Pentanuclear homoleptic M(5)L(6) (M = Mn(II), Co(II), Zn(II)) complexes formed by strict self-assembly

Recent developments in supramolecular complexes of azabenzenes containing one to four N atoms: synthetic strategies, structures, and magnetic properties

For the last couple of decades, azabenzene-based ligands have drawn much attention from inorganic chemists due to their ability to coordinate with different metal ions to form supramolecular clusters. These azabenzenes are weak σ donors and strong π acceptors and electron-deficient. Metallogrid complexes and non-grid oligomers are well-defined supramolecular clusters, formed by appropriate chelating ligands, and can show interesting optical, magnetic, and electronic properties. Self-assembly of [n × n] metallogrid complexes is dominated by the entropic factor while the formation of oligonuclear metal ion complexes is dominated by other effects like CFSE, electrostatic factors, ligand conformational characters, etc. Herein, the present article gives an overview of six-membered heterocyclic azine-based ligands and their potential for different metal ions to form polynuclear complexes. Moreover, their temperature-dependent magnetic properties and SCO phenomena are well described and tabulated.

A pentanuclear {Co5} cluster motif forming a capped breathing kagomé lattice

A new pentanuclear {Co5} cluster motif is found to have a D3h oblate trigonal bipyramidal geometry, which is extended into a 3D triangle network, forming a unique capped breathing kagomé lattice. Magnetic results confirmed a paramagnetism down to 2 K, accompanying the disappearance of two-thirds of the spin moment at low-temperature and the appearance of a 1/5 magnetization plateau.

Chelate ring stacking interactions in the supramolecular assemblies of Zn(ii)and Cd(ii) coordination compounds: a combined experimental and theoretical study

We report seven Zn(ii)/Cd(ii) complexes with picolinoyl/isonicotinoyl hydrazone based ligands exhibiting relevant chelate–π interactions.

Syntheses, crystal structures and magnetic properties of a novel family of penta-manganese complexes derived from an assembly system containing polydentate hydroxy-rich Schiff-base ligands

The syntheses, crystal structures, and magnetochemical characterization are reported of a novel family of four pentanuclear manganese complexes, namely, [Mn(III)(5)(mu(3)-O)(2)(L(1))(4)(O(2)CMe)(3)(CH(3)OH)].1.5CH(3)OH.2.5H(2)O (1), [Mn(III)(5)(mu(3)-O)(2)(L(1))(4)(O(2)CPh)(3)(CH(3)OH)].2CH(3)OH.2.25CH(3)CN.1.5H(2)O (), [Mn(II)Mn(III)(4)(HL(2))(2)(L(2))(2)(O(2)C Me)(4))].CH(3)OH.H(2)O (3) and [Mn(II)Mn(III)(4)(HL(2))(2)(L(2))(2)(O(2)CPh)(4))].1.5H(2)O (4), where H(2)L(1) is 3,5-dibromosalicylidene-2-ethanolamine and H(3)L(2) is 3-(2-hydroxy-3,5-dibromobenzylideneamino)propane-1,2-diol. All the complexes can be obtained from a reaction system containing the trinuclear species [Mn(3)O(O(2)CR)(6)(Py)(3)](0/+) (R = Me or Ph) and H(2)L(1) or H(3)L(2) with similar procedures. Both cores in complexes 1 and 2 feature two mu(3)-O(2-) atoms, four L(1)(2-) ligands together with three RCO(2)(-) groups (R = Me or Ph) bridging five Mn(III) atoms to form an incomplete cubane extended at one face by an incomplete adamantane unit, which is an unprecedented structural type in Mn chemistry. Complexes 3 and 4 both have a rare [Mn(II)Mn(III)(4)(mu(2)-O(alkoxide))(6)](8+) core, which can be regarded as two {Mn(II)Mn(III)(2)(mu(2)-O(alkoxide))(3)} scalene triangles, sharing the Mn(II) vertex. The dc magnetic susceptibility studies in the 2-300 K range for complexes 1-4 reveal the presence of overall antiferromagnetic intracluster interactions. A simple 3-J model was found to be adequate to describe the variable-temperature dc susceptibility data of complexes 1-4. The results have allowed us to compare the obtained magnetic exchange with magneto-structural correlations found previously for manganese-oxo clusters.

Structural motifs and topological representation of Mn coordination clusters

Polynuclear coordination clusters have become of particular interest in recent times as a result of their relevance to bioinorganic chemistry and to the special area of molecule-based magnetic materials where cluster compounds behave as single-molecule magnets (SMMs). In this review we have focused on describing Mn coordination cluster complexes. Adopting our topological approach for the description of coordination clusters we present a means of classifying the structural motifs found in manganese clusters which range in nuclearity from 5 to 84, as well as some representative heterometallic Mn-M (M = K, Na, Ca, Sr, Ln) cluster complexes that have been reported. This sheds new light on the classification of the types of core structure accessible which, in turn, provides a useful means for developing the so-far missing magneto-structural correlation algorithm for these finite 0-D systems (212 references).

Self-Assembly and Anion-Exchange Properties of a Discrete Cage and 3D Coordination Networks Based on Cage Structures

By using tridentate ligand 4-(3-pyridinyl)-1,2,4-triazole (pytrz), cage-like complexes of {[Cu(mu2-pytrz)2](ClO4)(SO4)0.5C2H5OH.0.25 H2O}6 (1), {[Cu3(mu3-pytrz)4(mu2-Cl)2(H2O)2](ClO4)2Cl(2).2 H2O}n (2), and {[Cu3(mu3-pytrz)3(mu3-O)(H2O)3](ClO4)2.5(BF4)(1.5)5.25 H2O}n (3) have been synthesized with different copper(II) salts. Complex 1 represents the second example of a M6L12 metal-organic octahedron with an overall Th symmetry. Complex 2 is constructed from a 3(8) cage-building unit (CBU) and each CBU connects six neighboring cages to give the first 3D metal-organic framework (MOF) based on octahedral M6L12. Complex 3 is built from Cu24(pytrz)12 CBUs with the trinuclear copper clusters serving as second building units (SBUs) and decorating each corner of the M24L12 polyhedron. The Cu24(pytrz)12 building unit is linked by extra ligands to give an extended 3D framework that has the formula Cu24(pytrz)24 and possesses a CaB6 topology. The mixed anions ClO4- and BF4- in 3 are both included in the inner cavity of the cage and can be completely exchanged by ClO4- through the open windows of the cage, as evidenced by the crystal structure of the 3D MOF {[Cu3(mu3-pytrz)3(mu3-O)(H2O)3](ClO4)(4)4.5 H2O}n (4). Complex 4 can also be synthesized when employing 1 as a precursor in an extensive study of the anion-exchange reaction. This represents the first successful conversion of a discrete cage into a 3D coordination network based on a cage structure. Complex 2 remains invariable during anion-exchange reactions because uncoordinated Cl- ions are located in the comparatively small inner cavity.

A self-assembled hexadecanuclear 4 × [2 × 2] Mn(ii)16square grid from a pyridazine bis(hydrazone) ligand: synthesis, structure and magnetism

A compartmentalized {4 x[2 x 2]} Mn(II)16 antiferromagnetically coupled square grid results from the self-assembly reaction of a tetratopic pyridazine bis(hydrazone) ligand and Mn(II).

Dinuclear versus tetranuclear cluster formation in zinc(II) nitrate/di-2-pyridyl ketone chemistry: synthetic, structural and spectroscopic studies

The use of di-2-pyridyl ketone, (py)2CO, in zinc(II) nitrate chemistry has yielded a dinuclear complex and a cationic tetranuclear cluster. The 1:1 Zn(NO3)2.4H2O/(py)2CO reaction system in EtOH gives [Zn2(NO3)2{(py)2C(OEt)O}2].0.5H2O (1.0.5H2O), whereas the same reaction system in MeCN yields [Zn4(NO3)3{(py)2C(OH)O}4(H2O)](NO3) (2). The monoanionic derivatives of the hemiacetal and the gem-diol forms of di-2-pyridyl ketone have been derived from the ZnII-mediated addition of solvent (EtOH, H2O involved in MeCN) on the carbonyl group of (py)2CO. Each (py)2C(OEt)O- ion functions as an eta1:eta2:eta1:mu2 ligand in 1.0.5H2O chelating the two ZnII atoms through the 2-pyridyl nitrogen atoms and the common bridging, deprotonated oxygen atom; one asymmetric chelating nitrate completes six coordination at each metal center. The tetranuclear cluster cation of 2 has a cubane topology with the ZnII ions and the deprotonated oxygen atoms from the four eta1:eta3:eta1:mu3 (py)2C(OH)O- ligands occupying alternate vertices. Three monodentate nitrates and one aqua ligand complete the sixth coordination site at the metal ions. The two complexes have been characterized by IR and far-IR spectroscopies. Characteristic bands are discussed in terms of the known structures and the coordination modes of the nitrato ligands. Upon excitation at 371 nm, complex 2 displays blue photoluminescence in the solid state at room temperature with two emission maxima at 430 and 455 nm.

2004 Alcan Award LectureFrom dinuclear to triakontahexanuclear complexes — Adventures in supramolecular coordination chemistry

Polynuclear coordination complexes result from the interplay between the arrangement of the binding sites of a ligand, and their donor content, and the coordination preferences of the metal ion involved. Rational control of the ligand properties, such as denticity, geometry, and size, can lead to large, and sometimes predictable, polynuclear assemblies. This Alcan Award Lecture highlights our "adventures" with polynucleating ligands over the last 25 years, with examples ranging from simple dinucleating to more exotic high-denticity ligands. Complexes with nuclearities ranging from 2 to 36 have been produced, many of which have novel magnetic, electrochemical, and spectroscopic properties. Self-assembly strategies using relatively simple "polytopic" ligands have been very successful in producing high-nuclearity clusters in high yield. For example, linear "tritopic" ligands produce M9 (M = Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II)) [3 × 3], flat grid-like molecules, which have quantum dot-like arrays of nine closely spaced metal centers in electronic communication. Some of these grids are discussed in terms of their novel magnetic and electrochemical properties, and also as multistable nanometer-scale platforms for potential molecular device behaviour. Bigger ligands with extended arrays of coordination pockets, and the capacity to self-assemble into much larger grids, are highlighted to illustrate our current and longer term goals of generating polymetallic molecular two-dimensional layers on surfaces.Key words: Alcan Award Lecture, transition metal, polynuclear, structure, magnetism, electrochemistry, surface studies, molecular device.

Copper(II) complexes of a series of alkoxy diazine ligands: mononuclear, dinuclear, and tetranuclear examples with structural, magnetic, and DFT studies

Picolyl hydrazide ligands have two potentially bridging functional groups (micro-O, micro-N-N) and consequently can exist in different coordination conformers, both of which form spin-coupled polynuclear coordination complexes, with quite different magnetic properties. The complex [Cu(2)(POAP-H)Br(3)(H(2)O)] (1) involves a micro-N-N bridge (Cu-N-N-Cu 150.6 degrees ) and exhibits quite strong antiferromagnetic coupling (-2J = 246(1) cm(-)(1)). [Cu(2)(PZOAPZ-H)Br(3)(H(2)O)(2)] (2) has two Cu(II) centers bridged by an alkoxide group with a very large Cu-O-Cu angle of 141.7 degrees but unexpectedly exhibits quite weak antiferromagnetic exchange (-2J = 91.5 cm(-)(1)). This is much weaker than anticipated, despite direct overlap of the copper magnetic orbitals. Density functional calculations have been carried out on compound 2, yielding a similar singlet-triplet splitting energy. Structural details are reported for [Cu(2)(POAP-H)Br(3)(H(2)O)] (1), [Cu(2)(PZOAPZ-H)Br(3)(H(2)O)(2)] (2), [Cu(2)(PAOPF-2H)Br(2)(DMSO)(H(2)O)].H(2)O (3), [Cu(4)(POMP-H))(4)](NO(3))(4).2H(2)O (4), and PPOCCO (5) (a picolyl hydrazide ligand with a terminal oxime group) and its mononuclear complexes [Cu(PPOCCO-H)(NO(3))] (6) and [Cu(PPOCCO-H)Cl] (7). Compound 1 (C(12)H(13)Br(3)Cu(2)N(5)O(4)) crystallizes in the monoclinic system, space group P2(1)/c, with a = 15.1465(3) A, b = 18.1848(12) A, c = 6.8557(5) A, beta = 92.751(4) degrees, and Z = 4. Compound 2 (C(10)H(13)Br(3)Cu(2)N(7)O(4)) crystallizes in the triclinic system, space group P, with a = 9.14130(1) A, b = 10.4723(1) A, c = 10.9411(1) A, alpha = 100.769(1), beta = 106.271(1) degrees, gamma = 103.447(1) degrees, and Z = 2. Compound 3 (C(23)H(22)Br(2)Cu(2)N(7)O(5.5)S) crystallizes in the monoclinic system, space group P2(1)/c, with a = 12.406(2) A, b = 22.157(3) A, c = 10.704(2) A, beta = 106.21(1) degrees, and Z = 4. Compound 4(C(52)H(48)Cu(4)N(20)O(18)) crystallizes in the monoclinic system, space group P2(1)/n, with a = 14.4439(6) A, b = 12.8079(5) A, c = 16.4240(7) A, beta = 105.199(1) degrees, and Z = 4. Compound 5 (C(15)H(14)N(4)O(2)) crystallizes in the orthorhombic system, space group Pna2(1), with a = 7.834(3) A, b = 11.797(4) A, c = 15.281(3) A, and Z = 4. Compound 6(C(15)H(13)CuN(5)O(5)) crystallizes in the monoclinic system, space group P2(1)/c, with a = 8.2818(9) A, b = 17.886(2) A, c = 10.828(1) A, beta = 92.734(2) degrees, and Z = 4. Compound 7 (C(15)H(13)CuClN(4)O(2)) crystallizes in the orthorhombic system, space group Pna2(1), with a = 7.9487(6) A, b = 14.3336(10) A, c = 13.0014(9) A, and Z = 4. Density functional calculations on PPOCCO are examined in relation to the anti-eclipsed conformational change that occurs on coordination to copper(II).

Self-assembled supramolecular M9 (Mn(II), Fe(III), Zn(II)), M5 (Fe(III)), and [M3]2 (Pb(II)) complexes: structural, magnetic, and Mössbauer properties

The tritopic ligand 2poap self-assembles in the presence of Zn(NO(3))(2) and Fe(NO(3))(3) to form homoleptic [3 x 3] nonanuclear M(9) (M = Zn(II), Fe(III)) square grid structures and with Pb(ClO(4))(2) to form a dimerized linear trinuclear [Pb(3)](2) structure. Cl2poap and Cl2poapz form self-assembled homoleptic [3 x 3] Mn(II)(9) square grids with Mn(ClO(4))(2) and Mn(NO(3))(2), respectively, but an unusual incompletely metalated Fe(III)(5) square grid is formed on reaction of Cl2poap with Fe(ClO(4))(3). X-ray structures are reported for [Mn(9)(Cl2poap-2H)(6)](ClO(4))(6).10H(2)O (3), [Mn(9)(Cl2poapz-2H)(6)] (NO(3))(6).22H(2)O (4), [Zn(9)(2poap-2H)(3)(2poap-H)(3)](NO(3))(9).24H(2)O (5), [Pb(3)(2poap-2H) (ClO(4))(4)](2).8H(2)O (6), and [Fe(5)(Cl2poap-H)(6)](ClO(4))(9).34.5H(2)O (7). Compound 3 crystallized in the monoclinic system, space group P(-)1, with a = 18.179(1) A, b = 18.857(1) A, c = 25.871(2) A, alpha = 70.506(2) degrees, beta = 86.440(1) degrees, gamma = 75.175(2) degrees, and z = 2. Compound 4 crystallized in the monoclinic system, space group P(-)1, with a = 16.900(2) A, b = 20.02393) A, c = 25.663() A, alpha = 84.743(3) degrees, beta = 84.885(2) degrees, gamma = 67.081(2) degrees, and z = 2. Compound 5 crystallized in the monoclinic system, space group P(-)1, with a = 18.482(1) A, b = 18.774(1) A, c = 28.112(2) A, alpha = 104.020(1) degrees, beta = 97.791(1) degrees, gamma = 117.036(1) degrees, and z = 2. Compound 6 crystallized in the monoclinic system, space group P(-)1, with a = 10.0513(6) A, b = 11.0958(6) A, c = 17.334(1) A, alpha = 100.932(1) degrees, beta = 100.387(1) degrees, gamma = 94.565(1) degrees, and z = 2. Compound 7 crystallized in the monoclinic system, space group P(-)1, with a = 19.164(1) A, b = 19.587(2) A, c = 26.673(2) A, alpha = 76.430(2) degrees, beta = 78.834(2) degrees, gamma = 64.973(1) degrees, and z = 2. Compound 3 exhibits intramolecular antiferromagnetic exchange within the nonanuclear [Mn(9)(mu-O)(12)] grid structure (J = -4.6 cm(-1)), while the analogous nonanuclear complex [Fe(9)(2poap-2H)(6)](NO(3))(15).18H(2)O (8) is dominated by intramolecular antiferromagnetic coupling at high temperatures but exhibits a low-temperature feature indicative of additional ferromagnetic interactions. The isolated pentanuclear Fe(5) [4 + 1] square grid in 7, with distant Fe-Fe bridging, exhibits very weak antiferromagnetic coupling (J = -0.2 cm(-1)). Mössbauer spectroscopy data are consistent with high-spin Fe(III)(9) and Fe(III)(5) structures.