Crystal Structures and Magnetic Properties of 2,3,5,6-Tetrakis(2-pyridyl)pyrazine (tppz)-Containing Copper(II) Complexes

Abstract

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, ...

Synthesis, spectroscopic characterization, X-ray structure, and DFT calculations of [Cu(tppz)(SCN)2]

“…The non-planarity of the pyrazine ring is unexceptional. It has been reported for the related structures [20,[23][24][25], and the factor responsible for destabilizing the planar geometry of the pyrazine ring has a pure electronic origin [38].…”

“…It has been also established that tppz exhibits a remarkable efficiency to mediate magnetic interactions between paramagnetic centers separated by more than 6.4 Å . The largest antiferromagnetic interaction between copper(II) ions has been found in the dinuclear complexes [Cu 2 10 ] n structures [20,[23][24][25].…”

Crystal structure of aquadiazidobipyridylcopper(II), Cu(H2O)(N3)2(C5H5N)2

“…Asubstantial amount of copper(II) azido complexes with neutral pyridine derivative ligands have been prepared, structurally characterized and shown to have awide variety of compositions, solid state stereochemistry and varying degrees of oligomerization [1][2][3][4].…”

Synthesis and spectroscopic characterization of tin(II) and tin(IV) complexes containing 2,3,5,6-tetrakis(alpha-pyridyl)pyrazine as a bridging ligand

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The seven chelating modes hitherto encountered for TPP are illustrated in Figure 1. The reactivity of this ligand towards transition metal species has attracted considerable attention over the past twenty years.…”

“…The reactivity of this ligand towards transition metal species has attracted considerable attention over the past twenty years. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, studies of reactions between TPP and main group metal compounds are absent in the literature. Owing to this paucity of information, we decided to investigate the reactivity and coordinating behavior of TPP towards Sn(II) and Sn(IV) compounds, namely SnCl 2 , SnX 4 (X = Cl or Br), SnRCl 3 (R = Ph or Me), and SnPh 2 Cl 2 .…”