)

Cover Picture: Alkali and Alkaline Earth Metal Complexes as Versatile Catalysts for Ring‐Opening Polymerization of Cyclic Esters (Chem. Rec. 8/2021)