the present invention provides in one embodiment a crystalline polymorph of 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine , referred to herein as form 5 . form 5 is a non - solvated crystalline form . form 5 can be described by one or more solid state analytical methods , for example , by its powder x - ray diffraction pattern which is provided in fig1 . powder x - ray diffraction 2 - theta values for form 5 are provided in table 1 below . in some embodiments , form 5 is characterized as having a powder x - ray diffraction pattern having two or more peaks , in terms of 2 - theta , selected from about 6 . 81 , 7 . 27 , 8 . 19 , 9 . 76 , 10 . 87 , 14 . 65 , 14 . 78 , 15 . 43 , 15 . 68 , 16 . 77 , 16 . 90 , 17 . 09 , 19 . 66 , 21 . 90 , 22 . 00 , 22 . 26 , 22 . 52 , 26 . 34 , 27 . 85 , 29 . 63 , 29 . 78 , and 33 . 23 degrees , at ambient temperature . in one aspect of this embodiment , form 5 is characterized by the peaks at 2 - theta values of about 9 . 76 , 10 . 87 , 14 . 65 and 16 . 90 degrees . in one aspect of this embodiment , form 5 is characterized as having a powder x - ray diffraction pattern peaks , in terms of 2 - theta , at each of about 6 . 81 , 8 . 19 , 9 . 76 , 10 . 87 , 14 . 65 , 15 . 43 , 16 . 77 , 16 . 90 , 17 . 09 , 22 . 52 , 29 . 63 , 29 . 78 and 33 . 23 degrees , at ambient temperature . in one embodiment , form 5 is characterized by any one of the peaks at 2 - theta values of about 6 . 81 and 8 . 19 ° 2θ . accordingly , any one of these peaks , or any combination of these peaks , may be used to characterize the compound of formula i . in still another embodiment , the two peaks , alone or in combination with the peaks at about 9 . 76 and 10 . 87 ° 2θ may be used to characterize form 5 . in still another embodiment , the peaks set forth in table 1 may be used to characterize form 5 . in a further embodiment , a diffraction pattern substantially similar to that of fig1 may be used to characterize form 5 . the relative intensities of the peaks can vary , depending upon the sample preparation technique , the sample mounting procedure , the particular instrument employed , and the morphology of the sample . moreover , instrument variation and other factors can affect the 2 - theta values . therefore , the xrpd peak assignments for form 5 and all other crystalline forms disclosed herein , can vary by ± 0 . 2 °. in another embodiment , form 5 is identified by its melting endotherm of 204 ° c . ( onset value ). at that temperature , form 5 then recrystallizes into form 4 , which subsequently melts at about 209 ° c . in one aspect of this embodiment , form 5 is characterized by a dsc with a dsc endotherm having an onset of about 204 ° c . in another embodiment , the peaks at any one or more of about 6 . 81 and 8 . 19 ° 2θ together with a dsc endotherm with an onset at about 204 ° c . may be used to characterize form 5 . in still another embodiment , one or more of these peaks together with one or both of the peaks at about 9 . 76 and 10 . 87 ° 2θ together with a dsc endotherm with an onset at about 209 ° c . may be used to characterize form 5 . in a further embodiment , the peaks set forth in table 1 together with a dsc endotherm with an onset at about 204 ° c . may be used to characterize form 5 . in still a further embodiment , a diffraction pattern substantially similar to that of fig1 together with a dsc endotherm with an onset at about 204 ° c . may be used to characterize form 5 . for dsc , it is known that the temperatures observed will depend upon the rate of temperature change as well as sample preparation technique and the particular instrument employed . thus , the values reported herein for form 5 relating to melting point and dsc thermograms can vary by ± 1 ° c . in another embodiment , form 5 is identified by the ft - raman spectrum shown in fig3 . the pattern shows ir shift peaks at 676 . 5 , 885 . 2 , 979 . 7 , 1064 . 3 , 1263 . 0 , 1394 . 1 , 1425 . 3 , 1488 . 7 , 1510 . 7 , 1533 . 9 , 1629 . 8 , 2129 . 2 , 2217 . 7 , 2958 . 5 , 3084 . 6 , and 3118 . 9 cm − 1 variation in the position of raman peaks exists and may be due to sample conditions as well as data collection and processing . the typical variability in raman spectra reported herein is on the order plus or minus 2 . 0 cm − 1 . thus , the use of the word “ about ” when referencing raman peaks is meant to include this variability and all raman peaks disclosed herein are intended to be reported with such variability . in one embodiment , form 5 is identified by the raman spectrum peaks at about 1064 . 3 and 3084 . 6 cm − 1 . the peaks at about 1064 . 3 and 3084 . 6 cm − 1 along with or in combination with the dsc onset and / or the xrpd data set forth herein may be used to characterize form 5 . for example , in one embodiment , the peaks at any one or more of about 6 . 81 and 8 . 19 ° 2θ together with a raman peaks at about 1064 . 3 and 3084 . 6 cm − 1 and optionally with a dsc endotherm with an onset at about 204 ° c . may be used to characterize form 5 . in another embodiment , one or more of the peaks at about 6 . 81 and 8 . 19 ° 2θ and one or both of the peaks at about 9 . 76 and 10 . 87 ° 2θ together with a raman peaks at about 1064 . 3 and 3084 . 6 cm − 1 and optionally with a dsc endotherm with an onset at about 204 ° c . may be used to characterize form 5 . in a further embodiment , the peaks set forth in table 1 together with raman peaks at about 1064 . 3 and 3084 . 6 cm − 1 and optionally with a dsc endotherm with an onset at about 204 ° c . may be used to characterize form 5 . in a further embodiment , a diffraction pattern substantially similar to that of fig1 together with raman peaks at about 1064 . 3 and 3084 . 6 cm − 1 and optionally with a dsc endotherm with an onset at about 204 ° c . may be used to characterize form 5 . in another embodiment , form 5 is further identified by ir shift peaks at 669 . 8 , 675 . 6 , 687 . 4 , 707 . 1 , 724 . 4 , 768 . 9 , 795 . 2 , 813 . 4 , 821 . 5 , 875 . 9 , 884 . 3 , 904 . 6 , 916 . 3 , 979 . 3 , 1005 . 4 , 1033 . 8 , 1061 . 0 , 1097 . 0 , 1136 . 7 , 1164 . 8 , 1196 . 9 , 1247 . 6 , 1274 . 0 , 1298 . 0 , 1328 . 6 , 1378 . 5 , 1394 . 4 , 1424 . 6 , 1459 . 4 , 1485 . 0 , 1511 . 1 , 1535 . 0 , 1594 . 3 , 1627 . 4 , and 2215 . 0 cm − 1 . in still another embodiment , form 5 is further identified by a dvs isotherm substantially similar to the one shown in fig4 . in yet another embodiment , form 1 may be characterized by a dvs plot substantially similar to that of fig4 in combination with any of the previous embodiments . form 5 is more thermodynamically stable than any of the other non - solvated forms at temperatures from between 22 ° c . and 70 ° c . ( i . e ., forms 1 , 3 and 4 , the preparation of which is disclosed below ). in one embodiment , the form 5 polymorph of 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine has at least 98 % deuterium incorporation at each position designated as deuterium in formula i as determined by 1 h - nmr . the invention is also directed to processes for the preparation of the form 5 polymorph . the invention also provides pyrogen - free pharmaceutical compositions comprising an effective amount of the form 5 polymorph of this invention ; and a pharmaceutically acceptable carrier . the carrier ( s ) are “ pharmaceutically acceptable ” in the sense of being not deleterious to the recipient thereof in an amount used in the medicament . in certain embodiments , the ratio of form 5 to other forms , including other crystalline forms such as the other crystalline forms disclosed herein , and / or amorphous forms ( e . g ., the ratio of the amount of form 5 to the sum of the amounts of all other polymorphic forms of l - 838417 ), in such pharmaceutical compositions is greater than 50 : 50 , equal to or greater than 80 : 20 , equal to or greater than 90 : 10 , equal to or greater than 95 : 5 , equal to or greater than 99 : 1 ; or 100 : 0 . pharmaceutically acceptable carriers , adjuvants and vehicles that may be used in the pharmaceutical compositions of this invention include , but are not limited to , ion exchangers , alumina , aluminum stearate , lecithin , serum proteins , such as human serum albumin , buffer substances such as phosphates , glycine , sorbic acid , potassium sorbate , partial glyceride mixtures of saturated vegetable fatty acids , water , salts or electrolytes , such as protamine sulfate , disodium hydrogen phosphate , potassium hydrogen phosphate , sodium chloride , zinc salts , colloidal silica , magnesium trisilicate , polyvinyl pyrrolidone , cellulose - based substances , polyethylene glycol , sodium carboxymethylcellulose , polyacrylates , waxes , polyethylene - polyoxypropylene - block polymers , polyethylene glycol and wool fat . in certain embodiments , the compound is administered orally . compositions of the present invention suitable for oral administration may be presented as discrete units such as capsules , sachets , or tablets each containing a predetermined amount of the active ingredient ; a powder or granules ; a solution or a suspension in an aqueous liquid or a non - aqueous liquid ; an oil - in - water liquid emulsion ; a water - in - oil liquid emulsion ; packed in liposomes ; or as a bolus , etc . soft gelatin capsules can be useful for containing such suspensions , which may beneficially increase the rate of compound absorption . in the case of tablets for oral use , carriers that are commonly used include lactose and corn starch . lubricating agents , such as magnesium stearate , are also typically added . for oral administration in a capsule form , useful diluents include lactose and dried cornstarch . when aqueous suspensions are administered orally , the active ingredient is combined with emulsifying and suspending agents . if desired , certain sweetening and / or flavoring and / or coloring agents may be added . compositions suitable for oral administration include lozenges comprising the ingredients in a flavored basis , usually sucrose and acacia or tragacanth ; and pastilles comprising the active ingredient in an inert basis such as gelatin and glycerin , or sucrose and acacia . according to another embodiment , the invention provides a method of treating a treating a mammal having a disorder of the central nervous system comprising the step of administering to said mammal an effective amount of the form 5 polymorph of 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine or a pharmaceutical composition comprising form 5 polymorph of 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine and a pharmaceutically acceptable carrier . in one particular embodiment , the method of this invention is used to treat a disease or condition in a human patient in need thereof selected from anxiety , convulsions , neuropathic pain , inflammatory pain , and migraine - associated pain . as used herein , the term “ effective amount ” refers to an amount which , when administered in a proper dosing regimen , is sufficient to reduce or ameliorate the severity , duration or progression of the disorder being treated , prevent the advancement of the disorder being treated , cause the regression of the disorder being treated , or enhance or improve the prophylactic or therapeutic effect ( s ) of another therapy . effective amounts of the form 5 polymorph of 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine can be determined by one of ordinary skill in the art . effective doses will vary , as recognized by those skilled in the art , depending on the diseases treated , the severity of the disease , the route of administration , the sex , age and general health condition of the patient , excipient usage , the possibility of co - usage with other therapeutic treatments such as use of other agents and the judgment of the treating physician . for example , guidance for selecting an effective dose can be determined by reference to the scientific literature for l - 838417 . in one embodiment , an effective amount of the form 5 polymorph can range from about 0 . 01 to about 5000 mg per treatment . in more specific embodiments , the range is from about 0 . 1 to 2500 mg , or from 0 . 2 to 1000 mg , or most specifically from about 1 to 500 mg . treatment typically is administered one to three times daily . methods delineated herein also include those wherein the patient is identified as in need of a particular stated treatment . identifying a patient in need of such treatment can be in the judgment of a patient or a health care professional and can be subjective ( e . g . opinion ) or objective ( e . g . measurable by a test or diagnostic method ). in another embodiment , any of the above methods of treatment comprises the further step of co - administering to the patient one or more second therapeutic agents . the second therapeutic agent may be selected from any compound or therapeutic agent known to have or that demonstrates advantageous properties when administered with a compound having the same mechanism of action as l - 838417 . preferably , the second therapeutic agent is an agent useful in the treatment or prevention of a disease or condition selected from disorders of the central nervous system , including anxiety and convulsions ; and neuropathic , inflammatory and migraine associated pain . the term “ co - administered ” as used herein means that the second therapeutic agent may be administered together with a compound of this invention as part of a single dosage form ( such as a composition of this invention comprising a compound of the invention and an second therapeutic agent as described above ) or as separate , multiple dosage forms . alternatively , the additional agent may be administered prior to , consecutively with , or following the administration of a compound of this invention . in such combination therapy treatment , both the compounds of this invention and the second therapeutic agent ( s ) are administered by conventional methods . the administration of a composition of this invention , comprising both a compound of the invention and a second therapeutic agent , to a patient does not preclude the separate administration of that same therapeutic agent , any other second therapeutic agent or any compound of this invention to said patient at another time during a course of treatment . effective amounts of these second therapeutic agents are well known to those skilled in the art and guidance for dosing may be found in patents and published patent applications referenced herein , as well as in wells et al ., eds ., pharmacotherapy handbook , 2nd edition , appleton and lange , stamford , conn . ( 2000 ); pdr pharmacopoeia , tarascon pocket pharmacopoeia 2000 , deluxe edition , tarascon publishing , loma linda , calif . ( 2000 ), and other medical texts . however , it is well within the skilled artisan &# 39 ; s purview to determine the second therapeutic agent &# 39 ; s optimal effective - amount range . in one embodiment of the invention , where a second therapeutic agent is administered to a subject , the effective amount of the compound of this invention is less than its effective amount would be where the second therapeutic agent is not administered . in another embodiment , the effective amount of the second therapeutic agent is less than its effective amount would be where the compound of this invention is not administered . in this way , undesired side effects associated with high doses of either agent may be minimized . other potential advantages ( including without limitation improved dosing regimens and / or reduced drug cost ) will be apparent to those of skill in the art . the following definitions are for solvents that are suitable in the preparation of the forms disclosed herein : acn acetonitrile dcm dichloromethane dmc dimethyl carbonate dmso dimethylsulfoxide etoac ethyl acetate etoh ethanol ipa 2 - propanol meoac methyl acetate meoh methanol n - proh 1 - propanol tbme t - butyl methyl ether t - buoh tert - butanol tfe trifluoroethanol thf tetrahydrofuran a mixture of 7 -( tert - butyl - d 9 )- 6 - chloro - 3 -( 2 , 5 - difluorophenyl )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine ( 130 g , 391 . 8 mmol , 1 equiv ) and 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methanol ( 53 g , 470 . 1 mmol , 1 . 2 equiv ) in anhydrous thf ( 1560 ml , 12 vol ) was stirred at 20 ° c . under nitrogen for 5 min . to this was added 1m potassium tertbutoxide in thf ( 470 ml , 470 . 1 mmol , 1 . 2 equiv ) drop wise over 45 min while maintaining the temperature at 20 - 25 ° c . the reaction mixture was stirred for another 45 min and then diluted with water ( 1300 ml , 10 vol , ph 12 - 13 ) and the ph was adjusted to 7 - 8 with 1 hcl ( 30 ml ). the organic solvent was removed and the aqueous layer was extracted with dcm ( 3 × 600 ml ). the combined dcm layers were washed with water ( 1 × 40 ml ) and brine ( 1 × 40 ml ). the organic layer was concentrated to 3 volumes , solvent swapped into 5 volumes of heptanes , aged at 22 ° c . for 1 h . the white solid was collected by filtration to afford crude 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine ( 150 g ; 92 . 8 a %). the crude product ( 150 g ) was dissolved in denatured anhydrous ethanol ( 1950 ml , 15 vol ) at 70 ° c . the solution was cooled to 60 ° c . and 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine form 1 seed ( 1 . 3 g ) were added . the mixture was cooled to 22 ° c . and stirred for 5 h . the white solid was collected by filtration and dried at 45 ° c . under vacuum for 10 h to produce solid 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine (“ starting material ”). the synthesis of 7 -( tert - butyl - d 9 )- 6 - chloro - 3 -( 2 , 5 - difluorophenyl )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine is described in united states patent publication no . 2010 / 0056529 . 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine form 1 was produced by dissolving starting material in anhydrous ethanol and heating to 50 ° c . to dissolve . the solution is then allowed to cool and resulting solids are isolated and air - dried . form 2 was prepared from form 1 as follows . form 1 ( 500 . 0 mg ) was manually weighed into an 8 - ml vial and combined with water ( 5 . 0 ml ). a stir bar was added and the suspension was stirred at room temperature for 72 hrs . the white solid was isolated on a büchner funnel by vacuum filtration and air - dried for 3 hrs . form 3 was produced by placing form 2 on a tga aluminum pan and heating to 190 ° c . form 4 was produced by placing form 2 on a tga aluminum pan and heating to 205 ° c . 7 -( tert - butyl - d9 )- 3 -( 2 , 5 - difluorophenyl )- 6 -(( 1 - methyl - 1h - 1 , 2 , 4 - triazol - 5 - yl ) methoxy )-[ 1 , 2 , 4 ] triazolo [ 4 , 3 - b ] pyridazine form 5 formed spontaneously during ripening studies carried out as follows . excess form 1 was combined with etoh ( 1 . 8 ml ) and the suspension was stirred at 57 ° c . for 6 hrs . the suspension was allowed to settle , and the saturated etoh solution was isolated , and added into a 2 - ml vial containing a mixture of forms 1 , form 3 , and form 4 (− 10 mg of each ). the suspension was stirred at 57 ° c . for 24 hrs . the solid was isolated on a büchner funnel and air - dried for ˜ 6 hrs . once the above preparation of form 5 was obtained , additional form 5 was produced as follows . form 1 ( 100 mg ) was weighed into a 4 - ml is placed in a 4 - ml vial containing a stir - bar . etoh ( 4 - ml ) was added and the suspension was stirred for 12 hrs and at 25 ° c . the suspension was filtered and the filtrate ( 1 . 8 ml ) was added into a 2 - mail vial containing equivalent amounts ( 10 mg ) of forms 3 , 4 , and 5 . an aliquot of the suspension was immediately sampled ; the solid was isolated by filtration , and analyzed by pxrd to verify the crystal - form . the suspension was stirred at 25 ° c . for an additional 24 hrs . a second aliquot was sampled ; the solid was isolated by filtration , and analyzed to verify the crystal - form . further stirring and aliquots sampling was continued , if needed , until a conversion to form 5 as a single crystal - form was confirmed for the isolated solid . once form 5 crystals were isolated they were used to prepare additional form 5 as follows . form 1 in excess was combined with etoh ( 1 . 8 ml ) and the suspension was stirred at 55 ° c . for 6 hrs . the suspension was allowed to settle , and the saturated etoh solution was isolated , and added into a 2 - ml vial containing either a ) a mixture of 10 mg each of form 1 , form 3 , form 4 , and form 5 ; or b ) 10 mg of form 5 . the resulting suspension was stirred at 55 ° c . for 24 hr . the solid was isolated on a büchner funnel and air - dried for ˜ 6 hrs and determined to be form 5 . alternatively , the following protocol can be used to create form 5 . a suspension form 1 ( 1 g ) and etoh ( anhydrous , denatured ) ( 10 ml ) were stirred at 22 ° c . under nitrogen atmosphere for 30 min . to this was added form 5 ( 3 wt %) seeds and stirring was continued for a week . the suspension was filtered and the solid isolated and dried to constant weight ( yield 82 %). form 5 is a non - solvated crystal form . the dsc trace indicated a melting / recrystallization event at 203 . 9 ° c . ( on - set ) followed by a melting endotherm at 208 . 8 ° c . ( on - set ). dvs analysis revealed that form 5 is non - hygroscopic (& lt ; 0 . 4 % wt . gain ). the hplc analysis indicated high chemical purity (& gt ; 99 % auc ). form 5 is physically stable when exposed to : ( i ) ambient conditions for at least 7 days ; and ( ii ) 75 % relative humidity (“ rh ”) for 5 days . form 5 becomes physically unstable and partially converts to hydrated crystal form 2 when exposed to 97 % rh for 5 days at room temperature . form 5 also converts to form 2 when suspended in meoh : water ( 98 : 2 % volume and 95 : 5 % volume ) and stirred for 72 hours at ambient temperature . without further description , it is believed that one of ordinary skill in the art can , using the preceding description and the illustrative examples , make and utilize the compounds of the present invention and practice the claimed methods . it should be understood that the foregoing discussion and examples merely present a detailed description of certain preferred embodiments . it will be apparent to those of ordinary skill in the art that various modifications and equivalents can be made without departing from the spirit and scope of the invention .