Structural and magnetic characterization of calcium copper formates, CaCu(HCOO)4 and Ca2Cu(HCOO)6: two new one-dimensional ferromagnetic bis(μ-oxo-ligand)-bridged chains

Abstract

The structures of two novel calcium and copper formates, CaCu(HCOO)4 (1) and Ca2Cu(HCOO)6 (2), have been determined by X-ray methods. Both formates crystallize in monoclinic systems, space groups P2/c (1) and C2/c (2), with Z = 2 (1) and Z = 4 (2). The dimensions of the cells are a = 7.300 (2) Å, b = 8.493 (2) Å, c = 6.449 (2) Å, and β = 97.57 (1)° for (1) and a = 22.296 (2) Å, b = 8.803 (2) Å, c = 6.377 (4) Å, and β = 101.00 (5)° for (2). Least-squares refinements of 595 (1) and 934 (2) reflections (I > 3σ) and 71 (1) and 106 (2) parameters gave a final R of 0.027 for (1) and 0.024 for (2). In both cases the structure involves chains of bis(μ-formate)-bridged copper(II) ions connected to calcium chains through formate bidentate groups. The metallic chains run practically parallel to the c axis and alternate along the a axis giving ...-Ca-Cu-Ca-... (1) and ...-Ca-Ca-Cu-Ca-Ca-... (2) sequences. Magnetic susceptibility measurements show a behavior typical of infinite arrays of spins ferromagnetically coupled. Single-crystal electron paramagnetic resonance spectroscopic data are characteristic of one-dimensional magnetic materials with line widths following a [(3 cos2 θ) - 1]4/3 dependence. © 1992 American Chemical Society.