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

The compounds 3D-{(Ph4P)2[ZnCu3(Hmesox)3Cl]·2.5H2O} (1) and 3D-{(Ph4P)2[NiCu3(Hmesox)3Cl]·2.5H2O} (2) have been prepared and their structure and magnetic properties investigated (H4mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are obtained by means of the same procedure followed to prepare 3D-{(Ph4P)2[MnCu3(Hmesox)3Cl]·3.5H2O}and 3D-{(Ph4P)2[CoCu3(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 {Cu3(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{Cu3(C3HO6)3Cl}]2n− and [Ni{Cu3(C3HO6)3Cl}]2n−, 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(S1S2 + S2S3 + S1S3), 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 Tc 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.

Graphical abstractThe {Cu3(Hmesox)3Cl}4− metalloligand is a good quality SBU for the preparation of high-dimensional magnetic MOFs since it has a S = 3/2 spin ground state, suitable bridging groups to mediate efficiently the magnetic coupling and to give rise to highly correlated high-dimensional frameworks.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A ferromagnetically coupled secondary building unit. ► A rational synthetic procedure for the synthesis of chiral molecule-based magnets. ► Two heterometallic MOFs with chiral 3D structures. ► A molecule based magnet with Tc of 7.0 K.