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

• Published in: Inorganic chemistry 2003-12, Vol.42 (26), p.8716-8727
• Main Authors: Carranza, José, Brennan, Conor, Sletten, Jorunn, Clemente-Juan, Juan Modesto, Lloret, Francesc, Julve, Miguel
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic030244v

Four new copper(II) complexes of formula [Cu2(tppz)(dca)3(H2O)]·dca·3H2O (1), [Cu5(tppz)(N3)10] n (2), {[Cu2(tppz)(N3)2][Cu2(N3)6]} n (3), and [Cu(tppz)(N3)2]·0.33H2O (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 [Cu2(tppz)(dca)3(H2O)]+ cations, uncoordinated dca anions, and crystallization water molecules. The copper−copper separation across bis-terdentate tppz is 6.5318(11) Å. 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) Å across bis-terdentate tppz, 3.7174(5) and 3.8477(5) Å across single end-on azido bridges, and from 3.0955(5) to 3.2047(7) Å across double end-on azido bridges. The double dca bridge linking the chains into sheets yields a copper−copper separation of 3.5984(7) Å. The structure of 3 consists of centrosymmetric [Cu2(tppz)(N3)2]2+ and [Cu2(N3)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) Å (across the bis-terdentate tppz ligand) and 3.1034(6) Å (across the double end-on azido bridges), whereas those between the units are 3.6652(4) Å (through the single end-on azido group) and 5.3508(4) Å (through the double end-to-end azido bridges). The structure of complex 4 is built of neutral [Cu(tppz)(N3)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) Å. 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 Ĥ = −J Ŝ A·Ŝ B). An o