Anion-directed synthesis of metal-organic frameworks based on 2-picolinate Cu(II) complexes: a ferromagnetic alternating chain and two unprecedented ferromagnetic fish backbone chains

Three new polynuclear copper(II) complexes of 2-picolinic acid (Hpic), {[Cu-2(pic)(3)(H2O)]ClO4}(n) (1), {[Cu-2(pic)(3)(H2O)]BF4}(n) (2), and [Cu-2(pic)3(H2O)(2)(NO3)](n) (3), have been synthesized by reaction of the "metalloligand" [Cu-(pic)(2)] with the corresponding copper(II) salts. The compounds are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. Compounds 1 and 2 are isomorphous and crystallize in the triclinic system with space group P (1) over bar, while 3 crystallizes in the monoclinic system with space group P2(1)/n. The structural analyses reveal that complexes 1 and 2 are constructed by "fish backbone" chains through syn-anti (equatorial-equatorial) carboxylate bridges, which are linked to one another by syn-anti (equatorial-axial) carboxylate bridges, giving rise to a rectangular grid-like two-dimensional net. Complex 3 is formed by alternating chains of syn-anti carboxylate-bridged copper(II) atoms, which are linked together by strong H bonds involving coordinated nitrate ions and water molecules and uncoordinated oxygen atoms from carboxylate groups. The different coordination ability of the anions along with their involvement in the H-bonding network seems to be responsible for the difference in the final polymeric structures. Variable-temperature (2-300 K) magnetic susceptibility measurement shows the presence of weak ferromagnetic coupling for all three complexes that have been fitted with a fish backbone model developed for 1 and 2 (J = 1.74 and 0.99 cm(-1); J' = 0.19 and 0.25 cm(-1), respectively) and an alternating chain model for 3 (J = 1.19 cm(-1) and J' = 1.19 cm(-1))

Physiological and molecular responses to magnesium nutritional imbalance in plants

BackgroundMagnesium (Mg) is pivotal for many biochemical and physiological processes in plants. Mg biological functions include a key role in photosynthesis, in protein synthesis, as well as in nucleotide metabolism. However, Mg nutrition of plants remains little examined compared with other essential elements.ScopeThe review summarizes the current knowledge on physiological targets of Mg imbalances. Recently generated transcriptome profiles in response to Mg shortage and excess are also presented.ConclusionsSugar accumulation in source leaves is a major consequence of Mg shortage that can limit plant growth most probably by down regulation of photosynthesis activity. Newly identified molecular targets of Mg imbalance are appraised in relation to their potential contribution to Mg deficiency phenotypic emergence. In particular a potential role of the circadian clock and change in phytohormones concentration and/or signalling in the orchestration of the Mg deficiency response is possible. The development of markers for incipient Mg deficiency appears to be a challenging taskSCOPUS: ar.jinfo:eu-repo/semantics/publishe