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5-(4-(N-tert-Butyl-N-aminoxylphenyl))pyrimidine (RL, 4PPN) forms crystallographically isostructural and isomorphic pseudo-octahedral M(RL)2(hfac)2 complexes with M(hfac)2, M = Zn, Cu, Ni, Co, and Mn. Multiple close contacts occur between sites of significant spin density of the organic radical units. Magnetic behavior of the Zn, Cu, Ni, Co complexes appears to involve multiple exchange pathways, with multiple close crystallographic contacts between sites that EPR (of 4PPN) indicates to have observable spin density. Powder EPR spectra at room temperature and low temperature are reported for each complex. Near room temperature, the magnetic moments of the complexes are roughly equal to those expected by a sum of non-interacting moments (two radicals plus ion). As temperature decreases, AFM exchange interactions become evident in all of the complexes. The closest fits to the magnetic data were found for a 1-D Heisenberg AFM chain model in the Zn(II) complex (J/k = (-)7 K), and for three-spin RL-M-RL exchange in the other complexes (J/k = (-)26 K, (-)3 K, (-)6 K, for Cu(II), Ni(II), and Co(II) complexes, respectively).

A final summary is given concerning the present state of attempts to generate very high spin organic molecules and polymers which possess ferromagnetic bulk properties. Methodology has been developed to predict the types of structures most likely to have such properties, and significant progress has been made toward photochemical generation of polyradicals in the solid state. This project was aimed at designing magnetic properties in new materials, particularly organic polyradicals. We desired to use semiempirical molecular orbital plus configuration interaction computational methods to predict what types of structural features are most important in maximizing desirable ferromagnetic exchange interactions within organic systems (intramolecular exchange). Once appropriate structural models were delineated by theory, we also aimed to develop a solid state photochemical method to generate phenoxyl radical sites in a polymeric material. Use of a solid-state polyradical synthesis method would allow masking techniques for production of magnetic sites on a surface, and would minimize the kinds of radical Quenching reactions that tend to reduce stability of radicals under free diffusion (solution) conditions.

Attempted synthesis of monomers bearing groups to allow generation of phenoxy moieties is described. In general, such monomers have not been readily isolated. We feel that functionalization of phenolic groups in an existing polymer will be more efficient, as demonstrated by synthesis and irradiation of poly(4-(2,4,6-tri-tert-butylphenyloxalyl)styrene). Keywords: Organic magnetic materials, Polymeric polyradicals, Electron spin resonance, ESR, Solid state chemistry, Paramagnetic material, Magnetic information, Storage materials.

Progress in theoretical and synthetic investigations of organic magnetic species is outlined by slides presented at the Office of Naval Research contractors' meeting of Fall, 1989. Overall, progress was made in synthesis of appropriate groups to allow photochemical and thermal generation of phenoxyl radicals in the solid phase. Thermal stability of a variety of substituted phenoxyl systems generated by these methods in PPMA matrices was investigated. Keywords: Organic radicals; Organic polyradicals; Theoretical and computational chemistry; Unimolecular radical synthesis.

Pi-conjugated polyradicals are of interest as potential superparamagnetic species with possible uses as organic magnetic information storage materials. Experimental results to date suggest that simple parity-based qualitative models are not entirely successful in making global predictions of ground state (GS) spin multiplicity for various connectivity classes of organic polyradicals. We show that a variety of experimentally known diradicals are well described by a semiempirical MO-CI model based on AM1, and that our semiempirical approach gives predictions in good accord with ab initio work where experiments are yet to be performed. The use of such predictive algorithms is described in making rational selection of model compounds for testing spin- magnetic interactions in organic systems. Keywords: Computational organic chemistry of polyradicals, Mechanisms of ferromagnetic coupling in organic polyradicals, Organic magnetic materials, Magnetic information storage materials.

Synthesis of a new photochemical unimolecular precursor to aryloxyl radicals is described, the bis-aryloxalate esters (BAO's). These molecules are readily synthesized, are thermally very stable, may be stored under ordinary benchtop laboratory conditions in the dark, make large and well-formed crystals, and are readily photolyzed either in solution or in solid phases. Solid state photochemical experiments may easily be carried out in polymer matrices (PPMA), frozen glassy matrix, microcystalline powders, or in single crystals. Photoefficiency is about half by comparison to analogous aryloxyoxalyl tert- butylperoxide precursors (described in ONR Technical Report 12), but in symmetrical BAO's generated the same number of radicals per unit quantum of photolysis greater than 300 nm. Unsymmetrical BAO's are also readily synthesized from the oxalyl chloride half-esters of 2,4,6-tri-tert-butylphenol. Keywords: Solid state unimolecular photochemical generation, Aryloxyl radicals.

INDO-C1 and AM1-CI semiempirical computations both give results in good agreement with qualitative theoretical expectations for organic polyradicals, as well as diradicaloid species related to tetramethylene ethane. Phenoxyradicals linked through conjugation should be experimentally accessible models for organic super paramagnetic species. Peroxyoxalate esters are useful thermal and photochemical phenoxy precursors (>70C) labile. Polymers.

Theoretical work shows that one-dimensional and three-dimensional spin-coupling in polymeric and solid materials will be small, but achievable in principle. The INDO-CI computational method gives results in accord with most qualitative theories for spin coupling to give multiplet ground states in polyradicals. Preliminary experimental work indicates that theoretically desirable phenoxy moieties may be readily generated via peroxyoxalate esters.

UV photolysis of readily synthesized aryloxyoxalyl chloride half- esters provides a new unimolecular source of aryloxyl radicals, as shown by ESR nd UV-vis spectroscopy. Although phenoxyl radicals have been generated and investigated for a long time, such studies have usually been carried out under solution phase bimolecular oxidative conditions, or by direct photolysis of phenols. We have recently had the occasion to desire a method for efficient unimolecular photochemical generation of phenoxyl and related aryloxyl radicals, and have found that aryloxyoxalyl chloride half-esters provide a readily available photochemical source of aryloxyl radicals. Synthesis (chemistry).

Spin-spin coupling in a number of aryloxyl-based polyradicals is computationally investigated using the AM1 semiempirical molecular method with configuration interaction. The qualitative accuracy of ground spin state prediction by parity based models is confirmed by computational predictions, and experimental results to date for a variety of model diradical systems is in accord with computationally predicted ground state multiplicities. The method is of general utility in identifying polyradical systems of potential interest for synthesis a possible organic high-spin magnetic materials. Organic radicals and polyradicals; Organic magnetic materials; High-spin organic molecules; Molecular orbital theory.

UV photolysis and mild (60-100 C) thermolysis of aryloxyoxalyl tert- butylperoxides provides a new unimolecular source of aryloxyl radicals, as shown by ESR and UV spectroscopy. Some side reactions are noted, but in general the method looks effective as a means of making a fairly stable precursor to phenoxy radicals, with radical generation under straightforward photochemical and thermal conditions., See also report 1, ADA210572.

Ab initio SCF-CI computations on methano and ethano bridged oxyallyl (CH2-CO-CH2) diradical shows that these species are ground state singlet diradicaloids, despite the possibility of being drawn as diradicals with a possible triplet ground spin state. The gap between the excited state triplet and the ground state singlet is 4-7 kcal/mol, depending on the system and on the level of theory used. This study shows that computational theory is of great value in checking the qualitative predictions of diradical ground state spin multiplicity as expressed in a variety of 'back of the envelope' parity-based models. Oxyallyl diradical substitution; Substitution effects; Diradical ground state spin multiplicity; Ab initio molecular orbital; Configuration interaction theory., Prepared in cooperation with Oberlin College, Oberlin, OH. Dept. of Chemistry.