ABSTRACT
"Tritopic" picolinic dihydrazone ligands with tridentate coordination pockets are designed to produce homoleptic [3 x 3] nonanuclear square grid complexes on reaction with transition-metal salts, and many structurally documented examples have been obtained with Mn(II), Cu(II), and Zn(II) ions. However, other oligomeric complexes with smaller nuclearities have also been discovered and identified structurally in some reactions involving Fe(II), Co(II), Ni(II), and Cu(II), with certain tritopic ligands. This illustrates the dynamic nature of the metal-ligand interaction and the conformationally flexible nature of the ligands and points to the possible involvement of some of these species as intermediates in the [3 x 3] grid formation process. Examples of mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear species involving Fe(II), Co(II), Ni(II), and Cu(II) salts with a series of potentially heptadentate picolinic dihydrazone ligands with pyrazine, pyrimidine, and pyridine end groups are described in the present study. Iron and cobalt complexation reactions are complicated by redox processes, which lead to mixed-oxidation-state Co(II)/Co(III) systems when starting with Co(II) salts, and reduction of Fe(III) to Fe(II) when starting with Fe(III). Magnetic exchange within the polynuclear structural frameworks is discussed and related to the structural features.
ABSTRACT
Complete donor-induced alkylaluminate cleavage of halfmetallocene complex Cp*Y(AlMe4)2, that is, treatment of Cp*Y(AlMe4)2 with 2 equiv of diethyl ether, produces [Cp*Y(mu2-Me)2]3 in high yield (95%). In contrast, the equimolar reaction of Cp*Y(AlMe4)2 with diethyl ether reproducibly formed complex [Cp*4Y4(mu2-CH3)2{(CH3)Al(mu2-CH3)2}4(mu4-CH)2] in low yield (10-30%) via a multiple C-H bond activation. The synthesis of the heterooctametallic yttrium-aluminum-methine cluster was also accomplished in moderate yield (47%) by the equimolar reaction of discrete Cp*Y(AlMe4)2 and [Cp*Y(mu2-Me)2]3 in the absence of any donor solvent and "free" AlMe3. This gives strong evidence that preformed heterometal-bridged Y-CH3-Al moieties are prone to multiple hydrogen abstraction in the presence of a highly basic reagent such as [Cp*Y(mu2-Me)2]3. The monocylopentadienyl complexes [Cp*Y(mu2-Me)2]3 and [Cp*4Y4(mu2-CH3)2{(CH3)Al(mu2-CH3)2}4(mu4-CH)2] were structurally characterized.
ABSTRACT
Mn(II)9 grid complexes with a [Mn9(mu-O)12] core, obtained by self-assembly of a series of tritopic picolinic dihydrazone ligands with Mn(II) salts, have been oxidized by both chemical and electrochemical methods to produce mixed oxidation state systems. Examples involving [Mn(III)3Mn(II)6] and [Mn(III)4Mn(II)5] combinations have been produced. Structures are reported for [Mn9(2poap-2H)6](NO3)6.14H2O (1), [Mn9(2poap-2H)6](ClO4)10.10H2O (3), and [Mn9(Cl2poap-2H)6](ClO4)9.14H2O.3CH3CN (10). Structural studies show distinct contraction of the corner grid sites on oxidation, with overall magnetic properties consistent with the resulting changes in electron distribution. Antiferromagnetic exchange in the outer ring of eight metal centers creates a ferrimagnetic subunit, which undergoes antiferromagnetic coupling to the central metal, leading to S=1/2 (3) and S2/2 (10) ground states. Two moderately intense absorptions are observed on oxidation of the Mn(II) grids in the visible and near-infrared (1000 nm, 700 nm), associated with charge transfer transitions (LMCT, IVCT respectively). Compound 1 crystallized in the monoclinic system, space group P2 1/n, with a=21.308(2) A, b=23.611(2) A, c=32.178(3) A, beta=93.820(2) degrees . Compound 3 crystallized in the tetragonal system, space group I, with a=b=18.44410(10) A, c = 24.9935(3) A. Compound 10 crystallized in the triclinic system, space group P, with a=19.1150(10) A, b=19.7221(10) A, c=26.8334(14) A, alpha=74.7190(10) degrees, beta=77.6970(10) degrees, gamma=64.7770(10) degrees. The facile oxidation of the Mn(II)9 grids is highlighted in terms of their potential use as molecular based platforms for switching and data storage.
ABSTRACT
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).
ABSTRACT
A series of [3 x 3] Mn(II)(9), antiferromagnetically coupled, alkoxide-bridged, square grid complexes, derived from a group of "tritopic" dihydrazide ligands, is described. The outer ring of eight Mn(II) centers in the grids is isolated magnetically from the central Mn(II) ion, leading to an S = 0 ground state for the ring, and an S = 5/2 ground state overall in each case. Exchange in the Mn(II)(8) ring can be represented by a 1D chain exchange model. Rich electrochemistry displayed by these systems has led to the production of Mn(II)/Mn(III) mixed-oxidation-state grids by both electrochemical and chemical means. Structures are reported for [Mn(9)(2poap)(6)](C(2)N(3))(6).10H(2)O (1), [Mn(9)(2poap)(6)](2)[Mn(NCS)(4)(H(2)O)](2)(NCS)(8).10H(2)O (2), [Mn(9)(2poapz)(6)](NO(3))(6).14.5H(2)O (3), [Mn(9)(2popp)(6)](NO(3))(6).12H(2)O (4), [Mn(9)(2pomp)(6)](MnCl(4))(2)Cl(2).2CH(3)OH.7H(2)O (5), and [Mn(9)(Cl2poap)(6)](ClO(4))(9).7H(2)O (6). Compound 1 crystallized in the tetragonal system, space group P4(2)/n, with a = 21.568(1) A, c = 16.275(1) A, and Z = 2. Compound 2 crystallized in the triclinic system, space group P, with a = 25.043(1) A, b = 27.413(1) A, c = 27.538(2) A, alpha = 91.586(2) degrees, beta = 113.9200(9) degrees, gamma = 111.9470(8) degrees, and Z = 2. Compound 3 crystallized in the triclinic system, space group P, with a = 18.1578(12) A, b = 18.2887(12) A, c = 26.764(2) A, alpha = 105.7880(12) degrees, beta = 101.547(2) degrees, gamma = 91.1250(11) degrees, and Z = 2. Compound 4 crystallized in the tetragonal system, space group P4(1)2(1)2, with a = 20.279(1) A, c = 54.873(6) A, and Z = 4. Compound 5 crystallized in the tetragonal system, space group I, with a = 18.2700(2) A, c = 26.753(2) A, and Z = 2. Compound 6 crystallized in the triclinic system, space group P, with a = 19.044(2) A, b = 19.457(2) A, c = 23.978(3) A, alpha = 84.518(3) degrees, beta = 81.227(3) degrees, gamma = 60.954(2) degrees, and Z = 2. Preliminary surface studies on Au(111), with a Mn(II) grid complex derived from a sulfur-derivatized ligand, indicate monolayer coverage via gold-sulfur interactions, and the potential for information storage at high-density levels.
ABSTRACT
The structures and magnetic properties of self-assembled copper(II) clusters and grids with the "tritopic" ligands 2poap (a), Cl2poap (b), m2poap (c), Cl2pomp (d), and 2pomp (e) are described [ligands derived by reaction of 4-R-2,6-pyridinedicarboxylic hydrazide (R = H, Cl, MeO) with 2-pyridinemethylimidate (a-c, respectively) or 2-acetylpyridine (d, R = Cl; e, R = H)]. Cl2poap and Cl2pomp self-assemble with Cu(NO(3))(2) to form octanuclear "pinwheel" cluster complexes [Cu(8)(Cl2poap-2H)(4)(NO(3))(8)].20H(2)O (1) and [Cu(8)(Cl2pomp-2H)(4)(NO(3))(8)].15H(2)O (2), built on a square [2 x 2] grid with four pendant copper arms, using "mild" reaction conditions. Similar reactions of Cl2pomp and 2pomp with Cu(ClO(4))(2) produce pinwheel clusters [Cu(8)(Cl2pomp-2H)(4)(H(2)O)(8)](ClO(4))(8).7H(2)O (3) and [Cu(8)(2pomp-2H)(4)(H(2)O)(8)](ClO(4))(8) (4), respectively. Heating a solution of 1 in MeOH/H(2)O produces a [3 x 3] nonanuclear square grid complex, [Cu(9)(Cl2poap-H)(3)(Cl2poap-2H)(3)](NO(3))(9).18H(2)O (5), which is also produced by direct reaction of the ligand and metal salt under similar conditions. Reaction of m2poap with Cu(NO(3))(2) produces only the [3 x 3] grid [Cu(9)(m2poap-H)(2)(m2poap-2H)(4)](NO(3))(8).17H(2)O (6) under similar conditions. Mixing the tritopic ligand 2poap with pyridine-2,6-dicarboxylic acid (picd) in the presence of Cu(NO(3))(2) produces a remarkable mixed ligand, nonanuclear grid complex [Cu(9)(2poap-H)(4)(picd-H)(3)(picd-2H)](NO(3))(9).9H(2)O (7), in which aromatic pi-stacking interactions are important in stabilizing the structure. Complexes 1-3 and 5-7 involve single oxygen atom (alkoxide) bridging connections between adjacent copper centers, while complex 4 has an unprecedented mixed micro-(N-N) and micro-O metal ion connectivity. Compound 1 (C(76)H(92)N(44)Cu(8)O(50)Cl(4)) crystallizes in the tetragonal system, space group I, with a = 21.645(1) A, c = 12.950(1) A, and Z = 2. Compound 2 (C(84)H(88)N(36)O(44)Cl(4)Cu(8)) crystallizes in the tetragonal system, space group I, with a = 21.2562(8) A, c = 12.7583(9) A, and Z = 2. Compound 4 (C(84)H(120)N(28)O(66)Cl(8)Cu(8)) crystallizes in the tetragonal system, space group I4(1)/a, with a = 20.7790(4) A, c = 32.561(1) A, and Z = 4. Compound 7(C(104)H(104)N(46)O(56)Cu(9)) crystallizes in the triclinic system, space group P, with a = 15.473(1) A, b = 19.869(2) A, c = 23.083(2) A, alpha = 88.890(2) degrees, beta = 81.511(2) degrees, gamma = 68.607(1) degrees, and Z = 2. All complexes exhibit dominant intramolecular ferromagnetic exchange coupling, resulting from an orthogonal bridging arrangement within each polynuclear structure.
