Engineering of flat bands and Dirac bands in two-dimensional covalent organic frameworks (COFs): Relationships among molecular orbital symmetry, lattice symmetry, and electronic-structure characteristics

Two-dimensional covalent organic frameworks (2D-COFs), also referred to as 2D polymer networks, display unusual electronic-structure characteristics, which can significantly enrich and broaden the fields of electronics and spintronics. In this...

Ultrasound-Assisted Synthesis and Crystal Structure of Novel 2D Cd (II) Metal–Organic Coordination Polymer with Nitrite End Stop Ligand as a Precursor for Preparation of CdO Nanoparticles

In the present research, a sonochemical approach was applied to prepare new cadmium(II) coordination 2D polymer, [Cd(L)(NO2)2]n (L = 1,2-bis(1-(pyridin-3-yl)ethylidene)hydrazine) and structurally characterized with various spectroscopic techniques including XRD, elemental analysis, SEM, and IR spectroscopy. The coordination number of cadmium (II) ions is seven (CdN2O5) by two nitrogen atoms from two organic Schiff base ligand and five oxygen of nitrite anions. The 2D sheet structures ended by nitrite anions and the nitrite anion displayed the end-stop role. The comprehensive system showed a three-dimensional structure with several weak interactions. The high-intensity ultrasound is regarded as an easy, environmentally-friendly, and flexible synthetic instrument for the compounds of coordination. CdO NPs was obtained by thermolysing 1 at 180 °C with oleic acid (as a surfactant). Further, the size and morphology of the produced CdO nanoparticles were investigated through SEM.

Versatile Reactivity of MnII Complexes in Reactions with N-Donor Heterocycles: Metamorphosis of Labile Homometallic Pivalates vs. Assembling of Endurable Heterometallic Acetates

Reaction of 2,2′-bipyridine (2,2′-bipy) or 1,10-phenantroline (phen) with [Mn(Piv)2(EtOH)]n led to the formation of binuclear complexes [Mn2(Piv)4L2] (L = 2,2′-bipy (1), phen (2); Piv− is the anion of pivalic acid). Oxidation of 1 or 2 by air oxygen resulted in the formation of tetranuclear MnII/III complexes [Mn4O2(Piv)6L2] (L = 2,2′-bipy (3), phen (4)). The hexanuclear complex [Mn6(OH)2(Piv)10(pym)4] (5) was formed in the reaction of [Mn(Piv)2(EtOH)]n with pyrimidine (pym), while oxidation of 5 produced the coordination polymer [Mn6O2(Piv)10(pym)2]n (6). Use of pyrazine (pz) instead of pyrimidine led to the 2D-coordination polymer [Mn4(OH)(Piv)7(µ2-pz)2]n (7). Interaction of [Mn(Piv)2(EtOH)]n with FeCl3 resulted in the formation of the hexanuclear complex [MnII4FeIII2O2(Piv)10(MeCN)2(HPiv)2] (8). The reactions of [MnFe2O(OAc)6(H2O)3] with 4,4′-bipyridine (4,4′-bipy) or trans-1,2-(4-pyridyl)ethylene (bpe) led to the formation of 1D-polymers [MnFe2O(OAc)6L2]n·2nDMF, where L = 4,4′-bipy (9·2DMF), bpe (10·2DMF) and [MnFe2O(OAc)6(bpe)(DMF)]n·3.5nDMF (11·3.5DMF). All complexes were characterized by single-crystal X-ray diffraction. Desolvation of 11·3.5DMF led to a collapse of the porous crystal lattice that was confirmed by PXRD and N2 sorption measurements, while alcohol adsorption led to porous structure restoration. Weak antiferromagnetic exchange was found in the case of binuclear MnII complexes (JMn-Mn = −1.03 cm−1 for 1 and 2). According to magnetic data analysis (JMn-Mn = −(2.69 ÷ 0.42) cm−1) and DFT calculations (JMn-Mn = −(6.9 ÷ 0.9) cm−1) weak antiferromagnetic coupling between MnII ions also occurred in the tetranuclear {Mn4(OH)(Piv)7} unit of the 2D polymer 7. In contrast, strong antiferromagnetic coupling was found in oxo-bridged trinuclear fragment {MnFe2O(OAc)6} in 11·3.5DMF (JFe-Fe = −57.8 cm−1, JFe-Mn = −20.12 cm−1).