Synthesis, crystal structure and magnetic properties of a new cyanide-bridged iron(III)–nickel(II) ferromagnetic chain

Abstract

The reaction of the iron(III) unit fac-[Fe{HB(pz) 3}(CN) 3] − [ HB ( pz ) 3 - = hydrotris ( 1 - pyrazolyl ) borate ] as the lithium salt ( 1) with the nickel(II) complex mer-[Ni(dpt)(H 2O) 3](ClO 4) 2 [dpt = dipropylenetriamine] in water affords the heterometallic compound of formula {[Fe III{HB(pz) 3}(CN) 3] 2[Ni II(dpt)]} n · 3 nH 2O ( 2). The structure of 2 has been determined by X-ray diffraction on single crystals and their magnetic properties have been investigated in the temperature range 1.9–300 K. Compound 2 is a zigzag chain compound with regular alternating bis-monodentate [Fe(1){HB(pz) 3}(CN) 3] − units and [Ni(dpt)] 2+ cations, the six coordination around the nickel atom being achieved by the coordination of another [Fe(2){HB(pz) 3}(CN) 3] − group acting as a monodentate end-cap ligand. Magnetic data of 2 show the occurrence of intrachain ferromagnetic coupling ( J = +11.4 cm −1 across bridging cyanide) and weak interchain antiferromagnetic interactions ( J′ ca. −0.07 cm −1). These last ones are responsible for the observed metamagnetic behaviour of 2, the value of the critical field being H c = 700 G. The incipient frequency-dependence of the out-of-phase signal of 2 under applied dc field H > H c that is observed at T < 4.5 K supports the occurrence a slow relaxation of the magnetization, a feature which is reminiscent of the behaviour of the single chain magnets (SCMs). The use of the heteroleptic species [Fe{HB(pz) 3}(CN) 3] − as a ligand toward fully solvated metal ions and coordinatively unsaturated preformed complexes to prepare heterometallic complexes with new spin topologies is analyzed and discussed in the light of the available magneto-structural data.