Two-dimensional homochiral manganese(II)-azido frameworks incorporating an achiral ligand: partial spontaneous resolution and weak ferromagnetism

By incorporating an achiral diazine ligand, 2-pyridylmethylketazine, which can be locked in a chiral conformation upon coordination, into the manganese(II)-azido system, we induced a homochiral 2D network, in which neighboring Mn(II) ions are bridged via a diazine and two end-on azido ligands into chiral dimeric units, and neighboring units are interlinked via single end-to-end azido bridges. The interdimer chirality preservation is achieved via the homochiral 1D helical linkage formed by Mn(II) and end-to-end azido ions. The 2D layers are stacked in hetero- and homochiral fashion to yield simultaneously racemic and chiral crystals, indicating a partial spontaneous resolution. Both compounds behave as spin-canted weak ferromagnets, but the critical temperatures are different.     

Magnetic properties and electronic structure of manganese(III) porphyrins

The average magnetic susceptibility (1.2-100 K) and magnetisation (100–15000 Oe at 4.2 K) of two perchlorato manganese(III) porphyrins establish them to be high-spin, in contrast to the “anomalous” behaviour of analogous iron(III) porphyrins. An explanation of the origin of the zero-field splitting in high-spin manganese(III) porphyrins is presented.     

Solvent dependence of the structure and magnetic ordering of ferrimagnetic manganese(III) meso-tetraphenylporphyrin tetracyanoethenide, [MnTPP]+[TCNE]*-

Tetraphenylporphinatomanganate(III) tetracyanoethenide, [MnTPP][TCNE], is the prototype of a growing family of linear chain (1-D) coordination polymers that magnetically order as ferrimagnets. [MnTPP][TCNE].xS [S = PhMe (x = 2), 1,2-C(6)H(4)Me(2) (x = 1), 1,2-C(6)H(4)Cl(2) (x = 3), 1,2,4-C(6)H(3)Cl(3) (x = 2), and 1,3-C(6)H(4)Cl(2) (x = 2)] have been prepared and structurally and magnetically characterized. All form 1-D chain structures with intrachain Mn.Mn separations ranging from 9.202 to 10.218 A. The 173 K crystal structure of [MnTPP][TCNE].2PhMe has been rerefined, revealing that the [TCNE](*)(-) is 2-fold-disordered and coordinated to Mn(III) by a pair of trans cyano nitrogen atoms to form parallel one-dimensional chains. The two orientations of [TCNE](*)(-) are related by a 180 degrees rotation about the diagonal axis joining the trans nitrogen atoms bound to Mn(III). The major form has an occupancy of 83.3(4)% with a Mn-N(TCNE) distance of 2.328(3) A and a MnNC angle of 146.8(8) degrees. The minor form, with 16.7(4)% occupancy, has a Mn-N(TCNE) distance of 2.176(15) A and a MnNC angle of 152.3(39) degrees. Lattice packing and molecular bonding imply static as opposed to dynamic disorder. The magnetic properties depend on the type and quantity of the solvent present in the structure. Desolvation via heating in n-octane (127 degrees C), n-dodecane (216 degrees C), and/or vacuum thermolysis (175 degrees C) leads to numerous different desolvated materials with differing magnetic properties. At higher temperatures the magnetic susceptibility can be fit by the Curie-Weiss expression, chi varies with (T - theta)(-1), with theta = 44, 52, 72, 55, and 77 K for the toluene, 1,2-xylene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene solvates, respectively. The T(c)'s were taken as the maximum in 10 Hz chi'(T) and are 7.8, 9.2, 11.3, 10.8, and 8.2 K for the PhMe, 1,2-xylene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene solvates, respectively. Upon desolvation the T(c)'s increase for the PhMe, 1,2-xylene, 1,2,4-trichlorobenzene solvates and decrease for the 1,2- and 1,3-dichlorobenezene solvates. The compounds show one-dimensional ferrimagnetic exchange behavior at high temperatures with intrachain exchange of J/k(b) = -63, -99, -234, -100, and -200 K for toluene, 1,2-xylene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene solvates, respectively, as determined from fits to the Seiden expression, which models isolated 1-D interactions among alternating S = 2 classical and S = (1)/(2) quantum spins. For variation in the temperature at which the peak occurs per decade of frequency, phi, (DeltaT(f)/T(f))/Delta(log omega) is 0.167, 0.168, 0.066, 0.171, and 0.024 for toluene, 1,2-xylene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene, respectively, typical of spin glass behavior. Since [TCNE](*)(-) is only disordered for the PhMe solvate and all five solvates exhibit spin glass behavior, the spin glass behavior cannot be attributed to this disorder.     

Two novel cyanide-bridged bimetallic magnetic chains derived from manganese(III) Schiff bases and hexacyanochromate(III) building blocks

Two novel complexes, [{Mn(salen)}(2){Mn(salen)(CH(3)OH)}{Cr(CN)(6)}](n)·2nCH(3)CN·nCH(3)OH (1) and [Mn(5-Clsalmen)(CH(3)OH)(H(2)O)](2n)[{Mn(5-Clsalmen)(μ-CN)}Cr(CN)(5)](n)·5.5nH(2)O (2) (salen(2-) = N,N'-ethylene-bis(salicylideneiminato) dianion; 5-Clsalmen(2-) = N,N'-(1-methylethylene)-bis(5-chlorosalicylideneiminato) dianion), were synthesized and structurally characterized by X-ray single-crystal diffraction. The structural analyses show that complex 1 consists of one-dimensional (1D) alternating chains formed by the [{Cr(CN)(6)}{Mn(salen)}(4){Mn(salen)(CH(3)OH)}(2)](3+) heptanuclear cations and [Cr(CN)(6)](3-) anions. While in complex 2, the hexacyanochromate(III) anion acts as a bis-monodentate ligand through two trans-cyano groups to bridge two [Mn(5-Clsalmen)](+) cations to form a straight chain. The magnetic analysis indicates that complex 1 shows three-dimensional (3D) antiferromagnetic ordering with the Ne?el temperature of 5.0 K, and it is a metamagnet displaying antiferromagnetic to ferromagnetic transition at a critical field of about 2.6 kOe at 2 K. Complex 2 behaves as a molecular magnet with Tc = 3.0 K.     

One-dimensional Schiff-base-bridged manganese(III) complex: Synthesis,crystal structure and magnetic property

A new one-dimensional Schiff-base ligand bridged manganese(III) complex with the formula [Mn(acacen)(H₂acacen)]ClO₄ (1) (acacen = N, N'-ethylenebis(acetylacetonylideneaminato) has been obtained from the reaction of [Mn(acacen)(H₂O)₂]ClO₄ with K[Fe(bpdBrb)(CN)₂] (bpdBrb^2– = 1,2-bis(pyridine-2-carboxamido)-4,5-dibromobenzenate), which has been characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals it’s onedimensional infinite structure consisting of alternating units of [Mn(acacen)]⁺ and the Schiff-base ligand H₂acacen with a trans conformation, forming a cationic polymeric chain with free ClO₄^- as the balanced anion. The one-dimensional chain structure can be can be further linked into three-dimensional supramolecular network under the help of the intermolecular weak interactions. Investigation over its magnetic property reveals the weak antiferromagnetic coupling between the adjacent Mn(III) ions.     

Energy transfer between manganese(II) and thulium(III) in transition-metal fluoride glasses

Lead zinc gallium fluoride glass containing 2 mole% TmF₃ is shown to luminesce from ¹I₆ (35200 cm⁻¹), ¹D₂(28000), ¹G₄ (21500) and ³H₄ (12800) to several lower J levels. When the 24 mole% ZnF₂ is replaced by MnF₂ in the absence of thulium, the (broad band) quartet-to-sextet (ground state) emission at 16800cm⁻¹ has a mean lifetime of 1 ms. If 2 mole% TmF₃ is added to the latter glass, energy transfer decreases the lifetime to below 0.03 ms. The high critical radius R₀ (above 20 Å) is rationalized by Mn-Mn energy migration (concomitant with a lifetime shortened from 24 ms) to be compared with R₀≈ 8 Å for low Mn(II) concentration, almost identical with energy transfer between 1 mole% each of MnF₂ and NdF₃ previously studied in an analogous glass.     

Spin-canting and weak ferromagnetism in two novel 1D alternating chains with single cis-end-to-end azido bridges

By combining trans-4-styrylprydine (tsp) with azide system, we obtained two rare 1D cis-EE-azido-bridged compounds of [M2(N3)4(tsp)4(H2O)2] [M = Mn (1), Co (2)]. The magnetic study reveals that metal ions are anti-ferromagnetically coupled by cis-EE-azido-bridges and they show weak ferromagnetism below 4.0 K (1) and 4.2 K (2) due to the spin-canting caused by asymmetric magnetic interaction.     

Honeycomb layer of cobalt(II) azide hydrazine showing weak ferromagnetism

Using hydrazine (N2H4) as a cobridge with azide, a honeycomb-layered cobalt(II) coordination polymer, Co(N2H4)(N3)2 (1), is obtained that exhibits spin-canted weak ferromagnetism with TN of 13.5 K.     

Simultaneous determination of soluble manganese(III), manganese(II) and total manganese in natural (pore)waters

A new spectrophotometric protocol was developed for the simultaneous determination of soluble Mn(III), Mn(II) and total Mn [sum of soluble Mn(III) and Mn(II)] in sediment porewaters using a water soluble meso-substituted porphyrin [α,β,γ,δ-tetrakis(4-carboxyphenyl)porphine (T(4-CP)P)]. A simple kinetic rate model is used to quantify soluble Mn(II), Mn(III) and total Mn concentrations during a metal substitution reaction. Under optimized conditions, the method accurately determines soluble Mn(II) and Mn(III) within a concentration range of 100 nM-10 μM. The detection limit of total soluble Mn is 50 nM. Using this method, soluble Mn(II) and Mn(III) concentrations were determined in standard solutions within 0.4-2% of the known values and agreed closely with results of inductively coupled plasma mass spectrometric and voltammetric analyses. The procedure was successfully applied to determine soluble Mn(II), Mn(III) and total Mn in sediment porewaters of the Lower St. Lawrence Estuary. Mn(III) represented up to 85% of the total soluble Mn pool in surface sediments.     

Synthesis of bis(diethyldithiocarbamato)manganese(II) and tris(diethyldithiocarbamato)manganese(III)

An ideal undergraduate introduction to the challenges of synthesis and characterization of air-sensitive compounds is accomplished in the preparation of bis(diethyldithiocarbamato)manganese(II). This economical experiment employs a glovebag, low-cost and low-toxicity chemicals, and is completed in one undergraduate laboratory period. For comparison purposes, the synthesis and characterization of air-stable tris(diethyldithiocarbamato)manganese(III) is also described.     

Synthesis and characterization of phase-pure manganese(II) and manganese(III) silicalite-2

Manganese silicalite-2 was synthesized at high pH using the molecular cluster Mn 12O 12(O 2CCH 3) 16 as a Mn source. The silicalite-2 (ZSM-11) materials were synthesized using 3,5-dimethyl- N, N-diethylpiperdinium hydroxide as a structure-directing agent to produce phase-pure ZSM-11 materials. No precipitation of manganese hydroxide was observed, and synthesis resulted in the incorporation of up to 2.5 mol % Mn into the silicalite-2 with direct substitution into the framework verified by the linear relationship between the unit cell volume and loading. The Mn is reduced to Mn (II) during hydrothermal synthesis and incorporated into the silicalite-2 framework during calcination at 500 degrees C. Further calcination at 750 degrees C does not affect the crystallinity but oxidizes essentially all of the Mn (II) to Mn (III) in the framework. The large difference in oxidation temperatures between the II and III oxidation states provides a means of producing relatively pure manganese(II) and manganese(III) silicalite-2 materials for applications such as catalysis.     

Synthesis, structure, and properties of low-spin manganese(III)-poly(pyrazolyl)borate complexes

The manganese(III)-bis[poly(pyrazolyl)borate] complexes, Mn(pzb)2SbF6, where pzb- = tetrakis(pyrazolyl)borate (pzTp) (1), hydrotris(pyrazolyl)borate (Tp) (2), or hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) (3), have been synthesized by oxidation of the corresponding Mn(pzb)2 compounds with NOSbF6. The Mn(III) complexes are low-spin in solution and the solid state (microeff = 2.9-3.8 microB). X-ray crystallography confirms their uncommon low-spin character. The close conformity of mean Mn-N distances of 1.974(4), 1.984(5), and 1.996(4) A in 1, 2, and 3, respectively, indicates absence of the characteristic Jahn-Teller distortion of a high-spin d4 center. N-Mn-N bite angles of slightly less than 90 degrees within the facially coordinated pzb- ligands produce a small trigonal distortion and effective D3d symmetry in 1 and 2. These angles increase to 90.0(4)degrees in 3, yielding an almost perfectly octahedral disposition of N donors in Mn(Tp*)2+. Examination of structural data from 23 metal-bis(pzb) complexes reveals systematic changes within the metal-(pyrazolyl)borate framework as the ligand is changed from pzTp to Tp to Tp*. These deformations consist of significant increases in M-N-N, N-B-N, and N-N-B angles and a minimal increase in Mn-N distance as a consequence of the steric demands of the 3-methyl groups. Less effective overlap of pyrazole lone pairs with metal atom orbitals resulting from the M-N-N angular displacement is suggested to contribute to the lower ligand field strength of Tp* complexes. Mn(pzb)2+ complexes undergo electrochemical reduction and oxidation in CH3CN. The electrochemical rate constant (ks,h) for reduction of t2g4 Mn(pzb)2+ to t2g3eg2 Mn(pzb)2 (a coupled electron-transfer and spin-crossover reaction) is 1-2 orders of magnitude smaller than that for oxidation of t2g4 Mn(pzb)2+ to t2g3 Mn(pzb)22+. ks,h values decrease as Tp* > pzTp > Tp for the Mn(pzb)2+/0 electrode reactions, which contrasts with the behavior of the comparable Fe(pzb)2+/0 and Co(pzb)2+/0 couples.     

Spin-crossover phenomena in tris(trifluoronicotinoylacetonato) iron (III)

Tris(trifluoronicotinoylacetonato) iron(III) has been shown to exhibit spin-crossover phenomenon between ⁶A_1g and ²T_2g terms which are about 322 cm^?1 apart.     

Importance of the C-H...N weak hydrogen bonding on the coordination structures of manganese(III) porphyrin complexes

The reactions between Mn(Por)Cl and Bu(4)N(+)CN(-) have been examined in various solvents by UV-vis and (1)H NMR spectroscopy, where Por's are dianions of meso-tetraisopropylporphyrin (T(i)PrP), meso-tetraphenylporphyrin (TPP), meso-tetrakis(p-(trifluoromethyl)phenyl)porphyrin (p-CF(3)-TPP), meso-tetramesitylporphyrin (TMP), and meso-tetrakis(2,6-dichlorophenyl)porphyrin (2,6-Cl(2)-TPP). Population ratios of the reaction products, Mn(Por)(CN) and [Mn(Por)(CN)(2)](-), have been sensitively affected by the solvents used. In the case of Mn(T(i)PrP)Cl, the following results are obtained: (i) The bis-adduct is preferentially formed in dipolar aprotic solvents such as DMSO, DMF, and acetonitrile. (ii) Both the mono- and bis-adduct are formed in the less polar solvents such as CH(2)Cl(2) and benzene though the complete conversion to the bis-adduct is achieved with much smaller amount of the ligand in benzene solution. (iii) Only the mono-adduct is formed in CHCl(3) solution even in the presence of a large excess of cyanide. (iv) Neither the mono- nor the bis-adduct is obtained in methanol solution. The results mentioned above have been explained in terms of the C-H.N and O-H.N hydrogen bonding in chloroform and methanol solutions, respectively, between the solvent molecules and cyanide ligand; hydrogen bonding weakens the coordination ability of cyanide and reduces the population of the bis-adduct. The importance of the C-H.N weak hydrogen bonding is most explicitly shown in the following fact: while the starting complex is completely converted to the bis-adduct in CH(2)Cl(2) solution, the conversion from the mono- to the bis-adduct is not observed even in the presence of 7000 equiv of Bu(4)N(+)CN(-) in CHCl(3) solution. The effective magnetic moments of the bis-adduct has been determined by the Evans method to be 3.2 micro(B) at 25 degrees C, suggesting that the complex adopts the usual (d(xy))(2)(d(xz), d(yz))(2) electron configuration despite the highly ruffled porphyrin core expected for [Mn(T(i)PrP)(CN)(2)](-). The spin densities of [Mn(T(i)PrP)(CN)(2)](-) centered on the pi MO have been determined on the basis of the (1)H and (13)C NMR chemical shifts. Estimated spin densities are as follows: meso-carbon, -0.0014; alpha-pyrrole carbon, -0.0011; beta-pyrrole carbon, +0.0066; pyrrole nitrogen, -0.022. The spin densities at the pyrrole carbon and meso nitrogen atoms are much smaller than those of the corresponding [Mn(TPP)(CN)(2)](-), which is ascribed to the nonplanar porphyrin ring of [Mn(T(i)PrP)(CN)(2)](-). This study has revealed that the C-H.N weak hydrogen bonding is playing an important role in determining the stability of the manganese(III) complexes.     

Gas chromatography of manganese(II) and manganese(III) trifluoroacetylacetonates by the ligand vapour technique

The thermal properties and gas Chromatographie behaviour of manganese(II) and manganese(III) trifluoroacetylacetonates (TFA) were investigated by using the ligand vapour technique. The two chelates, Mn(TFA); and Mn(TFA)₃, can be quantitatively eluted on a mixed-liquid phase (1.9% OV-17 ÷ 0.1% PEG-20M) at column temperatures above 210°C and 130–150°C, respectively; Mn(TFA)₃ is completely converted to Mn(TFA)₂ by thermal dissociation at column temperatures above 180°C and completely eluted as Mn(TFA)₂ above 210°C. The chelates can be determined separately within errors of about 1% after a preliminary extraction.     

Gadolinium and neodymium citrates: evidence for weak ferromagnetic exchange between gadolinium(III) cations

A new lanthanide citrate motif of general formula [Ln(Hcit)(H2O)2.H2O]n, where Ln = Gd (1) and Nd (2) and Hcit3- = C(OH)(COO-)(CH2COO-)2, has been synthesized hydrothermally from Ln2O3 and citric acid at 100 degrees C and characterized by elemental analysis, IR, TG-DTA, single-crystal X-ray diffraction, and magnetic measurements. The structures can be seen as "ladder chains" along the a axis, with dinuclear Ln2O2 units serving as "steps" and R-COO groups as "uprights", which are connected by H bonds. The magnetic susceptibility between 2 and 300 K and the magnetization at 2 K, as a function of magnetic field between 0 and 5 T, were measured for both compounds. By modeling the magnetic behavior of the Gd compound with a dinuclear Hamiltonian [symbol: see text](S) = gmu(B)(S(A) + S(B))B(o) - J(o)S(A)S(B) (S(A) = S(B) = 7/2), a ferromagnetic exchange interaction J(o) = 0.039 cm(-1) was evaluated between Gd ions situated at d(o) = 4.321 angstroms in dinuclear units bridged by two symmetry-related tridentate carboxylate oxygens. The EPR spectrum of the Gd compound is discussed. The temperature dependence of the susceptibility of the Nd compound is caused by the depopulation of the excited crystal-field levels when the temperature decreases. The magnetic-field dependence of the magnetization of 2 is attributed to the ground-state Kramers' doublet populated at 2 K. The g factor of this ground-state doublet is calculated from the data and compared with values for other compounds reported in the literature.     

Redox chemistry of mononuclear manganese(II), binuclear manganese(III) and binuclear mixed manganese(II)-manganese(III) complexes with 3-aminopyrazine-2-carboxylate in dimethylsulphoxide

Summary Mn^II forms a yellow mononuclear species with the title ligand having a 12 stoichiometry and whose conditional stability constant is 8.9 × 10¹⁰ m ^–2. The c.v. of this complex shows an oxidation at +0.78V versus s.c.e. Controlled-potential electrolysis at +0.80V versus s.c.e. yields a binuclear species of Mn^III with a 12 metal:ligand stoichiometry.The addition of Mn^III(urea)₆(ClO₄)₃ to a solution of the ligand produces a mononuclear complex of Mn^III if the concentration of the metal ion is less than 1 mM. At higher concentrations a binuclear species is obtained. The latter is reduced in two steps, at +0.24 and –0.58 V versus s.c.e. Controlled-potential electrolysis at 0.0 V produces a dark green complex after the transfer of 0.5 equivalents of charge per mole of Mn. This binuclear L₂Mn^II-Mn^IIIL₂ mixed-valence complex can be obtained only by electrolysis of the binuclear L₂Mn^IIIMn^IIIL₂ species. Attempts to prepare the complex chemically were unsuccessful - the binuclear Mn^III species was obtained in every case.Author to whom all correspondence should be directed.     

烃基膦酸单十六烷基酯的结构与其萃取镱(III)、镥(III)性能的 关系

探讨了一类具有高位阻特征的烃基膦酸单十六烷基酯萃取剂R^1(R^2O)P(O)OH从氯化物介质中萃取Yb(III)和Lu(III)的结构与性能关系。其中,R^1分别为CH~3,C~2H~5,i-C~3H~7,cyclo-C~6H~1~1和C~6H~5,R^2为C~4H~9CH(C~2H~5)C~2H~4CH(C~6H~1~3)或C~6H~1~3CH(CH~3)CH~2CH(C~6H~1~3)。结果表明,这类萃取剂对于Yb,Lu的萃取和分离能力随着其分子中取代基空间位阻的增大而降低。