From a square core to square opening: structural diversity and magnetic properties of the oxo-bridged [CrNb] complexes

• Published in: Dalton transactions : an international journal of inorganic chemistry 2018-03, Vol.47 (12), p.4183-419
• Main Authors: Juri, Marijana, Androš Dubraja, Lidija, Popovi, Jasminka, Mol anov, Krešimir, Tori, Filip, Paji, Damir, Lon ari, Ivor
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Carbonyls; Chemical bonds; Coupling (molecular); Diamagnetism; Diffraction; Hydrogen bonding; Infrared spectroscopy; Magnetic properties; Magnetization; Mathematical analysis; Single crystals; X ray powder diffraction
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt04724j

Three heterometallic oxo-bridged compounds, [Cr 2 (phen) 4 (μ-O) 4 Nb 2 (C 2 O 4 ) 4 ]·2H 2 O ( 1 ; phen = 1,10-phenanthroline), [Cr 2 (terpy) 2 (H 2 O) 2 (μ-O) 4 Nb 2 (C 2 O 4 ) 4 ]·4H 2 O ( 2 ; terpy = 2,2′;6′,2′′-terpyridine) and [Cr(terpy)(C 2 O 4 )(H 2 O)][Cr 2 (terpy) 2 (C 2 O 4 ) 2 (μ-O) 2 Nb(C 2 O 4 ) 2 ]·3H 2 O ( 3 ), have been synthesized using a building block approach and characterized by IR spectroscopy, single-crystal and powder X-ray diffraction, magnetization measurements, and DFT calculations. The molecular structures of 1 and 2 , crystallizing in P 4 2 2 1 2 and P 2 1 / n space groups, respectively, contain a square-shaped {Cr III 2 (μ-O) 4 Nb V 2 } unit, while that of complex salt 3 ( P 1&cmb.macr; space group) consists of a mononuclear cation containing Cr III and trinuclear anions in which two Cr III ions are bridged by a -O-Nb V -O- fragment. Besides hydrogen-bonding patterns resulting in a 1D- or 3D-supramolecular arrangement in 1-3 , an unusual intermolecular contact has been noticed between parallel oxalate moieties occurring due to the electrostatic attraction of electron-rich carbonyl oxygen and severely electron-depleted carbon atoms in the crystal packing of 2 . The antiferromagnetic coupling observed in all three compounds, determined from magnetization measurements ( J = −13.51(2), −8.41(1) and −7.44(4) cm −1 for 1 , 2 and 3 , respectively) and confirmed by DFT calculations, originates from two Cr III ions with spin 3/2 interacting through diamagnetic -O-Nb V -O- bridge(s). Three oxo-bridged [Cr III Nb V ] compounds exhibit antiferromagnetic coupling between Cr III ions mediated through the diamagnetic -O-Nb V -O- bridge, as observed by magnetization measurements and DFT calculations.