Ramon Vicente

Polynuclear NiII and MnII azido bridging complexes. Structural trends and magnetic behavior

Abstract The azide anion is a good bridging ligand for divalent metal ions, mainly Cu II , Ni II and Mn II . It may give end-to-end (1,3) or end-on (1,1) coordination modes. As a general trend, the 1,1 mode exhibits ferromagnetic coupling while the 1,3 mode creates antiferromagnetic coupling. This review focuses on polynuclear Ni II and Mn II azido bridging complexes. Polynuclear structures known to have these two cations are: discrete (normally dinuclear), one-, two- and three-dimensional nets. The main characteristics of these structures are reported together with their magnetic behavior. From a large number of known structures, magneto-structural correlations are made. Taking into account that M–N 3 distances are always similar, the angles within the M–(N 3 ) n –M unit are the main determinant of the type and magnitude of the exchange coupling. Moreover, some one-, two- and three-dimensional complexes exhibit cooperative effects (long-range magnetic order), behaving as molecular magnets. This behavior is also analyzed.

Unique Single-Atom Binding of Pseudohalogeno Ligands to Four Metal Ions Induced by Their Trapping into High-Nuclearity Cages

μ4 end-on coordination (through the N atom) of the pseudohalogeno ligands X- =N3- and NCO- has been observed in the isostructural nonanuclear CoII cages with the general formula [Co9 {(2-C5 H4 N)2 CO2 }4 (O2 CMe)8 X2 ]; this mode is imposed by the trapping of anions X- into cavities formed inside the cage. The change of X- modulates the magnetic behavior of the cage from antiferromagnetic coupling to a ferrimagnetic high-spin ground state.

Synthesis, Structural Characterisation, and Monte Carlo Simulation of the Magnetic Properties of the 3D-Stacked Honeycomb Csn[{Mn(N3)3}n] and the Irregular Double Chain [{N(C2H5)4}n][{Mn2(N3)5(H2O)}n]

Two new polymeric manganese-azido systems with formula Cs(n)-[[Mn(N3)3]n] (1) and [[N(C2H5)4]n][[Mn2-(N3)5(H2O)]n] (2) were synthesised and structurally characterised. Compound 1 crystallises in the P2(1)/n group and consists of a three-dimensional system with end-to-end and end-on azido bridges with the caesium atoms in the holes of the net. Magnetically, compound 1 is a rare case of a three-dimensional network with alternate ferro-antiferromagnetic interactions. Compound 2 crystallises in the P1 group and consists of double chains of manganese atoms bridged by end-on and, the exceptional, (mu-1,1,1)-azido bridges. Magnetically, compound 2 shows net ferromagnetic behaviour. Exact fit of the magnetic data was performed for the two compounds by means of Monte Carlo simulations based on the Metropolis algorithm on sets of 10 x 10 x 10 (1) and 1 x 1 x 320 (2) S = 5/2 classical spin centres.

Three new dinuclear copper(II) complexes with [Cu(μ1,3-N3)2Cu]2+ and [Cu(μ1,1-N3)2Cu]2+ asymmetrical cores: syntheses, structures and magnetic behaviour

Three new dinuclear copper(II) complexes, derived from end-to-end and end-on azido bridging ligands and triamine derivatives, have been synthesized and their crystal structures have been determined by X-ray diffraction methods. These are the dinuclear end-to-end compounds, [Cu2(μ1,3-N3)2(Et3dien)2](ClO4)2 (1) and [Cu2(μ1,3-N3)2(Medpt)2](ClO4)2 (2), and the dinuclear end-on compound [Cu2(μ1,1-N3)2(Medien)2](ClO4)2 (3) (Et3dien is triethyldiethylenetriamine, Medpt is methyldipropylenetriamine and Medien is methyldiethylenetriamine). The [Cu(μ-N3)2Cu]2+ cores are asymmetrical in all 3 compounds. Variable temperature magnetic susceptibility data were collected and fitted to the appropriate equation derived from the Hamiltonian H = −JS1S2. 1 shows unusual ferromagnetic interactions with J = 9 cm−1 through the end-to-end azido bridges while 2 shows an antiferromagnetic interaction through the end-to-end azido bridges with the highest reported absolute magnitude of J = −105 cm−1. The magnetic data of 1 and 2 have been correlated with the Addison parameter, τ, and mainly with the Cu–N3–Cu torsion angle, Δ. 3 shows an unusual antiferromagnetic interaction with J = −16.8 cm−1 through the end-on azido bridges.

Two new nickel(II) cubane compounds derived from pyridine-2-methoxide (Pym): {Ni4(Pym)4Cl4(CH3OH)4} and {Ni4(Pym)4(N3)4(CH3OH)4}. Crystal structures and magnetic properties

Abstract The pyridine-2-methoxide anion (Pym) allows the two new nickel(II) cubane compounds: {Ni 4 (Pym) 4 Cl 4 (CH 3 OH) 4 } ( 1 ) and {Ni 4 (Pym) 4 (N 3 ) 4 (CH 3 OH) 4 } ( 2 ), to be easily synthesized. 1 and 2 are structurally characterised. Complexes 1 and 2 crystallise in the tetragonal system. 1 and 2 have similar structures that consist of tetrameric cubane complexes with the alkoxide oxygen atoms of the pyridine-2-methoxide ligand and octahedrally co-ordinated nickel(II) atoms placed alternately at the corners of the cube. Magnetic susceptibility data, measured from 2 to 260 K show ferromagnetic behaviour for 1 and 2 . These data were fitted by using the equation derived from the Hamiltonian H =−2 J 1 ( S 1 S 2 + S 3 S 4 )−2 J 2 ( S 1 S 3 + S 1 S 4 + S 2 S 3 + S 2 S 4 ) including the Zero Field Splitting for the ground state S =4, giving the parameters J 1 =0.43, J 2 =5.28, D =−0.47 cm −1 , g =2.11 for 1 and J 1 =9.78, J 2 =2.42, D =−0.10 cm −1 , g =2.21 for 2 .

Significant antiferromagnetic exchange in copper(II) and nickel(II) dinuclear complexes of the substituted pyrazine ligand 2,3,5,6-tetra(2-pyridyl)pyrazine (TPPZ): magnetic properties, synthesis and crystal structure

Abstract The dinuclear compounds [Cu 2 (TPPZ)Cl 4 ]∗d5H 2 O ( 1 ), [Ni 2 (TPPZ)(H 2 O) 6 ](NO 3 ) 4 ∗d2.5H 2 O ( 3 ) and [Ni 2 (TPPZ)(H 2 O) 6 [-(squarate) 2 ∗d5H 2 O ( 4 ), where TPPZ is the ligand 2,3,5,6-tetra(2-pyridyl)pyrazine, have been synthesised and characterised crystallographically. [Cu 2 (TPPZ)Cl 4 ]∗d5H 2 O ( 1 ) crystallises in the monoclinic system, space group P2 1 /c, a = 15.030(3), b = 13.224(2), c = 15.320(2) A , β = 105.40(1)°, V = 2935.62(8) A 3 , Z = 4, R1 = 0.035 (observed data). [Ni 2 (TPPZ)(H 2 O) 6 ](NO 3 ) 4 ∗d2.5H 2 O ( 3 ) crystallises in the monoclinic system, space group I2/a, a = 20.660(2), b = 13.724(1), c = 25.436(3) A , β = 91.89(1)°, V = 7208.1(12) a 3 , Z = 8, R1 = 0.070 (observed data). [Ni 2 (TPPZ)(H 2 O) 6 ] (squarate) 2 ∗d5H 2 O ( 4 ) crystallises in the monoclinic system, space group A2/n, a = 19.014(2), b = 10.518(1), c = 19.131(2) A , β = 94.22(1)°, V = 3815.6(7) A 3 , Z = 4, R1 = 0.035 (observed data). Magnetic measurements show significant antiferromagnetic coupling for pyrazine bridged compounds: 2 J = −34.1 cm −1 , g = 2.05 for 1 ; 2 J = −7.6 cm −1 , D = −13.3 cm −1 , g = 2.16 for 3 ; 2 J = −7.5 cm −1 , D = −10.4 cm −1 , g = 2.17 for 4 . The magnetic behaviour of the related published compound [Cu 2 (TPPZ)(H 2 O) 4 ](ClO 4 ) 4 ∗d2H 2 O ( 2 ) has also been measured: 2 J = −61.6 cm −1 , g = 2.13. The possibility of a σ superexchange mechanism in these compounds is discussed.

Benzoate as terminal ligand in the defective double-cubane, tetranuclear cobalt(II) complex [Co4(N3)2(O2CPh)2{(py)2C(OH)O}4].2DMF with simultaneous μ1,1-azido and μ-o bridges [(py)2C(OH)O = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone]

The reaction of Co(O2CPh)2 with di-2-pyridyl ketone, (py)2CO, and NaN3 in DMF allows isolation of the tetranuclear compound [Co4(N3)2(O2CPh)2{(py)2C(OH)O}4]/2DMF (2) instead of the expected nonanuclear cage [Co9(N3)2(O2CPh)8{(py)2CO2}4]. The Xray diffraction analysis reveals a defective double-cubane, tetrameric entity in which the Co II atoms are linked by h 1 ,m2-N3 azide ligand and two kinds of O-bridges. The molar magnetic susceptibility measurements of 2 in the 2 � /300 K range indicate bulk ferromagnetic coupling. Some synthetic aspects of the Co II /(py)2CO/N3 � reaction system are also discussed. # 2002 Elsevier

Di-2-pyridyl ketone oxime [(py)2CNOH] in manganese carboxylate chemistry: mononuclear, dinuclear and tetranuclear complexes, and partial transformation of (py)2CNOH to the gem-diolate(2-) derivative of di-2-pyridyl ketone leading to the formation of NO3-

The use of di-2-pyridyl ketone oxime, (py)2CNOH, in manganese carboxylate chemistry has been investigated. Using a variety of synthetic routes complexes [Mn(O2CPh)2{(py)2CNOH}2].0.25H2O (1.0.25H2O), Mn4(O2CPh)2{(py)2CO2}2{(py)2CNO}2Br2].MeCN (2.MeCN), [Mn4(O2CPh)2{(py)2CO2}2{(py)2CNO}2Cl(2)].2MeCN (3.2MeCN), [Mn4(O2CMe)2{(py)2CO2}2{(py)2CNO}2Br2].2MeCN (4.2MeCN), [Mn4(O2CMe)2{(py)2CO2}2{(py)2CNO}2(NO3)2].MeCN.H2O (5.MeCN.H2O) and [Mn2(O2CCF3)2(hfac)2{(py)2CNOH}2] (6) have been isolated in good yields. Remarkable features of the reactions are the in situ transformation of an amount of (py)2CNOH to yield the coordination dianion, (py)2CO2(2-), of the gem-diol derivative of di-2-pyridyl ketone in 2-5, the coordination of nitrate ligands in 5 although the starting materials are nitrate-free and the incorporation of CF3CO2- ligands 6 in which was prepared from Mn(hfac)(2).3H2O (hfac(-)= hexafluoroacetylacetonate). Complexes 2-4 have completely analogous molecular structures. The centrosymmetric tetranuclear molecule contains two MnII and two MnIII six-coordinate ions held together by four mu-oxygen atoms from the two 3.2211 (py)2CO2(2-) ligands to give the unprecedented [MnII(mu-OR)MnIII(mu-OR)2MnIII(mu-OR)MnII]6+ core consisting of a planar zig-zag array of the four metal ions. Peripheral ligation is provided by two 2.111 (py)2CNO-, two 2.11 PhCO2- and two terminal Br- ligands. The overall molecular structure 5 of is very similar to that of 2-4 except for the X- being chelating NO3-. A tentative reaction scheme was proposed that explains the observed oxime transformation and nitrate generation. The CF3CO2- ligand is one of the decomposition products of the hfac- ligand. The two Mn(II) ions are bridged by two neutral (py)2CNOH ligands which adopt the 2.0111 coordination mode. A chelating hfac- ligand and a terminal CF3CO2- ion complete a distorted octahedral geometry at each metal ion. The CV of complex reveals irreversible reduction and oxidation processes. Variable-temperature magnetic susceptibility studies in the 2-300 K range for the representative tetranuclear clusters 2 and 4 reveal weak antiferromagnetic exchange interactions, leading to non-magnetic ST = 0 ground states. Best-fit parameters obtained by means of the program CLUMAG and applying the appropriate Hamiltonian are J(Mn(II)Mn((III))=-1.7 (2), -1.5 (4) cm(-1) and J(Mn(III)Mn(III))=-3.0 (2, 4) cm(-1).

Synthesis, characterization and properties of highly conducting organometallic polymers derived from the ethylene tetrathiolate anion

Abstract The preparation and electrical conductivity studies of a series of organometallic polymers, (MC2S4x−)n (M = Ni, Pd, Pt, Au), derived from the ethylene tetrathiolate anion are described. The synthesis of the precursor molecules or molecular complexes (PhCH2)4(C2S4), (AsPh4)2[M(C3OS4)2], (C3)OS4Pd(dppe) and (AsPh4)2[(C3OS4)Cu(C2S4)Cu(C3OS4)] is also described. From these results the different possible formation mechanisms of the polymers are discussed. The polymers show high compaction powder conductivity at room temperature (from 10−5 to 5Ω−1 cm−1). [Na0.31(NiC2S4)]ν, one of the most conductive polymers, exhibits a metal-like temperature dependence of conductivity, as evidenced by voltage shorted compaction (VSC) experiments. These conductivity properties are to be related with the degree of partial oxidation (DPO) observed in the polymers studied.

Structure and magnetic behaviour of the first singly bridged nickel cyanate chain and a new dinuclear complex: an approximation to the superexchange mechanism for the nickel pseudohalide system

Two new nickel(II) bridging-cyanate complexes of formula [{Ni(323-tet)(µ-OCN)}n][ClO4]n1[323-tet =N,N′-bis(3-aminopropyl)ethane-1,2-diamine] and [{Ni(Me6[14]aneN4)}2(µ-OCN)2][ClO4]22(Me6[14]aneN4=DL-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) have been synthesized and characterized. The crystal structures of 1 and 2 have been solved and in both compounds the cyanate ligand acts as an end-to-end bridge with the nickel atoms in a NiN5O octahedral environment. Compounds 1 is a chain in which the Ni(323-tet)fragments are linked by single cyanate bridges in a trans position, whereas compound 2 consists of dinuclear units with two cyanate bridges in a cis arrangement. Magnetic measurements in the 2–300 K range indicate weak ferromagnetism for 1 and antiferromagnetic behaviour for 2. Magneto-structural correlations have been obtained by Extended-Huckel calculations and a generic superexchange model for the nickel(II) pseudohalogen system is proposed.