form a , form b , form c , form d , form e , and form f atorvastatin magnesium can be characterized by one or more of x - ray powder diffraction -, solid state nmr carbon chemical shift -, and solid state nmr fluorine chemical shift patterns . the “ forms ” of atorvastatin magnesium disclosed in the present invention may exist as ordered crystals , disordered crystals , liquid crystals , plastic crystals , mesophases , and the like . in x - ray powder diffractograms forms that are related through disorder will have essentially the same major peak positions but the disordering process will cause broadening of these peaks . for many of the weaker peaks , the broadening may be so severe that they are no longer visible above the background . the peak broadening caused by disorder may in addition cause errors in the location of the exact peak position . for solid state nuclear magnetic resonance ( ssnmr ) spectra , significant differences in chemical shifts may be seen from crystalline to disordered phases . form a , form b , form c , form d , form e , and form f atorvastatin magnesium were characterized by their x - ray powder diffraction pattern . thus , the x - ray powder diffraction patterns of forms a , b , c , d , e , and f were carried out on a bruker d8 discover x - ray powder diffractometer with gadds ( general area diffraction detector system ) cs operating in reflection mode using cuk a radiation . the tube voltage and amperage were set to 40 kv and 40 ma , respectively . scans were collected with the sample to detector distance set at 15 . 0 cm . the samples were scanned for a period of 60 seconds covering a range of 4 . 5 ° to 38 . 7 ° in 2θ . the diffractometer was calibrated for peak positions in 20 using a corundum standard . samples were run in asc - 6 silicon sample holders purchased from gem dugout ( state college , pa .). all analyses were conducted at room temperature , which is generally 20 °- 30 ° c . data were collected and integrated using gadds for wnt software version 4 . 1 . 14t . diffractograms were evaluated using diffracplus software , release 2003 , with eva version 8 . 0 ( available from bruker axs , inc ., madison , wis .). to perform an x - ray diffraction measurement on a bruker d8 discover x - ray powder diffractometer with gadds cs used for measurements reported herein , the sample is typically placed into a cavity in the middle of the silicon sample holder . the sample powder is pressed by a glass slide or equivalent to ensure a random surface and proper sample height . the sample holder is then placed into the bruker instrument and the powder x - ray diffraction pattern is collected using the instrumental parameters specified above . measurement differences associated with such x - ray powder diffraction analyses result from a variety of factors including : ( a ) errors in sample preparation ( e . g ., sample height ), ( b ) instrument errors ( e . g . flat sample errors ), ( c ) calibration errors , ( d ) operator errors ( including those errors present when determining the peak locations ), and ( e ) the nature of the material ( e . g . preferred orientation and transparency errors ). calibration errors and sample height errors often result in a shift of all the peaks in the same direction . small differences in sample height when using a flat holder will lead to large displacements in xrpd peak positions . a systematic study showed that a sample height difference of 1 mm lead to peak shifts as high as 1 ° 2θ ( chen et al . ; j pharmaceutical and biomedical analysis , 2001 ; 26 , 63 ). these shifts can be identified from the x - ray diffractogram and can be eliminated by compensating for the shift ( applying a systematic correction factor to all peak position values ) or recalibrating the instrument . as mentioned above , it is possible to rectify measurements from the various instruments by applying a systematic correction factor to bring the peak positions into agreement . in general , this correction factor will bring the measured peak positions into agreement with the expected peak positions and is in the range of the expected 2θ value ± 0 . 2 ° 2θ . tables 1 - 6 list peak positions in degrees 2θ , relative intensities , and relative peak widths for x - ray powder diffraction patterns of each form of atorvastatin magnesium disclosed in the present application . the relatively narrow peak positions were picked by the diffracplus with eva version 8 . 0 software . the broader peak positions were visually determined . all peak positions were rounded to 0 . 1 ° 2θ . the following abbreviations areused in tables 1 - 6 to describe the peak intensity ( s = strong ; m = medium ; w = weak ) and the peak width ( b = broad ( where broad refers to peak widths of between 0 . 2 and 1 . 0 degrees 2θ , sh = shoulder , vb = very broad ( where very broad refers to peaks with & gt ; 1 degrees 2θ peak width )). for both 13 c —, and 19 f spectroscopy , approximately 80 mg of each sample were tightly packed into a 4 mm zro spinner . the spectra were collected at ambient conditions on a bruker - biospin 4 mm bl hfx cpmas probe ( bruker biospin corporation , 15 fortune drive , manning park , billerica , mass . 01821 - 3991 ) positioned into a wide - bore bruker - biospin avance dsx 500 mhz nmr spectrometer . the samples were positioned at the magic angle and spun at 15 . 0 khz , corresponding to the maximum specified spinning speed for the 4 mm spinners . the fast spinning speed minimized the intensities of the spinning side bands . the number of scans was adjusted to obtain adequate s / n . the 13 c solid state spectra were collected using a proton decoupled cross - polarization magic angle spinning experiment ( cpmas ). the hartman - hahn contact time was set to 2 . 0 ms . the proton decoupling field of approximately 90 khz was applied . 2048 scans were collected . the recycle delay was adjusted to 7 seconds . the shift values are listed in tables 8 to 13 . the spectra were referenced using an external standard of crystalline adamantane , setting its upfield resonance to 29 . 5 ppm . in each of tables 8 - 13 , “ a ” is referenced to external sample of solid phase adamantane at 29 . 5 ppm ; and “ b ” is defined as peak height . intensities can vary depending on the actual setup of the cpmas experimental parameters and the thermal history of the sample . cpmas intensities are not necessarily quantitative . the 19 f solid state spectra were collected using a proton decoupled magic angle spinning ( mas ) experiment . the proton decoupling field of approximately 90 khz was applied . 32 scans were collected . the recycle delay was set to 90 seconds to ensure acquisition of quantitative spectra . proton longitudinal relaxation times ( 1 h t 1 ) were calculated based on a fluorine detected proton inversion recovery relaxation experiment . fluorine longitudinal relaxation times ( 19 f t 1 ) were calculated based on a fluorine detected fluorine inversion recovery relaxation experiment . the spectra were referenced using an external sample of trifluoro - acetic acid ( 50 % v / v in h 2 o ), setting its resonance to − 76 . 54 ppm . tables 14 to 19 list the fluorine chemical shifts in ppm of forms a , b , c , d , e , and f atorvastatin magnesium respectively . the forms of atorvastatin magnesium described herein may exist in anhydrous forms as well as containing various amounts of water and / or solvents . anhydrous , hydrated and solvated forms of atorvastatin magnesium are intended to be encompassed within the scope of the present invention . the forms of atorvastatin magnesium described herein , regardless of the extent of water and / or solvent having equivalent x - ray powder diffractograms are within the scope of the present invention . the new forms of atorvastatin magnesium described herein have advantageous properties . the ability of a material to form good tablets at commercial scale depends upon a variety of physical properties of the drug , such as , for example , the tableting indices described in hiestand h . and smith d ., indices of tableting performance , powder technology , 1984 , 38 ; 145 - 159 . these indices may be used to identify forms of atorvastatin magnesium which have superior tableting performance . one such index is the brittle fracture index ( bfi ), which reflects brittleness , and ranges from 0 ( good - low brittleness ) to 1 ( poor high brittleness ). the present invention provides a process for the preparation of forms a , b , c , d , e and f atorvastatin magnesium which comprises forming atorvastatin magnesium ( e . g ., from a solution or slurry in solvents ) under conditions which yield forms a , b , c , d , e and f atorvastatin magnesium . the precise conditions under which forms a , b , c , d , e and f atorvastatin magnesium are formed may be empirically determined and described herein are methods which have been found to be suitable in practice . the compounds of the present invention can be prepared and administered in a wide variety of oral and parenteral dosage forms . the compounds of the present invention can be administered by injection , that is , intravenously , intramuscularly , intracutaneously , subcutaneously , intraduodenally , or intraperitoneally . also , the compounds of the present invention can be administered by inhalation , for example , intranasally . additionally , the compounds of the present invention can be administered transdermally . it will be obvious to those skilled in the art that the following dosage forms may comprise as the active component a compound of the present invention . for preparing pharmaceutical compositions from the compounds of the present invention , pharmaceutically acceptable carriers can be either solid or liquid . solid form preparations include powders , tablets , pills , capsules , cachets , suppositories , and dispersible granules . a solid carrier can be one or more substances which may also act as diluents , flavoring agents , solubilizers , lubricants , suspending agents , binders , preservatives , tablet disintegrating agents , or an encapsulation material . in powders , the carrier is a finely divided solid which is in a mixture with the finely divided active component . in tablets , the active component is mixed with the carrier having the necessary binding properties in suitable proportions and compacted in the shape and size desired . the powders and tablets preferably contain from two or ten to about seventy percent of the active compound . suitable carriers are magnesium carbonate , methylcellulose , sodium carboxymethylcellulose , a low melting wax , cocoa butter , and the like . the term ‘ preparation ’ is intended to include the formulation of the active compound with encapsulating material as a carrier providing a capsule in which the active component , with or without other carriers , is surrounded by a carrier , which is thus in association with it . similarly , cachets and lozenges are included . tablets , powders , capsules , pills , cachets , and lozenges can be used as solid dosage forms suitable for oral administration . for preparing suppositories , a low melting wax , such as a mixture of fatty acid glycerides or cocoa butter , is first melted and the active component is dispersed homogeneously therein , as by stirring . the molten homogeneous mixture is then poured into convenient sized molds , allowed to cool , and thereby to solidfy . liquid form preparations include solutions , suspensions , retention enemas , and emulsions , for example water or water propylene glycol solutions . for parenteral injection , liquid preparations can be formulated in solution in aqueous polyethylene glycol solution . aqueous solutions suitable for oral use can be prepared by dissolving the active component in water and adding suitable colorants , flavors , stabilizing and thickening agents , as desired . aqueous suspensions suitable for oral use can be made by dispersing the finely divided active component in water with viscous material , such as natural or synthetic gums , resins , methylcellulose , sodium carboxymethylcellulose , and other well - known suspending agents . also included are solid form preparations which are intended to be converted , shortly before use , to liquid form preparations for oral administration . such liquid forms include solutions , suspensions , and emulsions . these preparations may contain , in addition to the active component , colorants , flavors , stabilizers , buffers , artificial and natural sweeteners , dispersants , thickeners , solubilizing agents , and the like . the pharmaceutical preparation is preferably in unit dosage form . in such form , the preparation is subdivided into unit doses containing appropriate quantities of the active component . the unit dosage form can be a packaged preparation , the package containing discrete quantities of preparation , such as packeted tablets , capsules , and powders in vials or ampoules . also , the unit dosage form can be a capsule , tablet , cachet , or lozenge itself , or it can be the appropriate number of any of these in packaged form . the quantity of active component in a unit dosage preparation may be varied or adjusted from 0 . 5 mg to 100 mg , preferably 2 . 5 to 80 mg according to the particular application and the potency of the active component . the composition can , if desired , also contain other compatible therapeutic agents . in therapeutic use as hypolipidemic and / or hypocholesterolemic agents and agents to treat bph , osteoporosis , and alzheimer &# 39 ; s disease , the forms a , b , c , d , e , and f atorvastatin magnesium utilized in a method of this invention are administered at the initial dosage of about 2 . 5 mg to about 80 mg daily . useful daily doses includes those in the range of about 2 . 5 mg to about 20 mg . the dosages , however , may be varied depending upon the requirements of the patient , the severity of the condition being treated , and the compound being employed . determination of the proper dosage for a particular situation is within the skill of the art . generally , treatment is initiated with smaller dosages which are less than the optimum dose of the compound . thereafter , the dosage is increased by small increments until the optimum effect under the circumstance is reached . for convenience , the total daily dosage may be divided and administered in portions during the day if desired . form a of atorvastatin magnesium may be prepared by dissolving the lactone form of atorvastatin ( u . s . pat . no . 5 , 273 , 995 ) in a solvent in which both the lactone and sodium salt forms are soluble . useful solvents include lower weight alcohols , such as methanol and ethanol , water or tetrahydrofuran ( thf ) or mixtures thereof . naoh is added to the solution , with stirring , at a temperature from about 45 ° c . to about 55 ° c ., followed by slow addition of a magnesium salt , such as mgcl 2 or a hydrated form thereof . the mixture can them be cooled to ambient temperature to yield a suspension and a precipitate , which can be filtered from the suspension . water can then be slowly added to the resulting solution with stirring to produce a second precipitate of atorvastatin magnesium form a , which can then be removed by filtration . atorvastatin magnesium form b may be prepared by suspending a sample of form a , discussed above , in an aromatic organic solvent , such as benzene , xylene , ortho - xylene , para - xylene , meta - xylene , toluene , etc ., at a temperature from about 40 ° c . to about 80 ° c . and stirring until from b atorvastatin magnesium is obtained . atorvastatin magnesium form c may be obtained by suspending a sample of form a , described above , in a mixture of acetonitrile and water at ambient temperature , with the acetonitrile being no more than 80 % but no less than 50 % of the acetonitrile / water mixture ( volume / volume ). the resulting mixture may then be stirred at ambient temperature until form c is produced . form d atorvastatin magnesium may be prepared by suspending a sample of form a , described above , in a mixture of about 9 / 1 ( volume / volume ) 2 - propanol / water at ambient temperature and stirring the resulting mixture until form d is obtained . form e atorvastatin magnesium may be prepared by suspending a sample of form a , described above , in water at ambient temperature and stirring until form e is obtained . form f atorvastatin magnesium may be obtained by suspending a sample of form a , described above , in water at a temperature from about 45 ° c . to about 100 ° c . and stirring the resulting mixture until form f is obtained . those skilled in the art will understand the forms of atorvastatin magnesium will be obtained in different amounts depending upon the amount of time spent in the steps above . amounts of the desired forms may be obtained in periods from one day to 50 days by the methods above . it will also be understood that methods known in the art may be used to obtain the desired atorvastatin magnesium material from the resulting suspension , such as centrifuge filtration . the following nonlimiting examples illustrate methods for preparing the compounds of the invention : [ r —( r *, r *)]- 2 -( 4 - fluorophenyl )- β , δ - dihydroxy - 5 -( 1 - methylethyl )- 3 - phenyl - 4 -[( phenylamino ) carbonyl ]− 1h - pyrrole - 1 - heptanoic acid hemi magnesium salt ( forms a , b , c , d , e , and f atorvastatin magnesium ). a 6 . 0 g sample of the lactone form of atorvastatin ( u . s . pat . no . 5 , 273 , 995 ) was dissolved in 100 ml of methanol at room temperature . approximately 11 . 8 ml of 1n naoh ( 1 . 05 mol equivalents ) was then added to the mixture . the solution was then stirred at 50 ° c . for approximately 1 hour . a solution of 1 . 19 g mgcl 2 . 6h 2 o in 5 ml of h 2 o ( 0 . 55 mol equivalents ) was then slowly added to the reaction mixture . the mixture was then cooled to room temperature and the resulting precipitate was removed by vacuum filtration through a 0 . 45 - μm nylon membrane filter . approximately 100 ml of h 2 o was then slowly added to the filtered solution , which caused a white precipitate to form . the resulting suspension was then stirred for approximately 30 minutes . the solid sample was then isolated by vacuum filtration . the filtered solid was then dried under vacuum at 70 ° c . for approximately 2 hours to afford 5 . 8 g of form a atorvastatin magnesium . a 50 mg sample of form a atorvastatin magnesium ( prepared as described above ) was slurried in 0 . 25 ml of ortho - xylene at 45 ° c . for 28 days using magnetic stirring at 400 rpm . the solid sample was then isolated by centrifuge filtration through a 0 . 45 - μm nylon membrane filter . the filtered solid was then air dried under ambient conditions for approximately 5 hours to afford form b atorvastatin magnesium . a 50 mg sample of form a atorvastatin magnesium ( prepared as described above ) was slurried in 0 . 75 ml of acetonitrile : water ( 8 : 2 , v / v ) at ambient temperature for 28 days using magnetic stirring at 300 rpm . the solid sample was then isolated by centrifuge filtration through a 0 . 45 - μm nylon membrane filter . the filtered solid was then air dried under ambient conditions for approximately 5 hours to afford form c atorvastatin magnesium . a 50 mg sample of form a atorvastatin magnesium ( prepared as described above ) was slurried in 1 ml of 2 - propanol : water ( 9 : 1 , v / v ) at ambient temperature for 28 days using magnetic stirring at 300 rpm . the solid sample was then isolated by centrifuge filtration through a 0 . 45 - μm nylon membrane filter . the filtered solid was then air dried under ambient conditions for approximately 5 hours to afford form d atorvastatin magnesium . a 50 mg sample of form a atorvastatin magnesium ( prepared as described above ) was slurried in 3 ml of water at ambient temperature for 28 days using magnetic stirring at 300 rpm . the solid sample was then isolated by centrifuge filtration through a 0 . 45 - μm nylon membrane filter . the filtered solid was then air dried under ambient conditions for approximately 5 hours to afford form e atorvastatin magnesium . a 50 mg sample of form a atorvastatin magnesium ( prepared as described above ) was slurried in 1 ml of water at 45 ° c . for 28 days using magnetic stirring at 300 rpm at 400 rpm . the solid sample was then isolated by centrifuge filtration through a 0 . 45 - μm nylon membrane filter . the filtered solid was then air dried under ambient conditions for approximately 5 hours to afford form f atorvastatin magnesium .