ABSTRACT
The copper(II) complexes of protonated pentadentate Schiff-base ligands with [Cu(H(2)L(n))](ClO(4))(2) formula (n = 3-6, 3-6) have been synthesized and characterized (H(2)L(3) = N-((2-methylimidazol-4-yl)methylene)-3-aminpropyl-N'-((2-methylimidazol-4-yl)methylene)-4'-aminobutylamine, H(2)L(4) = N-((2-phenylimidazol-4-yl)methylene)-3-aminpropyl-N'-((2-phenyl-imidazol-4-yl)methylene)-4'-aminobutylamine, H(2)L(5) = N,N'-bis((2-phenylimidazol-4-yl)methylene)-3,3'-diaminodipropylmethylamine, H(2)L(6) = N-((2-methylimidazol-4-yl)methylene)-2-aminoethyl-N'-((2-methylimidazol-4-yl)methylene)-3'-aminopropylamine. The mono-deprotonated complexes 3', 4', and 5' contain one imidazole and one imidazolate groups per unit and are Delta (clockwise) or Lambda (anticlockwise) enantiomorphs due to the spiral arrangement of the ligand around copper(II) ion. They function as chiral building components for a self-assembly process resulting from the formation of hydrogen bonds between the imidazole and imidazolate groups of adjacent units to yield 1D zigzag-chain structures. The distance between hydrogen-bonded nitrogen atoms is 2.81(2), 2.832(9), and 2.875(9) Å for 3', 4', and 5', respectively. The crystal lattice of 3' yielded either.DeltaDeltaDelta. or.LambdaLambdaLambda. isotactic 1D zigzag-chains, while the crystal lattices of 4' and 5' yielded.DeltaLambdaDeltaLambda. syndiotactic 1D zigzag-chains. In 3', two adjacent methyl groups at the 2-position connected by hydrogen bond array in the same direction, thus allowing homochiral aggregation of the complex molecules in a 1D chain. On the other hand, in 4' and 5', two adjacent bulky phenyl groups require opposite orientations, thus allowing heterochiral aggregation. Enantioselective aggregation with homochirality or heterochirality can thus be controlled with suitable substituents. While its mononuclear precursor 6 is pentacoordinated with the N(5) donor set of the pentadentate ligand H(2)L(6), the deprotonated complex 6' has an imidazolate-bridged tetranuclear cyclic structure with a Cu-Cu distance of 6.086(2) Å. The ligand in 6' is tetradentate and includes an hexahydropyrimidine ring resulting from a deprotonation induced rearrangement reaction.
ABSTRACT
The manganese(III) complex K[MnL(py)(2)].py (H(4)L = 1,2-bis(2-hydroxybenzamido)benzene, py = pyridine) reacted as a ligand complex at the two phenoxo oxygen atoms with metal(II) ion and 2,2'-bipyridine to give a series of heterometal complexes [Mn(MeOH)L(OH)M(bpy)](2) (M(II) = Zn (1); Cu (2); Ni (3); Mn (4)). X-ray structures were determined 1, C(68)H(74)N(8)O(18)Mn(2)Zn(2): a = 12.367(3) Å, b = 12.844(2) Å, c = 12.262(2) Å, alpha = 106.58(1) degrees, beta = 117.89(1) degrees, gamma = 78.57(2) degrees, triclinic, P&onemacr;, and Z = 1. 2, C(68)H(74)N(8)O(18)Mn(2)Cu(2): a = 13.447(1) Å, b = 12.670(2) Å, c = 21.732(1) Å, beta = 107.076(5) degrees, monoclinic, P2(1)/n, and Z =2. 3, C(68)H(74)N(8)O(18)Mn(2)Ni(2): a = 12.358(3) Å, b = 12.847(3) Å, c = 12.315(3) Å, alpha = 106.63(2) degrees, beta = 118.71(1) degrees, gamma = 78.32(2) degrees, triclinic, P&onemacr;, and Z = 1. 4, C(66)H(66)N(8)O(16)Mn(4): a = 12.511(2) Å, b = 21.129(3) Å, c = 12.811(1) Å, beta = 110.12(1) degrees, monoclinic, P2(1)/n, and Z = 2. The X-ray analyses confirmed that each of the crystals consists of an incomplete double-cubane molecule with a [Mn(2)M(2)O(6)] core, in which two M(II) ions are bridged by two hydroxo groups to form a planar dinuclear moiety bridged by di-&mgr;-hydroxo groups [(bpy)M(OH)(2)M(bpy)](2+) and the dinuclear moiety is sandwiched between two Mn(III) complexes [Mn(MeOH)L](-). The Mn(III) ion and the dinuclear M(II) moiety are triply bridged by the one hydroxo oxygen of the dinuclear moiety and two phenoxo oxygen atoms of the Mn(III) ligand complex. The two phenoxo oxygen atoms of the Mn(III) ligand complex coordinate as an axial ligand to two independent metal(II) ions of the dinuclear moiety. The magnetic susceptibilities of 1-4 were measured in the temperature range of 2-300 K. All the Mn(III) ions in these complexes are in a high-spin state of S(Mn) = 2 with a d(4) electronic configuration, and the metal(II) ions are in the spin states of S(Zn) = 0, S(Cu) = 1/2, S(Ni) = 1, and S(Mn(II)) = 1/2 (low-spin). The magnetic susceptibility data are well reproduced by the following spin Hamiltonian based on the rhombus spin coupling model with spin (S(1), S(2), S(3), S(4)) = (2, S(M), 2, S(M)), including a zero-field splitting term for the Mn(III) centers: H = g(Mn)beta(S(1) + S(3)).H + g(M)beta(S(2) + S(4)).H - 2J(S(1).S(2) + S(2).S(3) + S(3).S(4) + S(4).S(1)) - 2J'(S(2).S(4)) + D(Mn)[S(1z)(2) + S(3z)(2)], in which g(Mn) and g(M) are the g factors of the Mn(III) and M(II) ions, J and J' are the Mn(III)-M(II) and M(II)-M(II) Heisenberg coupling constants, and D is the zero-field splitting parameter of Mn(III). The calculated best-fit parameters are as follows: g(Mn) = 1.91, g(Cu) = 2.39, J = -4.5 cm(-)(1), J' = -8.1 cm(-)(1), and D(Mn) = -4.9 cm(-)(1) for 2; g(Mn) = 1.97, g(Ni) = 2.23, J = -1.5 cm(-)(1), J' = -2.6 cm(-)(1), and D(Mn) = -5.5 cm(-)(1) for 3; and g(Mn) =1.95, g(Mn(II)) = 2.29, J = -3.5 cm(-)(1), J' = -14.1 cm(-)(1), and D(Mn) = -12.0 cm(-)(1) for 4. The spin frustration due to the incomplete double-cubane structure is discussed.
