Double-bridge

Here, the unknown resistance is compared with a known resistance using a suitable bridge. Resistance above I Q. can be measured by Wheatstone bridge. Resistance less than I Q can be measured by a Kelvin double bridge, where the lead resistance must also be compensated. 

The Kelvin double bridge is a more sophisticated variant used for the measurement of very low resistance such as ammeter shunts or short lengths of cable. This is also operated on D.C. In industrial terms the digital D.C. low-resistance instruments are more convenient although somewhat less accurate. 

So far we have considered only mechanisms involving a single Cr(II) ion, because the centers have been found to be isolated, at least for low Cr loadings. However, the intervention of multiplets of Cr(II) centers cannot be excluded. In fact, it can be hypothesized that an eventual cyclic intermediate formed initially (mechanism I and II) can also evolve into Cr(II)-(CH2) -Cr(II) species, where the chain is anchored to two different chromium centers. In these conditions chromium species carry only a linear chain and the system differs from all the double bridged structures illustrated up to now. 

Table 3.14 shows all the known dinuclear gold(II) complexes containing the AU2" core. As happened in gold(II) chemistry the most abundant are those containing a double bridge of the bis ylide CH2PPh2CH2. The first derivative [(C6F5)Au... 

The structure of coordination polymers formed with 3,6-bis(pyridin-3-yl)-l,2,4,5-tetrazine and zinc salts can be controlled by the choice of alcoholic solvents. Infinite lattice compounds of the form [Zn2L2(N03)4(Me0H)2(//-L)] and [Zn2(/U-L)3(N03)4](CH2C12)2) have been structurally characterized. The former structure shows an alternating single- and double-bridged species whereas the latter exists as a non-interpenetrated ladder complex.273... 

Pyridine derivatives with additional donor functions and sterically demanding substituents have been used with the intention of producing complexes of Cd (and of other metals) with low coordination number one of these ligands is the tridentate, planar-bonding 2,6-bis[(2,6-dimethyl-phenylimino)methyl] pyridine (pydim a Schiff base derived from 2,6-pyridine dialdehyde), which with Cd(BF4)2 and thiocyanate gives a dinuclear complex [(pydim)Cd(/x-NCS-S,N)]2(BF4)2 with N-dominated coordination sphere.191 As centrosymmetric Plijc, Z= 2), the complex has an antiparallel /x-1,3 NCS double bridge with Cd—N and Cd—S bonds (224.6 pm and 255.5 pm, respectively) the Cd—N(py) bond is clearly shorter than the Cd—N(imino) bonds (225.6 pm and 245.0 pm,... 

A reaction of the first type, in a broad sense, uses the mixture obtained from n-BuLi and the phosphinic acid (mes)2P(H)=0 (mes = 2,4,6-trimethylphenyl) in thf/hexane to which the Cd amide Cd[N(SiMe3)2]2 is added a mixed amide-phosphinite is obtained, namely [ MeSi)2N Cd (mes)2PO 2Li-2 thf]. The structure analysis (153 K) reveals that the two phosphinite ligands act as a double bridge between Cd and Li to give a six-membered, twisted ring with two independent Cd—P bonds (rav(Cd—P) 259.4 pm) the exocyclic Cd—N bond is rather short (213.6 pm).226... 

Fig. 7. Structure of [Vio028]6 . A triply-bridged oxygen is indicated by B and some double-bridged oxygens by C. (Adapted with permission from Capparelli, M. V., Good-game, D. M. L., Hayman, P. B., Skapski, A. C. J. Chem. Soc. Chem. Commun. 1986, 776.)...

The trans-bent structure was unexceptional and found to be energetically favored compared to the linear arrangement, but even more stable forms such as vinylidene, mono-bridged or double-bridged isomers exist. Compounds 392-395 are unexceptional monomeric in solution, as is typical for M(i) cluster compounds.297... 

In the double-bridging algorithm, an inner monomer of a chain attacks an inner monomer of another chain (or the same chain) and tries to form a... 

The formation of a double-bridged Co(III) complex from a single peroxo-bridged complex can take place by either (2.107) or (2.108), L = CHjNHj,... 

Fig. 10 Schematic representation of the linear chain of poly metal(II) phosphinates, alternating triple and single bridging phosphinate groups, and double bridging phosphi-...

The linear chain of polymeric metal(II) phosphinates consists of metal atoms linked either by alternating single and triple bridging phosphinate groups [79-81], or by double bridging phosphinate groups [82-86] (Fig. 10). 

Fig. 20. A centrosymmetrical dimeric molecule of CsNCS (XVIIF) showing the double bridge formed by shared thiocyanate ions...

In the thiol 79 and the sulfinic acid 80, two new acidic functionalities are now present in the 2 -position of a m-terphenyl system and should be incorporable into concave structures by a double bridging of the m-terphenyl. For the acetyl-protected thiol 78, the corresponding concave thiol acetate 42 (Scheme 7) could be obtained after tetrabromination of the four methyl groups and bridging with m-phenylenedithiol (see Sect. 2.3). 

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