Very Large Difference in Electronic Communication of Dimetal Species with Heterobiphenylene and Heteroanthracene Units

Hydrothermal Synthesis and Structure of a Dinuclear Molybdenum(III) Hydroxy Squarate with a Mo-Mo Bond

The reaction of molybdenum(II) and chromium(II) acetates with squaric acid in degassed and deionized water under hydrothermal conditions at 150 °C is described. The products have been formulated as M₂(μ-OH)₂(μ-C₄O₄)₂(H₂O)₄·2H₂O, where M = Cr (1) and Mo (2), based on combustion elemental analysis, infrared spectroscopy, magic angle spinning (MAS) solid-state carbon-13 nuclear magnetic resonance (NMR), and single-crystal X-ray diffraction. The edge-shared bioctahedral structures involve doubly bridging hydroxide ligands and μ-squarate ligands. The chromium compound lacks a direct metal-metal-bonding interaction, while in contrast the molybdenum compound contains a Mo-Mo bond [2.491(2) Å]. The nature of the Mo-Mo-bonding interaction is compared with that of other similar d³-d³ dimers.

The usefulness of EPR spectroscopy in the study of compounds with metal–metal multiple bonds

A discussion of how EPR spectroscopy has contributed to the understanding of the electronic structure of paddlewheel compounds with multiple bonds between metal atoms is presented while commemorating the 50th anniversary of the paper describing the quadruple bond and the identification of the delta bond in the Re₂Cl₈²⁻ anion.

From molecules to materials: molecular paddle-wheel synthons of macromolecules, cage compounds and metal-organic frameworks

Metal-organic frameworks (MOF) are becoming a more and more important class of functional materials. Yet, very often, the synthesis of MOFs is not easy to control and requires a profound knowledge and experience in solid state chemistry. One of the most frequently used metal connectors is the so-called 'paddle-wheel' (PW) unit, which is a well-known molecular compound type in inorganic coordination chemistry. Depending on the ligands, the geometry of PWs strictly directs the assembly of ordered networks. This review focuses on the question, to what extent ordered network structures can be accessed by typical molecular syntheses in solution, starting from molecular PW complexes to ordered macromolecules, finite cage compounds and finally, three-dimensional superstructures.

Lithium furyl and pyridyl amidinates as building blocks in coordination polymers, ladder and cage structures

Lithium N,N'-bis(trimethylsilyl)heterocyclic amidinate complexes with 3- and 4-pyridyl and 3-furyl carbon substituents were prepared by addition of the corresponding nitriles to LiN(SiMe(3))(2) (LiNTMS(2)) solution. In the presence of N,N,N',N' tetramethylethylene diamine (TMEDA), both pyridyl amidinates crystallize as coordination polymers with an amidinate-Li-pyridyl backbone. The 4-pyridyl derivative (7) creates a linear polymer with amidinate-Li-TMEDA units as side chains, whereas the 3-pyridyl polymer (6) has a two-dimensional (2D) network structure in which TMEDA serves as a cross-linker. Solvation of the reaction mixture of 3-furonitrile and LiNTMS(2) with TMEDA affords the monomeric 3-furyl amidinate Li TMEDA complex (3). Crystals of the Li(2)O complex {[3-furyl-C-(NTMS)(2)Li](4).Li(2)O}.C(7)H(8) (4) are obtained from toluene by partial hydrolysis of the unsolvated 3-furyl amidinate (2). Degradation of the polymer (7) to monomeric units can be achieved by solvation in toluene or by reaction with TMS(2)NLi.TMEDA that affords crystals of the complex {NTMS(2)Li.[4-C(5)H(4)N-C(NTMS)(2)Li.TMEDA]}(2).(NTMS(2)Li.TMEDA) (8). The formation of these aggregates can be rationalized by directed substitution of TMEDA with pyridyl moieties and by the laddering principle.