Adjacent Metal Centers Research Articles

Red photo- and electroluminescent half-lantern cyclometalated dinuclear platinum(II) complex

Abstract New cyclometalated dinuclear platinum(II) complex bearing bridged 4,6-dimethylpyrimidine-2(1H)-thiolate (μ-C6H7N2S-κN,S) ligands, [{Pt(ppy)(μ-C6H7N2S-κN,S)}2] (3) (ppy=(2-phenylpyridinato-C2,N)) was prepared via the reaction of chloro-bridged dimer [{Pt(ppy)Cl}2] with 4,6-dimethylpyrimidine-2(1H)-thione (C6H8N2S) in the presence of t-BuOK. The complex holds dinuclear frameworks with short Pt(II)···Pt(II) distance (2.8877(3) Å), and exhibit red intense luminescence from the triplet metal-metal-to-ligand charge-transfer at 697 nm in CH2Cl2 solution and at 649 nm in solid state at RT. Single crystal XRD analysis reveals the metallophilic interactions Pt···Pt with significant covalent contribution in the structure of 3 which were studied by quasi-relativistic and relativistic DFT calculations (viz., M06/MWB60(Pt) and 6-311+G* (other atoms); M06/DZP-DKH levels of theory) and topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method). Estimated strength of the Pt···Pt contact is 8.1–12.2 kcal/mol and it is mostly determined by crystal packing effects and weak attractive interactions between the adjacent metal centers due to overlapping of their dz2 and pz orbitals. An organic light-emitting diode based on this complex showed red electroluminescence with maximal luminance of 115 cd/m2 and current efficiency of 2.45 cd/A at this luminance.

Coordination Polymer of M(II)-Pyrazinamide (M = Co, Cd) with Double End-to-End Thiocyanate Bridge

Pyrazinamide (pza, C4N2H3-CONH2) is a good ligand for coordination polymer. Their transition metal complexes are known to have antibacterial activities, magnetic properties, etc. Coordination polymers of M(II)-pyrazinamide with thiocyanate (M = Co (a), Cd (b)), prepared using bench-top layering technique with M(II):pza:SCN ratio of 1:2:2, is successfully crystallised at room temperature. Single crystal XRD was used to determine the crystal structure. Infrared and melting point determination were also performed. Crystal structure of both complexes, solved in Triclinic P-1, show that each octahedral metal centre is connected to two adjacent metal centres by double end-to-end thiocyanate bridge forming a 1D polymeric structure with M···M distances of 5.524 Å (in a) and 5.887 Å (in b). Two monodentate pyrazinamide ligands occupy the rest of the coordination sites on the metal centre in a trans relationship. Only in complex a, one lattice pyrazinamide molecule is involved in the asymmetric unit. Crystal packing of both a and b are also displaying non-covalent networks as a result of hydrogen-bonding involving the pyrazine ring, amide and carbonyl groups between adjacent chains and π···π interactions (only occurred in a). In addition, the observed melting points of both a and b are relatively close to each other (around 180°C), and ATR-IR spectra support the presence of the bridging thiocyanate and terminal pyrazinamide.

Zinc Coordination Polymers Containing Isomeric Forms of p‐(Thiazolyl)benzoic Acid: Blue‐Emitting Materials with a Solvatochromic Response to Water

Two coordination polymers of assorted dimensionality (1D, 2D) have been prepared, namely [Zn3(L2Th)4(OH)2·2(HL2Th)]∞ (1) and [Zn(L5Th)(OAc)]∞ (2), starting from ZnII salts and the isomeric forms of the organic linker p‐(thiazolyl)benzoic acid: p‐(2‐thiazolyl)benzoic acid (HL2Th) and p‐(5‐thiazolyl)benzoic acid (HL5Th). The isomers have been prepared ad hoc, following straightforward Pd‐catalyzed C–C coupling reaction protocols. In 1, the deprotonated ligand is coordinated through its carboxylate group only, with dangling thiazole groups. The –COO– units are bridging adjacent metal centers, thus creating a 1D chain. The Zn3 cluster is made of one six‐coordinate (Oh) and two four‐coordinate (Td) ZnII ions; triple‐bridging µ3‐OH groups are balancing the overall positive charge. The structure of 2 is instead made of Zn2(carboxylate)4 “paddle‐wheel” dimers as the constituting inorganic node. The octahedral metal coordination sphere includes two µ‐(κ‐COO) benzoate spacers, two µ‐(κ‐COO) acetate ions, the thiazole N atoms coming from adjacent building blocks, and a weak Zn···Zn axial interaction. The resulting final assembly is two‐dimensional (2D), where p‐(5‐thiazolyl)benzoate adopts a genuine µ‐[κ(COO):κ(N)] bridging coordination mode. The luminescent properties of both polymers have been analyzed in the solid state; they feature ligand‐centered emissions at λ = 434 nm (1) and λ = 427 nm (2). These electronic transitions fall in the visible region, giving the samples a characteristic blue color under an ordinary UV lamp (excitation at λ = 254 nm). The theoretical analysis of the electronic features of the ligands and related molecular orbitals reveals that the observed transitions are mainly of π→π* nature, involving π orbitals delocalized on both aromatic cycles. A significant (reversible) blueshift of the emission maximum of ca. 60 nm, from the visible to the UV region, has been observed for 1 when suspended in water.

Synthesis, structures and magnetic properties of two 2D → 3D entangled Cobalt(II) coordination polymers

Two Co(II) coordination polymers, namely Co(HBTC)(4-bpdb)·H2O (1) and Co(HBTC)(3-bpdb)·H2O (2) (H3BTC = 1,3,5-benzenetricarboxylic acid, 4-bpdb = 1,4-bis-(4-pyridyl)-2,3-diaza-1,3-butadiene, 3-bpdb = 1,4-bis(3-pyridyl)-2,3-diaza-1,3- butadiene), have been hydrothermally synthesized and characterized both structurally and magnetically. Compound 1 exhibits a (2D → 3D) polythreaded architecture. It is assembled from HBTC2− ligands to form a 2D puckered (4,4) layer plus 4-bpdb ligands which are orientated above and below each layer. The structure of compound 2 consists of a 2D (3,5) wavelike sheet constructed from HBTC2− anions and 3-bpdb spacers. The uncoordinated carboxyl groups of the HBTC2− ligands protrude from both sides of the wavelike sheet to form a 2D → 3D interdigitated motif. The magnetic properties of both compounds are also investigated, indicating antiferromagnetic interactions between the adjacent metal centers.

Introducing 2-(2-carboxyphenoxy)terephthalic acid as a new versatile building block for design of diverse coordination polymers: synthesis, structural features, luminescence sensing, and magnetism

In this work, an ether-bridged aromatic carboxylic acid, 2-(2-carboxyphenoxy)terephthalic acid (H3cpta), was applied as an unexplored building block for the generation of a novel series of coordination compounds, which represent the first examples of structurally characterized products derived from H3cpta, thus opening up its use as a versatile building block in crystal engineering research. The obtained products were formulated as [Cd(μ-Hcpta)(phen)(H2O)]n (1), [Mn(μ-Hcpta)(phen)(H2O)]n (2), {[Cd3(μ3-Hcpta)(μ4-cpta)(μ-Cl)(H2O)4]·2H2O}n (3), {[Cd3(μ6-cpta)2(py)2]·5H2O}n (4), [Mn3(μ5-cpta)2(2,2′-bipy)2]n (5), [Mn3(μ4-cpta)2(phen)3(H2O)2]n (6), {[Zn3(μ3-cpta)2(phen)3]·3H2O} (7), [Cd2(μ4-cpta)(μ-Cl)(phen)2]n (8), [Cd3(μ5-cpta)2(phen)2(H2O)2]n (9), [Cd3(μ4-cpta)2(phen)3(H2O)2]n (10), [Cd3(μ5-cpta)2(H2biim)2]n (11), [Zn2(μ6-cpta)(μ-Hbiim)]n (12), and [Ni3(μ3-cpta)2(phen)3(py)3(H2O)3]n (13). These compounds were assembled in the presence of an optional N-donor ancillary ligand, which was selected from 1,10-phenanthroline (phen), pyridine (py), 2,2′-bipyridine (2,2′-bipy), or 2,2′-biimidazole (H2biim). The obtained compounds 1–13 were fully characterized, including by IR spectroscopy, elemental analysis, thermogravimetric analysis (TGA), powder (PXRD) and single-crystal X-ray diffraction. The structures of 1–13 vary from a discrete 0D dimer (1) to the 1D (2, 3, 7, and 13) and 2D (5, 6, and 8–11) coordination polymers, as well as to the 3D metal–organic frameworks (MOFs 4 and 12). Such a wide structural diversity of 1–13 is guided by the following factors: a type of metal(II) node and counter anion, a deprotonation degree of the principal H3cpta block, and/or a type of an auxiliary ligand. Topological classification of H-bonded (in 1) and metal–organic (in 2–13) underlying networks was performed, disclosing the following topological types: sql (in 1), 2C1 (in 2 and 7), 3,4,5L45 (in 5, 9, and 11), 3,4L128 (in 6 and 10), 3,3,4L29 (in 8), and SP 1-periodic net (in 13), as well as some topologically unique nets (in 3, 4, and 12). Besides, magnetic properties of 2, 5, 6, and 13 were studied and modeled, revealing antiferromagnetic interactions between adjacent metal(II) centers. In addition, luminescence properties were investigated for 1, 3, 4, and 7–12; MOF 4 can be used as a sensitive material for the detection of Fe3+ ions in aqueous solution through the luminescence quenching effect.

Zinc Coordination Polymers Containing the m-(2-thiazolyl)benzoic Acid Spacer: Synthesis, Characterization and Luminescent Properties in Aqueous Solutions

Four 1D coordination polymers have been prepared, starting from ZnII salts and the organic linker m-(2-thiazolyl)benzoic acid (HL), also combined with auxiliary ligands: [Zn2(L)4(H2O)⋅2(MeCN)]∞ (1), [Zn2(L)3(NO3)(bipy)]∞ (2; bipy = 4,4′-dipyridyl), [Zn2(L)4(bipy)]∞ (3), [Zn2(L)4(PyEtPy)]∞ [4; PyEtPy = 1,2-bis(4-pyridyl)ethane]. In all species, the Zn2(carboxylate)4 “paddle-wheel” dimer is the constituting inorganic node, where the carboxylate groups from L- are bridging two adjacent metal centers. The square pyramidal metal coordination environment is completed by aquo ligands and the N(thiazole) atoms (in 1) or by the N donors from auxiliary bridging spacers like bipy (in 2 and 3) or PyEtPy (in 4). The luminescent properties in aqueous solutions of 3 and 4 have been examined. The N and S donors dangling from the thiazole rings in these polymers can engage into further supramolecular interactions with (acidic) metal cations, inducing a luminescence quenching after complexation. The interaction of 3 and 4 with HgII (in the form of its chloride salt HgCl2) has been analyzed as a representative example of this behaviour.

Tetra-Fe(iii) and deca-Mn(iii) metallacrowns built from bis-salicylhydrazide ligands: synthesis, structures and magnetic properties

Four new coordination metallacrowns were obtained via self-assembly of Fe(III) and Mn(III) ions with N′1,N′5-bis(5-X-2-hydroxybenzoyl)glutarohydrazide (X = Cl, H6pentaCShz; X = Br, H6pentaBShz) in DMF at room temperature. These metallacrowns consist of four or ten [M–N–N] repeated units with M = Fe(III) for 1 and 2, and M = Mn(III) for 3 and 4. In the systems containing different metal salts, it has been demonstrated that the 12-membered rings in 1 and 2 can be augmented to 30-membered cycles in 3 and 4 due to their metal coordination nature. Quasi-tetrahedra are formed in the tetra-nuclear ferric compounds and two fused distorted tetrahedra are accommodated in the deca-nuclear manganic ones. In other words, the morphologies of the metallacrowns in 1–4 are controlled by varying the metal and flexibility of the glutaryl group in H6pentaXShz. Magnetic studies of all the four compounds indicate antiferromagnetic coupling interactions between adjacent metal centers.

Anion-directed assembly of two AgI complexes based on 2,2'-(4H-1,2,4-triazole-3,4-diyl)dipyridine

Reaction of the Ag+ ions with 2,2'-(4H-1,2,4-triazole-3,4-diyl)dipyridine (L22) in the presence of NO3- and CH3SO3-, respectively, affords two silver(I) coordination compounds, namely {[Ag3(NO3)2(C12H9N5)2](NO3)]}n (I) and [Ag(CH3SO3)(C12H9N5)]2 (II). Both complexes have been characterized by single-crystal X-ray diffraction (CIF file CCDC nos. 1051589 (I) and 1051590 (II)). In complex I, the adjacent metal centers are interconnected via L22 ligands to afford a 1D coordination chain. Complex II shows the discrete cage-like binuclear coordination pattern with the Ag···Ag distance of 4.358(1) A.

Theoretical studies of methyl iodide oxidative addition to adjacent metal centers in diplatinum(II) complexes

The density functional theory calculations were used to study the electronic and steric effects between two adjacent platinum centers on the oxidative addition of methyl iodide to dimeric complex [Me2Pt(μ-bipym)PtMe2], in which bipym=2,2′-bipyrimidine. A double MeI oxidative addition was considered and the classical SN2 mechanism was suggested for both steps, and the involved transition states and intermediates were proposed. Consistent with the suggested mechanism, large negative ΔS‡ values were found in each step. The calculated energy barrier was larger in the second step as compared to the first step because of the electronic effects transmitted through the 2,2′-bipyrimidine ligand and the steric effects. In a comparative study, the monomeric complex [PtMe2(bipym)] was used in the MeI oxidative reaction as a “calibration reaction” to evaluate the effect of bipym ligand on the rate of the reaction of MeI with dimeric complex, [Me2Pt(μ-bipym)PtMe2].

Synthesis, Characterization and Crystal Structure of Zn(II) and Cd(II) One- and Two-Dimensional Coordination Polymers Derived from Pyridine Based Schiff Base ligand

Four coordination polymers with the formulas [Zn(L)(NO3)]n (1), {[Zn(L)(NO2)]·CH3OH}n (2), [Cd(L)(NO2)]n (3) and [Cd(L)(NO3)]n (4) {HL=2-benzolypyridine-isonicotinoylhydrazone (HBPIH)} have been synthesized and characterized by elemental analyses, FT-IR spectroscopy, 1H and 13C NMR and single crystal X-ray data diffraction. The L ligand acts as a negatively charged tetradentae N3O-donor in 1–3 and pentadentate ligand in 4. The Schiff base ligand coordinates to a metal center as N2O-donor and coordinates to adjacent metal center via its Para-Nitrogen of pyridlyl group in 1–3 leading to formation of one-dimensional, 1D, coordination polymer. The oxygen atom of the ligand L also coordinates to the third metal center as a bridging atom in 4 and forms a two-dimensional, 2D, coordination polymer. Metal centers are six coordinated with distorted octahedral geometry in 1–3 and seven coordinated with pentagonal bipyramid geometry in 4. The nitrate and nitrite groups act as asymmetric bidentate ligands in all complexes.

Synthesis, structure and magnetic property of cobalt(II) and manganese(II) complexes with mixed organic ligands

Two new metal complexes with mixed nitrogen-donor heterocyclic monocarboxylate and dicarboxylate ligands {[Co2(L)2(BDC)(H2O)]·2H2O·6DMF}n (1) and [Mn(L)(OX)0.5]n (2) (HL=3,5-di(pyridine-4-yl)benzoic acid, H2BDC=1,4-benzenedicarboxylic acid, H2OX=oxalic acid) have been prepared and characterized by single crystal and powder X-ray diffractions, IR, and thermogravimetric analyses. Crystallographic and topological analyses identify that both complexes have new framework topologies. Complex 1 is a (3,8)-connected 2-nodal 3D net with a point (Schläfli) symbol of (42.5)2(44.510.67.76.8), while 2 is a (4,5)-connected binodal net with a point (Schläfli) symbol of (42.63.8)(42.65.83). Furthermore, magnetic investigation shows that both complexes exhibit overall weak antiferromagnetic coupling between the adjacent metal centers.

Three novel transition metal coordination polymers based on (2,3-f)-pyrazino(1,10)phenanthroline-2,3-dicarboxylic acid sodium salt: Hydrothermal syntheses, structures, and properties

Three novel transition metal coordination polymers including [Cd2(Na2PPDA)2Cl4]n (I), [Zn(Na2PPDA)(ClO4)2·4H2O]n (II) and [Ni(Na2PPDA)(ClO4)2·4H2O]n (III) were prepared under hydrothermal conditions based on (2,3-f)-pyrazino(1,10)phenanthroline-2,3-dicarboxylic acid sodium salt (Na2PPDA) and characterized by elemental analysis, infrared spectrometry and single crystal X-ray diffraction. The outstanding structural feature of I is that four cadmium atoms are linked into a zigzag-shaped polymeric chain in the sequence of Cd–(Cl)2–Cd–(Cl)2–Cd–(Cl)2–Cd by three μ2-Cl bridges. Findings indicate that I displays a three-dimensional (3D) network constructed via hydrogen bonds and C–H⋯π interactions. Both coordination polymers of II and III present isomorphous and isostructural characters, in which the adjacent metal centers in the same chain connected up and down through hydrogen bonds (generated through μ2-ClO4− anions) to construct the left- and right-handed helical chains which are further interconnected by hydrogen bonds, thereby affording a two-dimensional (2D) layer. Moreover, thermogravimetric (TG) analyses, the magnetic and luminescent properties of as-synthesized coordination polymers were also investigated.

Syntheses, thermal analyses, crystal structures, FT-IR and Raman spectra of 2D [Zn(NH3)2(μ–ampy)M′(μ–CN)2(CN)2]n (M′ = Ni(II), Pd(II) or Pt(II)) complexes

Three new cyano-bridged heteronuclear polymeric complexes, [Zn(NH3)2(μ–ampy)Ni(μ–CN)2(CN)2]n (1), [Zn(NH3)2(μ–ampy)Pd(μ–CN)2(CN)2]n (2) and [Zn(NH3)2(μ–ampy)Pt(μ–CN)2(CN)2]n (3) (ampy=4-aminomethylpyridine) have been synthesized and characterized by vibrational spectroscopy (FT-IR and Raman), thermal (TG, DTG and DTA) and elemental analyses. The crystal structures of complexes 1 and 2 have been determined by the X-ray single crystal diffraction technique. Complexes 1 and 2 crystallize in the triclinic system with the space group P1¯. Structural studies reveal that the Ni(II) or Pd(II) ions are four coordinate with four cyanide–carbon atoms in a square planar geometry and the Zn(II) ion exhibits a distorted octahedral coordination geometry completed by the six N atoms from two ammine, one ampy and two cyano ligands. The adjacent metal centers are bridged by bis-monodentate cyano ligands to form a one-dimensional linear chain. These chains are linked by ampy ligands into a 2D sheet structure. The 2D units are connected together via intramolecular C–H⋯N and intermolecular N–H⋯N hydrogen bonding to form 3D supramolecular networks. In additional, there are also interactions between the Ni(II) or Pd(II) ion and the aromatic π-system. Vibrational spectral data indicate the presence of two ν(CN) bands for the complexes, which can be assigned to the terminal and bridging cyanide ligands. Decomposition reactions take place in the temperature range 40–900°C in a static air atmosphere.

Two Ni(II) Coordination Polymers Constructed with a Bent Connector: Crystal Structures and Magnetic Properties

The hydrothermal reactions of a bent ligand, 1H-3,5-bis(4-pyridyl)-1,2,4-triazole (bpt), with Ni(II) ions as well as two carboxylate co-ligands yielded two new Ni(II) coordination polymers, {[Ni2(bptc)(bpt)2(H2O)2]·9H2O}n and [Ni(hb)2(bpt)2(H2O)]n (H4bptc = 3,3’,4,4′-benzophenone-tetracarboxylate acid, Hhb = p-Hydroxybenzoate acid). In the first complex, bptc acts as a μ4-bridge to link metal centres, forming a two-dimensional (2-D) layer architecture. The 2-D layer is further connected by bpt pillars to generate a 3-D non-interpenetrating open framework with a 4-connected 64.82 topology. A magnetic study revealed the occurrence of a weak ferromagnetic interaction within the Ni(II) centres. In the second complex, adjacent metal centres are connected by water molecules to furnish a metal–water chain, in which hb and bpt are both terminal ligands.

Functionalized Adamantane Tectons Used in the Design of Mixed-Ligand Copper(II) 1,2,4-Triazolyl/Carboxylate Metal–Organic Frameworks

Bistriazoles, 1,3-bis(1,2,4-triazol-4-yl)propane (tr(2)pr) and 1,3-bis(1,2,4-triazol-4-yl)adamantane (tr(2)ad), were examined in combination with the rigid tetratopic 1,3,5,7-adamantanetetracarboxylic acid (H(4)-adtc) platform for the construction of neutral heteroleptic copper(II) metal-organic frameworks. Two coordination polymers, [{Cu(4)(OH)(2)(H(2)O)(2)}{Cu(4)(OH)(2)}(tr(2)pr)(2)(H-adtc)(4)]·2H(2)O (1) and [Cu(4)(OH)(2)(tr(2)ad)(2)(H-adtc)(2)(H(2)O)(2)]·3H(2)O (2), were synthesized and structurally characterized. In complexes 1 and 2, the N(1),N(2)-1,2,4-triazolyl (tr) and μ(3)-OH(-) groups serve as complementary bridges between adjacent metal centers supporting the tetranuclear dihydroxo clusters. The structure of 1 represents a unique association of two different kinds of centrosymmetrical {Cu(4)(OH)(2)} units in a tight 3D framework, while in compound 2, another configuration type of acentric tetranuclear metal clusters is organized in a layered 3,6-hexagonal motif. In both cases, the {Cu(4)(OH)(2)} secondary building block and trideprotonated carboxylate H-adtc(3-) can be viewed as covalently bound six- and three-connected nodes that define the net topology. The tr ligands, showing μ(3)- or μ(4)-binding patterns, introduce additional integrating links between the neighboring {Cu(4)(OH)(2)} fragments. A variable-temperature magnetic susceptibility study of 2 demonstrates strong antiferromagnetic intracluster coupling (J(1) = -109 cm(-1) and J(2) = -21 cm(-1)), which combines for the bulk phase with a weak antiferromagnetic intercluster interaction (zj = -2.5 cm(-1)).

Insights into electrochemiluminescent enhancement through electrode surface modification

The electrochemiluminescent (ECL) properties of a luminescent metal centre, [Ru(bpy)(3)](2+), can be significantly modulated through its electronic interaction with neighbouring centres and the polymer backbone used to confine it on an electrode surface. From the perspective of ECL based sensing devices, an increase in the ECL efficiency of a metallopolymer film can result in enhanced sensor sensitivity and selectivity. This work probes the ECL properties of both conjugated, [Ru(bpy)(2)(PPyBBIM)(10)](2+), and non-conjugated, [Ru(bpy)(2)(PVP)(10)](2+), ruthenium based metallopolymer films based on a well documented reaction with sodium oxalate, where bpy is 2,2'-bipyridyl, PPYBBIM is poly[2-(2-pyridyl)-bibenzimidazole] and PVP is poly(4-vinylpyridine). Through a combination of ground state electrochemical studies and ECL measurements, the ECL efficiency for each film is determined. This study reveals that despite a dramatic influence in charge transfer rates between metal centres, as observed for the conducting polymer, mediated through the conducting polymer backbone, a corresponding increase in ECL efficiency is not always observed. The degree of communication between the adjacent excited state metal centres are an important consideration for ECL enhancement however self quenching, luminophore distribution and film porosity must also be considered.

Lanthanide N,N-Dimethylaminodiboranates as a New Class of Highly Volatile Chemical Vapor Deposition Precursors

New lanthanide N,N-dimethylaminodiboranate (DMADB) complexes of stoichiometry Ln(H(3)BNMe(2)BH(3))(3) and Ln(H(3)BNMe(2)BH(3))(3)(thf) have been prepared, where Ln = yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and lutetium, except that isolation of the desolvated complexes proved difficult for Eu and Yb. The tetrahydrofuran (thf) complexes are all monomeric, and most of them adopt 13-coordinate structures in which each DMADB group chelates to the metal center by means of four B-H···Ln bridges (each BH(3) group is κ(2)H; i.e., forms two B-H···Ln interactions). For the smallest three lanthanides, Tm, Yb, and Lu, the metal center is 12 coordinate because one of the DMADB groups chelates to the metal center by means of only three B-H···Ln bridges. The structures of the base-free Ln(H(3)BNMe(2)BH(3))(3) complexes are highly dependent on the size of the lanthanide ions: as the ionic radius decreases, the coordination number decreases from 14 (Pr) to 13 (Sm) to 12 (Dy, Y, Er). The 14-coordinate complexes are polymeric: each metal center is bound to two chelating DMADB ligands and to two "ends" of two ligands that bridge in a Ln(κ(3)H-H(3)BNMe(2)BH(3)-κ(3)H)Ln fashion. In the 13-coordinate complexes, all three DMADB ligands are chelating, but the metal atom is also coordinated to one hydrogen atom from an adjacent molecule. The 12-coordinate complexes adopt a dinuclear structure in which each metal center is bound to two chelating DMADB ligands and to two ends of two ligands that bridge in a Ln(κ(2)H-H(3)BNMe(2)BH(3)-κ(2)H)Ln fashion. The complexes react with water, and the partial hydrolysis product [La(H(3)BNMe(2)BH(3))(2)(OH)](4) adopts a structure in which the lanthanum and oxygen atoms form a distorted cube; each lanthanum atom is connected to three bridging hydroxyl groups and to two chelating DMADB ligands. One B-H bond of each chelating DMADB ligand forms a bridge to an adjacent metal center. Field ionization MS data, melting and decomposition points, thermogravimetric data, and NMR data, including an analysis of the paramagnetic lanthanide induced shifts (LIS), are reported for all of the complexes. The Ln(H(3)BNMe(2)BH(3))(3) compounds, which are highly volatile and sublime at temperatures as low as 65 °C in vacuum, are suitable for use as chemical vapor deposition (CVD) and atomic layer deposition (ALD) precursors to thin films.

Valence-directed assembly and magnetic properties of two polynuclear pyrazine-2-amidoxime Fe complexes

Abstract The reaction of FeCl3·6H2O/FeCl2·4H2O, pyrazine-2-amidoxime (H2pzaox) and triethylamine (1:1:2 mol ratio) in MeOH/H2O (v/v = 1:1) affords undecanuclear and trinuclear complexes [Fe11(μ4-O)7(μ2-O)3(Hpzaox)9(H2O)6Cl]Cl3·5CH3OH·5H2O (1) and [Fe3(Hpzaox)6]Cl2·10H2O (2), respectively. The compounds were characterized by IR, X-ray crystallography and temperature-/field-magnetic susceptibility measurements. Complexes 1 contains the [FeIII11(O)10]13 + core comprising eleven FeIII ions in a two floors ‘Tower’ disposition which was linked by nine oxime “N O” groups of the H2pzaox ligands. In complex 1, Hpzaox- anion shows μ2:η1η1η1 and μ3:η1η1η2 two coordination modes. Trinuclear complex 2 is a mix valence with Fe(III)–Fe(II)–Fe(III) coordinated compound in which the ligands are only coordinated through μ2:η1η1η1 mode. Three oxime groups “N O” bridge the adjacent metal centers with Fe⋯Fe separation of 3.5255(8) A. Magnetic measurements of undecanuclear and trinuclear compounds in the 2–300 K temperature range reveal anti-ferromagnetic interactions between the Fe ions.

Ferromagnetic interactions in EO-azido-bridged binuclear transition metal(II) systems: Syntheses, crystal structures and magnetostructural correlations

Three new isostructural binuclear transition metal complexes with azido ion and 1,2-bis(3-(pyridin-2-yl)- 1 H -pyrazol-1-yl)ethane (bppe), formulated as [M 2 (N 3 ) 2 (bppe) 2 ](ClO 4 ) 2 (M = Co, 1; Ni, 2; Cu, 3), were successfully synthesized. They were structurally and magnetically characterized. In 1-3, the double azido ions link two adjacent octahedral metal centers together in the end-to-on mode (EO), with the M-N EO -M angles of 99.41?, 100.24? and 99.80?, respectively. The co-ligand bppe acts as terminal ligand to saturate the remaining coordination sites. The magnetic properties of 1-3 have been investigated in the temperature range of 2-300 K. Fitting of the magnetic susceptibility data revealed the occurrence of the strong ferromagnetic interactions [ J = 26.32 cm -1 ( 1 ), J = 38.23 cm -1 ( 2 ) and J = 139.83 cm -1 ( 3 )]. Density functional theory calculations have been performed on 1-3 to provide a magneto-structural correlation of the ferromagnetic behavior.

Azide bridged dicopper(II), dicobalt(II) complexes and a rare double μ-chloride bridged ferromagnetic dicobalt(II) complex of a pyrazolyl-pyrimidine ligand: Synthesis, crystal structures, magnetic and DFT studies

Two new dinuclear copper(II) complexes [Cu2(PymPz)2(N3)2Cl2] (1), [Cu2(PymPz)2(N3)4] (2) and two new dinuclear cobalt(II) complexes [Co2(PymPz)2Cl4] (3), [Co2(PymPz)2(N3)4] (4) [PymPz=2-(3,5-dimethyl-1H-pyrazol-1-yl)-4,6-dimethylpyrimidine] have been synthesized and characterized crystallographically and spectroscopically. In each of the complexes 1, 2 and 4 the two adjacent metal centers are bridged by a pair of μ-1,1 azide groups whereas in 3 the metal centers are bridged by a pair of chloride ions. In the complexes, all the metal centers are pentacoordinated. In 1 and 2 the copper(II) centers have distorted square pyramidal geometry (τ=0.18 for 1 and 0.091 for 2) but in 3 and 4 cobalt(II) centers have distorted trigonal bipyramidal geometry (τ=0.619 for 3 and 0.557 for 4). Complexes 1 and 2 show antiferromagnetic interaction (J=−7.09cm−1 for 1 and J=−17.00cm−1 for 2) whereas 3 and 4 show ferromagnetic interaction (J=7.44cm−1 for 3 and J=10.45cm−1 for 4). Complex 3 displays an unprecedented ferromagnetic interaction over double μ-chloro bridges in the observed angle range (94.87°). The exchange pathways parameters for all the complexes have also been evaluated from density functional theoretical calculations to corroborate the bridging signatures with experimental findings.