Recent trends of general interest in high-resolution N M R of solids are mentioned, and some examples briefly discussed. Stress is laid on the use of the multiple-pulse technique, particularly when combined with magic-angle spinning to give CRAMPS. Two studies of proton CRAMPS are described, one concerning hydrogen bonding in carboxylic acids and the other involving phosphonic acid derivatives. The relationship between proton isotropic chemical shifts and hydrogen-bond distances is explored in some detail. A clear correlation is found.As was found by Carrington' in an earlier Special Issue of Faraday Transactions (on Reaction Dynamics and Spectroscopy), it is difficult to know how to formulate an introductory Keynote Paper, although in his case the paper was first delivered as a Faraday Lecture. To attempt a comprehensive review of the advances in solid-state NMR in recent years would clearly not be feasible in an article of reasonable length, yet to' write on a single topic would not provide anything different in kind from the ensuing articles. Consequently, we are attempting to use a mixture of these two approaches. First, we propose to highlight a few developments of major significance, with brief examples where appropriate from our own laboratory. Secondly, we will develop in a little more detail a particular area which appears to us to be underused, although it has a respectably long pedigree,' namely combined rotation and multiple-pulse spectroscopy (CRAMPS). In this approach we will inevitably be briefly mentioning work carried out by a number of our colleagues, to whom we are greatly indebted.The ensuing articles in this Special Issue show something of the wide diversity of solidstate NMR experiments and their areas of application. However, it must be said that it would have been easy to increase the number of articles by an order of magnitude and still have totally left out many important aspects. This Special Issue is thus by no means comprehensive, but perhaps gives readers a feel for the excitement and rapid pace of developments in the NMR of solids. Unfortunately, within the length of our own article it has not proved generally feasible to fully describe many of the experimental techniques discussed nor to give a suitable number of appropriate references. General Solid-state NMR DevelopmentsAlthough it is difficult to pick out the highlights of a rapidly developing area such as solid-state NMR, and doubtless any choice is subjective, the following appear to us to be some of the trends of general interest, at least as far as high-resolution spectroscopy is concerned (relaxation studies form a separate topic). 3649 3650 Perspectives in High-resolution Solid-state N M R(1) Multinuclear spin-; experiments. Most of the 24 elements having non-radioactive spin-; isotopes have now been studied by high-resolution NMR of solid samples using the magic-angle spinning (MAS) technique with or without cross-polarization (CP). Initially 13C was the favoured nucleus, followed by "Si and 31P, but the range is now much...

SummaryA practical method was elaborated for the synthesis of (aminomethylene)bisphosphine oxides comprising the catalyst- and solvent-free microwave-assisted three-component condensation of primary amines, triethyl orthoformate and two equivalents of diphenylphosphine oxide. The method is also suitable for the preparation of (aminomethylene)bisphosphonates using (MeO)2P(O)H/(MeO)3CH or (EtO)2P(O)H/(EtO)3CH reactant pairs and even secondary amines. Several intermediates referring to the reaction mechanism together with a few by-products could also be identified.

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Calculations reveal that the octahedral-trigonal prismatic-octahedral rearrangement has particularly low-energy barriers for MoF6, WF6, and (hypothetical) CrF6. Experimental evidence is obtained from the dynamic 19F NMR spectra of the derivatives CF3-CH2-O-MoF5, CF3-CH2-O-WF5, C6F5-O-MoF5, C6F5-O-WF5, and (CF3)3C-O-WF5. The ground-state structure of all these compounds is octahedral; at elevated temperatures the nonequivalent metal-bound fluorine atoms undergo an intramolecular exchange. The exchange mechanism could be a 3+3 or a 2+4 twist; calculations favor the 3+3 twist.

High-resolution 31P n.m.r. spectra have been obtained for a number of solid diphosphine disulphides under conditions of high-power decoupling, crosspolarization and magic-angle rotation. The results yield crystallographic information about the size of the asymmetric unit and are consistent with data from X-ray diffraction work when known. In one case, evidence of morphological variation is obtained.