Chromium(III) stars and butterflies: synthesis, structural and magnetic studies of tetrametallic clusters

We report the synthesis, structures and magnetic properties of a series of chromium(III) metal-centered triangle (or "star") clusters, [Cr(4){RC(CH(2)O)(3)}(2)(4,4'-R'(2)-bipy)(3)Cl(6)] [R = Et, R' = H (2); R = HOCH(2), R' = H (3); R = Et, R' = (t)Bu (4)], prepared by two-step solvothermal reactions starting from [CrCl(3)(thf)(3)]. The product of the first stage of this reaction is the salt [Cr(bipy)(2)Cl(2)](2)[Cr(2)Cl(8)(MeCN)(2)] (1). In the absence of the diimine, a different family of tetrametallics is isolated: the butterfly complexes [Cr(4){EtC(CH(2)O)(3)}(2){NH(C(R)NH)(2)}(2)Cl(6)] (R = Me (5), Et (6), Ph (7)] where the chelating N-acetimidoylacetamidine NH(C(R)=NH)(2) ligands are formed in situ via condensation of the nitrile solvents (RCN) under solvothermal conditions. Magnetic measurements show the chromium stars to have an isolated S = 3 ground state, arising from antiferromagnetic coupling between the central and peripheral metal ions, analogous to the well-known Fe(III) stars. Bulk antiferromagnetic ordering is observed at 0.6 K. The butterfly complexes have a singlet ground state, with a low-lying S = 1 first excited state, due to dominant wing-body antiferromagnetic coupling.     

Thermal analysis,synthesis and structural studies of heterometallic {Fe2MO} salicylate complexes

Journal of Thermal Analysis and Calorimetry - Four new trinuclear heterometallic molecular complexes with the {Fe2IIIMII μ3-O} core, where M?=?Mn(II), Ni(II), Cu(II) and Zn(II),...     

Record High‐Nuclearity Polyoxoniobates: Discrete Nanoclusters {Nb114}, {Nb81}, and {Nb52}, and Extended Frameworks Based on {Cu3Nb78} and {Cu4Nb78}

A series containing the highest nuclearity polyoxoniobate (PONb) nanoclusters, ranging from dimers to tetramers, has been obtained. They include one 114‐nuclear {Li₈⊂Nb₁₁₄O₃₁₆}, one 81‐nuclear {Li₃K⊂Nb₈₁O₂₂₅}, and one 52‐nuclear {H₄Nb₅₂O₁₅₀}. The Nb nuclearity of these PONbs is remarkably larger than those of all known high‐nuclearity PONbs (≤32). Furthermore, the introduction of 3d Cu²⁺ ions can lead to the generation of extended inorganic–organic hybrid frameworks built from novel, high‐nuclearity, nanoscale heterometallic PONb building blocks {H₃Cu₃Nb₇₈O₂₂₂} or {H₃Cu₄(en)Nb₇₈O₂₂₂}. These building blocks also contain the largest number of Nb centers of any heterometallic PONbs reported to date. The synthesis of new‐type PONbs has long been a challenging subject in PONb chemistry.     

Structures and magnetism of {Ni2Na2}, {Ni4} and {Ni6(II)Ni(III)} 2-hydroxy-3-alkoxy-benzaldehyde clusters

Three polynuclear complexes, [NiNa(μ(1,1,1)-N(3))(μ-hmb)(2)(DMF)](2), (1), [Ni(4)(μ(3)-OMe)(4)(heb)(4)(MeOH)(1.05)(H(2)O)(2.95)], (2) and [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)]·(ClO(4))(3) (3) (Hhmb = 2-hydroxy-3-methoxy-benzaldehyde; Hheb = 2-hydroxy-3-ethoxy-benzaldehyde), were prepared by reaction of the appropriate ligand with nickel(II) perchloride hexahydrate under solvothermal conditions. All compounds were characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Compound 1 exhibits a centrosymmetric heterotetranuclear cluster which represents the first nickel complex to possess two connected face-sharing cubes structure {Ni(2)Na(2)N(2)O(4)}. Compound 2 has a tetranuclear Ni cluster with a cubane topology in which the Ni(II) and the oxygen atoms from the methanol ligands occupying alternate vertices of the cube. Compound 3 consisits of a mixed-valence [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)](3+) subunits and it represents the first nickel {Ni(II)(6)Ni(III)} complex to possess a planar hexagonal disc-like structure. The results show that the minor ligand modifications or solvent change have a key role in the structural control of the self-assembly process. Magnetic properties of 1-3 in the 300-2 K have been discussed. The {Ni(2)Na(2)} (1) and {Ni(4)} (2) core display dominant ferromagnetic interactions from the nature of the binding modes through μ(3)-N(3)(-) or μ(3)-OCH(3)(-), while {Ni(II)(6)Ni(III)} core (3) displays dominant anti-ferromagnetic interactions from the nature of the binding modes through μ(3)-OH(-).     

Controlling transformations in the assembly of polyoxometalate clusters: {Mo11V7}, {Mo17V8} and {Mo72V30}

The reaction of molybdate with vanadium(V) in the presence of sulfite anions is explored showing how, via cation control, stepwise assembly through the {Mo(11)V(7)} cluster yields a {M(25)} cluster-based compound, [Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(μ(9)-SO(3))(Mo(VI)(6)V(V)O(22))](10-) (1a), which was first discovered using cryospray mass spectrometry, whereas switching the cation away from ammonium allows the direct formation of the spherical 'Keplerate' {Mo(72)V(30)} cluster.     

Synthesis, structural studies and reactivity of vanadium complexes with tridentate (OSO) ligand

The direct reaction between [VCl(3)(thf)3] or [VO(OEt)3] and 2,2'-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenol (tbopH(2)) leads to the formation of [V(2)(micro-tbop-kappa(3)O,S,O)2Cl(2)(CH(3)CN)(2)] (1).4CH(3)CN or [V(2)(micro-OEt)2(O)2(tbop-kappa(3)O,S,O)2] (2), respectively, in high yield. Compounds 1 and 2 were characterized by chemical and physical techniques including X-ray crystallography and variable temperature magnetic susceptibility studies (J = -29.1 cm(-1)) for 1. Complexes 1 and 2 were supported on MgCl2 and when activated with aluminium alkyls, were found to effectively polymerize ethene to produce polyethylene with a narrow molecular weight distribution M(w)/M(n) approximately 3.     

Synthesis, crystal structure, and magnetic properties of hexanuclear [{MnL2}4{Nb(CN)8}2] and Nonanuclear [{MnL2}6{Nb(CN)8}3] heterometallic clusters (L=bpy, phen)

A hexanuclear cyano-bridged {MnII4NbIV2} cluster (1) bearing 2,2'-bipyridine (bpy) as the blocking ligand at manganese is obtained from the reaction of cis-[MnCl2(bpy)2] and K4[Nb(CN)8]. When the blocking ligand is 1,10-phenanthroline (phen), a nonanuclear cluster {MnII6NbIV3} (2) is obtained. The structure of [{Mn(bpy)2}4{Nb(CN)8}2] has been solved by single-crystal X-ray crystallography, whereas the phen derivative has been confirmed by means of the structure analysis of the corresponding WIV analogue [{Mn(phen)2}6{W(CN)8}3(H2O)2]. Magnetic measurements revealed S=9 and 27/2 spin ground states for these aggregates as a result of antiferromagnetic Nb-Mn interaction with JNb-Mn=-18.1 cm(-1) (1) and -13.6 cm(-1) (2).     

Assembly of a family of mixed metal {Mo:V} polyoxometalates templated by TeO3(2-): {Mo12V12Te3}, {Mo12V12Te2} and {Mo17V8Te}

The influence of the pyramidal heteroanion, TeO(3)(2-) in the self-assembly of mixed metal (Mo/V) systems, is demonstrated by the isolation of three novel mixed-metal, mixed-valence architectures, {Mo(12)V(12)Te(3)} (1), {Mo(12)V(12)Te(2)} (2) and {Mo(17)V(8)Te} (3) with the tellurium centres exhibiting the novel μ(8)-TeO(4) and μ(9)-TeO(3) coordination modes while compounds 1 and 2 were discovered utilizing ESI mass spectrometry.     

Infrared Spectroscopy of \hbox {CH}_4/\hbox {N}_{2} and \hbox {C}_{2}\hbox {H}_{m}/\hbox {N}_{2} ({m = 2, 4, 6}) Gas Mixtures in a Dielectric Barrier Discharge

Fourier transform infrared spectroscopy of \(\hbox {CH}_{4}/\hbox {N}_{2}\) and \(\hbox {C}_{2}\hbox {H}_{m}/\hbox {N}_2\) ( \(m = 2, 4, 6\) ) gas mixtures in a medium pressure (300 mbar) dielectric barrier discharge was performed. Consumption of the initial gas and formation of other hydrocarbon and of nitrogen-containing HCN and \(\hbox {NH}_{3}\) molecules was observed. \(\hbox {NH}_{3}\) formation was further confirmed by laser absorption measurements. The experimental result for \(\hbox {NH}_{3}\) is at variance with simulation results.     

Sn-centred icosahedral Rh carbonyl clusters: synthesis and structural characterization and 13C-{103Rh} HMQC NMR studies

The reaction of [Rh(7)(CO)(16)](3-) with SnCl(2).2H(2)O in a 1 : 1 molar ratio under N(2) results in the formation of the new heterometallic cluster, [Rh(12)Sn(CO)(27)](4-), in very high yield (ca. 86%). Further controlled additions of SnCl(2).2H(2)O, or solutions of HCl, or [RhCl(COD)](2), give [Rh(12)(micro-Cl)(2)Sn(CO)(23)](4-). Similarly, addition of HBr to [Rh(12)Sn(CO)(27)](4-) gives the related cluster [Rh(12)(micro-Br)(2)Sn(CO)(23)](4-). Notably, if the addition of SnCl(2).2H(2)O to [Rh(12)Sn(CO)(27)](4-) is carried out under a CO atmosphere, the reaction takes a different course and leads to the formation of the new cluster, [Rh(12)Sn(micro(3)-RhCl)(CO)(27)](4-). All the above clusters have been shown by single-crystal X-ray diffraction studies to have a metal framework based on an icosahedron, which is centred by the unique Sn atom. Their chemical reactivity and (13)C-{(103)Rh} HMQC NMR spectroscopic characterization are also reported.     

Syntheses, structures, and properties of high-nuclear 3d-4f clusters with amino acid as ligand: {Gd6Cu24}, {Tb6Cu26}, and {(Ln6Cu24)2Cu} (Ln = Sm, Gd)

Four novel high-nuclear 3d-4f heterometallic clusters were obtained through the self-assembly of Ln(III), Cu(II), and amino acid ligands (2-methylalanine (mAla), glycine (Gly), and L-proline (Pro), respectively). The metal skeleton of cluster 1, [Gd6Cu24(mu3-OH)30(mAla)16(ClO4)(H2O)22].(ClO4)17.(OH)2.(H2O)2(0), may be described as a huge {Gd6Cu12} octahedron connected with 12 additional Cu(II) ions. The structure of cluster 2, Na4[Tb6Cu26(mu3-OH)30(Gly)18(ClO4)(H2O)22].(ClO4)25.(H2O)42, may be described as a {Tb6Cu24} main structure connected with two [Cu(Gly)(H2O)2]+ groups. Compounds {[Ln6Cu24(mu3-OH)30(Pro)12(Ac)6(ClO4)(H2O)13]2Cu(Pro)2}.(ClO4)18.(OH)16.(H2O)55 (Ln= Sm (3), Gd (4)) are 61-nuclear clusters, which represent the largest known 3d-4f clusters so far, the structure can be described as two {Ln6Cu24} octahedral units connected by a trans-Cu(proline)2 bridge. The electrical conductivity measurements reveal that they are temperature-sensitive semiconductors. The magnetic susceptibility measurements display that compound 4 is ferromagnetic.     

Synthesis, structural characterization, and magnetic studies of polynuclear iron complexes with a new disubstituted pyridine ligand

A series of novel polyiron species have been prepared from the reaction of iron chloride with the 2,5-disubstituted pyridines H2L(n) (H2L1) = N,N'-bis(n-butylcarbamoyl)pyridine-2,6-dicarboxamide; H2L2 = N,N'-bis(n-ethylcarbamoyl)pyridine-2,6-dicarboxamide). By small modifications of the experimental conditions under which the reactions are carried out, it has been possible to prepare the quadruply stranded diiron(II) complex [Fe2(mu-H2L1)4(mu-Cl)2][FeCl4]2 (1), the metallamacrocycle [Fe2(mu-H2L1)2(THF)4Cl2][FeCl4]2 (2), the hexairon(III) compound [Fe6(L1)2(mu-OMe)6(mu4-O)2Cl4] (3), and the mixed-valence trinuclear iron complexes [Fe3(L(n))3(mu3-O)] (n = 1, 4; n = 2, 5). The X-ray crystal structures of 3 and 5 and magnetic studies for all the compounds are herein presented. Interestingly, the structural analysis of 5 at room temperature indicates that one of the iron centers is Fe(III) while the other two have an average valence state between Fe(II) and Fe(III). The five complexes herein presented demonstrate the great versatility that the new ligand has as a building block for the formation of supramolecular coordination assemblies.     

Synthesis and Characterization of 1,3,2‐Bis (arylamino) phospholidine, 2‐oxide Derivatives: Crystal Structures of $\rm Cl(O)\overline{PN(p-Me-C_{6}H_{4})CH_{2}CH_{2}N}(p-Me-C_{6}H_{4})$ and $\rm ((CH_{2}C_{6}H_{5})(O)\overline{PN(p-Me-C_{6}H_{4})CH_{2}CH_{2}N}(p-Me-C_{6}H_{4})$

Using phosphoryl chloride as a substrate, a family of 1,3,2‐bis(arylamino) phospholidine, 2‐oxide of the general formula ; (X=Cl, 6a ; X=NMe₂, 1b ; X=N(CH₂C₆H₅)(CH₃), 2b ; X=NHC(O)C₆H₅, 3b ; X=4Me‐C₆H₄O, 4b ; X=C₆H₅O, 5b ; X=NHC₆H₁₁, 6b ; X=OC₄H₈N, 7b ; X=C₅H₁₀N, 8b ; X=NH₂, 9b ; X=F, 10b and Ar=4Me‐C₆H₄) was prepared and characterized by ¹H, ¹⁹F, ³¹P and ¹³C NMR and IR spectroscopy, and elemental analysis. A general and practical method for the synthesis of these compounds was selected. The structures of 6a and 2b were determined by single‐crystal X‐ray diffraction techniques. The low temperature NMR spectra of 2b revealed the restricted rotation of P‐N bond according to two independent molecules in crystalline lattice.     

Synthesis and structural studies on trivalent lanthanide 2-acetylpyridine-2-furoylhydrazone complexes

Summary Two types of [M(Hapfh)₂Cl]Cl₂ and [M(apfh)₂OH] complexes; Hapfh=2-acetylpyridine-2-furoylhydrazone [M=La^III, Pr^III, Nd^III, Eu^III or Dy^III], possessing the neutral and deprotonated ligand respectively, have been prepared and characterised by elemental analysis, molar conductance, magnetic susceptibility measurements, electronic, i.r. and n.m.r. (¹H and¹³C) spectral studies. The nephelauxetic ratio ( ), covalency () and bonding parameter (b^1/2) have been calculated for the Nd^III complexes. I.r. spectral studies reveal that Hapfh acts as a neutral tridentate in [M(Hapfh)₂Cl]Cl₂ and uninegative tridentate in [M(apfh)₂OH]. A coordination number of seven around the metal ions is proposed.     

Synthesis,structure, and properties of trinuclear pivalate {Zn2Eu} complexes with N-donor ligands

New luminescent heterometallic complexes of Eu³⁺ and Zn²⁺ were synthesized: Zn₂Eu(NO₃)(Piv)₆(L)₂ (Piv is pivalate anion, L = MeCN (1), 2,3-lutidine (2), 2,2′-bpy (3)) and [Zn₂(Piv)₃(2,2′-bpy)₂][ZnEu(NO₃)₃(Piv)₃(2,2′-bpy)] (4). In the case of 2,2′-bpy, the order of mixing of the reagents ([Zn(Piv)₂] _n , Eu(NO₃)₃·6H₂O, and 2,2′-bpy) affects the composition of the final reaction product: the reaction of [Zn(Piv)₂] _n and Eu(NO₃)₃·6H₂O (in the ratio Zn : Eu = 3 : 1) in MeCN affords complex 1 and the subsequent addition of 2,2′-bpy (Zn : L = 1 : 1) affords complex 3. Complex 4 is formed in the reaction of [Zn(Piv)₂] _n and 2,2′-bpy (Zn : L = 1 : 1) in MeCN followed by the addition of Eu(NO₃)₃·6H₂O (Zn : Eu = 3 : 1). The luminescence spectra of compounds 1–4 (Zn : Eu = 3 : 1) exhibit metal-centered luminescence of Eu³⁺. The most efficient ligand-antenna is 2,2′-bpy, which is due to the optimum position of the triplet level of this ligand.     

Structural Variety of Niobium(V) Polyoxo Clusters Obtained from the Reaction with Aromatic Monocarboxylic Acids: Isolation of {Nb2O}, {Nb4O4} and {Nb8O12} Cores

The reactivity of aryl monocarboxylic acids (benzoic, 1- or 2-naphtoic, 4’-methylbiphenyl-4-carboxylic, and anthracene-9-carboxylic acids) as complexing agents for the ethoxide niobium(V) (Nb(OEt)₅ precursor has been investigated. A total of eight coordination complexes were isolated with distinct niobium(V) nuclearities as well as carboxylate complexation states. The use of benzoic acid gives a tetranuclear core Nb₄(μ₂-O)₄(L)₄(OEt)₈] (L=benzoate ( 1 )) with four Nb−(μ₂-O)−Nb linkages in a square plane configuration. A similar tetramer, 7 , was obtained with 2-naphtoic acid by using a 55 % humid atmosphere synthetic route. Two types of dinuclear brick were identified with one central Nb−(μ₂-O)−Nb linkage; they differ in their complexation state, with one bridging carboxylate ([Nb₂(μ₂-O)(μ₂-OEt)(L)(OEt)₆], with L=1-naphtoate ( 3 ) or anthracene-9-carboxylate ( 5 )) or two bridging carboxylate groups ([Nb₂(μ₂-O)(L)₂(OEt)₆], with L=4’-methylbiphenyl-4-carboxylic ( 4 ) or anthracene-9-carboxylate ( 6 )). An octanuclear moiety [Nb₈(μ₂-O)₁₂(L)₈(η₁-L)_4−x(OEt)_4+x] (with L=2-naphtoate, x=0 or 2; 8 ) was obtained by using a solvothermal route in acetonitrile; it has a cubic configuration with niobium centers at each node, linked by 12 μ₂-O groups. The formation of the niobium oxo clusters was characterized by infrared and liquid ¹H NMR spectroscopy in order to analyze the esterification reaction, which induces the release of water molecules that further react through oxolation with niobium atoms, in different {Nb₂O}, {Nb₄O₄} and {Nb₈O₁₂} nuclearities.     

A family of cyanide-bridged molecular squares: structural and magnetic properties of [{MIICl2}2{CoII(triphos)(CN)2}2].xCH2Cl2, M = Mn, Fe, Co, Ni, Zn

The syntheses, structures, and magnetic properties of a series of tetranuclear cyanide-bridged compounds are reported. This family of molecular squares, [{M(II)Cl2}2{Co(II)(triphos)(CN)2}2] (M = Mn ([CoMn]), Fe ([CoFe]), Co ([CoCo]), Ni ([CoNi]), and Zn ([CoZn]), triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane), has been synthesized by the reaction of Co(II)(triphos)(CN)2 and MCl2 (M = Mn, Co, Ni, Zn) or Fe4Cl8(THF)6 in a CH2Cl2/EtOH mixture. These complexes are isostructural and consist of two pentacoordinate Co(II) and two tetrahedral M(II) centers. The resulting molecular squares are characterized by antiferromagnetic coupling between metal centers that generally follows the spin-coupling model S total = SM(II)1 - SCo1 + SM(II)2 - SCo2. Magnetic parameters for all the complexes were measured using SQUID magnetometry. Additionally, [CoZn] and [CoMn] were studied by both conventional and high-frequency and high-field electron paramagnetic resonance.     

Chloro and azido bonded manganese complexes: synthesis,structural, and magnetic studies

Two manganese complexes, [Mn₂(tptz)₂Cl₄] · CH₃CN (1) and [Mn(tptz(ac)(N₃)(H₂O)] · H₂O (2) (where tptz = 2,4,6-tri(2-pyridyl)-1,3,5-triazine, ac = acetate anion), were synthesized and characterized by elemental analyses, infrared spectra, and UV–Vis absorption spectral analyses. The structures of both the complexes were determined by single crystal X-ray diffraction analysis. Complex 1 is binuclear with chloro-bridged manganese ions at the Mn–Mn separation of 3.777(27) Å. Each manganese center in 1 is six coordinate with three nitrogens from a tridentate tptz, three chlorides (one terminal and two bridging), adopting a centrosymmetric distorted octahedral geometry. Various hydrogen bonds form 2-D spiral structures in 1 with Mn–Mn separation of 7.421(2) Å along a-axis and 9.121(2) Å along b-axis. Complex 2 is seven coordinate with pentagonal bipyramidal geometry. The metal center coordinates to three nitrogens from tptz, two oxygens from acetate, one nitrogen from azide, and one oxygen from water. It has a 1-D layered structure, where three independent molecules are linked by uncoordinated water present in the lattice. Magnetic susceptibility in the temperature range 5–300 K for 1 shows the presence of antiferromagnetic interaction between the local high-spin manganese(II) ions with J = ?0.17 cm^?1.     

Construction of three new metal-organic frameworks with distinct SBUs: trinuclear {Cd3(COO)6} clusters,inorganic -Cd-O-Cd- chains,and heterometallic trinuclear {Cd2Ba(COO)4} clusters

Three metal-organic frameworks (MOFs), [Cd₃(OABDC)₂(e-urea)₄]_n (1), [Cd₃(OABDC)₂(H₂O)₅)]_n (2) and [Cd₂Ba(OABDC)₂(H₂O)₇]_n (3) (H₃OABDC = 5-oxyacetate isophthalic acid, e-urea = 2-imidazolidinone), were prepared using H₃OABDC and metal salts. Single-crystal X-ray diffraction analyses reveal that 1 features a 2-D layered structure constructed from trinuclear {Cd₃(COO)₆} SBUs and represents a (3,6)-connected kgd topology. Compounds 2 and 3 are 3-D inorganic–organic hybrid frameworks; 2 employs infinite inorganic –Cd–O–Cd– chains as SBUs, whereas (3,6)-connected ant-type 3 employs heterometallic trinuclear {Cd₂Ba(COO)₄} clusters as SBUs. The structures of these three compounds indicate that the SBUs play an important role in the construction of MOFs. Moreover, the thermal stabilities and solid-state photoluminescent properties of these three compounds have also been investigated.     

Synthesis and physico-chemical studies of novel mixed-ligand cyanonitrosyl {CrNO}5 complexes of chromium with benzyl-, benzoyl- and acetyl-pyridines

Summary Novel mixed-ligand cyanonitrosyl complexes of chromium(I), [Cr(NO)(CN)₂(L)₂(H₂O)], (where L=2-, 3-, or 4-benzylpyridine, 2-(4-chlorobenzyl)pyridine, 2-, 3-, or 4-benzoylpyridine, 3-(4-methylbenzoyl)pyridine, or 2-, 3-, or 4-acetylpyridine) have been prepared by the interaction of potassium pentacyanonitrosylchromate(I) monohydrate, K₃[Cr(NO)(CN)₅]·H₂O with L. The complexes, characterized by elemental analyses, magnetic measurements, e.s.r. and i.r. spectral studies, contain chromium(I) in a low-spind ⁵-configuration. An octahedral structure, where CN istrans to CN, L istrans to L, and NO istrans to water is proposed for all the complexesEnemark and Feltham⁽¹⁾ have proposed circumventing the problem of the non-innocent nature of the nitrosyl ligand by considering nitrosyls as containing the {MNO} ⁿ group, wheren is the number of electrons of M, plus the number of electrons in the ^*-orbital of the NO (or more convenientlyn is the number of d-electrons if nitrosyl is regarded as being coordinated as NO⁺)