Magnetic Coupling through the Carbon Skeleton of Malonate in Two Polymorphs of {[Cu(bpy)(H₂O)][Cu(bpy)(mal)(H₂O)]}(ClO₄)₂ (H₂mal = Malonic Acid; bpy = 2,2‘-Bipyridine)

Abstract

Two polymorphic malonato-bridged copper(II) complexes of formula ([Cu(bpy)(H2O)][Cu(bpy)(mal)(H2O)])-(ClO4)2 (1 and 2) (bpy = 2,2'-bipyridine and mal = malonate dianion) have been prepared and their structures solved by X-ray diffraction methods. Compound 1 crystallizes in the monoclinic space group P2(1)/a, with a = 23.743(3) A, b = 9.7522(5) A, c = 27.731(2) A, beta = 114.580(10) degrees, and Z = 4. Compound 2 crystallizes in the orthorhombic space group Pbcn, with a = 23.700(5) A, b = 25.162(5) A, c = 9.693(5) A, and Z = 4. The structures of 1 and 2 are made up of uncoordinated perchlorate anions and malonate-bridged zigzag copper(II) chains grouped in an isosceles triangle running parallel to the b (1) and c (2) axes. These chains are built by a [Cu(bpy)(mal)(H2O)] unit acting as bis-monodentate ligand toward two [Cu(bpy)(H2O)] adjacent units through its OCCCO skeleton in an anti-anti conformation, whereas the OCO carboxylate bridges exhibit the anti-syn conformation. Compounds 1 and 2 contain four crystallographically independent copper(II) atoms, but the environment of all of them is distorted square pyramidal: the axial position is occupied by a water molecule, whereas the equatorial plane is formed by a chelating bpy and either a bidentate malonate or two carboxylate oxygens from two malonate groups. The equatorial Cu-O(mal) (1.911(4)-1.978(4) (1) and 1.897(5)-1.991(4) A (2)) and Cu-N(bpy) (1.983(4)-2.008(5) (1) and 1.971(6)-2.007(6) A (2)) bonds are somewhat shorter than the axial Cu-O(w) one (2.257(5)-2.524(5) (1) and 2.236(5)-2.505(6) A (2)). The angles subtended at the copper atom by the chelating bpy vary in the ranges 80.9(2)-81.8(2) degrees (1) and 80.4(2)-82.1(2) degrees (2), values which are somewhat smaller than those of the chelating malonate (80.4(2)-82.1(2) degrees (1) and 93.0(2)-93.6(2) degrees (2)). The intrachain copper-copper separations through the OCCCO fragment are 8.227(1) (1) and 8.206(2) A (2), whereas those through the OCO bridging unit are 4.579(1)-5.043(1) (1) and 4.572(2)-5.040(2) A (2). The magnetic behavior of 1 and 2 in the temperature range 2.0-290 K is very close, and it corresponds to an overall ferromagnetic coupling, the chi MT versus T curve exhibiting a maximum at 18 K. The analysis of the magnetic data through a numerical expression derived for the real topology of 1 and 2, that is, chains of isosceles triangles with two intrachain exchange pathways J1 (exchange coupling through the OCO carboxylate) and J2 (exchange coupling through the OCCCO malonate), indicates the occurrence of ferro- (J1 = +4.6 cm-1) and antiferromagnetic couplings (J2 = -4.2 cm-1). The magnetic coupling through these exchange pathways is further analyzed and substantiated by density functional theory calculations on a malonate-bridged trinuclear copper(II) model system.

Syntheses, Structures, and Characterization of Two Manganese(II)‐Aminobenzoic Complexes

“…[8b,9] The few examples involving the antianti mode indicated that this coupling is weakly ferromagnetic or antiferromagnetic. [9,25] Coupling J 1 arises from the double syn-syn carboxyl bridge and gives a weak antiferromagnetic coupling in this case, but coupling J 3 through the single anti-anti carboxyl bridge gives very weak ferromagnetic coupling. The J 1 value is larger than the J 3 value, which shows that the syn-syn carboxyl bridge is more favorable than the anti-anti mode for transmission of the magnetic coupling interaction.…”

A novel three-dimensional malonate-bridged complex {[Cu4(4,4′- bpy)8(mal)2(H2O)4](ClO4)2(H2O)4(CH3OH)2}n

“…The malonate ligand, with two neighbouring carboxylate groups, is a very flexible bridging ligand [2][3][4][5][6][7], because it can adopt several chelating bidentate coordination modes (bidentate chelation, bidentate chelation-unidentate, bidentate chelation-bis (unidentate)) and different carboxylatobridging coordination modes (syn-syn, syn-anti, and antianti) [6]. On the other hand, the malonate ligand occupies one or two coordination positions, allowing the inclusion of other ligands in the coordination sphere of the metal.…”

Liquid-Injection MOCVD of ZrO2 Thin Films using Zirconium Bis(diethlyamido)-bis(di-tert-butylmalonato) as a Novel Precursor

“…Malonate ligands are potentially useful stabilizing ligands for precursor synthesis and their potential has rarely been explored, except for a few examples. [7,8] Malonate ligands are better electron donors and it was anticipated that homoleptic malonate ligands would provide better stability to the resulting complex compared to heteroleptic b-ketoester ligands. In addition, sterically bulky tert-butoxy groups are expected to provide the necessary shielding of the metal center, and at the same time they would act as cleavage points inducing facile thermal decomposition.…”