Magneto‐structural Studies in Double Chloro‐ and Pseudohalo‐bridged Isomorphic Dinickel(II) Complexes

Abstract

Four new complexes, [NiL(NO 3)]⋅CH 3 OH (1), [Ni 2 L 2 (μ-Cl) 2 ] (2), [Ni 2 L 2 (μ 1,1-NCO) 2 ] (3) and [Ni 2 L 2 (μ 1,1-N 3) 2 ] (4) were synthesized from a tetradentate Schiff base (HL), prepared from the condensation reaction of N,N-dimethyldipropylenetriamine and 5-bromosalicylaldehyde. X-ray crystallography reveals that 2-4 are isostructural and isomorphic dinickel(II) compounds with bridging chloride or pseudohalides. All these three dinickel(II) complexes exhibit ferromagnetic interaction through bridging chloride or pseudohalides and their coupling constants are in the order 4 > 2 > 3, a replication of the average strength of exchange interactions found in such complexes characterised magnetically. Most importantly, compound 3 is a precious addition to the only four known examples of this family, and unprecedented high degree of structural and magnetic resemblances observed in 2-4 is the major achievement of the present work.

Magneto-structural studies on a number of doubly end-on cyanate and azide bridged dinuclear nickel(ii) complexes with {N3O} donor Schiff base ligands

“…The magnetic and relevant crystallographic data of all doubly μ 1,1 -NCO bridged dinuclear Ni II systems as given in Table 3 show the variation of J values in a narrow range of 1.7–9.1 cm −1 . 19–23 Remarkably, unlike azide-bridged systems, the cyanate analogues follow a general trend in which J value increases with increase in bridging angles (Fig. 5, left), similar to theoretical prediction that has been conducted by Ruiz et al for azide analogues.…”

“…In contrast to extensively rich magneto-structurally characterized μ 1,1 -N 3 bridged Ni II systems, only few doubly μ 1,1 -NCO bridged dinuclear Ni II complexes are available in the literature. 19–23 Therefore, the addition of six new examples in this series enriches the field of doubly μ 1,1 -NCO bridged dinuclear Ni II compounds. As can be seen from Table 3 that the magnetic coupling constants are weak compared to azide-bridged systems, which is because of the presence of polarizable π systems and two different N and O donor atoms in cyanate ion, rendering to be a poor magnetic coupler in comparison to azide analogue.…”

“…The Ni–N bond lengths of imine, secondary amine and tertiary amine of the Schiff base ligands span in the range 2.046(2) to 2.239(2) Å in 1–8 , which are comparable to those found in closely related Ni II complexes reported in the literature (Table 2). 17–23,31–51 The central {NiN 2 Ni} core in 1 and 3 is planar with the metal–metal separation and the Ni–N–Ni bridging angles are 3.355(1) and 3.374(1) Å, and 101.00(8)°–101.99(8)°, respectively. Similarly, the metal–metal separations (3.327(1)–3.235(1) Å) in the central {NiN 2 Ni} core structures in 2–8 are very similar as that found in 1 and 3 , but the Ni–N–Ni bridging angles in the range 96.79(9)–99.87(8)° are slightly lower than that found in 1 and 3 .…”

“…24,25 However, going through the only few examples available in the literature, one can assess that cyanate ion with EO bridging mode usually propagates ferromagnetic interaction between Ni II centres in a similar way that azide ion does, but weakly, while a mixed immersion has been observed through EE bridging mode. 17–23…”

“…26 Our recent studies disclosed that Schiff base ligands with N 3 O donor sets derived from condensation of salicylaldehyde or its derivative with N , N -dimethyldipropylenetriamine are capable to produce doubly EO azide or cyanate bridged ferromagnetically coupled dinuclear Ni II complexes. 20,22,23 Therefore, we anticipated that a large numbers of EO cyanate-bridged Ni II complexes can be synthesised using different carbonyl components of the Schiff base ligands derived from this triamine, which not only add few more examples to the only limited members of such complexes reported in the literature, but it is a possibility to establish precise magneto-structural corelation in this system. Consequently, in this present endeavour, a series of tetradentate N 3 O donor Schiff base (HL 1 –HL 6 , Scheme 1), derived from the condensation reaction of N , N -dimethyldipropylenetriamine with different carbonyl components, namely 2-hydroxy-3-methoxy-5-methylbenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 5-nitrosalicylaldehyde, 5-bromo-3-methoxysalicylaldehyde, 4-(diethylamino)salicylaldehyde and 2-hydroxy-1-naphthaldehyde, have been utilised to prepare closely related EO cyanate-bridged Ni II complexes.…”