Manganese (II) Coordination Complexes Involving Nitronyl Nitroxide Radicals (original) (raw)
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Inorganic Chemistry, 1997
The reaction of N-n-Bu 4 MnO 4 or NaMnO 4 with appropriate reagents in ethanol-pyridine leads to the high-yield formation of new mixed-valence trinuclear oxo-centered Mn III,III,II complexes of general formulation [Mn 3 O(Xbenzoato) 6 L 3 ] (1, X ) 2-fluoro, L ) pyridine; 2, X ) 2-chloro, L ) pyridine; 3, X ) 2-bromo, L ) pyridine; 4, X ) 3-fluoro, L ) 2 pyridine + 1 H 2 O; 5, X ) 3-chloro, L ) 2 pyridine + 1 H 2 O; 6, X ) 3-bromo, L ) 2 pyridine + 1 H 2 O). The crystal structures of 1, 5, and 6 were determined. Complex 1 crystallizes in the monoclinic system, space group C2/c with a ) 15.774(2) Å, b ) 17.269(2) Å, c ) 21.411(2) Å, ) 91.11(1)°, and Z ) 4. Complex 5 crystallizes in the monoclinic system, space group P2 1 /n with a ) 15.172(2) Å, b ) 17.603(2) Å, c ) 21.996(3) Å, ) 106.300(10), and Z ) 4. Complex 6 crystallizes in the monoclinic system, space group P2 1 /n with a ) 15.533(3) Å, b ) 17.884(2) Å, c ) 21.997(4) Å, ) 106.95(1)°, and Z ) 4. The three complexes are neutral and possess an oxo-centered Mn 3 O unit with peripheral ligands provided by bridging carboxylate and terminal pyridine or H 2 O groups. Each manganese ion is distorted octahedral, and consideration of overall charge necessitates a mixed-valence Mn II Mn III 2 description. In 1, the presence of a C 2 axis through the central O atom and one of the manganese atoms (Mn II ) and the absence of imposed symmetry elements in 5 and 6 (they have the two Mn III with a terminal pyridine group and the Mn II with a H 2 O terminal molecule) suggest a trapped-valence situation in all three cases. The Mn II is assigned on the basis of its longer metal-ligand distances. Variabletemperature magnetic susceptibility studies were performed on 1-6 in the temperature range 2-300 K. Satisfactory fits to the observed susceptibility data were obtained by assuming isotropic magnetic exchange interactions and using the appropriate spin Hamiltonian and susceptibility equation. The derived J and J* exchange parameters are all relatively small in magnitude, |J| < 10 cm -1 . J characterizes the Mn II ‚‚‚Mn III interactions and J* the Mn III ‚‚‚Mn III interaction. Magnetization measurements at 2 K up to 50 kG indicate the variability of the ground state: S ) 3 / 2 for 2 and 3; S ) 1 / 2 for 1, 4, and 5; and S ) 3 / 2 , 1 / 2 for 6. X-band EPR spectra measured from 4 K to room temperature on polycrystalline samples of 1-6 show highly significant differences when the ground state is 3 / 2 or 1 / 2 . For S ) 3 / 2 complexes (2 and 3), there is a transition centered at g ≈ 4, which decreases in intensity with increasing temperature. For S ) 1 / 2 complexes, this g ≈ 4 band does not appear but instead there are broad bands centered at g ≈ 2. These results are discussed in terms of spin frustration within the Mn 3 O core, which produces different spin ground states and susceptibility values. X
Polyhedron, 2005
Four complexes of M(NO 3) 2 (4NOPy-OMe) 2 , (4NOPy-OMe = 4-(N-tert-butyloxylamino)-2-(methoxymethylenyl)pyridine, and M = Mn II , 1; Co II , 2; Ni II , 3; Cu II , 4), were prepared and fully characterized. X-ray single crystal analysis reveals that four complexes are isostructural. The molecular structures are distorted octahedral in which the methoxy oxygen atoms coordinate to the metal ion by trans-configuration while the pyridyl nitrogen atoms and the nitrate oxygen atoms coordinate by cis-configuration. The magnetic properties of all complexes were investigated by SQUID magneto/susceptometry. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2-300 K indicated that the magnetic coupling between aminoxyl radicals and metal ion was antiferromagnetic in the complex 1 and were ferromagnetic in the complexes 2-4. The quantitative analysis based on the spin Hamiltonian, H = À2J(S 1 S M + S M S 2) yielded the best fit as J/k B = À13.4 ± 0.1 K, g = 1.94 ± 0.002, and h = À0.78 ± 0.02 K for the complex 1, J/k B = 48.7 ± 2.1 K, g = 2.07 ± 0.02, and h = À2.83 ± 0.41 K for the complex 3 (the data in the temperature range 300-50 K were used), and J/k B = 57.0 ± 1.2 K, g = 2.002 ± 0.004, and h = À9.8 ± 0.1 K for the complex 4.
CrystEngComm, 2014
The reaction of M(ox)‚2H 2 O (M ) Co(II), Ni(II)) or K 2 (Cu(ox) 2 )‚2H 2 O (ox ) oxalate dianion) with n-ampy (n ) 2, 3, 4; n-ampy ) n-aminopyridine) and potassium oxalate monohydrate yields one-dimensional oxalatobridged metal(II) complexes which have been characterized by FT-IR spectroscopy, variable-temperature magnetic measurements, and X-ray diffraction methods. The complexes M(µ-ox)(2-ampy) 2 (M ) Co (1), Ni (2), Cu ) are isomorphous and crystallize in the monoclinic space group C2/c (No. 15), Z ) 4, with unit cell parameters for 1 of a ) 13.885(2) Å, b ) 11.010(2) Å, c ) 8.755(1) Å, and ) 94.21 , Ni (5), Cu ) are also isomorphous and crystallize in the orthorhombic space group Pcnn (No. 52), Z ) 8, with unit cell parameters for 6 of a ) 12.387 , b ) 12.935(3), and c ) 18.632(2) Å. Compound Co(µ-ox)(4-ampy) 2 (7) crystallizes in the space group C2/c (No. 15), Z ) 4, with unit cell parameters of a ) 16.478(3) Å, b ) 5.484(1) Å, c ) 16.592(2) Å, and ) 117.76(1)°. Complexes M(µ-ox)(4-ampy) 2 (M ) Ni (8), Cu (9)) crystallize in the orthorhombic space group Fddd (No. 70), Z ) 8, with unit cell parameters for 8 of a ) 5.342(1), b ) 17.078 , and c ) 29.469(4) Å. All compounds are comprised of one-dimensional chains in which M(n-ampy) 2 2+ units are sequentially bridged by bis-bidentate oxalato ligands with M‚‚‚M intrachain distances in the range of 5.34-5.66 Å. In all cases, the metal atoms are six-coordinated to four oxygen atoms, belonging to two bridging oxalato ligands, and the endo-cyclic nitrogen atoms, from two n-ampy ligands, building distorted octahedral surroundings. The aromatic bases are bound to the metal atom in cis (1-6) or trans (7-9) positions. Magnetic susceptibility measurements in the temperature range of 2-300 K show the occurrence of antiferromagnetic intrachain interactions except for the compound 3 in which a weak ferromagnetic coupling is observed. Compound 7 shows spontaneous magnetization below 8 K, which corresponds to the presence of spin canted antiferromagnetism.
Antiferromagnetic coupling in [Mn12O12(O2CMe)6(p-CO2-phenyl nitronyl
Transition Metal Chemistry, 2004
The synthesis of [Mn 12 O 12 (O 2 CMe) 6 (p-CO 2-phenyl nitronyl nitroxide) 10 (H 2 O) 4 ] AE 4H 2 O, (1), by direct replacement of some of the acetate groups in [Mn 12 O 12 (O 2 CMe) 16 (H 2 O) 4 ] AE 4H 2 O AE 2MeCO 2 H, (2), with the organic radical p-HO 2 Cphenyl nitronyl nitroxide, (3), is reported. E.p.r. spectra show exchange narrowing in (1) due to coupling between the manganese ions and radicals. The isotropic hyperfine splitting constant from the manganese ions is a ¼ 96 Oe at 5.5 K. The magnetic susceptibility indicates antiferromagnetic exchange interactions between the manganese ions and the radicals with the Weiss constant h ¼)25 K. The spin was determined to be S ¼ 6 from magnetization data in the 2-30 K temperature range at 50 kOe, suggesting a mixture of ground state with excited states.
Inorganic Chemistry, 1998
Aerial oxidation of Mn II /ptt 3-(ptt 3-) propane-1,2,3-trithiolate) mixtures gives [Mn 2 (pttd) 2 ] 2-, where pttd 4is the mono(disulfide) of ptt 3-. (NEt 3 Bz) 2 [Mn 2 (pttd) 2 ] (2) crystallizes in space group P2 1 /c with (at -158°C) a ) 11.540(2) Å, b ) 12.115 Å, c ) 17.478(4) Å, ) 101.78(1)°, and Z ) 2. The anion contains a doublybridged [Mn 2 S 8 ] core (Mn‚‚‚Mn ) 3.598(2) Å) with five-coordinate Mn III ions, very similar to previously reported [Mn 2 (edt) 4 ] 2-(anion of 1; edt 2-) ethane-1,2-dithiolate). Aerial oxidation of Mn II /pdt 2-(pdt 2-) propane-1,3dithiolate) mixtures gives [Mn 3 (pdt) 5 ] 2-, which is mixed valent (Mn II , 2Mn III ). (PPh 4 ) 2 [Mn 3 (pdt) 5 ] (3) crystallizes in space group P1 h with (at -161°C) a ) 14.385(6) Å, b ) 23.734(11) Å, and Z ) 2. The anion contains a near-linear Mn III Mn II Mn III unit with five-coordinate Mn III , six-coordinate Mn II , and three thiolate bridges between each Mn 2 pair; Mn‚‚‚Mn separations are 3.123(3) and 3.101(3) Å. Aerial oxidation of Mn II /edt 2-/ImH (ImH ) imidazole) mixtures gives [Mn(edt) 2 (ImH)] -. (NEt 4 )[Mn(edt) 2 (ImH)] (4) crystallizes in space group P2 1 /n with (at -72°C) a ) 13.974(5) Å, b ) 14.317(5) Å, c ) 10.564(3) Å, ) 90.13(2)°, and Z ) 4. The anion is five-coordinate and square-pyramidal. Aerial oxidation of Mn II /edt 2-/Immixtures gave [Mn 2 (Im)(edt) 4 ] 3-, which contains two Mn III ions. (NMe 4 ) 3 [Mn 2 (Im)(edt) 4 ] (5) crystallizes in space group Pna2 1 with (at -160°C) a ) 17.965(5) Å, b ) 16.094(4) Å, c ) 14.789(3) Å, and Z ) 4. The five-coordinate Mn III ions are bridged by the Imgroup across a Mn‚‚‚Mn separation of 6.487(2) Å. The anion of 4 contains high-spin Mn III (S ) 2) and exhibits inter-anion antiferromagnetic exchange interactions (J ) -0.15 cm -1 , g ) 1.91) propagated by interanion NH‚‚‚S hydrogen bonds. Complexes 1-3 and 5 all possess intraanion antiferromagnetic exchange interactions; the fitting parameters are as follows: 1, J ) -19.0 cm -1 , g ) 1.96, D ) -0.22 cm -1 ; 2, J ) -16.4 cm -1 , g ) 1.96, D ) -0.22 cm -1 ; 3, J ) -18.8 cm -1 , g ) 2.00; 5, J ) -1.75 cm -1 , g ) 1.84, D ) -0.028 cm -1 (Ĥ ) -2JS i S j convention). Complexes 1, 2, and 5 have S ) 0 ground states, while that of 3 is S ) 3 / 2 . S0020-1669(97)Supporting Information Available: Textual and tabular summaries of the structure determinations, tables of atomic coordinates, thermal parameters, and bond distances and angles, fully labeled figures for complexes 2-5 and the m Vs T equation for 3 (68 pages). Ordering information is given on any current masthead page. IC970587R Manganese(II) Dithiolate Complexes
Inorganic Chemistry, 1999
Complexes of manganese(II)-containing aminoxyl radical substituted phosphine oxide ligands are reported. The compounds [(o-nitronyl nitroxide-phenyl)diphenylphosphine oxide]bis(hexafluoroacetylacetonato)manganese(II), 3, and bis{[(p-nitronyl nitroxide-phenyl) diphenylphosphine oxide]bis(hexafluoroacetylacetonato)manganese(II)}, 4, prepared by addition of the free radical phosphine oxides to Mn(hfac) 2 , were structurally characterized. Complex 3 is mononuclear, containing an O,O-chelating ortho-substituted radical phosphine oxide ligand, while in 4 the para-substituted ligands bridge two Mn(hfac) 2 units to yield a binuclear molecular rectangle. The magnetic behavior of both systems is dominated by a strong antiferromagnetic Mn(II)-aminoxyl interaction (J ) -213 , -218 (4) cm -1 with H ) -JS Mn ‚S rad ) to give effective S ) 2 ground state units. The S ) 3 excited state is populated at high temperatures. At low temperatures a decrease in M T in both complexes is attributable primarily to interor intramolecular antiferromagnetic interactions rather than zero-field splitting (ZFS) of the S ) 2 ground state. For the bimetallic compound, the magnetic data indicate that ligand-mediated interactions between the Mn(II) spin carriers are weak. The powder EPR spectra of both systems have been recorded and successfully simulated, giving a ZFS parameter D ) 0.112 cm -1 . Crystals of 3 are triclinic, space group P1 h with a ) 10.6672 Å, b ) 13.270(6) Å, c ) 15.363(3) Å, R ) 93.84(2)°, ) 108.054(16)°, γ ) 105.69(3)°, and Z ) 2. Crystals of 4 are monoclinic, space group P2 1 /a with a ) 12.463(6) Å, b ) 19.315(3) Å, c ) 17.084(9) Å, R ) 90°, ) 98.49(2)°, γ ) 90°, and Z ) 2.
Inorganic Chemistry, 2002
Four new mononuclear complexes of formula Cd(PN) 4 (NCS) 2 (A), Cd(PNN) 4 (N 3 ) 2 (B), Zn(PNN) 4 (N 3 ) 2 (C), and Zn(PNN) 2 (NCS) 2 (D), where PNN stands for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and PN for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl, were synthesized and structurally and magnetically characterized. The X-ray structures of compounds B and C were also determined at 90 K. Compounds A−C crystallize in the triclinic space group P1 h (No. 2), and D crystallizes in the monoclinic space group P2 1 /m (No. 11). A−C adopt a centrosymmetric distorted octahedral geometry in which the metal ions are bonded to four radical ligands through the nitrogen atom of the pyridyl rings and the azido or thiocyanato ligands occupy the apical positions. Compound D adopts a distorted tetrahedral geometry in which the zinc ion is bonded to two radicals and two thiocyanato ligands. As suggested by their magnetic behavior, the low-temperature X-ray structures of B and C show that these compounds undergo a clear structural change with respect to the room-temperature structures. The experimental magnetic behaviors were perfectly reproduced by a dimer model for A−C and an alternating chain model for D while the sudden breaks observed in the M T versus T curves for B and C were well accounted for by the highand low-temperature X-ray structures. For all these complexes the crystal structures favor significant overlap between molecular magnetic orbitals leading to rather strong intermolecular antiferromagnetic interactions. A criticism of the McConnell theory can be found in the following: Deumal, M.; Novoa, J. J.; Bearpark, M. J.; Celani, P.; Olivucci, M.; Robb, M. A.
New complexes of manganese(II) hexafluoroacetylacetonate [Mn(hfac)2] with 2-(1-R-3-pyrazol-4-yl)-4,4,5,5-tetramethyl-2-imidazoline-3-oxide-1-oxyl (R = CHF2, CH2CH2F, CH2CHF2 or CH2CF3) were synthesised and characterised structurally and magnetically. All complexes were prepared under similar conditions. Nonetheless, their crystal structures were considerably different. Depending on the structure of fluorinated alkyl substituent R, the complexation reaction led to complexes of three types: chain-polymeric complexes with the head-to-head or head-to-tail motif and complexes of molecular structure. All complexes show strong antiferromagnetic behaviour in a high-temperature region (150−300 K) and weak ferro- or antiferromagnetic exchange interactions at low temperatures. The stronger antiferromagnetic exchange, –101.7 ± 1.5 or –136 ± 10 cm–1, –82.3 ± 1.3 cm–1 and –87.4 ± 1.3 cm–1, was attributed to the magnetic interaction in three- or two-spin clusters: {>N∸O–Mn2+–O∸N<} or {>N∸...
Dalton Transactions, 2009
The reaction of H 2 phpzR (R = Me, Ph; H 2 phpzMe = 3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole and H 2 phpzPh = 3(5)-(2-hydroxyphenyl)-5(3)-phenylpyrazole) with Mn(O 2 CR¢)·nH 2 O (R¢ = Me and Ph) and ( n Bu 4 N)MnO 4 in ethanol (EtOH) affords three new manganese(III) compounds, [Mn 3 (m 3 -O)-(phpzMe) 3 (O 2 CMe)(EtOH)]·EtOH (1), ( n Bu 4 N)[Mn 3 (m 3 -O)(phpzMe) 3 (O 2 CPh) 2 ] (2) and ( n Bu 4 N)[Mn 3 (m 3 -O)(phpzPh) 3 (O 2 CPh) 2 ] (3). Their synthesis, crystal structure and magnetic properties are reported. Compounds 1-3 are m 3 -oxido-centered trinuclear manganese(III) compounds whose edges are bridged by phpzR 2with average intracluster separations of 3.25 Å . The three Mn-O-Mn angles are distorted from the equilateral triangle with values in the range of 113 • to 124 • ; 117 • to 125 • ; and 117 • to 126 • for complexes 1-3, respectively. Hydrogen bonding interactions between the trinuclear units of 1 result in a one-dimensional chain structure. Compounds 2 and 3 have isolated trinuclear units, perhaps as a result of the presence of the bulky n Bu 4 N + cation. Temperature-dependent magnetic susceptibility studies indicate the presence of both antiferromagnetic and ferromagnetic interactions in compound 1 (J 1 = -10.3 cm -1 , J 2 = +10.9 cm -1 ), while only antiferromagnetic interactions are present in compounds 2 and 3 (J 1 = -4.2 cm -1 , J 2 = -10.3 cm -1 for 2; and J 1 = -4.8 cm -1 , J 2 = -10.2 cm -1 for 3), with J 1 representing the similar Mn-O-Mn angles and J 2 representing the unique Mn-O-Mn angle (Mn(1)-O(1)-Mn(2)). of the [Mn 3 (m 3 -O)] 7+ core, where the Mn-O-Mn angle is smaller than 120 • (the value for an equilateral triangle); 15,16,19 a switch from antiferromagnetic to ferromagnetic exchange is observed at angles below approximately 120 • . 20 Recently, it has been shown that the ligand distortion, i.e. the Mn-N-O-Mn torsion angle in oximate ligands, plays an important role as well; a larger torsion angle gives rise to a stronger ferromagnetic coupling. 9,10,16,19
Journal of Coordination Chemistry
Two mononuclear complexes [(Et 3 NH)[M(hfac) 2 L] (M = Ni, 1 Zn, 2) have been synthesized using a nitronyl-nitroxide radical substituted nitrophenol, i.e., 2-(2-Hydroxy-3-methoxy-5nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl, HL, as a proligand. The crystal structures of the two compounds have been solved and indicate an octahedral coordination geometry of the metal ions. The magnetic behavior for compound 1 is characterized by a strong antiferromagnetic metal-radical interaction (J =-351 ± 1 cm-1 ; H =-JS Ni S Rad). This exchange interaction was rationalized by DFT calculations. The EPR spectra recorded both in solution and solid state at 120 K confirm the S = ½ ground state for compound 1.