Novel Square Arrangements in Tetranuclear and Octanuclear Iron(III) Complexes with Asymmetric Iron Environments Created by the Unsymmetric Bridging Ligand N,N,N'-Tris((N-methyl)-2-benzimidazolylmethyl)-N'-methyl-1,3-diamino-2-propanol

Carboxylate free μ-oxo bridged ferric wheel with a record exchange coupling

An oxo-bridged, carboxylate free ‘ferric wheel’ was isolated with the molecular formula [FeIII8(μ-O)₄(L²⁻)₈] (1). The strength of antiferromagnetic interaction between the Fe(iii) ions is revealed by magnetic simulation (J₁ = −26.4 and J₂ = −170 cm⁻¹). The exchange value of −170 cm⁻¹ is the largest exchange value known for any homometallic or heterometallic wheels reported to date.

High nuclearity single-molecule magnets: a mixed-valence Mn26 cluster containing the di-2-pyridylketone diolate dianion

The employment of the dianion (dpkd(2-)) of the gem-diol form of di-2-pyridylketone (dpk) as a tetradentate chelate in manganese chemistry is reported, and the synthesis, crystal structure, and magnetochemical characterization of [Mn26O16(OMe)12(dpkd)12(MeOH)6](OH)6 x solv (3 x solv) are described. The reaction of Mn(ClO4)2 x 6 H2O, dpk, NaOMe, and NEt3 (2:1:4:2) in MeCN/MeOH affords complex 3, which possesses a rare metal topology and is mixed-valence (4 Mn(II), 22 Mn(III)). The complicated [Mn26(mu4-O)10(mu3-O)6(mu3-OMe)12(mu-OR)12](18+) core of 3 consists of an internal Mn(III)16 cage of adjacent Mn4 tetrahedra surrounded by an external Mn(II)4Mn(III)6 shell. The latter is held together by the alkoxide arms of twelve eta(1):eta(2):eta(1):eta(1):mu3 dpkd(2-) groups. Variable-temperature, solid-state direct current (dc), and alternating current (ac) magnetization studies were carried out on 3 in the 1.8-300 K range. Complex 3 is predominantly antiferromagnetically coupled with a resulting S = 6 ground state, a conclusion confirmed by the in-phase (chi'(M)) ac susceptibility data. The observation of out-of-phase (chi''(M)) ac susceptibility signals suggested that 3 might be a single-molecule magnet, and this was confirmed by single-crystal magnetization vs dc field sweeps that exhibited hysteresis, the diagnostic property of a magnet. Combined ac chi''(M) and magnetization decay vs time data collected below 1.1 K were used to construct an Arrhenius plot; the fit of the thermally activated region above approximately 0.1 K gave U(eff) = 30 K, where U(eff) is the effective relaxation barrier. At lower temperatures, the complex exhibits temperature-independent relaxation, characteristic of ground-state quantum tunneling of magnetization between the lowest-lying M(s) = +/-6 levels. The combined work demonstrates the ligating flexibility of dipyridyl-diolate chelates and their usefulness in the synthesis of polynuclear Mn(x) clusters with interesting magnetic properties, without requiring the co-presence of carboxylate ligands.

Polymetallic clusters of iron(III) with derivatised salicylaldoximes

The synthesis and magnetic properties of the compounds [HNEt(3)][Fe(2)(OMe)(Ph-sao)(2) (Ph-saoH)(2)].5MeOH (1.5MeOH), [Fe(3)O(Et-sao)(O(2)CPh)(5)(MeOH)(2)].3MeOH (2.3MeOH), [Fe(4)(Me-sao)(4)(Me-saoH)(4)] (3), [HNEt(3)](2)[Fe(6)O(2)(Me-sao)(4)(SO(4))(2)(OMe)(4)(MeOH)(2)] (4), [Fe(8)O(3)(Me-sao)(3)(tea)(teaH)(3)(O(2)CMe)(3)] (5), [Fe(8)O(3)(Et-sao)(3)(tea)(teaH)(3)(O(2)CMe)(3)] (6), and [Fe(8)O(3)(Ph-sao)(3)(tea)(teaH)(3)(O(2)CMe)(3)] (7) are reported (Me-saoH(2) is 2'-hydroxyacetophenone oxime, Et-saoH(2) is 2'-hydroxypropiophenone oxime and Ph-saoH(2) is 2-hydroxybenzophenone oxime). 1-7 are the first Fe(III) compounds synthesised using the derivatised salicylaldoxime ligands, R-saoH(2). 1 is prepared by treatment of Fe(2)(SO(4))(3).6H(2)O with Ph-saoH(2) in the presence of NEt(3) in MeOH; 2 prepared by treatment of Fe(ClO(4))(2).6H(2)O with Et-saoH(2) and NaO(2)CPh in the presence of NEt(4)OH in MeOH; 3 prepared by treatment of Fe(ClO(4))(2).6H(2)O with Me-saoH(2) and NaO(2)CCMe(3) in the presence of NEt(4)OH in MeOH; and 4 prepared by treatment of Fe(2)(SO(4))(3).6H(2)O with Me-saoH(2) in the presence of NEt(3) in MeOH. 4 is a rare example of a polynuclear iron complex containing a coordinated SO(4)(2-) ion. Compounds 5-7 are prepared by treatment of Fe(O(2)CMe)(2) with Me-saoH(2) (5), Et-saoH(2) (6), Ph-saoH(2) (7) in the presence of H(3)tea (triethanolamine) in MeOH, and represent the largest nuclearity Fe(III) clusters containing salicyladoxime-based ligands, joining a surprisingly small family of characterised octanuclear Fe complexes. Variable temperature magnetic susceptibilty measurements of 1, 3 and 5-7 reveal all five complexes possess S = 0 spin ground states; 2 possesses an S = 1/2 spin ground state, while 4 has an S = 4 +/- 1 spin ground state.

Mononuclear metal complexes with Piroxicam: Synthesis, structure and biological activity

Piroxicam (=Hpir) is a non-steroidal anti-inflammatory and an anti-arthritic drug. VO(2+), Mn(2+), Fe(3+), MoO(2)(2+) and UO(2)(2+) complexes with deprotonated piroxicam have been prepared and characterized with the use of infrared, UV-Vis, nuclear magnetic resonance and electron paramagnetic resonance spectroscopies. The experimental data suggest that piroxicam acts as a deprotonated bidentate ligand in all complexes and is coordinated to the metal ion through the pyridine nitrogen and the amide oxygen. Molecular mechanics calculations in the gas state have been performed in order to propose a model for the Fe(3+), VO(2+) and MoO(2)(2+) complexes. Potential anticancer cytostatic and cytotoxic effects of piroxicam complexes with VO(2+), Mn(2+) and MoO(2)(2+) on human promyelocytic leukemia HL-60 cells have been investigated. Among all complexes, only VO(pir)(2)(H(2)O) clearly induces apoptosis after 24-h incubation, whereas piroxicam induces apoptosis after 57-h incubation.

Methanolysis and Phenolysis Routes to Fe6, Fe8, and Fe10 Complexes and Their Magnetic Properties: A New Type of Fe8 Ferric Wheel

Alcoholysis of preformed tetranuclear and hexanuclear iron(III) clusters has been employed for the synthesis of four higher-nuclearity clusters. Treatment of [Fe(4)O(2)(O(2)CMe)(7)(bpy)(2)](ClO(4)) with phenol affords the hexanuclear cluster [Fe(6)O(3)(O(2)CMe)(9)(OPh)(2)(bpy)(2)](ClO(4)) (1). Reaction of [Fe(6)O(2)(OH)(2)(O(2)CR)(10)(hep)(2)] (R = Bu(t) or Ph) with PhOH affords the new "ferric wheel" complexes [Fe(8)(OH)(4)(OPh)(8)(O(2)CR)(12)] [R = Bu(t) (2) or Ph (3)]. Complexes 2 and 3 exhibit the same structure, which is an unprecedented type for Fe(III). In contrast, treatment of [Fe(6)O(2)(OH)(2)(O(2)CBu(t))(10)(hep)(2)] with MeOH leads to the formation of [Fe(10)(OMe)(20)(O(2)CBu(t))(10)] (4), which exhibits the more common type of ferric wheel seen in analogous complexes with other carboxylate groups. Solid-state variable-temperature magnetic susceptibility measurements indicate spin-singlet ground states for complexes 2 and 4. The recently developed semiempirical method ZILSH was used to estimate the pairwise exchange parameters (J(AB)) and the average spin couplings S(A)[empty set].S(B)[empty set] between the Fe(III) centers, providing a clear depiction of the overall magnetic behavior of the molecules. All exchange interactions between adjacent Fe(III) atoms are antiferromagnetic.

A phenolysis route to a new type of octanuclear iron(III) wheel: [Fe8(OH)4(OPh)8(O2CBut)12]

Alcoholysis of [Fe6O2(OH)2(O2CBut)10(hep)2] (1) affords ferric wheels of different nuclearities: methanol yields [Fe10(OMe)20(O2CBut)10], whereas phenol gives the structurally unprecedented wheel [Fe8(OH)4(OPh)8(O2CBut)12], and the first to contain phenoxide.

Novel one-dimensional tubelike and two-dimensional polycatenated metal-organic frameworks

Two novel metal-organic frameworks (MOFs) [Zn(TITMB)(OAc)](OH).8.5H(2)O (1) and [Ag(TITMB)N(3)].H(2)O (2) [TITMB = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene, OAc = acetate anion] were synthesized and their structures were determined by X-ray crystallography. Complex 1 crystallizes in tetragonal space group P(-)4 with a = 23.2664(7) and c = 11.9890(3) A and Z = 8. 1 has a one-dimensional tubelike structure with large inner pore size of approximately 17 A. Complex 2 crystallizes in monoclinic space group C2 with a = 20.7193(10), b = 11.5677(8), and c = 12.2944(6) A, beta = 125.5770(10) degrees, and Z = 4. 2 consists of two-dimensional honeycomb networks that interpenetrate each other to generate a polycatenated structure. In these two complexes, both zinc(II) and silver(I) atoms are four-coordinated with the same tetrahedral coordination geometry. The topologies of 1 and 2 are predominated by the conformations of TITMB, which are cis, trans, trans in 1 and cis, cis, cis in 2, respectively.

Novel rectangular [Fe4(mu4-OHO)(mu-OH)(2)](7+) versus "butterfly" [Fe4(mu3-O2](8+) core topology in the Fe(III)/RCO2(-)/phen reaction systems (R = Me, Ph; phen = 1,10-phenanthroline): preparation and properties of [Fe4(OHO)(OH)(2)(O2CMe)(4)(phen)(4)](ClO4)(3), [Fe4O2(O2CPh)(7)(phen)(2)](ClO4), and [Fe4O2(O2CPh)(8)(phen)(2)]

The preparations, X-ray structures, and detailed physical characterizations are presented for three new tetranuclear Fe(III)/RCO(2)(-)/phen complexes, where phen = 1,10-phenanthroline: [Fe(4)(OHO)(OH)(2)(O(2)CMe)(4)(phen)(4)](ClO(4))(3).4.4MeCN.H(2)O (1.4.4MeCN.H(2)O); [Fe(4)O(2)(O(2)CPh)(7)(phen)(2)](ClO(4)).2MeCN (2.2MeCN); [Fe(4)O(2)(O(2)CPh)(8)(phen)(2)].2H(2)O (3.2H(2)O). Complex 1.4.4MeCN.H(2)O crystallizes in space group P2(1)/n, with a = 18.162(9) A, b = 39.016(19) A, c = 13.054(7) A, beta = 104.29(2) degrees, Z = 4, and V = 8963.7 A(3). Complex 2.2MeCN crystallizes in space group P2(1)/n, with a = 18.532(2) A, b = 35.908(3) A, c = 11.591(1) A, beta = 96.42(1) degrees, Z = 4, and V = 7665(1) A(3). Complex 3.2H(2)O crystallizes in space group I2/a, with a = 18.79(1) A, b = 22.80(1) A, c = 20.74(1) A, beta = 113.21(2) degrees, Z = 4, and V = 8166(1) A(3). The cation of 1 contains the novel [Fe(4)(mu(4)-OHO)(mu-OH)(2)](7+) core. The core structure of 2 and 3 consists of a tetranuclear bis(mu(3)-O) cluster disposed in a "butterfly" arrangement. Magnetic susceptibility data were collected on 1-3 in the 2-300 K range. For the rectangular complex 1, fitting the data to the appropriate theoretical chi(M) vs T expression gave J(1) = -75.4 cm(-1), J(2) = -21.4 cm(-1), and g = 2.0(1), where J(1) and J(2) refer to the Fe(III)O(O(2)CMe)(2)Fe(III) and Fe(III)(OH)Fe(III) pairwise exchange interactions, respectively. The S = 0 ground state of 1 was confirmed by 2 K magnetization data. The data for 2 and 3 reveal a diamagnetic ground state with antiferromagnetic exchange interactions among the four high-spin Fe(III) ions. The exchange coupling constant J(bb) ("body-body" interaction) is indeterminate due to prevailing spin frustration, but the "wing-body" antiferromagnetic interaction (J(wb)) was evaluated to be -77.6 and -65.7 cm(-1) for 2 and 3, respectively, using the appropriate spin Hamiltonian approach. Mössbauer spectra of 1-3 are consistent with high-spin Fe(III) ions. The data indicated asymmetry of the Fe(4) core of 1 at 80 K, which is not detected at room temperature due to thermal motion of the core. The spectra of 2 and 3 analyze as two quadrupole-split doublets which were assigned to the body and wing-tip pairs of metal ions. (1)H NMR spectra are reported for 1-3 with assignment of the main resonances.

A mixed oxidation state, binuclear iron complex containing an unsymmetrically coordinating ligand. A ligand-induced switch in redox behavior

Binuclear [FeIIFeIII(BMDP)(O2CPh)3](BF4) (1) was obtained by treating an acetonitrile solution of the fully reduced [FeIIFeII(BMDP)(O2CPh)(MeOH)1.5(H2O)0.5](BF4)2 with 5 equiv of benzoate and then exposing the mixture to oxygen. Examination of [FeIIFeIII(BMDP)(O2CPh)3](BF4) by X-ray crystallography reveals the localized, mixed oxidation state nature of the cation in the solid state. 1H NMR and magnetic susceptibility data for the new complex are also reported. In the absence of dioxygen and other oxidants, treatment of FeIIFeII(BMDP)(O2CPh)(MeOH)1.5(H2O)0.5](BF4)2 with excess benzoate results in the formation of [FeIIFeII(BMDP)(O2CPh)2](BF4)2, which has also been characterized by X-ray diffraction.

Mono- and dinuclear zinc complexes derived from unsymmetric binucleating ligands: synthesis, characterization, and formation of tetranuclear arrays

Zinc complexes of the unsymmetric, binucleating Schiff base ligands 3-(N-[2-(dimethylamino)ethyl]iminomethyl)-salicylic acid (H2L1) and 3-[N-(2-pyridylmethyl)iminomethyl]-salicylic acid (H2L2) have been studied in the solid state as well as in solution. Reaction of ZnX2 (X = NO3-, CH3CO2-) with 3-formylsalicylic acid and N,N-dimethylethylenediamine at neutral or slightly acidic pH afforded the dinuclear complexes [Zn2(HL1)2(H2O)2](NO3)2.2H2O (1a) and [Zn2(HL1)2(CH3CO2)2].6H2O (1b). The Zn ions, which are 3.126(1) A (1a) and 3.2665(7) A (1b) apart, are bridged by two phenolate oxygens. Further coordination sites of the ligand are the imine nitrogen and carboxylate oxygen, while the amino nitrogen is protonated. On dissolution in DMSO or DMF, 1a and 1b are converted into the mononuclear species [Zn(HL1)]+. Cleavage of the dinuclear complexes is accompanied by migration of the ammonium proton to the carboxylate group and coordination of the amino nitrogen to Zn. Reaction of 1b with base yielded the novel tetranuclear Zn complex [Zn4(L1)4].6.5H2O (2) that exhibits coordination number asymmetry. The four Zn ions having N2O3 and N2O4 coordination environments are located at the corners of a nearly square-planar rectangle. H2L2 binds Zn via the phenolate oxygen and, imine and pyridine nitrogens in acidic solution. Deprotonation of the carboxyl group in alkaline solution gave the tetranuclear compound [Zn4(L2)4].4.5H2O (4) with a cubane-like Zn4O4 core.