Atoms Of Ligand Research Articles

A crystallographic conundrum

Organometallics X-ray crystallography is often construed as the most direct means of characterizing molecular structure. Nonetheless, it still relies on an accurate assessment of elemental composition to begin with. Amemiya et al. report a strange case in which a structure previously assigned to a cadmium carbonyl compound appears much more consistent with a rhenium carbonyl. Although the initial refinement statistics seemed reasonable, the ratio of displacement parameters for the metal versus the ligand atoms was unusually small. The authors further concluded that coordinative carbon and chlorine sites in the ligands were more likely to be nitrogen and sulfur, respectively. Chem. Sci. 10.1039/d0sc04596a (2020).

Sonication-assisted synthesis of a strawberry-like nano-structure triphenyltin(IV) adduct as precursor for preparation of nano-sized SnP2O7: Crystal structure and DFT calculations

A triphenyltin(IV) adduct of phosphoramide with a formula of [Sn(Ph)3Cl(L1)] (C1), L1 = N-phenyl-N´,N´´-bis(pentamethylene) phosphoric triamide, has been synthesized and characterized by elemental analyses and IR spectroscopy. In the crystal structure, the tin(IV) environment adopts a distorted trigonal bipyramidal geometry with three phenyl groups in the equatorial plane, one chloro atom and the oxygen atom of ligand at the axial sites. Hirshfeld surface analysis and fingerprint plots were used to investigat of the intermolecular interactions, responsible for the crystal architecture. The complex was also prepared under ultrasonic irradiation (C1a) and characterized by elemental analyses, IR, and X-ray powder diffraction (XRPD). The effects of two different concentrations of initial reagents on the size and morphology of the nanomaterial were studied by scanning electron microscopy (SEM), which shows that C1a grown as nano-strawberry morphology. The calcination of triorganotin complex in air atmosphere led to production of nano-structured tin pyrophosphate. The thermal stabilities of the single crystal and of the nano-crystalline form were investigated by thermal gravimetric and differential thermal analyses. The structural and electronic properties of L1, C1 and similar molecules were evaluated by density functional theory (DFT) calculations. Parameters derived from NBO and QTAIM analyses suggest that the nature of Sn-O interaction is electrostatic with a small amount of covalent character and donor-acceptor delocalization from the ligand oxygen atom to the tin center. Moreover, the electronic parameters including HOMO-LUMO orbitals, bond gap, chemical hardness-softness, electronegativity, and electrophilicity were calculated.

Structure of tetra-kis-(μ-deca-noato-κ2 O:O')bis-[(4-methyl-pyridine-κN)copper(II)], a dimeric copper(II) complex.

The 4-methyl-pyridine (4-Mepy) based dimeric copper(II) carboxyl-ate complex [Cu2(C10H19O2)4(C6H7N)2] or [Cu2(μ-O2CC9H19)4(4-Mepy)2] crystallizes with triclinic (P ) symmetry. The two CuII ions exhibit a distorted square-pyramidal environment and are connected into a centrosymmetric paddle-wheel dinuclear cluster [Cu⋯Cu = 2.6472 (8) Å] via four bridging carboxyl-ate ligands arranged in the syn-syn coordination mode. The apical positions around the paddle-wheel copper centers are occupied by the N atoms of the 4-methyl-pyridine ligands. The structure exhibits disorder of the terminal alkyl carbon atoms in the deca-noate chains.

Size-Selective Urea-Containing Metal-Organic Frameworks as Receptors for Anions.

Anion recognition by neutral hosts that function in aqueous solution is an emerging area of interest in supramolecular chemistry. The design of neutral architectures for anion recognition still remains a challenge. Among neutral anion receptor systems, urea and its derivatives are considered as "privileged groups" in supramolecular anion recognition, since they have two proximate polarized N-H bonds exploitable for anion recognition. Despite promising advancements in urea-based structures, the strong hydrogen bond drives detrimental self-association. Therefore, immobilizing urea fragments onto the rigid structures of a metal-organic framework (MOF) would prevent this self-association and promote hydrogen-bond-accepting substrate recognition. With this aim, we have synthesized two new urea-containing metal-organic frameworks, namely [Zn(bpdc)(L2)]n·nDMF (TMU-67) and [Zn2(bdc)2(L2)2]n·2nDMF (TMU-68) (bpdc = biphenyl-4,4'-dicarboxylate; bdc = terephthalate; L2 = 1,3-bis(pyridin-4-yl)urea), and we have assessed their recognition ability toward different anions in water. The two MOFs show good water stability and anion affinity, with a particular selectivity toward dihydrogen arsenate for TMU-67 and toward fluoride for TMU-68. Crystal structure characterizations reveal 3-fold and 2-fold interpenetrated 3D networks for TMU-67 and TMU-68, respectively, where all single interpenetrated networks are hydrogen bonded to each other in both cases. Despite the absence of self-quenching, the N-H urea bonds are tightly hydrogen bonded to the oxygen atoms of the dicarboxylate ligands and cannot be directly involved in the recognition process. The good performance in anion sensing and selectivity of the two MOFs can be ascribed to the network interpenetration that, shaping the void, creates monodimensional channels, decorated by exposed oxygen atom sites selective for arsenate sensing in TMU-67 and isolated cavities, covered by phenyl groups selective for fluoride recognition in TMU-68.

Synthesis and crystal structure of a zinc(II) coordination polymer: N-(2-pyridylmethyl)- L-alanine)isothiocyanate Zn(II)

The title compound, N-(2-pyridylmethyl)-L-alanine) zinc(II), [Zn(C10H11N3O2S)], a coordination polymer derived from the mixed ligands, N-(2-pyridylmethyl)-L-alanine (HL1) and ammonium thiocyanide (L2) has been synthesized and characterized by IR spectroscopy, 1H-NMR, elemental analysis, thermogravimetric analysis and single crystal x-ray structure determination.The single crystal X-ray structure analysis of the title compoundreveals a molecular polymeric compound that crystallizes in the orthorhombic crystal system and P2(1)2(1)2(1) space group. The ligand acts as a bridge between adjacent zinc(II) centres, each of which adopts a five-coordinate geometry. Zinc bonds to two N atoms and one O atom of HL1, one N atom of L2 and one O atom of another HL1 ligand. This is confirmed by IR spectroscopy. Thermogravimetric analysis shows a one-step decomposition of the complex to leave a zinc sulfide residue.
 
 KEY WORDS: Zinc(II), N-(2-pyridylmethyl)-(L)-alanine) ligand, Isothiocyanate, Coordination polymer, Single crystal structure
 
 Bull. Chem. Soc. Ethiop. 2020, 34(2), 285-293
 DOI: https://dx.doi.org/10.4314/bcse.v34i2.7

Catena-Poly[[[bis-(aceto-nitrile-κN)(4,4'-dimeth-oxy-2,2'-bi-pyridine-κ2 N,N')copper(II)]-μ-tri-fluoro-methane-sulfonato-κ2 O:O'] tri-fluoro-methane-sulfonate

The central copper(II) atom of the title salt, {[Cu(CF3SO3)(CH3CN)2(C12H12N2O2)](CF3SO3)} n or [[Cu(CH3CN)2(diOMe-bpy)(CF3SO3)](CF3SO3)] n where diOMe-bpy is 4,4'-dimeth-oxy-2,2'-bi-pyridine, C12H12N2O2, is sixfold coordin-ated by the N atoms of the chelating bi-pyridine ligand, the N atoms of two aceto-nitrile mol-ecules, and two tri-fluoro-methane-sulfonate O atoms in a tetra-gonally distorted octa-hedral shape. The formation of polymeric chains [Cu(CH3CN)2(diOMe-bpy)(CF3SO3)]+ n leaves voids for the non-coordinating tri-fluoro-methane-sulfonate anions that inter-act with the complex through weak hydrogen bonds. The presence of weakly coordinating ligands like aceto-nitrile and tri-fluoro-methane-sulfonate makes the title compound a convenient starting material for the synthesis of novel metal-organic frameworks.

Synthesis and characterization of novel four heterodimetallic mixed metal complexes of 2,6-pyridinedicarboxylic acid

Four novel hetero dimetallic mixed metal complexes of 2,6-pyridinedicarboxylic acid (H2dipic), [Ni(H2O)5Co(dipic)2] (1), [Co(H2O)5Co(dipic)2][Ni(H2O)5Ni(dipic)2][Co(dipic)(H2O)3] (2), [Cu(H2O)5Ni(dipic)2]2[Co(dipic)(H2O)] (3) and [Ni(H2O)5Cu(dipic)2]2[Co(dipic)(H2O)] (4) have been prepared and characterized by elemental, AAS, spectral (IR and UV-Vis), and thermal analyses, as well as by using magnetic measurement and molar conductivity techniques. The results indicate that metal ions coordinate with 2,6-pyridinedicarboxylate ions (dipic2-) nitrogen atoms and carboxylate oxygen atoms of ligands. The mole ratio of dipic2- and metal ions in the complexes have been determined to be 2:2 (Co, Ni) for 1, 5:5 (3Co, 2Ni) for 2, 5:5 (Co, 2Ni and 2Cu) for 3 and 5:5 (Co, 2Ni and 2Cu) for 4 according to the results of elemental analysis. The structures of 1-4 might be proposed as octahedral ([Cu(dipic)(H2O)] unit for 2 square plane) according to results of spectroscopic analysis. The TG and DTA properties of compounds have been studied.
 
 KEY WORDS: 2,6-Pyridinedicarboxylic acid, Mixed metal, Metal complex
 
 Bull. Chem. Soc. Ethiop. 2020, 34(2), 313-321
 DOI: https://dx.doi.org/10.4314/bcse.v34i2.9

Synergistic interaction between Ru and MgAl-LDH support for efficient hydrogen transfer reduction of carbonyl compounds under visible light

Coordinated Ru species, Ru/LDH, were applied to the reduction of carbonyl compounds via blue light irradiation under mild (45 °C, atmospheric argon pressure), ligand-free, and additive-free conditions. LDH can act as an efficient base catalyst to assist in formation of isopropoxide, requiring no additional base, because basic OH groups form an ordered distribution on LDH surface. The coordinated Ru species containing one OH and three oxygen atoms ligands deriving from the OH groups of LDH are a crucial component, for securing the active electron-deficient Ru species that favours formation of Ru-isopropoxide. The photocatalytic activity is related to the adsorption capacity of isopropyl alcohol near the electron-deficient Ru species and the formation of Ru-isopropoxide. The strong-metal-support interactions between Ru and LDH affect the coordination and the electronic surroundings of the Ru centres and have a significant effect on the photocatalytic activity.

Synthesis and characterization of bis (5-phenyl-1,3,4-oxadiazole-2-ylthio) mercury complexes with Pd(II) and Pt(II) metal ions

A complexes of Pd(II) and Pt(II) have been synthesized from a reaction of one mole of (5-phenyl-1,3,4-oxadiazole-2-ylthio)mercury (HgL2) with two mole of PdCl2 and PtCl2 to give the colored complexes with general formula [M2Cl4(HgL2)] [where M=Pd(II) or Pt(II)]. The results of identification indicated that all complexes have square planer shapes, which the metal coordinates to the ligand through Nitrogen, and Sulfur atoms of ligand (HgL2). Characterization have been done by using FT- IR Spectroscopy, H1-NMR spectroscopy, UV-visible spectra, melting point and CHNS analysis.

Synthesis, crystal structures and magnetic properties of a 1D chain based on trinuclear Cu subunits and a Cu4Dy2 complex

A one-dimensional (1D) chain [Cu3(HL)2(N3)(Mtta)]n.0.5CH3CN (1, H3L = 2-((2-hydroxybenzylidene)amino)propane-1,3-diol and Mtta = 5-methyl tetrazolate) and a Cu4Dy2 complex [Cu4Dy2{(py)2CO2}2{(py)2C(OH)O}2(CH3COO)4(N3)4].3CH3CN (2, (py)2C(OH)2 = the gem-diol form of di-2-pyridyl ketone) were obtained by the assemblies of the H3L ligand and Dy(NO3)3·5H2O with copper nitrate or with copper acetate and di-2-pyridyl ketone under the MeCN solution containing triethylamine or containing NaOH. In 1, three CuII ions were linked into a trinuclear Cu unit by three neighboring N atoms of Mtta ligand and two alkoxido-type O atoms from two HL2− ligands, then these units were further linked into a one-dimensional (1D) chain by two phenoxido O atoms from two HL2− ligands. In 2, two CuII and two DyIII ions formed a butterfly-type topology, which was further linked another two CuII by the O atoms from (py)2CO22– or from acetate ligands. Magnetic studies indicated that, in 1, the magnetic coupling through the paths of CuNNCu and Cu-Oalkoxido-Cu is antiferromagnetic (J1 = −14.81 cm−1), and its value was first determined in the polynuclear Cu complexes containing Mtta ligand. However, the magnetic coupling through the path of Cu-Ophenoxido-Cu is ferromagnetic (J2 = 24.61 cm−1). Magnetic studies revealed that 1 exhibits slow magnetic relaxation behavior, with an energy barrier Ueff of 6.06 K. The orientations of the easy magnetization axes of DyIII ions in 2 was estimated by Magellan program, indicating that the easy axes of DyIII in 2 are roughly aligned along alkoxido-type O atoms (O3 and O3a), which is slightly longer than other Dy-O distances.

How is Nitric Oxide (NO) Converted into Nitrosonium Cations (NO+) in Living Organisms? (Based on the Results of Optical and EPR Analyses of Dinitrosyl Iron Complexes with Thiol-Containing Ligands).

The present work provides theoretical and experimental foundations for the ability of dinitrosyl iron complexes (DNICs) with thiol-containing ligands to be not only the donors of neutral NO molecules, but also the donors of nitrosonium cations (NO+) in living organisms ensuring S-nitrosation of various proteins and low-molecular-weight compounds. It is proposed that the emergence of those cations in DNICs is related to disproportionation reaction of NO molecules, initiated by their binding with Fe2+ ions (two NO molecules per one ion). At the same time, possible hydrolysis of iron-bound nitrosonium cations is prevented by the electron density transition to nitrosonium cations from sulfur atoms of thiol-containing ligands, which are included in the coordination sphere of iron. It allows supposing that iron in iron–nitrosyl complexes of DNICs has a d7 electronic configuration. This supposition is underpinned by experimental data revealing that a half of nitrosyl ligands are converted into S-nitrosothiols (RSNOs) when those complexes decompose, with the other half of those ligands released in the form of neutral NO molecules.

Influence of halogens on organometallic open pentadienyl lanthanum complexes XLa(C5H7)2 (X = H, F–I)

The electron and structural understanding of metal-coordinated pentadienyl ligands is essential for their subsequent use in different areas of chemistry, especially in the area of organometallic chemistry. Thus, in this work we have analyzed in gas-phase the influence of group 17 elements in complexes formed with the lanthanum atom and the open pentadienyl ligand, XLa(C5H7)2, where X = H, F, Cl, Br, and I. The results, using density functional theory (PBE0/def2-TZVP) and NBO analysis, suggest that all carbon atoms of both ligands are η5 coordinated to the lanthanum atom, and X atoms play a very important role in affecting the electron transfer from the ligands to the central atom due to their electronegativity. In addition, the NBO analysis and the geometry of each structure suggest that the atoms that contribute the most as charge donors to the lanthanum atom are those at the center of the pentadienyl ligand. Energies were computed with the domain based local pair-natural orbital coupled-cluster (DLPNO-CCSD(T)) method.

Unlocking the Full Evolutionary Potential of Artificial Metalloenzymes Through Direct Metal-Protein Coordination

Generation of artificial metalloenzymes (ArMs) has gained much inspiration from the general understanding of natural metalloenzymes. Over the last decade, a multitude of methods generating transition metal-protein hybrids have been developed and many of these new-to-nature constructs catalyse reactions previously reserved for the realm of synthetic chemistry. This perspective will focus on ArMs incorporating 4d and 5d transition metals. It aims to summarise the significant advances made to date and asks whether there are chemical strategies, used in nature to optimise metal catalysts, that have yet to be fully recognised in the synthetic enzyme world, particularly whether artificial enzymes produced to date fully take advantage of the structural and energetic context provided by the protein. Further, the argument is put forward that, based on precedence, in the majority of naturally evolved metalloenzymes the direct coordination bonding between the metal and the protein scaffold is integral to catalysis. Therefore, the protein can attenuate metal activity by positioning ligand atoms in the form of amino acids, as well as making non-covalent contributions to catalysis, through intermolecular interactions that pre-organise substrates and stabilise transition states. This highlights the often neglected but crucial element of natural systems that is the energetic contribution towards activating metal centres through protein fold energy. Finally, general principles needed for a different approach to the formation of ArMs are set out, utilising direct coordination inspired by the activation of an organometallic cofactor upon protein binding. This methodology, observed in nature, delivers true interdependence between metal and protein. When combined with the ability to efficiently evolve enzymes, new problems in catalysis could be addressed in a faster and more specific manner than with simpler small molecule catalysts.

A comparative study of palladium-based coordination compounds with bidentate (N,N, P,P and P,O) ligands; Design, synthesis, X-ray structural, catalytic activity and DFT studies

This account describes our recent studies on four new asymmetric cyclometallated Pd(II) complexes with a formula [L1 → Pd ← L2](ClO4) (L1 = benzylamine and L2 = bis (diphenylphosphino) methane oxide (dppmo) (3), 1,2-bis (diphenylphosphino) ethane (dppe) (4), bispyridine (bipy) (5) and 1, 10-phenanthroline (phen) (6)). These complexes have been prepared by the reaction of palladium(II) acetate with benzylamine ligand in equimolar ratios in toluene produced the [Pd(C6H4CH2NH2)(µ-OAc)]2 complex 1. A metathesis reaction between complex 1 and NaCl in water/acetone (1:10) exchanged the acetato ligands of 1 with chloro ligands. This produced the dinuclear cyclopalladated compound [Pd(C6H4CH2NH2)(µ-Cl)]2 complex 2. The following addition of dppmo, dppe, bipyridine and phenanthroline ligands, respectively, to the solution of 2 in CH2Cl2 generated the corresponding complexes. These complexes have been fully characterized by FT-IR, 1H, 13C and 31P NMR spectroscopic methods and other conventional techniques such as elemental analysis (CHN). Further, the solid-state structure of the complex 3 was determined by the single-crystal X-ray diffraction methods, showing that this complex consist of two five-membered rings formed by coordination of the dppmo ligand through the one phosphorus atom and one oxygen atom and coordination of the benzylamine ligand through the one carbon atom and one nitrogen atom to the metal center. Therefore, the catalytic activity of complex 3, using Suzuki and Heck coupling reactions, has been evaluated and compared. Using theoretical methods the structures of the asymmetric palladacycle complexes [L1 → Pd ← L2](ClO4) with different coordination mode, (where L1 = benzylamine (N,C coordination) and L2 = dppmo (P,O coordination) (3), dppe (P,P coordination) (4) and phen (N,N coordination) (6)), were compared with each other. In this regard density function theory (DFT) calculations at the BP86/def2-SVP level of theory were applied. The strength and nature of donor-acceptor bonds between the L1 and L2 and Pd fragments in the [L1 → Pd ← L2](ClO4) were carried out by natural bond orbital analysis (NBO) and energy-decomposition analysis (EDA) as well as their natural orbitals for chemical valence variation (EDA-NOCV).

Theory-Guided Machine Learning Finds Geometric Structure-Property Relationships for Chemisorption on Subsurface Alloys

Summary Developing physically transparent and quantitatively accurate models that relate the chemical interaction (chemisorption strength) between an adsorbate and a solid surface to the adsorption site's geometry is critical for our understanding of catalysis, corrosion, and electrochemistry. We develop a theory-guided machine-learning (ML) approach, which uses an interpretable class of ML models called generalized additive models (iGAM models), to discover predictive structure-property models that can quantify and explain the link between the geometric structure of an adsorption site and the chemisorption strength. We demonstrate the approach through several case studies, where we analyze the chemisorption strength of chemically distinct adsorbates (O, OH, S, and Cl) on subsurface metal alloy surfaces subjected to various strain- and ligand-induced changes in the local geometric structure. By comparing the ML-derived chemisorption models to previously established electronic-structure models, we clarify the critical physical parameters that control the chemisorption process on metal surfaces.

Impact of ligand substituents on the crystal structures, optical and conducting properties of phenylmercury(II) β-oxodithioester complexes

New phenylmercury(II) complexes 1–5 with functionalized β-oxodithioester ligands, [PhHg(II) (β-oxodithioester)], β-oxodithioester = methyl-3-hydroxy-3-(4-pyridyl)-2-propenedithioate L1 1, methyl-3-hydroxy-3-(p-chlorophenyl)-2-propenedithioate L2 2, methyl-3-hydroxy-3-(naphthyl)-2-propenedithioate L3 3, methyl-3-hydroxy-3-(9-anthracenyl)-2-propenedithioate L4 4 and methyl-3-hydroxy-3-(p-fluorophenyl)-2-propenedithioate L5 5, were synthesized and characterized by elemental (C, H, N) analysis, IR, UV-Vis., 1H and 13C{1H} NMR spectroscopy. Their structures have been investigated by single crystal X-ray diffraction. Linear two-coordinate geometry about the Hg atom, via ipso-C of the phenyl group and by S15 atom of the β-oxodithioester ligands is revealed in all complexes. Intramolecular Hg···O bonding at 2.622(10)–2.813(6) Å is present in all the complexes. In 1–3, the asymmetric unit contains a single discrete molecule whereas complexes 4 and 5 contain two. Except for 4 having bulky anthracene substituent, intriguing supramolecular networks are sustained through intermolecular metal assisted Hg···S and Hg···N and Cl···Cl, Cl···π, S···S, C–H···S, C–H···F, C–H···π interactions in these complexes. In 1 the pyridyl N on 4-position on the substituent is involved in Hg···N bonding interactions on the neighboring molecule at 2.938(7) Å generating a 2-D net-like polymeric structure. All the complexes showed bright green luminescent emissions both in solution and solid phase. The complexes (σrt values = 10−3–10−6 S cm−1) show semiconducting characteristics with Ea values = 0.14–0.64 eV. The electronic and steric properties of the substituents on the dithioester unit significantly influence their structures and properties.

Synthesis, Crystal Structures and Catalytic Property of Oxidovanadium(V) Complexes with N’-(4-Oxopentan-2-ylidene)nicotinohydrazide and 4-Bromo-N’-(4-oxopentan

A pair of structurally similar oxidovanadium(V) complexes with the general formula [VOLL’], with the hydrazone compounds N' -(4-oxopentan-2-ylidene)nicotinohydrazide (H 2 L 1 ) and 4-bromo- N' -(4-oxopentan-2-ylidene)benzohydrazide (H 2 L 2 ), and the acetohydroxamic acid (HL’) as ligands, have been synthesized and structurally characterized by physico-chemical methods and single crystal X-ray determination. Single crystal X-ray analysis indicates that the V atoms in the complexes are in octahedral coordination, with the ONO donor atoms of the hydrazone ligands, and the OO donor atoms of the acetohydroxamate ligands, as well as an oxido O atom. The complexes showed good property for the catalytic epoxidation of styrene.

Synthesis, structure and magnetic properties of cyclic 3d metal clusters based on N–N single bonds of diacylhydrazine ligand

Two cyclic high-nuclearity 3d metal clusters formulated as [CoII8CoIII4(bdsh)4(Py)12(MeOH)4(OAc)4]·14CH3OH·4H2O ({Co12} cluster) and [MnII4MnIII12MnIV4(bdsh)10(Py)2(DMF)8(H2O)8]·16DMF·2CH3OH·8H2O ({Mn20} cluster), (H6bdsh = N,N'-bis(2-salicylhydrazide)isophthalohydrazide, Py = pyridine, and DMF = N,N'-dimethylformamide), were synthesized by a conventional solution method. The {Co12} cluster presents a dodecanuclear ring structure consisting of two symmetrical hemicyclic skeletons bridged with two cobalt ions through the phenolic hydroxyl oxygen atom of H6bdsh ligand, the hemicyclic skeleton in which five cobalt ions are bridged by four N–N single bonds of diacylhydrazine ligands. The {Mn20} cluster exhibits a double cyclic structure comprising of two decanuclear ring skeleton bridged with two phenolic hydroxyl oxygen atoms of H6bdsh ligands, the decanuclear skeleton in which ten manganese ions are bridged by ten N–N single bonds of five H6bdsh ligands. Magnetic studies reveal the existence of antiferromagnetic interactions in both {Co12} and {Mn20} clusters.

Two-Dimensional Heteronuclear Coordination Polymers Constructed by Cyanide and 3-(2-Aminoethyl)pyridine Ligands

Two new heteronuclear (Ni/Cd and Pd/Cd) 2D coordination polymers formulated as namely {[Cd(μ-3aepy)2Ni(μ-CN)2(CN)2]⋅2H2O}n (1) and [Cd(3aepy)Pd(μ4-CN)4]n (2) (3aepy = 3-(2-aminoethyl)pyridine) were obtained and determined using different techniques (FT-IR and Raman spectroscopies, single crystal X-ray diffraction, elemental, SEM–EDX and thermal analyses). Single crystal X-ray study of the complexes revealed that the Ni(II) and Pd(II) ions are coordinated with four cyanide-carbon atoms in square planar geometries. The Cd(II) ions are bridged by 3aepy ligands to generate [Cd2(3aepy)2]2+ cation and adjacent cations are further linked to cyanide ligands from [Ni(μ-CN)4]2− anion, generating corrugated rectangular grid-like 2D sheets in 1. Whereas, the Cd(II) and Pd(II) ions are bridged by cyanide ligands, generating corrugated rectangular grid-like 2D sheets in 2. The Cd1 is possessed the distorted octahedral coordination geometry with six nitrogen atoms from two 3aepy and four cyanide ligands. The Cd2 is coordinated by four nitrogen atoms from cyanide ligands to form a square-planar geometry. Furthermore, the most remarkable properties of the complexes are the existence of the intermolecular C–H⋯M interactions between M(II) and hydrogen atoms of the 3aepy ligands (M(II) = Ni and Pd).

Synthesis of two lanthanide clusters LnIII4 (Gd4 and Dy4) with [2 × 2] square grid shape: Magnetocaloric effect and slow magnetic relaxation behaviors

Two isostructural tetranuclear lanthanide clusters named [Ln4(L)4(CH3O)4]·CH3OH (Ln = Gd(III) for 1, Dy(III) for 2, H2L = N′-(2-hydroxy-3-methoxybenzylidene)-6-(hydroxymethyl) picolinohydrazide) were successfully isolated by using a polydentate Schiff based ligand and Ln(III) nitrate salts. The structures of 1 and 2 were characterized by X-ray structural analyses, they are held by four double deprotonated ligands L2−. In them all the lanthanide ions are eight-coordinated and distributed over four vertices of a parallelogram, presenting a Ln4 cluster with a strict [2 × 2] square grid pattern. The details of magnetic analysis show that 1 displays weak anti-ferromagnetic exchange between neighboring Gd(III) ions through carboxylate oxygen and methanol oxygen ligand atoms. Furthermore, 1 exhibits significant magnetocaloric effect with the maximum entropy change –ΔSm value of 28.5 J/(kg·K) for ΔH = 7.0 T at 2.0 K. For compound 2, remarkable slow magnetic relaxation behaviors are observed in the presence of zero magnetic field with τ0 = 1.02 × 10−6 s and energy barrier ΔE/kB = 43.24 K.