Entrapment of [Ru(bpy)3]2+ in the anionic metal-organic framework: novel photoluminescence behavior exhibiting dual emission at room temperature

[Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine) ions were entrapped into the cavities of two-dimensional anionic sheet-like coordination polymeric networks of [M(dca)(3)](-) (dca = dicyanamide; M = Mn(II) and Fe(II)). The prepared compounds, {[Ru(bpy)(3)][Mn(dca)(3)](2)}(n) (1) and {[Ru(bpy)(3)][Fe(dca)(3)](2)}(n) (2), were structurally characterized by X-ray single crystal analysis. The spectroscopic properties of the [Ru(bpy)(3)](2+) ion dramatically changed on its entrapment in [M(dca)(3)](-). The [Ru(bpy)(3)](2+) moiety present in 1 and 2 exhibits novel dual photo-emission at room temperature.     

Synthesis,Structure and Magnetic Properties of Two Cobalt(II) Dicyanamide (dca) Complexes with Heterocyclic Nitrogen Donors Tetra(2‐pyridyl)pyrazine (tppz) and 2,4,6‐Tri(2‐pyridyl)‐1,3,5‐triazine (tptz): [Co2(tppz)(dca)4]·CH3CN and [Co(tptz)(dca)(H2O)](dca)

Two new transition metal dicyanamide complexes [Co₂(tppz)(dca)₄]·CH₃CN ( 1 ) [tppz=tetra(2‐pyridyl)pyrazine, dca=dicyanamide] and [Co(tptz)(dca)(H₂O)](dca) ( 2 ) [tptz=2,4,6‐tri(2‐pyridyl)‐1,3,5‐triazine] were synthesized and characterized by single crystal X‐ray diffraction analysis. In 1 each cobalt(II) atom is coordinated to three dca anions and one tppz molecule to form a distorted octahedral geometry, the neigbour two cobalt(II) atoms are bridged by one tppz ligand to form a dimer, then the cobalt(II) atoms in each dimer are joined together to form a ladder chain structure. In 2 the coordination geometry around the central metal is also distorted octahedral, each cobalt(II) atom is coordinated by two dca anions, one tptz molecule and one water ligand to form a cationic part, and the cationic part is linked with the free dca anions via the electrostatic attraction to give an infinite chain structure. Magnetic susceptibility measurement in the range of 2–300 K indicates that there are antiferromagnetic couplings between adjacent metal ions in 1 (T>29 K, (=?9.78 K, C=4.92 cm³·K·mol^?1) and ferromagnetic couplings in 2 (T>150 K, (=7.97 K, C=2.59 cm³·K·mol^?1) respectively.     

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.     

Synthesis, structure, and magnetochemical analysis of selected first-row transition-metal anilino- and anisolesquarate compounds

The isomorphous polymeric complexes [M(mu-C(6)H(5)NHC(4)O(3))(2)(CH(3)OH)(2)](n) [M = Mn (1), Co (2), Cu (4), Zn (5)] are produced by reacting the anilinosquarate anion with the appropriate metal nitrates in a methanolic solution. Each of these complexes contains the central metal atom in a slightly distorted octahedral environment, with the coordination polyhedron consisting of four mu-1,2-bridging anilinosquarate ligands and two trans-oriented methanols. The polymer chains propagate to form a two-dimensional net of metal centers, with the conformation of the component sheets in the net being controlled by intramolecular N-H...O and O-H...O hydrogen bonds. Under reaction conditions similar to those used in the synthesis of the polymers 1, 2, 4, and 5, the nickel(II) monomer [Ni(C(6)H(5)NHC(4)O(3))(2)(H(2)O)(4)].2H(2)O (3) is produced in which each nickel center is attached to two cis-coordinated anilinosquarate and four aqua ligands in a distorted octahedral arrangement. The ligand conformation in 3 is stabilized by both intra- and intermolecular hydrogen bonding, which results in the formation of a sheet polymer having distinct hydrophobic and hydrophilic surfaces. Magnetochemical analysis of 1 and 4 reveals normal paramagnetic behavior for 1 and a very weak ferromagnetic interaction in 4; the absence of significant magnetic interactions is attributed to the distortion of the C(4) cycle of the anilinosquarate ligand (lower than C(2)(v) symmetry) in these complexes. Reaction of anisolesquarate with M(NO(3))(2).xH(2)O in acetonitrile produced the set of isomorphous salts [M(H(2)O)(6)][CH(3)OC(6)H(5)C(4)O(3)](2) [M = Mn (6), Co (7), Ni (8), Zn (9)]. The anisolesquarate anions in 6-9 are hydrogen bonded to the [M(H(2)O)(6)](2+) ions to form polymer chains, which are further linked by hydrogen bonds to form complex sheets. Complexation of the anisolesquarate ligand was not observed even when other solvents and reaction conditions were employed.     

Cationic assembly of metal complex aggregates: structural diversity,solution stability,and magnetic properties

The tetradentate imino-carboxylate ligand [L](2)(-) chelates the equatorial sites of Ni(II) to give the complex [Ni(L)(MeOH)(2)] in which a Ni(II) center is bound in an octahedral coordination environment with MeOH ligands occupying the axial sites. Lanthanide (Ln) and Group II metal ions (M) template the aggregation of six [Ni(L)] fragments into the octahedral cage aggregates (M[Ni(L)](6))(x)(+) (1: M = Sr(II); x = 2,2: M = Ba(II); x = 2, 3: M = La(III); x = 3, 4: M = Ce(III); x = 3, 5: M = Pr(III); x = 3, and 6: M = Nd(III); x = 3). In the presence of Group I cations, however, aggregates composed of the alkali metal-oxide cations template various cage compounds. Thus, Na(+) forms the trigonal bipyramidal [Na(5)O](3+) core within a tricapped trigonal prismatic [Ni(L)](9) aggregate to give ((Na(5)O) subset [Ni(L)](9)(MeOH)(3))(BF(4))(2).OH.CH(3)OH, 7. Li(+) and Na(+) together form a mixed Li(+)/Na(+) core comprising distorted trigonal bipyramidal [Na(3)Li(2)O](3+) within an approximately anti-square prismatic [Ni(L)](8) cage in ((Na(3)Li(2)O) subset [Ni(L)](8)(CH(3)OH)(1.3)(BF(4))(0.7))(BF(4))(2.3).(CH(3)OH)(2.75).(C(4)H(10)O)(0.5), 8, while in the presence of Li(+), a tetrahedral [Li(4)O](2+) core within a hexanuclear open cage [Ni(L)](6) in ((Li(4)O) subset [Ni(L)](6)(CH(3)OH)(3))2ClO(4).1.85CH(3)OH, 9, is produced. In the presence of H(2)O, the Cs(+) cation induces the aggregation of the [Ni(L)(H(2)O)(2)] monomer to give the cluster Cs(2)[Ni(L)(H(2)O)(2)](6).2I.4CH(3)OH.5.25H(2)O, 10. Analysis by electronic spectroscopy and mass spectrometry indicates that in solution the trend in stability follows the order 1-6 > 7 > 8 approximately 9. Magnetic susceptibility data indicate that there is net antiferromagnetic exchange between magnetic centers within the cages.     

Dinuclear cobalt(II) and copper(II) complexes with a Py2N4S2 macrocyclic ligand

The interaction between Co(II) and Cu(II) ions with a Py(2)N(4)S(2)-coordinating octadentate macrocyclic ligand (L) to afford dinuclear compounds has been investigated. The complexes were characterized by microanalysis, conductivity measurements, IR spectroscopy and liquid secondary ion mass spectrometry. The crystal structure of the compounds [H(4)L](NO(3))(4), [Cu(2)LCl(2)](NO(3))(2) (5), [Cu(2)L(NO(3))(2)](NO(3))(2) (6), and [Cu(2)L(μ-OH)](ClO(4))(3)·H(2)O (7) was also determined by single-crystal X-ray diffraction. The [H(4)L](4+) cation crystal structure presents two different conformations, planar and step, with intermolecular face-to-face π,π-stacking interactions between the pyridinic rings. Complexes 5 and 6 show the metal ions in a slightly distorted square-pyramidal coordination geometry. In the case of complex 7, the crystal structure presents the two metal ions joined by a μ-hydroxo bridge and the Cu(II) centers in a slightly distorted square plane or a tetragonally distorted octahedral geometry, taking into account weak interactions in axial positions. Electron paramagnetic resonance spectroscopy is in accordance with the dinuclear nature of the complexes, with an octahedral environment for the cobalt(II) compounds and square-pyramidal or tetragonally elongated octahedral geometries for the copper(II) compounds. The magnetic behavior is consistent with the existence of antiferromagnetic interactions between the ions for cobalt(II) and copper(II) complexes, while for the Co(II) ones, this behavior could also be explained by spin-orbit coupling.     

Ferromagnetic interaction in mu1,3-cyanamido-derived copper(II) cryptates

The reaction of dinuclear copper(II) cryptates with calcium cyanamide, CaNCN, and sodium dicyanamide, Na[N(CN)(2)] results in dinuclear compounds of formulae [Cu(2)(HNCN)(R3Bm)](ClO(4))(3) (1), [Cu(2)(dca)(R3Bm)](ClO(4))(3)4H(2)O (2), and [Cu(2)(NCNCONH(2))(R3Bm)](CF(3)SO(3))(3) (3), in which R3Bm=N[(CH(2))(2)NHCH(2)(C(6)H(4)-m)CH(2)NH(CH(2))(2)](3)N and dca=dicyanamido ligand (NCNCN(-)). The X-ray diffraction analysis reveals for both 1 and 3 a dinuclear entity in which the copper atoms are bridged by means of the -NCN- unit. The molar magnetic susceptibility measurements of 1-3 in the 2-300 K range indicate ferromagnetic coupling. The calculated J values, by using theoretical methods based on density functional theory (DFT) are in excellent agreement with the experimental data. Catalytic hydration of a nitrile to an amide functional group is assumed responsible for the formation of 3 from a mu(1,3)-dicyanamido ligand.     

Crystal structures and magnetic properties of 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)-containing copper(II) complexes

Four new copper(II) complexes of formula [Cu(2)(tppz)(dca)(3)(H(2)O)].dca.3H(2)O (1), [Cu(5)(tppz)(N(3))(10)](n)() (2), [[Cu(2)(tppz)(N(3))(2)][Cu(2)(N(3))(6)]](n)() (3), and [Cu(tppz)(N(3))(2)].0.33H(2)O (4) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and dca = dicyanamide anion] have been synthesized and structurally characterized by X-ray diffraction methods. The structure of complex 1 is made up of dinuclear tppz-bridged [Cu(2)(tppz)(dca)(3)(H(2)O)](+) cations, uncoordinated dca anions, and crystallization water molecules. The copper-copper separation across bis-terdentate tppz is 6.5318(11) A. Complex 2 is a sheetlike polymer whose asymmetric unit contains five crystallographically independent copper(II) ions. These units are building blocks in double chains in which the central part consists of a zigzag string of copper atoms bridged by double end-on azido bridges, and the outer parts are formed by dinuclear tppz-bridged entities which are bound to the central part through single end-on azido bridges. The chains are furthermore connected through weak, double out-of-plane end-on azido bridges, yielding a sheet structure. The intrachain copper-copper separations in 2 are 6.5610(6) A across bis-terdentate tppz, 3.7174(5) and 3.8477(5) A across single end-on azido bridges, and from 3.0955(5) to 3.2047(7) A across double end-on azido bridges. The double dca bridge linking the chains into sheets yields a copper-copper separation of 3.5984(7) A. The structure of 3 consists of centrosymmetric [Cu(2)(tppz)(N(3))(2)](2+) and [Cu(2)(N(3))(6)](2)(-) units which are linked through axial Cu.N(azido) (single end-on and double end-to-end coordination modes) type interactions to afford a neutral two-dimensional network. The copper-copper separations within the cation and anion are is 6.5579(5) A (across the bis-terdentate tppz ligand) and 3.1034(6) A (across the double end-on azido bridges), whereas those between the units are 3.6652(4) A (through the single end-on azido group) and 5.3508(4) A (through the double end-to-end azido bridges). The structure of complex 4 is built of neutral [Cu(tppz)(N(3))(2)] mononuclear units and uncoordinated water molecules. The mononuclear units are grouped by pairs to give a rather short copper-copper separation of 3.9031(15) A. The magnetic properties of 1-4 have been investigated in the temperature range 1.9-300 K. The magnetic behavior of complexes 1 and 4 is that of antiferromagnetically coupled copper(II) dimers with J = -43.7 (1) and -2.1 cm(-)(1) (4) (the Hamiltonian being H = -JS(A).S(B)). An overall ferromagnetic behavior is observed for complexes 2 and 3. Despite the structural complexity of 2, its magnetic properties correspond to those of magnetically isolated tppz-bridged dinuclear copper(II) units with an intermediate antiferromagnetic coupling (J = -37.5 cm(-)(1)) plus a ferromagnetic chain of hexanuclear double azido-bridged copper(II) units (the values of the magnetic coupling within and between the hexameric units being +61.1 and +0.0062 cm(-)(1), respectively). Finally, the magnetic properties of 3 were successfully analyzed through a model of a copper(II) chain with regular alternating of three ferromagnetic interactions, J(1) = +69.4 (across the double end-on azido bridges in the equatorial plane), J(2) = +11.2 (through the tppz bridge), and J(3) = +3.4 cm(-)(1) (across the single end-on azido bridge).     

Dinuclear complexes of chiral tetradentate pyridylimine ligands: diastereoselectivity, positive cooperativity, anion selectivity, ligand self-sorting based on chirality, and magnetism

The synthesis and coordination chemistry of two chiral tetradentate pyridylimine Schiff base ligands are reported. The ligands were prepared by the nucleophilic displacement of both bromides of 1,3-bis(bromomethyl)benzene (2) or 3,5-bis(bromomethyl)toluene (3) by the anion of (S)-valinol, followed by capping of both amine groups with pyridine-2-carboxaldehyde. Both ligands react with CoCl(2) and NiCl(2) to give [M(2)L(2)Cl(2)](2+) complexes. Remarkably, neither fluoride nor bromide ions can act as bridging ligands. The formation of [Co(2)((S)-3)(2)Cl(2)](2+) is highly diastereoselective, and X-ray crystallography shows that both metal centers in the [Co(2)((S)-3)(2)Cl(2)](CoCl(4)) complex adopt the lambda configuration (crystal data: [Co(2)(C(31)H(40)N(4)O(2))(2)Cl(2)](CoCl(4)).(CH(3)CN)(3), monoclinic, P2(1), a = 11.595(2) A, b = 22.246(4) A, c = 15.350(2) A, V = 3705(1) A(3), beta = 110.643(3) degrees, Z = 2). Structurally, the dinuclear complex can be viewed as a helicate with the helical axis running perpendicular to the [Co(2)Cl(2)] plane. The reaction of racemic 2 with CoCl(2) was shown by (1)H NMR spectroscopy to yield a racemic mixture of Lambda,Lambda-[Co(2)((S)-2)(2)Cl(2)](2+) and delta,delta-[Co(2)((R)-2)(2)Cl(2)](2+) complexes; that is, a homochiral recognition process takes place. Spectrophotometric titrations were performed by titrating (S)-3 with Co(ClO(4))(2) followed by Bu(4)NCl, and the global stability constants of [Co((S)-3)](2+) (log beta(110) = 5.7), [Co((S)-3)(2)](2+) (log beta(120) = 11.6), and [Co(2)((S)-3)(2)Cl(2)](2+) (log beta(110) = 23.8) were calculated. The results revealed a strong positive cooperativity in the formation of [Co(2)((S)-3)(2)Cl(2)](2+). Variable-temperature magnetic susceptibility curves for [Co(2)((S)-2)(2)Cl(2)](BPh(4))(2) and [Co(2)((S)-3)(2)Cl(2)](BPh(4))(2) are very similar and indicate that there are no significant magnetic interactions between the cobalt(II) centers.     

1-D and 2-D homoleptic dicyanamide structures, [Ph4P]2[CoII[N(CN)2]4] and [Ph4P][M[N(CN)2]3] (M = Mn, Co)

The homoleptic complexes [Ph(4)P](2)[Co[N(CN)(2)](4)] and [Ph(4)P][M[N(CN)(2)](3)] [M = Co, Mn] have been structurally as well as magnetically characterized. The complexes containing [M[N(CN)(2)](4)](2-) form 1-D chains, which are bridged via a common dicyanamide ligand in [M[N(CN)(2)](3)](-) to form a 2-D structure. The five-atom [NCNCN](-) bridging ligands lead to weak magnetic coupling along a chain. The six [NCNCN](-) ligands lead to a (4)T(1g) ground state for Co(II) which has an unquenched spin-orbit coupling that is reflected in the magnetic properties. Long-range magnetic ordering was not observed in any of these materials.     

Encapsulation of cyanometalates by a tris-macrocyclic ligand tricopper(II) complex: syntheses, structural variation, and magnetic exchange coupling pathways

The reaction of [M(CN)(6)](3-) (M = Cr(3+), Mn(3+), Fe(3+), Co(3+)) and [M(CN)(8)](4-/3-) (M = Mo(4+/5+), W(4+/5+)) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu(3)(L)](6+)) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu(3)(L)](6+) forms the isostructural host-guest complexes [[[Cu(3)(L)(OH(2))(2)][M(CN)(6)](2)][M(CN)(6)]][M(CN)(6)]30 H(2)O with one bridging, two partially encapsulated, and one isolated [M(CN)(6)](3-) unit. The octacyanometalates of Mo(4+/5+) and W(4+/5+) are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)(8)](4-) were obtained. The Mo(4+) and W(4+) complexes were crystallized in two different structural forms: [[Cu(3)(L)(OH(2))](2)[Mo(CN)(8)]](NO(3))(8)15 H(2)O with a structural motif that involves isolated spherical [[Cu(3)(L)(OH(2))](2)[M(CN)(8)]](8+) ions and a "string-of-pearls" type of structure [[[Cu(3)(L)](2)[M(CN)(8)]][M(CN)(8)]](NO(3))(4) 20 H(2)O, with [M(CN)(8)](4-) ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the CuCu pairs in the [Cu(3)(L)](6+) "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr(3+), exchange coupling of Mn(3+) and Fe(3+) is very small, and the octacoordinate Mo(4+) and W(4+) systems have a closed-shell ground state.     

Directed synthesis of μ-1,3,5 bridged dicyanamides by thermal decomposition of μ-1,5 bridged precursor compounds

Reaction of transition-metal dicyanamides with pyridazine leads to the formation of the ligand-rich 1 : 2 (1 : 2 = ratio between metal salt and organic co-ligand) compounds [M(dca)(2)(pydz)(2)](n) (dca = dicyanamide, pydz = pyridazine) with M = Mn (1-Mn), Fe (1-Fe), Co (1-Co), Ni (1-Ni). In their crystal structures linear polymeric M-(dca)(2)-M chains are found, in which the M(ii) cations are μ-1,5 bridged by the dca anions. The pydz ligands are terminally N-bonded to the cations, which are octahedrally coordinated by two pydz ligands and four dca anions. On heating these precursor compounds, 1-Mn, 1-Fe and 1-Co transform quantitatively into new ligand-deficient 1 : 1 intermediate compounds of composition [M(dca)(2)(pydz)](n) with M = Mn (2-Mn), Fe (2-Fe) and Co (2-Co). Investigations by IR spectroscopy, and single crystal X-ray structure analysis, show that the intermediates form a more condensed layered structure in which half of the pristine μ-1,5 bridged dca anions become μ-1,3,5 bridging. This structural transformation is accompanied by a pronounced change of their magnetic properties: whereas the ligand-rich 1 : 2 compounds show only Curie-Weiss paramagnetism, the ligand-deficient 1 : 1 intermediates show either antiferro- or ferromagnetic ordering at lower temperatures mediated by the three-atom pathway of the μ-1,3,5 bridging dca anions.     

Selenadiazolopyridine: a synthon for supramolecular assembly and complexes with metallophilic interactions

The synthesis and characterization of the complexes of Cu(I), Ag(I), Cu(II), and Co(II) ions with 1,2,5-selenadiazolopyridine (psd) is reported. The following complexes have been prepared: [Cu(2)(psd)(3)(CH(3)CN)(2)](2+)2(PF(6)(-)); [(CuCl)(2)(psd)(3)]; [Cu(2)(psd)(6)](2+)2(ClO(4))(-); [Ag(2)(psd)(2)](2+)2(NO(3))(-); [Ag(2)(psd)(2)](2+)2(CF(3)COO)(-); [Cu(psd)(2)(H(2)O)(3)](2+)2(ClO(4))(-)·(psd)(2); [Cu(psd)(4)(H(2)O)](2+)2(ClO(4))(-)·(CHCl(3)); [Cu(psd)(2)(H(2)O)(3)](2+)2(NO(3))(-)·(H(2)O)·(psd)(2), and [Co(psd)(2)(H(2)O)(4)](2+)2(ClO(4))(-)·(psd)(2). The electronic structure of ligand psd, in particular the bond order of Se-N bonds, has been probed by X-ray diffraction, (77)Se NMR, and computational studies. A detailed analysis of the crystal structures of the ligand and the complexes revealed interesting supramolecular assembly. The assembly was further facilitated by the presence of neutral ligands for some complexes (Cu(II) and Co(II)). The molecular structure of the ligand showed that it was present as a dimer in the solid state where the monomers were linked by strong secondary bonding Se···N interactions. The crystal structures of Cu(I) and Ag(I) complexes revealed the dinuclear nature with characteristic metallophilic interactions [M···M] (M = Cu, Ag), while the Cu(II) and Co(II) complexes were mononuclear. The presence of M···M interactions has been further probed by Atoms in Molecules (AIM) calculations. The paramagnetic Cu(II) and Co(II) complexes have been characterized by UV-vis, ESI spectroscopy, and room temperature magnetic measurements.     

Self assembled tetranuclear Cu4(II), Ni4(II) [2 × 2] square grids and a dicopper(II) complex of heterocycle based polytopic ligands - Magnetic studies

The ditopic ligand PyPzOAP (N-[(Z)-amino(pyridin-2-yl)methylidene]-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid) and the polytopic ligand 2-PzCAP (N'(3),N'(5)-bis[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3,5-dicarbohydrazide) were synthesized in situ by condensation of methyl imino picolinate with 5-methyl-1-(2-pyridyl) pyrazole-3-carbohydrazide and 2-acetyl pyridine with pyrazole-3,5-dicarbohydrazide respectively. The ligands PyPzOAP and PzOAP (reported earlier, Dalton Trans., 2007, 1229) self-assemble to form homoleptic [2 × 2] tetranuclear M(4) (M = Cu(II) and Ni(II)) square grids structures [Cu(4)(PyPzOAP)(4)](NO(3))(4) (1), [Cu(4)(PzOAP)(4)](ClO(4))(4) (2) and [Ni(4)(PyPzOAP)(4)](NO(3))(4)·8H(2)O·2CH(3)CN (3). While the ligand 2-PzCAP forms a dicopper(II) complex [Cu(2)(2-PzCAP)(OH)(NO(3))(H(2)O)](NO(3))·2H(2)O (4). The complex 1 is a perfect square grid (a = 4.201 ?), whereas, 2 and 3 are almost square grids. All these compounds have been characterized by X-ray structural analyses and variable temperature magnetic susceptibility measurements. EPR studies have also been carried out for complexes 1, 2 and 4. In the Cu(4) grid (1), all the Cu(II) centers are in a distorted octahedral environment with N(4)O(2) chromophore, while, in complex 2, all four Cu(II) centers have a square pyramidal environment with N(3)O(2) chromophore. In complex 3, all four Ni(II) centers have distorted octahedral geometry with N(4)O(2) chromophore. In compound 4, the Cu(II) centers are in square pyramidal environment with N(3)O(2) chromophore. The magnetic properties of compounds 1 and 2 show the presence of intramolecular ferromagnetic exchange interaction (J = 5.88 cm(-1) for 1 and 4.78 cm(-1) for 2). The complex 3 shows weak intramolecular antiferromagnetic interaction (J = -4.02 cm(-1)). While, complex 4, shows strong antiferromagnetic behavior (J = -443 cm(-1)).     

Synthesis,crystal structures and magnetic behaviors of two dicyanamide bridged di- and polynuclear complexes of cobalt(II) derived from 2,4,6-tris(2-pyridyl)1,3,5-triazine and imidazole

Two new dicyanamido-bridged di- and polynuclear complexes of Co(II), [Co(dca)(tptz)(H₂O)]₂·2(ClO₄) (1) and [Co(dca)₂(imz)₂]_n (2) [dca, dicyanamide; tptz, 2,4,6-tris(2-pyridyl)1,3,5-triazine; and imz, imidazole] have been synthesized and characterized structurally, as well as magnetically. The X-ray single crystal structure determination of complex 1 shows that two symmetry related octahedral Co(II) ions are separated by dca ligand and other coordination sites are satisfied by tptz and aquo ligands. Each dinuclear unit is associated with each other by intramolecular hydrogen bonding interactions, giving rise to a 1D chain structure. On the other hand complex 2 is a 1D coordination polymer having [Co(II)(imz)₂] units connected by double bridging dca ligands. These 1D chains interact through face-to-face π–π stacking interactions of the imz rings extending the dimensionality to a 2D supramolecular network. The variable temperature (300–2 K) magnetic measurements of both compounds reveal that dicyanamide exhibits a weak antiferromagnetic interaction between the metal centers.     

Self-penetration--a structural compromise between single networks and interpenetration: magnetic properties and crystal structures of

The three-dimensional coordination polymers [Mn(dca)2(H2O)] (1) and [M(dca)(tcm)], M =Co (2), Ni (3), Cu (4), dca =dicyanamide, N(CN)2-, tcm = tricyanomethanide, C(CN)3-, have isomorphous structures. In 1 half the dca ligands coordinate directly (through all three nitrogen atoms) to three Mn atoms (all metal atoms are six-coordinate), while the other half coordinate to two Mn atoms (through the nitrile nitrogens) and hydrogen bond to water molecules coordinated to a third Mn atom (through the amide nitrogen). This dca. H2O structural moiety is disordered over a mirror plane, and is replaced by the structurally equivalent tcm ligand in compounds 2-4. The resulting structures display a new self-penetrating 3,6-connected (2:1) network topology that can be related to, but is different from, the rutile net. The self-penetrating [M(dca)(tcm)] network can be viewed as a structural compromise between the two interpenetrating rutile-like networks of [M(tcm)2] and the single rutile-like network of alpha-[M(dca)2]. The temperature and field dependence of the DC and AC magnetic susceptibilities and magnetisations has been measured for complexes 1-4. Compounds 1-3 exhibit long-range magnetic order with critical temperatures of 6.3 K for 1, 3.5 K for 2 and 8.0 K for 3. The Cu11 compound 4 does not order and is essentially a paramagnet. Hysteresis measurements of coercive field and remnant magnetisation show that 1, 2 and 3 are soft magnets, 1 being a canted-spin antiferromagnet (weak ferromagnet), while 2 and 3 are ferromagnets that display some unusual features in their high-field magnetisation isotherms in comparison to their related alpha-[M(dca)2] phases.     

Structures and magnetic behavior of 1-, 2-, and 3D coordination polymers in the Cu(II)-dicyanamide-pyrimidine family

Using aqueous conditions, three new coordination polymers containing Cu(2+) cations, dicyanamide (dca) anions, and pyrimidine (pym) were isolated and structurally and magnetically characterized. Comprising the bulk of the product yield, Cu(dca)(2)(pym)(2), 1, crystallizes in the monoclinic space group P2(1)/c with a = 7.3569(5) A, b = 13.4482(9) A, c = 7.4559(5) A, beta = 98.984(3) degrees, and V = 728.6(1) A and forms linear 1D chains. The second compound, Cu(dca)(NO(3))(pym)(H(2)O), 2, is also monoclinic, P2(1)/n, with a = 7.6475(3) A, b = 12.2422(5) A, c = 11.0286(4) A, beta = 106.585(2) degrees, and V = 989.6(1) A(3). A 2D network structure consisting of both bridging mu-dca and pym ligands is formed while the NO(3)(-) and H(2)O are axially bonded to the Cu center. Cu(3)(dca)(6)(pym)(2).0.75H(2)O, 3, is triclinic, Ponemacr;, with a = 7.7439(4) A, b = 9.3388(5) A, c = 10.1779(5) A, alpha = 86.014(2) degrees, beta = 88.505(2) degrees, gamma = 73.623(2) degrees, and V = 704.46(9) A(3). The structure of 3 is quite unique in that [Cu(3)(pym)(2)](6+) trimers are interconnected via mu-dca ligands affording a complex 3D self-penetrating framework. Magnetically, 1 exhibits extremely weak exchange interactions along the Cu-(dca)(2)-Cu ribbons while 2 and 3 display very strong magnetic couplings mediated by the mu-bonded pym ligands. Moreover, 2 shows a broad maximum in chi(T) at 40 K and behaves as a uniform 1D antiferromagnetic chain with g = 2.09(1), J/k(B) = -42.6(1) K, and TIP = -66 x 10(-)(6) emu/mol. An S = (1)/(2) trimer model that includes intertrimer interactions successfully described the magnetic behavior of 3, yielding g = 2.10(1), J/k(B) = -69.4(5) K, theta = -0.28(3) K, and TIP = -180 x 10(-)(6) emu/mol. It is found that mu-bonded dca and pym ligands mediate very weak and very strong exchange interactions, respectively, between Cu(2+) centers.     

Reexamination of the magnetic properties of Cu(2)(dca)(4)(2,5-me(2)pyz) [dca = dicyanamide; me(2)pyz = dimethylpyrazine]: isolated spin-1/2 dimers versus long-range magnetic ordering

The magnetic properties of Cu(2)(dca)(4)(2,5-me(2)pyz) have been reexamined. The extended structure of Cu(2)(dca)(4)(2,5-me(2)pyz) can be viewed in terms of Cu(2)(2,5-me(2)pyz)(4+) dimer units interconnected via mu(1,5)-dca ligands. The bulk magnetic susceptibility chi(T) and the isothermal M(H) of Cu(2)(dca)(4)(2,5-me(2)pyz) are shown to be well described by an isolated dimer model. This finding was confirmed by carrying out a spin dimer analysis based on tight-binding calculations, which shows that the 2,5-me(2)pyz ligand provides a substantial spin exchange interaction between the Cu(2+) ions while the dca ligands do not.     

Au(CN)4]- as a supramolecular building block for heterobimetallic coordination polymers

A series of the first coordination polymers using the [Au(CN)(4)](-) anion as a building block has been prepared. The planar tetracyanoaurate anion uses one, two, or four cyano groups to bridge to Ni(II) or Cu(II) centers and exhibits weak Au(III)-N(cyano) interactions between anions. Ni(en)(2)[Au(CN)(4)](2).H(2)O (1, en = ethylenediamine) is a molecular compound with the two [Au(CN)(4)](-) anions coordinating in a trans orientation to Ni(II) without further cyanide coordination. Cu(dien)[Au(CN)(4)](2) (2, dien = diethylenetriamine) forms a similar molecular complex; however, the dimensionality is increased through weak intermolecular Au-N(cyano) interactions of 3.002(14) A to form a 1-D zigzag chain. Cu(en)(2)[Au(CN)(4)](2) (3) also forms a molecular complex similar to 1, but with elongated axial bonds. The complex further aggregates through Au-N(cyano) interactions of 3.035(8) A to form a 2-D array. In [Cu(dmeda)(2)Au(CN)(4)][Au(CN)(4)] (4, dmeda = N,N-dimethylethylenediamine) one [Au(CN)(4)](-) anion coordinates via two cis-N(cyano) donors to the axial sites of two Cu(II) centers to form a 1-D zigzag chain of alternating [Cu(dmeda)(2)](2+) and [Au(CN)(2)](-) units; the other [Au(CN)(4)](-) anion forms a 1-D chain via Au-N(cyano) interactions. In [Cu(bipy)(H(2)O)(2)(Au(CN)(4))(0.5)][Au(CN)(4)](1.5) (5, bipy = 2,2'-bipyridine) one [Au(CN)(4)](-) anion uses all four cyano moieties to bridge four different Cu(II) centers, creating a 1-D chain.     

Serendipity and design in the generation of new coordination polymers: an extensive series of highly symmetrical guanidinium-templated, carbonate-based networks with the sodalite topology

The serendipitous discovery of a 3D [Cu(CO(3))(2)(2-)](n) network with the topology of the 4(2)6(4) sodalite net in [Cu(6)(CO(3))(12)(CH(6)N(3))(8)].K(4).8H(2)O paved the way for the deliberate engineering of an extensive series of structurally related guanidinium-templated metal carbonates of composition [M(6)(CO(3))(12)(CH(6)N(3))(8)]Na(3-)[N(CH(3))(4)].xH(2)O, where the divalent metal M in the framework may be Mg, Mn, Fe, Co, Ni, Cu, Zn, or Cd. A closely related crystalline material with a [Ca(CO(3))(2)(2-)](n) sodalite-like framework, but containing K(+) rather than Na(+), of composition [Ca(6)(CO(3))(12)(CH(6)N(3))(8)]K(3)[N(CH(3))(4)].3H(2)O was also isolated. All of these compounds were obtained under the simplest possible conditions from aqueous solution at room temperature, and their structures were determined by single-crystal X-ray diffraction. Pairs of guanidinium cations are associated with the hexagonal windows of the sodalite cages, alkali-metal cations are associated with their square windows, and N(CH(3))(4)(+) ions are located at their centers. Structures fall into two classes depending on the metal, M(II), in the framework. One type, the BC type (Im3m), comprising the compounds for which M(2+) = Ca(2+), Mn(2+), Cu(2+), and Cd(2+), has a body-centered cubic unit cell, while the second type, the FC type (Fd3c), for which M(2+) = Mg(2+), Fe(2+), Co(2+), Ni(2+), and Zn(2+), has a face-centered cubic unit cell with edges on the order of twice those of the BC structural type. The metal M in the BC structures has four close carbonate oxygen donors and four other more distant ones, while M in the FC structures has an octahedral environment consisting of two bidentate chelating carbonate ligands and two cis monodentate carbonate ligands.