Juan Cano

[Cr(phen)(ox)2]−: a versatile bis-oxalato building block for the design of heteropolymetallic systems. Crystal structures and magnetic properties of AsPh4[Cr(phen)(ox)2]·H2O, [NaCr(phen)(ox)2(H2O)]·2H2O and {[Cr(phen)(ox)2]2[Mn2(bpy)2(H2O)2(ox)]}·6H2O

The new complexes of formula AsPh4[Cr(phen)(ox)2]·H2O (1), [NaCr(phen)(ox)2(H2O)]·2H2O (2) and {[Cr(phen)(ox)2]2[Mn2(bpy)2(H2O)2(ox)]}·6H2O (3) (AsPh4=tetraphenylarsonium cation; phen=1,10-phenanthroline; ox=oxalate dianion; bpy=2,2′-bipyridine) have been prepared and characterized by single-crystal X-ray diffraction. The structure of 1 consists of discrete [Cr(phen)(ox)2]− anions, tetraphenylarsonium cations and uncoordinated water molecules. The chromium environment in 1 is distorted octahedral with Cr–O bond distances between 1.959(3) and 1.947(3) A and Cr–N bonds of 2.083(4) and 2.072(4) A. The angles subtended at the chromium atom by the two oxalates are 83.6(2) and 83.3(1)° whereas the N–Cr–N angle is 79.9(2)°. The [Cr(phen)(ox)2]− unit of 1 is also present in 2 and 3 but it accomplishes different coordination functions, acting as a bridging (2) or terminal (3) ligand. 2 has a layered structure made up of oxalato-bridged bimetallic CrIII–NaI helical chains that are interconnected through centrosymmetric Na2O2 units. The two oxalates of [Cr(phen)(ox)2]− in 2 are bis-chelating within the bimetallic chain but one of them is in addition monodentate towards a sodium atom of a neighbouring chain, yielding a sheetlike structure. The sodium atom in 2 has a distorted octahedral geometry with five Na–O(ox) bonds ranging from 2.453(5) to 2.319(4) A and the sixth position being occupied by an aqua ligand with Na–O(w)=2.384(6) A. The intralayer chromium–sodium and sodium–sodium separations through bridging oxalate in 2 are 5.560(4) and 3.643(8) A, respectively. The structure of 3 consists of neutral tetranuclear Cr2IIIMn2II units in which two terminal [Cr(phen)(ox)2]− entities act as monodentate ligands towards a central oxalato-bridged manganese(II) dimer. Each manganese atom is six-coordinated as MnN2O4: two nitrogen atoms of a chelating bpy, one aqua ligand and three oxalate oxygens build a distorted octahedron around the manganese atom. The Mn–O(ox) and Mn–N(bpy) bond lengths vary in the ranges 2.219(12)–2.160(13) and 2.33(2)–2.14(2) A, respectively. The intramolecular chromium–manganese separation [5.507(5) and 5.502(5) A for Cr(2)···Mn(2) and Cr(1)···Mn(1)] is somewhat shorter that the manganese–manganese one [5.703(2) A]. The magnetic properties of 1–3 have been investigated in the temperature range 1.9–300 K. Very weak antiferromagnetic interactions between the chromium centers are observed in 1 and 2 in agreement with their crystal structures. In the case of 3, significant intramolecular antiferromagnetic interactions between the adjacent chromium(III) and manganese(II) ions ( j=−1.1 cm−1, through the chelating/monodentate oxalato) and between the two manganese(II) ions (J=−2.2 cm−1, through the bis-chelating oxalato) occur, the Hamiltonian being defined as Ĥ=−JŜMn1· ŜMn2−j[ŜCr1·ŜMn1+ŜCr2·ŜMn2].

Significant antiferromagnetic coupling in a terephthalate (ta)-bridged manganese(II) compound: preparation, crystal structure and magnetic properties of the chain [Mn2(bipy)4(ta)][ClO4]2(bipy = 2,2′-bipyridine)

A new manganese(II) compound [Mn2(bipy)4(ta)][ClO4]21(bipy = 2,2′-bipyridme, ta = terephthalate dianion) has been synthesised and its crystal structure determined by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group P, with a= 9.516(2), b= 11.613(3), c= 11.615(3)A, α= 70.92(2), β= 80.16(2), γ= 76.64(2)° and Z= 1. The structure consists of canonic terephthalate-bridged [Mn2(bipy)4(ta)]2+ chains and non-co-ordinated perchlorate anions. Each terephthalate is bound to four manganese atoms through carboxylate oxygens with the sym-sym bridging mode, affording manganese(II) pairs which are linked by the terephthalate group to yield a one-dimensional chain running along the a axis. The intrachain Mn ⋯ Mn separations through the double carboxylate and terephthalate bridges are 4.643(1) and 9.637(2)A, respectively The manganese(II) ion displays a severely distorted octahedral co-ordination being linked to four nitrogen atoms of two bipy ligands and to two oxygen atoms of two carboxylate groups from two terephthalate ligands. The magnetic susceptibility of 1 as a function of temperature (4.2–290 K) exhibits a sharp maximum at 6.0 K which is consistent with a significant antiferromagnetic coupling between the metal centres. This magnetic behaviour has been interpreted in terms of a dimer with a molecular field approximation, the values obtained for J, g and zJ′ being –1.35 cm–1,1.97 and –0.04cm–1, respectively. In the light of the structural data, it can be concluded that the double-carboxylate bridge between the manganese(II) pairs provides a more efficient exchange pathway than that of terephthalate and most likely is responsible for the observed J value.

Ability of terephthalate (ta) to mediate exchange coupling in ta-bridged copper( II ), nickel( II ), cobalt( II ) and manganese( II ) dinuclear complexes

The exchange coupling between the unpaired electrons of divalent first-row transition-metal ions M II (M = Cu, Ni, Co or Mn) bridged by the terephthalate (ta) ligand (intramolecular metal–metal separation ca. 10 A) has been systematically studied. The following complexes have been synthesized: [Cu 2 (bipy) 4 (ta)][ClO 4 ] 2 1, [Cu 2 (terpy) 2 (H 2 O) 2 (ta)] [ClO 4 ] 2 2, [Ni 2 (bipy) 4 (ta)][ClO 4 ] 2 3, [Co 2 (bipy) 4 (ta)][ClO 4 ] 2 4, [Mn 2 (phen) 4 (H 2 O) 2 (ta)][ClO 4 ] 2 5 and [Mn 2 (phen) 4 (ta)][ClO 4 ] 2 6 (bipy = 2,2′-bipyridine, terpy = 2,2′:6′,2″- terpyridine, phen = 1,10-phenanthroline). Complexes 1, 2, 4 and 5 have been characterized by single-crystal X-ray analysis. Complex 6 was obtained by thermal dehydration of 5 at 60 °C or under vacuum at room temperature. The structures have in common the presence of cationic terephthalate-bridged [M 2 (ta)] 2+ dinuclear units with bidentate (1, 3–6) and terdentate (2) blocking ligands and unco-ordinated perchlorate counter ions. A co-ordinated water molecule per metal ion is present in complexes 2 and 5. Variable-temperature magnetic susceptibility data for all the complexes have been measured over the range 2.0–298 K. In 1–5 only very weak antiferromagnetic coupling has been observed [J ca. -2.2 (1), -0.01 (2), -0.6 (3), -0.3 (4) and -0.065 cm -1 (5), the Hamiltonian being ; = -J A · B with S A = S B = ½ (1, 2), 1 (3), 3/2 (4) and 5/2 (5)]. In contrast to the lack of magnetic interaction detected for complex 5, a significant antiferromagnetic coupling (J = -1.6 cm -1 ; maximum of susceptibility at 8.0 K) is observed in its dehydrated phase (6). The magnetostructural data and theoretical calculations demonstrate the low efficiency of terephthalate as a bridge to mediate exchange interactions between first-row transition-metal ions. The significant exchange coupling observed in 6 is due to the occurrence of a carboxylate bridge between the manganese(II) ions induced by a carboxylate-assisted loss of the co-ordinated water molecule.

Syntheses, crystal structures and electronic properties of [Cu(bipym)(C4O4)(H2O)3]·2H2O and [Cu2(bipym)(C4O4)2(H2O)6](bipym = 2,2′-bipyrimidine)

Two new mixed-ligand complexes [Cu(bipym)(C4O4)(H2O)3]·2H2O 1 and [Cu2(bipym)(C4O4)2(H2O)6]2[bipym = 2,2′-bipyrimidine and C4O42–= dianion of squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione)] have been obtained from aqueous solutions containing Cu(NO3)2·3H2O, bipym and Li2[C4O4] in 1 : 1 : 0.25 and 2 : 1 : 0.5 (Cu2+ : bipym: C4O42–) molar ratio, respectively. The structures of both complexes have been characterized by single-crystal X-ray analysis. Compound 1 consists of mononuclear [Cu(bipym)(C4O4)(H2O)3] units in which the copper atom exhibits a slightly distroted elongated-octahedral co-ordination with two bipym nitrogens, one squarate oxygen and one water oxygen forming the equatorial plane, and two water molecules in the axial positions. The structure of 2 is built by centrosymmetric bipym-bridged dinuclear [Cu2(bipym)(C4O4)2(H2O)6] units, the geometry of each copper atom being similar to that found in 1. Squarate acts as a monodentate ligand in both compounds whereas bipym exhibits chelating and bis(chelating) co-ordination modes in 1 and 2, respectively. The intramolecular metal–metal separation in 2[5.542(1)A] is the largest found in bipym-bridged copper(II) complexes. The magnetic behaviour of 2 has been investigated over the temperature range 10–300 K. Fitting of the magnetic susceptibility data for 2 by a simple Bleaney–Bowers expression yields a value for the singlet–triplet energy gap (J) of –139 cm–1. The magnitude of the observed antiferromagnetic interaction is the smallest found in bipym-bridged copper(II) complexes for which the σ in-plane exchange pathway is operative. Extended-Huckel calculations have been used to analyse how the magnitude of the exchange coupling is influenced by small structural distortions in this family of complexes.

SPINPOLARISIERUNG UND FERROMAGNETISMUS IN ZWEIDIMENSIONALEN COII-SCHICHTPOLYMEREN : CO(L)2(NCS)2 (L = PYRIMIDIN, PYRAZIN)

Wie vorhergesagt antiferro- und ferromagnetisch sind die beiden Schichtpolymere [Co(NCS)2(pyz)2] 1 bzw. [Co(NCS)2(pym)2] 2 (Strukturausschnitt im Bild). Die Verbindungen sowie der einkernige Komplex [Co(NCS)2(pyd)4] 3, der zu Vergleichszwecken synthetisiert wurde, konnten aus Losungen von Co(NCS)2 und Pyrazin (pyz; 1), Pyrimidin (pym; 2) bzw. Pyridazin (pyd; 3) in Methanol erhalten, strukturell charakterisiert und ihre magnetischen Eigenschaften untersucht werden.

Host molecules containing electroactive cavities obtained by the molecular assembly of redox-active ligands and metal ions

Self-assembly processes of nickel ions with the redox-active ligand 1,4,8,11-tetra(ferrocenylmethyl)-1,4,8,11-tetraazacyclotetradecane (Fc4cyclam) induces the formation of a redox-active cavity of potential use in electrocatalysis.

Tuning the nature of the exchange interaction in out-of-plane oximato-bridged dinuclear copper(II) complexes

The dinuclear copper(II) complexes of formula [{Cu(Hdmg) 2 } 2 ] 1, [{Cu(Hbdmg)} 2 ][ClO 4 ] 2 2, [{Cu(Hdeg) 2 } 2 ] 3 and [{Cu(Hchd) 2 } 2 ] 4 (H 2 dmg, H 2 bdmg, H 2 deg and H 2 chd = dimethylglyoxime, 3,10-dimethyl-4,9-diazadodeca-3,9- diene-2,11-dione dioxime, diethylglyoxime and cyclohexane-1,2-dione dioxime) have been synthesized. The structures of 3 and 4 have been determined by single-crystal X-ray diffraction methods. Both consist of centrosymmetric dinuclear bis(alkyl)glyoximatocopper(II) entities where the units are staggered so that the copper atom of one unit is directly opposite to the oxime-oxygen atom of the other, as previously found for 1 and 2. Each metal atom in 3 and 4 is five-co-ordinate with four imine-nitrogen atoms comprising the basal plane and an oximate-oxygen atom in the apical position. The copper–imine nitrogen bond lengths (average 1.957 and 1.953 A in 3 and 4, respectively) are shorter than that of the axial copper–oximate oxygen [2.263(3) (3) and 2.242(3) A (4)]. An oxime proton is lost from the ligand in the complex formation, the remaining oxime proton being involved in a hydrogen bond between the peripheral oxime oxygens of the same bis(alkyl)glyoximatocopper(II) unit. The intramolecular copper–copper separation is 3.898(1) (3) and 3.825(1) A (4). Variable-temperature magnetic susceptibility measurements showed the occurrence of intramolecular ferro- (1, 3 and 4) and antiferro-magnetic exchange interactions (2), the singlet–triplet energy gap J being +9.1 (1), -1.9 (2), +1.0 (3) and +3.1 cm -1 (4). The analysis of the exchange pathway through the out-of-plane oximato bond in this family has been substantiated by extended-Huckel calculations and a quasi-linear correlation between the value of J and the angle at the Cu–O–N (α) has been found. The influence of the size of the imine-carbon alkyl substituents on both the nature and magnitude of J is discussed in the light of the available structural information.

Cooperative layer-2 based routing approach for hybrid wireless mesh networks

In a Wireless Mesh Network (WMN), the convenience of a routing strategy strongly depends on the mobility of the intermediate nodes that compose the paths. Taking this behaviour into account, this paper presents a routing scheme that works differently accordingly to the node mobility. In this sense, a proactive routing scheme is restricted to the backbone to promote the use of stable routes. Conversely, the reactive protocol is used for searching routes to or from a mobile destination. Both approaches are simultaneously implemented in the mesh nodes so that the routing protocols share routing information that optimises the network performance. Aimed at guaranteeing the IP compatibility, the combination of the two protocols in the core routers is carried out in the Medium Access Control (MAC) layer. In contrast to the operation in the IP layer where two routing protocols cannot work concurrently, the transfer of the routing tasks to the MAC layer enables the use of multiple independent forwarding tables. Simulation results show the advantage of the proposal in terms of packet losses and data delay.

Syntheses, crystal structures and magnetic properties of one- and two-dimensional pap-containing copper(II) complexes (pap = pyrazino[2,3- f ][4,7]phenanthroline)

Three polynuclear complexes containing copper(II) and pyrazino[2,3-f][4,7]phenanthroline (pap) as the basic building blocks have been prepared [Cu2(pap)(H2O)2(NO3)3]n[NO3]n1, [Cu4(pap)4Cl7]nCln·15nH2O 2, and [Cu4(pap)4(H2O)4(C4O4)2]n[C4O4]n[NO3]2n·12nH2O 3, and their crystal structures and variable-temperature magnetic susceptibilities determined. Compound 1 is a single stranded zigzag chain where pap and nitrate alternate as bridges between the copper atoms. The copper coordination geometry is to a first approximation distorted square pyramidal, but with an additional semi-coordinated oxygen from non-bridging nitrate groups. The bridging nitrate coordinates in the apical position to both copper atoms. In 2 the basic structural unit is a cyclic, tetranuclear entity where copper atoms are bridged by pap. Two different pap bridges are present, one through only equatorial positions, the other coordinating equatorially and axially. These tetranuclear units are linked, through diagonally opposite corners, into chains by single atom chloro-bridges. The copper coordination geometry is distorted elongated octahedral. In 3 a tetranuclear building block, with structural characteristics similar to those found in 2, is present, but in this case coordinated squarate (3,4-dihydroxycyclobut-3-en-1,2-dionate) links these units into sheets. Neighbouring sheets are firmly connected by hydrogen bonds through uncoordinated squarate and water into a three-dimensional supramolecular structure featuring channels running normal to the sheets. The Cu⋯Cu separations across bridging pap are 6.809 A in 1, 6.887 and 7.297 A in 2, and 6.936 and 7.250 A in 3. Variable-temperature susceptibility measurements on 1–3 reveal the occurrence of very weak intramolecular antiferromagnetic interactions between copper(II) ions through bridging pap (the largest value of J being −2.5 cm−1).