Structure and properties of Mn(n), Mn(n)-, and Mn(n)+ clusters (n = 3-10)

Electronic and geometrical structures of Mn(3)-Mn(10) together with their singly negatively and positively charged ions are computed using density functional theory with generalized gradient approximation. The ground-state spin multiplicities in the neutral series are 16, 21, 4, 9, 6, 5, 2, and 5, for Mn(3)-Mn(10), respectively. Thus, there is a transition from a ferromagnetic ground state to a ferrimagnetic ground state at Mn(5). The energy difference between ferrimagnetic and ferromagnetic states in Mn(n) grows rapidly with increasing n and exceeds 2 eV in Mn(10). The corresponding change from ferro- to ferrimagnetic ground state occurs at Mn(6)(-) and Mn(3)(+) in the anionic and cationic series, respectively. Beginning with Mn(6), the ion spin multiplicities differ from that of the neutral by +/-1 (i.e., they obey the empirical "+/-1 rule"). We found that the energy required to remove an Mn atom is nearly independent of the charge state of an Mn(n) cluster and the number of atoms in the cluster, except for Mn(3). The results of our calculations are in reasonable agreement with experiment, except for the experimental data on the magnetic moments per atom, where, in general, we predict smaller values than the experiment.     

High-nuclearity 3d-4f [FeIII5LnIII8] complexes: synthesis, structure and magnetic properties

The isostructural tridecanuclear mixed-metal [FeIII5LnIII8] (Ln = Pr, Nd, Gd) aggregates are the largest [Fe-Ln] clusters reported to date and the magnetic properties suggest a ferrimagnetic arrangement in [Fe5Pr8] and [Fe5Nd8], whereas for [Fe5Gd8] ferromagnetic interactions are dominant leading to a large spin ground state.     

Electronic structure of bis(imino)pyridine iron dichloride, monochloride, and neutral ligand complexes: a combined structural, spectroscopic, and computational study

The electronic structure of a family of bis(imino)pyridine iron dihalide, monohalide, and neutral ligand compounds has been investigated by spectroscopic and computational methods. The metrical parameters combined with M?ssbauer spectroscopic and magnetic data for ((i)PrPDI)FeCl(2) ((i)PrPDI = 2,6-(2,6-(i)Pr(2)C(6)H(3)N=CMe)(2)C(5)H(3)N) established a high-spin ferrous center ligated by a neutral bis(imino)pyridine ligand. Comparing these data to those for the single electron reduction product, ((i)PrPDI)FeCl, again demonstrated a high-spin ferrous ion, but in this case the S(Fe) = 2 metal center is antiferromagnetically coupled to a ligand-centered radical (S(L) = (1)/(2)), accounting for the experimentally observed S = (3)/(2) ground state. Continued reduction to ((i)PrPDI)FeL(n) (L = N(2), n = 1,2; CO, n = 2; 4-(N,N-dimethylamino)pyridine, n = 1) resulted in a doubly reduced bis(imino)pyridine diradical, preserving the ferrous ion. Both the computational and the experimental data for the N,N-(dimethylamino)pyridine compound demonstrate nearly isoenergetic singlet (S(L) = 0) and triplet (S(L) = 1) forms of the bis(imino)pyridine dianion. In both spin states, the iron is intermediate spin (S(Fe) = 1) ferrous. Experimentally, the compound has a spin singlet ground state (S = 0) due to antiferromagnetic coupling of iron and the ligand triplet state. Mixing of the singlet diradical excited state with the triplet ground state of the ligand via spin-orbit coupling results in temperature-independent paramagnetism and accounts for the large dispersion in (1)H NMR chemical shifts observed for the in-plane protons on the chelate. Overall, these studies establish that reduction of ((i)PrPDI)FeCl(2) with alkali metal or borohydride reagents results in sequential electron transfers to the conjugated pi-system of the ligand rather than to the metal center.     

Thermally induced two-step, two-site incomplete 6A1<-->2T2 crossover in a mononuclear iron(III) phenolate-pyridyl Schiff-base complex: a rare crystallographic observation of the coexistence of pure S=5/2 and 1/2 metal centers in the asymmetric unit

The six-coordinate mononuclear iron(III) complexes [Fe(salpm)2]ClO(4).0.5EtOH, [Fe(salpm)2]Cl, [Fe{(3,5-tBu2)-salpm}2]X (X=ClO4- or Cl-), and [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O [Hsalpm=N-(pyridin-2-ylmethyl)salicylideneamine; H(3,5-tBu2)-salpm=N-(pyridin-2-ylmethyl)-3,5-di-tert-butylsalicylideneamine] have been synthesized and isolated in crystalline form; their chemical identities have been ascertained by elemental analyses, FAB mass spectrometry, and infrared spectroscopy. The room-temperature effective magnetic moments [(8chiMT)1/2 approximately 5.85-5.90 microB] of these complexes are consistent with the high-spin (S=5/2) ground state. These complexes are intensely colored on account of the strong ppi-->dpi* LMCT visible absorptions. Definitive evidence for the structures of [Fe(salpm)2]ClO(4).0.5EtOH and [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O has been provided by single-crystal X-ray crystallography. The monomeric complex cations in both compounds comprise two uninegative phenolate-pyridyl tridentate Schiff-base ligands coordinated meridionally to the iron(III) to afford a distorted octahedral geometry with a trans,cis,cis-[FeO2N4] core. Whereas [Fe(salpm)2]ClO(4).0.5EtOH undergoes a thermally induced 6A1<-->2T2 crossover, [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O retains its spin state in the solid state down to 5 K. However, EPR spectroscopy reveals that the latter complex does exhibit a spin transformation in solution, albeit to a much lesser extent than does the former. The spin crossover in [Fe(salpm)2]ClO(4).0.5EtOH has resulted in an unprecedented crystallographic observation of the coexistence of high-spin and low-spin iron(III) complex cations in equal proportions around 100 K. At room temperature, the two crystallographically distinct ferric centers are both high spin; however, one [Fe(salpm)2]+ complex cation undergoes a complete spin transition over the temperature range approximately 200-100 K, whereas the other converts very nearly completely between 100 and 65 K; approximately 10% of the complex cations in [Fe(salpm)2]ClO(4).0.5EtOH remain in the high-spin state down to 5 K.     

Synthesis of new [8Fe-7S] clusters: a topological link between the core structures of P-cluster, FeMo-co, and FeFe-co of nitrogenases

A coordinatively unsaturated dinuclear iron(II) complex of bulky thiolates, [(TipS)Fe(micro-SDmp)]2 (1; Tip = 2,4,6-(i)Pr(3)C(6)H(2), Dmp = 2,6-(mesityl)(2)C(6)H(3)), was synthesized from stepwise reactions of Fe{N(SiMe(3))2}2 with 1 equiv of HSDmp and then with 1 equiv of HSTip. Complex 1 was found to react with elemental sulfur (S8) in toluene to generate a new class of [8Fe-7S] cluster, [(DmpS)Fe(4)S(3)]2(micro-SDmp)2(micro-STip)(micro(6)-S) (2). The cluster 2 was also produced from one-pot reactions of Fe{N(SiMe(3))2}2 + HSDmp + HSTip + S8 (8:6:10:7/8) and Fe3{N(SiMe(3))2}2(micro-STip)4 + HSDmp + S8 (8/3:16/3:7/8), where another [8Fe-7S] cluster, [(TipS)Fe(4)S(3)]2(micro-SDmp)2{micro-N(SiMe(3))2}(micro(6)-S) (3), was also found as a minor byproduct. In either of the clusters, two Fe(4)S(3) incomplete cubane units are connected by three anionic ligands, namely three thiolate S atoms for 2 or two thiolate S atoms and one amide N atom for 3, and one hexa-coordinate S atom resides at the center of the [8Fe-7S] core. They have a common Fe(II)(5)Fe(III)3 oxidation states, and an S = 1/2 ground spin state was indicated by rhombic EPR signals at 10 K with g = 2.19, 2.07, and 1.96 for 2 and g = 2.13, 2.06, and 1.93 for 3. The structural relevance of clusters 2 and 3 to P-cluster, FeMo-co, and FeFe-co of nitrogenases is discussed.     

Bismercaptoethanediazacyclooctane as a N2S2 chelating agent and Cys-X-Cys mimic for Fe(NO) and Fe(NO)2

The N-protonated bismercaptoethanediazacyclooctane serves as a bidentate dithiolate ligand to oxidized Fe(NO)(2) of Enemark-Feltam notation, E-F [Fe(NO)(2)],(9) mimicking Cys-X-Cys binding of Fe(NO)(2) to proteins or thio-biomolecules. The neutral compound is characterized by the well-known g = 2.03 EPR signal which is a hallmark of dinitrosyl iron complexes, DNIC's. The Fe(NO)(2) unit can be removed from the chelate by excess PhS(-), producing (PhS)(2)Fe(NO)(2)(-). Transfer of NO from Fe(H(+)bme-daco)(NO)(2) (nu(NO) = 1740, 1696 cm(-)(1)) to Fe(II) of [(bme-daco)Fe](2) yields the five-coordinate, square-pyramidal N(2)S(2)Fe(NO) (nu(NO) = 1649 cm(-)(1)), where NO is in the apical position. Its isotropic EPR signal at g = 2.05 is consistent with E-F [Fe(NO)](7) formulation. In excess NO, Roussin's red ester-type molecules are formed as dinuclear or tetranuclear species, [(micro-SRS)[Fe(2)(NO)(4)]](n)() (n =1, 2). These well-characterized molecules furnish reference points for positions and patterns in nu(NO) vibrational spectroscopy expected to be useful for in vivo studies of NO degradation of iron-sulfur clusters in ferredoxins.     

Reactions of synthetic [2Fe-2S] and [4Fe-4S] clusters with nitric oxide and nitrosothiols

The interaction of nitric oxide (NO) with iron-sulfur cluster proteins results in degradation and breakdown of the cluster to generate dinitrosyl iron complexes (DNICs). In some cases the formation of DNICs from such cluster systems can lead to activation of a regulatory pathway or the loss of enzyme activity. In order to understand the basic chemistry underlying these processes, we have investigated the reactions of NO with synthetic [2Fe-2S] and [4Fe-4S] clusters. Reaction of excess NO(g) with solutions of [Fe2S2(SR)4](2-) (R = Ph, p-tolyl (4-MeC6H4), or 1/2 (CH2)2-o-C6H4) cleanly affords the respective DNIC, [Fe(NO)2(SR)2](-), with concomitant reductive elimination of the bridging sulfide ligands as elemental sulfur. The structure of (Et4N)[Fe(NO)2(S-p-tolyl)2] was verified by X-ray crystallography. Reactions of the [4Fe-4S] clusters, [Fe4S4(SR)4](2-) (R = Ph, CH2Ph, (t)Bu, or 1/2 (CH2)-m-C6H4) proceed in the absence of added thiolate to yield Roussin's black salt, [Fe4S3(NO)7](-). In contrast, (Et4N)2[Fe4S4(SPh)4] reacts with NO(g) in the presence of 4 equiv of (Et4N)(SPh) to yield the expected DNIC. For all reactions, we could reproduce the chemistry effected by NO(g) with the use of trityl-S-nitrosothiol (Ph3CSNO) as the nitric oxide source. These results demonstrate possible pathways for the reaction of iron-sulfur clusters with nitric oxide in biological systems and highlight the importance of thiolate-to-iron ratios in stabilizing DNICs.     

Exchange and Delocalization Effects in [Fe6S6]2+ Superclusters

A theoretical study of Heisenberg exchange and double exchange (delocalization) effects in the iron-sulphur supercluster is presented. Such clusters can play important role in biological systems (proteins and enzymes) acting as so-called active centres. The cluster with valence 2+ can be modelled by two Fe(III) and four Fe(II) ions. An idealized structure of double cubane has been considered instead of a more realistic defected double cubane structure of lower symmetry. Energies of the lowest spin states have been calculated numerically depending on the Heisenberg exchange J _i and double exchange b parameters. Possible spin ground states (S=0, 1, 2, 3, 4, 5) have been predicted. The ground state of a given total spin Sis usually achieved for the intermediate spin value of S ₅₆=4 in the case of fully antiferromagnetic as well as partially ferromagnetic spin interactions. In the case of no double exchange, the ground state with the total spin S=3 should always be observed, while a nonzero hopping effect results in narrowing a parameter region of the ground state. If the double exchange is taken into account, then the spin values depend on the Heisenberg integrals. The model results can be applied in order to interpret many structural and magnetic properties of proteins and enzymes possessing the Fe-S active centres.     

基于非血红素铁模型配合物[FeⅣ(O)(N4Py)]2+的新型N杂环卡宾配合物的理论设计

基于四价非血红素铁模型配合物[FeⅣ(O)(N4Py)]2+, 通过理论计算设计出一种新型N杂环卡宾配合物[FeⅣ(O)(N4Py)]2+. 采用密度泛函理论B3LYP方法, 计算了[FeⅣ(O)(N4Py)]2+的几何结构和电子结构, 并研究了[FeⅣ(O)(N4Py)]2+使环己烷C-H键羟基化的反应机理. 结果表明, [FeⅣ(O)(N4Py)]2+的五重态能量比基态三重态能量高约5.7 kJ/mol, 故五重态几乎不能参与反应. 赤道方向的配位基N杂环卡宾(NHC)对FeO单元的σ-贡献要大于N4Py的贡献, 而它的空间位阻效应也大于N4Py, 因此2+的稳定性强于[FeⅣ(O)(N4Py)]2+. [FeⅣ(O)(N4Py)]2+的三重态的反应能垒比[FeⅣ(O)(N4Py)]2+的三重态反应能垒高2.0 kJ/mol, 且为单态反应, 所以[FeⅣ(O)(N4Py)]2+的反应活性要高于[FeⅣ(O)(N4Py)]2+.     

A new N,N,O chelate for transition metal chemistry: Fe5 and Fe6 clusters from the use of 6-hydroxymethyl-2,2'-bipyridine (hmbpH)

The initial use of the anion of 6-hydroxymethyl-2,2'-bipyridine (hmbpH) as a chelate in coordination chemistry is described. The syntheses, crystal structures, and magnetochemical characterization are reported of four new iron(III) clusters [Fe5O2(OH)(O2CMe)5(hmbp)3](ClO4)2 (1) and [Fe6O2(OH)2(O2CR)6(hmbp)4](NO3)2 (R=Ph (2), Me (3), But (4); hmbpH=6-hydroxymethyl-2,2'-bipyridine). The reaction of Fe(ClO4)3, hmbpH, and sodium acetate in a 1:1: approximately 4 ratio in EtOH gave 1, and the reaction between [Fe3O(O2CR)6(H2O)3](NO3) (R=Ph, Me, But) and hmbpH in a 1:1 ratio in MeCN gave 2-4, respectively. The core of 1 consists of a [Fe4(mu3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by bridging O atoms. The core of 2-4 also consists of a [Fe4(mu3-O)2]8+ butterfly unit to which are attached an Fe atom on either side by bridging O atoms. Variable-temperature (T) and -field (H) solid-state DC and AC magnetization (M) studies were carried out on complexes 1-4 in the 5.0-300 K range. Fitting of the data revealed that 1 has an S=5/2 ground state spin whereas 2-4 possess an S=5 ground state. Fitting of the M/NmicroB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave values of the axial ZFS parameter |D| of 0.75, 0.36, 0.46, and 0.36 cm(-1) for 1-4, respectively.     

The role of diisopropanolamine (dipaH3) in cluster dimerisation and polymerisation: from spin frustrated S= 5 FeIII 6 clusters to the novel 1-D covalent polymer of mixed valence [CoII3CoIII] tetramers

The synthesis, crystal structures and magnetic properties of two hexanuclear Fe(6) clusters of general formula [Fe(6)(O)(2)(OH)(2)(O(2)CR)(10)(dipaH(2))(2)].xMeCN.yH(2)O (R = Ph, x= 5.5, y= 1 (1), R = C(Me)(3), x= 2, y= 3 (2)) are reported. The presence of the flexible amino-alcohol ligand diisopropanolamine (dipaH(3)) induces the dimerisation of two trinuclear Fe(III) complexes, [Fe(3)O(O(2)CPh)(6)(H(2)O)(3)](NO(3)) and [Fe(3)O(O(2)CC(Me)(3))(6)(H(2)O)(3)](O(2)CC(Me)(3)), to form the hexanuclear clusters 1 and 2. DC magnetic susceptibility measurements on 1 and 2 assign ground spin states of S= 5, with zero-field splitting parameters (D) of ca. 0.25 cm(-1) obtained from magnetisation isotherms. AC susceptibilities showed no maxima as a function of frequency, at low temperatures, and this confirmed the lack of single-molecule magnetic behaviour. Clusters 1 and 2 are isostructural, consisting of two fused {Fe(3)O} trinuclear units, bridged in two positions by one mu(2)-OH(-) unit and two mu(2)-O(2)CR(-) bridging carboxylates (R = Ph (), C(Me)(3)()). The two singly deprotonated dipaH(2)(-) bridging ligands span the Fe1-Fe2 edges in and via one micro(2)-bridging alcohol arm and one terminal nitrogen atom while the second alcohol arm remains free. The ground spin state of S= 5 in 1 and 2 can be attributed to the presence of spin frustration within the system. 1 and 2 join a small family of spin frustrated S= 5 Fe(6) systems the magnetism of which give weight to a recent report that it is the trans position of the two shortest Fe(2) pair frustrated exchange pathways in these Fe(6) clusters that gives rise to a ground spin state of S= 5 (trans) and not a ground spin state of S= 0 (cis). The M?ssbauer spectra of 1 and 2 show two quadrupole doublets, as expected, at 295 K, but a broad asymmetric lineshape at 77 K. The synthesis and magnetic properties of {[Co(II)(3)Co(III)(OH)(O(2)CC(Me)(3))(4)(HO(2)CC(Me)(3))(2)(dipaH)(2)].2MeCN}(n)(3) are reported. 3 is a covalently bonded 1D polymer of tetrameric cobalt clusters. The presence of the dipaH(3) ligand here not only dimerises the [Co(II)(2)(micro-H(2)O)(O(2)CC(Me)(3))(4)(HO(2)CC(Me)(3))(4)] starting complex into the tetranuclear species but also polymerises the [Co(II)(3)Co(III)] clusters in 3 by acting as the propagating ligand in the 1D chain. Magnetic susceptibility measurements on show each [Co(4)] moiety exhibits weak antiferromagnetic coupling between the three Co(II)S= 3/2 metal centres and fitted J values are given. The ambiguity in assignment of the spin ground state of S= 1/2 or 3/2 is discussed.     

New Fe4, Fe6, and Fe8 clusters of iron(III) from the use of 2-pyridyl alcohols: structural, magnetic, and computational characterization

The syntheses, crystal structures, magnetochemical characterization, and theoretical calculations are reported for three new iron clusters [Fe 6O 2(NO3) 4(hmp) 8(H 2O) 2](NO3)2 (1), [Fe4(N3)6(hmp)6] (2), and [Fe8O3(OMe)(pdm)4(pdmH) 4(MeOH)2](ClO4)5 (3) (hmpH=2-(hydroxymethyl)pyridine; pdmH2=2,6-pyridinedimethanol). The reaction of hmpH with iron(III) sources such as Fe(NO3) 3.9H2O in the presence of NEt 3 gave 1, whereas 2 was obtained from a similar reaction by adding an excess of NaN3. Complex 3 was obtained in good yield from the reaction of pdmH 2 with Fe(ClO4)3.6H2O in MeOH in the presence of an organic base. The complexes all possess extremely rare or novel core topologies. The core of 1 comprises two oxide-centered [Fe3(mu3-O)](7+) triangular units linked together at two of their apexes by two sets of alkoxide arms of hmp(-) ligands. Complex 2 contains a zigzag array of four Fe (III) atoms within an [Fe4(mu-OR) 6](6+) core, with the azide groups all bound terminally. Finally, complex 3 contains a central [Fe 4(mu4-O)](10+) tetrahedron linked to two oxide-centered [Fe3(mu3-O)](7+) triangular units. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1-3 in the 5.0-300 K range. Fitting of the obtained magnetization versus field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting, ZFS) established that 1 possesses an S=3 ground-state spin, with g=2.08, and D=-0.44 cm(-1). The magnetic susceptibility data for 2 up to 300 K were fit by matrix diagonalization and gave J1=-9.2 cm(-1), J2=-12.5 cm(-1), and g=2.079, where J 1 and J 2 are the outer and middle nearest-neighbor exchange interactions, respectively. Thus, the interactions between the Fe(III) centers are all antiferromagnetic, giving an S=0 ground state for 2. Similarly, complex 3 was found to have an S=0 ground state. Theoretically computed values of the exchange constants in 2 were obtained with DFT calculations and the ZILSH method and were in good agreement with the values obtained from the experimental data. Exchange constants obtained with ZILSH for 3 successfully rationalized the experimental S = 0 ground state. The combined work demonstrates the ligating flexibility of pyridyl-alcohol chelates and their usefulness in the synthesis of new polynuclear Fex clusters without requiring the copresence of carboxylate ligands.     

Unusual structural types in polynuclear iron chemistry from the use of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (edteH4): Fe5, Fe6, and Fe12 clusters

The syntheses, crystal structures, and magnetochemical characterization of five new iron clusters [Fe5O2(O2CPh)7(edte)(H2O)] (1), [Fe6O2(O2CBut)8(edteH)2] (2), [Fe12O4(OH)2(O2CMe)6(edte)4(H2O)2](ClO4)4 (3), [Fe12O4(OH)8(edte)4(H2O)2](ClO4)4 (4), and [Fe12O4(OH)8(edte)4(H2O)2](NO3)4 (5) (edteH4= N,N,N',N'-tetrakis(2-hydroxyethyl) ethylenediamine) are reported. The reaction of edteH4 with [Fe3O(O2CPh)6(H2O)3](NO3) and [Fe3O(O2CBut)6(H2O)3](OH) gave 1 and 2, respectively. Complex 3 was obtained from the reaction of edteH4 and NaO2CMe with Fe(ClO4)3, whereas 4 and 5 were obtained from the reaction of edteH4 with Fe(ClO4)3 and Fe(NO3)3, respectively. The core of 1 consists of a [Fe4(mu3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by four bridging O atoms. The core of 2 consists of two triangular [Fe3(mu3-O)]7+ units linked together by six bridging O atoms. Finally, the cores of 3-5 consist of an [Fe12(mu4-O)4(mu-OH)2]26+ unit. Variable-temperature (T) and -field (H) solid-state direct and alternating current magnetization (M) studies were carried out on complexes 1-3 in the 1.8-300 K range. Analysis of the obtained data revealed that 1, 2, and 3-5 possess an S = 5/2, 5, and 0 ground-state spin, respectively. The fitting of the obtained M/N(muB) vs H/T data was carried out by matrix diagonalization, and this gave values for the axial zero-field splitting (ZFS) parameter D of -0.50 cm-1 for 1 and -0.28 cm-1 for 2.     

Density functional theory study of an all ferrous 4Fe-4S cluster

The all-ferrous, carbene-capped Fe(4)S(4) cluster, synthesized by Deng and Holm (DH complex), has been studied with density functional theory (DFT). The geometry of the complex was optimized for several electronic configurations. The lowest energy was obtained for the broken-symmetry (BS) configuration derived from the ferromagnetic state by reversing the spin projection of one of the high spin (S(i) = 2) irons. The optimized geometry of the latter configuration contains one unique and three equivalent iron sites, which are both structurally and electronically clearly distinguishable. For example, a distinctive feature of the unique iron site is the diagonal Fe···S distance, which is 0.3 ? longer than for the equivalent irons. The calculated (57)Fe hyperfine parameters show the same 1:3 pattern as observed in the M?ssbauer spectra and are in good agreement with experiment. BS analysis of the exchange interactions in the optimized geometry for the 1:3, M(S) = 4, BS configuration confirms the prediction of an earlier study that the unique site is coupled to the three equivalent ones by strong antiferromagnetic exchange (J > 0 in J Σ(j<4)?(4)·?(j)) and that the latter are mutually coupled by ferromagnetic exchange (J' < 0 in J' Σ(i相似文献   

Cluster-based copper(II) coordination polymers with azido bridges and chiral magnets

Three homochiral layered complexes, [Cu3(R-chea)2(N3)6]n (1), [Cu3(S-chea)2(N3)6]n (2) (chea = 1-cyclohexylethylamine) and [Cu3(S-phpa)2(N3)6]n (3) (phpa = 1-phenylpropylamine), and three novel cluster-based coordination polymers, [Cu6(1,2-pn)4(N3)12]n (4) (1,2-pn = 1,2-diaminopropane), [[Cu8(en)4(N3)16] x H2O]n (5) (en = ethylenediamine) and [Cu6(N-Ipren)2(N3)12]n (6) (N-Ipren = N-isopropylethylenediamine), have been synthesized by the self-assembly reactions of Cu(NO3)2 x 3H2O, NaN3 and small organic amine ligands. Their crystal structures are determined by single-crystal X-ray diffraction. Complexes are composed of neutral 2D brick wall networks with only end-on azido bridges. Complexes and are 3D coordination polymers featuring copper-azido clusters and [Cu(diamine)2]2+ units which are linked by the azido bridges. Complex is a 3D coordination framework based on the hexanuclear copper(II) clusters [Cu6(N3)12(N-Ipren)2]. Magnetic studies show that complexes are interesting chiral ferromagnets with the magnetic transition temperature at ca. 5.0 K. Complexes and show ferromagnetic coupling in the copper-azido cluster units and antiferromagnetic interaction between neighboring units, while complex shows ferromagnetic ordering at 3.2 K.     

New twisted-saddle dodecanuclear iron(III) clusters with adamantane-like [Fe4O6] core

Reactions of a hexadentate ligand N,N,N’,N’-tetrakis(2-hydroxyethyl)ethylenediamine (H₄edte) with different iron(III) salts in different solvents yielded three new twisted-saddle Fe12 clusters with adamantane-like [Fe₄O₆] inner core. Preliminary magnetic studies show that strong intracluster anti-ferromagnetic interaction exists in both 1 and 3, generating the S _T = 0 spin ground state.     

Contribution of spin and anisotropy to single molecule magnet behavior in a family of bell-shaped Mn11Ln2 coordination clusters

The synthesis, structures, and magnetic properties of a family of isostructural "bell-shaped" heterometallic coordination clusters [Mn(III)(9)Mn(II)(2)La(III)(2)(μ(4)-O)(7)(μ(3)-O)(μ(3)-OH)(2)(piv)(10.8)(O(2)CC(4)H(3)O)(6.2)(NO(3))(2)(OH(2))(1.5)(MeCN)(0.5)]·12CH(3)CN·2H(2)O (1) and [Mn(III)(9)Mn(II)(2)Ln(2)(μ(4)-O)(7)(μ (3)-O)(μ(3)-OH)(2)(piv)(10.6)(O(2)CC(4)H(3)O)(6.4)(NO(3))(2)(OH(2))]·nCH(3)CN·H(2)O (Ln = Pr(III), n = 8 (2); Ln = Nd(III), n = 10 (3); Ln = Eu(III), n = 17 (4); Ln = Gd(III), n = 13 (5); piv = pivalate) are reported. The complexes were obtained from the reaction of [Mn(III)(2)Mn(II)(4)O(2)(piv)(10)(4-Me-py)(2.5)(pivH)(1.5)] and Ln(NO(3))(3)·6H(2)O in the presence of 2-furan-carboxylic acid (C(4)H(3)OCOOH) in CH(3)CN. Compounds 1-5 are isomorphous, crystallizing in the triclinic space group P1 with Z = 2. The Mn(III) and Mn(II) centers together form the shell of the bell, while the two Ln(III) centers can be regarded as the bell's clapper. The magnetic properties of 1-4 reveal dominant antiferromagnetic interactions between the magnetic centers leading to small spin ground states; while those of 5 indicate similar antiferromagnetic interactions between the manganese ions but with unusually strong ferromagnetic interactions between the Gd(III) ions leading to a large overall spin ground state of S = 11-12. While ac and dc magnetic measurements confirmed that Mn(11)Gd(2) (5) is a single-molecule magnet (SMM) showing hysteresis loops at low temperatures, compounds 1-4 do not show any slow relaxation of the magnetization, indicating that the S = 7 spin of the ferromagnetic Gd(2) unit in 5 is a necessary contribution to its SMM behavior.     

Monomeric, trimeric, and tetrameric transition metal complexes (Mn, Fe, Co) containing N,N-bis(2-pyridylmethyl)-2-aminoethanol/-ate: preparation, crystal structure, molecular magnetism and oxidation catalysis

The reaction of N,N-bis(2-pyridylmethyl)-2-aminoethanol (bpaeOH), NaSCN/NaN(3), and metal (M) ions [M = Mn(II), Fe(II/III), Co(II)] in MeOH, leads to the isolation of a series of monomeric, trimeric, and tetrameric metal complexes, namely [Mn(bpaeOH)(NCS)(2)] (1), [Mn(bpaeO)(N(3))(2)] (2), [Fe(bpaeOH)(NCS)(2)] (3), [Fe(4)(bpaeO)(2)(CH(3)O)(2)(N(3))(8)] (4), [Co(bpaeOH)(NCS)(2)] (5), and [Co(3)(bpaeO)(2)(NO(3))(N(3))(4)](NO(3)) (6). These compounds have been investigated by single crystal X-ray diffractometry and magnetochemistry. In complex 1 the Mn(II) is bonded to one bpaeOH and two thiocyanate ions, while in complex 2 it is coordinated to a deprotonated bpaeO(-) and two azide ions. The oxidation states of manganese ions are 2+ for 1 and 3+ for 2, respectively, indicating that the different oxidation states depend on the type of binding anions. The structures of monomeric iron(II) and cobalt(II) complexes 3 and 5 with two thiocyanate ions are isomorphous to that of 1. Compounds 1, 2, 3, and 5 exhibit high-spin states in the temperature range 5 to 300 K. 4 contains two different iron(III) ions in an asymmetric unit, one is coordinated to a deprotonated bpaeO(-), an azide ion, and a methoxy group, and the other is bonded to three azide ions and two oxygens from bpaeO(-) and a methoxy group. Two independent iron(III) ions in 4 form a tetranuclear complex by symmetry. 4 displays both ferromagnetic and antiferromagnetic couplings (J = 9.8 and -14.3 cm(-1)) between the iron(III) ions. 6 is a mixed-valence trinuclear cobalt complex, which is formulated as Co(III)(S = 0)-Co(II)(S = 3/2)-Co(III)(S = 0). The effective magnetic moment at room temperature corresponds to the high-spin cobalt(II) ion (～4.27 μ(B)). Interestingly, 6 showed efficient catalytic activities toward various olefins and alcohols with modest to excellent yields, and it has been proposed that a high-valent Co(V)-oxo species might be responsible for oxygen atom transfer in the olefin epoxidation and alcohol oxidation reactions.     

Cyano-bridged bimetallic assemblies from hexacyanometalate, [M(CN)6](3-) (M = Mn(III) and Fe(III)), and [M(N4-macrocycle)]2+ (M=Fe(III), Ni(II) and Zn(II)) building blocks. Syntheses, multidimensional structures, and magnetic properties

Reactions between [M(N(4)-macrocycle)](2+) (M = Zn(II) and Ni(II); macrocycle ligands are either CTH = d,l-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane or cyclam = 1,4, 8, 11-tetrazaazaciclotetradecane) and [M(CN)(6)](3-) (M = Fe(III) and Mn(III)) give rise to cyano-bridged assemblies with 1D linear chain and 2D honeycomblike structures. The magnetic measurements on the 1D linear chain complex [Fe(cyclam)][Fe(CN)(6)].6H(2)O 1 points out its metamagnetic behavior, where the ferromagnetic interaction operates within the chain and the antiferromagnetic one between chains. The Neel temperature, T(N), is 5.5 K and the critical field at 2 K is 1 T. The unexpected ferromagnetic intrachain interaction can be rationalized on the basis of the axially elongated octahedral geometry of the low spin Fe(III) ion of the [Fe(cyclam)](3+) unit. The isostructural substitution of [Fe(CN)(6)](3-) by [Mn(CN)(6)](3-) in the previously reported complex [Ni(cyclam)](3)[Fe(CN)(6)](2).12H(2)O 2 leads to [Ni(cyclam)](3)[Mn(CN)(6)](2).16 H(2)O 3, which exhibits a corrugated 2D honeycomblike structure and a metamagnetic behavior with T(N) = 16 K and a critical field of 1 T. In the ferromagnetic phase (H > 1 T) this compound shows a very important coercitive field of 2900 G at 2 K. Compound [Ni(CTH)](3)[Fe(CN)(6)](2).13H(2)O 4, C(60)H(116)Fe(2)N(24)Ni(3)O(13), monoclinic, A 2/n, a = 20.462(7), b = 16.292(4), c = 27.262(7) A, beta = 101.29(4) degrees, Z = 4, also has a corrugated 2D honeycomblike structure and a ferromagnetic intralayer interaction, but, in contrast to 2 and 3, does not exhibit any magnetic ordering. This fact is likely due to the increase of the interlayer separation in this compound. ([Zn(cyclam)Fe(CN)(6)Zn(cyclam)] [Zn(cyclam)Fe(CN)(6)].22H(2)O.EtOH) 5, C(44)H(122)Fe(2)N(24)O(23)Zn(3), monoclinic, A 2/n, a = 14.5474(11), b = 37.056(2), c = 14.7173(13) A, beta = 93.94(1) degrees, Z = 4, presents an unique structure made of anionic linear chains containing alternating [Zn(cyclam)](2+) and [Fe(CN)(6)](3)(-) units and cationic trinuclear units [Zn(cyclam)Fe(CN)(6)Zn(cyclam)](+). Their magnetic properties agree well with those expected for two [Fe(CN)(6)](3-) units with spin-orbit coupling effect of the low spin iron(III) ions.