A ferromagnetically coupled copper(II) trinuclear secondary building unit as precursor for the preparation of molecule-based magnets

Abstract

The compounds 3D-{(Ph 4P) 2[ZnCu 3(Hmesox) 3Cl]·2.5H 2O} ( 1) and 3D-{(Ph 4P) 2[NiCu 3(Hmesox) 3Cl]·2.5H 2O} ( 2) have been prepared and their structure and magnetic properties investigated (H 4mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are obtained by means of the same procedure followed to prepare 3D-{(Ph 4P) 2[MnCu 3(Hmesox) 3Cl]·3.5H 2O}and 3D-{(Ph 4P) 2[CoCu 3(Hmesox) 3Cl]}, to which 1 and 2 are isostructural as deducted from the X-ray powder diffraction patterns and IR spectra. During the synthesis the {Cu 3(Hmesox) 3Cl} 4− unit is generated which acts as ferromagnetically coupled secondary building unit (SBU) to give 3D chiral networks with (10,3)-a topology, the [Zn{Cu 3(C 3HO 6) 3Cl}] 2 n − and [Ni{Cu 3(C 3HO 6) 3Cl}] 2 n −, in 1 and 2, respectively. The tetraphenylphosphonium cations are located in the voids of the 3D anion framework giving a supramolecular 3D cation net with the same (10,3)-a topology as the anion framework and both can be thought of forming interpenetrating supramolecular and covalent (10,3)-a nets. Because of the different nature of the interpenetrated 3D (10,3)-a frameworks a single crystal of 1 and 2 is chiral and enantiopure. The analysis of the magnetic properties in 1 by means of the isotropic spin Hamiltonian, H = − J( S 1 S 2 + S 2 S 3 + S 1 S 3), reveal a ferromagnetic coupling with J = +11.2 cm −1 in the copper(II) trinuclear unit of 1. Compound 2 exhibits long-range magnetic ordering with a T c of 7.0 K due to a ferrimagnetic coupling between the ferromagnetically coupled copper(II) ions of the trinuclear unit, antiferromagnetically coupled to the Ni(II) ions.