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The reaction of borazines, (-BRNR'-)3, with pyrazole, Hpz, gives (µ-pyrazolato)(#i-amido)diboron species of the type R(pz)B-(µ-)(µ-') ( ) (3) containing a central B2N3 ring system. Four compounds of type 3 with R = C2H5 or C6H5 and R' = H or CH3, respectively, were prepared. Identical species can be obtained on interaction of bis((dimethylamino)boryl)amines of the type R'N[BRN(CH3)2]2 with Hpz; they are closely related to the pyrazaboles, 2 (µ-)2 2, which contain a central B2N4 ring. A pathway for the formation of 3 is postulated and supported by NMR data. Conformational isomers of 3 could be identified but not separated. In contrast, RB[N(CH3)2]2 (R = C2H5) reacts with Hpz at room temperature to give (CH3)2HNBR(pz)2 and in refluxing toluene to yield the pyrazabole R(pz) (µ-)2 ( ). The latter compound was also obtained from (-BRNR'-)3 (R' = H, CH3) or 3 (R = C2H5, R' = H) and boiling Hpz (at temperatures near 180-200 °C). The compound could be separated into conformational isomers. The lower melting one with the terminal pz groups in cis (equatorial) position crystallizes tetragonally in space group 14{/acd, a = b = 14.876 A, c = 34.932 A, and Z = 16, with the central B2N4 ring in a boat conformation. The higher melting trans isomer crystallizes monoclinically in space group P2fc, a = 8.

Two mononuclear cobalt(III) Schiff base complexes with azide [Co(L)(N 3 )(L′)] (1) and [Co(L)(N 3 )(L′′)] (2) {where HL = 1-((2-(diethylamino)ethylimino)methyl)naphthalene-2-ol, HL′ = 2-hydroxy-1-naphthaldehyde and HL′′ = acetylacetone} have been synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy and single crystal X-ray diffraction studies. Both complexes show mononuclear structures with azide as terminalcoligand. Structural features have been examined in detail that reveal the formation of interesting supramolecular networks generated through non-covalent forces including hydrogen bonding, C-2 H···H-C and C-H/π interactions. These interactions have been studied energetically by means of theoretical DFT calculations. We have also analyzed the unexpected O···O interactions observed in one complex between the oxygen atoms of the coordinated aldehyde groups using several computational tools, including Bader's "atoms-in-molecules" (AIM) and natural bond orbital (NBO) analyses.

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A dinuclear and a novel bi-cyclic hetero trinuclear bis(μ-tetrazolato) bridged nickel(II) Schiff base complexes [Ni2(L(1))2(PTZ)2] (1) and [Ni2(L(2))2(PTZ)2Na(H2O)]ClO4·H2O (2) {where HL(1) = 2-((2-(dimethylamino)ethylimino)methyl)-6-methoxyphenol, HL(2) = 2-((2-(methylamino)ethylimino)methyl)-6-methoxyphenol and HPTZ = 5-(2-pyridyl)tetrazole} have been synthesized by in situ 1,3-dipolar cyclo-addition and characterized by spectral analysis, X-ray crystallography, and variable-temperature magnetic susceptibility measurements. Both the complexes crystallize in monoclinic space group P2(1)/c. Both the complexes feature double μ-NN'-tetrazolato bridged dinickel(II) structures, in which each nickel(II) is coordinated meridionally by a depronated terdentate Schiff base [(L(1))(-) for 1 and (L(2))(-) for 2] and two nitrogen atoms of the (PTZ)(-). A nitrogen atom from a symmetry related bridging (PTZ)(-) coordinates to complete the distorted octahedral geometry of nickel(II). The phenoxo and methoxo oxygen atoms from two [NiL(2)] units and a water molecule coordinate to a sodium(I) to form the unique bi-cyclic trinuclear nickel(II)-sodium(I)-nickel(II) core in complex 2. Very strong π···π stacking is observed in complex 2 to form a supramolecular chain. The variable-temperature (1.8-300 K) magnetic susceptibility measurements show the presence of anti-ferromagnetic coupling between two nickel(II) centers for both complexes with J = -2.14(1) cm(-1) (for 1) and J = -1.20(2) cm(-1) (for 2). To obtain a better understanding of the magnetic exchange mechanism, quantum mechanical (DFT) calculations have been performed. The calculated J values [J(theo) = -4.53 cm(-1) (for 1) and J(theo) = -2.48 cm(-1) (for 2)] are in agreement with the values obtained experimentally.

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