Dinuclear cyano complexes of cobalt(III) and Iron(III) containing noninnocent 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene bridging ligands

Two new dinucleating ligands 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene, H(4)(tpb), and 1,2,4,5-tetrakis(4-tert-butyl-2-pyridinecarboxamido)benzene, H(4)(tbpb), have been synthesized, and the following dinuclear cyano complexes of cobalt(III) and iron(III) have been isolated: Na(2)[Co(III)(2)(tpb)(CN)(4)] (1); [N(n-Bu)(4)](2)[Co(III)(2)(tbpb)(CN)(4)] (2); [Co(III)(2)(tbpb(ox2))(CN)(4)] (3); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(N(3))(4)] (4); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(CN)(4)] (5); [N(n-Bu)(4)](2)[Fe(III)(2)(tbpb)(CN)(4)] (6). Complexes 2-4 and 6 have been structurally characterized by X-ray crystallography at 100 K. From electrochemical and spectroscopic (UV-vis, IR, EPR, M?ssbauer) and magnetochemical investigations it is established that the coordinated central 1,2,4,5-tetraamidobenzene entity in the cyano complexes can be oxidized in two successive one-electron steps yielding paramagnetic (tbpb(ox1))(3)(-) and diamagnetic (tbpb(ox2))(2)(-) anions. Thus, complex 6 exists in five characterized oxidation levels: [Fe(III)(2)(tbpb(ox2))(CN)(4)](0) (S = 0); [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Fe(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Fe(III)Fe(II)(tbpb)(CN)(4)](3)(-) (S = (1)/(2)); [Fe(II)(2)(tbpb)(CN)(4)](4)(-) (S = 0). The iron(II) and (III) ions are always low-spin configurated. The electronic structure of the paramagnetic iron(III) ions and the exchange interaction of the three-spin system [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) are characterized in detail. Similarly, for 2 three oxidation levels have been identified and fully characterized: [Co(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Co(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Co(III)(2)(tbpb(ox2))(CN)(4)](0). The crystal structures of 2 and 3 clearly show that the two electron oxidation of 2 yielding 3 affects only the central tetraamidobenzene part of the ligand.     

Redox-noninnocence of the S,S'-coordinated ligands in bis(benzene-1,2-dithiolato)iron complexes

The electronic structures of complexes of iron containing two S,S'-coordinated benzene-1,2-dithiolate, (L)(2)(-), or 3,5-di-tert-butyl-1,2-benzenedithiolate, (L(Bu))(2)(-), ligands have been elucidated in depth by electronic absorption, infrared, X-band EPR, and Mossbauer spectroscopies. It is conclusively shown that, in contrast to earlier reports, high-valent iron(IV) (d(4), S = 1) is not accessible in this chemistry. Instead, the S,S'-coordinated radical monoanions (L(*))(1)(-) and/or (L(Bu)(*))(1)(-) prevail. Thus, five-coordinate [Fe(L)(2)(PMe(3))] has an electronic structure which is best described as [Fe(III)(L)(L(*))(PMe(3))] where the observed triplet ground state of the molecule is attained via intramolecular, strong antiferromagnetic spin coupling between an intermediate spin ferric ion (S(Fe) = (3)/(2)) and a ligand radical (L(*))(1)(-) (S(rad) = (1)/(2)). The following complexes containing only benzene-1,2-dithiolate(2-) ligands have been synthesized, and their electronic structures have been studied in detail: [NH(C(2)H(5))(3)](2)[Fe(II)(L)(2)] (1), [N(n-Bu)(4)](2)[Fe(III)(2)(L)(4)] (2), [N(n-Bu)(4)](2)[Fe(III)(2)(L(Bu))(4)] (3); [P(CH(3))Ph(3)][Fe(III)(L)(2)(t-Bu-py)] (4) where t-Bu-py is 4-tert-butylpyridine. Complexes containing an Fe(III)(L(*))(L)- or Fe(III)(L(Bu))(L(Bu)(*))- moiety are [N(n-Bu)(4)][Fe(III)(2)(L(Bu))(3)(L(Bu)(*))] (3(ox)()), [Fe(III)(L)(L(*))(t-Bu-py)] (4(ox)()), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))] (7), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))(2)] (8), and [Fe(III)(L(Bu))(L(Bu)(*))(PPr(3))] (9), where Pr represents the n-propyl substituent. Complexes 2, 3(ox)(), 4, [Fe(III)(L)(L(*))(PMe(3))(2)] (6), and 9 have been structurally characterized by X-ray crystallography.     

Molecular and electronic structure of five-coordinate complexes of iron(II/III) containing o-diiminobenzosemiquinonate(1-) pi radical ligands

The reaction of the ligand N-phenyl-1,2-benzenediamine (N-phenyl-o-phenylenediamine), H2[L(PDI)], in dry acetonitrile with [FeIII(dmf)6](ClO4)3 (dmf = N,N-dimethylformamide) affords the dimer (mu-NH,NH)[FeIII(L(ISQ))(L(PDI))]2 (1), where (L(ISQ))*- represents the pi radical monoanion N-phenyl-o-diiminobenzosemiquinonate and (L(PDI))2- is its one-electron-reduced, closed-shell form. Complex 1 possesses a diamagnetic ground-state St = 0. Addition reactions of tri-n-butylphosphane, tert-butyl isocyanide, cyclohexyl isocyanide, 4,5-diphenylimidazole, and 4-(1-phenylpentyl)pyridine with 1 in acetonitrile or toluene yields [FeII(L(ISQ))2(PBu3)] (2), [Fe(II)(L(ISQ))2(CN-tBu)] (4), [FeII(L(ISQ))2(CNCy)] (5), [FeIII(L(ISQ))2(Ph2Im)] (6), and [FeIII(L(ISQ))(L(PDI))(BuPhCH-py)].BuPhCH-py (7). Oxidation of 1 with iodine affords [FeIII(L(ISQ))2I] (3), and oxidation of 2 with ferrocenium hexafluorophosphate yields [FeIII(L(ISQ))2(PBu3)](PF6) (2ox). The structures of complexes 2, 2ox, 3, 5, 6, and 7 have been determined by X-ray crystallography at 100(2) K. Magnetic susceptibility measurements and EPR, UV-vis, and M?ssbauer spectroscopy have established that mononuclear complexes containing the [FeII(L(ISQ))2X] chromophore (2, 4, 5) are diamagnetic (St = 0) whereas those with an [FeIII(L(ISQ))2X]n chromophore (3, 2(ox), 6) are paramagnetic (St = 1/2) and those with an [FeIII(L(ISQ))(L(PDI))X] chromophore (7) possess an St = 1 ground state. It is established that all ferric species have an intrinsic intermediate spin (SFe = 3/2) which is intramolecularly antiferromagnetically coupled to one or two (L(ISQ))*- ligand radicals yielding an St = 1 (7) or St = 1/2 (2ox, 3, 6) ground state, respectively. In the ferrous complexes 2, 4, and 5 the intrinsic spin at the iron ion is either low spin (SFe = 0) or intermediate spin (SFe = 1). Antiferromagnetic coupling between two radicals (L(ISQ))*- or, alternatively, between the intermediate spin ferrous ion and two radicals yields then the observed diamagnetic ground state. In 1 two [FeIII(L(ISQ))(L(PDI))] halves with S = 1 couple antiferromagnetically affording an St = 0 ground state.     

Synthesis, structure, and magnetic ordering of layered (2-D) V-based tris(oxalato)metalates

The reaction of K3[M(III)(ox)3].3H2O [M = V (1), Cr; ox = oxalate], Mn(II)/V(II), and [N(n-Bu)4]Br in water leads to the isolation of 2-D V-based coordination polymers, [[N(n-Bu)4][Mn(II)V(III)(ox)3]]n (2), [[N(n-Bu)4][V(II)Cr(III)(ox)3]]n (3), [[N(n-Bu)4][V(II)V(III)(ox)3]]n (4), and an intermediate in the formation of 4, [[N(n-Bu)4][V(II)V(III)(ox)3(H2O)2]]n.2.5H2O (4a), while 1-D [V(II)(ox)(H2O)2]n (5) is obtained by using Na2ox and [V(OH2)6]SO4 in water. The structures of 1-5 have been investigated by single crystal and/or powder X-ray crystallography. In 1, V(III) is coordinated with three oxalate dianions as an approximately D3 symmetric, trigonally distorted octahedron. 1 is paramagnetic [mu(eff) = 2.68 mu(B) at 300 K, D = 3.84 cm(-1) (D/k(B) = 5.53 K), theta = -1.11 K, and g = 1.895], indicating an S = 1 ground state. 2 exhibits intralayer ferromagnetic coupling below 20 K, but does not magnetically order above 2 K, and 3 shows a strong antiferromagnetic interaction between V(II), S = 3/2 and Cr(III), S = 3/2 ions (theta = -116 K) within the 2-D layers. 4 and 4a magnetically order as ferrimagnets at T(c)'s, taken as the onset of magnetization, of 11 and 30 K, respectively. The 2 K remanent magnetizations are 2440 and 2230 emu.Oe mol(-1) and the coercive fields are 1460 and 4060 Oe for 4 and 4a, respectively. Both 4 and 4a clearly show frequency dependence, indicative of spin-glass-like behavior. The glass transition temperatures were at 6.3 and 27 K, respectively, for 4 and 4a. 1-D 5 exhibits antiferromagnetic coupling of -4.94 cm(-1) (H = -2Jsigma(i=1)n.S(i-1) - gmu(B)sigma(i=0)(n)H.S(i)) between the V(II) ions.     

Molecular and electronic structure of square-planar gold complexes containing two 1,2-Di(4-tert-butylphenyl)ethylene-1,2-dithiolato ligands: [Au(2L)2]1+/0/1-/2-. A combined experimental and computational study

From the reaction of in situ generated 1,2-di(4-tert-butylphenyl)ethylene-1,2-dithiol, 2LH2, and Na[AuCl4].2H2O in 1,4-dioxane, green brown crystals of diamagnetic [N(n-Bu)4][AuIII(2L)2] (1) were obtained. As shown by cyclic voltammetry, 1 is a member of an electron-transfer series comprising the dianion [AuII(2L)2]2-, the monoanion [AuIII(2L)2]-, the neutral species [AuIII(2L*)(2L)]0 <--> [AuIII(2L)(2L*)]0, and the monocation [AuIII(2L*)2]+. (2L*)1- represents the pi radical anion (Srad = 1/2) of the one-electron oxidized closed-shell dianion (2L)2-. Oxidation of 1 in CH2Cl2 with ferrocenium hexafluorophosphate affords green, paramagnetic microcrystals of [AuIII(2L*)(2L)] <--> [AuIII(2L)(2L*)] (2) (S = 1/2). Complexes 1 and 2 have been characterized by X-ray crystallography. Both species possess square-planar monoanions and neutral molecules, respectively. From the oxidation reaction of 1 or [N(n-Bu)4][AuIII(3L)2] with 2-3 equiv of [NO]BF4 in CH2Cl2, a green solution of [AuIII(2L*)2]+ and green microcrystals of [AuIII(3L*)2]BF4 (3) were obtained, respectively; (3L)2- represents the dianion 1,2-di(4-diphenyl)ethylene-1,2-dithiolate, and (3L*)1- is its pi radical monoanion. The electronic structures of this series of gold species have been elucidated by UV-vis, EPR spectroscopies, and DFT calculations. It is shown computationally by density functional theoretical (DFT) methods that the electronic structure of [AuIII(1L*)2]+ is best described as a singlet diradical (St = 0); the ligand mixed valency in the neutral species 2 is of class (III) (delocalized); the monoanion in 1 contains a AuIII ion and two closed-shell dianionic ligands; and the corresponding dianions [Au(L)2]2- are best described as an intermediate AuII/AuIII species with a metal-ligand delocalized SOMO (25% Au 5d, 75% 3p of four S atoms). (1L)2- is the dianion 1,2-di(phenyl)ethylene-1,2-dithiolate, and (1L*)1- is the pi radical monoanion. The neutral species [PdII(2L*)2] (4) has also been synthesized and characterized by X-ray crystallography. Its electronic structure is the same as described for [AuIII(1L*)2]+ (singlet diradical), whereas that of the monoanion [PdII(2L*)(2L)]- <--> [Pd(2L)(2L*)]- corresponds to that of the neutral gold complex 2. Anodic oxidation of the analogous monoanion [AuIII(mnt)2]-, where mnt = maleonitriledithiolate, gave the neutral complex [Au(mnt)(mnt*)] (E1/2 = 0.91 V vs Fc+/Fc). The optical and EPR spectroscopies of [Au(mnt)(mnt*)] were consistent with those observed for the corresponding di(tert-butylphenyl)ethylenedithiolate complex 2.     

Dinuclear Bis(1,2-diaryl-1,2-ethylenedithiolato)iron complexes: [FeIII2(L)4]n (n = 2-, 1-, 0, 1+)

The electronic structures of four members of the electron-transfer series [Fe2(1L)4]n (n = 2-, 1-, 0, 1+) have been elucidated in some detail by electronic absorption, IR, X-band electron paramagnetic resonance (EPR), and M?ssbauer spectroscopies where (1L)(2-) represents the ligand 1,2-bis(4-tert-butylphenyl)-1,2-ethylenedithiolate(2-) and (1L*)- is its pi-radical monoanion. It is conclusively shown that all redox processes are ligand-centered and that high-valent iron(IV) is not accessible. The following complexes have been synthesized: [FeIII2(1L*)2(1L)2]0 (1), [FeIII2(2L*)2(2L)2].2CH2Cl2 (1') where (2L)(2-) is 1,2-bis(p-tolyl)-1,2-ethylenedithiolate(2-) and (2L*)- represents its pi-radical monoanion, [Cp2Co][FeIII2(1L*))(1L)3].4(toluene).0.5Et2O (2), and [Cp2Co]2[FeIII2(1L)4].2(toluene) (3). The crystal structures of 1' and 2 have been determined by single-crystal X-ray crystallography at 100 K. The ground states of complexes have been determined by temperature-dependent magnetic susceptibility measurements and EPR spectroscopy: 1' and 1 are diamagnetic (S(t) = 0); 2 (S(t) = 1/2); 3 (S(t) = 0); the monocation [Fe(III)2(1L*)3(1L)]+ possesses an S(t) = 1/2 ground state (S(t) = total spin ground state of dinuclear species). All species contain pairs of intermediate-spin ferric ions (S(Fe) = 3/2), which are strongly antiferromagnetically coupled (H = -2JS(1).S(2), where S1 = S2 = 3/2 and J = approximately -250 cm(-1)).     

Syntheses, structures and properties of a series of non-heme alkoxide-Fe(III) complexes of a benzimidazolyl-rich ligand as models for lipoxygenase

The treatment of Fe(ClO(4))(2)·6H(2)O or Fe(ClO(4))(3)·9H(2)O with a benzimidazolyl-rich ligand, N,N,N',N'-tetrakis[(1-methyl-2-benzimidazolyl)methyl]-1,2-ethanediamine (medtb) in alcohol/MeCN gives a mononuclear ferrous complex, [Fe(II)(medtb)](ClO(4))(2)·?CH(3)CN·?CH(3)OH (1), and four non-heme alkoxide-iron(III) complexes, [Fe(III)(OMe)(medtb)](ClO(4))(2)·H(2)O (2, alcohol = MeOH), [Fe(III)(OEt)(Hmedtb)](ClO(4))(3)·CH(3)CN (3, alcohol = EtOH), [Fe(III)(O(n)Pr)(Hmedtb)](ClO(4))(3)·(n)PrOH·2CH(3)CN (4, alcohol = n-PrOH), and [Fe(III)(O(n)Bu)(Hmedtb)](ClO(4))(3)·3CH(3)CN·H(2)O (5, alcohol = n-BuOH), respectively. The alkoxide-iron(III) complexes all show 1) a Fe(III)-OR center (R = Me, 2; Et, 3; (n)Pr, 4; (n)Bu, 5) with the Fe-O bond distances in the range of 1.781-1.816 ?, and 2) a yellow color and an intense electronic transition around 370 nm. The alkoxide-iron(III) complexes can be reduced by organic compounds with a cis,cis-1,4-diene moiety via the hydrogen atom abstraction reaction.     

Cyano-bridged structures based on [MnIIN3O2-macrocycle)]2+: a synthetic, structural, and magnetic study

Reactions between the complex [MnII(L)]2+, where L is a N3O2 macrocyclic ligand, and different cyanometalate precursors such as [M(CN)n]m- (M(III) = Cr, Fe; M(II) = Fe, Ni, Pd, Pt) lead to cyano-bridged molecular assemblies exhibiting a variety of structural topologies. The reaction between [MnII(L)]2+ and [FeII(CN)6]4- forms a trinuclear complex with formula [(MnII(L)(H2O))2(FeII(micro-CN)2(CN)4)] x 2MeOH x 10H2O (1) which crystallizes in the triclinic space group P1. The reaction between [MnII(L)]2+ and [M(II)(CN)4]2-, where M(II) = Ni (2), Pd (3), Pt (4), gives rise to three isostructural linear chain compounds with stoichiometry [(MnII(L))(M(II)(micro-CN)2(CN)2)]n and which crystallize in the monoclinic space group C2/c. The self-assembly between [MnII(L)]2+ with [M(III)(CN)6]3-, where M(III) = Cr (5), Fe (6, 7, 8), forms three types of compounds. Compounds 5 and 6 are isostructural (monoclinic, space group P2(1)/n), and the structures comprise anionic linear chains [(MnII(L))(M(III)(micro-CN)2(CN)4)]n(n-) with cationic trinuclear complexes [(MnII(L)(H2O))2(M(III)(micro-CN)2(CN)4)]+ as counterions. Using an excess of K3[FeIII(CN)6], an analogous compound to 6 but with K+ as counterion is obtained (7), which crystallizes in the triclinic space group P1. Compound 8 consists of 2-D layers with formula [(MnII(L))3(FeIII(micro-CN)4(CN)2)(FeIII(micro-CN)2(CN)4)]n x 2nMeOH; it crystallizes in the monoclinic space group P2(1)/n. The magnetic properties were investigated for all samples. In particular, compound 5, which shows antiferromagnetic exchange interactions between Mn(II) and Cr(III) ions through cyanide bridging ligands, has been studied in detail; the magnetic exchange parameter amounts to J = -7.5(7) cm(-1). Compound 8 shows a magnetically ordered phase below 6.4 K which is confirmed by M?ssbauer spectroscopy; two hyperfine split spectra were observed below Tc from which IJI values of 2.1 and 1.6 cm(-1) could be deduced.     

4,2-Ribbon like ferromagnetic cyano-bridged Fe(III)2Ni(II) chains: a magneto-structural study

The low-spin iron(III) complex AsPh(4)[Fe(III)(bpy)(CN)(4)].CH(3)CN (1) [AsPh(4) = tetraphenylarsonium cation] and the heterobimetallic chains [{Fe(III)(L)(CN)(4)}(2)Ni(II)(H(2)O)(2)].4H(2)O with L = bpy (2) and phen (3) [bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline] have been prepared and their structures determined by X-ray diffraction methods. The structure of 1 consists of mononuclear [Fe(bpy)(CN)(4)](-) anions, tetraphenylarsonium cations and acetonitrile molecules of crystallization. The iron(III) is hexacoordinated with two nitrogen atoms of the bidentate bpy and four carbon atoms of four terminal cyanide groups building a distorted octahedral surrounding around the metal atom. 2 and 3 are isomorphous compounds whose structure is made up of neutral 4,2-ribbon like bimetallic chains of formula [{Fe(III)(L)(CN)(4)}(2)Ni(II)(H(2)O)(2)] where the [Fe(III)(L)(CN)(4)](-) unit acts as a bis-monodentate bridging ligand toward the trans-diaquanickel(II) units through two of its four cyanide groups in cis positions. The chains exhibit two orientations in the unit cell and they interact with each other through hydrogen bonds involving the coordination and crystallization water molecules together with the uncoordinated cyanide nitrogen atoms of the [Fe(L)(CN)(4)](-) units. Compounds 2 and 3 behave as ferromagnetic Fe(III)(2)Ni(II) chains which interact ferromagnetically at very low temperatures in the case of 2, whereas metamagnetic-like behaviour is observed for with a critical field (H(c)) around 200 G. For H > H(c) the ferromagnetic Fe(III)(2)Ni(II) chains of 3 exhibit a frequency dependence of the out-of-phase ac susceptibility signal at T < 3.5 K.     

Synthesis and spectroscopic and magnetic characterization of tris(3,5-dimethylpyrazol-1-yl)borate iron tricyanide building blocks, a cluster, and a one-dimensional chain of squares

The synthesis and spectroscopic and magnetic characterization of several hydridotris(3,5-dimethylpyrazol-1yl)borate (Tp*) iron(II) and iron(III) tricyanide complexes, a rectangular cluster, and a one-dimensional chain of squares are described. Treatment of [NEt4][(Tp*)Fe(III)(CN)3] (3) with manganese(II) triflate in dimethylformamide (DMF) affords rectangular clusters (6, {[(Tp)Fe(CN)2(mu-CN)Mn(DMF)4]2[OTf]2}.2DMF), while tosylate salts afford one-dimensional networks (5, {Mn(II)(DMF)2(mu-OTs)(mu-NC)2(NC)Fe(III)(Tp*)}n) containing embedded [(Tp*)2Fe(III)2Mn(II)2(CN)6]2+ clusters via in situ trapping; the cluster and network crystallize in the monoclinic (6, P2(1)/n) and triclinic (5, P1) space groups, respectively. The 1-D network (5) appears to be derived from {cis-(mu-O3SC6H4Me)2Mn(II)(DMF)4}n (4, P2(1)/n), which is obtained via crystallization of Mn(OTs)2 from DMF/Et2O mixtures. For 4, magnetic studies indicate that the Mn(II) centers are magnetically isolated, with calculated J, g, and theta constants of 6.7 x 10(-3) cm(-1), 2.03, and -0.52 K. Additional magnetic studies of 5 and 6 indicate that the [(Tp*)Fe(III)(CN)3]- centers are highly anisotropic (g = 2.9) and are antiferromagnetically coupled to adjacent Mn(II) centers. For 5 and 6, fitting of the chiT vs T data via the Curie-Weiss expression affords Curie (6.25 and 10.8 cm(3) K mol(-1)) and Weiss (-14.37 and -8.80 K) constants that are consistent with antiferromagnetically coupled low-spin Fe(III) and high-spin Mn(II) centers; least-squares fitting of the chiT vs T data using molecular field theory affords g(avg.), J1, J2, and J' values of 2.25, -1.72, -0.58, and -0.12 cm(-1) for 5. Overall, bridging tosylates appear to be poor communicators of spin information. For 6, the g, J1, and J2 (2.15, -2.02, and -0.78 cm(-1)) values were obtained via least-squares fitting of the chiT vs T data using an expression derived using the Kambe vector coupling method; simulations of the data via MAGPACK afford g(avg.) and J(iso) values of 2.1 and -2.1 cm(-1).     

An S = 2 cyanide-bridged trinuclear Fe(III)2Ni(II) single-molecule magnet

Treatment of [NEt4][(pzTp)Fe(III)(CN)3] (1) with Ni(II)(OTf)2 (OTf = trifluoromethanesulfonate) and 1,5,8,12-tetraazadodecane (L) affords {[(pzTp)Fe(III)(CN)3]2[Ni(II)L]} x 1/2MeOH (2), while 2,2'-bipyridine (bipy) affords {[(pzTp)Fe(III)(CN)3]2[Ni(II)(bipy)2]} x 2 H2O (3). Magnetic measurements indicate that 2 and 3 have S = 2 ground states and that 3 exhibits slow relaxation of the magnetization above 2 K.     

Cyclic voltammetry of the electron transfer reaction between bis(cyclopentadienyl)iron in 1,2-dichloroethane and hexacyanoferrate in water.

The electron transfer (ET) reaction between bis(cyclopentadienyl)iron(II) ([Fe(II)(C(5)H(5))2]) in 1,2-dichloroethane (1,2-DCE) and hexacyanoferrate redox couple ([Fe(II/III)(CN)6](4-/3-)) in water (W) at the interface has been studied by using cyclic voltammetry. The voltammetric results can be explained well by a theoretical equation for the so-called IT-mechanism, in which a homogeneous ET reaction between [Fe(C(5)H(5))2] (partially distributed from 1,2-DCE) and [Fe(CN)6](3-) takes place in the W phase and the resultant [Fe(C(5)H(5))2]+ ion is responsible for current passage across the interface. The forward rate constant of the homogeneous ET reaction, [Fe(C(5)H(5))2] + [Fe(CN)6](3-) = [Fe(C(5)H(5))2]+ + [Fe(CN)6](4-) in W phase, k(f)(IT), was determined to be (2.9 +/- 2.2)x 10(10) M(-1) s(-1), which was in good agreement with k(f)(IT) = (3.2 +/- 2.0)x 10(10) M(-1) s(-1), which had been determined by using normal-pulse voltammetry.     

Synthesis, structures, and magnetic properties of a series of cyano-bridged Fe-Mn bimetallic complexes

The preparation and crystal structures of five cyano-bridged Fe-Mn complexes, [(bipy)2Fe(II)(CN)2Mn(II)(bipy)2]2(ClO4)4 (1), [(bipy)2Fe(II)(CN)2Mn(II)(DMF)3(H2O)]2(ClO4)4 (2), {[(Tp)Fe(III)(CN)3]2Mn(II)(DMF)2(H2O)}2 (3), {[(Tp)Fe(III)(CN)3]2Mn(II)(DMF)2}n (4), and Na2[Mn(II)Fe(II)(CN)6] (5) (bipy = 2,2'-bipyridine, Tp = tris(pyrazolyl)hydroborate), are reported here. Compounds 1-4 contain the basic Fe2(CN)4Mn2 square building units, of which 1-3 show the motif of discrete molecular squares of Fe2(CN)4Mn2 and 4 possesses a 1D double-zigzag chain-like structure, while compound 5 is a 3D cubic framework analogous to that of Prussian blue. Compounds 1 and 2 show weak ferromagnetic interactions between two Mn(II) ions through the bent -NC-Fe(II)-CN- bridges. Compound 3 shows weak antiferromagnetic coupling between the Fe(III) and Mn(II) ions, while compound 4 displays a metamagnetic-like behavior with TN = 5.2 K and Hc = 10.5 kOe. Compound 5 exhibits a ferromagnetic ordering with Tc= 3.5 K, coercive field, Hc, = 330 G, and a remnant magnetization of 503 cm3 Oe mol(-1).     

Chiral, Three-Dimensional Supramolecular Compounds: Homo- and Bimetallic Oxalate- and 1,2-Dithiooxalate-Bridged Networks. A Structural and Photophysical Study

In analogy to the [M(II)(bpy)(3)](2+) cations, where M(II) is a divalent transition-metal and bpy is 2,2'-bipyridine, the tris-chelated [M(III)(bpy)(3)](3+) cations, where M(III) is Cr(III) or Co(III), induce the crystallization of chiral, anionic three-dimensional (3D) coordination polymers of oxalate-bridged (&mgr;-ox) metal complexes with stoichiometries [M(II)(2)(ox)(3)](n)()(2)(n)()(-) or [M(I)M(III)(ox)(3)](n)()(2)(n)()(-). The tripositive charge is partially compensated by inclusion of additional complex anions like ClO(4)(-), BF(4)(-), or PF(6)(-) which are encapsulated in cubic shaped cavities formed by the bipyridine ligands of the cations. Thus, an elaborate structure of cationic and anionic species within a polymeric anionic network is realized. The compounds isolated and structurally characterized include [Cr(III)(bpy)(3)][ClO(4)] [NaCr(III)(ox)(3)] (1), [Cr(III)(bpy)(3)][ClO(4)][Mn(II)(2)(ox)(3)] (2), [Cr(III)(bpy)(3)][BF(4)] [Mn(II)(2)(ox)(3)] (3), [Co(III)(bpy)(3)][PF(6)][NaCr(III)(ox)(3)] (4). Crystal data: 1, cubic, P2(1)3, a = 15.523(4) ?, Z = 4; 2, cubic, P4(1)32, a = 15.564(3) ?, Z = 4; 3, cubic, P4(1)32, a = 15.553(3) ?, Z = 4; 4, cubic, P2(1)3, a = 15.515(3) ?, Z = 4. Furthermore, it seemed likely that 1,2-dithiooxalate (dto) could act as an alternative to the oxalate bridging ligand, and as a result the compound [Ni(II)(phen)(3)][NaCo(III)(dto)(3)].C(3)H(6)O (5) has successfully been isolated and structurally characterized. Crystal data: 5, orthorhombic, P2(1)2(1)2(1), a = 16.238(4) ?, b = 16.225(4) ?, c = 18.371(5) ?, Z = 4. In addition, the photophysical properties of compound 1 have been investigated in detail. In single crystal absorption spectra of [Cr(III)(bpy)(3)][ClO(4)][NaCr(III)(ox)(3)] (1), the spin-flip transitions of both the [Cr(bpy)(3)](3+) and the [Cr(ox)(3)](3)(-) chromophores are observed and can be clearly distinguished. Irradiating into the spin-allowed (4)A(2) --> (4)T(2) absorption band of [Cr(ox)(3)](3)(-) results in intense luminescence from the (2)E state of [Cr(bpy)(3)](3+) as a result of rapid energy transfer processes.     

A study of structural and bonding variations in the homologous series [Mo(2)(CN)(6)(dppm)(2)](n-) (n = 2, 1, 0)

Reaction of Mo(2)Cl(4)(dppm)(2) (dppm = bis(diphenylphosphino)methane) with 6 equiv of [n-Bu(4)N][CN] or [Et(4)N][CN] in dichloromethane yields [n-Bu(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (1) and [Et(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (2), respectively. The corresponding one- and two-electron oxidation products [n-Bu(4)N][Mo(2)(CN)(6)(dppm)(2)] (3) and Mo(2)(CN)(6)(dppm)(2) (4)were prepared by reactions of 1 with the oxidant NOBF(4). Single-crystal X-ray structures of 2.2CH(3)CN, 3.2CH(3)CN.2H(2)O, and 4.2CH(3)NO(2) were performed, and the results confirmed that all three complexes contain identical ligand sets with trans dppm ligands bisecting the Mo(2)(mu-CN)(2)(CN)(4) equatorial plane. The binding of the bridging cyanide ligands is affected by the oxidation state of the dimolybdenum core as evidenced by an increase in side-on pi-bonding overlap of the mu-CN in going from 1 to 4. The greater extent of pi-donation into Mo orbitals is accompanied by a lengthening of the Mo-Mo distance (2.736(1) A in Mo(2)(II,II) (2), 2.830(1) A in Mo(2)(II,III) (3), and 2.936(1) A in Mo(2)(III,III) (4)). A computational study of the closed-shell members of this homologous series, [Mo(2)(CN)(6)(dppm)(2)](n)() (n = 2-, 0), indicates that the more pronounced side-on pi-donation evident in the X-ray structure of 4 leads to significant destabilization of the delta orbital and marginal stabilization of the delta() orbitals with respect to nearly degenerate delta and delta orbitals in the parent compound, 2. The loss of delta contributions combined with the reduced orbital overlap due to higher charges on molybdenum centers in oxidized complexes 3 and 4 is responsible for the observed increase in the length of the Mo-Mo bond.     

Synthesis and characterization of di- and trivalent pyrazolylborate β-diketonates and cyanometalates

The syntheses, structures, and magnetic properties of a series of di- and trivalent hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) cyanomanganates are described. Treatment of tris(acetylacetonate)manganese(III) [Mn(acac)(3)] with KTp* and tetra(ethyl)ammonium cyanide affords [NEt(4)][(Tp*)Mn(II)(κ(2)-acac)(CN)] (1), as the first monocyanomanganate(II) complex; attempted oxidation of 1 with iodine affords {(Tp*)Mn(II)(κ(2)-acac(3-CN))}(n) (2) as a one-dimensional chain and bimetallic {[NEt(4)][(Tp*)Mn(II)(κ(2)-acac(3-CN))](2)(μ-CN) (3) as the major and minor products, respectively. A fourth complex, [NEt(4)][(Tp*)Mn(II)(η(2)-acac(3-CN))(η(1)-NC-acac)] (4), is obtained via treatment of Mn(acac(3-CN))(3) with KTp* and [NEt(4)]CN, while [NEt(4)](2)[Mn(II)(CN)(4)] (5) was prepared from manganese(II) trifluoromethanesulfonate and excess [NEt(4)]CN. Tricyanomanganate(III) complexes, [cat][(Tp*)Mn(III)(CN)(3)] [cat = NEt(4)(+), 7; PPN(+), 8], are prepared via sequential treatment of Mn(acac(3-CN))(3) with KTp*, followed by [NEt(4)]CN, or [cat](3)[Mn(III)(CN)(6)] with (Tp*)SnBu(2)Cl. Magnetic measurements indicate that 1, 2, and 4 contain isotropic Mn(II) (S = (5)/(2); g = 2.00) centers, and no long-range magnetic ordering is found above 1.8 K. Compounds 7 and 8 contain S = 1 Mn(III) centers that adopt singly degenerate spin ground states without orbital contributions to their magnetic moments.     

1,2-bis(pyridine-2-carboxamido)benzenate(2-), (bpb)2-: a noninnocent ligand. Syntheses, structures, and mechanisms of formation of [(n-Bu)4N][FeIV2(mu-N)(bpb)2(X)2] (X = CN-, N3-) and the electronic structures of [MIII(bpbox1)(CN)2] (M = Co, Fe)

The well-known tetradentate ligand 1,2-bis(pyridine-2-carboxamido)benzenate(2-), (bpb)2-, and its 4,5-dichloro analogue, (bpc)2-, are shown to be "noninnocent" ligands in the sense that in coordination compounds they can exist in their radical one- and diamagnetic two-electron-oxidized forms (bpbox1)- and (bpbox2)0 (and (bpcox1)- and (bpcox2)0), respectively. Photolysis of high-spin [(n-Bu)4N][FeIII(bpb)(N3)2] and its (bpc)2- analogue in acetone solution at room temperature generates the diamagnetic dinuclear complex [(n-Bu)4N][FeIV2(mu-N)(bpb)2(N3)2] and its (bpc)2- analogue; the corresponding cyano complex [(n-Bu)4N][FeIV2(mu-N)(bpb)2(CN)2] has been prepared via N3- substitution by CN-. Photolysis in frozen acetonitrile solution produces a low-spin ferric species (S = 1/2) which presumably is [FeIII(bpbox2)(N)(N3)]-, as has been established by EPR and M?ssbauer spectroscopy. The mononuclear complexes [(n-Bu)4N][FeIII(bpb)(CN2)] (low spin), [Et4N][CoIII(bpb)(CN)2] and Na[CoIII(bpc)-(CN)2].3CH3OH can be electrochemically or chemically one-electron-oxidized to give [FeIII(bpbox1)(CN)2]0 (S = 0), [CoIII(bpbox1)(CN)2]0 (S = 1/2), and [CoIII(bpcox1)(CN)2]0 (S = 1/2). All complexes have been characterized by UV-vis, EPR, and M?ssbauer spectroscopy, and their electro- and magnetochemistries have been studied. The crystal structures of [(n-Bu)4N][FeIII(bpb)(N3)2].1/2C6H6CH3, Na[FeIII(bpb)(CN)2], Na[CoIII(bpc)(CN)2].3CH3OH, [(n-Bu)4N][FeIV2(mu-N)(bpb)2(CN)2], and [(n-Bu)4N][FeIV2(mu-N)(bpb)(N3)2] have been determined by single-crystal X-ray diffraction.     

Efficient energy transfer via the cyanide bridge in dinuclear complexes containing Ru(II) polypyridine moieties

We report the synthesis, structure and properties of the cyanide-bridged dinuclear complex ions [Ru(L)(bpy)(μ-NC)M(CN)(5)](2-/-) (L = tpy, 2,2';6',2'-terpyridine, or tpm, tris(1-pyrazolyl)methane, bpy = 2,2'-bipyridine, M = Fe(II), Fe(III), Cr(III)) and the related monomers [Ru(L)(bpy)X](2+) (X = CN(-) and NCS(-)). All the monomeric compounds are weak MLCT emitters (λ = 650-715 nm, ? ≈ 10(-4)). In the Fe(II) and Cr(III) dinuclear systems, the cyanide bridge promotes efficient energy transfer between the Ru-centered MLCT state and a Fe(II)- or Cr(III)-centered d-d state, which results either in a complete quenching of luminescence or in a narrow red emission (λ ≈ 820 nm, ? ≈ 10(-3)) respectively. In the case of Fe(III) dinuclear systems, an electron transfer quenching process is also likely to occur.     

Heterometallic Cr-Mn complexes containing cyanide and oxalate bridges

Three heterometallic Cr-Mn compounds, {Mn(mu-ox)0.5(H2O) [Cr(phen)(CN)4]}n.n H2O.2n CH3OH, (1), {Mn(mu-ox)0.5(H2O)[Cr(bpy)(CN)4]}n.2n H2O x n CH3OH, (2), and {Mn(mu-ox)0.5(bpy)[Cr(bpy)(CN)4]}n, (3) (ox = oxalate), containing cyanide and oxalate bridges based on building blocks [Cr(L)(CN)4]- (L = phen and 2,2'-bipyridine) have been prepared. A new approach was first employed to synthesize ox-bridged compounds via facile oxidation-hydrolysis reactions of diaminomaleonitrile. X-ray crystallography revealed that the structures of 1 and 2 are similar, where cyano-bridged corrugated ladderlike chains are further connected through bis-bidentate oxalato bridges to unique two-dimensional layered structures. Of note is that the introduction of 2,2'-bipyridine led to an interesting cluster-based chainlike compound (3) with cyano-bridged squares [Mn2Cr2] extended by ox bridges. Magnetic studies show antiferromagnetic (AF) interaction between cyano-bridged Cr(III)-Mn(II) and ox-bridged Mn(II)-Mn(II) ions, with the result that 1 and 2 exhibit AF ordering with spin-flop behaviors below 18 and 19 K, respectively.     

Dioxygen Reactivity of Biomimetic Iron-Catecholate and Iron-o-Aminophenolate Complexes of a Tris(2-pyridylthio)methanido Ligand: Aromatic CC Bond Cleavage of Catecholate versus o-Iminobenzosemiquinonate Radical Formation

An iron(III)-catecholate complex [L(1) Fe(III) (DBC)] (2) and an iron(II)-o-aminophenolate complex [L(1) Fe(II) (HAP)] (3; where L(1) =tris(2-pyridylthio)methanido anion, DBC=dianionic 3,5-di-tert-butylcatecholate, and HAP=monoanionic 4,6-di-tert-butyl-2-aminophenolate) have been synthesised from an iron(II)-acetonitrile complex [L(1) Fe(II) (CH(3) CN)(2) ](ClO(4) ) (1). Complex 2 reacts with dioxygen to oxidatively cleave the aromatic C?C bond of DBC giving rise to selective extradiol cleavage products. Controlled chemical or electrochemical oxidation of 2, on the other hand, forms an iron(III)-semiquinone radical complex [L(1) Fe(III) (SQ)](PF(6) ) (2(ox) -PF(6) ; SQ=3,5-di-tert-butylsemiquinonate). The iron(II)-o-aminophenolate complex (3) reacts with dioxygen to afford an iron(III)-o-iminosemiquinonato radical complex [L(1) Fe(III) (ISQ)](ClO(4) ) (3(ox) -ClO(4) ; ISQ=4,6-di-tert-butyl-o-iminobenzosemiquinonato radical) via an iron(III)-o-amidophenolate intermediate species. Structural characterisations of 1, 2, 2(ox) and 3(ox) reveal the presence of a strong iron?carbon bonding interaction in all the complexes. The bond parameters of 2(ox) and 3(ox) clearly establish the radical nature of catecholate- and o-aminophenolate-derived ligand, respectively. The effect of iron?carbon bonding interaction on the dioxygen reactivity of biomimetic iron-catecholate and iron-o-aminophenolate complexes is discussed.